Mixing parameters specify the non-advective transport of water quality constituents in 1D reservoirs and reaches. In general, the mixing coefficients and algorithms parameterize physical mechanisms that cannot be explicitly represented in the simplified water quality model.
In reservoirs, mixing takes place in the vertical dimension and is typically referred to as diffusion. It is parameterized using wind speeds, which tend to mix the upper layers of the reservoir, and stratification, which tends to dampen vertical mixing. An explanation of the parameterizations available for use in the WQ Engine is given in the Vertical Mixing section.
In reaches, mixing along the longitudinal dimension is of interest, and occurs primarily due to velocity variations in the cross-stream direction. It is referred to as dispersion, and parameterizations are described in the Longitudinal Mixing section.