Factors controlling discharge-suspended sediment hysteresis in karst basins, southwest China: Implications for sediment management

Abstract

Assessment of river sediment sources, transport, and controlling factors in karst regions is critical to the development of effective soil erosion and sediment management strategies. This 2-year study used a hysteresis index of discharge and suspended sediment data, combined with the basin's inherent geological characteristics, to assess sediment sources and hydrological connectivity at six sites in an agricultural karst watershed of southwest China. Principal component analysis was further used to describe sediment control by rainfall (antecedent precipitation, precipitation duration, amount, and intensity) and stream hydrology (maximum and total discharge, flood intensity, and runoff coefficient). Results indicate that the annual sediment yield (0.8–6.6 Mg km2 a−1) is low and sediment transport in karst areas is dependent on continuous rainfall. Ground substance component (GSC) and geomorphology characteristics determine the hydrology connectivity and sediment availability. In a sub-basin (CQ) marked by a peak cluster depression with good vegetation, sediment mainly comes from the paddy land, and the surface stream shows clockwise hysteresis. During storms, surface water enters the underground system from sinkholes, resulting in Figure-8 hysteresis with multiple sediment peaks. In another predominantly agricultural sub-basin (HTP), the thick layers of paddy and loess soil surrounding the river channel provide an accessible sediment source, resulting in clockwise hysteresis. The surface outlet of the watershed (HZ) is affected by an upstream reservoir, but bank erosion and sediment activation are evident during storms. The subsurface outlet (MSK) of the watershed shows more anti-clockwise hysteresis due to the activation of the conduit network in the wet season, surface water draining into the underground river and the distant sediment sources. This study shows that discharge-suspended sediment concentration hysteresis analysis can provide a reference for soil and water conservation decision-making in karst areas.