Difference between revisions of "Gameren"

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=Gameren=
 
  
<googlemap width="100%" zoom="15" lon="5.203614" lat="51.80689" version="0.9">
 
(A) 51.806159, 5.199992
 
lake
 
(B) 51.805576, 5.207374
 
another lake
 
6#FFC57575 (#66C57575)
 
51.805643, 5.195332
 
51.804661, 5.200224
 
51.804886, 5.20291
 
51.803983, 5.206086
 
51.804567, 5.21321
 
51.805151, 5.216214
 
51.806902, 5.219476
 
51.809025, 5.221278
 
51.809237, 5.216901
 
51.808548, 5.208661
 
51.80876, 5.202052
 
51.809556, 5.196216
 
51.80929, 5.193812
 
51.805749, 5.195203
 
</googlemap>
 
 
<Forecasterlink type="getProjectInfoBox" code="5" />
 
 
 
==Key features of the case study==
 
 
 
 
==Site description==
 
 
[[Image:Gameren_Oblique_view.jpg|thumb|left|View on side channel set of Floodplain "Gameren", downstream direction. Photo: Rijkswaterstaat (NL)]]
 
 
<p>Under the authority of the Ministry of Transport, Public Works and Water Management (Eastern Netherlands division), the Institute for Inland Water Management and Waste Water Treatment RIZA executed a monitoring program on secondary channels in the Gamerensche Waard. During the period 1996-2002 a broad and complete program was executed with three main objectives: 1) evaluation of the desired effects, 2) assessment of the undesirable side-effects (risks) and 3) increase of the knowledge about secondary channels.</p>
 
<p>In the period 1995-1999 three secondary channels were excavated in the Gamerensche Waard along the river Waal (the main side branch of the river Rhine). Regarding the dimensions, these channels are unique for Dutch rivers. These channels are digged out partly from former agricultural grassland and partly they ecxists of connected former sand and clay exctraction pits. The three secondary channels vary with regard to location (inside and outside the summer embankment), length (0.5-2 km), width, depth (0-20 m), discharge (1-3%) and the like. Just one of the channels is flowing permanently, the other two
 
contain flowing water in respectively 4 and 11 months a year.</p>
 
 
===Summary===
 
====Hydrology====
 
The monitoring period (1996-2002) was characterized by relatively
 
high river discharges. Therefore the secondary channels were connected
 
to the stream flow more frequently than planned. The total discharge
 
of the three secondary channels is about 2% of the average river
 
discharge. The maximum flow ve-locity in the secondary channels
 
appeared at narrows; the strongest turbulences just downstream of
 
those narrows. With low river discharges, a large influence of navigation
 
on the flow velocity was visible in the channels; this led sometimes to
 
a turnover of the flow direction. The discharge capacity of the Waal
 
with high floods was not lowered significantly by the sedimentation in
 
the secondary channels. The vegetation development led to only a
 
minimal decrease of the discharge capacity of the river.
 
 
====Morphology====
 
The predicted sedimentation in the main channel parallel to the
 
Gamerensche Waard did indeed occur, but it appeared difficult to
 
prove because of the inter-ference with slowly passing sand
 
waves/dunes on the bottom of the Waal. The sedimentation resulting
 
from the construction of the secondary channels was of the same order
 
as the measurement uncertainty and the autonomous developments in
 
the riverbed.
 
Roughly no large morphological changes were measured in the secondary
 
channels of the Gamerensche Waard. The erosion- and sedimentation
 
rates in the first years after construction were larger than in the
 
later years. Locally some clear (bank) erosion and sedimentation were
 
recognized.
 
It is expected that the former sand extraction pit will be filled up to the
 
level of the rest of the channel around the year 2050 (net sedimentation
 
rate is about 0.05 to 0.11 m/year).
 
 
====Soil quality and ecological risks====
 
The bed soil in the secondary channels consists mainly of sand (in the
 
former sand extraction a mixture of silt and sand). The soil quality of
 
the secondary channels has improved during the monitoring period
 
(sedimentation of clean sand).
 
Although the concentrations of toxic substances in the bottom are so
 
high that negative ecological effects can be expected, the determined
 
risks are not so high that these can block the ecological recovery
 
seriously. These risks are gradually decreasing because the sediment
 
becomes more and more sandy and this means also cleaner.
 
There are no possibilities for (a cost-effective) extraction of the sediment
 
due to the heterogeneous composition. Distribution of the sediment to
 
elsewhere in the river system is possible due to the tolerable quality of
 
the sediment.
 
 
====Ecology, vegetation====
 
The abundance of trees and bushes in the Gamerensche Waard is still
 
limited because of the imperfect germination and establishment
 
conditions: on the islands because of the dense grass cover and on the
 
banks of the channels because of the large water level fluctuations.
 
With regard to the floristic com-position, hardly any target species,
 
Red-list species or protected species were found in or near the secondary
 
channels. In spite of this, the floristic quality of the muddy banks of
 
the channels is (very) good, but not exceptional in com-parison with
 
other nature developments projects along the river Waal.
 
In the biggest secondary channel in the Gamerensche Waard some
 
small fields with aquatic vegetation were found in 2002 (''Myriophyllum''
 
''spicatum'' and ''Potamogeton'' ''pectinatus'').
 
 
====Ecology, macro invertebrats====
 
In the secondary channels of the Gamerensche Waard about 75% of
 
the recently recorded species of the river Rhine occurs. The species
 
diversity of the secondary channels is much higher than in the groyne
 
fields of the main channel. In the slow flowing parts of the secondary
 
channels significantly less exotic species occur than in the main river
 
bed.
 
From the 46 (macroinvertebrate) target species, only 3 species were
 
discovered in the secondary channels of the Gamerensche Waard. The
 
absence of other target species can largely be attributed to the lacking of
 
some specific habitats e.g. gravel, woody debris and aquatic vegetation.
 
Those chironomid species that are characteristic for stable sandy flats
 
recolonised the area quite fast.
 
The sediment type, the water depth, the flow velocity, the
 
morphodynamics, the organic matter content and the soil chemistry
 
together determine the spe-cies composition of the macroinvertebrate
 
community. All these factors are mutually strong dependent on each
 
other; evident relations are difficult to prove. The highest species
 
diversity occurs on silt or vegetation in shallow, slow flowing water
 
with a limited erosion or sedimentation. These factors seem to be of a
 
larger influence on the macroinvertebrate composition than the degree
 
of soil pollution.
 
 
====Ecology, fish====
 
In the secondary channels of the Gamerensche Waard various reophilic
 
fish species (preference for flowing water) were found, including five
 
target species (''Barbus barbus'', ''Leuciscus cephalus'', ''Chondrostoma nasus'', ''Leuciscus idus'' and ''Lampetra fluviatilis''). For these reophilic fish
 
the secondary channels function mainly as a growing up area during
 
their earliest stages of life. Later on they migrate to the main channel.
 
The most reophilic fish enters the secondary channels passively by
 
means of larval drift.
 
 
====Conclusions relating to navigation/shipping, Safety, Ecological restoration and management====
 
Problems for navigation were not detected in spite of the slight
 
sedimentation in the main channel, which is a result of the construction
 
of the secondary channels. The sedimentation as a result of the
 
secondary channels interferes with other large-scale ’autonomous’
 
processes. Consequently one should al-ways bear in mind the
 
temporal fluctuations in bed level. Inland navigation was not hindered
 
by (cross) currents at the in- or outlet of the channels.
 
The increase of the river discharge capacity resulting from the
 
construction of secondary channels was annulled for a small part (± 15%)
 
by the sedimentation in the bed of the channels and by the bush
 
encroachment elsewhere in the Gamerensche Waard. At this moment
 
dredging or digging the secondary chan-nels in order to maintain the
 
flowing character of the channels is not needed.
 
At one location local bank erosion required intervention to prevent
 
safety problems.
 
Because of the large variation of water types, the secondary channels
 
in the Gamerensche Waard offer suitable habitats for a wide range of
 
species. How-ever, concerning the species composition according to
 
the intended nature target type, it is clear that the secondary channels
 
are not yet complete.
 
The secondary channels in the Gamerensche Waard remained largely at
 
their original location, although locally distinct (bank) erosion appeared.
 
Regular visual inspection of the banks of secondary channels is and
 
will be necessary in future.
 
A slight improvement of the soil quality occurred, because the new
 
sediments in the secondary channels consist mainly of (clean) sand.
 
The sand (transport) turned out to be a much more outstanding factor
 
than the silt (transport).
 
A deep extraction pit as part of a secondary channel functions as a
 
sediment catch indeed, but it does not seem to be necessary at all to
 
prevent filling up with sand.
 
 
 
==Measures selection==
 
 
==Success criteria==
 
 
==Ecological response==
 
 
==Hydromorphological response==
 
 
==Monitoring before and after implementation of the project==
 
 
==Socio-economic aspects==
 
 
==Contact person within the organization==
 
 
==Extra background information==
 
 
 
==References==
 
<references/>
 
[[Media:Evaluatie_nevengeulen_Gamerensche_Waard_-.pdf |Evaluatie nevengeulen Gamerensche Waard (Dutch with summary in English) ]]<br>
 
[[Media:Case_study_Gameren_powerpoint_aquatic_habitat_evaluation.pdf | Powerpoint (English) Habitat Evaluation Case study Gameren]]
 
 
[[Category:Case_studies]]
 
 
== Related Measures ==
 
 
<Forecasterlink type="getMeasuresForProject" code="5" />
 
 
== Related Pressures ==
 
 
<Forecasterlink type="getPressuresForProject" code="5" />
 
 
[[Category:River depth and width variation]] [[Category:Structure of the riparian zone]] [[Category:Phytoplankton]][[Category:Macrophytes and phytobenthos]] [[Category:Benthic invertebrates]] [[Category:Fish]]
 

Revision as of 11:08, 24 November 2010