Present Sea Level Rise, Land Subsidence, and Coastal Erosion at Freeport, Texas, USA

Coastal submergence and erosion associated with land subsidence and sea level rise exert significant impacts on coastal economic development and ecosystems. This study investigates present sea-level rise, land subsidence, and coastal erosion at Freeport, Texas using long-history datasets from tide gauges, groundwater wells, GPS, and LiDAR surveys. A stable Gulf of Mexico geodetic reference frame 2020 (GOM20) is established to precisely delineate sea-level rise and coastal subsidence along the Gulf coast. GOM20 is realized with long-history observations at 55 GPS sites located in the stable portion of the Gulf coastal plain. The frame stability is 0.3 mm/year in the horizontal direction and 0.5 mm/year in the vertical direction. Groundwater withdrawal-induced land subsidence was remarkable along the Texas coast region during the 1940s to 1970s. A rapid subsidence with an average rate of 15 mm/year was observed at Freeport from 1954 to the mid-1970s because of excessive groundwater withdrawals. The subsidence ceased due to groundwater regulations since the 1980s. Present coastal subsidence at Freeport is dominated by natural subsidence with a steady rate of 1.5 mm/year, which is consistent with the average subsidence rate along the 600-km Texas coastline. The sea-level rise rate at Freeport is 2.6 mm/year from the1970s to 2010s with respect to GOM20. The ongoing land submergence rate at Freeport is approximately 4.1 mm/year. Beach and dune morphology change at Bryan beach in Freeport have been heavily investigated using airborne topographic mapper (ATM), repeated terrestrial laser scanning (TLS), and unmanned aerial vehicle (UAV) data. Comparing the digital elevation model (DEM) of 2017 June with the DEM acquired immediately after Hurricane Harvey, the beach and foredune lose 27,622 m3 of sediments while the back dune at Bryan beach gained 36,749 m3 of sediments during the hurricane season. The shoreline retreating rate at Bryan beach from 2001 to 2018 is 2.64 m/year on average, with maximum of 4.88 m/year at X = 1586 m. The results from this study will be important for coastal geohazards mitigation at Freeport and long-term natural resource planning and management along the whole Texas coast.Earth and Atmospheric Sciences, Department o