ABSTRACT
ABSTRACT: Risks: The 26 km long international stretch of the Alpine Rhine River between the confluence of the River Ill and the estuary into Lake Constance was canalised at the end of the 19th as well as at the beginning of the 20th century in order to alleviate the problems caused by severe major floods in the preceding years. The river alterations enabled an economic as well as an agricultural boom in the lower Rhine River valley. Today approx. 300’000 people live and work within this region due to the rectification work by the International Rhine Regulation IRR. Within the last decades the geotechnical as well as the safety standards have changed along with ecological restoration issues. Due to the significant increase of urban areas, the potential risk and vulnerability have increased tremendously. Flood control as a main goal: The main objective for the Alpine Rhine Project is an improvement of the current flood protection system. The design discharge of the project is 4’300 m3/s (equivalent to a 300-year flood), while also taking into account an extreme event of 5’800 m3/s. In order to achieve this goal, heavy construction measures with new levees and widening of the existing riverbed are necessary. All measures must fulfil today’s requirements of both neighbouring countries Austria and Switzerland. This includes an improvement of the ecological situation, the preservation of the existing drinking water supply and a minimal impact on the environment during construction. Ecology and flood protection-a double win: According to the European Water Framework Directive (WFD) the lower stretch of the Alpine Rhine River is considered to be “heavily modified”. In order to fulfil the WFD the river needs to be ecologically restored. According to the Swiss Water Protection Act the natural river state must be achieved as far as possible. However, all parties involved agree that the original historic morphology of the Rhine River can never be fully restored. Therefore the main goal of the project is to allow as much lateral river widening as feasible. A wider cross section of the Alpine Rhine River allows both ecological restoration and the required flood protection level.
