Suspended sediment dynamics at different time scales in the Loushui River, south-central China

Abstract

Suspended sediment dynamics were investigated in the Loushui River basin, a secondary tributary of the Yangtze River in southern China. The variations of suspended sediment transport were analyzed at different time scales (among different years, monthly and seasonal, and within-flood event) based on 25-year hydrological data from the outlet hydrometric station, and explained by the contribution of flood events, precipitation and human activities. Four stages were classified by the non-parametric statistical method of Pettitt change-point test and Cumulative anomaly test. At the annual scale, the relationship between suspended sediment concentration (SSC) and water discharge (Q) varied at four stages. The suspended sediment load (SSL) showed parabolic relationship with annual precipitation and significantly influenced by floods (contribution averaged at 78% before 1985; at 55% after 2007). SSL drastically decreased after 2007, mainly induced by the construction of the Jiangya reservoir. Sediment ‘store-release’ phenomenon was used to explain the seasonal variations of suspended sediment load. Monthly SSC–Q hysteresis loops indicated that the sediment storage seasons swung between winter/spring and late autumn at different stages. At the within-flood scale, three types of SSC–Q hysteresis loops were observed for the maximum flood events, including clockwise pattern (44%), counter-clockwise pattern (24%) and figure-eight pattern (32%). The variations of SSC–Q hysteresis patterns at four stages implicated the changing suspended sediment source materials with time. During the years 1966–1978, the suspended sediment mainly came from channels for the maximum flood events, while, materials from the upper reaches or slopes dominated the later period 1979–1985 and 2007–2011.