Grand Isle, LA Coastal Erosion Rate
Is the coast eroding 8.7 miles southwest of Grand Isle, LA?
Averaged across every transect USGS ran 8.7 miles southwest of Grand Isle, LA, the shoreline has been moving inland at 13.52 feet a year, a real measured rate, not a regional estimate applied to this stretch. At that rate, the shoreline has lost roughly 135.2 feet over the last decade.
The grain of this number
Grand Isle, LA is the nearest named place, 8.7 miles away, to a ~3.5-mile stretch of coast USGS has surveyed - the reading below covers that whole stretch, not a single property in it. Segment center: 29.14, -90.15. 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 13.52 ft/yr means over time
Run 8.7 miles southwest of Grand Isle, LA's 13.52 ft/yr rate forward 25 years and it implies about 338 feet of further retreat, assuming nothing changes, which is exactly the assumption a seawall or nourishment project exists to break.
How solid is this number
116 transects feed this segment's number; 100% of them individually measured retreat. The published margin on this reading runs ±1.1 ft/yr. This segment ranks 16 of 1211 measured US coastal segments, ordered from fastest erosion to fastest growth. Source: USGS Open-File Report 2004-1089. Pacifica, CA sits at national rank 270 for erosion (0.6 ft/yr), one reference point among the 1211 scored segments, 1945 miles from here. 2 miles away, Grand Isle, LA is the nearest other measured stretch: severe erosion at 17.96 ft/yr.
One address near Grand Isle: the Coastal Change Hazards Portal zooms past this stretch to the underlying map.