Assessing the variations of the available flood storage capacity in a flood retention basin due to the changing environment

Flood retention basin (FRB) is an important measure for the flood control. As the available flood storage capacity of FRB reflects the maximum amount of flood that can be stored, it is often varied due to the changing environment, which impacts on the its flood control function. Based on the principle of allowing only specific areas to be inundated for flood control, a systematic framework is proposed to quantify the variations of the available flood storage capacity of an FRB due to the combined effects of human activities and climate change. The Variable Infiltration Capacity hydrological model is a tool of simulation of flood flow in the framework. A Geodetector model is applied to figure out the contributions of human activities and climate change. Applying the framework to 42 FRBs in the middle reaches of the Changjiang River Basin, the results show a significant 9.6% decrease in total available flood storage capacity from 2000 to 2020, with human activities contributing more than climate change. The decrease of available flood storage capacities in the FRBs bring the increases of frequencies (i.e., the decrease of the standard of flood control) of the flood inflows that represents the maximum preventing flood for FRBs from 0.111%, 0.167%, 0.100% to 0.143%, 0.250% and 0.167%, respectively. Our study will not only help assess variations of the available flood storage capacity, but also contribute to the protection of the FRBs.