In the past, locally heavy rainfall has caused heavy flooding with significant property damage all over Germany. The actual design philosophy for sewer system in Germany and all over Europe did not consider flooding so far, but bases upon full pipe flow or surcharge based on statistical return periods.
The new DWA M-119 guideline gives recommendations for the risk management for municipal flood prevention. This guideline include an assessment for the risk of flooding as a result from the analysis of the water levels and a subsequent assessment of the risks. The water levels are analyzed for a certain storm event or design storm. Here the guideline recommends methods with different costs and accuracies. In order to assess the risk of flooding, the water levels are evaluated for the potential of flooding and for the potential of damage.