Impacts of precipitation variation and soil and water conservation measures on runoff and sediment yield in the Wuding River Basin,middle reaches of the Yellow River

In this study,we analyzed the data of annual precipitation,runoff,sediment yield and soil and water conservation ( SWC) measures from 1957 to 1996 in the Wuding River Basin,China.Using MannKendall-Sneyers trend test,we found that runoff and sediment yield changed significantly in 1972.The time series data was in turn divided into two parts: i) a baseline period ( BP) (1957-1971) and ii) a period of change (CP) (1972-1996).By using the methods of double mass curve,an empirical formula and a correction coefficient,the impacts of precipitation variation and SWC measures on runoff and sediment yield were analyzed and the contributions of variation in precipitation and SWC measures to runoff and sediment yield were assessed by fitting a multiple regression model.The results showed that during the CP,SWC measures caused the reduction of mean annual runoff by 3.16 × 108-3.42 × 108m3 /year,accounting for 23.0% -24.4% of the values obtained during the BP.SWC measures caused the reduction of mean annual sediment yield by 0.71 × 108-1.07 × 108 t /year,accounting for 47.1% -57.3% of values during the BP.The variation in precipitation caused the reduction of runoff and sediment yield by 0.46 × 108 m3 /year and 0.13 × 108 t /year,respectively,which were 11.6% of the total runoff reduction and 11.4% of the total sediment reduction.The reduction of runoff due to the SWC measures via vegetation restoration (planting trees + grass) was 2.78 × 108 m3 /year,which was 70.2% of the total reduction of runoff.The reduction of sediment yield due to the SWC measures via engineering projects ( terraces + sediment-trapping dams) was 0.46 × 108 t /year,which was 40.3% of the total reduction of sediment yield.Because of the variation in precipitation and the limitation of engineering measures,their effects on runoff and sediment yield varied among different periods.Therefore,in the integrated soil and water management of the Wuding River Basin,it is important to apply countermeasures to ensure that the SWC measures are sustainable,i.e.rational allocation of the ratio of the SWC measures via vegetation restoration and engineering projects,paying attention to the maintenance of established terraces and replacing the destroyed SWC engineering in time.