Two-Fraction Model of Initial Sediment Motion in Gravel-Bed Rivers

Abstract

The prediction of sediment transport in gravel-bed rivers is essential to the management of land, water, and ecological resources in mountain regions. Dividing the bed sediment into two populations—sand and gravel—permits realistic and useful predictions of the onset of sediment transport. The critical flow initiating grain motion decreases rapidly with sand content over the transition from a gravel-framework bed to a sand-matrix bed. The two-fraction model provides a simple means of forecasting the movement of excess fine sediment supply. The model also helps to explain the development of the abrupt gravel-sand transition commonly observed in natural rivers.