Identification and Comprehensive Diagnosis of Sharp Change of Annual Runoff Volume and Silt Discharge Series at Toudaoguai Hydrometric Station in the Upper Reaches of the Yellow River

Based on the hydrological data measured at Toudaoguai Hydrometric Station during the period of1950- 2010,the Mann-Kendall Ranking test( M-K test method),Pettitt method,Mann-Whitney-Pettitt method( MWP method),sequential clustering analysis and independent identically distributed test were used to identify and comprehensively assess the trends of annual runoff volume and annual silt discharge as well as their sharp changes along the desert wide-valley in the upper reaches of the Yellow River,these changes were validated with the double mass curve of streamflow and silt discharge,and the physical causes resulting in the sharp changes were analyzed.The results showed that the most significant effect on the inflow and silt discharge at Toudaoguai Hydrometric Station was the operation of Liujiaxia and the Longyangxia reservoirs. The measured results revealed that the sharp changes of streamflow and silt discharge at the station occurred in 1986 and 1985,and the second sharp change occurred during the period 1968- 1970. The results could provide a basis for analyzing the changes of streamflow and silt discharge and their driving factors at Toudaoguai Hydrometric Station.