M.1 Self shading

Photosynthetically available radiation is provided to the WQ Module from TUFLOW for each computational cell at each water quality timestep. It is this two- or three-dimensional field that the WQ Module uses to compute phytoplanktonic responses to light. The WQ Module allows, however, for modification of this TUFLOW field to incorporate the effect of light attenuation due to the presence of phytoplankton. This additional light extinction is computed dynamically at each water quality timestep, based on instantaneous phytoplanktonic concentrations in individual computational cells, as per Equation (M.1).

\[\begin{equation} Ke_{\langle computed \rangle}^{phy} = Ke^{phy} \times \left[PHY\right] \tag{M.1} \end{equation}\]

For each phytoplankton group, \(Ke^{phy}\) is the user specified (or default) self shading coefficient and \(\left[PHY\right]\) is the instantaneous phytoplankton concentration in each cell. For each cell and at each timestep, this quantity \(Ke_{\langle computed \rangle}^{phy}\) is computed for each phytoplankton group. Results are then summed within each cell and returned to TUFLOW as a two- or three-dimensional field which TUFLOW then includes these in subsequent light distribution calculations.