Shoreline change at Gulf Islands National Seashore, Florida and Mississippi: 2018–2022 data summary

Abstract

In May and June 2018, April 2021, and April 2022 the Gulf Coast Network (GULN) surveyed shoreline position at Gulf Islands National Seashore (GUIS) as a part of the NPS Vital Signs Monitoring Program. Monitoring was conducted following methods detailed in Monitoring Shoreline Position at Gulf Coast Network Parks: Protocol Implementation Plan (PIP; Bracewell 2017). Shoreline change was calculated using the Digital Shoreline Analysis System developed by USGS (Theiler et al. 2008). Key findings from this effort are as follows: In Florida, the mean shoreline change rate from 2018 to 2022 was -5.14 meters/year (-17.75 feet[ft]/year) with a standard deviation of 4.57 meters (14.99 ft). Approximately 91% of transects exhibited landward retreat. In Mississippi, the mean change in island width from 2018 to 2022 was -7.46 meters/year (-24.5 ft/year) with a standard deviation of 12.49 meters (41.0 ft). Approximately 73% of transects exhibited a loss in width. The 2020 hurricane season was extremely active, causing high shoreline retreat rates from 2018 to 2021. The 2021 hurricane season was much calmer in comparison, and concordantly, rates of shoreline retreat were generally lessened or reversed to shoreline advance between 2021 and 2022. A beach nourishment project on the eastern end of Perdido Key advanced the shoreline an average of 42.2 meters (138.5 ft) within the project area. This report expands on the previous GULN Shoreline Position report (Bracewell 2022a), to document “storminess” and current sea level rise trends. This project is in the early phases of implementation and will benefit from future surveys to better understand the influence of slight changes in survey timing and other environmental variations.