The brook valley of the Vledder Aa in the province of Drenthe (East of the Netherlands) is currently in agricultural use. The government of the Drenthe has allocated the brook valley as a nature reserve. The upper part of the brook (spring area) was restored in 2002. Witteveen+Bos has made a design to restore the middle part.
First of all Witteveen+Bos has formulated the following goals:
for the brook
- restoration of the original meanders and stream pattern of the brook as it was in the 1950´s
- creating a 'good ecological status' (EU´s Water Framework Directive)
for the brook valley
- rewetting the valley and by creating suitable hydrological conditions for groundwater-dependent species
- restoring surface water dynamics: allow flooding in combination with storage of water (anticipate on climate change)
for the area outside the brook valley
- allowing no negative hydrological effects outside the brook valley on buildings, roads and agricultural areas.
Integrating the groundwater and surface water system in an extensive model has led to the optimized fluctuation of the groundwater table and surface water level. With these levels the aimed groundwater table will be achieved and suitable hydrological conditions for the groundwater-dependent species will be created.
In order to re-establish the middle part of the brook valley, a design was made, based on the results of the modelling. This led to the following measures that should be taken in order to restore the middle part of the valley: filling up the current brook; digging a new shallow and narrow brook bed; removing all the agricultural weirs and realizing a fish friendly weir; protecting buildings by natural dams and protecting the nearby road by making a ditch.
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