Study On Effects Of Sublayer And Land-cover Change On Flood In Massif Areas Of Daqinghe River Basin

The conditions of the underlayer in Haihe River Basin has changed dramatically during the past few years, which affected annual runoff and flood peaks and volumes. Due to the complexity of hydrological phenomenon, the paper mainly employed mathematical statistics method, the theory of stochastic hydrology and hydrological model to describe hydrological phenomenon and to analyze storm flood characteristics quantitatively in Daqing river basin. The main results are as follows:(1) The Mann-Kendall trend test, moving average method, and regression analysis method are employed to analyze the trends of rainfall amount, flood peaks and flood volumes in Zijingguan, Fuping and Longmen sub-catchment. It is shown that there is no obvious trend for rainfall amount, while flood volumes and peaks are decreased, especially in Zijingguan sub-catchment.(2) The trends of maximum soil moisture capacity(Im), water evaporation and basin evapotranspiration, the regression coefficient of soil moisture, the lag time of flood peak, and unit hydrograph are analyzed, and the relationship of rainfall and runoff is studied as well. The results show that the maximum soil moisture content increased after 1980 due to human activities. Water evaporation decreased, and the regression coefficient of soil moisture shows a increasing trend which varies between 2~5%. The lag time of flood peak increased after 1980, however, the variation is limited if rainfall intensity is large enough.(3) A hydrological model is established and the parameters in the model are calibrated using the hydrological data before and after 1980 respectively, which can reflect the sublayer changes. The parameters calibrated by hydrological data after 1980 are used for input to simulate the flood before 1980 , thereby, the difference between the simulated flood volume and peak are considered to be the influence of sublayer changes. The modelled results indicate that the sublayer changes have a small effect on large floods and a large effect on small floods.(4) A hydrological model considering land use/land cover change is established to assess the effect of land use change on flood quantitatively. The model can simulate flood processes well. So The flood processes after 1980 were simulated based on parameters of 1980; and flood processes before 1980 were simulated based on land surface parameters of 2004. It is used to analyze the impacts of different land use and land cover on flood with the same rainfall process, especially to study the changes of LUCC impacts on peak flow and flood volume.