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Uilenkamp - Meander reconnection

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Key features of the case study

Site description

The Vecht river has served as a shipping route in the past. Nowadays it is no longer used for this commercial function. This has made it possible to go from a deep, straightened river to a more natural situation. A first step in this direction was taken by the local water authority with funding of the EU Interreg project. The site of Uilenkamp is a meander that was cut off at the start of the last century to make the Vecht river more suitable for navigation. The banks of the river were fixated and the channel straightened and deepened. This has led to an unnatural channel with relatively few chances for biota to flourish due to the lack of habitat diversity.

Measures selection

To reintroduce natural dynamics and create a more natural river the old meander of Uilenkamp was reconnected to the river Vecht. Bank fixation was removed along the (former) main channel and used to construct a dam that blocks of the main channel during normal flow conditions. This forces the main flow through the reconnected meander and allows for natural processes such as erosion to take place. During peak flows and high water conditions the dam is flooded and water can also flow through the former channel. This measure has led to an increase in river length of 1 km, which leads to increased water retention in dry periods. Also, the water storage capacity of the area was increase. Part of this was done by lowering a nearby floodplain (formerly agricultural land) and digging a number of pools in the area.

Success criteria

• Reintroduction of natural processes
• Increased water retention
• Preservation of flood protection for surrounding areas

Ecological response

Macrophytes and phytobenthos

The macrophytes have developed quite well at the site. No historical reference has been determined, leading to a limited knowledge of the reference condition of the site. However, it can be stated that the vegetation shows more diversity in species than nearby, unaltered, sites. Despite this improvement it should be stated that the development of reed-like vegetation has been largely absent. This can be explained by the unnatural water level fluctuations in the river. This leads to the banks being flooded during the germination season of the vegetation, thus making it impossible for the plants to colonise the banks successfully. The phytobenthos, in the form of diatoms, shows no characteristic or rare species. Analysis shows that the species that occur in the channel are indicative of eutrophic water.

Benthic invertebrates

The benthic invertebrates are largely non-rheophilic species. Some rheophelic, and thus characteristic species for the current situation, do occur in the channel but only during spring. This is caused by the stagnation of the water flow during summer due to the operation of weirs in the river system. This leads to an unnatural but agriculturally desirable system. To further improve the system for rheophilic species a different hydrological regime is needed.

Fish

Not monitored

Other biota

Dragonflies

A number of dragon fly species were found in the area. The new channel is home to brood of a number of these species, indicating colonisation of the channel. The bank of the old channel are poor in dragonflies due to the lack of diversity in the vegetation. Overall an increase in dragonfly species diversity was found in the meander compared to the former channel.

Hydromorphological response

Though hydromorphological response has not been studied intensively some general observations can be presented.

Hydrological regime

The hydrology of the river has changed in the sense that the water retention has been improved and that the storage capacity of the system was increased by lowering the nearby floodplain. This, in turn, improved the lateral connectivity and the inundation of the floodplain area. The unnatural water level fluctuations and stagnation of the water flow are the major hydrological pressures acting upon the system, and they persist still.

River continuity

Unaffected

Morphological conditions

Erosion and sedimentation has begun in the side channel and is creating a more natural river. Characteristic bank faces have formed which serve as habitat for numerous biota. The variation in river depth has increased and the channel bed is taking on a more natural form and dimension now that it is no longer fixated.

Monitoring before and after implementation of the project

The project has not been monitored prior to the implementation of the project. In 2005 and 2006 data on both benthic invertebrates and macrophytes was collected by Klink Ecological Advisory under contract by the local water authority Velt & Vecht. In 2005 the study included dragonflies and in 2006 diatoms were monitored.

Socio-economic aspects

Ecosystem goods and services

Not affected.

Conflicts and synergies

The project is an example of recycling on site material for the restoration project. The dam that was build in the former main channel was constructed by using the bank fixation which was removed as part of the project.

Project costs

Unknown

Contact person within the organization

Jan van der Molen, Waterschap Velt & Vecht, e-mail

Extra background information

• Project website Velt & Vecht _{(language: dutch)}

References

• Klink, A., 2005 Overijsselse Vecht Uilenkamp. Monitoring macrofauna, libellen en diatomeeën 2005 Adviesburo Klink Analyserapport 153: 10 pp. _{(type: abstract; language: dutch)}
• [http://www.klinkhydrobiologie.nl/99%20Ov.%20Vecht%202006.pdf Klink, A., 2007 Overijsselse Vecht Uilenkamp. Monitoring macrofauna, hogere planten en diatomeeën 2006

Adviesburo Klink Rap. Med. 99: 13 pp. + bijl.] _{(type: abstract; language: dutch)}

• Waterschap Velt & Vecht, Brochure Uilenkamp

Related Measures

• Improve water retention
• Improve/Create water storage
• Increase flood frequency and duration in riparian zones or floodplains
• Shorten the length of impounded reaches
• Remeander water courses
• Initiate natural channel dynamics to promote natural regeneration
• Remove bank fixation
• Adjust land use to develop riparian vegetation
• Lower river banks or floodplains to enlarge inundation and flooding
• Reconnect backwaters and wetlands
• Retain floodwater

Related Pressures

• Hydrological regime modification
• Artificial barriers upstream from the site
• Artificial barriers downstream from the site
• Channelisation / cross section alteration
• Alteration of riparian vegetation
• Alteration of instream habitat
• Embankments, levees or dikes
• Loss of vertical connectivity