The name of the reservoir and wetland sediment record is a primary key referenced by the foreign keys sed in reservoir.res and sed in wetland.wet. All names in the sediment.res file must be unique.

SWAT+ calculates the median sediment particle diameter for impoundments located within a landscape unit using the equation

where $d_{50}$ is the median particle size of the sediment (µm), $m_c$ is percent clay in the surface soil layer, $m_{silt}$ is the percent silt in the surface soil layer, and $m_s$ is the percent sand in the surface soil layer.

Because reservoirs are located on the channel network and receive sediment from the entire area upstream, defaulting the sand, silt, and clay fractions to those of a single LSU or HRU in the upstream area is not appropriate. Instead, the user may set the median particle size diameter to a representative value.

The table below lists the D50 values of different sediment classes:

The amount of suspended solid settling that occurs in the water body on a given day is calculated as a function of concentration. Settling occurs only when the sediment concentration in the water body exceeds the equilibrium sediment concentration specified by the user.