Laboratory Study of Degradation and Aggradation

Using a laboratory flume, investigation has been made on the degradation of the bed profile caused by cutting off completely the sediment supply upstream, and aggradation caused by supplying sediment upstream in excess of the carrying capacity of the flow. An equation is established for the bed profile of a degrading channel with unerodible banks and mainly uniform sediment material. During degradation, the friction factor due to form resistance reduces with time for sands coarser than 0.6 mm and increases with time for sands finer than 0.6 mm. When the incoming sediment exceeds the transport capacity of a channel, it deposits at the upstream reach with a resulting increase in slope and decrease in depth. The upstream aggrading reach is modified by the deposit in such a way that the new hydraulic condition will then carry the incoming sediment. The downstream reach of the channel remains undisturbed until the aggrading front reaches it.