Difference between revisions of "Gameren"

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<googlemap width="100%" zoom="15" lon="5.203614" lat="51.80689" version="0.9">
(A) 51.806159, 5.199992
(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
<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>
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.
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
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
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==
[[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]]
== 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 12:08, 24 November 2010