Flows involve the movement of dense mixtures
of sediment and water (or sediment, water, and air). The way a sediment
flows depends on the relative proportions of solids, water, and air in
the mixture and on the physical and chemical properties of the sediment.
All streams carry at least some sediment,
but if the sediment becomes so concentrated that the water can no longer
transport it, a sediment-laden stream becomes a very fluid sediment flow.
In such a case the water helps promote flow, but the pull of gravity remains
the primary reason for movement.
The following types of flow are distinguished: