Study On The Effect Of Underlying Surface Change On Inflow Of Yuqiao Reservoir Watershed

YuQiao reservoir is relatively important in the HaiHe watershed, and is the biggest one in Tianjin as a water head site. YuQiao reservoir has long taken on the duty to provide domestic water to Tianjin, and been the important short-time storage reservoir in the Diversion Project from Luan-he to Tianjin. The inflow of YuQiao reservoir decreases gradually for years. The effect factors are divided into two parts .One is precipitation ,the other is human activity. The human activity contains the direct effect factor such as water consumption change, and indirect effect factor such as underlying surface change and runoff yield characters change subsequently. The text puts emphasis on the underlying surface change on the runoff effect. Based on the cognition on the hydrological phenomena in the research watershed and rainfall–runoff basis data, analyzing the cause of formation and relations between every factors, the hydrological model can be set up on account of mathematical method to simulate gydrologic processes. The method supplies a effective approach for analyzing the hydrologic effect of underlying surface change. Making use of the parameters in the basis data before the underlying surface change,We can use the parameters in the basis data before the underlying surface change to calibrate the parameters in the model, and examine the parameters again. Than the calibrated model can be used to simulate the runoff process after underlying surface change, and compare with the measured basis data. We adopt this method to differentiate the effect on the underlying surface change on runoff.The research watershed of this text is YuQiao reservoir controlled watershed (above the Shuipingkou staff gauge station).Applying the distributed hydrology model SWAT to analyze the underlying surface change for the research watershed in 1980,2000 and 2004,after then ,the runoff from 1975 to 2000 can be simulated when the situation of underlying surface and different rainfall distribution is the same as 2004.Comparing the simulated results to the runoff at original underlying surface , the results show that :the change on the land use type principally indicate that arable land is reducing and the reduced area is transforming to grass mostly ,some to land for construction. Because the increased grass area is the most in the five land use type, and the increased grass leads to reduced runoff, grass is the main point giving rise to runoff reducing. The general trend of runoff change whether monthly runoff or annual runoff is both decreasing. For the high flow year, the effect of land use type is less, which shows that the effect of underlying surface change on runoff is less .For monthly runoff ,it shows that the effect of underlying surface on runoff is variational seasonally, more effect on the less precipitation. The rangeability of other months is less. The simulated results show that SWAT model can reflect the rainfall-runoff process in the YuQiao reservoir controlled watershed truthfully. The model is suitable for the meso and micro-scale weather,supplying the scientific proof for the water resource research in the future.