Revision as of 12:36, 25 June 2010

Rijkelse Bemden - River bed widening

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Key features of the case study

Site description

The area of Rijkelse Bemden is situated along the river Meuse and is an area that historically consisted of two river terraces. The area was predominantly used as grassland with a low-intensity agricultural purpose. Parts of the area were used for as an orchard. Around 1950 the Meuse was straightened and canalized in this region. As a result a number of gravel bars and small islands which were previously present in the channel and floodplain area disappeared. The banks of the river were also fixated. From 1965 to 1985 the area was used as a source of sand and gravel and was mined intensively. This led to a lake forming in the area which filled up with water. The banks of the lake have been used from 1985 onward as low-intensive agricultural land.

Measures selection

In 1996 the area was designated as an area for nature development and work was started on the spit between the river channel and the lake. The bank area was added to the area and a number of islands of differing sizes were made along the banks of the lake. Also a few pools were dug. All of this was done to create a greater diversity in available habitats and thus increase biotic diversity. Between 1998 and 2001 the Meuse was widened for the Project Zandmaas, a project striving to restore some of the natural characteristics of the Meuse while improving the flood protection for the nearby inhabited areas. This was also done near the Rijkelse Bemden. The river was widened by 40 meters, giving it more room and thereby a higher capacity during peak discharges. The sediment material that became available from this exercise was used on the banks and in the lake of the Rijkelse Bemden, creating more natural banks and locally making the lake more shallow. The entrance to the lake was closed off by means of a buoy line to minimize disturbance in the lake by recreational activity.

Success criteria

No clear criteria were formulated for the area.

Ecological response

Macrophytes and phytobenthos

The area has been investigated for macrophytes. Macrophytes occurred only sporadically in the lake. This is most likely related to the depth of the lake and the relatively recent physical alteration of the system by the deposition of bank material from the Meuse widening.

Benthic invertebrates

Not monitored.

Fish

No structural fish monitoring has been carried out for the lake. In the main channel a normal species composition of fish has been found in the 90's. It is expected that the lake will serve as a spawning and rearing ground for limnophilic fish species.

Other biota

Vegetation

The flora in the area has developed very well since the restoration has started. A characteristic vegetation for the local circumstances on site has developed with a somewhat higher diversity compared to the pre-restoration period and a much higher diversity than can be found in nearby, non-restored, areas. Also, due to the work on the banks chances were created for pioneer species to settle in the area, leading to a greater overall diversity in plant species in the area. Rare or protected species in the area are quite common in the area as well. In fact the area has more red list species than ever before in the known history of vegetation data of the area.

Birds

The area has a history of bird monitoring in a number of regional projects. Comparison of pre- and post-project data shows that the territories have the breeding birds have expanded and that a number of new species have visited the area over the past years. Also, there have been a few sightings of rare and/or protected species in the area.

Hydromorphological response

Hydrological regime

The hydrological regime in the area has been modified somewhat by the widening of the river channel by 40 metres. The hydrology of the lake area is characterised by flooding during high discharge conditions. Also, locally some upwelling takes place from higher terraces, creating locally different circumstances and habitat conditions.

River continuity

Unaffected

Morphological conditions

The morphological changes in the lake can be affected by natural dynamics. As the water is largely static in the area sedimentation takes place which slowly fills up the lake. The river channel itself is less dynamic. Banks are fixated, severing the natural erosive and sedimentation processes. This is unlikely to change however, as the river is used for navigational purposes.

Monitoring before and after implementation of the project

Socio-economic aspects

Ecosystem goods & services

Gravel, sand and clay mining (historical).

Synergies and conflicts

The project was carried out to increase the room for the river and thereby improve flood protection during high discharges. At the same time the clay and sand that was taken from the river bed widening was used in the banks of the Rijkelse Bemden. Locally it was also used to shallow the ponds in the area.

Costs

The total project of the river bed widening and restoration of the Rijkelse Bemden was estimated to cost 13 million euro.

Contact person within the organization

Extra background information

References

Related Measures

• Link flood reduction with ecological restoration
• Widen water courses
• Shallow water courses
• Allow/increase lateral channel migration or river mobility
• Recreate gravel bar and riffles
• Adjust land use to develop riparian vegetation
• Adjust land use to reduce nutrient, sediment input or shore erosion
• Lower river banks or floodplains to enlarge inundation and flooding
• Set back embankments, levees or dikes
• Retain floodwater

Related Pressures

• Hydrological regime modification
• Impoundment
• Channelisation / cross section alteration
• Alteration of riparian vegetation
• Alteration of instream habitat
• Embankments, levees or dikes
• Sand and gravel extraction