Flood simulation using HEC-RAS model calibrated with remotely sensed water mask: a case study of Mulde River, Germany

Kurzfassung

Flood is one of worldwide disasters, and it causes great amounts of damage every year. Among the means to study this natural disaster, hydraulic modelling and remote sensing detection are ones of the most valuable. Both present advantages and disadvantages. The hydraulic model is capable of simulating and predicting the flowing of the flood in a continuous time discretization, but lots of parameters should be locally calibrated to improve the performance of the model in a given study area. Satellite remote sensing can provide observations that are further used to derive reliable flood inundation maps or water masks for large areas, but such satellite observations can be only made in periodically discretized manner; the temporal difference between two successive satellite observations over a given study area can be several hours up to days depending on satellites and the temporal resolutions. This project arises with the objective to combine the own advantage of the hydraulic model and satellite remote sensing. The approach consists of calibrating the hydraulic model using the remotely sensed extent of the water mask. If this procedure is repeated successively during an event, calibrating the model with the water extents gradually provided by the satellite, a full simulation of an inundation event would be produced. This work evaluates the feasibility in calibrating the hydraulic model with an optical satellite sensor derived water mask. After that, the model is validated using a Synthetic Aperture Radar (SAR) satellite-based flood inundation product. An analysis is carried on about the possible under-/overestimation of the SAR satellite product and a possible use in the emergency management cycle of this methods is also assessed. This report first presents a general overview on the satellite remote sensing techniques, with a focus on the SAR-based algorithm in deriving flood inundation map or water mask. Then the general background about the hydraulic modelling is presented and the selected HEC-RAS model is described in more details. Every single important element that has to be considered in the procedure of calibration and validation is explained. The Mulde river located in the East of Germany is selected as case study in this study project. Results show a good performance of the hydraulic model in simulating the flow on the floodplains, with a good estimation of the flooded area and a more heterogeneous coverage in respect to SAR water mask product.