Unstructured-Grid Approach to Model Complex Aquifer System and Assess Groundwater Depletion in the Capital Area of Louisiana
Abstract
Groundwater levels in the Capital Area of Louisiana continue to decline due to excessive groundwater withdrawals since the 1950s such that groundwater sustainability becomes a concern. This study developed a three-dimensional groundwater model with an unstructured Voronoi grid using MODFLOW-USG to deal with areal refinement, discontinuity across faults, and aquifer coalesce and pinch-out. The groundwater model aims to understand the dynamics of groundwater flow in multiple aquifers under anthropogenic pumping, including irrigation wells (shallow), public supply wells and industrial wells (deep). A complex groundwater model structure was constructed with lithologic data of 5,304 well logs over a depth of approximately 1,000 m. In particular, mesh refinement was applied to the areas around the Baton Rouge fault system to better capture groundwater flow through the faults, which were considered as horizontal flow barriers in the model. Model calibration was achieved by using the Covariance Matrix Adaptation-Evolution Strategy (CMA-ES) in parallel computing. The model indicates that the general groundwater flow direction in the aquifer system is from northeast to south and southwest in accordance with the dip direction of the aquifers towards the Gulf of Mexico. However, excessive pumping near the Baton Rouge fault locally reverses hydraulic gradient and creates northward flow direction. Groundwater storage in the aquifer system is significantly influenced by anthropogenic pumping as well as interactions between Mississippi River and Mississippi River alluvial aquifer. A noticeable cone of depression is centered at the Baton Rouge Metropolitan Area. The Baton Rouge fault behaves as a low-permeable barrier that intercepts the cone of depression to the south region. Groundwater storage in this area is generally declining with respect to 2004. However, groundwater storage turns to increase after 2018 because of deactivation of some major industrial wells.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.H15L1179C