Long-Term Average Annual Erosion Rate Study
Maps prepared by:
North Carolina's long-term (approximately 50 years) average annual oceanfront erosion rates are calculated for the purpose of establishing oceanfront construction Setback Factors, and the Ocean Erodible Areas of Environmental Concern (OEA AEC), which were initially established by the Coastal Resource Commission (CRC) under the Coastal Area Management Act (CAMA) in 1979 .
Oceanfront shoreline change rates have been calculated using the end-point method since the first study completed in 1979. This method simply uses the earliest and most current shoreline data points where they intersect any given shore-perpendicular transect line. The distance between the two shorelines (shore-transect intersect) divided by the time between the two establishes the rate. The use of current mapping and spatial analysis technology make this process repeatable and precise; ESRI's Geographic Information Systems (GIS), and USGS's Digital Shoreline Analysis System (DSAS). To explore shoreline change rates (erosion and accretion) simply use the Google Map provided to zoom in/out, and click on blue (accretion) or red (erosion) lines to see rates; or click on white-border "boxes" to see setback factors.
A setback factor is one of two criteria used to calculate construction setbacks on the oceanfront, the other criterion is based on size of structure (see table below). The terms "setback factor" and "erosion rate" have often been interchangeably used when referring to long-term average annual changes in shoreline movement, however, there is a difference. "Setback factors" are statistically derived from the actual shoreline change rate (erosion or accretion), yet for sections of shoreline where erosion rates are equal to 2 feet per year or less, or where a section is accreting (growing seaward), the setback factor defaults to 2 feet per year as specified in Rule 15A NCAC 7H .0304(1)(a). The default setback factor value can be a source of confusion when trying to differentiate between accreting and eroding sections of shoreline since the actual rate of accretion is not directly reflected in the setback factor. Where setback factors are greater than 2 feet per year, those values do correspond directly to average rates of erosion for that section of shoreline.
The shoreline change information presented here is not predictive, nor does it reflect the short-term erosion that occurs during storms. The most current erosion rates depicted in these data were adopted (February-2013) by the Coastal Resources Commission for incorporation into oceanfront setback rules. Please contact your CAMA Local Permit Officer or the nearest regional field office of the N.C. Division of Coastal Management for more information.