Abstract: This paper examines the behavior of floodwater in a flood detention basin and uses quantitative methods to establish the benefits and losses of floodwater utilization. The Dahuangpu Wa flood detention basin was taken to demonstrate semi-quantified functions of benefit and loss. A hydraulic mathematical model was applied to reveal the temporal and spatial conversion during three floods events, with specified return periods, using local hydrological and land-use information. The study indicates that critical water depth is the key parameter for optimum floodwater utilization. The inflow area, benefit area, average water depth and maximum water depth are non-linear and proportional to the flood inflow. Floodwater utilization is strongly linked to topographic features and land-use change.