Flood Stages
The height of the water in the river is referred to as the stage. This height (or depth) of water is related to the amount of water moving down the stream channel and to the amount of sediment being carried by the river.
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This model shows the same reach of river at three different stages:
at a low stage, at bankfull stage, and at flood stage.
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Two factors control how much sediment (and consequently how much erosion) is contributed by each stage: the stage itself, and how often the stage occurs.
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During low stages very little sediment is transported on a daily basis, but the river is almost always at a low stage. Despite its frequent occurence the river moves only a moderate amount of sediment at this stage.
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During bankfull stages a great amount of sediment is transported on a daily basis. The height of the water, and its consequent velocity, result in a large ability to erode and move sediment. The river reaches this level, on the average, every year and a half. Given the relatively frequent occurance and the large ability to move sediment, the river moves moves a large amount of sediment at this stage.
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During flood stages a huge amount of sediment is transported on a daily basis, but the river may only flood once every hundred years or so. Because of its rare occurance the river moves only a moderate amount of sediment at this stage despite the huge rate of transport when it does occur.
