Flusskorridore und Auenstrukturen im schweizerischen Mittelland (nördliches Alpenvorland) | River corridors and alluvial structures in Central Switzerland (northern sub-alpine area)
Long-term spatial variation of river channel distribution in this alluvial valley zone is described for two examples by analysing historical maps covering a period of over 300 years. Such a time series enables the identification of the occupied river corridor or «Pendelband». Two river sections in northern Switzerland were chosen, one of the Aare river and one of the Reuss river to analyse the spatial evolution of the river channels over time, as well as alluvial structures. Knowledge of the river corridor as an historical reference give us an important guideline when developing appropriate regional measures for river restoration projects.
Ableitung und Analyse flussmorphologisch relevanter Parameter von historischen Karten
Increasing morphological problems are being encountered with watercourses in central Europe, related to impacts on sediment regime with lack and surplus of material, higher bed shear stresses due to narrowing of river beds, and subsequent river bed degradation. Ecological deficits result from the lack of gravel bars, a missing of dynamic river morphology and a lowering of the groundwater table. Up to now, practical studies have generally used descriptive analyses of historical conditions of rivers and their morphology (e.g. defining the morphology as braiding or meandering). This paper deals with the qualitative and especially the quantitative analysis of parameters derived from historical maps. Parameters such as river bed width, radius, slope and sinuosity are first described in a scaling context and then derived from two historical and the present situation at the river Mur in Austria. It is shown that this approach improves the quality of results based on historical maps and gives first ideas about the solution of morphological problems.
Ecological rehabilitation of the River Rhine: Plans, progress and perspectives
The River Rhine has suffered because of numerous drastic environmental changes — for example, the regulation of the river bed and the construction of weirs and dams. Furthermore, discharges of agricultural, industrial and municipal wastewater have caused a deterioration in the water quality. This problem became particularly acute in the 1960s and 1970s. After the Sandoz accident in Basle in November 1986, the states bordering the River Rhine agreed the Rhine Action Programme for its ecological rehabilitation. This programme has the following four aims, which should be realized by the year 2000: (1) to create conditions which will enable the return of higher species (such as salmon); (2) to safeguard Rhine water as a source for the preparation of drinking water; (3) to abate the contamination of sediments due to toxic compounds; and (4) to fulfil the requirements of the North Sea Action Plan, as the River Rhine flows into the North Sea. Water quality criteria have been developed for about 50 contaminants or contaminant groups and for phosphorus and ammonium. Early signs of the ecological recovery of some aquatic communities in the River Rhine have been observed, but eutrophication and pollution by micropollutants, in particular polychlorinated biphenyls found in suspended matter, sediments and biota, still form a serious threat. In addition to further improving the water quality, river habitats must be improved, reversing the artificial river control measures taken in the past for the return of a number of characteristic riverine organisms such as migratory fish. The ‘Ecological Master Plan for the River Rhine’ aims to restore the mainstream, along with the main tributaries, as habitats for migratory fish (e.g. salmon). This involves protecting, preserving and improving ecologically important reaches of the River Rhine and the Rhine valley. The first steps for realizing the hydrological and morphological modifications have been taken, starting with the development of a specific ecological network focusing on the most important floodplain areas along the Rhine. Habitat improvement measures started later than the pollution abatement measures and, so far, relatively few studies on the effectiveness of the ecological rehabilitation techniques concerning habitat improvements in the Lower Rhine have been published. A major task for research programmes will be to identify the detailed quantifiable and verifiable ecological objectives (e.g. water quality criteria, hydrological and morphological targets) to guarantee the actual ecological rehabilitation of the River Rhine.