Continuity of sediment transport

Sediment is material ranging from clay to gravel (or even larger) that is transported in flowing water and that settles or tends to settle in areas where the flow slows down.

Rivers not only convey water but they also transport sediment from the catchment to the sea or outfall of the river. Under most circumstances the flow of water forms both the river channel and the plan form of the river. As a result, all natural rivers are subject to change, either through erosion, deposition or plan form change. River engineering works are normally carried out to alter the flow of water in some way. Such changes normally also result in altering the sediment movement within the channel and hence the channel shape and plan form.

Sediment processes, by shaping the river channel, also affect the flow conditions in a river and hence the conveyance of a river, the distribution of velocity and depth and the composition of the bed sediments. Thus sediment processes are intimately connected with both flood defence and also the ecology of rivers.

Thus sediment processes are of interest to:

• those concerned with the design or appraisal of flood risk management schemes,
• those concerned with river maintenance and,
• those interested in conservation and fisheries.

Some of the present sediment problems that engineers face arise from engineering works carried in the past when less consideration was given to such problems.

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