Calibration of a hydrodynamic model (HEC-RAS) using UAV imagery to delineate high-water mark of a flood event

Abstract:

Two-dimensional (2D) hydrodynamic modelling proved to be an important tool for understanding flood events. Traditionally, the channel Manning’s roughness coefficient is calibrated with in situ measurements (water height, flow). However, it is often difficult to obtain measurements, and then calibrate the Manning’s roughness coefficient, in the floodplain where accessibility, safety, and/or cost might be prohibitive. Observations of high-water mark allow adjustment of the Manning’s roughness coefficient of the floodplain. In this study, we used unmanned aerial vehicle (UAV) camera imagery to get a global view of the floodplain and to identify high-water marks after a flood event. The HEC-RAS model (v 5.0.7), one of the most popular hydrodynamic model, was implemented on the Au Saumon River, Québec, Canada. The positional and vertical accuracy of the UAV products were evaluated using Real Time Kinematic GPS (RTK-GPS) points measurements during image acquisition as reference coordinates. Orthophotomosaics at <0.05 m spatial resolution were generated with photogrammetric software. The analyses show that the methodology is especially powerful to delineate high-water mark. The calibration of the Manning’s roughness coefficient of the channel was traditionally carried out with in situ measurements of flows and water heights acquired in various conditions while calibration of the Manning’s roughness coefficient of the floodplain was carried out with UAV derived high-water mark. Accuracy of the UAV products is high in XYZ directions and sufficient for river monitoring purposes.