Quantifying Seasonal Deformation Signals Using InSAR and Groundwater Models in the Mississippi River Delta, Baton Rouge, Louisiana

Seasonal land motion can be caused by processes above or below Earth's surface, often linked to natural changes in the hydrological cycle. In coastal deltaic systems, the coupling of water level changes between rivers and aquifers may cause significant surface deformation, but this process is poorly understood. In this research, we show that land motion can be a proxy for groundwater level changes in layered and semi-confined aquifers, with implications for other delta systems worldwide. We investigate the processes driving the >15 mm seasonal deformation in the Mississippi River Delta near Baton Rouge, Louisiana. We consider elastic deformation due to surface loading and poroelastic deformation caused by changes in groundwater levels. The underlying aquifer system is formed by almost-independent sands, crossed by the Mississippi and Amite Rivers, and cut by the Baton Rouge fault, which is a leaky barrier. We quantify seasonal deformation using Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR), between 2016 and 2022 and validate the results with Global Navigation Satellite Systems (GNSS) data. We find that the amplitude of the seasonal response has spatial variations related to the distance to the Mississippi River and the Baton Rouge Fault. We identify which aquifer layers are in phase with the observations and are thus most likely to cause poroelastic deformation. Our results are supported by hydraulic properties from the literature for the aquifer system. We conclude that seasonal motion in the area is dominantly driven by the poroelastic response to Mississippi River level changes that recharge the shallower aquifer layers.