Sanibel, FL Coastal Erosion Rate
Shoreline change 3.4 miles east of Sanibel, FL
The coast 3.4 miles east of Sanibel, FL is actually gaining ground, not losing it: USGS's transects measure 0.99 feet of accretion a year here, sediment building up rather than washing away. At that rate, the shoreline has gained roughly 9.9 feet over the last decade.
What "Sanibel" means on this page
This is a roughly 3.5-mile stretch of coast, not one address or parcel - USGS's own transects run every few hundred feet, but that's finer than any one property needs, so this page reports the stretch nearest Sanibel, FL. Centered near 26.45°N, 82.05°W. 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.
25 years at this rate
Holding the 0.99 ft/yr accretion rate 3.4 miles east of Sanibel, FL for 25 years would add roughly 25 feet of shoreline, again assuming nothing about the local sediment supply changes.
What backs this reading up
122 transects feed this segment's number; 4% of them individually measured retreat. USGS's confidence interval here is ±0.38 ft/yr. This segment ranks 1104 of 1211 measured US coastal segments, ordered from fastest erosion to fastest growth. Source: USGS Open-File Report 2004-1089. Rank 958 nationally for growth belongs to Moss Landing, CA, 2426 miles from this stretch, measured at 0.27 ft/yr, 0.3x this stretch's rate. 2 miles up the coast, Punta Rassa, FL shows the same lack of a significant trend.
Sanibel, FL on the source map: try the Coastal Change Hazards Portal, zoomable well past this page's ~3.5-mile grain.