Aquifers

Within St. Lucie County, Florida, a network of canals has been cut to provide flood protection, drainage, and irrigation. Many of these canals maintain a permanent to semi-permanent hydraulic connection with the surficial aquifer. MODFLOW code was used to simulate St. Lucie County groundwater levels. One of stresses that contributed to the solution of the groundwater levels, was the volume of water that flowed into or out of the aquifer through the canal system. In MODFLOW, the flow calculation between a canal and the aquifer is independent of the canal's location within the grid cell. The flow calculation was modified to incorporate canal location. Simulation results showed 34 percent of the model area realized groundwater levels that were plus or minus two-tenths to one-half foot when compared to the original levels. These results can be significant for model applications such as wetland protection and salt water intrusion.

Natural and anthropogenic processes have altered wetland habitats. The simulation of surface water movement and its interaction with groundwater and slough channels as it relates to wetlands is very important for many projects. Currently, most groundwater flow models incorporate the wetland system as general head boundary nodes. The purpose of this research was to develop a computer package for the widely used MODFLOW code to simulate three-dimensional wetland flow hydroperiods interacting with aquifers and slough channels. The groundwater flow model was used to reproduce surface water flow process through wetlands, estimating new flow rates and values using a Manning type of equation. This package represents flow routing, the export/import of water, and the evapotranspiration from wetlands during different hydroperiods. The verification procedure for the numerical solution was based on a test-case that was solved using a two-dimensional surface water model. This test-case example is a transient solution to the diffusion equation starting with initial conditions depicted by a sinusoidal water surface profile and a flat bottom.