Bellport, NY Coastal Erosion Rate
What USGS measures 3.1 miles south of Bellport, NY
Good news, and an honest one: USGS's data can't distinguish this stretch, 3.1 miles south of Bellport, NY, from a flat trend. Whatever small movement it measured here is statistical noise, not a reliable direction, so none is claimed.
What "Bellport" 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 Bellport, NY, rather than showing one arbitrary line. Segment center: 40.71, -72.95. The survey behind it runs to 2007-2009, in USGS's New England / Mid-Atlantic 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 backs this reading up
This reading comes from 92 individual transects averaged together, 50% of which measured erosion rather than growth. USGS's confidence interval here is ±0.18 ft/yr. The unadjusted figure here, -0.01 ft/yr, would place it 759 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 2010-1119. Long Beach, CA sits at national rank 1135 for growth (1.31 ft/yr), one reference point among the 1211 scored segments, 2506 miles from here. 2.4 miles up the coast, Bellport, NY shows 0.56 ft/yr of eroding.
Bellport, NY on the source map: try the Coastal Change Hazards Portal, zoomable well past this page's ~3.5-mile grain.