Estimation of suspended sediment supply to the stream network of the River Rhine under present-day climate and land use

Abstract

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The supply of sediment to the drainage network of the River Rhine is estimated for present-day climate and land use. A distributed model was developed, which would enable us to identify areas that actively deliver sediment to the drainage system, assuming soil erosion on hill slopes to be the primary sediment source. The amount of mobilised sediment that actually reaches the stream network depends on the proximity of the sediment source to the stream, the occurrence of overland flow and on the character of the flow path. The sediment supply model makes use of a GIS database containing information about relief/morphology, soil, land use and the drainage network, and is linked to the RHINEFLOW model. The results show that for present-day conditions, sediment supply is high during late spring and early summer and low later in the growing season and in the winter months. Sediment production is highest in periods when severe rain falls on unprotected soil. The temporal pattern in the sediment supply is largely determined by the course of the rainfall erosion and crop growth stages during the year. The temporal pattern of basin sediment yield is not related to the timing of sediment supplied by soil erosion, but governed by the discharge regime. This suggests that suspended sediment is stored in the alluvial system in the summer and removed during the runoff season. Furthermore, a large part of the sediment produced in the Alps and in the Swiss middle mountains is stored in the alluvial system further downstream where stream power decreases.