Quantifying land subsidence rates in the Coastal Bend of Texas using temporal gravimetry, campaign and permanent GNSS, and interferometric radar techniques

Land subsidence and local sea level rise are well-known, ongoing problems that are negatively impacting the Coastal Bend of Texas. Land subsidence in this area increases the vulnerability of coastal communities to effects of flood and hurricane events. In this study, four different approaches were used for quantifying land subsidence rates over the Coastal Bend of Texas on both local and regional scales. The first approach was a gravity survey, which employed a relative gravimeter to measure temporal gravity changes every two weeks for a period of two years (Oct. 2020 – Sept. 2022) on a local scale over six different areas around Corpus Christi, North Padre Island, Mustang Island, and Rockport. The second approach was to utilize campaign Global Navigation Satellite System (GNSS) elevation measurements, which were collected in a campaign congruent with the gravity survey. The third approach used the Interferometric Synthetic Aperture Radar (InSAR) to generate land deformation rates over the central Coastal Bend region on a reginal scale during from January 2017 to November 2021. The fourth approach used fifteen permanent GNSS stations to quantify land subsidence rates on a regional scale over a time period similar to that of the InSAR. The gravity- and campaign GNSS-derived deformation rates were compared with each other, while the InSAR and permanent GNSS rates were compared. Factors driving InSAR-derived subsidence rates were also investigated. While both local and regional integrations showed significant correlation, land subsidence results from the gravity and campaign GNSS surveys could be enhanced with an extended campaign period and more frequent data acquisition. Additionally, the gravity-derived land subsidence rates could be improved by selecting a more stable base station location, utilizing high precision relative gravimeter and/or an absolute gravimeter, and target a noise-free acquisition days and times. The InSAR-derived rates were consistent with the permanent GNSS-derived rates (R: 0.7). Results of this study showed that land subsidence rates exhibited spatial and temporal variations across the Coastal Bend of Texas. Four regions were identified to experience significant InSAR-derived land subsidence rates: inland towns (total: 17); coastal towns (total: 6); cities (total: 6); industrial plants (total: 8). Four coastal towns subsided at an average rate of -2 ± 3 mm/yr (range: -4 ± 4 to -0.4 ± 3 mm/yr), likely driven by sediment compaction and growth faulting. Three regions classified as city around the Corpus Christi urban area experienced an average subsidence rate of -2 ± 3 mm/yr (range: -4 ± 3 to -0.2 ± 3 mm/yr), with subsidence being attributed to increased groundwater extraction rates, sediment compaction, and growth faulting. Three inland towns experienced average subsidence rates of -4 ± 4 mm/yr (range: -8 ± 8 to -0.7 ± 3 mm/yr); two inland towns close in proximity to the coastline experienced subsidence that is likely attributed to a high density of growth faults, while the town located further inland could have experienced subsidence due to enhanced groundwater extraction activities. Seven industrial plants experienced subsidence at an average rate of -4 ± 6 mm/yr (range: -8 ± 6 mm/yr to -0.2 ± 5 mm/yr). The localized subsidence observed within these areas is thought to be driven by sediment compaction by overburden from storage tanks. Quantifying land subsidence is important in estimating local sea level rise, determining the local geoid, and improving understanding of their controlling factors. Land subsidence rates, generated from this study, could be useful for supporting coastal communities in mitigating the effects of natural forces and improving their resilience against them.