Temporal changes in suspended sediment transport during the past five decades in a mountainous catchment, eastern China

Abstract

Analysis of sediment transport is an effective approach for identifying sediment sources and for catchment management. However, a long-term analysis of sediment variability at multiple time scales is less available, especially in mountainous catchments. This study aims to determine sediment sources and to identify sediment transport dynamics, as well as the influencing factors, through analyzing long-term sediment fluxes at different time scales. In this paper, 32 years of sediment flux in an instrumented mountainous catchment in eastern Zhenjiang Province, China, was investigated at multiple time scales (i.e., monthly, seasonal, annual, and event). Sediment yields (SYs) during three time periods (i.e., 1964–1977, 1978–1989, and 2010–2015) were first classified by the Mann-Kendall and cumulative anomaly tests, and then sediment fluxes for each period were investigated and compared at multiple time scales. Annual SYs ranged from 29 to 308 t year−1 during the recording period and were significantly influenced by several high magnitude flood events. The mean annual SYs decreased from 153.82 t year−1 in 1964–1977, to 97.79 t year−1 in 1978–1989, and to 91.08 t year−1 in 2010–2015 due to improved soil conservation measures and increased reservoirs. At the seasonal scale, over 92% of the sediment was transported in spring and summer over the recording period. Heterogeneous sediment sources, partial areal distribution of rainfalls, and other factors led to complex suspended sediment concentration versus water discharge hysteresis loop patterns at the event and monthly scales. The improved soil conservation measures and increased reservoirs over the recent decades decreased sediment availability, and the number and the magnitude of flood events from 1964 onward. However, the flood sediment fluxes in a few months were still high due to extreme precipitation events in recent years. The work can provide guidance for addressing sediment problems in this and/or other similar catchments.