The SZ module supports the following three types of boundary conditions:
1. Head boundary - Dirichlet conditions, (Type 1) where the hydraulic head is prescribed on the boundary
2. Gradient boundary - Neumann conditions, (Type 2) where the gradient of the hydraulic head (flux) across the boundary is prescribed
3. Head-dependent flux - Fourier conditions, (Type 3) where the head dependent flux is prescribed on the boundary.
The head can be prescribed for all grid nodes (i.e. at the catchment boundary, as well as inside the model area) and for all computational layers. The head may be time-invariant equal to the initial head or can vary in time as specified by the user. An important option is the transfer of space- and time interpolated head boundaries from a larger model to a sub-area model with a finer discretisation.
Prescribed gradients and fluxes can be specified in all layers at the model boundary. Sinks and sources in terms of pumping or injection rates can be specified in all internal nodes. If the unsaturated zone component is not included in the model, the ground water recharge can be specified.
The exchange flow to the river system is included in the source/sink terms and can be regarded as a Type 3 boundary condition for cells with 'contact' to the river system. The exchange flow is a function of the water level in the river, the river width, the elevation of the riverbed, as well as the hydraulic properties at the riverbed and aquifer material.