Poro-elastic modulation of aquifers explain seasonal and decadal geodetic signals in Southern Louisiana.

Coastal Louisiana experiences ground subsidence, exacerbating flooding and land loss from sea level rise. Natural and anthropogenic causes induce spatially and temporally varying subsidence in this sector of the Gulf of Mexico passive margin. The geodetic displacements in the Baton Rouge area over the period of 2018-2024 show cyclic seasonal displacement superposed on long-term subsidence, implying a small seasonal loading component. We assert that the seasonal fluctuations are controlled by seasonal changes in Mississippi River discharge that infiltrate sandstone aquifers separated by shales.   

Here we theoretically examine a simple radial analytical formulation of poroelastic dilation and compaction responses induced by seasonal fluctuation in groundwater levels assuming a hydrostatic response, using Darcy’ law. Due to the semi-confined nature of the aquifer, we assume a hydrostatic infiltration response, yet at the same time we assume a confined poroelastic response of the aquifer. Using a reasonable range of aquifer specific storage (Kuang et al., 2020), the predicted seasonal dilation and compaction agrees with the geodetic data on both spatial and temporal scales, exhibiting ground deformation associated with both long term groundwater extraction or recharge and seasonal groundwater fluctuation. We hence argue that the poroelasticity of aquifers can explain seasonal and long term signals in geodetic observations in Southern Louisiana without requiring additional processes like fault creep or salt movement.