Research On The Theory Of Watershed Runoff Generation And Flow Routing Processes And Its Application

Hydrological model is an effective tool for flood prediction, a very important non-project measure for flood loss reduction, and for reasonable water resources utilization. So we need the support of hydrological model in decision-making, run of the hydraulic engineering, and flood control and so on.The simulated flood results by any hydrological model are not good in semi-arid and semi-humid areas. In this paper, Haihe river basin which is a typical semi-arid and semi-humid watershed in China is selected. Runoff response to rainfall is analyzed to understand the runoff generation mechanisms in the basin and to research the influential parameters on runoff generation. Thereby, two runoff generation models considering macropore flow are established and applied in Haihe river basin to search the effects of land use/land cover change on flood. The main results are as follows.(1) Runoff response to rainfall is analyzed, and the results are found that not a single runoff generation mechanism exists in the basin, but relates to the rainfall characteristics and the initial soil moisture. If the rainfall intensity is low and the initial soil moisture is high, saturation-excess runoff is dominant; if the rainfall intensity is high and initial soil moisture is low, infiltration-excess runoff is dominant. Thereby, taking soil macropore into consideration, infiltration-excess runoff generation model and saturation-excess runoff model are established and calibrated in Liuhe and Zijingguan basin.(2) The simulation precision depends on unit hydrograph. The unit hydrographs obtained from observed rainfall and runoff data are different if the rainfall is of different amount, intensity and center. SCS dimensionless unit hydrograph and unit hydrographs derived by probability distributions are a feasible way in the areas without data.(3) Two global sensitivity analysis methods, RSA(Regional sensitivity analysis) and Sobol'methods, are adopted to improve model calibration efficiency. The results of the study show that model parameter sensitivities are not impacted by the selection of analysis method, as well as objective functions, but a little difference in different basins. So, in the process of parameter calibration, only the sensitive parameters are calibrated, and the values of non-sensitive parameters are made by experience. The results of RSA method are not single values, but a narrow range. (4) Land use/land cover change can affect the flood frequency. Two sub-basins of Haihe river basin are selected and the change in trend of runoff generation and flow routing parameters are made analysis to confirm the effect of land use/land cover change on flood. We use the rainfall and runoff data before 1980 and after 1990 to calibrate the models, and obtained two different series of parameters. And then, the two series of parameters are used to simulate all the floods in order to make comparisons. The results show that the peak flow and flood volume all decreased after 1990, and in Liuhe basin, they decreased by 4.9% and 1.7% respectively, and in Zijingguan basin 4.8% and 1.7% respectively.