Using hydrologic model data to inform time-lapse ERT investigations of coastal processes

Abstract

Due to the effects of global climate change on the frequency and severity of tropical cyclones (Knutson et al., 2010), coastal communities are experiencing an increase in the rate of salinization of their freshwater resources. This study investigated the dynamics of saltwater intrusion that occur in the wake of storm surges by incorporating electrical resistivity tomography (ERT) in hydrologic modeling of coastal saline transport at a field site on Assateague Island, MD. Due to the sensitivity of ERT to saline content, these methods were able to resolve the more fine-scale transport structures (e.g., density fingering) that hydrologic models often lack the spatial resolution to resolve. A model developed in HydroGeoSphere to investigate the inundation and flushing of the field site was used to simulate a synthetic ERT array to test the sensitivity of different ERT array sequences to gradual lateral changes in salinity by applying a petrophysical transform to the data to yield a spatial distribution of bulk resistivity values. These distributions were then analyzed in ResIPy to run synthetic forward models and invert them to investigate the lateral sensitivity of different array sequences to gradual changes in electrolytic salinity (and therefore, bulk resistivity). The compared ERT arrays were then tested with time lapse surveys at the field site to investigate their viability in a real-world saline environment.