No abstract

In the German-Czech border regions throughout the Ore Mountains, storm runoff frequently causes severe damage in headwater areas and lower reaches. The fact that settlements along smaller tributaries and towns near the receiving water are affected simultaneously requires a flood control concept with measures applied throughout the entire drainage area. Modern concepts of flood protection offer a large number of potential natural measures, such as a number of small, decentralized retarding basins, river revitalization, afforestation of flood plains or landuse changes. The study presented here is part of the Interreg-IIIA research project "DINGHO". Its aim is to show how decentralized measures can contribute to improving flood protection in the Upper Flöha catchment. The advantages and limits of such natural flood protection measures will be illustrated.The study area extends between the large Rauschenbach reservoir and the town of Olbernhau (Saxony), including two main tributaries -the Natzschung and Schweinitz rivers. In a first step the local potentials were investigated on the basis of GIS analyses and field surveys. The second step included the assessment of the efficiency of the decentralized measures in different scenarios using the rainfall-runoff models NASIM and WaSiM-ETH.Particularly in higher regions with gentle slopes (above ~700 m a.s.l.), wide areas along the river channels can be used for water retention in small, decentralized retarding basins. In addition, some areas can be reforested, since they have recently recovered from the SO 2 pollution, which affected the area until the late 1980s. By contrast, potentials for river channel renaturation are strongly limited. The modelling results clearly indicate that small retarding basins would reduce peak discharges with a 100-year return period by up to 48% at some tributaries and 10% downstream in Olbernhau. River restoration measures do not show any significant effect. Reforestation of forest decline areas can reduce peak discharge by about 13%.Hence an effective improvement of flood protection in the Upper Flöha catchment can be achieved through the application of decentralized measures. The reduction of flood peaks includes the Flöha River itself, tributaries and headwater areas.