Discharge increases during a flood, leading to both faster velocities and deeper water. Sediment is eroded as discharge increases and deposited as discharge decreases. Deposition may take place on the flood plain, in natural levees, or in the stream bed. All deposition is forced to occur within the river channel. In rivers with old, continuous levees, the river bed elevation will increase through time, forcing people to continually build the levees higher and higher to prevent floods from inundating the countryside.
Dams create lakes.
Because water is still in lakes, the sediment load of a river is deposited in the lake. The river downstream of the dam carries no sediment, and is likely to erode its bed.