Assessment of impact in groundwater levels and stream-aquifer interaction due to increased groundwater withdrawal in the lower Apalachicola-Chattahoochee-Flint (ACF) River Basin using MODFLOW

Abstract

Study region: Lower Apalachicola-Chattahoochee-Flint (ACF) River Basin, southeastern United States (U.S.). Study focus: Excessive groundwater withdrawal for irrigation from the Upper Floridan Aquifer is an important issue in the lower ACF River Basin as it has led to decline in groundwater levels as well as reduction in baseflows. Since the withdrawal is projected to further increase in the future, this study evaluated the impacts of the projected increase in irrigation on the groundwater levels as well as the stream-aquifer flux in the region. The study also identified regions that are most important for groundwater recharge. New hydrological insights into the region: Evaluation of the geohydrologic zones identified Upland Instream Karst as the most sensitive zone for recharge into the aquifer while zones in the region where the aquifer thickness was comparatively lower and close to the land surface was generally identified as sensitive. Simulation of the projected irrigation scenario predicted a reduction in groundwater levels by as much as 2.38 m, while a general reduction was predicted in much of the model domain. Large groundwater level reductions were mostly predicted in regions where the aquifer is comparatively thinner. Evaluation of the changes in stream-aquifer flux showed that flux reduced by as much as 33 % with large reductions predicted in the Lower Flint and Kinchafoonee watersheds. This study also helped identify localized zones and stream sections most susceptible to the impacts of increase in irrigation.

Keywords

• MODFLOW
• Lower ACF River Basin
• Groundwater irrigation
• Groundwater-surface water interaction
• Upper Floridan Aquifer