http://snowgeology.blogspot.com/2011/06/beaches.html
Beaches along the sides of rivers are formed by deposition of sand by the river during periods of high discharge. Discharge is amount of water flowing through a river a given point of time. Discharge is measured in cubic feet per second or "cfs" and is calculated by multiplying the width(in ft) x depth (in ft) x velocity (in ft/sec) . Discharge of a river increases during periods of snow melt and periods of heavy or prolonged rainfall. During periods of high discharge the height of the river increases. If the river is in a deep canyon like the Green River in the canyon of the Lodore, it doesn’t tend to get much wider. It just gets deeper and flows faster. This faster flow allows the river to
scour (pick up) the sediment from the bottom. Also, when the river is flowing faster it can pick up and transport larger sediment like sand.
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