Decentralised water retention along the river channels in a mesoscale catchment in south-eastern Germany

摘要

Throughout the Ore Mountains, a low mountain area located in the German-Czech border region, storm runoff frequently causes severe damage in headwater areas as well as in lower reaches. Settlements along smaller tributaries and towns at the receiving water are affected simultaneously, so measures distributed throughout the entire drainage area (decentralised measures) have to be considered for flood protection planning in such areas. The concept of decentralised flood protection, which is well established in the German literature, offers a large number of potential flood control schemes including measures along the river channels, in agriculture and forestry as well as in settlements. The investigations presented here focus on the group of measures along the river channels, including small, distributed retarding basins, river renaturation and afforestation of floodplains. Based on rainfall-runoff models, its aim is to show how such measures influence flood hydrographs in low mountain areas with a 100-year recurrence interval, using the example of the Upper Fl?ha watershed in the Central Ore Mountains.The results indicate that along the tributaries of the Fl?ha very high local peak reductions can be achieved with small retarding basins. The efficiency of the basins is related to the available storage capacity in the valleys upstream of the settlements. On a supralocal level, i.e. at the Fl?ha River, an additional reduction of the peak discharge occurs in the model. Other significant supralocal effects can be observed for the scenarios with an increased floodplain roughness (afforestation). In a combination of both scenarios the supralocal effects increase further, whereas the local effects are as high as in the retarding basin scenario. By contrast, the river renaturation scenario does not show a significant impact on the flood hydrographs. However, the limited effect is a result of the local characteristics of the study area, where the number of suitable river sections is limited and the slope gradients are high.On the whole, it can be concluded that decentralised measures along the rivers can be efficient elements in the framework of flood protection strategies. The reduction of flood peaks includes not only the receiving water, but also the tributaries, so that an improvement of flood protection extending across the entire watershed can be achieved.