Analysis of sediment rating loops and particle size distributions to characterize sediment source at mid-sized plot scale

Estimates of spatio-temporal variations of sediment concentration with discharge are needed for the assessment of aquatic ecosystems, estimates of contaminant export from catchments. The relationship between discharge and sediment concentration is available for different watersheds. However, elucidating flow discharge-soil loss-contribution area relationships under simulated controlled conditions has not been adequately considered for better understanding of soil erosion processes. The objective of this study therefore is to employ sediment rating loops and PSD to characterize erosion source contribution of a mid-sized plot subjected to different input driving forces of slope steepness (S = 5 to 25%) and rainfall intensity (I = 30 to 90 mm h−1). A cause-and-effect conceptual approach was employed for investigating erosion by individual storm events. Results of the study showed that the interrelationships among variables varied as erosion processes developed owing to increasing slope or rainfall intensity. The sediment rating mainly followed downward linear or semi clockwise hysteretic loops except for slopes of 15 and 25%, and rainfall intensity of 30 mm h−1. It was further found that the high rainfall intensity event under steep slope had limited contributing area and more contribution of coarse particles with lesser coefficient of variation. Understanding the relationships among runoff, sediment and PSD can greatly improve our understanding of sediment transport mechanisms and the contributing areas that facilitate better soil erosion modeling leading to proper planning of soil and water management measures.