Changes in Sediment and Water Yield Downstream on a Small Watershed

In this study, sediment variation and water yield in a downstream direction over a six month period are presented for a watershed with mixed land use/cover, located in eastern Alabama, USA. The relative effects of pastoral, forested, and clear-cut areas on soil erosion, sediment delivery, and water yield are compared, and the efficacy of a streamside management zone (SMZ) at trapping sediment from a clear-cut was also explored. As expected, water and sediment yields increased in a downstream direction in the watershed study area. The furthest downstream section generally had the highest sediment concentration with the forested middle section having the lowest. The highest sediment yield per unit area originated from the pastoral portion of the watershed during rainfall events. The forested section generated less sediment than other parts of the watershed during storm events. Sediment loading increased due to clear cutting on the downstream section. The SMZ appeared incapable of trapping the sediment originating from the clear-cut during storm events. This study shows the importance of factoring in upstream land use/cover conditions when designing SMZs for sediment trapping.