Revision as of 14:12, 23 June 2010

Buiten Ooij - Sluice operation

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Key features of the case study

Site description

The area of Buiten Ooij is a floodplain area along the river Waal, a major tributary of the Rhine in the Netherlands. The area is part of a larger nature area, the Geldersche Poort. The area is situated between the summer and the winter dyke. In the area there are a number of pools that originated from historical gravel and sand mining pits. A remainder of an old river arm, the Oude Waal, is located in the south-west corner of the area. This old arm is permanently filled with water, but not connected to the current river. The summer dyke around the area was constructed in multiple phases, leading to differences in height in comparison to the water level. It is also outfitted with a sluice which was historically used to let in water during peak discharges. The dyke is higher on north-eastern part of the area. Flooding of the area is rare; an active water flow through the area is even rarer due to the height differences in the summer dyke. This leads to an unnatural situation in the floodplain where flooding occurs only sporadically and incompletely.

Measures selection

To improve flooding of the area and stimulate the formation of floodplain marshland an experiment was started with letting water into the area through the sluice during winter and closing the sluice during summer to retain the water in the area. This was both a cheap and easy way to improve the inundation of the area. This measure by no means fully removes the pressures acting upon the system, but it is a first step. Plans are being made to further improve the area by means of floodplain lowering and active side channel constructions.

Success criteria

The project was carried out as an experiment, no clear success criteria were formulated though the goal was to create wet natural habitat.

Ecological response

Macrophytes and phytobenthos

In 1999 the coverage of macrophytes was quite high. The current situation shows a very different image with only sporadic occurrences of macrophytes in the area. This would suggest that the macrophytes have been negatively affected by the measure. Data from monitoring in 2005 shows that this conclusion is a tad too easy. The macrophytes in the area show a collapse in 2005 and a (nearly) complete absence in 2006. As this collapse occurred prior to the sluice operation experiment it seems unlikely that the project has anything to do with the difference in macrophytes observed between the present day situation and the historical data (1999). If there has been a positive effect or not is difficult to say definitively, however macrophytes have increased in the area since 2006. The area has an 'acceptable' Ecological Quality in WFD terms. This is mostly caused by the low species diversity and relatively low abundance of macrophytes.

Benthic invertebrates

The benthic invertebrates show a significantly higher abundance and species richness than they do in the main channel. This leads to the conclusion that the wet floodplain is a suitable habitat for benthic invertebrates. These invertebrates in turn serve as food for both fish and water birds, leading to the expectation that in due time those groups will also be positively affected.

Fish

The (near-)stagnant water bodies of the area form excellent breeding and mating grounds for fish. Especially the areas where macrophytes are present show a good deal of limnophilic species. The presence of spawning and rearing habitat is vital to the structural presence of fish species. The first indicators are there that the measure is positively affecting the fish population in the river Waal.

Hydromorphological response

There has not been any monitoring of hydromorphology. It should be noted that it is known that the area is affected by sedimentation of the floodplain and water bodies. This sedimentation takes place at a rate which is fairly standard for Waal floodplains (1-2 cm/year). This sedimentation may become a problem in time. To avoid this plans are being developed to lower the floodplain by digging off the top soil.

Monitoring before and after implementation of the project

Some pre-project data on macrophytes exists, both in the form of a monitoring survey (1999 & 2005) and a number of aerial photographs that show the macrophyte coverage (property of Rijkswaterstaat). For benthic invertebrates and fish no pre-project data was found. The post-project monitoring was carried out in the Rijn in Beeld project. Macrophytes, fish and benthic invertebrates were collected and identified. The project is a cooperation between nature organisations, Dienst Landelijk Gebied, Staatsbosbeheer, Rijkswaterstaat and the Ministry of Agriculture, Nature and Food quality.

Socio-economic aspects

Ecosystem goods and services

None

Conflicts and synergies

Some hiking routes around the area exist. To protect the delicate system the area itself is not accessible for recreation.

Project costs

Project costs are next to non-existent as the sluice was already in place and all that has been required is changing the time that it is opened and closed. It should be noted that the costs of the floodplain lands, that previously had agricultural purpose, is not considered in this reasoning. If the buying of those lands is to be included with the project costs the costs are significantly higher.

Contact person within the organization

Forester Gerrit van Scherrenburg, Staatsbosbeheer e-mail

Extra background information

References

Related Measures

• Lower river banks or floodplains to enlarge inundation and flooding
• Improve water retention
• Increase flood frequency and duration in riparian zones or floodplains
• Adjust land use to develop riparian vegetation
• Retain floodwater
• Improve backwaters

Related Pressures

• Hydrological regime modification
• Artificial barriers upstream from the site
• Impoundment
• Channelisation / cross section alteration
• Alteration of riparian vegetation
• Alteration of instream habitat
• Sand and gravel extraction
• Loss of vertical connectivity