Effects of spatial resolution of digital terrain obtained by drone on mountainous urban fluvial flood modelling

The effect of resolution and quality of terrain data, as the most sensitive input to 2D hydrodynamic modelling, has been one of the main research areas in flood modelling. However, previous studies have lacked the discussion on the limitation of the target area and the data source, as well as the underlying causes of simulation bias due to different resolutions. This study first discusses the performance of high-resolution DSM acquired by drone for flood modelling in a mountainous riverine city, and the effect of DSM resolution on results using grid resolutions from 6 cm to 30 m. The study then investigates the root causes of the effect based on topographic attributes. Xuanhan city, a riverine city in the mountainous region of southwest China, was used as the study area. The HEC-RAS 2D model was used for all simulations, and the results generated using 6 cm DSM acquired by drone were used as a benchmark. Results show that the simulation effect of flood characteristics shows a certain step change with the change of DSM resolution. DSMs with a resolution within 10 m can better capture the undulating features of the topography in the study area, which is crucial for the modelling of the inundation area. However, if features with specific elevation difference values are involved, it is best to keep the resolution within 5 m, which will have a direct impact on the accuracy of the modelling of the flood depth. The analysis of topographic attributes provides theoretical support for obtaining the optimal resolution to match simulation requirements.