Multi-scenario simulation study on flash floods in the Zhaigang River Basin under the influence of hydraulic engineering

Abstract

[Objective] Flash floods are one of the most common and destructive natural disasters globally. With the continuous intensification of climate change, both the frequency and intensity of flash floods have notably increased. Consequently, the significance of flash flood simulation research in the fields of disaster prevention, mitigation, and risk assessment has become increasingly prominent. However, the use of a single hydrological or hydrodynamic model often has limitations in flash floods simulation and frequently overlooks the cumulative effects of hydraulic structures, such as bridges and weirs, on flood progression in mountainous areas. This oversight can lead to the underestimation of flash floods susceptibility and potential risks. [Methods] A coupled hydrological and hydrodynamic model(CNFF-IFMS) was developed to improve the accuracy and reliability of flash flood simulations in the Zhaigang River Basin. The coupled model was further employed to quantitatively analyze the flash floods response mechanisms of three bridges(i.e., B1, B2 and B3) and one weir(W1) located in the river defense sections of the basin under multiple return period(i.e., 2 a, 5 a, 10 a, 20 a, 50 a and 100 a). Additionally, flood risk analysis and assessment for the basin were conducted. [Results] After the construction of the bridge and weir, the water levels at the cross-sections during various return periods have all increased compared to the situation without the bridge and weir, exacerbating the risk of overtopping and inducing backwater effects. According to the intensity of the backwater effects, they are ranked from strongest to weakest as W1, B1, B3, and B2. The velocities at the cross-sections during various return periods have all decreased compared to the situation without the bridge and weir, but they have generally increased the scouring of the two-dimensional area around the project. The flooded area and the range of water depth during various return periods have all increased compared to the situation without the bridge and weir. The total flooded area increased by 4.732 km² from the 2-year to the 100-year flood event, an increase of 0.046 km² compared to the situation without the bridge and weir. [Conclusion] The result indicated that the coupled hydrological and hydrodynamic model effectively reflected the basin rainfall-runoff response and its flood propagation mechanism in mountain gullies, realizing the dynamic evolution of mountain floods in time and space. Moreover, the importance of hydraulic structures such as bridges and weirs cannot be ignored, as they exacerbate the impacts of flash flood disasters to some extent. It is crucial to incorporate these structures into basin flash floods simulation studies to reduce uncertainty in the simulation result. The research can provide technical support and reference for disaster prevention and reduction in the Zhaigang River and other similar mountainous watersheds.

Keywords

flash floods / coupled hydrology and hydrodynamics / hydraulic structures / flood / risk assessment / climate change / precipitation / numerical simulation