Assessment of Groundwater Depletion in Southern Hills Aquifer System, Southeastern Louisiana

Abstract:

The Southern Hills Aquifer System (SHAS) is part of the Coastal Lowlands Aquifer System of the Gulf Coastal Plain and includes more than 10 fresh aquifers that provide abundant high-quality low-cost groundwater to the region. In the Capital Area in 2014, 88 million gallons of groundwater were pumped every day for public supply and 79 million gallons of groundwater were pumped every day by industry. Prolonged excessive groundwater pumping in the Southern Hills Aquifer System has caused significant groundwater depletion. To deal with the alarming issue, the study developed a groundwater model using the USGS MODFLOW-USG to represent a complete hydrology-geology system for the Southern Hills Aquifer System and estimate groundwater storage changes. The model’s geological structure was constructed by using 4,577 drillers’ logs and 727 electric logs through an indicator interpolation method. The drillers’ logs and electric logs were interpreted into high-permeability sand facies and low-permeability clay facies. The geological structure includes the aquifers from the Mississippi River Alluvial Aquifer to the depth 850 m below land surface. Mesh refinements (from 1 km to 32 m) were applied to the areas around the Baton Rouge fault systems and major rivers (i.e., Mississippi River, Atchafalaya River, Amite River and Comite River) to better capture the irregular geometry. The groundwater model simulated river-aquifer interactions using river stage data measured by the USGS and the USACE. Surficial recharge was determined by a fraction of the USGS groundwater recharge data. The groundwater model included 360 pumping wells for the industries and the public supply and 198 agricultural pumping wells at various depths. This study utilized the USGS daily groundwater level data from 2004 to 2013 and sequential quadratic programming (SQP) to calibrate the simulation model and estimate hydrogeological parameters in the groundwater model. Groundwater depletion in the Capital Area was estimated via water budget analysis and was compared with the measured groundwater storage changes from NASA’s GRACE (Gravity Recovery and Climate Experiment) data.