Understanding sediment dumping

Posted on May 26, 2009

Where the width of a stream is artificially reduced, for example by channelisation or levee construction, the flow velocity, and thus the capacity of the stream to transport sediment, are increased.  However, stream narrowing can sometimes cause sediment to be unexpectedly dumped rather than removed, and there are cases where sediment has built up so much that the river is raised above the level of the floodplain, and where levees have failed in extreme floods.  Mathematical modeling has shown how unexpected sediment dumping can be caused by the way that stretches of narrowed channel alternate with unconfined, wider reaches, and demonstrates the potential dangers associated with sharp variations in channel width.   The model gives a picture of how the river bed evolves through time by showing how waves of sediment erosion and deposition propagate up and down the stream from a point of narrowing.

Reference:  Siviglia, A., Repetto, R., Zolezzi, G. & Tubino, M.  2008.   River bed evolution due to channel expansion: general behaviour and application to a case study (Kugart River, Kyrgyz Republic).  River Research & Applications 24, 1271–1287.