O.3 Attachment

Enteric organisms may exist in isolation or be associated with either organic or inorganic suspended particles, depending on the surface properties of the organism and the nature of the suspended material within the system. The simulation of this attachment (and detachment) is therefore allowed for within the TUFLOW WQ Module as an attachment to total suspended sediment.

At each water quality timestep, the instantaneous attachment flux \(F_{att}^{pth}\) is estimated via Equation (O.4). \[\begin{equation} \href{AppDiags.html#WQDiagAttach}{F_{att}^{pth}} = \frac{1}{7}\times \left(f_{att}^{pth} \times \left(\left[PTH_a \right] + \left[PTH_t \right]\right) - \left[PTH_a \right]\right) \tag{O.4} \end{equation}\] \(f_{att}^{pth}\) is the user specified target attachment fraction, and \(\left[PTH_a\right]\) and \(\left[PTH_t\right]\) are the concentrations of free and attached pathogens, respectively. This assumes that left unperturbed, equilibrium would be reached in seven days. A positive (negative) flux represents attachment (detachment). The target attachment fraction is defined as follows, where the concentrations are relative targets, not actual simulated quantities (i.e. so cannot be algebraically cancelled if the expression for \(f_{att}^{pth}\) in Equation (O.5) is substituted into Equation (O.4)). \[\begin{equation} f_{att}^{pth} = \frac{\left[PTH_a \right]}{\left[PTH_a \right] + \left[PTH_t \right]} \tag{O.5} \end{equation}\]