Application and comparison of two different dual drainage models to assess urban flooding

Two types of dual drainage models were set up to assess urban flooding for a study area in Germany: (1) a static model based on a conventional method in Germany; the overflow volumes of the manholes are gained by the sewer solver HYSTEM-EXTRAN. Using these water volumes and geographic information system (GIS) tools, an overland flow network, composed of flow paths and accumulated water in sinks, is produced, (2) a HYSTEM-EXTRAN 2D model; a two-dimensional (2D) overland flow module is coupled bi-directionally with HYSTEM-EXTRAN. The overland flow and the flow in the sewer system are simulated alternately.

Both models were supplied with a synthetic design rainfall and 25 extreme storms. After comparing the models and the results, a practical approach to assess urban flooding is proposed. In this approach the 2D model will compute the depth, extent, and propagation of floods only in the prone areas specified by the static model.