Assessment of flooding risk on the lower Saar River by using 2-dimensional hydrodynamic calculations

Parallel to the development of the River Saar into a navigable waterway flood defences have been built which reduced the risks of extreme streamflow events. However, the flood of 1993 showed that the assumptions used in designing these projects are no longer valid for the lower reach of the river. Thus, a river reach of 14 km length, which branches into a free-flowing arm and a locking canal, was examined with a 2-dimensional hydrodynamic model. Protection of riparian dwellers and property was the priority target of the computations. An area where ecological side-effects of the training were compensated by planting dense riparian vegetation was suspected to aggravate the flood risk. Modifications of river cross sections downstream of an endangered village were assumed to have a similar effect. The 2-dimensional model, which also included weir control options, allowed to simulate various scenarios. The results revealed that the ecological compensation as well as the modified cross sections had only minor influence on streamflow. However, a partial diversion of flow through the locking channel could reduce the water levels. These effects were quantified, so that the options were accessible to evaluation. So, a valuable tool for decision making was provided, allowing to optimise flood protection on the Lower Saar River.