Grand Isle, LA Coastal Erosion Rate
Shoreline change 4.1 miles southwest of Grand Isle, LA
USGS's shoreline-change data puts this stretch, 4.1 miles southwest of Grand Isle, LA, at 6.6 feet of erosion a year on average, a long-term rate for this specific ~3.5-mile section, not one storm's damage. At that rate, the shoreline has lost roughly 66 feet over the last decade.
What "Grand Isle" means on this page
USGS surveys the coast in transects spaced a few hundred feet apart; this page groups the nearest ones into a single ~3.5-mile reading for the stretch closest to Grand Isle, LA, rather than showing one arbitrary line. Segment center: 29.19, -90.09. The survey behind it runs to 2001, in USGS's Gulf of Mexico assessment, using the LRR method. Shoreline surveys aren't repeated every year, so this is the most recent long-term measurement USGS has published for this coast, not a live reading.
What 6.6 ft/yr means over time
Run 4.1 miles southwest of Grand Isle, LA's 6.6 ft/yr rate forward 25 years and it implies about 165 feet of further retreat, assuming nothing changes, which is exactly the assumption a seawall or nourishment project exists to break.
What backs this reading up
83 transects feed this segment's number; 100% of them individually measured retreat. Uncertainty on this specific number: 1.93 ft/yr either side. Among the 1211 US coastal segments with a measurable trend, this one ranks 38 for erosion, 1 being the fastest-retreating coast in the dataset. Source: USGS Open-File Report 2004-1089. Edgartown, MA sits at national rank 110 for erosion (2.47 ft/yr), one reference point among the 1211 scored segments, 1383 miles from here. 2.1 miles up the coast, Grand Isle, LA shows 8.92 ft/yr of eroding.
Grand Isle, LA on the source map: try the Coastal Change Hazards Portal, zoomable well past this page's ~3.5-mile grain.