Runoff sediment characteristics affected by erosive rainfall patterns in a small watershed in karst areas of southwest China

Abstract

Few studies have focused on observing long-term localized runoff and sediment yield at a small watershed scale in karst areas in southwest China. In addition, the study of soil erosion mechanisms have also been unsatisfactory. Using hydrological data from 2014 to 2019, this study investigated the rainfall, runoff, and sediment yields in the Mahuangtian small watershed, where covered an area of 2.26 km2. The results showed mean values of 124 t/(km2·a) and 13.8 mm for the sediment modulus and runoff depth, respectively. Using the K-medoids clustering method, 112 erosive rainfall events were classified into three types of rainfall patterns based on duration (TR), rainfall depth (R), and maximum 30-minute rainfall intensity (I30). Pattern A was characterized by the shortest TR, lowest R, and highest I30; pattern B was characterized by medium TR, R, and I30; and pattern C was characterized by the longest TR, highest R, and lowest I30. Pattern B caused the largest runoff and sediment yield in the watershed, implying that further attention should be focused on this rainfall pattern to control soil and water loss. In addition, hysteretic loop analyses of suspended sediment concentration and flood discharge suggest that complex and clockwise loops were dominant for all events. This study found that the deposition stored in the subterranean river was the main source of sediment for the watershed. The results of this study provide useful information regarding the relationship between rainfall and runoff sediment in a small karst watershed and advance research on soil erosion mechanisms in karst areas.