ABSTRACT - DELIVERABLE 196
Report on the restoration success of two lowland streams following re-meandering projects
Lowland streams are characterised by a gentle slope of terrain (zero to five per mill) and sandy soil. They occur in the flat lowland areas of the Western European plain. Lowland streams are fed by rainwater; they often lack a well-defined source. Thus, their discharge shows a smoothed relation with the amount and frequency of precipitation in the various seasons.
Lowland streams occur in the eastern and southern part of the Netherlands. Their current velocity varies from 5-30 cm s-1 in summer and early autumn and from 30-60 cm s-1 in late autumn to spring. Often the rainwater fed upper courses dry up in summer, though sometimes they are fed by a helocrene spring and then show a more constant discharge pattern (Verdonschot, 1990).
After a long period of adapting lowland streams and their catchments to agricultural, domestic, drinking water and industrial needs, awareness of the damages of these alterations has increased. In the Netherlands, only about 4% of the streams still have a natural hydro-morphology. On the last ten years, the ecological importance of streams has become more and more apparent.
Currently, stream restoration is one of the answers to the lowland stream deterioration. In order to make the proper choices in stream restoration; one firstly has to understand the complex spatial and temporal interactions between physical, chemical and biological components. The success of restoration depends on steering the appropriate key factor(s). Whichever factor this is, differs for each stream and each site.
To provide a more detailed idea of the status of the ecological effects of lowland stream restoration projects a pragmatic approach is to analyse current project. This means learning by doing!. The examples analysed examples represent an average overview of stream restoration in The Netherlands. They make clear what can be expected looking more in detail at the positive and negative aspects from an ecological point of view.
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