Grand Isle, LA Coastal Erosion Rate
What USGS measures 3.8 miles northeast of Grand Isle, LA
Good news, and an honest one: USGS's data can't distinguish this stretch, 3.8 miles northeast of Grand Isle, LA, from a flat trend. Whatever small movement it measured here is statistical noise, not a reliable direction, so none is claimed.
The grain of this number
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: 29.26, -90.00. 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.
How solid is this number
117 transects feed this segment's number; 7% of them individually measured retreat. Uncertainty on this specific number: 2.15 ft/yr either side. The unadjusted figure here, 1.21 ft/yr, would place it 1123 of 1211 if ranked directly - but an unreliable rank isn't a useful one, which is exactly why "no significant trend" is the headline instead. Source: USGS Open-File Report 2004-1089. Stone Harbor, NJ sits at national rank 1069 for growth (0.73 ft/yr), one reference point among the 1211 scored segments, 1101 miles from here. Grand Isle, LA, 1.6 miles off, is the adjacent measured stretch, reading accretion (beach growing) at 4.73 ft/yr.
Grand Isle, LA on the source map: try the Coastal Change Hazards Portal, zoomable well past this page's ~3.5-mile grain.