Coastal changes resulting from storms or management actions are often compared to conditions as they were at a single point in time prior to the event. Because storm recovery and coastal management timelines can extend to a decade or longer, it is helpful to consider these changes relative to historical variability. Landsat satellite imagery provides a consistent, long-term data source that can be used to quantify natural variability of coastal-system land cover, geomorphic boundaries, and morphologic metrics over timescales of years to decades. This allows for comparisons of short-term changes to long-term variability and for monitoring storm recovery and/or restoration actions. 

Using 179 Landsat 8 and 9 satellite images acquired between 2013 and 2024, we mapped land cover, shoreline position, and the sand-vegetation boundary along the Louisiana coast from the Louisiana-Texas border to the Mississippi River delta. The analysis extent encompasses considerable complexity in coastal geomorphology, including the chenier plain; Marsh and Point au Fer Islands; and delta-plain marshes, headlands, and barrier islands. To evaluate regional variability in shoreline changes over the last decade, we extracted shoreline position for each image along transects spaced 500 m alongshore.

Preliminary analyses assessed the magnitude of change between the earliest and most recent shoreline for each transect. Of 743 transects measured, 12% prograded, 52% eroded, and 36% underwent changes of less than +/- 30 m (equivalent to 1 image pixel; hereafter “no change”). The distribution of shoreline retreat or advance also varied by geomorphic setting. In the western chenier plain, the shoreline prograded on 36% of transects, occurring along reaches adjacent to the Sabine and Calcasieu River mouths, and eroded on 7% of transects. Along the eastern chenier plain, Marsh and Point au Fer Islands, and the delta-plain marshes, no progradation was resolvable and shoreline erosion occurred on 83% of transects. Along delta-plain barrier islands and headlands, shoreline retreat was measured on 29% of transects and 19% of transects prograded. 

These results show that shorelines derived from medium-resolution satellite imagery can resolve coastal changes that occur across regional areas including along both sandy and non-sandy coastlines; furthermore, they represent only a fraction of what can be learned from this dataset. Future analyses will move beyond the endpoint assessment presented here to quantify historical variability and trends in shoreline position using all the shoreline data. Historical variability and changes in sand-vegetation boundaries and land-cover extents will also be evaluated. This information can be used to explore how changes affected by storm events such as Hurricanes Laura, Delta, Zeta (2021) and Ida (2021) and/or recent restoration actions compare to long-term natural variability.