Evaluating sediment connectivity and its effects on sediment reduction in a catchment on the Loess Plateau, China

Sediment connectivity is a principal element for revealing sediment yield variations in catchments. Although several methods for quantifying this element have been tested, there is still much room for improvement as manifested in many recent discussions on this issue. In this study, we defined a new revised sediment connectivity index (RIC) by incorporating the functional with the structural components of a sediment routing system. The index was applied to the Gushanchuan catchment on the Chinese Loess Plateau to produce yearly RIC maps of sediment connectivity based on the datasets of topography, rainfall erosivity, land use and land cover, soil erodibility in 39 years (1980–2018). The RIC maps were combined with the distribution histogram of RIC to identify hotspots of sediment detachment and transport. Moreover, the temporal evolution of sediment connectivity was tested by using sediment discharge observed at the outlet. The results showed that values of sediment connectivity were higher in the gullies than in the hill slopes. After differentiating the impacts of rainfall, land use and land cover change (LUCC), check dams on the sediment reduction in the catchment, the contribution rates of the check dams were estimated to be 63% (1990–1999) and 9% (2000–2018) of the total sediment yield reduction. The remaining 37% and 91% were explained by the variations of sediment connectivity induced by rainfall change and LUCC. Among them, the average sediment reduction benefit was −33% and −39% for rainfall variation, and 70% and 130% for LUCC. The land use statistics showed a decreasing trend of cropland (231.91 km2) from 1980 to 2018. The cropland conversion resulted in an annual sediment reduction of 757 × 104 t in the 1990s and 1 408 × 104 t in 2001–2018 compared with the period of 1980–1989. The new RIC was illustrated to be an easy-to-run and suitable tool for studying the changing soil erosion and sediment delivery in catchments.