APPLICATION OF A THREE-DIMENSIONAL SATURATED-UNSATURATED TRANSIENT GROUNDWATER FLOW MODEL TO A WETLAND RESTORATION SITE IN NORTHWEST INDIANA

This project involves a three-dimensional saturated-unsaturated transient groundwater flow model based on Freeze, 1971. The model is applied to a drained wetland in northwest Indiana that is being subjected to restoration. The model utilizes van Genuchten’s characteristic equations to describe flow and storage in the unsaturated zone. The model uses daily inputs of precipitation and evaporation from three nearby weather stations, as well as stream-level elevations along the southern border as time-dependent boundary conditions. Additional boundary conditions include the elevation of the water table in a dune field that forms the northern boundary of the site, and the elevation of a drainage ditch that lies along the western boundary. A geologic model was constructed from information derived from 21 bore holes over the study area. The geologic model shows the presence of an overlying layer of marl 4.5 m thick. Slug tests revealed hydraulic conductivity values of the marl were on the order of 10^-5 cm/s.

A sensitivity analysis indicated that the average water table elevation and its temporal fluctuation were most sensitive to hydraulic conductivity values. Calibration of the simulated water table to a 3-year record of actual water table elevations revealed that changes in hydraulic conductivity values as low as 12.5 % could reduce mean error by 0.76 m. Initial results of the wetland model are analyzed for error, and strategies for minimizing any errors are discussed. Once the model has been adequately calibrated to observed conditions, the wetland flow fields and water balance are examined. Moreover, probable extent and duration of hydroperiods that are required for establishment of wetland plant species are identified.