Variation trends analysis of runoff and sediment time series based on R/S method in Wuding River Basin

Changes in runoff and sediment are caused by precipitation, evaporation, and underlying surface conditions. The policy-making basis for the water resources reasonable use was provided by revealed the variation trends of runoff and sediment time series and causes in this paper. To study the complex stochastic and undulatory property of the runoff and sediment time series, an R/S method was used. Through the time-varying Hurst index, the variation trends of runoff and sediment time series were investigated. Results showed that the Hurst indices of runoff time series were 0.56, 0.61 in Zhaoshiyao Hydrological Station and Baijiachuan Hydrological Station, a long-term positive correlation of runoff time series was showed. There were two jump points in the Hurst index of sediment time series in Zhaoshiyao Hydrological Station, occurred in 1966 and 1979, respectively, which showed fractal properties. There were three jump points in the Hurst index of sediment time series in Bjiajiachuan Hydrological Station, occurred in 1966, 1972 and 1979, with the four-scale distribution of the Hurst index of 0.59,0.41,0.99 and 0.81, respectively. The first two scale range of Hurst index was 0.5 or so, subject to Brownian motion; while the latter two scale range of Hurst index approached to 1.0, with fractal characteristics. Therefore, the runoff and sediment time series at the two hydrological stations in future will be the same trends as in the past period, i.e., with continued downward trend. Human activity is the main reason for this change.