Monitoring sediment yield for soil and water conservation planning in rural catchments

Sediment yield in river catchments can cause siltation of reservoirs and channels, carries contaminants adhered to sediment particles, and represents water erosion at the catchment scale, leading to decreased agricultural productivity. Hydrological monitoring enables the understanding of overland flow and soil erosion dynamics. In this study, we analyzed whether the relationship between precipitation (P), water flow (Q), and suspended sediment concentration (SSC) during rainfall events shows the usefulness of hydrological and sedimentological monitoring in soil and water conservation projects to river catchments. We conducted a study in the Lajeado Ferreira catchment in southern Brazil. This catchment is characterized by high soil fragility and erosion rates because of relief and intense tobacco cultivation. The small size of the catchment (120 ha) allowed a better understanding of the processes that occurred between hillslope and watercourses. We analyzed 43 rainfall-runoff events (P-Q), and we selected characteristic variables of each event and related them to independent variables (climate, land use, and soil management) and their seasonality using regression techniques. We also conducted a hysteresis analysis to understand the behavior of SSC in relation to runoff. The results showed a high relation of sediment yield (SY) with maximum water flow of the event (Q_max), and linear regression models showed the best performance between characteristic variables. In addition, the seasonal variability of the land coverage presented greater influence on the SY than the precipitation itself.