Estimation of Groundwater Loads into a Coastal Estuary Using SEAWAT
Abstract
The research of regional groundwater flow is of vital importance at the Indian
River Lagoon (IRL) due to the potential contribution groundwater flow has on
nutrients into the IRL. If too many nutrients are introduced into the IRL, algal
blooms could occur and impact the health of IRL system. The IRL is a coastal
estuary located on the east coast of Florida. Submarine groundwater seepages
(SGD) and groundwater loads into the IRL were numerically estimated by using
SEAWAT, a program designed to simulate variable-density groundwater flow
coupled with multi-species solute transport. Models were completed at three
different study transects that were set in the longitudinal direction, perpendicular to
the estuary coastline. The modeling domain for each transect extended from the
water table divide on the mainland to either the neighboring barrier island or to the
Atlantic Ocean depending on the transect location. Groundwater seepages along
with groundwater loads were determined after calibrating the models by comparing
measured and predicted freshwater hydraulic head distributions in the unconfined
aquifer. Three statistical analysis tests were performed in order to further validate
the model calibrations, the root mean square error (RMSE), the two-sided test, and
the Nash-Sutcliffe efficiency (NSE) index. A new approach was used for the statistical analysis of calibrated models where additional points from the measured
equipotential head distributions were added to the statistical analysis in order to
improve calibration results. The leakage from the Floridian Aquifer into the
unconfined aquifer of the IRL, via the Hawthorn Formation, was estimated at
different sites. A slug test was conducted at a study site in order to compare the
measured lateral hydraulic conductivity (Kx) values to the previously calibrated
model.
This research presents the following results: a) introduces new statistical analysis
methods, b) shows the impact of recharge on the SGD, groundwater loads, and
direction of flow to the IRL through the unconfined aquifer, c) compares the slug
test variable Kx value to the previous Kx and d) estimates the salinity distribution in
the unconfined aquifer.