Portland, ME Coastal Erosion Rate
Is the coast eroding 4.8 miles southwest of Portland, ME?
The coast 4.8 miles southwest of Portland, ME shows no statistically significant trend either way. USGS's transects measured a rate here, but it's smaller than the survey's own margin of error for this stretch, so calling it "eroding" or "growing" would overstate what the data actually shows.
The grain of this number
Nothing here is parcel-level. USGS's raw transects run every few hundred feet along the shore; this page averages the ones nearest Portland, ME into one ~3.5-mile reading rather than picking a single arbitrary line to represent the area. Centered near 43.57°N, 70.22°W. USGS's New England / Mid-Atlantic assessment last surveyed this stretch through 2007-2009, 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 backs this reading up
2 transects feed this segment's number; 100% of them individually measured retreat. The published margin on this reading runs ±0.29 ft/yr. Taken at face value, this segment's raw -0.07 ft/yr reading would land it 689 of 1211 nationally - a number worth ignoring, since it's statistical noise rather than a real trend. Source: USGS Open-File Report 2010-1119. For scale: Beach Haven, NJ, 344 miles away, ranks 995 of 1211 nationally for growth, 0.4 ft/yr. 0.5 miles away, South Portland, ME is the nearest other measured stretch: also no significant trend.
Not this whole stretch, just Portland itself: the Coastal Change Hazards Portal is USGS's own live version of this data.