Towards a high-resolution modelling scheme for local-scale urban flood risk assessment based on digital aerial photogrammetry

With the rapid development of cities and the impact of climate change, cities located near rivers are facing an increasingly serious flood threat. Urban flood risk prediction management is pressing. The peak discharge and duration are important factors in urban flood management as well as the important characteristics of flood hygrograph. Mostly, hydrological model is used to obtain the upstream flood hygrograph to drive inundation model. However, lack of information on reservoirs, barrage structures and land use make it difficult to construct high-precision hydrological models, especially in upstream cities where data is lacking. In this study, therefore, we propose an approach to urban flood management based on measured flood data from urban hydrological stations in close proximity to derive flood hydrography for different return periods, and establish a high-precision urban-scale river flood risk management method by combining with Unmanned Aerial Vehicle (UAV) survey data. This method can allow information on river construction and underlying surface change to be introduced into the flood hygrograph implicitly, thus avoiding the difficulty of establishing hydrological and hydrodynamic coupling of the whole basin. The applicability and accuracy of the methodology are explored in this article with reference to Chenxi City in the upper reaches of Yuanshui River. Comparison the flood process of the 10-year with the actual flood in 2016 indicates that the extent of inundation is strongly dependent on the instantaneous discharge, with the peak flow largely determining the maximum inundation extent and risk level. This illustrates the feasibility of risk assessment of urban flooding based on flood hygrograph with different period levels derived from measured flood processes at adjacent sites. Subsequently, the different return periods scenario is simulated and analyzed. This approach provides technical guidance for flood risk assessment in areas where data is lacking (e.g., upstream mountainous cities).