A reservoir offers an ideal setting for the gradual removal of suspended sediment from water. In this tranquil water body, where there is minimal horizontal water movement, sediment particles gradually lose their buoyancy and settle to the reservoir's bed. The settling process, however, is not instantaneous due to the minute frictional interactions between each sediment grain and the surrounding water molecules. This friction generates turbulence, which retards the descent of individual sediment particles. The settling velocity of a particular particle depends primarily on its size, with density and shape playing secondary roles. Larger grains descend rapidly, while smaller ones settle more slowly. Extremely fine-grained sediments, such as silt and clay, may require several years to fully settle from the water column.
The duration of sediment residence in the reservoir significantly impacts the proportion of incoming sediment that ultimately settles at the bottom. Nevertheless, the tiniest clay particles may never settle due to electrical charges inherent in the mineral composition of these particles and the electrical charges within water molecules, arising from hydrogen bonding.
The influx of sediment into a reservoir, leading to sediment settling, reduces the available storage capacity of the reservoir. Over time, the cumulative loss of storage space due to sediment accumulation can become substantial. If you choose the Reservoir Capacity Method, the program will calculate the sediment balance within the reservoir across time intervals. It will update the Elevation-Area and Elevation-Storage curves for each time step using efficient trapping mechanisms based on the sediment and debris inflow from the upstream watersheds.