Vreugderijkerwaard - Side channel
Vreugderijkerwaard - Side channel
Key features of the case study
Site description
The Vreugderijkerwaard is a floodplain situated on the river IJssel, a tributary of the Rhine in the Netherlands. The area is characterized by a number of river dunes, which are a rare occurrence for the Netherlands. Since 1982 the area has been subjected to extensive grazing to preserve and develop the rivePart of the area, namely the river dune part, has been the property of a nature conservation organisation since 1962. This has led to a variety of rare plant species occurring in the area. The IJssel river was artificially connected to the Rhine in roman times, leading to the Rhine being the main factor of the IJssel's flow. The river was largely fixated through the use of groynes. Part of the natural meanders were removed through channelization measures.
Measures selection
Through the Vreugderijkerwaard a side channel was dug. This was done with for the Room for the River project in which flood protection,by increase in water retention area, and ecological recovery are linked. The project was co-funded by the EU-IRMA project. The measure of a flowing side channel was chosen to increase dynamic river processes in the otherwise fixated IJssel system. The side channel is artificially limited in its flow by divers. This measure was taken to avoid sedimentation of the main channel. The side channel has a flow-through of 1.5% of the average flow-through of the main channel. The flow speed of the side channel is lower then that of the main channel. This leads to sedimentation of sand and clay. To avoid the formation of islands in the channel and clogging of the channel a sand trap was installed.
Success criteria
In the project plan four main goals were formulated for the project:
- Maintaining the unique river dunes in the area
- Increasing diversity
- Increasing river dynamics and promoting communities of organisms that benefit from higher dynamics
- Attention for relations and connections to tributaries of the IJssel.
Another (secondary) goal was to keep recreational use of the area intact.
Ecological response
Macrophytes and phytobenthos
Macrophytes have shown a strong improvement over the last few years in both abundance and species diversity. In 2006 only a few scarce plants were present while in 2008 the channel was filled with them at some places, especially near the diver at the inlet of the channel. The fast colonization of the channel is likely caused by the presence of source populations. Also, the side channel has a continues low flow regime which is a suitable habitat for the macrophytes. Also, the river has a relatively low water fluctuation. All in all macrophytes have been positively affected by the measure.
Fish
No rare fish species were encountered prior to the project implementation. After the implementation a limited sampling of fish was undertaken. A number of fish of a rare species type were encountered. It is speculated, though unproven, that a larger number of rheophilic species use the side channel as habitat.
Other biota
Dry land flora
The dry land flora of the area are very diverse and conform the expected ecotype.
Hydromorphological response
Monitoring before and after implementation of the project
Socio-economic aspects
Contact person within the organization
Extra background information
References
Related Measures
- Improve water retention
- Trap sediments
- Increase flood frequency and duration in riparian zones or floodplains
- Link flood reduction with ecological restoration
- Allow/increase lateral channel migration or river mobility
- Remove sediments
- Remove or modify in-channel hydraulic structures
- Lower river banks or floodplains to enlarge inundation and flooding
- Reconnect backwaters and wetlands
- Remove hard engineering structures that impede lateral connectivity
- Restore wetlands
