Flash Flood Simulation using Hydrodynamic Rainfall-Runoff Modeling with Spatially Distributed Rainfall from Radar Data

During the national cooperation project HiOS (2017-2021), studies on flash floods were carried out using hydrological and hydrodynamic models. Namely, the open-source software TELEMAC-2D for hydrodynamic simulation was used. TELEMAC-2D is a well-known and established hydrodynamic model solving the shallow water equations. Since 2013, the SCS-CN-method has been implemented in TELEMAC-2D. Since 2019, a module for spatially distributed rainfall from radar data was added. Newer developments integrate the effect of re-infiltration using the Green&Ampt approach. With these supplements, the runoff generation using precipitation from radar data is linked to overland flow and TELEMAC-2D is extended to a Hydrodynamic Rainfall-Runoff Model (HDRRM). Thus, the most important requisites are fulfilled to simulate heavy rainfall and flash flood events without the essential need for an additional hydrological model. The quality of the resulting method is demonstrated using the severe flash flood event in the district Rottal-Inn in Bavaria on June 1st in 2016. In the first step, the simulation is calibrated using a gauging station in the catchment Simbach a. Inn. After this, a first validation followed by applying the same methodology to the adjacent catchment Triftern. The results gained in both catchments showed good agreement with the event data. The infiltration methods were compared with each other and with measured discharges and water levels. The simulations required the use of high-performance computer systems. The enhanced TELEMAC-2D model proved to be an efficient and versatile tool for the simulation of flash floods usable for forecasting flash floods. As part of their engineering education, students should not only be introduced to current research topics, but also have the opportunity to participate in them directly. The students of a seminar on rainfall-runoff modeling accompanied the creation process of this publication and contributed to it through calculations, analyses and graphical design work.