Revision as of 07:08, 10 May 2010

Meers - Floodplain lowering

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Key features of the case study

Site description

The site near the village of Meers is home to a very dynamic stretch of the Meuse river. The river has a strong declining slope near the current exit of the pool. This leads to a rapid in the river which has led to the formation of both the 'old' and the 'new island'. At the same time the river's dynamics have, in the past, led to the river trying to cut off the meander near Meers. This led to dangerous situations for the nearby inhabitants. To protect the village dikes were build to restrain the river. The banks and floodplain of the area are used for gravel mining.

Measures selection

To restore the dynamic character of the river a cooperation between the Dutch Water Authority (Rijkswaterstaat), a nature protection organisation (Natuurmonumenten) and the local gravel mining company (L'Ortye) was initiated. The dykes were lowered to allow more inundation of the floodplain. At the same time the gravel mining company started to lower the area by undeep mining of the gravel in the floodplain. This was done in such a way that a slow rising gradient was created in the landscape; the area being lowest near the river slowly rising. Also, a high water channel was dug as a safety measure during peak discharges. The area held an old pool which originated from earlier gravel mining activities. This pool was partially filled with excess materials of the site. This to make the pool more shallow and through this a more suitable habitat. All this work has led to dynamic landscape with many different habitats and river dynamics. The main advantage was that part of this project could be carried out by making arrangements with a gravel mining company in such a way that both the company and the ecological state of the area benefited.

Success criteria

No clear success criteria were found, perhaps because this was a trial project.

Ecological response

Macrophytes and phytobenthos

There has been a study into some indicative species of macrophytes in the area. It was shown that the site is home to a number of rare and characteristic species. Most of these occurred in the rapid, and are characteristic species for high flow velocities. Prior to the project a study was carried out which identified much of the same macrophytes, however it should be noted that the study was carried out in a year with very favorable conditions for macrophytes. All in all it is difficult to say with certainty if the macrophytes have been positively affected by the measure. In the worst case scenario they have remained the same, whereas in the best case they have developed well.

Benthic Invertebrates

No study was conducted into benthic invertebrates.

Fish

The site is suitable for rheophilic fish, particularity the rapid and adjacent whirling pools serve as ideal habitat for these types of fish. MORE DATA NEEDED!

Other biota

Flora

The flora of the area shows a remarkable diversity in species. This diversity is much higher then it was prior to the project. As such it can be stated that the creation of a more diverse landscape has led to a more diverse floral composition. At the same time it should be noted that as succession progresses some rare species may well disappear and also the diversity may decline.

Birds

Traditionally the area of the project has been relatively scarce in the sense of bird occurrences. Since the project the numbers and species of birds have remained fairly constant. However, there has been a distinct change in the species composition in comparison to the composition prior to the project. The bird species have shifted towards a more characteristic composition for a river valley landscape.

Insects

The insects have been positively affected by the project. Both butterflies and dragonflies show an increase in rare species. The butterflies seem to be increasing still.

Hydromorphological response

Hydrological regime

The river's hydrology has been affected in such a manner that it now has more space to flow into its floodplains. At the same time the high water channel was made to limit small peak discharges of the river, this to protect adjacent areas from flooding. As sensible as this is, it in fact limits the natural hydrology of the river somewhat.

River continuity

Unaffected

Morphological conditions

The river has room to freely erode and deposit its sediment again. This has led to the formation of an island in the channel. The rising gradient of the floodplain has led to a gradient in flooding frequency which in turn is reflected in the flora of the site. Especially the rapid and the whirling pools nearby are great examples of morphological freedom of the river.

Monitoring before and after implementation of the project

Socio-economic aspects

Contact person within the organization

Extra background information

References

Related Measures

• Lower river banks or floodplains to enlarge inundation and flooding
• Shallow water courses
• Reduce water consumption
• Reduce erosion
• Create low flow channels in over-sized channels
• Construct semi-natural/articificial wetlands or aquatic habitats

Related Pressures

• Alteration of instream habitat