Flow in Erodible Material
In this chapter, consideration is given to the relationship which exists between the flow in a channel and its boundaries. This relationship is only static, and therefore of no interest here, when the channel boundaries are non-erodible under all conditions of flow (concrete lined channels and canals) and when in addition, no water-borne sediment is introduced into the channel. In natural rivers and unlined canals the channel boundary is always erodible to a greater or lesser extent and sediment is carried into the channel both from the bed upstream and from the surrounding land. The flow in such a channel is always adjusting itself to the presence of this movable material whose behaviour in turn depends upon the action of the flowing water upon it. The whole will therefore form a single, highly complex, flow phenomenon: part fluid, part solid, in a channel of variable geometry.
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