River Braiding in Relation to Unsteady Water and Sediment Transport

Abstract

In Europe nearly all larger rivers were channelised over the last 100 years, beginning mostly at the second half of the 19th century (Vischer, 1986). Thereby especially Alpine rivers experienced a remarkable reduction of river bed width, combined with shortening of flow length (Habersack & Schneider, 2000). Longterm negative consequence is river bed degradation, following increased shear stresses and prohibition of side erosion and bedload input from the catchments. This leads also to a change in river morphology from former often braided sections to single thread channels. In order to compensate these effects over the past ten years a significant increase in channel widening can be observed (Habersack et al., 2000). Increases in effective bed channel widths cause changes in river morphology, eventually beginning of braiding (if sediment input is sufficient). For planning purposes (e.g. river bank protection) the prediction of river morphology is essential, therefore knowledge of involved processes is necessary.