As streamflow goes up and down during a storm, hydrologists take measurements of how much sediment is in the water at different streamflows. Once we know how much water is flowing and the amount of sediment in the water at different flow conditions, we can compute the tonnage of sediment that moves past the measurement site during a day, during the storm, and even during the whole year. On the plus side, sediment deposited on the banks and flood plains of a river is often mineral-rich and makes excellent farmland. The Nile in Egypt and the Mississippi River here in the United States are good examples. You may recall the disastrous effects of the Midwest flooding of 1995 and 1997.
Sediments can also harm dams and reservoirs.
When a river is dammed and a reservoir is created, the sediments that used to flow along with the relatively fast-moving river water are, instead, deposited in the reservoir. Reservoirs slowly fill up with sediment and mud, eventually making them unusable for their intended purposes.