|De oevers langs de Zeeschelde: van uniformiteit naar structuurdiversiteit|
Hoffmann, M.; Graré, W.; Meire, P. (1997). De oevers langs de Zeeschelde: van uniformiteit naar structuurdiversiteit. Water 16(95): 138-146
In: Water: Tijdschrift over Waterproblematiek. VLARIO vzw/vzw Water: Wijnegem. ISSN 0770-7193, more
River banks; Belgium, Zeeschelde [Marine Regions]; Marine; Brackish water; Fresh water
|Authors|| || Top |
- Hoffmann, M., more
- Graré, W.
- Meire, P., more
After a thorough analysis of the present-day river bank structure quality along the Zeeschelde (25), recently some ecologically sound maintenance measures were taken on an experimental scale : - Fresh water tidal marshes showing erosion cliffs of more than 1 m high were formerly protected against further erosion with a surface layer of allochtonous boulders. Recently an alternative, (landscape) ecologically more sound construction of superficially hardly visible vertical poles and in between wattle of osiers was used. Three terraces were created at different levels creating narrow zones with different flooding regime suitable for the growth of different kind of vegetation.The construction proved its strength under severe circumstances (several storms and drifting ice during the winter of 1996/97). No spontaneous vegetation development was detected yet. - Although several bulrush species are known from the Zeeschelde, colonisation of free mud flats by bulrushes was not observed for a long time along the Zeeschelde; these specific fresh water estuarine species are nonetheless known as good mud flat fixators which might help stabilize river banks with large mud flats. Therefore bulrush (Schoenoplectus tabernaemontani) was planted on an experimental scale at two sites in the fresh water tidal zone. After three years of monitoring it became clear that bulrushes can only grow in a narrow zone just underneath MHW, where the population base is flooded twice a day. Unlike in other estuaries bulrushes can not maintain themselves until the MLW line. Water or sediment quality do not seem to effect the populations negatively. Seed germination, juvenile and adult plants from seed were observed frequently. At high water velocities and severe wave action the bulrushes will not suppress mud flat erosion, since the mud flats are too steep and the zone suitable for bulrush survival is too narrow. Ecologically more sound alternatives for dike construction and dike relocation are presented; these alternatives are not realised yet and could therefore not be evaluated yet. A precursor dike construction in the brackish tidal zone appeared to have a positive effect on mud flat colonization and succession to brackish water tidal marsh.