Truncating Cross-Sectional Groundwater Models under Wetlands

Cross-sectional models, which represent two-dimensional flow in the vertical plane, tend to have problematic aspect ratios since the aquifer thickness is often small compared to the lateral extent of the flow domain. For that reason, the model domain is usually limited to the immediate area of interest, for instance the aquifer section underneath a dam. We propose a Cauchy boundary condition to represent flow from remote wetlands that are left out of the truncated model. The resistance to flow inherent to such a boundary depends on the aquifer properties and the resistance to flow through the wetland bottom. While the Cauchy boundary condition is based on the Dupuit-Forchheimer approximation to flow underneath the remote wetlands, the error appears to be negligible (less than 0.6%) for most practical cases, including flow in stratified aquifers. For the case of multiple aquifers underneath the wetlands, the total flow in the truncated model can be a few percent in error, which is typically acceptable for most engineering applications. The approach is illustrated with an application near a levee-borrow canal setting in the Florida Everglades.