Agricultural, construction, and other activities and land-use practices can either mitigate or exacerbate sedimentation. Some impoundments store very little sediment because dam operation flushes out accumulations of sediment. The sediment that is deposited in an impoundment gradually fills it. Periodic dredging of this sediment may be necessary to keep the impoundment from filling in completely or becoming too shallow to be useful. These scour holes in turn can erode the base of the dam itself, leading to dam failure.
Water flowing over the top of a dam erodes a scour hole at the base of the dam.
High-energy flow of water over the Rockdale Dam eroding a scour hole. Free-flowing systems One of the most important functions of a river is to erode and carry sediment. Rivers carry sediment, but also natural debris, most commonly branches and logs from fallen trees. The total amount of sediment that a river is capable of carrying is the capacity of the river, which depends on the speed and volume of the flow of the river. The greater this volume and speed, the more sediment the river can carry.