Determinant factors of sediment graphs and rating loops in a reforested watershed

Abstract

Summary Sediment graphs and hydrographs were analyzed in a small, high-gradient reforested watershed in Mie Prefecture, Japan, which was instrumented to measure discharge and sediment transport. The study was conducted to recognize determinant factors on sediment graphs and hydrographs relationships, and corresponding rating loops using eight storm events that occurred in 2004. A cause-and-effect analytical approach was employed in the investigation of factors controlling individual hydrological events. The results showed that in a single event, the sediment peak preceded the peak discharge, following a clockwise hysteretic loop. The rating loops exhibited hysteresis with a greater suspended sediment concentration for a given discharge occurring on the rising limb rather than on the falling limb. Furthermore, the reduction in suspended sediment concentrations in a sequence of events and the falling limbs could mainly be associated with sediment exhaustion and contributions of throughfall and throughflow. We concluded that a combination of sediment availability, rainfall characteristics, soil water repellency, and contribution of different flow components control the variations in event-wise sediment graphs and rating loops in the study area. Understanding the relationship between controlling factors and sediment yield dynamics in the study area should greatly improve our understanding of sediment transport mechanisms and predictions in reforested watersheds, which should ultimately lead to better management of forest ecosystems.