Evolution Processes and Characteristics of Annual Runoff and Sediment in Xiangjiang River from 1951 to 2011

Based on long-time series data of annual runoff and sediment at key stations along the Xiangjing River from 1951to 2011,evolution characteristics and laws of annual runoff and sediment were revealed by means of Mann—Kendall,wavelet analysis and average difference T methods,and its driving forces were analyzed.(1)The amount of annual runoff showed a slightly increasing trend and the amount of annual sediment,an obviously decreasing trend.(2)Temporally,runoff process did not show any mutation characteristic and annual sediment process,some mutation characteristics in 1997.After 1997,however,annual sediment declined significantly.(3)Wavelet analysis indicated periodicities of 20years and 7years for annual runoff and sediment processes,respectively.(4)The annual runoff series of the Xiangjing River can be divided into two plentiful phases of 1951—1954and 1992—2002and two drought phases of 1955—1991and 2003—2011.Analyses of concentration ratio and period of annual runoff and sediment indicated that the inhomogeneity of inter-annual sediment distribution was more obvious than runoff,which mainly concentrated in June every year.(5)Significant reduction in annual sediment transportation was mainly contributed from sand controlling by water resource engineering and soil and water conservation engineering measures.