https://wiki.reformrivers.eu/api.php?action=feedcontributions&user=Carlos+alonso&feedformat=atomREFORM wiki - User contributions [en]2024-03-28T10:44:36ZUser contributionsMediaWiki 1.23.5https://wiki.reformrivers.eu/index.php?title=Other_pressuresOther pressures2015-09-01T08:45:03Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Other pressures=<br />
05. Other hydromorphological pressures<br />
==General description==<br />
Other than hydromorphological pressures are beyond the scope of this review. However, there are several hydromorphological processes which in parallel also determine physico-chemical properties of the water. Thus, HYMO pressures affecting such processes will definitely also affect the related physico-chemical variables as well as potential feedbacks to hydromorphology and / or biota. Relevant other processes and potential effects have been indicated in the conceptual figures and are briefly listed here without further detailed explanation and discussion.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
*Water temperature modification cold<br />
Cooler water released by stratified reservoirs will have greater viscosity and therefore its capacity to erode channels will be reduced because it will reach lower flow velocities.<br />
<br />
*Water temperature modification warm<br />
Shainberg et al. (1996) concluded that high water content and high temperature (which induces high Brownian motion) during aging enhance clay-to-clay contacts and cementation of soil particles into a cohesive structure that resists rill erosion. Sidorchuk (1999), through field and laboratory experiments, found that water temperature became the main factor of gully erosion in frozen soil or in soil with the permafrost (so called thermoerosion).<br />
<br />
*Toxic substances – pollution<br />
The impacts of toxics on aquatic biological organisms may be increased or hidden depending on HYMO processes. Channel and bank erosion may unearth contaminants and promote their dissolution in water increasing their toxicity. On the contrary, sedimentation processes can bury pollutants at the channel bed and thereby reduce their toxicity.<br />
<br />
*Eutrophication – nutrient enrichment<br />
Vegetation encroachment will have a high demand on dissolved nutrients and thus, reducing eutrophication impacts on aquatic biota. Also, riparian vegetation with an extended canopy has a dense root system that filters nutrients from phreatic waters.<br />
<br />
*Organic pollution<br />
Excessive growth of macrophytes in eutrophic conditions and the leaf fall of riparian species in autumn, accumulate organic matter in the water. Hydraulic turbulent conditions favoring reaeration of the water column and hence the oxygen entrance which promotes the decomposition of this organic matter, reducing the impact of anoxic conditions due to organic contamination.<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P21" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P21" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:05. Other hydromorphological pressures]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Other_pressuresOther pressures2015-09-01T08:43:11Z<p>Carlos alonso: /* General description */</p>
<hr />
<div>=Other pressures=<br />
05. Other hydromorphological pressures<br />
==General description==<br />
Other than hydromorphological pressures are beyond the scope of this review. However, there are several hydromorphological processes which in parallel also determine physico-chemical properties of the water. Thus, HYMO pressures affecting such processes will definitely also affect the related physico-chemical variables as well as potential feedbacks to hydromorphology and / or biota. Relevant other processes and potential effects have been indicated in the conceptual figures and are briefly listed here without further detailed explanation and discussion.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
*HYMO (general and specified per HYMO element)<br />
*physico - chemical parameters<br />
*Biota (general and specified per Biological quality elements)<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P21" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P21" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:05. Other hydromorphological pressures]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Sedimentation_and_sediment_inputSedimentation and sediment input2015-09-01T08:41:42Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div><br />
=Sedimentation and sediment input=<br />
04. Morphological alterations<br />
==General description==<br />
Delivery of sediment from hillslopes to river systems is heavily disrupted by human activities. The nature of the disruption varies widely according to the broad environmental context as well as the nature of the human activities. Sudden discharges of sediments to rivers can occur in relation to natural processes such as major bank erosion, slope mass movements and glacial meltwater outbursts. However, these natural events cannot be viewed as ‘pressures’ unless they are accelerated by human activities.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
*Hillslope erosion<br />
Silt and fine sediments that clog interstices in river beds and cause colmation are mainly produced by forestry and agriculture (Brunke and Gonser, 1997). Clogging reduces the numbers and activity of hyporrheic invertebrates, which in turn, affects the porosity of interstitial sediments through the absence of their feeding and burrowing (Brunke and Gonser 1997). Jacobson and Gran (1999) found that agricultural development in the Ozarks, USA, contributed gravel-sized sediments to the Current River, Missouri. Fine sediment inputs to rivers come from bank erosion of fine floodplain sediments and erosion of the soil surface. The latter is strongly affected by land use and management, and increases for the same soil and land use with increases in topographic slope. As soil erosion becomes increasingly accelerated (i.e. exceeds the rate of soil production), finer soil particles are removed and gullies develop, channeling flows of water and allowing mobilization of coarser sediments. Where drains are constructed to remove surface water, these make delivery of sediment to river systems more efficient, and if their gradient is sufficiently steep, they may become sources of both fine and coarse sediment, as has been observed in drains associated with commercial forestry. Superficially, delivery of coarse sediment might offset gravel losses from river bed mining, but both processes would have to be in balance. Large accumulations of instream sediment can lead to channel instability, a decrease in channel capacity, and remobilisation of silt stored in floodplain sediments by overbank flows (Jacobson and Gran 1999, after Hancock 2002).<br />
Dirt roads, particularly those associated with forestry have been widely recognized as important sediment sources, conduits for sediment and water, and potential locations from which landslides may be triggered (Brunke and Gonser, 1997; Forman and Alexander, 1998).<br />
<br />
*Sediments discharges to rivers<br />
Slugs of sediment are also introduced into rivers directly as a result of human activities such as accidental dam breaching or deliberate dam removal. Bednarek (2001) showed that dam removal produced an increased sediment load causing suffocation and abrasion to various biota and habitats. However, observations of several dam removals suggest that these increased sediment loads are a relatively short-term effect.<br />
Deliberate flushing of sediment from reservoirs can release excessive fine sediment pulses into the river causing fine sediment infiltration and burial of the river bed. The Cachí Reservoir on the Reventazón River, Costa Rica, is flushed on an almost yearly basis. The material was found to both deposit in between flushings and to be eroded during flushing, mainly in the uppermost and lowermost parts of the old river channel. A major factor in explaining the amounts and distribution of deposits was shown to be the phase lag between water discharge and suspended-sediment concentration peaks (Brandt and Swenning 1999). Such sediments can be mobilized by larger flow releases from reservoirs, and methods are available to clean fine particles from gravel at specific sites, including pump-washing, high-pressure jet washing, and tractor<br />
rotovating. However, local loosening of gravel by such methods can lead to resuspension of silt to cause colmation in downwelling zones downstream (Hancock 2002).<br />
<br />
[[File:Sediment input.jpg|thumbnail|Conceptual framework of sediment input effects on HYMO processes and variables.]]<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P18" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P18" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=File:Sediment_input.jpgFile:Sediment input.jpg2015-09-01T08:40:43Z<p>Carlos alonso: </p>
<hr />
<div></div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Sedimentation_and_sediment_inputSedimentation and sediment input2015-09-01T08:40:05Z<p>Carlos alonso: /* General description */</p>
<hr />
<div><br />
=Sedimentation and sediment input=<br />
04. Morphological alterations<br />
==General description==<br />
Delivery of sediment from hillslopes to river systems is heavily disrupted by human activities. The nature of the disruption varies widely according to the broad environmental context as well as the nature of the human activities. Sudden discharges of sediments to rivers can occur in relation to natural processes such as major bank erosion, slope mass movements and glacial meltwater outbursts. However, these natural events cannot be viewed as ‘pressures’ unless they are accelerated by human activities.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
*Hillslope erosion<br />
Silt and fine sediments that clog interstices in river beds and cause colmation are mainly produced by forestry and agriculture (Brunke and Gonser, 1997). Clogging reduces the numbers and activity of hyporrheic invertebrates, which in turn, affects the porosity of interstitial sediments through the absence of their feeding and burrowing (Brunke and Gonser 1997). Jacobson and Gran (1999) found that agricultural development in the Ozarks, USA, contributed gravel-sized sediments to the Current River, Missouri. Fine sediment inputs to rivers come from bank erosion of fine floodplain sediments and erosion of the soil surface. The latter is strongly affected by land use and management, and increases for the same soil and land use with increases in topographic slope. As soil erosion becomes increasingly accelerated (i.e. exceeds the rate of soil production), finer soil particles are removed and gullies develop, channeling flows of water and allowing mobilization of coarser sediments. Where drains are constructed to remove surface water, these make delivery of sediment to river systems more efficient, and if their gradient is sufficiently steep, they may become sources of both fine and coarse sediment, as has been observed in drains associated with commercial forestry. Superficially, delivery of coarse sediment might offset gravel losses from river bed mining, but both processes would have to be in balance. Large accumulations of instream sediment can lead to channel instability, a decrease in channel capacity, and remobilisation of silt stored in floodplain sediments by overbank flows (Jacobson and Gran 1999, after Hancock 2002).<br />
Dirt roads, particularly those associated with forestry have been widely recognized as important sediment sources, conduits for sediment and water, and potential locations from which landslides may be triggered (Brunke and Gonser, 1997; Forman and Alexander, 1998).<br />
<br />
*Sediments discharges to rivers<br />
Slugs of sediment are also introduced into rivers directly as a result of human activities such as accidental dam breaching or deliberate dam removal. Bednarek (2001) showed that dam removal produced an increased sediment load causing suffocation and abrasion to various biota and habitats. However, observations of several dam removals suggest that these increased sediment loads are a relatively short-term effect.<br />
Deliberate flushing of sediment from reservoirs can release excessive fine sediment pulses into the river causing fine sediment infiltration and burial of the river bed. The Cachí Reservoir on the Reventazón River, Costa Rica, is flushed on an almost yearly basis. The material was found to both deposit in between flushings and to be eroded during flushing, mainly in the uppermost and lowermost parts of the old river channel. A major factor in explaining the amounts and distribution of deposits was shown to be the phase lag between water discharge and suspended-sediment concentration peaks (Brandt and Swenning 1999). Such sediments can be mobilized by larger flow releases from reservoirs, and methods are available to clean fine particles from gravel at specific sites, including pump-washing, high-pressure jet washing, and tractor<br />
rotovating. However, local loosening of gravel by such methods can lead to resuspension of silt to cause colmation in downwelling zones downstream (Hancock 2002).<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P18" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P18" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Sedimentation_and_sediment_inputSedimentation and sediment input2015-09-01T08:39:44Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div><br />
=Sedimentation and sediment input=<br />
04. Morphological alterations<br />
==General description==<br />
Delivery of sediment from hillslopes to river systems is heavily disrupted by human activities. The nature of the disruption varies widely according to the broad environmental context as well as the nature of the human activities.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
*Hillslope erosion<br />
Silt and fine sediments that clog interstices in river beds and cause colmation are mainly produced by forestry and agriculture (Brunke and Gonser, 1997). Clogging reduces the numbers and activity of hyporrheic invertebrates, which in turn, affects the porosity of interstitial sediments through the absence of their feeding and burrowing (Brunke and Gonser 1997). Jacobson and Gran (1999) found that agricultural development in the Ozarks, USA, contributed gravel-sized sediments to the Current River, Missouri. Fine sediment inputs to rivers come from bank erosion of fine floodplain sediments and erosion of the soil surface. The latter is strongly affected by land use and management, and increases for the same soil and land use with increases in topographic slope. As soil erosion becomes increasingly accelerated (i.e. exceeds the rate of soil production), finer soil particles are removed and gullies develop, channeling flows of water and allowing mobilization of coarser sediments. Where drains are constructed to remove surface water, these make delivery of sediment to river systems more efficient, and if their gradient is sufficiently steep, they may become sources of both fine and coarse sediment, as has been observed in drains associated with commercial forestry. Superficially, delivery of coarse sediment might offset gravel losses from river bed mining, but both processes would have to be in balance. Large accumulations of instream sediment can lead to channel instability, a decrease in channel capacity, and remobilisation of silt stored in floodplain sediments by overbank flows (Jacobson and Gran 1999, after Hancock 2002).<br />
Dirt roads, particularly those associated with forestry have been widely recognized as important sediment sources, conduits for sediment and water, and potential locations from which landslides may be triggered (Brunke and Gonser, 1997; Forman and Alexander, 1998).<br />
<br />
*Sediments discharges to rivers<br />
Slugs of sediment are also introduced into rivers directly as a result of human activities such as accidental dam breaching or deliberate dam removal. Bednarek (2001) showed that dam removal produced an increased sediment load causing suffocation and abrasion to various biota and habitats. However, observations of several dam removals suggest that these increased sediment loads are a relatively short-term effect.<br />
Deliberate flushing of sediment from reservoirs can release excessive fine sediment pulses into the river causing fine sediment infiltration and burial of the river bed. The Cachí Reservoir on the Reventazón River, Costa Rica, is flushed on an almost yearly basis. The material was found to both deposit in between flushings and to be eroded during flushing, mainly in the uppermost and lowermost parts of the old river channel. A major factor in explaining the amounts and distribution of deposits was shown to be the phase lag between water discharge and suspended-sediment concentration peaks (Brandt and Swenning 1999). Such sediments can be mobilized by larger flow releases from reservoirs, and methods are available to clean fine particles from gravel at specific sites, including pump-washing, high-pressure jet washing, and tractor<br />
rotovating. However, local loosening of gravel by such methods can lead to resuspension of silt to cause colmation in downwelling zones downstream (Hancock 2002).<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P18" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P18" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Sedimentation_and_sediment_inputSedimentation and sediment input2015-09-01T08:39:03Z<p>Carlos alonso: /* General description */</p>
<hr />
<div><br />
=Sedimentation and sediment input=<br />
04. Morphological alterations<br />
==General description==<br />
Delivery of sediment from hillslopes to river systems is heavily disrupted by human activities. The nature of the disruption varies widely according to the broad environmental context as well as the nature of the human activities.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
*Hillslope erosion<br />
Silt and fine sediments that clog interstices in river beds and cause colmation are mainly produced by forestry and agriculture (Brunke and Gonser, 1997). Clogging reduces the numbers and activity of hyporrheic invertebrates, which in turn, affects the porosity of interstitial sediments through the absence of their feeding and burrowing (Brunke and Gonser 1997). Jacobson and Gran (1999) found that agricultural development in the Ozarks, USA, contributed gravel-sized sediments to the Current River, Missouri. Fine sediment inputs to rivers come from bank erosion of fine floodplain sediments and erosion of the soil surface. The latter is strongly affected by land use and management, and increases for the same soil and land use with increases in topographic slope. As soil erosion becomes increasingly accelerated (i.e. exceeds the rate of soil production), finer soil particles are removed and gullies develop, channeling flows of water and allowing mobilization of coarser sediments. Where drains are constructed to remove surface water, these make delivery of sediment to river systems more efficient, and if their gradient is sufficiently steep, they may become sources of both fine and coarse sediment, as has been observed in drains associated with commercial forestry. Superficially, delivery of coarse sediment might offset gravel losses from river bed mining, but both processes would have to be in balance. Large accumulations of instream sediment can lead to channel instability, a decrease in channel capacity, and remobilisation of silt stored in floodplain sediments by overbank flows (Jacobson and Gran 1999, after Hancock 2002).<br />
Dirt roads, particularly those associated with forestry have been widely recognized as important sediment sources, conduits for sediment and water, and potential locations from which landslides may be triggered (Brunke and Gonser, 1997; Forman and Alexander, 1998).<br />
<br />
*Sediments discharges to rivers<br />
Sudden discharges of sediments to rivers can occur in relation to natural processes such as major bank erosion, slope mass movements and glacial meltwater outbursts. However, these natural events cannot be viewed as ‘pressures’ unless they are accelerated by human activities. Slugs of sediment are also introduced into rivers directly as a result of human activities such as accidental dam breaching or deliberate dam removal. Bednarek (2001) showed that dam removal produced an increased sediment load causing suffocation and abrasion to various biota and habitats. However, observations of several dam removals suggest that these increased sediment loads are a relatively short-term effect.<br />
Deliberate flushing of sediment from reservoirs can release excessive fine sediment pulses into the river causing fine sediment infiltration and burial of the river bed. The Cachí Reservoir on the Reventazón River, Costa Rica, is flushed on an almost yearly basis. The material was found to both deposit in between flushings and to be eroded during flushing, mainly in the uppermost and lowermost parts of the old river channel. A major factor in explaining the amounts and distribution of deposits was shown to be the phase lag between water discharge and suspended-sediment concentration peaks (Brandt and Swenning 1999). Such sediments can be mobilized by larger flow releases from reservoirs, and methods are available to clean fine particles from gravel at specific sites, including pump-washing, high-pressure jet washing, and tractor<br />
rotovating. However, local loosening of gravel by such methods can lead to resuspension of silt to cause colmation in downwelling zones downstream (Hancock 2002).<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P18" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P18" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Sedimentation_and_sediment_inputSedimentation and sediment input2015-09-01T08:38:35Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div><br />
=Sedimentation and sediment input=<br />
04. Morphological alterations<br />
==General description==<br />
<br />
==Effect/Impact on (including literature citations)==<br />
*Hillslope erosion<br />
Silt and fine sediments that clog interstices in river beds and cause colmation are mainly produced by forestry and agriculture (Brunke and Gonser, 1997). Clogging reduces the numbers and activity of hyporrheic invertebrates, which in turn, affects the porosity of interstitial sediments through the absence of their feeding and burrowing (Brunke and Gonser 1997). Jacobson and Gran (1999) found that agricultural development in the Ozarks, USA, contributed gravel-sized sediments to the Current River, Missouri. Fine sediment inputs to rivers come from bank erosion of fine floodplain sediments and erosion of the soil surface. The latter is strongly affected by land use and management, and increases for the same soil and land use with increases in topographic slope. As soil erosion becomes increasingly accelerated (i.e. exceeds the rate of soil production), finer soil particles are removed and gullies develop, channeling flows of water and allowing mobilization of coarser sediments. Where drains are constructed to remove surface water, these make delivery of sediment to river systems more efficient, and if their gradient is sufficiently steep, they may become sources of both fine and coarse sediment, as has been observed in drains associated with commercial forestry. Superficially, delivery of coarse sediment might offset gravel losses from river bed mining, but both processes would have to be in balance. Large accumulations of instream sediment can lead to channel instability, a decrease in channel capacity, and remobilisation of silt stored in floodplain sediments by overbank flows (Jacobson and Gran 1999, after Hancock 2002).<br />
Dirt roads, particularly those associated with forestry have been widely recognized as important sediment sources, conduits for sediment and water, and potential locations from which landslides may be triggered (Brunke and Gonser, 1997; Forman and Alexander, 1998).<br />
<br />
*Sediments discharges to rivers<br />
Sudden discharges of sediments to rivers can occur in relation to natural processes such as major bank erosion, slope mass movements and glacial meltwater outbursts. However, these natural events cannot be viewed as ‘pressures’ unless they are accelerated by human activities. Slugs of sediment are also introduced into rivers directly as a result of human activities such as accidental dam breaching or deliberate dam removal. Bednarek (2001) showed that dam removal produced an increased sediment load causing suffocation and abrasion to various biota and habitats. However, observations of several dam removals suggest that these increased sediment loads are a relatively short-term effect.<br />
Deliberate flushing of sediment from reservoirs can release excessive fine sediment pulses into the river causing fine sediment infiltration and burial of the river bed. The Cachí Reservoir on the Reventazón River, Costa Rica, is flushed on an almost yearly basis. The material was found to both deposit in between flushings and to be eroded during flushing, mainly in the uppermost and lowermost parts of the old river channel. A major factor in explaining the amounts and distribution of deposits was shown to be the phase lag between water discharge and suspended-sediment concentration peaks (Brandt and Swenning 1999). Such sediments can be mobilized by larger flow releases from reservoirs, and methods are available to clean fine particles from gravel at specific sites, including pump-washing, high-pressure jet washing, and tractor<br />
rotovating. However, local loosening of gravel by such methods can lead to resuspension of silt to cause colmation in downwelling zones downstream (Hancock 2002).<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P18" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P18" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Sand_and_gravel_extractionSand and gravel extraction2015-09-01T08:33:33Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Sand and gravel extraction=<br />
04. Morphological alterations<br />
==General description==<br />
<br />
Sand and gravel are crucial resources for economic development activities, such as road building and concrete production. As a result, sand and gravel mining is a major economic activity that is often carried out within river channels and floodplains. Because annual extraction rates often greatly exceed fluvial transport, these activities lead to river bed incision, disconnection of the river from its floodplain, depression of water table levels in the alluvial aquifer, and sometimes a complete change in channel style, for example from braiding to single thread planforms.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
The extraction of sand and gravel from river beds, banks and floodplains is driven by human needs for raw materials for concrete, glass and paint making, and construction works.<br />
Direct extraction of alluvial material from river channels causes far greater impacts than floodplain extraction. According to Rinaldi et al. (2005), the effects of bed sediment mining are more severe: where material is extracted at a rate greatly exceeding the replenishment rate where extraction is from single-thread rivers, that are generally associated with relatively low rates of catchment sediment supply; from channelized reaches, where sediment supply is also limited; from channels where there is only a thin cover of alluvium over bedrock; and at locations where mining coincides with other human activities that reduce upstream sediment delivery (especially large dams).<br />
Bed sediment mining alters flood magnitude and frequency (Rinaldi et al., 2005) and local flow hydraulics, inducing supplementary erosion on both sides of the extraction pit (Rivier and Seguier 1985); reduces sediment availability, changing sediment dynamics and inducing bed incision (Kondolf, 1997) and armouring (Kelly et al., 2005). These changes in sediment dynamics can lead to either bed siltation or armouring downstream (Rinaldi et al. 2005), local destabilization of the substratum (Rivier and Seguier 1985), and upstream erosion (López 2004, Rinaldi et al. 2005). In addition, bed incision lowers alluvial water tables and affects vegetation dynamics (Kondolf, 1994, 1997). These effects extend well beyond the sites affected by extraction, including reduction in flood levels, changes in longitudinal and transverse channel profiles, and alterations in stream bed, bank and riparian community characteristics.<br />
Gravel extraction from the river bed can also lead to bank erosion and failure. Altered bank dynamics change the bank profile and stream course, potentially inducing a loss of vegetation on stream banks and reduced delivery and retention of large wood.<br />
The nature of channel adjustments depends on local factors, most notably the local sediment budget and the method of gravel extraction (Wishart et al., 2008). However, Brown et al. (1998) reported that stream morphology is changed after gravel mining mainly by a lack of gravel bedload to replace the mined sediment, rather than by how the bed material removed. Examples of the effects of morphological degradation caused by gravel mining are numerous. Erskine et al. (1985) predicted imminent channel degradation as a result of rates of extraction from temporary sediment stores within the Hunter River, Australia, upstream of Denman, greatly exceeding contemporary transport rates. Similarly, gravel extraction from Stony Creek, California, USA that greatly exceeds delivery rates has induced channel incision of over 5 m of channel bed incision, necessitating bridge repairs costing US$1.4 million (Kondolf and Swanson 1993).<br />
In addition to channel incision and degradation, gravel extraction can lead to changes in the patterns of water exchange between surface and subsurface (Mori et al. 2011) and indirect effects that include a reduction in shading and bank cover; an increase in stream temperature that favours the rapid growth of algae and weeds that cover the water surface; release and redistribution of adsorbed pollutants; and changes in the turbidity of the water column (Rivier and Seguier 1985, Tamunobereton-ari and Omubo-Pepple 2011). In downstream locations, a decline in<br />
the level of the alluvial water table can result in salt water intrusion, as was observed by Mas-Pla et al. (1999) within the aquifer-river system close to the coast of the Baix Fluviá area (NE Spain).<br />
While in-channel mining commonly causes bed incision and severe upstream and downstream effects, floodplain gravel pits produced by gravel extraction have more local effects and have the potential to become wildlife habitat. However, they may be captured by migration of the active river channel (Kondolf 1997) and eventually contribute to the morphological and ecological changes observed in the main channel.<br />
<br />
[[File:Gravel extraction.jpg|thumbnail|Conceptual framework of gravel extraction effects on HYMO processes and variables.]]<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P19" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P19" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=File:Gravel_extraction.jpgFile:Gravel extraction.jpg2015-09-01T08:32:38Z<p>Carlos alonso: </p>
<hr />
<div></div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Sand_and_gravel_extractionSand and gravel extraction2015-09-01T08:32:11Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Sand and gravel extraction=<br />
04. Morphological alterations<br />
==General description==<br />
<br />
Sand and gravel are crucial resources for economic development activities, such as road building and concrete production. As a result, sand and gravel mining is a major economic activity that is often carried out within river channels and floodplains. Because annual extraction rates often greatly exceed fluvial transport, these activities lead to river bed incision, disconnection of the river from its floodplain, depression of water table levels in the alluvial aquifer, and sometimes a complete change in channel style, for example from braiding to single thread planforms.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
The extraction of sand and gravel from river beds, banks and floodplains is driven by human needs for raw materials for concrete, glass and paint making, and construction works.<br />
Direct extraction of alluvial material from river channels causes far greater impacts than floodplain extraction. According to Rinaldi et al. (2005), the effects of bed sediment mining are more severe: where material is extracted at a rate greatly exceeding the replenishment rate where extraction is from single-thread rivers, that are generally associated with relatively low rates of catchment sediment supply; from channelized reaches, where sediment supply is also limited; from channels where there is only a thin cover of alluvium over bedrock; and at locations where mining coincides with other human activities that reduce upstream sediment delivery (especially large dams).<br />
Bed sediment mining alters flood magnitude and frequency (Rinaldi et al., 2005) and local flow hydraulics, inducing supplementary erosion on both sides of the extraction pit (Rivier and Seguier 1985); reduces sediment availability, changing sediment dynamics and inducing bed incision (Kondolf, 1997) and armouring (Kelly et al., 2005). These changes in sediment dynamics can lead to either bed siltation or armouring downstream (Rinaldi et al. 2005), local destabilization of the substratum (Rivier and Seguier 1985), and upstream erosion (López 2004, Rinaldi et al. 2005). In addition, bed incision lowers alluvial water tables and affects vegetation dynamics (Kondolf, 1994, 1997). These effects extend well beyond the sites affected by extraction, including reduction in flood levels, changes in longitudinal and transverse channel profiles, and alterations in stream bed, bank and riparian community characteristics.<br />
Gravel extraction from the river bed can also lead to bank erosion and failure. Altered bank dynamics change the bank profile and stream course, potentially inducing a loss of vegetation on stream banks and reduced delivery and retention of large wood.<br />
The nature of channel adjustments depends on local factors, most notably the local sediment budget and the method of gravel extraction (Wishart et al., 2008). However, Brown et al. (1998) reported that stream morphology is changed after gravel mining mainly by a lack of gravel bedload to replace the mined sediment, rather than by how the bed material removed. Examples of the effects of morphological degradation caused by gravel mining are numerous. Erskine et al. (1985) predicted imminent channel degradation as a result of rates of extraction from temporary sediment stores within the Hunter River, Australia, upstream of Denman, greatly exceeding contemporary transport rates. Similarly, gravel extraction from Stony Creek, California, USA that greatly exceeds delivery rates has induced channel incision of over 5 m of channel bed incision, necessitating bridge repairs costing US$1.4 million (Kondolf and Swanson 1993).<br />
In addition to channel incision and degradation, gravel extraction can lead to changes in the patterns of water exchange between surface and subsurface (Mori et al. 2011) and indirect effects that include a reduction in shading and bank cover; an increase in stream temperature that favours the rapid growth of algae and weeds that cover the water surface; release and redistribution of adsorbed pollutants; and changes in the turbidity of the water column (Rivier and Seguier 1985, Tamunobereton-ari and Omubo-Pepple 2011). In downstream locations, a decline in<br />
the level of the alluvial water table can result in salt water intrusion, as was observed by Mas-Pla et al. (1999) within the aquifer-river system close to the coast of the Baix Fluviá area (NE Spain).<br />
While in-channel mining commonly causes bed incision and severe upstream and downstream effects, floodplain gravel pits produced by gravel extraction have more local effects and have the potential to become wildlife habitat. However, they may be captured by migration of the active river channel (Kondolf 1997) and eventually contribute to the morphological and ecological changes observed in the main channel.<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P19" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P19" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Loss_of_vertical_connectivityLoss of vertical connectivity2015-09-01T08:28:05Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Loss of vertical connectivity=<br />
04. Morphological alterations<br />
==General description==<br />
<br />
Vertical fragmentation can be produced by physical processes that reduce river bed permeability such as siltation of the riverbed surface and clogging of pore spaces within stream bed gravels (Hancock 2002<ref>Hancock, P.J., 2002. Human impacts on the stream–groundwater exchange zone. Environmental Management 29: 763–781.</ref>). This may result from increased delivery of fine sediment to the river as a result of for example changes in land use or agricultural practices, as well from reduced flow energy, for example due to flow regulation. In either case, the balance between sediment supply and sediment transport is disrupted, leading to the accumulation of fine sediments within the river bed (Kondolf and Wilcock, 1996<ref>Kondolf, G. M., and P. R. Wilcock 1996. The flushing flow problem: defining and evaluating objectives. Water Resources Research 32: 2589-2599.</ref>). In addition, physical modification of river channels, such as straightening and simplifying channel form (Kondolf ''et al''., 2006<ref>Kondolf, G. M., A. J. Boulton, S. O'Daniel, G. C. Poole, F. J. Rahel, E. H. Stanley, E. Wohl, A. Bång, J. Carlstrom, C. Cristoni, H. Huber, S. Koljonen, P. Louhi, and K. Nakamura. 2006. Process-based ecological river restoration: visualizing three-dimensional connectivity and dynamic vectors to recover lost linkages. Ecology and Society 11(2): 5. http://www.ecologyandsociety.org/vol11/iss2/art5/</ref>) may reduce water depth and retention within the channel, adversely affecting vertical connectivity.<br />
<br />
Riparian and floodplain soils may lose their infiltration capacity (vertical connectivity with groundwater) as a result of urban development, road and pavement construction, the weight of vehicle traffic, soil trampling, and recreational activities.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
Colmation of the upper layers of the channel bed and riparian and floodplain soils by fine sediment particles can hinder exchange processes between surface water and groundwater (Brunke and Gonser 1997).<br />
Natural colmation processes usually occur through the siltation of fine material during low flow episodes; whereas spate or exfiltration episodes reopen the interstices and reverse the process. Increased current velocities can flush fine material out of the surface layers of the river bed, but bedload movement is needed to reopen deeper interstices (Brunke and Gonser 1997). Due to the position of the surface bed layers between surface water and groundwater, the balanced alternation between colmation and scour can be disturbed by impacts affecting both surface and groundwater habitats (Hancock 2002), which can cause permanent colmation.<br />
The most common causes of colmation are organic and fine sediment inputs to the river channel, river channel engineering, and increased filtration through the channel margins during water extraction for drinking, industrial and irrigation water (Petts, 1988). External colmation can result from increased sewage loading that promotes the development of dense algal mats, or causes sedimentation of an organic layer on the river bed. Internal colmation is caused by the infiltration / intrusion of fine particulate organic or inorganic matter into the cavities within the bed sediments (Schalchli, 1993, after Brunke and Gonser 1997). Land use practices which increase seston and sediment loading are directly responsible for the extent of the unbalanced colmation processes (Karr & Schlosser, 1978; Platts et al., 1989, after Brunke and Gonser 1997).<br />
By preventing the communication between surface and groundwater, cascading effects in ecosystem structure and function may occur (Brunke and Gonser 1997). For instance, siltation of the interstices reduces the shelter for invertebrates, and thus the impacts of natural and anthropogenic disturbances, such as urban stormwater runoff, are magnified. Sealed interstices cannot function as nurseries for the benthos. Colmation can diminish or prevent the reproductive success of fish spawning on gravel.<br />
On the other hand, a clogged bed may act as an intrusion barrier that prevents the contamination of groundwater by polluted surface water (Younger et al., 1993; Komatina, 1994, after Brunke and Gonser 1997).<br />
Colmation might not be the only cause of the loss of vertical connectivity. The water velocity near the most superficial sediment layers determines the dominant flow direction between the surface and groundwater. If the temporal distribution of water velocities change, more subtle disturbances in the flow between both systems can be noticed. For instance, Curry et al. (1994) found that discharge fluctuations caused by hydroelectric power generation alter the mixing relationships between surface water and groundwater in the hyporrheic zone. And this could have severe impacts on the reproductive success of gravel spawning fish. This effect was found to occur naturally in some reaches along an upland salmon spawning catchment by Malcolm et al. (2005). They found that at sites dominated by surface water, hyporrheic DO remained high throughout and rates of embryo survival were correspondingly high.<br />
Restoration actions have been conducted and benefits in both the hyporrheos and the groundwater table near the river have been reported. After restoration programs, Sarriquet et al. (2007) detected an increase in vertical exchanges of water between surface and interstitial habitats, with an increase in the depth of hypoxia. Golz et al. (1991, after Brunke and Gonser 1997) reported that the mechanical opening of a clogged section of the Rhine’s stream bed near a drinking water bank filtration site induced a 1 m rise in the groundwater table near the river, but after a few weeks the opened section had become sealed again. Therefore, the viability of such restoration works may be associated with catchment management designed to reduce fine<br />
sediment inputs to the river (Sarriquet et al. 2007).<br />
Loss of vertical connectivity not only affects interactions between channel and adjacent terrain but also between the land surface and underlying and aquifers. In urbanised areas, previously permeable surfaces are replaced by paved impermeable surfaces (Schick et al. 1999). This may cause a general decline in the water table and a deterioration in groundwater quality with urbanization (Jat et al. 2009).<br />
<br />
[[File:Loss vertical conectivity.jpg|thumbnail|Conceptual framework of loss of vertical connectivity effects on HYMO processes and variables.]]<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P20" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P20" /><br />
==Useful references==<br />
<br />
Hancock, P.J., 2002. Human impacts on the stream–groundwater exchange zone. Environmental Management 29: 763–781.<br />
Kondolf, G. M., and P. R. Wilcock 1996. The flushing flow problem: defining and<br />
evaluating objectives. Water Resources Research 32: 2589-2599.<br />
Kondolf, G. M., A. J. Boulton, S. O'Daniel, G. C. Poole, F. J. Rahel, E. H. Stanley, E. Wohl, A. Bång, J. Carlstrom, C. Cristoni, H. Huber, S. Koljonen, P. Louhi, and K. Nakamura. 2006. Process-based ecological river restoration: visualizing three-dimensional connectivity and dynamic vectors to recover lost linkages. Ecology and Society 11(2): 5. http://www.ecologyandsociety.org/vol11/iss2/art5/<br />
<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=File:Loss_vertical_conectivity.jpgFile:Loss vertical conectivity.jpg2015-09-01T08:27:06Z<p>Carlos alonso: </p>
<hr />
<div></div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Loss_of_vertical_connectivityLoss of vertical connectivity2015-09-01T08:26:43Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Loss of vertical connectivity=<br />
04. Morphological alterations<br />
==General description==<br />
<br />
Vertical fragmentation can be produced by physical processes that reduce river bed permeability such as siltation of the riverbed surface and clogging of pore spaces within stream bed gravels (Hancock 2002<ref>Hancock, P.J., 2002. Human impacts on the stream–groundwater exchange zone. Environmental Management 29: 763–781.</ref>). This may result from increased delivery of fine sediment to the river as a result of for example changes in land use or agricultural practices, as well from reduced flow energy, for example due to flow regulation. In either case, the balance between sediment supply and sediment transport is disrupted, leading to the accumulation of fine sediments within the river bed (Kondolf and Wilcock, 1996<ref>Kondolf, G. M., and P. R. Wilcock 1996. The flushing flow problem: defining and evaluating objectives. Water Resources Research 32: 2589-2599.</ref>). In addition, physical modification of river channels, such as straightening and simplifying channel form (Kondolf ''et al''., 2006<ref>Kondolf, G. M., A. J. Boulton, S. O'Daniel, G. C. Poole, F. J. Rahel, E. H. Stanley, E. Wohl, A. Bång, J. Carlstrom, C. Cristoni, H. Huber, S. Koljonen, P. Louhi, and K. Nakamura. 2006. Process-based ecological river restoration: visualizing three-dimensional connectivity and dynamic vectors to recover lost linkages. Ecology and Society 11(2): 5. http://www.ecologyandsociety.org/vol11/iss2/art5/</ref>) may reduce water depth and retention within the channel, adversely affecting vertical connectivity.<br />
<br />
Riparian and floodplain soils may lose their infiltration capacity (vertical connectivity with groundwater) as a result of urban development, road and pavement construction, the weight of vehicle traffic, soil trampling, and recreational activities.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
Colmation of the upper layers of the channel bed and riparian and floodplain soils by fine sediment particles can hinder exchange processes between surface water and groundwater (Brunke and Gonser 1997).<br />
Natural colmation processes usually occur through the siltation of fine material during low flow episodes; whereas spate or exfiltration episodes reopen the interstices and reverse the process. Increased current velocities can flush fine material out of the surface layers of the river bed, but bedload movement is needed to reopen deeper interstices (Brunke and Gonser 1997). Due to the position of the surface bed layers between surface water and groundwater, the balanced alternation between colmation and scour can be disturbed by impacts affecting both surface and groundwater habitats (Hancock 2002), which can cause permanent colmation.<br />
The most common causes of colmation are organic and fine sediment inputs to the river channel, river channel engineering, and increased filtration through the channel margins during water extraction for drinking, industrial and irrigation water (Petts, 1988). External colmation can result from increased sewage loading that promotes the development of dense algal mats, or causes sedimentation of an organic layer on the river bed. Internal colmation is caused by the infiltration / intrusion of fine particulate organic or inorganic matter into the cavities within the bed sediments (Schalchli, 1993, after Brunke and Gonser 1997). Land use practices which increase seston and sediment loading are directly responsible for the extent of the unbalanced colmation processes (Karr & Schlosser, 1978; Platts et al., 1989, after Brunke and Gonser 1997).<br />
By preventing the communication between surface and groundwater, cascading effects in ecosystem structure and function may occur (Brunke and Gonser 1997). For instance, siltation of the interstices reduces the shelter for invertebrates, and thus the impacts of natural and anthropogenic disturbances, such as urban stormwater runoff, are magnified. Sealed interstices cannot function as nurseries for the benthos. Colmation can diminish or prevent the reproductive success of fish spawning on gravel.<br />
On the other hand, a clogged bed may act as an intrusion barrier that prevents the contamination of groundwater by polluted surface water (Younger et al., 1993; Komatina, 1994, after Brunke and Gonser 1997).<br />
Colmation might not be the only cause of the loss of vertical connectivity. The water velocity near the most superficial sediment layers determines the dominant flow direction between the surface and groundwater. If the temporal distribution of water velocities change, more subtle disturbances in the flow between both systems can be noticed. For instance, Curry et al. (1994) found that discharge fluctuations caused by hydroelectric power generation alter the mixing relationships between surface water and groundwater in the hyporrheic zone. And this could have severe impacts on the reproductive success of gravel spawning fish. This effect was found to occur naturally in some reaches along an upland salmon spawning catchment by Malcolm et al. (2005). They found that at sites dominated by surface water, hyporrheic DO remained high throughout and rates of embryo survival were correspondingly high.<br />
Restoration actions have been conducted and benefits in both the hyporrheos and the groundwater table near the river have been reported. After restoration programs, Sarriquet et al. (2007) detected an increase in vertical exchanges of water between surface and interstitial habitats, with an increase in the depth of hypoxia. Golz et al. (1991, after Brunke and Gonser 1997) reported that the mechanical opening of a clogged section of the Rhine’s stream bed near a drinking water bank filtration site induced a 1 m rise in the groundwater table near the river, but after a few weeks the opened section had become sealed again. Therefore, the viability of such restoration works may be associated with catchment management designed to reduce fine<br />
sediment inputs to the river (Sarriquet et al. 2007).<br />
Loss of vertical connectivity not only affects interactions between channel and adjacent terrain but also between the land surface and underlying and aquifers. In urbanised areas, previously permeable surfaces are replaced by paved impermeable surfaces (Schick et al. 1999). This may cause a general decline in the water table and a deterioration in groundwater quality with urbanization (Jat et al. 2009).<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P20" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P20" /><br />
==Useful references==<br />
<br />
Hancock, P.J., 2002. Human impacts on the stream–groundwater exchange zone. Environmental Management 29: 763–781.<br />
Kondolf, G. M., and P. R. Wilcock 1996. The flushing flow problem: defining and<br />
evaluating objectives. Water Resources Research 32: 2589-2599.<br />
Kondolf, G. M., A. J. Boulton, S. O'Daniel, G. C. Poole, F. J. Rahel, E. H. Stanley, E. Wohl, A. Bång, J. Carlstrom, C. Cristoni, H. Huber, S. Koljonen, P. Louhi, and K. Nakamura. 2006. Process-based ecological river restoration: visualizing three-dimensional connectivity and dynamic vectors to recover lost linkages. Ecology and Society 11(2): 5. http://www.ecologyandsociety.org/vol11/iss2/art5/<br />
<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=ImpoundmentImpoundment2015-09-01T08:21:45Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Impoundment=<br />
04. Morphological alterations<br />
==General description==<br />
<br />
Any transverse barrier to the flow in a river impounds water upstream. When this barrier is small (e.g. less than 10 m high) it may be called a weir, dike or small dam. Barriers that are taller than 15 m are all termed dams. All of these barriers are used for retaining water for many purposes and the river is transformed into an impoundment upstream.<br />
Natural flow velocity is reduced due to the presence of the impoundment, resulting in the deposition of transported sediments. The effectiveness of a reservoir as a sediment trap is mainly dependent upon its storage capacity and the length of time that it stores water (Brune, 1953<ref>Brune, G.M., 1953. Trap efficiency of Reservoirs. Transactions American Geophysical Union 34: 407–419.</ref>), but even the smallest reservoirs are likely to trap most sand sized and finer particles, and large reservoirs are likely to trap close to 100% of transported mineral sediment particles.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
This type of pressure changes the hydraulic conditions on the impounded river reach, from lotic to lentic. A transverse obstacle such as a weir increases water depth and reduces water velocity, and as a result fine sediment is deposited, clogging interstitial habitats. However, when high flows occur, these fine sediments can be mobilised and washed out over these relatively small structures.<br />
Small impoundments flood areas that were previously part of the channel margin and floodplain. Such flooding can have physical and chemical effects both within the impoundment and downstream. For example, in relatively dry environments, more frequent inundation can exaccerbate salinization, as was observed in association with flooding of once-temporary wetlands in Australia (Walker & Toms 1993).<br />
Increased inundation can benefit native fishes, as was observed in southwestern streams of the USA, by disproportionately displacing non-native fishes (Schultz et al. 2003). Moreover, the beneficial effects of impoundments for certain species can have indirect effects on HYMO processes such as suspended load chemical composition. Barton et al. (2000) found significantly higher concentrations of suspended inorganic matter in the outflows than the inflows of three impoundments along an urban stream in southern Ontario during baseflow conditions, due to carp (''Cyprinus carpio'') feeding activities.<br />
The impact of small impoundments can also be assessed by observing the impact of their removal and the restoration of natural flow dynamics. Stanley et al. (2002) observed a significant decrease in the width of the active channel within the impoundment (from 59 m 2 to 11 m 2 ) as a result of the removal of a low-head dam at Baraboo River, Wisconsin. There was an increase in the extent of ‘loose’ bed sediments including an increase in the sand fraction immediately following dam removal, but the channel adjusted rapidly to an equilibrium form, particularly following the occurrence of the first significant flood. Overall, only small and transient geomorphological and ecological changes and no alteration of channel dimensions were observed in<br />
downstream reaches. Within one year of removal, there were no significant differences in macroinvertebrate assemblages among the formerly impounded reaches, an upstream reference site, or reaches downstream of the dam site. The small changes and rapid recovery reflect the relatively large channel size and the small volume of stored sediment associated with this relatively small impoundment.<br />
<br />
[[File:Impoundment.jpg|thumbnail|Conceptual framework of impoundment effects on HYMO processes and variables.]]<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P12" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P12" /><br />
==Useful references==<br />
<br />
Brune, G.M., 1953. Trap efficiency of Reservoirs. Transactions American Geophysical<br />
Union 34: 407–419.<br />
<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=File:Impoundment.jpgFile:Impoundment.jpg2015-09-01T08:20:45Z<p>Carlos alonso: </p>
<hr />
<div></div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=ImpoundmentImpoundment2015-09-01T08:20:28Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Impoundment=<br />
04. Morphological alterations<br />
==General description==<br />
<br />
Any transverse barrier to the flow in a river impounds water upstream. When this barrier is small (e.g. less than 10 m high) it may be called a weir, dike or small dam. Barriers that are taller than 15 m are all termed dams. All of these barriers are used for retaining water for many purposes and the river is transformed into an impoundment upstream.<br />
Natural flow velocity is reduced due to the presence of the impoundment, resulting in the deposition of transported sediments. The effectiveness of a reservoir as a sediment trap is mainly dependent upon its storage capacity and the length of time that it stores water (Brune, 1953<ref>Brune, G.M., 1953. Trap efficiency of Reservoirs. Transactions American Geophysical Union 34: 407–419.</ref>), but even the smallest reservoirs are likely to trap most sand sized and finer particles, and large reservoirs are likely to trap close to 100% of transported mineral sediment particles.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
This type of pressure changes the hydraulic conditions on the impounded river reach, from lotic to lentic. A transverse obstacle such as a weir increases water depth and reduces water velocity, and as a result fine sediment is deposited, clogging interstitial habitats. However, when high flows occur, these fine sediments can be mobilised and washed out over these relatively small structures.<br />
Small impoundments flood areas that were previously part of the channel margin and floodplain. Such flooding can have physical and chemical effects both within the impoundment and downstream. For example, in relatively dry environments, more frequent inundation can exaccerbate salinization, as was observed in association with flooding of once-temporary wetlands in Australia (Walker & Toms 1993).<br />
Increased inundation can benefit native fishes, as was observed in southwestern streams of the USA, by disproportionately displacing non-native fishes (Schultz et al. 2003). Moreover, the beneficial effects of impoundments for certain species can have indirect effects on HYMO processes such as suspended load chemical composition. Barton et al. (2000) found significantly higher concentrations of suspended inorganic matter in the outflows than the inflows of three impoundments along an urban stream in southern Ontario during baseflow conditions, due to carp (''Cyprinus carpio'') feeding activities.<br />
The impact of small impoundments can also be assessed by observing the impact of their removal and the restoration of natural flow dynamics. Stanley et al. (2002) observed a significant decrease in the width of the active channel within the impoundment (from 59 m 2 to 11 m 2 ) as a result of the removal of a low-head dam at Baraboo River, Wisconsin. There was an increase in the extent of ‘loose’ bed sediments including an increase in the sand fraction immediately following dam removal, but the channel adjusted rapidly to an equilibrium form, particularly following the occurrence of the first significant flood. Overall, only small and transient geomorphological and ecological changes and no alteration of channel dimensions were observed in<br />
downstream reaches. Within one year of removal, there were no significant differences in macroinvertebrate assemblages among the formerly impounded reaches, an upstream reference site, or reaches downstream of the dam site. The small changes and rapid recovery reflect the relatively large channel size and the small volume of stored sediment associated with this relatively small impoundment.<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P12" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P12" /><br />
==Useful references==<br />
<br />
Brune, G.M., 1953. Trap efficiency of Reservoirs. Transactions American Geophysical<br />
Union 34: 407–419.<br />
<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Embankments,_levees_or_dikesEmbankments, levees or dikes2015-09-01T08:14:09Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Embankments, levees or dikes=<br />
04. Morphological alterations<br />
==General description==<br />
<br />
Levees or dikes along a stream or river channel are longitudinal structures designed<br />
to prevent water passing from the river channel to the floodplain. Frequently river<br />
banks are reinforced and their level is raised by the construction of a bank top mound<br />
for flood control. Such bank stabilization eliminates river planform dynamics, and the<br />
addition of levees or dikes prevents lateral hydrological connectivity, which is crucial to hydromorphological complexity and the provision of diverse habitats, including<br />
refugee, for aquatic organisms.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
Artificial bank protection affects channel morphology and dynamics by restricting the channel width and ability to migrate, by reducing energy consumption as a result of bank friction, by restricting bank sediment sources and thus sediment supply, and so enhancing erosion of the river bed (Winterbottom, 2000; Rinaldi, 2003). Extensive levee construction along both banks also contributes to greater stresses on the riverbed. High flows are associated with deeper water depth and higher flow velocities and hence, greater shear stresses on the river bed that lead to bed incision.<br />
Bed incision associated with bank reinforcement and levee construction reduces connectivity between the river and its floodplain, but levee construction also directly reduces connectivity by increasing channel capacity (Gergel et al. 2002, Henry et al. 2002). The consequent loss of the floodplain as flood storage reduces downstream attenuation of flood peaks, potentially increasing flood risk. Such reductions in lateral connectivity not only damage functioning of the riparian zone but also reduce productivity, nutrient exchange, and dispersal of biota more widely across the<br />
floodplain (Jenkins and Boulton 2003).<br />
<br />
[[File:Embankment.jpg|thumbnail|Conceptual framework of alteration of embankments, levees or dikes effects on HYMO processes and variables (POM=Particulate Organic Matter; LWD=Large Woody Debris).]]<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P17" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P17" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=File:Embankment.jpgFile:Embankment.jpg2015-09-01T08:13:00Z<p>Carlos alonso: </p>
<hr />
<div></div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Embankments,_levees_or_dikesEmbankments, levees or dikes2015-09-01T08:12:47Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Embankments, levees or dikes=<br />
04. Morphological alterations<br />
==General description==<br />
<br />
Levees or dikes along a stream or river channel are longitudinal structures designed<br />
to prevent water passing from the river channel to the floodplain. Frequently river<br />
banks are reinforced and their level is raised by the construction of a bank top mound<br />
for flood control. Such bank stabilization eliminates river planform dynamics, and the<br />
addition of levees or dikes prevents lateral hydrological connectivity, which is crucial to hydromorphological complexity and the provision of diverse habitats, including<br />
refugee, for aquatic organisms.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
Artificial bank protection affects channel morphology and dynamics by restricting the channel width and ability to migrate, by reducing energy consumption as a result of bank friction, by restricting bank sediment sources and thus sediment supply, and so enhancing erosion of the river bed (Winterbottom, 2000; Rinaldi, 2003). Extensive levee construction along both banks also contributes to greater stresses on the riverbed. High flows are associated with deeper water depth and higher flow velocities and hence, greater shear stresses on the river bed that lead to bed incision.<br />
Bed incision associated with bank reinforcement and levee construction reduces connectivity between the river and its floodplain, but levee construction also directly reduces connectivity by increasing channel capacity (Gergel et al. 2002, Henry et al. 2002). The consequent loss of the floodplain as flood storage reduces downstream attenuation of flood peaks, potentially increasing flood risk. Such reductions in lateral connectivity not only damage functioning of the riparian zone but also reduce productivity, nutrient exchange, and dispersal of biota more widely across the<br />
floodplain (Jenkins and Boulton 2003).<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P17" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P17" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Channelisation_/_cross_section_alterationChannelisation / cross section alteration2015-09-01T08:09:49Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Channelisation / cross section alteration=<br />
04. Morphological alterations<br />
==General description==<br />
<br />
Channelization refers to river and stream channel engineering undertaken for the<br />
purposes of flood control, navigation, drainage improvement, and reduction of channel<br />
migration potential (Brookes, 1990<ref>Brookes, A., 1990. Restoration and enhancement of engineered river channels: Some european experiences. River Research & Applications 5: 45–56.</ref>). When channelization involves cross section<br />
alteration, this includes activities such as channel enlargement through widening or<br />
deepening, the reduction of flow resistance through clearing or snagging of riparian,<br />
and sometimes aquatic, vegetation and other roughness elements, and the<br />
introduction of bank facing and reinforcement materials. These forms of morphological<br />
modification typically transform channel cross profiles into uniform, smooth,<br />
trapezoidal or rectangular forms.<br />
Cross section alteration can also include embankment, levee or dike construction,<br />
which further enlarge the channel capacity, prevent channel-floodplain connectivity,<br />
and can induce very high flow velocities within the river channel during floods.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
Channelization involves changes in channel planform and gradient (usually straightening); channel cross profile form and flow resistance (usually channel enlargement and removal of morphological and vegetation roughness elements); and in some cases it involves the introduction of artificial materials to reinforce the modified channel form (e.g. concrete, metal, stone, bricks). Thus, McIninch and Garman (2001) defined three significant aspects of channelization of streams in Illinois: stream alteration (the extent to which the stream channel form has been altered or modified (Barbour et al. 1999); sinuosity (the extent to which the stream channel has been straightened); and riparian canopy (the degree to which the stream coverage by vegetation has changed).<br />
These physical changes not only increase the flow energy (increased gradient, decreased flow resistance), but they may modify sediment supply, remove important habitats within the channel, and restrict both lateral and vertical connectivity, leading to severe ecological effects (e.g. Poole et al., 2006). Hydromorphology and ecology are not only directly impacted by channelization, but channelization induces a range of hydromorphological responses that also have ecological significance.<br />
Hydromorphological responses to channelization are as complex as those following dam construction and river impoundment and vary with the type of channelization scheme and its impact on channel gradient, the flow regime, the calibre of bed and bank materials, the supply of sediment, and the ability of the riparian vegetation to colonise and reinforce disturbed sediments.<br />
If any adjustment is to occur, the affected stream has to have sufficient energy to move sediment and thus to remodel the form of the channelized stream. Research by Urban and Rhoads (2003) on the Embarras River basin of east central Illinois, illustrates that where stream gradients are very low (typically between 0.001 and 0.0001 m m -1 in their study site), channel responses to widespread and severe channel straightening and enlargement are extremely slow and channels persist in their modified state for decades following channelization. In such environments, further human modification by river restoration is essential to the re-establishment of a healthy ecosystem.<br />
However, in moderate to high energy environments, responses to channelisation are rapid, far-reaching and complex. One example of this complexity is provided by Simon’s (1989) model of channel evolution following channelization of sand bed rivers in Tennessee. The model identifies six stages of morphological development from (i) the premodified channel and its modification to form (ii) the constructed channel, through a phase of (iii) degradation leading to a (iv) bank slope threshold stage and then a phase of (v) aggradation until (vi) restabilization is reached. Following channel ‘construction’, which usually involves realignment, deepening and bank steepening, channel degradation occurs within the affected reach and propagates upstream. This<br />
involves channel bed incision accompanied by erosion of the bank toe, which together steepen the banks. Eventually the banks reach a critical angle and enter the threshold stage, during which bank failures are widespread and the channel widens. Widening slows and ceases as the bank angles reduce and the channel width allows sediment to be retained at the bank toe. Sediment deposition at the toe and across the bed is enhanced by vegetation colonisation leading to significant bed aggradation and recovery to a restabilised state. Aggradation is often achieved by the formation of alternate bars, which are sediment stores that guide channel planform development. All of these phases are observed within the modified channel and they propagate upstream with bed incision and knick point retreat, leading to widespread morphological impacts.<br />
Although Simon’s (1989) model provides an excellent conceptual framework, responses to channelization deviate from it with local circumstances. For example, Simon and Thomas (2002) illustrate a significant downstream response to channelization following the propagation of the degradation and threshold stages upstream that provides an important extension to the model. They observed that the upstream migration of knick points associated with the degradation phase on the Yalobusha River, Mississippi, resulted in the delivery of large quantities of sediment<br />
and woody vegetation to downstream reaches from bank failures. These materials accumulated at the downstream end of the channelized reach to form a large sediment/debris plug at the junction with an unmodified sinuous reach. Such a plug has the potential to produce a local higher base level which may accelerate the propagation of bed aggradation and channel recovery upstream. Furthermore, plug removal could reactivate incision and bank failure, with the potential for enhanced failure due to groundwater drainage through the basal bank layers. In addition, the<br />
presence of erosion resistant clay beds in some reaches, rather than the sand beds of the original model, was observed to restrict bed incision and knick-point propagation, leading to channel adjustments that were more dependent upon channel widening and bank failure.<br />
In the coarser-bed, steeper, rivers of northern Italy, Surian & Rinaldi (2003) found rather different and even more extreme responses to those recorded by Simon (1989). While Simon’s (1989) research focused entirely upon the effects of channelization, Surian and Rinaldi (2003) observed responses to a range of human interventions including dam and weir construction, in-channel gravel mining, reforestation and more general flow regime changes as well as river channelization and embanking. They proposed a classification of adjusted channel types, which were combined into a model of stages of channel adjustment. The model describes how progressive bed incision of typically 3-4 m (up to 10 m in some examples) and narrowing (by up to 50%) of single-thread, transitional and multi-thread (braided) rivers lead to the development of a sequence of degraded channel types. These responses reflect not only channelization processes but also a heavily reduced supply of sediment, and in many cases a modified flow regime.<br />
Observations of adjustment in the Raba river, Poland, by Wyzga (1993) provide a detailed record of the processes similar to those that have contributed to the changes observed in the Italian rivers. Wyzga observed up to 3 m of bed incision, with the progression of headcutting increasingly moderated by energy-dissipating mid-channel bars in upstream reaches. Incision was accompanied by the erosion and removal of finer bed material, and a reduction in the susceptibility of the remaining, armoured bed to particle entrainment. Incision resulted in an increasingly efficient channel cross profile and a consequential magnification of peak discharges and more flashy flood waves. The increase in channel depth, bed coarsening and decreased bed gradient that was created as erosion propagated upstream led to re-establishment of a new equilibrium at higher flow velocities and stream power than before channelization.<br />
These examples illustrate that channelization by straightening, steepening and simplifying the cross profile of stream channels generally increases flow velocities and therefore often significantly alter bed sediment by removing silt and other easily moved particles to create an armoured bed. In urban rivers, the quality of the bed material may also change, as has been observed on the River Tame, UK, where heavy metal concentrations within the urbanized matrix sediment are up to 3000 times greater than background levels (Thoms 1987). Straightening of stream channels generally reduces the amount of substrate available for epifaunal colonization by<br />
reducing the roughness of the channel boundary (through removal of woody debris and other potential habitat such as rocks and boulders) and by removing stream bends where pool development, bank undercutting and exposure of vegetation roots supply a variety of habitats.<br />
Some channelization schemes incorporate in-channel structures, such as weirs and rip-rap at the bank toe, to reduce the channel gradient locally, increase the flow resistance and thus dissipate the increased flow energy that may otherwise accompany channelization. These structures increase the physical complexity and thus habitat diversity of channelized reaches (Silva-Santos et al. 2004). Research by Bombino and others (Bombino et al. 2007, 2008, 2009) has investigated the sedimentary and plant ecological changes induced by the introduction of check dams into steep, confined mountain torrent streams in Calabria, Italy. They found pronounced increases in channel and riparian zone width, decreased channel gradient and fining of bed<br />
sediment calibre upstream of the check dams, which was associated with an increase in plant species richness, and in vegetation cover and development relative to reaches downstream of or unaffected by check dams. In this case, the physical changes induced by the check dams have increased the range of habitats available for plant colonization, and have provided a range of lower energy, more water retentive patches, where a variety of species can establish.<br />
The effects of grade control structures (GCS: weirs with stone-protected stilling basins) combined with streambank protection were assessed in the much lower gradient environment of Twentymile Creek, Mississippi by Shields and Hoover (1991). Here bank-line woody vegetation cover increased by 8% in 4 years on the more stable channel margins, reaches immediately upstream and downstream of GCS were deeper with slower flow velocities, and differences in aquatic habitat diversity among sites along the river were primarily due to the bed scour holes downstream of GCS and inthe low-flow channel. Comparison with reaches without GCS, showed a 29% higher index of fish diversity, which was positively correlated with substrate diversity and<br />
mean depth, and with fourteen species collected exclusively at GCS. Abundance of several of the numerically dominant species was positively associated with deeper water and lower flow velocities.<br />
Despite the positive impacts of some channelization structures in some environmental settings, the ecological impacts of channelization are usually negative. The simplified channels that are created, particularly in association with land drainage and flood alleviation, lead to significant ecological degradation. For example, the main channel of the River Morava (a tributary of the Danube) has been totally isolated by channelization from its flood plain and regulated by weirs. Here, Jurajda (1995) found that the young of the year of phytophilous species (pike ''Esox lucius'' L., rudd ''Scardinius erythrophthalmus'' (L), silver bream ''Blicca bjoerkna'' (L), tench ''Tinca tinca'' (L), carp ''Cyprinus carpio'' (L.) had almost disappeared, and a decline in density was also found for rheophils, such as vimba ''Vimba vimba'' (L.), barbel ''Barbus barbus'' (L.) and nase ''Chondrostoma nasus'' (L.), previously the dominant species in the river. Such degradation may affect riparian as well as aquatic habitats and species, and can feed through to impacts on birds as well as terrestrial organisms (Frederickson, 1979).<br />
However, morphological recovery from channelisation is accompanied by vegetation and other ecological recovery that is also complex but has some characteristic features. Hupp (1992) observed vegetation recovery in the same Tennessee channels studied by Simon (1989). In particular, he noted the importance of riparian vegetation in facilitating recovery through the aggradation and restabilisation stages. He noted that woody vegetation initially establishes on lower bank surfaces in association with bank toe accretion, helping to trap and stabilise the depositing sediment. At this early phase, the vegetation is dominated by hardy, fast growing, pioneer species that can tolerate moderate amounts of slope instability and sediment deposition (e.g. ''Betula nigra'', ''Salix nigra'', ''Acer negundo'', and ''Acer saccharinum''). They grow in dense stands with dense root-mass development that enhances bank stability. As aggradation<br />
progresses and banks become increasingly stable, other species colonise the channel margins, and the analysis of tree rings suggested that 65 yrs may typically be required for restabilisation to be complete.<br />
Morphological and vegetation recovery are accompanied by recolonisation by macroinvertebrate and fish species, and such recovery can be enhanced by deliberate, appropriately-designed, restoration. For example, Friberg et al. (1994) found that two years after restoration of a meandering course to a 1.3 km straightened and channelized reach of the River Gelså, macroinvertebrate density and diversity was greater than in the upstream control reach and species preferring a stony habitat seemed to favour the new reach, including ''Heptagenia sulphurea'' Müll., ''Ancylus fluviatilis'' Müller and ''Hydropsyche pellucidula'' Curtis.<br />
<br />
[[File:Channelization.jpg|thumbnail|Conceptual framework of channelization effects on HYMO processes and variables (POM=Particulate Organic Matter; LWD=Large Woody Debris).]]<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P13" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P13" /><br />
==Useful references==<br />
<br />
Brookes, A., 1990. Restoration and enhancement of engineered river channels: Some<br />
european experiences. River Research & Applications 5: 45–56.<br />
<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=File:Channelization.jpgFile:Channelization.jpg2015-09-01T08:08:35Z<p>Carlos alonso: </p>
<hr />
<div></div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Channelisation_/_cross_section_alterationChannelisation / cross section alteration2015-09-01T08:07:35Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Channelisation / cross section alteration=<br />
04. Morphological alterations<br />
==General description==<br />
<br />
Channelization refers to river and stream channel engineering undertaken for the<br />
purposes of flood control, navigation, drainage improvement, and reduction of channel<br />
migration potential (Brookes, 1990<ref>Brookes, A., 1990. Restoration and enhancement of engineered river channels: Some european experiences. River Research & Applications 5: 45–56.</ref>). When channelization involves cross section<br />
alteration, this includes activities such as channel enlargement through widening or<br />
deepening, the reduction of flow resistance through clearing or snagging of riparian,<br />
and sometimes aquatic, vegetation and other roughness elements, and the<br />
introduction of bank facing and reinforcement materials. These forms of morphological<br />
modification typically transform channel cross profiles into uniform, smooth,<br />
trapezoidal or rectangular forms.<br />
Cross section alteration can also include embankment, levee or dike construction,<br />
which further enlarge the channel capacity, prevent channel-floodplain connectivity,<br />
and can induce very high flow velocities within the river channel during floods.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
Channelization involves changes in channel planform and gradient (usually straightening); channel cross profile form and flow resistance (usually channel enlargement and removal of morphological and vegetation roughness elements); and in some cases it involves the introduction of artificial materials to reinforce the modified channel form (e.g. concrete, metal, stone, bricks). Thus, McIninch and Garman (2001) defined three significant aspects of channelization of streams in Illinois: stream alteration (the extent to which the stream channel form has been altered or modified (Barbour et al. 1999); sinuosity (the extent to which the stream channel has been straightened); and riparian canopy (the degree to which the stream coverage by vegetation has changed).<br />
These physical changes not only increase the flow energy (increased gradient, decreased flow resistance), but they may modify sediment supply, remove important habitats within the channel, and restrict both lateral and vertical connectivity, leading to severe ecological effects (e.g. Poole et al., 2006). Hydromorphology and ecology are not only directly impacted by channelization, but channelization induces a range of hydromorphological responses that also have ecological significance.<br />
Hydromorphological responses to channelization are as complex as those following dam construction and river impoundment and vary with the type of channelization scheme and its impact on channel gradient, the flow regime, the calibre of bed and bank materials, the supply of sediment, and the ability of the riparian vegetation to colonise and reinforce disturbed sediments.<br />
If any adjustment is to occur, the affected stream has to have sufficient energy to move sediment and thus to remodel the form of the channelized stream. Research by Urban and Rhoads (2003) on the Embarras River basin of east central Illinois, illustrates that where stream gradients are very low (typically between 0.001 and 0.0001 m m -1 in their study site), channel responses to widespread and severe channel straightening and enlargement are extremely slow and channels persist in their modified state for decades following channelization. In such environments, further human modification by river restoration is essential to the re-establishment of a healthy ecosystem.<br />
However, in moderate to high energy environments, responses to channelisation are rapid, far-reaching and complex. One example of this complexity is provided by Simon’s (1989) model of channel evolution following channelization of sand bed rivers in Tennessee. The model identifies six stages of morphological development from (i) the premodified channel and its modification to form (ii) the constructed channel, through a phase of (iii) degradation leading to a (iv) bank slope threshold stage and then a phase of (v) aggradation until (vi) restabilization is reached. Following channel ‘construction’, which usually involves realignment, deepening and bank steepening, channel degradation occurs within the affected reach and propagates upstream. This<br />
involves channel bed incision accompanied by erosion of the bank toe, which together steepen the banks. Eventually the banks reach a critical angle and enter the threshold stage, during which bank failures are widespread and the channel widens. Widening slows and ceases as the bank angles reduce and the channel width allows sediment to be retained at the bank toe. Sediment deposition at the toe and across the bed is enhanced by vegetation colonisation leading to significant bed aggradation and recovery to a restabilised state. Aggradation is often achieved by the formation of alternate bars, which are sediment stores that guide channel planform development. All of these phases are observed within the modified channel and they propagate upstream with bed incision and knick point retreat, leading to widespread morphological impacts.<br />
Although Simon’s (1989) model provides an excellent conceptual framework, responses to channelization deviate from it with local circumstances. For example, Simon and Thomas (2002) illustrate a significant downstream response to channelization following the propagation of the degradation and threshold stages upstream that provides an important extension to the model. They observed that the upstream migration of knick points associated with the degradation phase on the Yalobusha River, Mississippi, resulted in the delivery of large quantities of sediment<br />
and woody vegetation to downstream reaches from bank failures. These materials accumulated at the downstream end of the channelized reach to form a large sediment/debris plug at the junction with an unmodified sinuous reach. Such a plug has the potential to produce a local higher base level which may accelerate the propagation of bed aggradation and channel recovery upstream. Furthermore, plug removal could reactivate incision and bank failure, with the potential for enhanced failure due to groundwater drainage through the basal bank layers. In addition, the<br />
presence of erosion resistant clay beds in some reaches, rather than the sand beds of the original model, was observed to restrict bed incision and knick-point propagation, leading to channel adjustments that were more dependent upon channel widening and bank failure.<br />
In the coarser-bed, steeper, rivers of northern Italy, Surian & Rinaldi (2003) found rather different and even more extreme responses to those recorded by Simon (1989). While Simon’s (1989) research focused entirely upon the effects of channelization, Surian and Rinaldi (2003) observed responses to a range of human interventions including dam and weir construction, in-channel gravel mining, reforestation and more general flow regime changes as well as river channelization and embanking. They proposed a classification of adjusted channel types, which were combined into a model of stages of channel adjustment. The model describes how progressive bed incision of typically 3-4 m (up to 10 m in some examples) and narrowing (by up to 50%) of single-thread, transitional and multi-thread (braided) rivers lead to the development of a sequence of degraded channel types. These responses reflect not only channelization processes but also a heavily reduced supply of sediment, and in many cases a modified flow regime.<br />
Observations of adjustment in the Raba river, Poland, by Wyzga (1993) provide a detailed record of the processes similar to those that have contributed to the changes observed in the Italian rivers. Wyzga observed up to 3 m of bed incision, with the progression of headcutting increasingly moderated by energy-dissipating mid-channel bars in upstream reaches. Incision was accompanied by the erosion and removal of finer bed material, and a reduction in the susceptibility of the remaining, armoured bed to particle entrainment. Incision resulted in an increasingly efficient channel cross profile and a consequential magnification of peak discharges and more flashy flood waves. The increase in channel depth, bed coarsening and decreased bed gradient that was created as erosion propagated upstream led to re-establishment of a new equilibrium at higher flow velocities and stream power than before channelization.<br />
These examples illustrate that channelization by straightening, steepening and simplifying the cross profile of stream channels generally increases flow velocities and therefore often significantly alter bed sediment by removing silt and other easily moved particles to create an armoured bed. In urban rivers, the quality of the bed material may also change, as has been observed on the River Tame, UK, where heavy metal concentrations within the urbanized matrix sediment are up to 3000 times greater than background levels (Thoms 1987). Straightening of stream channels generally reduces the amount of substrate available for epifaunal colonization by<br />
reducing the roughness of the channel boundary (through removal of woody debris and other potential habitat such as rocks and boulders) and by removing stream bends where pool development, bank undercutting and exposure of vegetation roots supply a variety of habitats.<br />
Some channelization schemes incorporate in-channel structures, such as weirs and rip-rap at the bank toe, to reduce the channel gradient locally, increase the flow resistance and thus dissipate the increased flow energy that may otherwise accompany channelization. These structures increase the physical complexity and thus habitat diversity of channelized reaches (Silva-Santos et al. 2004). Research by Bombino and others (Bombino et al. 2007, 2008, 2009) has investigated the sedimentary and plant ecological changes induced by the introduction of check dams into steep, confined mountain torrent streams in Calabria, Italy. They found pronounced increases in channel and riparian zone width, decreased channel gradient and fining of bed<br />
sediment calibre upstream of the check dams, which was associated with an increase in plant species richness, and in vegetation cover and development relative to reaches downstream of or unaffected by check dams. In this case, the physical changes induced by the check dams have increased the range of habitats available for plant colonization, and have provided a range of lower energy, more water retentive patches, where a variety of species can establish.<br />
The effects of grade control structures (GCS: weirs with stone-protected stilling basins) combined with streambank protection were assessed in the much lower gradient environment of Twentymile Creek, Mississippi by Shields and Hoover (1991). Here bank-line woody vegetation cover increased by 8% in 4 years on the more stable channel margins, reaches immediately upstream and downstream of GCS were deeper with slower flow velocities, and differences in aquatic habitat diversity among sites along the river were primarily due to the bed scour holes downstream of GCS and inthe low-flow channel. Comparison with reaches without GCS, showed a 29% higher index of fish diversity, which was positively correlated with substrate diversity and<br />
mean depth, and with fourteen species collected exclusively at GCS. Abundance of several of the numerically dominant species was positively associated with deeper water and lower flow velocities.<br />
Despite the positive impacts of some channelization structures in some environmental settings, the ecological impacts of channelization are usually negative. The simplified channels that are created, particularly in association with land drainage and flood alleviation, lead to significant ecological degradation. For example, the main channel of the River Morava (a tributary of the Danube) has been totally isolated by channelization from its flood plain and regulated by weirs. Here, Jurajda (1995) found that the young of the year of phytophilous species (pike ''Esox lucius'' L., rudd ''Scardinius erythrophthalmus'' (L), silver bream ''Blicca bjoerkna'' (L), tench ''Tinca tinca'' (L), carp ''Cyprinus carpio'' (L.) had almost disappeared, and a decline in density was also found for rheophils, such as vimba ''Vimba vimba'' (L.), barbel ''Barbus barbus'' (L.) and nase ''Chondrostoma nasus'' (L.), previously the dominant species in the river. Such degradation may affect riparian as well as aquatic habitats and species, and can feed through to impacts on birds as well as terrestrial organisms (Frederickson, 1979).<br />
However, morphological recovery from channelisation is accompanied by vegetation and other ecological recovery that is also complex but has some characteristic features. Hupp (1992) observed vegetation recovery in the same Tennessee channels studied by Simon (1989). In particular, he noted the importance of riparian vegetation in facilitating recovery through the aggradation and restabilisation stages. He noted that woody vegetation initially establishes on lower bank surfaces in association with bank toe accretion, helping to trap and stabilise the depositing sediment. At this early phase, the vegetation is dominated by hardy, fast growing, pioneer species that can tolerate moderate amounts of slope instability and sediment deposition (e.g. ''Betula nigra'', ''Salix nigra'', ''Acer negundo'', and ''Acer saccharinum''). They grow in dense stands with dense root-mass development that enhances bank stability. As aggradation<br />
progresses and banks become increasingly stable, other species colonise the channel margins, and the analysis of tree rings suggested that 65 yrs may typically be required for restabilisation to be complete.<br />
Morphological and vegetation recovery are accompanied by recolonisation by macroinvertebrate and fish species, and such recovery can be enhanced by deliberate, appropriately-designed, restoration. For example, Friberg et al. (1994) found that two years after restoration of a meandering course to a 1.3 km straightened and channelized reach of the River Gelså, macroinvertebrate density and diversity was greater than in the upstream control reach and species preferring a stony habitat seemed to favour the new reach, including ''Heptagenia sulphurea'' Müll., ''Ancylus fluviatilis'' Müller and ''Hydropsyche pellucidula'' Curtis.<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P13" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P13" /><br />
==Useful references==<br />
<br />
Brookes, A., 1990. Restoration and enhancement of engineered river channels: Some<br />
european experiences. River Research & Applications 5: 45–56.<br />
<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Alteration_of_riparian_vegetationAlteration of riparian vegetation2015-09-01T07:54:27Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Alteration of riparian vegetation=<br />
04. Morphological alterations<br />
==General description==<br />
<br />
Many different pressures impact on riparian vegetation driven by processes acting<br />
at local up to global scales from. In this particular context we are specifically referring<br />
to activities carried out immediately adjacent to the river (e.g. cultivation of crops) or<br />
in the riparian zone itself (e.g. logging, grazing and trampling, gravel and water<br />
extraction, and recreation).<br />
<br />
==Effect/Impact on (including literature citations)==<br />
The encroachment of agriculture has had a major effect on river margins. This is particularly true of lowland floodplain rivers, where river margin soils are often moist and rich. As a result, the edges of many rivers are directly in contact with agriculture and, as a consequence, riparian zones are fragmented and are often reduced to narrow strips or isolated trees on the river banks. Agricultural practices of tilling and harvesting prevent riparian vegetation regeneration and lead to degradation of the riparian seed bank.<br />
The rough canopy of natural riparian vegetation traps sediment from flood waters, leading to bank aggradation and extension. At the same time, the roots of riparian vegetation reinforce river banks, limiting their erosion during high flows, and enabling channel banks to extend into the channel and aggrade vertically. In particular, riparian vegetation retains and stabilizes fine sediments and narrows river channels to increase flow velocities. Both of these processes reduce fine sediment supply and settlement within the channel and thus its potential to infiltrate channel bed sediments causing interstitial siltation and clogging of the bed.<br />
<br />
*Logging & tree removal<br />
The presence of riparian woodland is crucial to the structure, morphology and dynamics of river margins, since it interacts with flows of water and sediment to create and reinforce river margin landforms (Gurnell, 2013). As a result, clearance of riparian woodland can lead to simplification of river margins, channel widening, and in extreme cases a change in river planform from meandering to braiding. These fundamental morphological impacts affect the moisture regime of river margins; exchanges of water, suspended and dissolved material between the river and its riparian zone; as well as numerous biogeochemical and ecological processes (Gurnell and Petts, 2011).<br />
Removal of riparian trees has an immediate effect on river ecosystems by reducing shading and thus increasing stream temperatures and light penetration. Removal also decreases bank stability, inputs of litter and wood, and retention of nutrients and contaminants; reduces sediment trapping and increases bank and channel erosion; alters the quantity and character of dissolved organic carbon reaching streams; lowers retention of benthic organic matter owing to loss of direct input and retention structures; and alters trophic structure (Allan, 2004).<br />
Sabater et al. (2008) studied the effects of riparian vegetation removal on algal dynamics and stream nutrient retention efficiency by comparing NH4-N and PO4-P uptake lengths from a logged and an unlogged reach in a forested Mediterranean stream. Their study showed that the elimination of riparian vegetation altered in-stream ecological features that lead to changes in stream nutrient retention efficiency. Moreover, it emphasizes that alteration of the tight linkage between the stream channel and the adjacent riparian zone may directly and indirectly impact biogeochemical processes with implications for stream ecosystem functioning. In this<br />
context, the role of the riparian vegetation in filtering nutrients coming from agricultural watersheds, is well known, and underpins the use of buffer strips to prevent river eutrophication (Osborne & Kavacic, 1993).<br />
Removal of riparian vegetation inevitably leads to a severe reduction in the supply of wood to the aquatic system. Furthermore, large wood is often deliberately removed from forested rivers for flood defense purposes. Large wood plays a complex and important role in aquatic ecosystems. It affects flow hydraulics, sediment dynamics and sorting, channel morphology and stability, physical habitat composition, dynamics and diversity, and nutrient cycling (Gurnell et al., 1995), with effects varying with channel size and planform, and with riparian tree species (Gurnell et al., 2002; Gurnell, 2013). Loss of large wood debris in a stream alters flow hydraulics, causing a simplification of channel bed sediments and habitats, a reduction in organic matter retention, and often a reduction in bed and bank stability. Diez et al. (2001) identified large wood as the main hydromorphic element in river channels in forested basins.<br />
<br />
*Transformation into farming lands<br />
Riparian vegetation acts with flow, sediment and topography to influence channel form, instream habitat, nutrient dynamics, and temperature and flow patterns. Therefore, removal of upland and riparian vegetation through farming and urbanization disrupts land-water linkages leading to reductions in water quality, simplification of stream channels, less stable thermal and flow regimes, and ultimately, reduced biological integrity (Snyder et al. 2003). However, removal or modification of natural riparian vegetation where trees are not naturally present, may not result in such deep-seated and long-lasting effects because agriculture in such areas usually consists of grazing (Williamson et al. 1992).<br />
Riparian ecological degradation and transformation to agricultural uses often leads to invasion by alien plants (Planty-Tabacchi et al., 1996). Plant invasions are increased directly or indirectly by many types of human-mediated disturbances to rivers and riparian zones (Richardson et al., 2007). Once introduced and established in a catchment, many alien plants can exploit opportunities provided both by natural flood events and by anthropogenic disturbances to which they are better attuned than native species (Planty-Tabacchi et al., 1996).<br />
<br />
[[File:Alteration Riparian vegetation.jpg|thumbnail|Conceptual framework of alteration of riparian vegetation effects on HYMO processes and variables (POM= Particulate Organic Matter; LWD= Large Woody Debris).]]<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P14" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P14" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=File:Alteration_Riparian_vegetation.jpgFile:Alteration Riparian vegetation.jpg2015-09-01T07:53:26Z<p>Carlos alonso: </p>
<hr />
<div></div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Alteration_of_riparian_vegetationAlteration of riparian vegetation2015-09-01T07:53:10Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Alteration of riparian vegetation=<br />
04. Morphological alterations<br />
==General description==<br />
<br />
Many different pressures impact on riparian vegetation driven by processes acting<br />
at local up to global scales from. In this particular context we are specifically referring<br />
to activities carried out immediately adjacent to the river (e.g. cultivation of crops) or<br />
in the riparian zone itself (e.g. logging, grazing and trampling, gravel and water<br />
extraction, and recreation).<br />
<br />
==Effect/Impact on (including literature citations)==<br />
The encroachment of agriculture has had a major effect on river margins. This is particularly true of lowland floodplain rivers, where river margin soils are often moist and rich. As a result, the edges of many rivers are directly in contact with agriculture and, as a consequence, riparian zones are fragmented and are often reduced to narrow strips or isolated trees on the river banks. Agricultural practices of tilling and harvesting prevent riparian vegetation regeneration and lead to degradation of the riparian seed bank.<br />
The rough canopy of natural riparian vegetation traps sediment from flood waters, leading to bank aggradation and extension. At the same time, the roots of riparian vegetation reinforce river banks, limiting their erosion during high flows, and enabling channel banks to extend into the channel and aggrade vertically. In particular, riparian vegetation retains and stabilizes fine sediments and narrows river channels to increase flow velocities. Both of these processes reduce fine sediment supply and settlement within the channel and thus its potential to infiltrate channel bed sediments causing interstitial siltation and clogging of the bed.<br />
<br />
*Logging & tree removal<br />
The presence of riparian woodland is crucial to the structure, morphology and dynamics of river margins, since it interacts with flows of water and sediment to create and reinforce river margin landforms (Gurnell, 2013). As a result, clearance of riparian woodland can lead to simplification of river margins, channel widening, and in extreme cases a change in river planform from meandering to braiding. These fundamental morphological impacts affect the moisture regime of river margins; exchanges of water, suspended and dissolved material between the river and its riparian zone; as well as numerous biogeochemical and ecological processes (Gurnell and Petts, 2011).<br />
Removal of riparian trees has an immediate effect on river ecosystems by reducing shading and thus increasing stream temperatures and light penetration. Removal also decreases bank stability, inputs of litter and wood, and retention of nutrients and contaminants; reduces sediment trapping and increases bank and channel erosion; alters the quantity and character of dissolved organic carbon reaching streams; lowers retention of benthic organic matter owing to loss of direct input and retention structures; and alters trophic structure (Allan, 2004).<br />
Sabater et al. (2008) studied the effects of riparian vegetation removal on algal dynamics and stream nutrient retention efficiency by comparing NH4-N and PO4-P uptake lengths from a logged and an unlogged reach in a forested Mediterranean stream. Their study showed that the elimination of riparian vegetation altered in-stream ecological features that lead to changes in stream nutrient retention efficiency. Moreover, it emphasizes that alteration of the tight linkage between the stream channel and the adjacent riparian zone may directly and indirectly impact biogeochemical processes with implications for stream ecosystem functioning. In this<br />
context, the role of the riparian vegetation in filtering nutrients coming from agricultural watersheds, is well known, and underpins the use of buffer strips to prevent river eutrophication (Osborne & Kavacic, 1993).<br />
Removal of riparian vegetation inevitably leads to a severe reduction in the supply of wood to the aquatic system. Furthermore, large wood is often deliberately removed from forested rivers for flood defense purposes. Large wood plays a complex and important role in aquatic ecosystems. It affects flow hydraulics, sediment dynamics and sorting, channel morphology and stability, physical habitat composition, dynamics and diversity, and nutrient cycling (Gurnell et al., 1995), with effects varying with channel size and planform, and with riparian tree species (Gurnell et al., 2002; Gurnell, 2013). Loss of large wood debris in a stream alters flow hydraulics, causing a simplification of channel bed sediments and habitats, a reduction in organic matter retention, and often a reduction in bed and bank stability. Diez et al. (2001) identified large wood as the main hydromorphic element in river channels in forested basins.<br />
<br />
*Transformation into farming lands<br />
Riparian vegetation acts with flow, sediment and topography to influence channel form, instream habitat, nutrient dynamics, and temperature and flow patterns. Therefore, removal of upland and riparian vegetation through farming and urbanization disrupts land-water linkages leading to reductions in water quality, simplification of stream channels, less stable thermal and flow regimes, and ultimately, reduced biological integrity (Snyder et al. 2003). However, removal or modification of natural riparian vegetation where trees are not naturally present, may not result in such deep-seated and long-lasting effects because agriculture in such areas usually consists of grazing (Williamson et al. 1992).<br />
Riparian ecological degradation and transformation to agricultural uses often leads to invasion by alien plants (Planty-Tabacchi et al., 1996). Plant invasions are increased directly or indirectly by many types of human-mediated disturbances to rivers and riparian zones (Richardson et al., 2007). Once introduced and established in a catchment, many alien plants can exploit opportunities provided both by natural flood events and by anthropogenic disturbances to which they are better attuned than native species (Planty-Tabacchi et al., 1996).<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P14" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P14" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Alteration_of_instream_habitatAlteration of instream habitat2015-09-01T07:48:31Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Alteration of instream habitat=<br />
04. Morphological alterations<br />
==General description==<br />
<br />
Natural instream habitats offer refuge and shelter, food resources and spawning<br />
grounds to aquatic biota. Recognition of instream habitat alteration should be based on<br />
changes in surface flow type, hydraulic attributes (flow depth, velocity and bed<br />
roughness, shear velocity, Reynolds and Froude numbers), channel morphology, and<br />
bed substrate calibre.<br />
Instream habitat degradation may be an effect of a hydrogeomorphological process<br />
(natural or caused by other pressures), or of a direct human activity (e.g. channel<br />
dredging, gravel bed extraction). The latter activities are those pressures we are<br />
refering to here.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
All hydromorphological pressures affect instream habitat, but in this section, we refer to those pressures that directly destroy the aquatic habitat, such as channel dredging and mining, and the reinforcement of channel bed and banks with introduced materials such as concrete or rip-rap. These activities generally reduce channel boundary roughness, leading to increased flow velocities and other consequences similar to those resulting from channelization. Assessing the effects of these specific pressures is difficult due to their association with other potential habitat-altering variables. For example, increases in turbidity and siltation can easily arise from<br />
agricultural land use (i.e. cattle grazing) in both channelized and reference streams.<br />
<br />
*Channel dredging<br />
Channel dredging lowers and usually steepens the channel bed. Even if further incision is not induced, channel banks become higher and more exposed to erosion and, as a result, bank erosion is a likely consequence of dredging. The degree of impact of the dredging depends on the quantities of sediment delivered by the river to the dredged reach. The smaller the ratio of dredged to supplied sediment the smaller the likely HYMO effects. Lagasse and Winkley (1980) concluded that gravel dredging in the lower Mississippi River caused bed degradation, reduced flow resistance and thus reduced flood heights and groundwater table levels. Lou et al. (2007) identified increased grade slope, bank instability, and brackish-water intrusion as negative HYMO<br />
effects of dredging, while positive effects included decreased flooding. They also cited a study by Han et al. (2005, in Chinese) that identified changes in the river regime as a result of dredging, including lowered water levels, alteration of surface water and groundwater recharge, and re-balancing of salt and fresh water in tidal regions.<br />
<br />
* Bed Reinforcement<br />
Not many references dealing with HYMO processes and variables have been found. Urban development transforms the hydrological system through construction of impervious surfaces and stormwater drainage systems, and river channels are completely reinforced precluding any morphological adjustment. Gurnell et al (2007) have analyzed of Urban River Survey data from 143 urban channel reaches in three European rivers (the River Tame, UK; the River Emscher, Germany; and the River Botic, Czech Republic) and have demonstrated the strong influence of river channel engineering on channel structure, physical habitat features and vegetation patterns.<br />
<br />
[[File:Alteration instream habitat.jpg|thumbnail|Conceptual framework of alteration of in-stream habitat effects on HYMO processes and variables (LWD = Large Woody Debris).]]<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P15" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P15" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=File:Alteration_instream_habitat.jpgFile:Alteration instream habitat.jpg2015-09-01T07:47:24Z<p>Carlos alonso: </p>
<hr />
<div></div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Alteration_of_instream_habitatAlteration of instream habitat2015-09-01T07:47:06Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Alteration of instream habitat=<br />
04. Morphological alterations<br />
==General description==<br />
<br />
Natural instream habitats offer refuge and shelter, food resources and spawning<br />
grounds to aquatic biota. Recognition of instream habitat alteration should be based on<br />
changes in surface flow type, hydraulic attributes (flow depth, velocity and bed<br />
roughness, shear velocity, Reynolds and Froude numbers), channel morphology, and<br />
bed substrate calibre.<br />
Instream habitat degradation may be an effect of a hydrogeomorphological process<br />
(natural or caused by other pressures), or of a direct human activity (e.g. channel<br />
dredging, gravel bed extraction). The latter activities are those pressures we are<br />
refering to here.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
All hydromorphological pressures affect instream habitat, but in this section, we refer to those pressures that directly destroy the aquatic habitat, such as channel dredging and mining, and the reinforcement of channel bed and banks with introduced materials such as concrete or rip-rap. These activities generally reduce channel boundary roughness, leading to increased flow velocities and other consequences similar to those resulting from channelization. Assessing the effects of these specific pressures is difficult due to their association with other potential habitat-altering variables. For example, increases in turbidity and siltation can easily arise from<br />
agricultural land use (i.e. cattle grazing) in both channelized and reference streams.<br />
<br />
*Channel dredging<br />
Channel dredging lowers and usually steepens the channel bed. Even if further incision is not induced, channel banks become higher and more exposed to erosion and, as a result, bank erosion is a likely consequence of dredging. The degree of impact of the dredging depends on the quantities of sediment delivered by the river to the dredged reach. The smaller the ratio of dredged to supplied sediment the smaller the likely HYMO effects. Lagasse and Winkley (1980) concluded that gravel dredging in the lower Mississippi River caused bed degradation, reduced flow resistance and thus reduced flood heights and groundwater table levels. Lou et al. (2007) identified increased grade slope, bank instability, and brackish-water intrusion as negative HYMO<br />
effects of dredging, while positive effects included decreased flooding. They also cited a study by Han et al. (2005, in Chinese) that identified changes in the river regime as a result of dredging, including lowered water levels, alteration of surface water and groundwater recharge, and re-balancing of salt and fresh water in tidal regions.<br />
<br />
* Bed Reinforcement<br />
Not many references dealing with HYMO processes and variables have been found. Urban development transforms the hydrological system through construction of impervious surfaces and stormwater drainage systems, and river channels are completely reinforced precluding any morphological adjustment. Gurnell et al (2007) have analyzed of Urban River Survey data from 143 urban channel reaches in three European rivers (the River Tame, UK; the River Emscher, Germany; and the River Botic, Czech Republic) and have demonstrated the strong influence of river channel engineering on channel structure, physical habitat features and vegetation patterns.<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P15" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P15" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Alteration_of_instream_habitatAlteration of instream habitat2015-09-01T07:44:57Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Alteration of instream habitat=<br />
04. Morphological alterations<br />
==General description==<br />
<br />
Natural instream habitats offer refuge and shelter, food resources and spawning<br />
grounds to aquatic biota. Recognition of instream habitat alteration should be based on<br />
changes in surface flow type, hydraulic attributes (flow depth, velocity and bed<br />
roughness, shear velocity, Reynolds and Froude numbers), channel morphology, and<br />
bed substrate calibre.<br />
Instream habitat degradation may be an effect of a hydrogeomorphological process<br />
(natural or caused by other pressures), or of a direct human activity (e.g. channel<br />
dredging, gravel bed extraction). The latter activities are those pressures we are<br />
refering to here.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
All hydromorphological pressures affect instream habitat, but in this section, we refer to those pressures that directly destroy the aquatic habitat, such as channel dredging and mining, and the reinforcement of channel bed and banks with introduced materials such as concrete or rip-rap. These activities generally reduce channel boundary roughness, leading to increased flow velocities and other consequences similar to those resulting from channelization. Assessing the effects of these specific pressures is difficult due to their association with other potential habitat-altering variables. For example, increases in turbidity and siltation can easily arise from<br />
agricultural land use (i.e. cattle grazing) in both channelized and reference streams.<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P15" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P15" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:04. Morphological alterations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Artificial_barriers_downstream_from_the_siteArtificial barriers downstream from the site2015-09-01T07:42:24Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Artificial barriers downstream from the site=<br />
03. River fragmentation<br />
==General description==<br />
River fragmentation is caused by discontinuity in any of the river’s three spatial dimensions: longitudinal, lateral and vertical. Such discontinuities disrupt hydrological connectivity (Pringle, 2003), interrupt the transfer of water, mineral sediment, organic matter and organisms within and between elements of the river system, and thus impact on the river’s biotic and physical components (Bunn and Arthington, 2002).<br />
Longitudinal fragmentation may be produced directly by the presence of dams or artificial barriers, but it may also be produced indirectly by certain conditions caused by HYMO processes and water quality degradation. Hydrological connectivity is water-mediated. For example, reduction of flows, especially of base flow, during some periods may disconnect habitats and species’ populations. Anoxic water conditions along stream reaches, or thermal discharges may also act as barriers for riverine aquatic organisms.<br />
Lateral fragmentation is caused by the presence of lateral barriers such as levees and dikes that disconnect river ecosystems from their floodplains by preventing overbank flooding. The integrity of both riparian and aquatic ecosystems is thought to be dependent, in part, upon exchanges of energy and matter between the main river channel and adjacent floodplain surface and the patches present within and between them during periods of flooding (Amoros and Roux, 1988; Junk et al., 1989, Junk and Wantzen, 2004). Disturbances or flow regulations that eliminate or reduce flood flow magnitude, or lateral barriers that limit the extent of inundation of the floodplain,<br />
disrupt connectivity between river and floodplain. In addition, certain indirect effects of pressures, through their correponding HYMO proccesses, may cause floodplain isolation. For example, restriction in sediment supply to a river may induce river bed incision, which in turn reduces hydrological connectivity between river and floodplain.<br />
Processes such as channel bed incision or riparian and floodplain accretion, which both disrupt river-floodplain connectivity are frequently found in disturbed rivers.<br />
Henceforth, this review will only focus on the pressures involved in longitudinal fragmentation, as lateral fragmentation will be incorporated in pressures related to channelization (embankments and levees) and vertical fragmentation will be incorporated in pressures related to substrate siltation and clogging, and riparian soil sealing and compaction.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
River fragmentation is mainly assumed to be caused by barriers that interrupt the longitudinal gradient or by lateral dikes that disconnect the channel and floodplain. Thus the fragmentation effects of large dams is superimposed on their effects on the flow, sediment and physico-chemical regimes and is recognizable along the entire river continuum and laterally across floodplains (Ward and Stanford, 1983, 1995). However, reaches of river channel that are subjected to artificial drought or heavy pollution can also act as river fragmentation factors. Furthermore, riparian corridors are frequently fragmented by forestry and farming activities.<br />
River fragmentation is of wide significance, since most large rivers of the world are fragmented due to flow regulation schemes, and only a few river systems in the northern third of the world are free flowing (Dynesius & Nilsson 1994).<br />
The impact of dams and related flow regulation and fragmentation on riparian vegetation has been well-studied. Andersson et al (2000) found that riparian floristic continuity was reduced below dams, and Merritt et al. (2010) suggested that water dispersal of plant propagules may be reduced and the long-term species richness of the riparian community may decrease. However, there is no evidence that dams reduce the abundance and diversity of water-dispersed propagules by acting as barriers for plant dispersal (Jansson et al, 2005).<br />
The construction of weirs and other embankments on the lower Macintyre River floodplain has had lateral fragmentation effects by preventing water movement through a series of anabranch channels thereby reducing the availability of these floodplain patches by 55% (Thoms et al 2005), and thus reducing the potential dissolved organic carbon supply from some anabranch channels to the main channel by up to 98% (Thoms et al 2005).<br />
The ways in which dams and weirs act as physical barriers to the migration of fish and other biota have long been recognized (Kingsford 2000a,b). Barriers located near the river mouth have the greatest impact on fish with diadromous life histories while those located near the center of the river network have the most impact on fish with potadromous life histories (Cote et al. 2009).<br />
Sanches et al. (2006) showed a clear decline in densities and number of fish species caught after the closure of the Porto Primavera dam, Brazil. Also, larvae of migratory species, were restricted to the confluence of non-dammed tributaries, indicating that the closure of the dam had caused negative impacts on fish reproduction downstream of the dam.<br />
In a fish population modeling experiment Jager et al. (2001) found that increased fragmentation by dams produced a reduction in genetic diversity and an exponential decline in the likelihood of persistence, but no extinction threshold that would suggest a minimum viable length of river. They also found that migration patterns played a significant role in determining the viability of riverine fishes, with those populations with high downstream, and low upstream, migration rates showing a higher risk of extinction.<br />
<br />
[[File:River fragmentation.jpg|thumbnail|Conceptual framework of river fragmentation effects on HYMO processes and variables.]]<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P10" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P10" /><br />
==Useful references==<br />
Amoros C. & Roux A.L. (1988) Interaction between water bodies within the floodplain<br />
of large rivers: function and development of connectivity. Münstersche Geographische Arbeiten 29: 125–130.<br />
Bunn, S.E. & Arthington, A.H., 2002. Basic Principles and Ecological Consequences of<br />
Altered Flow Regimes for Aquatic Biodiversity. Environmental Management 30: 492–507.<br />
Hancock, P.J., 2002. Human impacts on the stream–groundwater exchange zone. Environmental Management 29: 763–781.<br />
Kondolf, G. M., A. J. Boulton, S. O'Daniel, G. C. Poole, F. J. Rahel, E. H. Stanley, E.<br />
Wohl, A. Bång, J. Carlstrom, C. Cristoni, H. Huber, S. Koljonen, P. Louhi, and K.<br />
Nakamura. 2006. Process-based ecological river restoration: visualizing three-dimensional connectivity and dynamic vectors to recover lost linkages. Ecology and Society 11(2): 5. http://www.ecologyandsociety.org/vol11/iss2/art5/<br />
Kondolf, G. M., and P. R. Wilcock 1996. The flushing flow problem: defining and evaluating objectives. Water Resources Research 32: 2589-2599.<br />
Junk, W.J., P.B. Bayley, R.E. Sparks, 1989. The flood pulse concept in river-floodplain<br />
systems. Canadian Journal of Fisheries and Aquatic Sciences 106: 110–127.<br />
Junk, W.J., Wantzen, K.M., 2004. The flood pulse concept: new aspects, approaches and applications–an update, in: Proceedings of the Second International Symposium on the Management of Large Rivers for Fisheries. pp. 117–140.<br />
Pringle, C., 2003. What is hydrologic connectivity and why is it ecologically important? Hydrological Processes 17: 2685–2689.<br />
<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:03. River fragmentation]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=File:River_fragmentation.jpgFile:River fragmentation.jpg2015-09-01T07:40:55Z<p>Carlos alonso: </p>
<hr />
<div></div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Artificial_barriers_downstream_from_the_siteArtificial barriers downstream from the site2015-09-01T07:40:32Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Artificial barriers downstream from the site=<br />
03. River fragmentation<br />
==General description==<br />
River fragmentation is caused by discontinuity in any of the river’s three spatial dimensions: longitudinal, lateral and vertical. Such discontinuities disrupt hydrological connectivity (Pringle, 2003), interrupt the transfer of water, mineral sediment, organic matter and organisms within and between elements of the river system, and thus impact on the river’s biotic and physical components (Bunn and Arthington, 2002).<br />
Longitudinal fragmentation may be produced directly by the presence of dams or artificial barriers, but it may also be produced indirectly by certain conditions caused by HYMO processes and water quality degradation. Hydrological connectivity is water-mediated. For example, reduction of flows, especially of base flow, during some periods may disconnect habitats and species’ populations. Anoxic water conditions along stream reaches, or thermal discharges may also act as barriers for riverine aquatic organisms.<br />
Lateral fragmentation is caused by the presence of lateral barriers such as levees and dikes that disconnect river ecosystems from their floodplains by preventing overbank flooding. The integrity of both riparian and aquatic ecosystems is thought to be dependent, in part, upon exchanges of energy and matter between the main river channel and adjacent floodplain surface and the patches present within and between them during periods of flooding (Amoros and Roux, 1988; Junk et al., 1989, Junk and Wantzen, 2004). Disturbances or flow regulations that eliminate or reduce flood flow magnitude, or lateral barriers that limit the extent of inundation of the floodplain,<br />
disrupt connectivity between river and floodplain. In addition, certain indirect effects of pressures, through their correponding HYMO proccesses, may cause floodplain isolation. For example, restriction in sediment supply to a river may induce river bed incision, which in turn reduces hydrological connectivity between river and floodplain.<br />
Processes such as channel bed incision or riparian and floodplain accretion, which both disrupt river-floodplain connectivity are frequently found in disturbed rivers.<br />
Henceforth, this review will only focus on the pressures involved in longitudinal fragmentation, as lateral fragmentation will be incorporated in pressures related to channelization (embankments and levees) and vertical fragmentation will be incorporated in pressures related to substrate siltation and clogging, and riparian soil sealing and compaction.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
River fragmentation is mainly assumed to be caused by barriers that interrupt the longitudinal gradient or by lateral dikes that disconnect the channel and floodplain. Thus the fragmentation effects of large dams is superimposed on their effects on the flow, sediment and physico-chemical regimes and is recognizable along the entire river continuum and laterally across floodplains (Ward and Stanford, 1983, 1995). However, reaches of river channel that are subjected to artificial drought or heavy pollution can also act as river fragmentation factors. Furthermore, riparian corridors are frequently fragmented by forestry and farming activities.<br />
River fragmentation is of wide significance, since most large rivers of the world are fragmented due to flow regulation schemes, and only a few river systems in the northern third of the world are free flowing (Dynesius & Nilsson 1994).<br />
The impact of dams and related flow regulation and fragmentation on riparian vegetation has been well-studied. Andersson et al (2000) found that riparian floristic continuity was reduced below dams, and Merritt et al. (2010) suggested that water dispersal of plant propagules may be reduced and the long-term species richness of the riparian community may decrease. However, there is no evidence that dams reduce the abundance and diversity of water-dispersed propagules by acting as barriers for plant dispersal (Jansson et al, 2005).<br />
The construction of weirs and other embankments on the lower Macintyre River floodplain has had lateral fragmentation effects by preventing water movement through a series of anabranch channels thereby reducing the availability of these floodplain patches by 55% (Thoms et al 2005), and thus reducing the potential dissolved organic carbon supply from some anabranch channels to the main channel by up to 98% (Thoms et al 2005).<br />
The ways in which dams and weirs act as physical barriers to the migration of fish and other biota have long been recognized (Kingsford 2000a,b). Barriers located near the river mouth have the greatest impact on fish with diadromous life histories while those located near the center of the river network have the most impact on fish with potadromous life histories (Cote et al. 2009).<br />
Sanches et al. (2006) showed a clear decline in densities and number of fish species caught after the closure of the Porto Primavera dam, Brazil. Also, larvae of migratory species, were restricted to the confluence of non-dammed tributaries, indicating that the closure of the dam had caused negative impacts on fish reproduction downstream of the dam.<br />
In a fish population modeling experiment Jager et al. (2001) found that increased fragmentation by dams produced a reduction in genetic diversity and an exponential decline in the likelihood of persistence, but no extinction threshold that would suggest a minimum viable length of river. They also found that migration patterns played a significant role in determining the viability of riverine fishes, with those populations with high downstream, and low upstream, migration rates showing a higher risk of extinction.<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P10" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P10" /><br />
==Useful references==<br />
Amoros C. & Roux A.L. (1988) Interaction between water bodies within the floodplain<br />
of large rivers: function and development of connectivity. Münstersche Geographische Arbeiten 29: 125–130.<br />
Bunn, S.E. & Arthington, A.H., 2002. Basic Principles and Ecological Consequences of<br />
Altered Flow Regimes for Aquatic Biodiversity. Environmental Management 30: 492–507.<br />
Hancock, P.J., 2002. Human impacts on the stream–groundwater exchange zone. Environmental Management 29: 763–781.<br />
Kondolf, G. M., A. J. Boulton, S. O'Daniel, G. C. Poole, F. J. Rahel, E. H. Stanley, E.<br />
Wohl, A. Bång, J. Carlstrom, C. Cristoni, H. Huber, S. Koljonen, P. Louhi, and K.<br />
Nakamura. 2006. Process-based ecological river restoration: visualizing three-dimensional connectivity and dynamic vectors to recover lost linkages. Ecology and Society 11(2): 5. http://www.ecologyandsociety.org/vol11/iss2/art5/<br />
Kondolf, G. M., and P. R. Wilcock 1996. The flushing flow problem: defining and evaluating objectives. Water Resources Research 32: 2589-2599.<br />
Junk, W.J., P.B. Bayley, R.E. Sparks, 1989. The flood pulse concept in river-floodplain<br />
systems. Canadian Journal of Fisheries and Aquatic Sciences 106: 110–127.<br />
Junk, W.J., Wantzen, K.M., 2004. The flood pulse concept: new aspects, approaches and applications–an update, in: Proceedings of the Second International Symposium on the Management of Large Rivers for Fisheries. pp. 117–140.<br />
Pringle, C., 2003. What is hydrologic connectivity and why is it ecologically important? Hydrological Processes 17: 2685–2689.<br />
<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:03. River fragmentation]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Hydrological_regime_modificationHydrological regime modification2015-08-31T12:55:26Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Hydrological regime modification=<br />
02. Flow regulations<br />
==General description==<br />
River regulation imposes fundamental changes on flow and sediment transfer, which<br />
are the principal controls on fluvial morphodynamics (Church, 1995).<br />
<br />
In order to significantly modify the natural flow regime, a major artificial water<br />
store, in the form of a reservoir, or a major water transfer scheme from another<br />
watershed is usually needed, although groundwater resources are sometimes used to<br />
augment or regulate river flow regimes to match water demand (e.g. Cowx, 2000). The impacts caused by dams and reservoirs in rivers is a problem of global nature that affects the major rivers around the world (Petts, 1984; Dynesius & Nilsson, 1994; Jalon Garcia et al., 1992, Nilsson & Berggren, 2000; etc.).<br />
<br />
The hydrological changes produced by this type of regulation are strongly influenced<br />
by its purpose: flood control, hydropower, water supply and irrigation (Ward &<br />
Stanford, 1979, Petts, 1984). Each type of water use produces a different type of<br />
regulated flow regime that results in different ecological alterations, and often the<br />
same reservoir is operated for multiple purposes. For example, reservoirs for irrigation are operated to store water during humid seasons and to release it during dry seasons, usually producing a regime of more seasonally constant flows. Reservoirs designed for irrigation, domestic or industrial water supply and hydropower generation all tend to attenuate and delay the seasonal regime of flows to the downstream water body. Vörösmarty et al. (1997) estimated that in the mid 1980s the maximum water storage of the 746 World’s largest dams was equivalent to 20% of global mean annual runoff and the median water residence time in these impoundments was 0.40 years. <br />
<br />
Regarding irrigation reservoirs in Mediterranean rivers, first there is the very significant transformation of the natural flow regime into a regulated regime in opposed phase: minimum monthly flows that naturally occur in summer, are increased into maximum ones due to the demand for water for irrigation, while the minimum flows occur in the winter months. colder and more precipitation, which tries to fill the reservoirs (see Figure 1).<br />
<br />
<br />
[[Image:regulacion4.jpg|400px|thumb|center|Figure 1.- Flow Regime river Porma (Spain) affected by the dam Juan Benet (irrigation reservoir), distinguishing two periods, an unregulated (1942-1968) and other post-exploitation of the dam (1969-2004).]] <br />
<br /><br /><br />
<br />
<br />
With the filling of reservoirs during the months of rain (winter) are eliminated or ordinary floods of higher frequency, which are of great importance in maintaining the natural channel morphology and the renovation of habitat and regeneration of the riparian vegetation, and generating a flow regime much more uniform in time, where only keep the avenues overtime (Figure 2). <br />
<br />
The transformation of the natural flow generated from the regulation for irrigation depends on the location on the river network of the stretch of river in question. It can only mean a change of the times in which they occur peak flows, or also include a drastic reduction of water flowing through the channels with respect to the contribution natural, downstream from the derivations of water for use in agriculture.<br />
<br />
<br />
[[Image:regulacion5.jpg|400px|thumb|center|Figure 2.- River Aragon flow regime, downstream of the dam of Yesa. Since 1970 at which the regulation for irrigation significantly reduces the frequency of regular floods, between 100 and 200 m3/s, and increases the length of minimum flows, so will these impacts over time.]] <br />
<br /><br /><br />
<br />
<br />
The regulation of the flow affects very significantly to the physical habitat of the rivers where they live aquatic communities of plants and animals, or those associated with moisture inland. The affections to the aquatic habitat may refer to the emergence of hydraulic conditions relating to the depth of the water, speed of current, shear stress,.., unsuitable for native species and may affect a mismatch of spawning for fish reproduction, lack of deep areas of refuge for individuals larger, and so on. They can also alter the physical and chemical characteristics of water, with reduced forms of dissolved salts, problems of dissolved oxygen content, or altering the temperature regime in connection with fund outflows of reservoirs, with summer temperatures in much colder that the air which impacts on the development of biological cycles of aquatic insects.<br />
<br />
In the stretches of rivers are also regulated extensions or modify the surface useful for each species, to vary the area of film and the distribution of water depths in each section of the channel depending on the flow circulating. It also changes the size and arrangement of sediment to the bed and banks; when traveling on a prolonged the minimum flows (during autumn and winter) is the siltation of the bed by accumulation of thin, with a seal of microhabitats, while when traveling on a continuous peak flows (months irrigation) increases the drag forces on the bed, causing instability in the macro, and how the banks are a size too thick to retain moisture and germination and growth of seeds.<br />
<br />
Dams are barriers that inhibit fish migrations, but their effect on the river continuum is much more important because affects all its components though the fragmentation of all the fluvial network (Dynesius & Nilsson, 1994).<br />
<br />
Some of these effects result immediate from the starting of the reservoir regulation and others show a delay in their appearance, especially the changes in the composition and structure of communities biological. In general, new water controlled conditions are less favorable to native species adapted to a natural with Mediterranean avenues regular season marked a certain magnitude and in the warmer months, and more favorable for exotic species from other regions They can be more competitive than the first in the schemes covered more uniform, similar to those of the rivers of origin. <br />
<br />
This irrigation regulation produces impacts that affect in more or less degree the aquatic system and the dependant environments. Changes in the river flows (in terms of quantity, timing, and frequency) can lead directly to biologic and geomorphic changes, and geomorphic changes lead indirectly to ecological adjustments (Whiting, 2002), altering ecosystem stability in terms of resistance and resilience (Connel & Wayne, 1983). As some authors have mentioned, under regulated conditions Mediterranean stream species cannot compete successfully with many introduced (generalist and limnethic) species (García de Jalón et al., 1992; Morillo et al., 2002), diminishing the ability of aquatic systems to maintain a balanced, integrated, and adaptable community of autochthonous organisms.<br />
<br />
The effects of regulating the flow into the fish species have been studied in depth in Spain and are well documented in different jobs (Elvira, 1995; Elvira and Almodovar, 2001, etc.). It is clear that the maintenance of regulated flow regimes, with neither annual or interannual fluctuations, including bankfull discharges floods for natural regeneration of the river habitat, has created a different fluvial habitat that has favor a strong invasion of mediterranean rivers for many species, both fish (e.g., catfish, sun-fish, carp, pike, salmon of the Danube, etc.). as other animal species (e.g., zebra mussel) or aquatic plants (e.g. water hyacinth).<br />
<br />
Mediterranean streams have natural regimes with an important torrential component that is reflected in strong seasonal and interannual fluctuations. At evolutionary scale, the geological and biogeographical history of these rivers (together with these particular hydrological features), has produced a large number of endemic species since many fluvial basins have remained isolated for a long time. As a consequence, the degree of endemicism of primary and secondary freshwater fishes in Spain is remarkable (Elvira, 1995). These species are not adapted to the new habitats and cannot compite successfully with introduced ones.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
<br />
The implementation of river impoundments and inter-basin transfers may increase or decrease flows, but they also have aggregate effects on other properties of the flow regime, including flow variability and timing. Magilligan and Nislow (2004) reviewed pre- and post-dam hydrological changes downstream of dams that covered the spectrum of hydrological and climatic regimes across the United States. In general, the most significant changes occurred in minimum and maximum flows of different duration. The 1-day through 90-day minimum flows increased significantly and the 1-day through 7-day maximum flows decreased significantly following impoundment.<br />
Other significant adjustments across the majority of sites following impoundment included: an increase in the number of hydrograph reversals; an increase in the number of flow pulses but a decrease in their duration; and a decrease in the mean rate of hydrograph rise and fall.<br />
At a basin scale, Batalla et al. (2004) showed that the presence of 187 large dams in the Ebro basin, with a total capacity equivalent to 57% of the total mean annual runoff, reduced flood magnitude, with Q 2 and Q 10 reduced over 30% on average, particularly in rivers with higher values of the impounded runoff index, (i.e., reservoir capacity divided by mean annual runoff). Also, they found that the variability of mean daily flows was reduced in most cases due to storing of winter floods and increased baseflows in summer for irrigation.<br />
The important role of physical stability, defined in relation to hydrological (frequency, duration and timing of inundation) and channel parameters (channel dynamics, bedform and sediment size) on fluvial ecosystems was emphasized by Petts (2000). Thus, regulated flows disturb the bedform, surface-water and groundwater interactions and the channel form dynamics and associated changing hydraulic conditions that alter both benthic and riparian community patterns.<br />
Decreased flow dynamics can reduce vertical hydrological connectivity by reducing hydraulic gradients (Kondolf et al. 2006). <br />
Flood peaks are typically reduced by river regulation, which reduces the frequency and extent of floodplain inundation and flow through side channels (Gergel et al. 2002, and Henry et al. 2002). The reduction in channel-forming flows reduces channel migration, an important phenomenon in maintaining high levels of habitat diversity across floodplains (Ward & Stanford, 2006): the rich mosaic of habitat patches across the floodplain due to a wide range of successional stages is transformed into an uniform mature riparian forest. Hydrological connectivity with the remaining floodplain geomorphic features is also reduced, as illustrated by flow regulation on the lower Macintyre River, Australia. Here flow regulation has limited exchanges between the<br />
river and its floodplain, (Walker & Thoms 1993), including a reduction in the frequency of hydrological connections to a series of anabranch channels by up to 22% (Thoms et al 2005); induced a stepped profile in the main channel; and changed the nature of the littoral zone, creating an environment inimical to many native species, notably fish (Walker & Thoms 1993).<br />
Flushing flows are often employed in an attempt to impede or reverse some of these effects. Such flows are particularly effective in removing fine particulate materials and chemicals that may have accumulated under supressed flow conditions. For example, flushing flows from Beervlei Dam on the Groot River were effective in removing accumulated salts from riverine pools. The flushing flows were followed by reduced flows which initiated spawning of the potamodromous minnow species in the riffle areas (Cambray 2006).<br />
<br />
[[File:Regime modification.jpg|thumbnail|Conceptual framework representing aggregate impacts of impoundments and interbasin transfers on hydromorphological (HYMO) processes and variables.]]<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P05" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P05" /><br />
==Useful references==<br />
<br />
Church, M., 1995. Geomorphic response to river flow regulation: Case studies and<br />
time-scales. Regulated Rivers: Research & Management 11: 3–22.<br />
<br />
Cowx, I. 2000. Potential impact of groundwater augmentation of river flows on<br />
fisheries: a case study from the River Ouse, Yorkshire, UK. Fisheries<br />
Management and Ecology 7: 85-96.<br />
<br />
<br />
Dynesius, M. y C. Nilsson. 1994. Fragmentation and flow regulation of river systems in the northern third of the world. Science, 266: 753-762.<br />
<br />
García de Jalón, D., M. González del Tánago y C. Casado. 1992. Ecology of regulated rivers in Spain: An overview. Limnetica, 8: 161-166.<br />
<br />
González del Tánago, M. 1996. Impacto de la agricultura en los sistemas fluviales. Técnicas de restauración para la conservación del suelo y del agua. Agricultura y Sociedad, 78: 211-236.<br />
<br />
Kriakeas, S.A. y M.C. Watzin. 2006. Effects of adjacent agricultural activities and watershed characteristics on stream macroinvertebrate communities. Journal of the American Water Resources Association, 42(2): 425-441.<br />
<br />
MAPA (Ministerio de Agricultura, Pesca y Alimentación) 2003. El Libro Blanco de la Agricultura y el Desarrollo Rural. Publ. Ministerio de Agricultura, Pesca y Alimentación, Madrid.<br />
<br />
MMA (Ministerio de Medio Ambiente). 1998. Libro Blanco del Agua. Ministerio de Medio Ambiente, Madrid.<br />
<br />
Morillo, M., A. Gimenez and D. Garcia de Jalón. 2002. “Evolución de las<br />
poblaciones piscícolas del río Manzanares aguas abajo del embalse de El Pardo<br />
(Madrid).” Limnetica, 17: 13–26.<br />
<br />
Nilsson, C. y K. Berggren. 2000. Alterations of Riparian Ecosystems caused by River regulation. BioScience, 50(9): 783-792.<br />
<br />
Petts, G.E. 1984. Impounded Rivers. John Wiley & sons, Chichester.<br />
<br />
Vörösmarty, C.J.,Fekete, B., Sharma, K. 1997. The potential impact of neo-Castorization on sediment transport by the global network of rivers. Procs. Human impact on erosion and sedimentation 261.<br />
<br />
Ward J.V. & Stanford J.A, 1979. The ecology of regulated streams. New York: Plenum<br />
Press.<br />
<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:02. Flow regulations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Discharge_diversions_and_returnsDischarge diversions and returns2015-08-31T12:54:46Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Discharge diversions and returns=<br />
02. Flow regulations<br />
==General description==<br />
Removal and downstream return of water from the river through a man-made<br />
diversion structure called a ''bypass'' often results in significant flow reduction in the intervening section of the river’s course. This is a typical pressure that affects rivers used for hydropower, whereby flow is diverted from the river by a weir at higher altitude and conducted through a near horizontal bypass channel into turbines that are located downstream at a much lower altitude.<br />
A similar pressure occurs in association with irrigation of farmlands located in the<br />
floodplain and near the river margins, but in this case the return flows are greatly<br />
reduced by plant water consumption, evaporation and infiltration, and may also suffer<br />
from a reduction in water quality.<br />
Diversion also takes place to supply urban areas and industries with water, and in these cases the return flow is affected by significant reductions in both water quality and quantity.<br />
''Flood diversion'' is a special case of flow diversion and return that is designed to<br />
alleviate flooding.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
<br />
Although in temperate regions water abstractions may have relatively minor impacts, in Mediterranean countries they can represent major alterations with the potential to turn perennial rivers into intermittent rivers and to severely degrade physico-chemical conditions, if base flow becomes limited in relation to emissions or discharge of effluents (Prat & Munné, 2000; Menció ''et al''., 2010).<br />
A review of low flow river conditions during dry periods of the year, as well as the<br />
problem of changing minimum river flows as a consequence of climate variability is<br />
presented by Smakhtin (2001).<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P03" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P03" /><br />
==Useful references==<br />
Menció, A., Folch, A., Mas-Pla, J., 2010. Analyzing Hydrological Sustainability Through<br />
Water Balance. Environmental Management 45: 1175–1190.<br />
<br />
Prat, N., A. Munne, 2000. Water use and quality and stream flow in a Mediterranean<br />
stream. Water Research 34: 3876–3881.<br />
<br />
Smakhtin, V.U., 2001. Low flow hydrology: a review. Journal of Hydrology 240: 147–<br />
186.<br />
<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:02. Flow regulations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=HydropeakingHydropeaking2015-08-31T12:53:51Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Hydropeaking=<br />
02. Flow regulations<br />
==General description==<br />
The production of electricity by hydropower plants is often implemented to satisfy<br />
peaks in electricity demand. For this reason these plants work intermittently, creating<br />
periodic and extremely rapid and short-term fluctuations in flow in the receiving water<br />
body. These fluctuations are called hydropeaking and usually show a marked weekly<br />
and daily rhythm.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
<br />
Hydropeaking is a unique form of flow regulation, in that it introduces frequent, short duration, artificial flow events to the river. The impacts of hydropeaking on channel size and morphology are highly dependent on the size and frequency of hydropeaks in relation to size of geomorphological effective flows prior to regulation.<br />
Where extreme hydropeaking leads to frequent geomorphological-effective flows (i.e. flows close to the bankfull stage), the hydropeaks dominate channel size and form because they readily mobilize bed sediments until the bed becomes heavily armoured by very coarse particles or scoured to bed rock. Such severe hydropeaking leaves few alluvial habitats and in-channel vegetation, and an abrupt transition between unvegetated and vegetated surfaces at the channel boundary. However, where hydropeaks are smaller and thus less competent to move bed sediment and the pre-existing geomorphologically-effective flows are significantly less frequent or no longer occur under the new hydropower dominated regime, physical adjustments may occur within the pre-existing channel. Sear (1995) describes an example of the latter situation, where the observed adjustments to the gravel-bed North Tyne River are indicative of channel narrowing and retention of fine sediment in the bed, in response to diurnal adjustments of river stage by approximately 0.6 m from hydropeaking:<br />
a) the development of fine sediment berms along channel margins,<br />
b) the aggradation of pools,<br />
c) the encroachment of vegetation on former gravel shoals<br />
d) the growth of tributary confluence bars.<br />
e) degradation of riffle spawning grounds: characterized by higher percentages of fines within spawning gravels, coarsening of surface gravels and the development of a stable, strong bed fabric.<br />
Hydropeaking has been found to have other more indirect hydromorphological impacts beyond those on channel morphology and sediments. Thus, Curry et al. (1994) found that short-term flow fluctuations affected hyporheos dynamics.<br />
Fluctuating flow levels altered groundwater pathways, chemistry, and flow potentials within the river bed. Rising river levels introduced river water into the bank where various degrees of mixing with groundwater occurred. Subsequent recessions of river levels increased the potentials for groundwater flow into the river channel. They found that these effects were significant at spawning and incubation sites and were thus potentially important for river ecology.<br />
Further indirect hyporheic effects were identified by Arnzten et al. (2007) who found empirical evidence of how changes in flow regime and in bed sediment permeability, relating to ingress of fine sediments, altered the vertical hydraulic gradient and water quality of the hyporheic zone within the Hanford Reach of the Columbia River in response to 2 m daily water level fluctuations due to hydropower generation.<br />
A range of ecological consequences of hydropower development have also been recorded. Nilsson et al. (1991) evaluated the effects of an old hydropower reservoir on river margin vegetation. While he found no difference in mean annual discharge, number of types of substrate, and width and height of the river margin (relative to the summer low-water level), the regulated river had fewer frequent and more infrequent species, and the proportion of annual plus biennial species-richness was higher, while the proportion of perennial species-richness was lower. Also, vegetation cover was lower in the regulated river.<br />
Reduced biotic productivity in reaches below hydroelectric reservoirs may be due directly to flow variations or indirectly to a variety of factors related to flow variations, such as changes in water depth or temperature, or scouring of sediments. Many riverine fish and invertebrate species have a limited range of conditions to which they are adapted. The pattern of daily fluctuations in flow imposed by hydropeaking is not one to which most species are adapted; thus, such conditions can reduce the abundance, diversity, and productivity of these riverine organisms (Cushman, 1985).<br />
Thus, Trotzky & Gregory (1974) focussed specifically on the effect of severe low flows associated with flow fluctuations on the upper Kennebec River. In particular they observed that the very slow currents during low flows between hydropeaks appeared to limit the diversity and abundance of swift-water aquatic insects (Rhyacophila, Chimarra, Iron, Blepharocera, Acroneuria, and Paragnetina) on the river-bottom below the dam.<br />
In relation to high flows, Robertson et al. (2004) subjected Atlantic salmon par to simulated short term flow fluctuations and found that fish habitat use was not affected; there was little effect on fish activity within diel periods; and stranding rates during flow reduction were also very low. However, most research has indicated significant impacts of hydropeaks on both macroinvertebrates and fish.<br />
Bain et al. (1988) found that the fish guild of small-species and size classes that occupied habitats characterized as shallow in depth, slow in current velocity, and concentrated along stream margins, were eliminated or reduced in abundances at a study site subject to large flow fluctuations.<br />
Furthermore, Moog (2006) identified significant impacts of intermittent power generation on the fish fauna and benthic invertebrates of several Austrian rivers.<br />
Hydropeaking was found to disturb long sections of rivers, with a breakdown of the benthic invertebrate biomass of between 75 and 95% within the first few kilometres of river length, and a reduction of between 40 and 60% of biomass within the following 20–40 km. The reduction of the fish fauna was of the same order of magnitude and correlated well with the amplitude of the flow fluctuations.<br />
Similar biotic effects were detected in a Pyrenean river affected by a hydropower impoundment by Garcia de Jalón et al. (1988). At a single sampling station 2.4 km below the dam, there was a significant (p < 0.05) decrease in total macrophyte biomass, although the species composition remained dominated by two species (Myriophyllum verticillatum and Ranunculus fluitans), and the macroinvertebrate community exhibited a significant (p < 0.05) decrease in taxonomic richness, total density and total biomass. In general, planarians, ephemeropterans, coleopterans,<br />
plecopterans and trichopterans disappeared or decreased their abundances. Scrapers (as relative biomass) were the functional feeding group most adversely affected by the new flow regulation. With regard to the fish community, the most significant change was the absence of all resident coarse fishes (cyprinids, primarily) at the sampling site during the 1990 and 1991 sampling surveys.<br />
<br />
[[File:Hydropeaking.jpg|thumbnail|Conceptual framework of hydropeaking hydromorphological (HYMO) processes and variables.]]<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P06" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P06" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:02. Flow regulations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=HydropeakingHydropeaking2015-08-31T12:53:28Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Hydropeaking=<br />
02. Flow regulations<br />
==General description==<br />
The production of electricity by hydropower plants is often implemented to satisfy<br />
peaks in electricity demand. For this reason these plants work intermittently, creating<br />
periodic and extremely rapid and short-term fluctuations in flow in the receiving water<br />
body. These fluctuations are called hydropeaking and usually show a marked weekly<br />
and daily rhythm.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
*HYMO (general and specified per HYMO element)<br />
Hydropeaking is a unique form of flow regulation, in that it introduces frequent, short duration, artificial flow events to the river. The impacts of hydropeaking on channel size and morphology are highly dependent on the size and frequency of hydropeaks in relation to size of geomorphological effective flows prior to regulation.<br />
Where extreme hydropeaking leads to frequent geomorphological-effective flows (i.e. flows close to the bankfull stage), the hydropeaks dominate channel size and form because they readily mobilize bed sediments until the bed becomes heavily armoured by very coarse particles or scoured to bed rock. Such severe hydropeaking leaves few alluvial habitats and in-channel vegetation, and an abrupt transition between unvegetated and vegetated surfaces at the channel boundary. However, where hydropeaks are smaller and thus less competent to move bed sediment and the pre-existing geomorphologically-effective flows are significantly less frequent or no longer occur under the new hydropower dominated regime, physical adjustments may occur within the pre-existing channel. Sear (1995) describes an example of the latter situation, where the observed adjustments to the gravel-bed North Tyne River are indicative of channel narrowing and retention of fine sediment in the bed, in response to diurnal adjustments of river stage by approximately 0.6 m from hydropeaking:<br />
a) the development of fine sediment berms along channel margins,<br />
b) the aggradation of pools,<br />
c) the encroachment of vegetation on former gravel shoals<br />
d) the growth of tributary confluence bars.<br />
e) degradation of riffle spawning grounds: characterized by higher percentages of fines within spawning gravels, coarsening of surface gravels and the development of a stable, strong bed fabric.<br />
Hydropeaking has been found to have other more indirect hydromorphological impacts beyond those on channel morphology and sediments. Thus, Curry et al. (1994) found that short-term flow fluctuations affected hyporheos dynamics.<br />
Fluctuating flow levels altered groundwater pathways, chemistry, and flow potentials within the river bed. Rising river levels introduced river water into the bank where various degrees of mixing with groundwater occurred. Subsequent recessions of river levels increased the potentials for groundwater flow into the river channel. They found that these effects were significant at spawning and incubation sites and were thus potentially important for river ecology.<br />
Further indirect hyporheic effects were identified by Arnzten et al. (2007) who found empirical evidence of how changes in flow regime and in bed sediment permeability, relating to ingress of fine sediments, altered the vertical hydraulic gradient and water quality of the hyporheic zone within the Hanford Reach of the Columbia River in response to 2 m daily water level fluctuations due to hydropower generation.<br />
A range of ecological consequences of hydropower development have also been recorded. Nilsson et al. (1991) evaluated the effects of an old hydropower reservoir on river margin vegetation. While he found no difference in mean annual discharge, number of types of substrate, and width and height of the river margin (relative to the summer low-water level), the regulated river had fewer frequent and more infrequent species, and the proportion of annual plus biennial species-richness was higher, while the proportion of perennial species-richness was lower. Also, vegetation cover was lower in the regulated river.<br />
Reduced biotic productivity in reaches below hydroelectric reservoirs may be due directly to flow variations or indirectly to a variety of factors related to flow variations, such as changes in water depth or temperature, or scouring of sediments. Many riverine fish and invertebrate species have a limited range of conditions to which they are adapted. The pattern of daily fluctuations in flow imposed by hydropeaking is not one to which most species are adapted; thus, such conditions can reduce the abundance, diversity, and productivity of these riverine organisms (Cushman, 1985).<br />
Thus, Trotzky & Gregory (1974) focussed specifically on the effect of severe low flows associated with flow fluctuations on the upper Kennebec River. In particular they observed that the very slow currents during low flows between hydropeaks appeared to limit the diversity and abundance of swift-water aquatic insects (Rhyacophila, Chimarra, Iron, Blepharocera, Acroneuria, and Paragnetina) on the river-bottom below the dam.<br />
In relation to high flows, Robertson et al. (2004) subjected Atlantic salmon par to simulated short term flow fluctuations and found that fish habitat use was not affected; there was little effect on fish activity within diel periods; and stranding rates during flow reduction were also very low. However, most research has indicated significant impacts of hydropeaks on both macroinvertebrates and fish.<br />
Bain et al. (1988) found that the fish guild of small-species and size classes that occupied habitats characterized as shallow in depth, slow in current velocity, and concentrated along stream margins, were eliminated or reduced in abundances at a study site subject to large flow fluctuations.<br />
Furthermore, Moog (2006) identified significant impacts of intermittent power generation on the fish fauna and benthic invertebrates of several Austrian rivers.<br />
Hydropeaking was found to disturb long sections of rivers, with a breakdown of the benthic invertebrate biomass of between 75 and 95% within the first few kilometres of river length, and a reduction of between 40 and 60% of biomass within the following 20–40 km. The reduction of the fish fauna was of the same order of magnitude and correlated well with the amplitude of the flow fluctuations.<br />
Similar biotic effects were detected in a Pyrenean river affected by a hydropower impoundment by Garcia de Jalón et al. (1988). At a single sampling station 2.4 km below the dam, there was a significant (p < 0.05) decrease in total macrophyte biomass, although the species composition remained dominated by two species (Myriophyllum verticillatum and Ranunculus fluitans), and the macroinvertebrate community exhibited a significant (p < 0.05) decrease in taxonomic richness, total density and total biomass. In general, planarians, ephemeropterans, coleopterans,<br />
plecopterans and trichopterans disappeared or decreased their abundances. Scrapers (as relative biomass) were the functional feeding group most adversely affected by the new flow regulation. With regard to the fish community, the most significant change was the absence of all resident coarse fishes (cyprinids, primarily) at the sampling site during the 1990 and 1991 sampling surveys.<br />
<br />
[[File:Hydropeaking.jpg|thumbnail|Conceptual framework of hydropeaking hydromorphological (HYMO) processes and variables.]]<br />
<br />
*physico - chemical parameters<br />
*Biota (general and specified per Biological quality elements)<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P06" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P06" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:02. Flow regulations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Hydrological_regime_modificationHydrological regime modification2015-08-31T12:47:16Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Hydrological regime modification=<br />
02. Flow regulations<br />
==General description==<br />
River regulation imposes fundamental changes on flow and sediment transfer, which<br />
are the principal controls on fluvial morphodynamics (Church, 1995).<br />
<br />
In order to significantly modify the natural flow regime, a major artificial water<br />
store, in the form of a reservoir, or a major water transfer scheme from another<br />
watershed is usually needed, although groundwater resources are sometimes used to<br />
augment or regulate river flow regimes to match water demand (e.g. Cowx, 2000). The impacts caused by dams and reservoirs in rivers is a problem of global nature that affects the major rivers around the world (Petts, 1984; Dynesius & Nilsson, 1994; Jalon Garcia et al., 1992, Nilsson & Berggren, 2000; etc.).<br />
<br />
The hydrological changes produced by this type of regulation are strongly influenced<br />
by its purpose: flood control, hydropower, water supply and irrigation (Ward &<br />
Stanford, 1979, Petts, 1984). Each type of water use produces a different type of<br />
regulated flow regime that results in different ecological alterations, and often the<br />
same reservoir is operated for multiple purposes. For example, reservoirs for irrigation are operated to store water during humid seasons and to release it during dry seasons, usually producing a regime of more seasonally constant flows. Reservoirs designed for irrigation, domestic or industrial water supply and hydropower generation all tend to attenuate and delay the seasonal regime of flows to the downstream water body. Vörösmarty et al. (1997) estimated that in the mid 1980s the maximum water storage of the 746 World’s largest dams was equivalent to 20% of global mean annual runoff and the median water residence time in these impoundments was 0.40 years. <br />
<br />
Regarding irrigation reservoirs in Mediterranean rivers, first there is the very significant transformation of the natural flow regime into a regulated regime in opposed phase: minimum monthly flows that naturally occur in summer, are increased into maximum ones due to the demand for water for irrigation, while the minimum flows occur in the winter months. colder and more precipitation, which tries to fill the reservoirs (see Figure 1).<br />
<br />
<br />
[[Image:regulacion4.jpg|400px|thumb|center|Figure 1.- Flow Regime river Porma (Spain) affected by the dam Juan Benet (irrigation reservoir), distinguishing two periods, an unregulated (1942-1968) and other post-exploitation of the dam (1969-2004).]] <br />
<br /><br /><br />
<br />
<br />
With the filling of reservoirs during the months of rain (winter) are eliminated or ordinary floods of higher frequency, which are of great importance in maintaining the natural channel morphology and the renovation of habitat and regeneration of the riparian vegetation, and generating a flow regime much more uniform in time, where only keep the avenues overtime (Figure 2). <br />
<br />
The transformation of the natural flow generated from the regulation for irrigation depends on the location on the river network of the stretch of river in question. It can only mean a change of the times in which they occur peak flows, or also include a drastic reduction of water flowing through the channels with respect to the contribution natural, downstream from the derivations of water for use in agriculture.<br />
<br />
<br />
[[Image:regulacion5.jpg|400px|thumb|center|Figure 2.- River Aragon flow regime, downstream of the dam of Yesa. Since 1970 at which the regulation for irrigation significantly reduces the frequency of regular floods, between 100 and 200 m3/s, and increases the length of minimum flows, so will these impacts over time.]] <br />
<br /><br /><br />
<br />
<br />
The regulation of the flow affects very significantly to the physical habitat of the rivers where they live aquatic communities of plants and animals, or those associated with moisture inland. The affections to the aquatic habitat may refer to the emergence of hydraulic conditions relating to the depth of the water, speed of current, shear stress,.., unsuitable for native species and may affect a mismatch of spawning for fish reproduction, lack of deep areas of refuge for individuals larger, and so on. They can also alter the physical and chemical characteristics of water, with reduced forms of dissolved salts, problems of dissolved oxygen content, or altering the temperature regime in connection with fund outflows of reservoirs, with summer temperatures in much colder that the air which impacts on the development of biological cycles of aquatic insects.<br />
<br />
In the stretches of rivers are also regulated extensions or modify the surface useful for each species, to vary the area of film and the distribution of water depths in each section of the channel depending on the flow circulating. It also changes the size and arrangement of sediment to the bed and banks; when traveling on a prolonged the minimum flows (during autumn and winter) is the siltation of the bed by accumulation of thin, with a seal of microhabitats, while when traveling on a continuous peak flows (months irrigation) increases the drag forces on the bed, causing instability in the macro, and how the banks are a size too thick to retain moisture and germination and growth of seeds.<br />
<br />
Dams are barriers that inhibit fish migrations, but their effect on the river continuum is much more important because affects all its components though the fragmentation of all the fluvial network (Dynesius & Nilsson, 1994).<br />
<br />
Some of these effects result immediate from the starting of the reservoir regulation and others show a delay in their appearance, especially the changes in the composition and structure of communities biological. In general, new water controlled conditions are less favorable to native species adapted to a natural with Mediterranean avenues regular season marked a certain magnitude and in the warmer months, and more favorable for exotic species from other regions They can be more competitive than the first in the schemes covered more uniform, similar to those of the rivers of origin. <br />
<br />
This irrigation regulation produces impacts that affect in more or less degree the aquatic system and the dependant environments. Changes in the river flows (in terms of quantity, timing, and frequency) can lead directly to biologic and geomorphic changes, and geomorphic changes lead indirectly to ecological adjustments (Whiting, 2002), altering ecosystem stability in terms of resistance and resilience (Connel & Wayne, 1983). As some authors have mentioned, under regulated conditions Mediterranean stream species cannot compete successfully with many introduced (generalist and limnethic) species (García de Jalón et al., 1992; Morillo et al., 2002), diminishing the ability of aquatic systems to maintain a balanced, integrated, and adaptable community of autochthonous organisms.<br />
<br />
The effects of regulating the flow into the fish species have been studied in depth in Spain and are well documented in different jobs (Elvira, 1995; Elvira and Almodovar, 2001, etc.). It is clear that the maintenance of regulated flow regimes, with neither annual or interannual fluctuations, including bankfull discharges floods for natural regeneration of the river habitat, has created a different fluvial habitat that has favor a strong invasion of mediterranean rivers for many species, both fish (e.g., catfish, sun-fish, carp, pike, salmon of the Danube, etc.). as other animal species (e.g., zebra mussel) or aquatic plants (e.g. water hyacinth).<br />
<br />
Mediterranean streams have natural regimes with an important torrential component that is reflected in strong seasonal and interannual fluctuations. At evolutionary scale, the geological and biogeographical history of these rivers (together with these particular hydrological features), has produced a large number of endemic species since many fluvial basins have remained isolated for a long time. As a consequence, the degree of endemicism of primary and secondary freshwater fishes in Spain is remarkable (Elvira, 1995). These species are not adapted to the new habitats and cannot compite successfully with introduced ones.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
*HYMO (general and specified per HYMO element)<br />
<br />
The implementation of river impoundments and inter-basin transfers may increase or decrease flows, but they also have aggregate effects on other properties of the flow regime, including flow variability and timing. Magilligan and Nislow (2004) reviewed pre- and post-dam hydrological changes downstream of dams that covered the spectrum of hydrological and climatic regimes across the United States. In general, the most significant changes occurred in minimum and maximum flows of different duration. The 1-day through 90-day minimum flows increased significantly and the 1-day through 7-day maximum flows decreased significantly following impoundment.<br />
Other significant adjustments across the majority of sites following impoundment included: an increase in the number of hydrograph reversals; an increase in the number of flow pulses but a decrease in their duration; and a decrease in the mean rate of hydrograph rise and fall.<br />
At a basin scale, Batalla et al. (2004) showed that the presence of 187 large dams in the Ebro basin, with a total capacity equivalent to 57% of the total mean annual runoff, reduced flood magnitude, with Q 2 and Q 10 reduced over 30% on average, particularly in rivers with higher values of the impounded runoff index, (i.e., reservoir capacity divided by mean annual runoff). Also, they found that the variability of mean daily flows was reduced in most cases due to storing of winter floods and increased baseflows in summer for irrigation.<br />
The important role of physical stability, defined in relation to hydrological (frequency, duration and timing of inundation) and channel parameters (channel dynamics, bedform and sediment size) on fluvial ecosystems was emphasized by Petts (2000). Thus, regulated flows disturb the bedform, surface-water and groundwater interactions and the channel form dynamics and associated changing hydraulic conditions that alter both benthic and riparian community patterns.<br />
Decreased flow dynamics can reduce vertical hydrological connectivity by reducing hydraulic gradients (Kondolf et al. 2006). <br />
Flood peaks are typically reduced by river regulation, which reduces the frequency and extent of floodplain inundation and flow through side channels (Gergel et al. 2002, and Henry et al. 2002). The reduction in channel-forming flows reduces channel migration, an important phenomenon in maintaining high levels of habitat diversity across floodplains (Ward & Stanford, 2006): the rich mosaic of habitat patches across the floodplain due to a wide range of successional stages is transformed into an uniform mature riparian forest. Hydrological connectivity with the remaining floodplain geomorphic features is also reduced, as illustrated by flow regulation on the lower Macintyre River, Australia. Here flow regulation has limited exchanges between the<br />
river and its floodplain, (Walker & Thoms 1993), including a reduction in the frequency of hydrological connections to a series of anabranch channels by up to 22% (Thoms et al 2005); induced a stepped profile in the main channel; and changed the nature of the littoral zone, creating an environment inimical to many native species, notably fish (Walker & Thoms 1993).<br />
Flushing flows are often employed in an attempt to impede or reverse some of these effects. Such flows are particularly effective in removing fine particulate materials and chemicals that may have accumulated under supressed flow conditions. For example, flushing flows from Beervlei Dam on the Groot River were effective in removing accumulated salts from riverine pools. The flushing flows were followed by reduced flows which initiated spawning of the potamodromous minnow species in the riffle areas (Cambray 2006).<br />
<br />
[[File:Regime modification.jpg|thumbnail|Conceptual framework representing aggregate impacts of impoundments and interbasin transfers on hydromorphological (HYMO) processes and variables.]]<br />
<br />
*physico - chemical parameters<br />
*Biota (general and specified per Biological quality elements)<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P05" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P05" /><br />
==Useful references==<br />
<br />
Church, M., 1995. Geomorphic response to river flow regulation: Case studies and<br />
time-scales. Regulated Rivers: Research & Management 11: 3–22.<br />
<br />
Cowx, I. 2000. Potential impact of groundwater augmentation of river flows on<br />
fisheries: a case study from the River Ouse, Yorkshire, UK. Fisheries<br />
Management and Ecology 7: 85-96.<br />
<br />
<br />
Dynesius, M. y C. Nilsson. 1994. Fragmentation and flow regulation of river systems in the northern third of the world. Science, 266: 753-762.<br />
<br />
García de Jalón, D., M. González del Tánago y C. Casado. 1992. Ecology of regulated rivers in Spain: An overview. Limnetica, 8: 161-166.<br />
<br />
González del Tánago, M. 1996. Impacto de la agricultura en los sistemas fluviales. Técnicas de restauración para la conservación del suelo y del agua. Agricultura y Sociedad, 78: 211-236.<br />
<br />
Kriakeas, S.A. y M.C. Watzin. 2006. Effects of adjacent agricultural activities and watershed characteristics on stream macroinvertebrate communities. Journal of the American Water Resources Association, 42(2): 425-441.<br />
<br />
MAPA (Ministerio de Agricultura, Pesca y Alimentación) 2003. El Libro Blanco de la Agricultura y el Desarrollo Rural. Publ. Ministerio de Agricultura, Pesca y Alimentación, Madrid.<br />
<br />
MMA (Ministerio de Medio Ambiente). 1998. Libro Blanco del Agua. Ministerio de Medio Ambiente, Madrid.<br />
<br />
Morillo, M., A. Gimenez and D. Garcia de Jalón. 2002. “Evolución de las<br />
poblaciones piscícolas del río Manzanares aguas abajo del embalse de El Pardo<br />
(Madrid).” Limnetica, 17: 13–26.<br />
<br />
Nilsson, C. y K. Berggren. 2000. Alterations of Riparian Ecosystems caused by River regulation. BioScience, 50(9): 783-792.<br />
<br />
Petts, G.E. 1984. Impounded Rivers. John Wiley & sons, Chichester.<br />
<br />
Vörösmarty, C.J.,Fekete, B., Sharma, K. 1997. The potential impact of neo-Castorization on sediment transport by the global network of rivers. Procs. Human impact on erosion and sedimentation 261.<br />
<br />
Ward J.V. & Stanford J.A, 1979. The ecology of regulated streams. New York: Plenum<br />
Press.<br />
<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:02. Flow regulations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=HydropeakingHydropeaking2015-08-31T12:44:58Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Hydropeaking=<br />
02. Flow regulations<br />
==General description==<br />
The production of electricity by hydropower plants is often implemented to satisfy<br />
peaks in electricity demand. For this reason these plants work intermittently, creating<br />
periodic and extremely rapid and short-term fluctuations in flow in the receiving water<br />
body. These fluctuations are called hydropeaking and usually show a marked weekly<br />
and daily rhythm.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
*HYMO (general and specified per HYMO element)<br />
Hydropeaking is a unique form of flow regulation, in that it introduces frequent, short duration, artificial flow events to the river. The impacts of hydropeaking on channel size and morphology are highly dependent on the size and frequency of hydropeaks in relation to size of geomorphological effective flows prior to regulation.<br />
Where extreme hydropeaking leads to frequent geomorphological-effective flows (i.e. flows close to the bankfull stage), the hydropeaks dominate channel size and form because they readily mobilize bed sediments until the bed becomes heavily armoured by very coarse particles or scoured to bed rock. Such severe hydropeaking leaves few alluvial habitats and in-channel vegetation, and an abrupt transition between unvegetated and vegetated surfaces at the channel boundary. However, where hydropeaks are smaller and thus less competent to move bed sediment and the pre-existing geomorphologically-effective flows are significantly less frequent or no longer occur under the new hydropower dominated regime, physical adjustments may occur within the pre-existing channel. Sear (1995) describes an example of the latter situation, where the observed adjustments to the gravel-bed North Tyne River are indicative of channel narrowing and retention of fine sediment in the bed, in response to diurnal adjustments of river stage by approximately 0.6 m from hydropeaking:<br />
a) the development of fine sediment berms along channel margins,<br />
b) the aggradation of pools,<br />
c) the encroachment of vegetation on former gravel shoals<br />
d) the growth of tributary confluence bars.<br />
e) degradation of riffle spawning grounds: characterized by higher percentages of fines within spawning gravels, coarsening of surface gravels and the development of a stable, strong bed fabric.<br />
Hydropeaking has been found to have other more indirect hydromorphological impacts beyond those on channel morphology and sediments. Thus, Curry et al. (1994) found that short-term flow fluctuations affected hyporheos dynamics.<br />
Fluctuating flow levels altered groundwater pathways, chemistry, and flow potentials within the river bed. Rising river levels introduced river water into the bank where various degrees of mixing with groundwater occurred. Subsequent recessions of river levels increased the potentials for groundwater flow into the river channel. They found that these effects were significant at spawning and incubation sites and were thus potentially important for river ecology.<br />
Further indirect hyporheic effects were identified by Arnzten et al. (2007) who found empirical evidence of how changes in flow regime and in bed sediment permeability, relating to ingress of fine sediments, altered the vertical hydraulic gradient and water quality of the hyporheic zone within the Hanford Reach of the Columbia River in response to 2 m daily water level fluctuations due to hydropower generation.<br />
<br />
[[File:Hydropeaking.jpg|thumbnail|Conceptual framework of hydropeaking hydromorphological (HYMO) processes and variables.]]<br />
<br />
*physico - chemical parameters<br />
*Biota (general and specified per Biological quality elements)<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P06" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P06" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:02. Flow regulations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=HydropeakingHydropeaking2015-08-31T12:44:18Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Hydropeaking=<br />
02. Flow regulations<br />
==General description==<br />
The production of electricity by hydropower plants is often implemented to satisfy<br />
peaks in electricity demand. For this reason these plants work intermittently, creating<br />
periodic and extremely rapid and short-term fluctuations in flow in the receiving water<br />
body. These fluctuations are called hydropeaking and usually show a marked weekly<br />
and daily rhythm.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
*HYMO (general and specified per HYMO element)<br />
Hydropeaking is a unique form of flow regulation, in that it introduces frequent, short duration, artificial flow events to the river. The theoretical framework related to the effects of hydropeaking is shown in Figure 6. The impacts of hydropeaking on channel size and morphology are highly dependent on the size and frequency of hydropeaks in relation to size of geomorphological effective flows prior to regulation.<br />
Where extreme hydropeaking leads to frequent geomorphological-effective flows (i.e. flows close to the bankfull stage), the hydropeaks dominate channel size and form because they readily mobilize bed sediments until the bed becomes heavily armoured by very coarse particles or scoured to bed rock. Such severe hydropeaking leaves few alluvial habitats and in-channel vegetation, and an abrupt transition between unvegetated and vegetated surfaces at the channel boundary. However, where hydropeaks are smaller and thus less competent to move bed sediment and the pre-existing geomorphologically-effective flows are significantly less frequent or no longer occur under the new hydropower dominated regime, physical adjustments may occur within the pre-existing channel. Sear (1995) describes an example of the latter situation, where the observed adjustments to the gravel-bed North Tyne River are indicative of channel narrowing and retention of fine sediment in the bed, in response to diurnal adjustments of river stage by approximately 0.6 m from hydropeaking:<br />
a) the development of fine sediment berms along channel margins,<br />
b) the aggradation of pools,<br />
c) the encroachment of vegetation on former gravel shoals<br />
d) the growth of tributary confluence bars.<br />
e) degradation of riffle spawning grounds: characterized by higher percentages of fines within spawning gravels, coarsening of surface gravels and the development of a stable, strong bed fabric.<br />
Hydropeaking has been found to have other more indirect hydromorphological impacts beyond those on channel morphology and sediments. Thus, Curry et al. (1994) found that short-term flow fluctuations affected hyporheos dynamics.<br />
Fluctuating flow levels altered groundwater pathways, chemistry, and flow potentials within the river bed. Rising river levels introduced river water into the bank where various degrees of mixing with groundwater occurred. Subsequent recessions of river levels increased the potentials for groundwater flow into the river channel. They found that these effects were significant at spawning and incubation sites and were thus potentially important for river ecology.<br />
Further indirect hyporheic effects were identified by Arnzten et al. (2007) who found empirical evidence of how changes in flow regime and in bed sediment permeability, relating to ingress of fine sediments, altered the vertical hydraulic gradient and water quality of the hyporheic zone within the Hanford Reach of the Columbia River in response to 2 m daily water level fluctuations due to hydropower generation.<br />
<br />
[[File:Hydropeaking.jpg|thumbnail|Conceptual framework of hydropeaking hydromorphological (HYMO) processes and variables.]]<br />
<br />
*physico - chemical parameters<br />
*Biota (general and specified per Biological quality elements)<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P06" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P06" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:02. Flow regulations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=File:Hydropeaking.jpgFile:Hydropeaking.jpg2015-08-31T12:43:31Z<p>Carlos alonso: </p>
<hr />
<div></div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=HydropeakingHydropeaking2015-08-31T12:43:03Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Hydropeaking=<br />
02. Flow regulations<br />
==General description==<br />
The production of electricity by hydropower plants is often implemented to satisfy<br />
peaks in electricity demand. For this reason these plants work intermittently, creating<br />
periodic and extremely rapid and short-term fluctuations in flow in the receiving water<br />
body. These fluctuations are called hydropeaking and usually show a marked weekly<br />
and daily rhythm.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
*HYMO (general and specified per HYMO element)<br />
Hydropeaking is a unique form of flow regulation, in that it introduces frequent, short duration, artificial flow events to the river. The theoretical framework related to the effects of hydropeaking is shown in Figure 6. The impacts of hydropeaking on channel size and morphology are highly dependent on the size and frequency of hydropeaks in relation to size of geomorphological effective flows prior to regulation.<br />
Where extreme hydropeaking leads to frequent geomorphological-effective flows (i.e. flows close to the bankfull stage), the hydropeaks dominate channel size and form because they readily mobilize bed sediments until the bed becomes heavily armoured by very coarse particles or scoured to bed rock. Such severe hydropeaking leaves few alluvial habitats and in-channel vegetation, and an abrupt transition between unvegetated and vegetated surfaces at the channel boundary. However, where hydropeaks are smaller and thus less competent to move bed sediment and the pre-existing geomorphologically-effective flows are significantly less frequent or no longer occur under the new hydropower dominated regime, physical adjustments may occur within the pre-existing channel. Sear (1995) describes an example of the latter situation, where the observed adjustments to the gravel-bed North Tyne River are indicative of channel narrowing and retention of fine sediment in the bed, in response to diurnal adjustments of river stage by approximately 0.6 m from hydropeaking:<br />
a) the development of fine sediment berms along channel margins,<br />
b) the aggradation of pools,<br />
c) the encroachment of vegetation on former gravel shoals<br />
d) the growth of tributary confluence bars.<br />
e) degradation of riffle spawning grounds: characterized by higher percentages of fines within spawning gravels, coarsening of surface gravels and the development of a stable, strong bed fabric.<br />
Hydropeaking has been found to have other more indirect hydromorphological impacts beyond those on channel morphology and sediments. Thus, Curry et al. (1994) found that short-term flow fluctuations affected hyporheos dynamics.<br />
Fluctuating flow levels altered groundwater pathways, chemistry, and flow potentials within the river bed. Rising river levels introduced river water into the bank where various degrees of mixing with groundwater occurred. Subsequent recessions of river levels increased the potentials for groundwater flow into the river channel. They found that these effects were significant at spawning and incubation sites and were thus potentially important for river ecology.<br />
Further indirect hyporheic effects were identified by Arnzten et al. (2007) who found empirical evidence of how changes in flow regime and in bed sediment permeability, relating to ingress of fine sediments, altered the vertical hydraulic gradient and water quality of the hyporheic zone within the Hanford Reach of the Columbia River in response to 2 m daily water level fluctuations due to hydropower generation.<br />
<br />
<br />
*physico - chemical parameters<br />
*Biota (general and specified per Biological quality elements)<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P06" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P06" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:02. Flow regulations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Hydrological_regime_modificationHydrological regime modification2015-08-31T12:39:59Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Hydrological regime modification=<br />
02. Flow regulations<br />
==General description==<br />
River regulation imposes fundamental changes on flow and sediment transfer, which<br />
are the principal controls on fluvial morphodynamics (Church, 1995).<br />
<br />
In order to significantly modify the natural flow regime, a major artificial water<br />
store, in the form of a reservoir, or a major water transfer scheme from another<br />
watershed is usually needed, although groundwater resources are sometimes used to<br />
augment or regulate river flow regimes to match water demand (e.g. Cowx, 2000). The impacts caused by dams and reservoirs in rivers is a problem of global nature that affects the major rivers around the world (Petts, 1984; Dynesius & Nilsson, 1994; Jalon Garcia et al., 1992, Nilsson & Berggren, 2000; etc.).<br />
<br />
The hydrological changes produced by this type of regulation are strongly influenced<br />
by its purpose: flood control, hydropower, water supply and irrigation (Ward &<br />
Stanford, 1979, Petts, 1984). Each type of water use produces a different type of<br />
regulated flow regime that results in different ecological alterations, and often the<br />
same reservoir is operated for multiple purposes. For example, reservoirs for irrigation are operated to store water during humid seasons and to release it during dry seasons, usually producing a regime of more seasonally constant flows. Reservoirs designed for irrigation, domestic or industrial water supply and hydropower generation all tend to attenuate and delay the seasonal regime of flows to the downstream water body. Vörösmarty et al. (1997) estimated that in the mid 1980s the maximum water storage of the 746 World’s largest dams was equivalent to 20% of global mean annual runoff and the median water residence time in these impoundments was 0.40 years. <br />
<br />
Regarding irrigation reservoirs in Mediterranean rivers, first there is the very significant transformation of the natural flow regime into a regulated regime in opposed phase: minimum monthly flows that naturally occur in summer, are increased into maximum ones due to the demand for water for irrigation, while the minimum flows occur in the winter months. colder and more precipitation, which tries to fill the reservoirs (see Figure 1).<br />
<br />
<br />
[[Image:regulacion4.jpg|400px|thumb|center|Figure 1.- Flow Regime river Porma (Spain) affected by the dam Juan Benet (irrigation reservoir), distinguishing two periods, an unregulated (1942-1968) and other post-exploitation of the dam (1969-2004).]] <br />
<br /><br /><br />
<br />
<br />
With the filling of reservoirs during the months of rain (winter) are eliminated or ordinary floods of higher frequency, which are of great importance in maintaining the natural channel morphology and the renovation of habitat and regeneration of the riparian vegetation, and generating a flow regime much more uniform in time, where only keep the avenues overtime (Figure 2). <br />
<br />
The transformation of the natural flow generated from the regulation for irrigation depends on the location on the river network of the stretch of river in question. It can only mean a change of the times in which they occur peak flows, or also include a drastic reduction of water flowing through the channels with respect to the contribution natural, downstream from the derivations of water for use in agriculture.<br />
<br />
<br />
[[Image:regulacion5.jpg|400px|thumb|center|Figure 2.- River Aragon flow regime, downstream of the dam of Yesa. Since 1970 at which the regulation for irrigation significantly reduces the frequency of regular floods, between 100 and 200 m3/s, and increases the length of minimum flows, so will these impacts over time.]] <br />
<br /><br /><br />
<br />
<br />
The regulation of the flow affects very significantly to the physical habitat of the rivers where they live aquatic communities of plants and animals, or those associated with moisture inland. The affections to the aquatic habitat may refer to the emergence of hydraulic conditions relating to the depth of the water, speed of current, shear stress,.., unsuitable for native species and may affect a mismatch of spawning for fish reproduction, lack of deep areas of refuge for individuals larger, and so on. They can also alter the physical and chemical characteristics of water, with reduced forms of dissolved salts, problems of dissolved oxygen content, or altering the temperature regime in connection with fund outflows of reservoirs, with summer temperatures in much colder that the air which impacts on the development of biological cycles of aquatic insects.<br />
<br />
In the stretches of rivers are also regulated extensions or modify the surface useful for each species, to vary the area of film and the distribution of water depths in each section of the channel depending on the flow circulating. It also changes the size and arrangement of sediment to the bed and banks; when traveling on a prolonged the minimum flows (during autumn and winter) is the siltation of the bed by accumulation of thin, with a seal of microhabitats, while when traveling on a continuous peak flows (months irrigation) increases the drag forces on the bed, causing instability in the macro, and how the banks are a size too thick to retain moisture and germination and growth of seeds.<br />
<br />
Dams are barriers that inhibit fish migrations, but their effect on the river continuum is much more important because affects all its components though the fragmentation of all the fluvial network (Dynesius & Nilsson, 1994).<br />
<br />
Some of these effects result immediate from the starting of the reservoir regulation and others show a delay in their appearance, especially the changes in the composition and structure of communities biological. In general, new water controlled conditions are less favorable to native species adapted to a natural with Mediterranean avenues regular season marked a certain magnitude and in the warmer months, and more favorable for exotic species from other regions They can be more competitive than the first in the schemes covered more uniform, similar to those of the rivers of origin. <br />
<br />
This irrigation regulation produces impacts that affect in more or less degree the aquatic system and the dependant environments. Changes in the river flows (in terms of quantity, timing, and frequency) can lead directly to biologic and geomorphic changes, and geomorphic changes lead indirectly to ecological adjustments (Whiting, 2002), altering ecosystem stability in terms of resistance and resilience (Connel & Wayne, 1983). As some authors have mentioned, under regulated conditions Mediterranean stream species cannot compete successfully with many introduced (generalist and limnethic) species (García de Jalón et al., 1992; Morillo et al., 2002), diminishing the ability of aquatic systems to maintain a balanced, integrated, and adaptable community of autochthonous organisms.<br />
<br />
The effects of regulating the flow into the fish species have been studied in depth in Spain and are well documented in different jobs (Elvira, 1995; Elvira and Almodovar, 2001, etc.). It is clear that the maintenance of regulated flow regimes, with neither annual or interannual fluctuations, including bankfull discharges floods for natural regeneration of the river habitat, has created a different fluvial habitat that has favor a strong invasion of mediterranean rivers for many species, both fish (e.g., catfish, sun-fish, carp, pike, salmon of the Danube, etc.). as other animal species (e.g., zebra mussel) or aquatic plants (e.g. water hyacinth).<br />
<br />
Mediterranean streams have natural regimes with an important torrential component that is reflected in strong seasonal and interannual fluctuations. At evolutionary scale, the geological and biogeographical history of these rivers (together with these particular hydrological features), has produced a large number of endemic species since many fluvial basins have remained isolated for a long time. As a consequence, the degree of endemicism of primary and secondary freshwater fishes in Spain is remarkable (Elvira, 1995). These species are not adapted to the new habitats and cannot compite successfully with introduced ones.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
*HYMO (general and specified per HYMO element)<br />
<br />
The implementation of river impoundments and inter-basin transfers may increase or decrease flows, but they also have aggregate effects on other properties of the flow regime, including flow variability and timing (Figure 5). Magilligan and Nislow (2004) reviewed pre- and post-dam hydrological changes downstream of dams that covered the spectrum of hydrological and climatic regimes across the United States. In general, the most significant changes occurred in minimum and maximum flows of different duration. The 1-day through 90-day minimum flows increased significantly and the 1-day through 7-day maximum flows decreased significantly following impoundment.<br />
Other significant adjustments across the majority of sites following impoundment included: an increase in the number of hydrograph reversals; an increase in the number of flow pulses but a decrease in their duration; and a decrease in the mean rate of hydrograph rise and fall.<br />
At a basin scale, Batalla et al. (2004) showed that the presence of 187 large dams in the Ebro basin, with a total capacity equivalent to 57% of the total mean annual runoff, reduced flood magnitude, with Q 2 and Q 10 reduced over 30% on average, particularly in rivers with higher values of the impounded runoff index, (i.e., reservoir capacity divided by mean annual runoff). Also, they found that the variability of mean daily flows was reduced in most cases due to storing of winter floods and increased baseflows in summer for irrigation.<br />
The important role of physical stability, defined in relation to hydrological (frequency, duration and timing of inundation) and channel parameters (channel dynamics, bedform and sediment size) on fluvial ecosystems was emphasized by Petts (2000). Thus, regulated flows disturb the bedform, surface-water and groundwater interactions and the channel form dynamics and associated changing hydraulic conditions that alter both benthic and riparian community patterns.<br />
Decreased flow dynamics can reduce vertical hydrological connectivity by reducing hydraulic gradients (Kondolf et al. 2006). <br />
Flood peaks are typically reduced by river regulation, which reduces the frequency and extent of floodplain inundation and flow through side channels (Gergel et al. 2002, and Henry et al. 2002). The reduction in channel-forming flows reduces channel migration, an important phenomenon in maintaining high levels of habitat diversity across floodplains (Ward & Stanford, 2006): the rich mosaic of habitat patches across the floodplain due to a wide range of successional stages is transformed into an uniform mature riparian forest. Hydrological connectivity with the remaining floodplain geomorphic features is also reduced, as illustrated by flow regulation on the lower Macintyre River, Australia. Here flow regulation has limited exchanges between the<br />
river and its floodplain, (Walker & Thoms 1993), including a reduction in the frequency of hydrological connections to a series of anabranch channels by up to 22% (Thoms et al 2005); induced a stepped profile in the main channel; and changed the nature of the littoral zone, creating an environment inimical to many native species, notably fish (Walker & Thoms 1993).<br />
Flushing flows are often employed in an attempt to impede or reverse some of these effects. Such flows are particularly effective in removing fine particulate materials and chemicals that may have accumulated under supressed flow conditions. For example, flushing flows from Beervlei Dam on the Groot River were effective in removing accumulated salts from riverine pools. The flushing flows were followed by reduced flows which initiated spawning of the potamodromous minnow species in the riffle areas (Cambray 2006).<br />
<br />
[[File:Regime modification.jpg|thumbnail|Conceptual framework representing aggregate impacts of impoundments and interbasin transfers on hydromorphological (HYMO) processes and variables.]]<br />
<br />
*physico - chemical parameters<br />
*Biota (general and specified per Biological quality elements)<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P05" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P05" /><br />
==Useful references==<br />
<br />
Church, M., 1995. Geomorphic response to river flow regulation: Case studies and<br />
time-scales. Regulated Rivers: Research & Management 11: 3–22.<br />
<br />
Cowx, I. 2000. Potential impact of groundwater augmentation of river flows on<br />
fisheries: a case study from the River Ouse, Yorkshire, UK. Fisheries<br />
Management and Ecology 7: 85-96.<br />
<br />
<br />
Dynesius, M. y C. Nilsson. 1994. Fragmentation and flow regulation of river systems in the northern third of the world. Science, 266: 753-762.<br />
<br />
García de Jalón, D., M. González del Tánago y C. Casado. 1992. Ecology of regulated rivers in Spain: An overview. Limnetica, 8: 161-166.<br />
<br />
González del Tánago, M. 1996. Impacto de la agricultura en los sistemas fluviales. Técnicas de restauración para la conservación del suelo y del agua. Agricultura y Sociedad, 78: 211-236.<br />
<br />
Kriakeas, S.A. y M.C. Watzin. 2006. Effects of adjacent agricultural activities and watershed characteristics on stream macroinvertebrate communities. Journal of the American Water Resources Association, 42(2): 425-441.<br />
<br />
MAPA (Ministerio de Agricultura, Pesca y Alimentación) 2003. El Libro Blanco de la Agricultura y el Desarrollo Rural. Publ. Ministerio de Agricultura, Pesca y Alimentación, Madrid.<br />
<br />
MMA (Ministerio de Medio Ambiente). 1998. Libro Blanco del Agua. Ministerio de Medio Ambiente, Madrid.<br />
<br />
Morillo, M., A. Gimenez and D. Garcia de Jalón. 2002. “Evolución de las<br />
poblaciones piscícolas del río Manzanares aguas abajo del embalse de El Pardo<br />
(Madrid).” Limnetica, 17: 13–26.<br />
<br />
Nilsson, C. y K. Berggren. 2000. Alterations of Riparian Ecosystems caused by River regulation. BioScience, 50(9): 783-792.<br />
<br />
Petts, G.E. 1984. Impounded Rivers. John Wiley & sons, Chichester.<br />
<br />
Vörösmarty, C.J.,Fekete, B., Sharma, K. 1997. The potential impact of neo-Castorization on sediment transport by the global network of rivers. Procs. Human impact on erosion and sedimentation 261.<br />
<br />
Ward J.V. & Stanford J.A, 1979. The ecology of regulated streams. New York: Plenum<br />
Press.<br />
<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:02. Flow regulations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=File:Regime_modification.jpgFile:Regime modification.jpg2015-08-31T12:38:26Z<p>Carlos alonso: </p>
<hr />
<div></div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Hydrological_regime_modificationHydrological regime modification2015-08-31T12:38:03Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Hydrological regime modification=<br />
02. Flow regulations<br />
==General description==<br />
River regulation imposes fundamental changes on flow and sediment transfer, which<br />
are the principal controls on fluvial morphodynamics (Church, 1995).<br />
<br />
In order to significantly modify the natural flow regime, a major artificial water<br />
store, in the form of a reservoir, or a major water transfer scheme from another<br />
watershed is usually needed, although groundwater resources are sometimes used to<br />
augment or regulate river flow regimes to match water demand (e.g. Cowx, 2000). The impacts caused by dams and reservoirs in rivers is a problem of global nature that affects the major rivers around the world (Petts, 1984; Dynesius & Nilsson, 1994; Jalon Garcia et al., 1992, Nilsson & Berggren, 2000; etc.).<br />
<br />
The hydrological changes produced by this type of regulation are strongly influenced<br />
by its purpose: flood control, hydropower, water supply and irrigation (Ward &<br />
Stanford, 1979, Petts, 1984). Each type of water use produces a different type of<br />
regulated flow regime that results in different ecological alterations, and often the<br />
same reservoir is operated for multiple purposes. For example, reservoirs for irrigation are operated to store water during humid seasons and to release it during dry seasons, usually producing a regime of more seasonally constant flows. Reservoirs designed for irrigation, domestic or industrial water supply and hydropower generation all tend to attenuate and delay the seasonal regime of flows to the downstream water body. Vörösmarty et al. (1997) estimated that in the mid 1980s the maximum water storage of the 746 World’s largest dams was equivalent to 20% of global mean annual runoff and the median water residence time in these impoundments was 0.40 years. <br />
<br />
Regarding irrigation reservoirs in Mediterranean rivers, first there is the very significant transformation of the natural flow regime into a regulated regime in opposed phase: minimum monthly flows that naturally occur in summer, are increased into maximum ones due to the demand for water for irrigation, while the minimum flows occur in the winter months. colder and more precipitation, which tries to fill the reservoirs (see Figure 1).<br />
<br />
<br />
[[Image:regulacion4.jpg|400px|thumb|center|Figure 1.- Flow Regime river Porma (Spain) affected by the dam Juan Benet (irrigation reservoir), distinguishing two periods, an unregulated (1942-1968) and other post-exploitation of the dam (1969-2004).]] <br />
<br /><br /><br />
<br />
<br />
With the filling of reservoirs during the months of rain (winter) are eliminated or ordinary floods of higher frequency, which are of great importance in maintaining the natural channel morphology and the renovation of habitat and regeneration of the riparian vegetation, and generating a flow regime much more uniform in time, where only keep the avenues overtime (Figure 2). <br />
<br />
The transformation of the natural flow generated from the regulation for irrigation depends on the location on the river network of the stretch of river in question. It can only mean a change of the times in which they occur peak flows, or also include a drastic reduction of water flowing through the channels with respect to the contribution natural, downstream from the derivations of water for use in agriculture.<br />
<br />
<br />
[[Image:regulacion5.jpg|400px|thumb|center|Figure 2.- River Aragon flow regime, downstream of the dam of Yesa. Since 1970 at which the regulation for irrigation significantly reduces the frequency of regular floods, between 100 and 200 m3/s, and increases the length of minimum flows, so will these impacts over time.]] <br />
<br /><br /><br />
<br />
<br />
The regulation of the flow affects very significantly to the physical habitat of the rivers where they live aquatic communities of plants and animals, or those associated with moisture inland. The affections to the aquatic habitat may refer to the emergence of hydraulic conditions relating to the depth of the water, speed of current, shear stress,.., unsuitable for native species and may affect a mismatch of spawning for fish reproduction, lack of deep areas of refuge for individuals larger, and so on. They can also alter the physical and chemical characteristics of water, with reduced forms of dissolved salts, problems of dissolved oxygen content, or altering the temperature regime in connection with fund outflows of reservoirs, with summer temperatures in much colder that the air which impacts on the development of biological cycles of aquatic insects.<br />
<br />
In the stretches of rivers are also regulated extensions or modify the surface useful for each species, to vary the area of film and the distribution of water depths in each section of the channel depending on the flow circulating. It also changes the size and arrangement of sediment to the bed and banks; when traveling on a prolonged the minimum flows (during autumn and winter) is the siltation of the bed by accumulation of thin, with a seal of microhabitats, while when traveling on a continuous peak flows (months irrigation) increases the drag forces on the bed, causing instability in the macro, and how the banks are a size too thick to retain moisture and germination and growth of seeds.<br />
<br />
Dams are barriers that inhibit fish migrations, but their effect on the river continuum is much more important because affects all its components though the fragmentation of all the fluvial network (Dynesius & Nilsson, 1994).<br />
<br />
Some of these effects result immediate from the starting of the reservoir regulation and others show a delay in their appearance, especially the changes in the composition and structure of communities biological. In general, new water controlled conditions are less favorable to native species adapted to a natural with Mediterranean avenues regular season marked a certain magnitude and in the warmer months, and more favorable for exotic species from other regions They can be more competitive than the first in the schemes covered more uniform, similar to those of the rivers of origin. <br />
<br />
This irrigation regulation produces impacts that affect in more or less degree the aquatic system and the dependant environments. Changes in the river flows (in terms of quantity, timing, and frequency) can lead directly to biologic and geomorphic changes, and geomorphic changes lead indirectly to ecological adjustments (Whiting, 2002), altering ecosystem stability in terms of resistance and resilience (Connel & Wayne, 1983). As some authors have mentioned, under regulated conditions Mediterranean stream species cannot compete successfully with many introduced (generalist and limnethic) species (García de Jalón et al., 1992; Morillo et al., 2002), diminishing the ability of aquatic systems to maintain a balanced, integrated, and adaptable community of autochthonous organisms.<br />
<br />
The effects of regulating the flow into the fish species have been studied in depth in Spain and are well documented in different jobs (Elvira, 1995; Elvira and Almodovar, 2001, etc.). It is clear that the maintenance of regulated flow regimes, with neither annual or interannual fluctuations, including bankfull discharges floods for natural regeneration of the river habitat, has created a different fluvial habitat that has favor a strong invasion of mediterranean rivers for many species, both fish (e.g., catfish, sun-fish, carp, pike, salmon of the Danube, etc.). as other animal species (e.g., zebra mussel) or aquatic plants (e.g. water hyacinth).<br />
<br />
Mediterranean streams have natural regimes with an important torrential component that is reflected in strong seasonal and interannual fluctuations. At evolutionary scale, the geological and biogeographical history of these rivers (together with these particular hydrological features), has produced a large number of endemic species since many fluvial basins have remained isolated for a long time. As a consequence, the degree of endemicism of primary and secondary freshwater fishes in Spain is remarkable (Elvira, 1995). These species are not adapted to the new habitats and cannot compite successfully with introduced ones.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
*HYMO (general and specified per HYMO element)<br />
<br />
The implementation of river impoundments and inter-basin transfers may increase or decrease flows, but they also have aggregate effects on other properties of the flow regime, including flow variability and timing (Figure 5). Magilligan and Nislow (2004) reviewed pre- and post-dam hydrological changes downstream of dams that covered the spectrum of hydrological and climatic regimes across the United States. In general, the most significant changes occurred in minimum and maximum flows of different duration. The 1-day through 90-day minimum flows increased significantly and the 1-day through 7-day maximum flows decreased significantly following impoundment.<br />
Other significant adjustments across the majority of sites following impoundment included: an increase in the number of hydrograph reversals; an increase in the number of flow pulses but a decrease in their duration; and a decrease in the mean rate of hydrograph rise and fall.<br />
At a basin scale, Batalla et al. (2004) showed that the presence of 187 large dams in the Ebro basin, with a total capacity equivalent to 57% of the total mean annual runoff, reduced flood magnitude, with Q 2 and Q 10 reduced over 30% on average, particularly in rivers with higher values of the impounded runoff index, (i.e., reservoir capacity divided by mean annual runoff). Also, they found that the variability of mean daily flows was reduced in most cases due to storing of winter floods and increased baseflows in summer for irrigation.<br />
The important role of physical stability, defined in relation to hydrological (frequency, duration and timing of inundation) and channel parameters (channel dynamics, bedform and sediment size) on fluvial ecosystems was emphasized by Petts (2000). Thus, regulated flows disturb the bedform, surface-water and groundwater interactions and the channel form dynamics and associated changing hydraulic conditions that alter both benthic and riparian community patterns.<br />
Decreased flow dynamics can reduce vertical hydrological connectivity by reducing hydraulic gradients (Kondolf et al. 2006). <br />
Flood peaks are typically reduced by river regulation, which reduces the frequency and extent of floodplain inundation and flow through side channels (Gergel et al. 2002, and Henry et al. 2002). The reduction in channel-forming flows reduces channel migration, an important phenomenon in maintaining high levels of habitat diversity across floodplains (Ward & Stanford, 2006): the rich mosaic of habitat patches across the floodplain due to a wide range of successional stages is transformed into an uniform mature riparian forest. Hydrological connectivity with the remaining floodplain geomorphic features is also reduced, as illustrated by flow regulation on the lower Macintyre River, Australia. Here flow regulation has limited exchanges between the<br />
river and its floodplain, (Walker & Thoms 1993), including a reduction in the frequency of hydrological connections to a series of anabranch channels by up to 22% (Thoms et al 2005); induced a stepped profile in the main channel; and changed the nature of the littoral zone, creating an environment inimical to many native species, notably fish (Walker & Thoms 1993).<br />
Flushing flows are often employed in an attempt to impede or reverse some of these effects. Such flows are particularly effective in removing fine particulate materials and chemicals that may have accumulated under supressed flow conditions. For example, flushing flows from Beervlei Dam on the Groot River were effective in removing accumulated salts from riverine pools. The flushing flows were followed by reduced flows which initiated spawning of the potamodromous minnow species in the riffle areas (Cambray 2006).<br />
<br />
<br />
<br />
*physico - chemical parameters<br />
*Biota (general and specified per Biological quality elements)<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P05" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P05" /><br />
==Useful references==<br />
<br />
Church, M., 1995. Geomorphic response to river flow regulation: Case studies and<br />
time-scales. Regulated Rivers: Research & Management 11: 3–22.<br />
<br />
Cowx, I. 2000. Potential impact of groundwater augmentation of river flows on<br />
fisheries: a case study from the River Ouse, Yorkshire, UK. Fisheries<br />
Management and Ecology 7: 85-96.<br />
<br />
<br />
Dynesius, M. y C. Nilsson. 1994. Fragmentation and flow regulation of river systems in the northern third of the world. Science, 266: 753-762.<br />
<br />
García de Jalón, D., M. González del Tánago y C. Casado. 1992. Ecology of regulated rivers in Spain: An overview. Limnetica, 8: 161-166.<br />
<br />
González del Tánago, M. 1996. Impacto de la agricultura en los sistemas fluviales. Técnicas de restauración para la conservación del suelo y del agua. Agricultura y Sociedad, 78: 211-236.<br />
<br />
Kriakeas, S.A. y M.C. Watzin. 2006. Effects of adjacent agricultural activities and watershed characteristics on stream macroinvertebrate communities. Journal of the American Water Resources Association, 42(2): 425-441.<br />
<br />
MAPA (Ministerio de Agricultura, Pesca y Alimentación) 2003. El Libro Blanco de la Agricultura y el Desarrollo Rural. Publ. Ministerio de Agricultura, Pesca y Alimentación, Madrid.<br />
<br />
MMA (Ministerio de Medio Ambiente). 1998. Libro Blanco del Agua. Ministerio de Medio Ambiente, Madrid.<br />
<br />
Morillo, M., A. Gimenez and D. Garcia de Jalón. 2002. “Evolución de las<br />
poblaciones piscícolas del río Manzanares aguas abajo del embalse de El Pardo<br />
(Madrid).” Limnetica, 17: 13–26.<br />
<br />
Nilsson, C. y K. Berggren. 2000. Alterations of Riparian Ecosystems caused by River regulation. BioScience, 50(9): 783-792.<br />
<br />
Petts, G.E. 1984. Impounded Rivers. John Wiley & sons, Chichester.<br />
<br />
Vörösmarty, C.J.,Fekete, B., Sharma, K. 1997. The potential impact of neo-Castorization on sediment transport by the global network of rivers. Procs. Human impact on erosion and sedimentation 261.<br />
<br />
Ward J.V. & Stanford J.A, 1979. The ecology of regulated streams. New York: Plenum<br />
Press.<br />
<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:02. Flow regulations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Discharge_diversions_and_returnsDischarge diversions and returns2015-08-31T12:29:53Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Discharge diversions and returns=<br />
02. Flow regulations<br />
==General description==<br />
Removal and downstream return of water from the river through a man-made<br />
diversion structure called a ''bypass'' often results in significant flow reduction in the intervening section of the river’s course. This is a typical pressure that affects rivers used for hydropower, whereby flow is diverted from the river by a weir at higher altitude and conducted through a near horizontal bypass channel into turbines that are located downstream at a much lower altitude.<br />
A similar pressure occurs in association with irrigation of farmlands located in the<br />
floodplain and near the river margins, but in this case the return flows are greatly<br />
reduced by plant water consumption, evaporation and infiltration, and may also suffer<br />
from a reduction in water quality.<br />
Diversion also takes place to supply urban areas and industries with water, and in these cases the return flow is affected by significant reductions in both water quality and quantity.<br />
''Flood diversion'' is a special case of flow diversion and return that is designed to<br />
alleviate flooding.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
*HYMO (general and specified per HYMO element)<br />
Although in temperate regions water abstractions may have relatively minor impacts, in Mediterranean countries they can represent major alterations with the potential to turn perennial rivers into intermittent rivers and to severely degrade physico-chemical conditions, if base flow becomes limited in relation to emissions or discharge of effluents (Prat & Munné, 2000; Menció ''et al''., 2010).<br />
A review of low flow river conditions during dry periods of the year, as well as the<br />
problem of changing minimum river flows as a consequence of climate variability is<br />
presented by Smakhtin (2001).<br />
<br />
*physico - chemical parameters<br />
*Biota (general and specified per Biological quality elements)<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P03" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P03" /><br />
==Useful references==<br />
Menció, A., Folch, A., Mas-Pla, J., 2010. Analyzing Hydrological Sustainability Through<br />
Water Balance. Environmental Management 45: 1175–1190.<br />
<br />
Prat, N., A. Munne, 2000. Water use and quality and stream flow in a Mediterranean<br />
stream. Water Research 34: 3876–3881.<br />
<br />
Smakhtin, V.U., 2001. Low flow hydrology: a review. Journal of Hydrology 240: 147–<br />
186.<br />
<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:02. Flow regulations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Discharge_diversions_and_returnsDischarge diversions and returns2015-08-31T12:29:29Z<p>Carlos alonso: /* General description */</p>
<hr />
<div>=Discharge diversions and returns=<br />
02. Flow regulations<br />
==General description==<br />
Removal and downstream return of water from the river through a man-made<br />
diversion structure called a ''bypass'' often results in significant flow reduction in the intervening section of the river’s course. This is a typical pressure that affects rivers used for hydropower, whereby flow is diverted from the river by a weir at higher altitude and conducted through a near horizontal bypass channel into turbines that are located downstream at a much lower altitude.<br />
A similar pressure occurs in association with irrigation of farmlands located in the<br />
floodplain and near the river margins, but in this case the return flows are greatly<br />
reduced by plant water consumption, evaporation and infiltration, and may also suffer<br />
from a reduction in water quality.<br />
Diversion also takes place to supply urban areas and industries with water, and in these cases the return flow is affected by significant reductions in both water quality and quantity.<br />
''Flood diversion'' is a special case of flow diversion and return that is designed to<br />
alleviate flooding.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
*HYMO (general and specified per HYMO element)<br />
*physico - chemical parameters<br />
*Biota (general and specified per Biological quality elements)<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P03" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P03" /><br />
==Useful references==<br />
Menció, A., Folch, A., Mas-Pla, J., 2010. Analyzing Hydrological Sustainability Through<br />
Water Balance. Environmental Management 45: 1175–1190.<br />
<br />
Prat, N., A. Munne, 2000. Water use and quality and stream flow in a Mediterranean<br />
stream. Water Research 34: 3876–3881.<br />
<br />
Smakhtin, V.U., 2001. Low flow hydrology: a review. Journal of Hydrology 240: 147–<br />
186.<br />
<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:02. Flow regulations]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Surface_water_abstractionSurface water abstraction2015-08-31T12:27:20Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Surface water abstraction=<br />
01. Water abstractions<br />
==General description==<br />
Water abstractions may be taken directly from the flowing waters in the channel (surface water abstraction), or indirectly from wells by pumping water from aquifers<br />
that may be closely connected to rivers (groundwater abstraction). Furthermore, water<br />
abstraction from rivers can be achieved through inter-basin flow transfer schemes, whereby the donor river system has its flow reduced below its diversion.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
<br />
Dewson ''et al''. (2007)<ref>Dewson, Z.S., James, A.B.W. & Death, R.G., 2007. Stream ecosystem functioning under reduced flow conditions. Ecological Applications 17: 1797–1808.</ref> found that water abstraction decreased water velocity, water depth, and wetted channel width and changes in thermal regime and water chemistry in 90 % of the case studies analysed; James ''et al''. (2008)<ref>James, A.B.W., Dewson, Z.O.Ë.S., Death, R.G., 2008. Do stream macroinvertebrates use instream refugia in response to severe short-term flow reduction in New Zealand streams? Freshwater Biology 53: 1316–1334.</ref> found that flow reduction significantly decreased water velocity (60–69%) in all streams, while depth (18–61%) and wetted width (24–31%) also tended to decrease. Kleynhans (1996)<ref>Kleynhans, C., 1996. A qualitative procedure for the assessment of the habitat integrity status of the Luvuvhu River (Limpopo system, South Africa). Journal of Aquatic Ecosystem Stress and Recovery 5: 41–54.</ref> described loss of fast flowing instream habitat types in streams affected by water abstraction.<br />
Sedimentation process may increase and fine sediment deposition increases the most in farmland streams affected by water abstraction (James ''et al''. 2008)<ref>James, A.B.W., Dewson, Z.O.Ë.S., Death, R.G., 2008. Do stream macroinvertebrates use instream refugia in response to severe short-term flow reduction in New Zealand streams? Freshwater Biology 53: 1316–1334.</ref>. Also, with decreased flows the Coarse Particulate Organic Matter (CPOM) retention rate is increased (Dewson ''et al'', 2007)<ref>Dewson, Z.S., James, A.B.W. & Death, R.G., 2007. Stream ecosystem functioning under reduced flow conditions. Ecological Applications 17: 1797–1808.</ref>. If floods are reduced in main stem river channels, fine sediments delivered by less abstracted tributaries may no longer be flushed downstream but may accumulate on the river bed, reducing its permeability (Kondolf and Wilcock 1996)<ref>Kondolf, G. M., and P. R. Wilcock 1996. The flushing flow problem: defining and evaluating objectives. Water Resources Research 32: 2589-2599.</ref>. When water abstraction is intense, channel drought impacts may be disproportionately severe, especially when certain critical thresholds are exceeded. For example, ecological changes may be gradual while a riffle dries but cessation of flow causes abrupt loss of a specific habitat, alteration of physico-chemical conditions in pools downstream, and fragmentation of the river ecosystem (Boulton, 2003)<ref>Boulton, 2003. Parallels and contrasts in the effects of drought on stream macroinvertebrate assemblages - Google Académico. Freshwater Biology 48: 1173–1185.</ref>.<br />
<br />
Changes in thermal regime and water chemistry were found in rivers affected by flow withdrawals by Dewson ''et al''., (2007)<ref>Dewson, Z.S., James, A.B.W. & Death, R.G., 2007. Stream ecosystem functioning under reduced flow conditions. Ecological Applications 17: 1797–1808.</ref>, and James ''et al''. (2008)<ref>James, A.B.W., Dewson, Z.O.Ë.S., Death, R.G., 2008. Do stream macroinvertebrates use instream refugia in response to severe short-term flow reduction in New Zealand streams? Freshwater Biology 53: 1316–1334.</ref> found that flow reduction decreased the water temperature range by 18–26%, although it had little effect on average surface water temperatures.<br />
<br />
Reduced flows within some river reaches may present impassable obstacles for fish migrations, either by decreasing water depths to below critical levels or by completely drying up entire reaches of river, as occurs on the San Joaquin River of California as a consequence of diversions from Friant Dam (Cain 1997<ref>Cain, J. R. 1997. Hydrologic and geomorphic changes to the San Joaquin River between Friant Dam and Gravely Ford and implications for restoration of Chinook salmon (Oncorhynchus tshawytscha). Thesis. University of California, Berkeley, California, USA.</ref>). Also, where baseflows are artificially reduced, dissolved oxygen levels fall to lethal levels in reaches affected by eutrophic or high temperature discharges (e.g., Loire River, France), or dredging (e.g., the Lower San Joaquin River, California), preventing anadromous salmonids from migrating upstream to suitable habitats (Kondolf ''et al''., 2006<ref>Kondolf, G. M., A. J. Boulton, S. O'Daniel, G. C. Poole, F. J. Rahel, E. H. Stanley, E. Wohl, A. Bång, J. Carlstrom, C. Cristoni, H. Huber, S. Koljonen, P. Louhi, and K. Nakamura. 2006. Process-based ecological river restoration: visualizing three-dimensional connectivity and dynamic vectors to recover lost linkages. Ecology and Society 11(2): 5. http://www.ecologyandsociety.org/vol11/iss2/art5/</ref>).<br />
<br />
Water extraction can also entrain aquatic organisms. For example, Pringle and Scatena (1999)<ref>Pringle, C. M., and F. N. Scatena 1999 Freshwater resource development. case studies from Puerto Rico and Costa Rica. Pages 114-121 in L. U. Hatch and M. E. Swisher, editors. Managed ecosystems: the mesoamerican experience. Oxford University Press, New York, New York.</ref> showed that water extraction removes more than 50% of migrating shrimp larvae in a river located in the Caribbean National Forest in Puerto Rico.<br />
<br />
In relation to macroinvertebrates, flow reduction has not been observed to impact on the abundance of common pool macroinvertebrates or on the abundance, vertical distribution or community composition of hyporheic macroinvertebrates. James ''et al''. (2008)<ref>James, A.B.W., Dewson, Z.O.Ë.S., Death, R.G., 2008. Do stream macroinvertebrates use instream refugia in response to severe short-term flow reduction in New Zealand streams? Freshwater Biology 53: 1316–1334.</ref> found that aquatic macroinvertebrates are resistant to short-term, severe flow reduction as long as some water remains. However, in general, invertebrate abundance may increase or decrease in response to decreased flow, whereas invertebrate richness commonly decreases because habitat diversity decreases (Dewson ''et al''., 2007<ref>Dewson, Z.S., James, A.B.W. & Death, R.G., 2007. A review of the consequences of decreased flow for instream habitat and macroinvertebrates. Journal Information, 26(3).</ref>). Furthermore, Muñoz & Prat (1996) found a highly significant reduction of macroinvertebrate density and taxon number at disturbed stations as consequences of increased pollutant concentrations under abstraction conditions.<br />
<br />
In dry countries, deterioration of riparian habitat integrity is a widespread consequence of water abstraction: during droughts tree deaths are common (Kleynhans, 1996)<ref>Kleynhans, C., 1996. A qualitative procedure for the assessment of the habitat integrity status of the Luvuvhu River (Limpopo system, South Africa). Journal of Aquatic Ecosystem Stress and Recovery 5: 41–54.</ref>.<br />
<br />
[[File:Water abstraction SI.jpg|thumbnail|Conceptual framework representing water abstraction effects on HYMO processes and variables and their ecological impacts (HYMO is for Hydromorphological and PQ for Physico-chemical).]]<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P01" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P01" /><br />
==Useful references==<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:01. Water abstractions]]</div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=File:Water_abstraction_SI.jpgFile:Water abstraction SI.jpg2015-08-31T12:17:53Z<p>Carlos alonso: </p>
<hr />
<div></div>Carlos alonsohttps://wiki.reformrivers.eu/index.php?title=Groundwater_abstractionsGroundwater abstractions2015-02-16T17:13:58Z<p>Carlos alonso: /* Effect/Impact on (including literature citations) */</p>
<hr />
<div>=Groundwater abstractions=<br />
01. Water abstractions<br />
==General description==<br />
Groundwater over-abstraction can lead to decline in groundwater levels within<br />
aquifers and drying up or causing severe flow reduction in rivers. Surface seepage<br />
from aquifers supports groundwater-fed ecosystems such as wetlands and springs.<br />
Riparian vegetation affected by declining phreatic levels rapidly shows signs of water<br />
stress, leading in extreme cases to widespread riparian plant death.<br />
<br />
==Effect/Impact on (including literature citations)==<br />
<br />
While surface water abstractions directly affect river flows, groundwater abstractions (both from shallow and deep aquifers) indirectly lower the discharge of streams and rivers, thereby decreasing the flow velocity and water depth in these water bodies. Acreman ''et al''. (2000)<ref>Acreman, M. C., B. Adams, P. Birchall, B. Connorton, 2000. Does Groundwater Abstraction Cause Degradation of Rivers and Wetlands? Water and Environment Journal 14: 200–206.</ref> stated that large groundwater abstractions have a detrimental effect on rivers and wetlands. Additionally, status assessments of groundwater bodies in Denmark (Fyn region) and Scotland (East Lothian area), have shown reductions in base flow by 11% and 52%, respectively, due to groundwater abstractions (Henriksen ''et al''., 2007<ref>Henriksen, H.J., Troldborg, L., Nyegaard, P. Hojberg, A.L., Sonnenborg., T.O., Refsgaard, J.C., 2007. Evaluation of the quantitive status of groundwater- surface water interaction at the national level. In: groundwater Science and Policy, an internationale overview, editor: Philippe Quevauviller. ISBN 978-0- 85404-294-4.</ref>; Ward and Fitzsimons, 2008<ref>Ward, R.S. and V. Fitzsimons, 2008. A European Framework for quantitative status. EU Groundwater Policy Developements Conference – UNESCO, Paris, France.</ref>).<br />
<br />
Groundwater abstractions for irrigation can pose significant risks to groundwater conditions, and hence baseflow (Taylor ''et al''., 2012). For example, in two sandy lowland catchments in the Netherlands, groundwater abstractions have caused a base flow reduction of 5-28% (Hendriks ''et al''., in review<ref>Hendriks, D.M.D., Kuijper, M.J.M., Van Ek, R., In review, 2013. Groundwater impact on environmental flow needs of streams in sandy catchments in The Netherlands. Hydrological Sciences Journal.</ref>), even though the density of groundwater abstraction points for spray irrigation in these catchments is relatively low compared to some sandy catchments in the province of Noord-Brabant that show stream discharge reductions of 22% to 56% due to intensive spray irrigation (> 6 irrigation points per km 2 ) (De Louw, 2000<ref>De Louw P., 2000. Spray irrigation form groundwater influences seepage. Informatie – edition on groundwater and soil (TNO-NITG), no. 6, pp.-4 (In Dutch)</ref>). Importantly, since spray irrigation occurs mainly during the summer growing season, it mostly affects groundwater levels and stream discharge during naturally low flow periods when water availability in streams is crucial for aquatic life.<br />
<br />
==Case studies where this pressure is present==<br />
<Forecasterlink type="getProjectsForPressures" code="P02" /><br />
==Possible restoration, rehabilitation and mitigation measures==<br />
<Forecasterlink type="getMeasuresForPressures" code="P02" /><br />
==Useful references==<br />
De Louw P., 2000. Spray irrigation form groundwater influences seepage. Informatie – edition on groundwater and soil (TNO-NITG), no. 6, pp.-4 (In Dutch)<br />
Custodio, E. 2001. Aquifer overexploitation: what does it mean? Hydrogeology Journal, 10:254–277.<br /><br />
Sousa A.,García-Murillo P., Morales J. and García-Barrón L. 2009.Anthropogenic and natural effects on the coastal lagoons in the southwest of Spain (Doñana National Park). ICES Journal of Marine Science, 66 (7), 1508-1514.<br /><br />
Suso J. and M.R Llamas. 1993. Influence of groundwater develop-ment on the Doñana National Park ecosystems (Spain). Journal of Hydrology, 141, 239-269.<br /><br />
Sousa A.,García-Murillo P., Morales J. and García-Barrón L. 2009.Anthropogenic and natural effects on the coastal lagoons in the southwest of Spain (Doñana National Park). ICES Journal of Marine Science, 66 (7), 1508-1514.<br /><br />
Trick T and E. Custodio. 2004. Hydrodynamic characteristics of the western Doñana Region (area of El Abalario), Huelva, Spain.Hydrogeology Journal, 12:321–335.<br /><br />
Tularam, G. A. and M. Krishna, 2009. Long Term Consequences of Groundwater Pumping in Australia: A Review OfImpacts Around The Globe.Journal of Applied Sciences in Environmental Sanitation, 4 (2): 151-166.<br /><br />
<br />
==Other relevant information==<br />
<br />
[[Category:Pressures]][[Category:01. Water abstractions]]</div>Carlos alonso