Responses of the Water and Sediment Behavior to Vegetation Restoration in Tipical Catchments on the Loess Plateau

This paper compared the runoff and sediment characteristics from 1963-1979,analyzed the effects of the soil and water conservation comprehensive harness between 1980-2002,especially,the variation of runoff and sediment behavior patterns and characteristics of catchment with the effects of conversion of cropland to forest and grassland between 2003-2011 by using the hydrological data of the Wuqi hydrological station on the upper catchment of Beiluo River.The results showed that:Over the 50 years,the volume of runoff and sediment displayed obvious decreasing tendency.Contrasting with between 1963 and 1979,the mean volume of runoff and sediment between 1980 and 2002 were abated about 22.80% and 45.63%respectively.The decreasing fluctuations of the mean volume of runoff and sediment were stronger with53.03% and 89.33%respectively.The volume of runoff and sediment during high flow and median flow of the three periods showed decreasing tendency and the decreasing level of the volume of sediment is higher than the volume of runoff,however,the volume of base low increased gradually in low flow.The volumes of sediment of 2003-2011 were vanished completely.In three periods,the annual relationships between runoff and sediment manifested statistical obvious variation.Comparing with 1963-1979,the sediment of unitrunoff were decreased about 12.08% in period of 1980-2002,the capacity of runoff and sediment were declined about 17.27% and they decreased about 1/4and 1/3respectively in 2003-2011.At monthly scale,the volume of runoff and sediment showed a circle of 8,the decreasing fluctuations of extends of them were stronger,especially during 2003-2011.Over the 50 years,the volume of runoff and sediment,the conditions of runoff and sediment and the relationships of runoff and sediment were decreased gradually under the background of the water conservation comprehensive harness,especially the conversion of cropland to forest and grassland.It shows that thegrain for green projectplayed its ecological role on saving water and soil,multiplying base low and also abating runoff and sediment.