Analyses on trend and driving force of runoff and sediment load in the Wuding River

Since the late 1950s,extensive soil and water conservation measures have been implemented in the Wuding River basin to reduce surface runoff and soil erosion.The measured runoff and sediment load exhibited a decreasing trend over the period.The objectives of this work are to quantify the decreasing trends of precipitation,runoff and sediment load during 1956-2006 and to statistically identify change points or transition years in the changing trends.Results show that strong decreasing trends in annual precipitation,runoff and sediment load have existed since the late 1950s at Baijiachuan hydrologic station of the Wuding River(P=0.01).Change point analyses reveal that more rapid declines for runoff began in 1979,and sediment load began in 1971 at the station(P=0.05).Two methods of the duration curve and double mass curves were applied to quantitatively analyze the change of runoff and sediment load in the Wuding River basin.Finally the reasons for the trends and change-points of the runoff and sediment load are analyzed.