Grand Isle, LA Coastal Erosion Rate
Is the coast eroding 12.6 miles southwest of Grand Isle, LA?
USGS's shoreline-change data puts this stretch, 12.6 miles southwest of Grand Isle, LA, at 17.17 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 171.7 feet over the last decade.
What this reading actually covers
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: 29.11, -90.20. USGS's Gulf of Mexico assessment last surveyed this stretch through 2001, computing the rate with its LRR method. Other US regions were surveyed in different years, sometimes decades apart, so this page states its own rather than implying one national vintage.
What 17.17 ft/yr means over time
Run 12.6 miles southwest of Grand Isle, LA's 17.17 ft/yr rate forward 25 years and it implies about 429 feet of further retreat, assuming nothing changes, which is exactly the assumption a seawall or nourishment project exists to break.
Where this fits nationally
Averaging 116 separate transects produced this segment's rate, with 100% individually reading as erosion, rather than relying on any single survey line. USGS's confidence interval here is ±5.87 ft/yr. This segment ranks 8 of 1211 measured US coastal segments, ordered from fastest erosion to fastest growth. Source: USGS Open-File Report 2004-1089. Rank 342 nationally for erosion belongs to Sand City, CA, 1900 miles from this stretch, measured at 0.42 ft/yr, a small fraction of this stretch's own rate. 2 miles up the coast, Grand Isle, LA shows 17.96 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.