Analysis on the contribution rate of driving factors for the annual water and sediment variations at the Toudaoguai hydrological station in the Yellow River

Based on those observing series of annual water and sediment volumes from 1950 to 2010, a nonlinear response model was built statistically at the Toudaoguai gauging station in the Upper Yellow River in this paper. And the contribution rate of those leading driving factors in the model were estimated quantitatively. The results showed that: From 1950 to 2010, the annual mean runoff reduction is 0.223 billion m³/a, the annual mean sediment reduction is 2.7 million t/a. Especially from 1987 to 2010, the decreasing trends of annual runoff and sediment are more obvious, and the sediment reduction is greater than runoff reduction significantly. From 1969 to 2010, the contribution rate of climatic factors and underlying surface factors for annual runoff and sediment reducing modulus at the Toudaoguai gauging station is 2:8 approximately, underlying surface factors occupied a dominant position. Among them the water diversion in the Ningmeng Irrigation Area is the largest driving factor on the runoff reduction at the Toudaoguai gauging station, whose contribution rate reached 42％. The reservoir operation of Longyangxia and Liujiaxia reservoirs is the largest driving factor on the sediment reduction, whose contribution rate reached 34％. It can be predictable that in the future, the variation of runoff in the main channel of upper reach of Lanzhou, and sediment volume from those tributaries between Lanzhou and Toudaoguai will be the two natural driving factors for the annual water and sediment variations at the Toudaoguai gauging station in the Yellow River. Therefore the water diversion from the main channel for irrigating and integrated management of soil and water conservation in those tributaries will be key methods for controlling the variations of water and sediment.