Half Moon Bay, CA Coastal Erosion Rate
What USGS measures 3.7 miles south of Half Moon Bay, CA
USGS's shoreline-change data puts this stretch, 3.7 miles south of Half Moon Bay, CA, at 0.36 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 3.6 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 Half Moon Bay, CA, rather than showing one arbitrary line. Segment center: 37.41, -122.43. The survey behind it runs to 1852-2016, in USGS's California 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 0.36 ft/yr means over time
Run 3.7 miles south of Half Moon Bay, CA's 0.36 ft/yr rate forward 25 years and it implies about 9 feet of further retreat, assuming nothing changes, which is exactly the assumption a seawall or nourishment project exists to break.
Where this fits nationally
This reading comes from 35 individual transects averaged together, 91% of which measured erosion rather than growth. The published margin on this reading runs ±0.35 ft/yr. Sorted from fastest erosion to fastest growth across all 1211 measured segments nationally, this one lands at 372. Source: USGS National Shoreline Change data release (ScienceBase, DOI 10.5066/P94J0K7Z), Kratzmann 2024 / Data Report 1187. Rank 98 nationally for erosion belongs to South Padre Island, TX, 1662 miles from this stretch, measured at 2.9 ft/yr, 8.1x this stretch's rate. 1.7 miles up the coast, Half Moon Bay, CA shows the same lack of a significant trend.
One address near Half Moon Bay: the Coastal Change Hazards Portal zooms past this stretch to the underlying map.