What You Should Know About Erosion and Oceanfront Development

When you choose to build or buy on the oceanfront, you take risks. Those risks may come in the form of dramatic storms such as nor’easters or hurricanes that can destroy a home in a matter of hours. Or the risks may develop more gradually, caused by the daily forces of winds, waves and tides. These forces cause North Carolina’s beaches to shift. A beach may lose sand (erosion) or gain it (accretion).

Erosion tends to occur faster in some areas than in others, especially near inlets and capes, where sand shifts rapidly. An eroding beach may lose several feet of sand a year.

In spite of these risks, many people want to build along our ocean shore. So the N.C. Coastal Resources Commission (CRC) has established rules and development standards to reduce the risk to life and property.

These rules include erosion setbacks for oceanfront construction. These setbacks are based on average long-term erosion rates that reflect changes in our shoreline over nearly half a century.

Tracing shoreline changes

North Carolina first evaluated long-term average erosion rates for the state’s 300-mile ocean coastline in 1979. The Division of Coastal Management evaluates these erosion rates about every five years. It’s an exacting process that takes about a year to complete.

Coastal Management begins each update by obtaining new aerial photographs of the ocean shoreline. The photographs have been taken under specific conditions to ensure that the coast is in as normal a condition as possible.

The photos show the shoreline — defined as the high water line, or the edge of the wet sand visible on the photographs. The shoreline is marked, then its position (relative to a fixed shoreline baseline) is added to an existing database. A sophisticated computer program corrects for distortion created by the aerial photographs.

Another computer program determines an average long-term erosion rate by comparing the current shoreline position to the earliest available position and dividing the distance between them by the number of years that have passed between the dates the photographs were taken. For example, if the 1992 shoreline is compared with the 1942 shoreline, the distance the shoreline has moved is divided by 50. If the difference between 1942 and 1992 is 200 feet, the long-term average erosion rate is 4 feet per year.

This work yields thousands of numbers. For practical purposes, Coastal Management groups the data into continuous blocks along the oceanfront, with each block having approximately the same erosion rate.

Once the erosion rates are determined, the CRC holds hearings to receive public comment on proposed changes to erosion rates. The Commission must adopt the rates before they can be used.

How erosion rates affect you

If you’re considering buying an existing house or building a new one on the oceanfront, you should know the erosion rate at your property.

These rates are not predictors. If the long-term average erosion rate at a certain location is 3 feet per year, it doesn’t mean that beach will lose 3 feet of sand this year. It might lose less, or more. Still, the rates are useful for giving you an idea of what has happened in the past.

And if you’re planning to build along the oceanfront, the average annual erosion rate will determine where you can put your house.

CRC rules require that oceanfront buildings be set back from the sea. The erosion setback is a line, measured landward from the first line of stable, natural vegetation, behind which you will be required to build your house or other building.

Setbacks are designed to increase the life of your building, and they are based on long-term average erosion rates. Oceanfront construction setbacks are measured landward from the first line of stable natural vegetation, or a static vegetation line when applicable. Setback distance is determined by two variables; (1) size of structure; (2) a setback factor based on shoreline position change rates (see table below). As specified in Rule 15A NCAC 7H .0304(1)(a), the minimum setback factor is 2, unless the shoreline is eroding at a rate greater than 2 feet per year. Therefore, when the shoreline is accreting (moving seaward), or eroding at a rate less than 2 feet per year, the default setback factor is 2, thus making the minimum construction setback equal to 60 feet (2x30=60) for structures less than 5,000 sqft.

Structure Size Setback (ft) example using setback factor = 2
less than 5,000 sqft 60 feet or 30 times the setback factor 2 x 30 = 60 feet
greater than or equal to 5,000 sqft 120 feet or 60 times the setback factor 2 x 60 = 120 feet
greater than or equal to 10,000 sqft 130 feet or 65 times the setback factor 2 x 65 = 130 feet
greater than or equal to 20,000 sqft 140 feet or 70 times the setback factor 2 x 70 = 140 feet
greater than or equal to 40,000 sqft 150 feet or 75 times the setback factor 2 x 75 = 150 feet
greater than or equal to 60,000 sqft 160 feet or 80 times the setback factor 2 x 80 = 160 feet
greater than or equal to 80,000 sqft 170 feet or 85 times the setback factor 2 x 85 = 170 feet
greater than or equal to 100,000 sqft 180 feet or 90 times the setback factor 2 x 90 = 180 feet

All buildings must be behind the frontal dune and landward of the crest of the primary dune, where those exist. A state or local Coastal Management representative determines setbacks on a case-by-case basis when development is proposed.

Building in accordance with setbacks doesn’t guarantee that the ocean never will threaten your house. But it reduces your risk of property loss, it reduces the encroachment of development onto public beaches, and it can reduce the amount of tax money spent responding to problems that are exacerbated by poorly sited development.

Erosion in your area

The Division of Coastal Management provides several ways for you to explore erosion rates and setback factors along the oceanfront:

For more information, contact:

N.C. Division of Coastal Management 
400 Commerce Ave.
Morehead City, N.C. 28557
252-808-2808 / 1-888-4RCOAST
 

For the name and address of the local permit officer in your area, click here.

Find out how to protect oceanfront property from erosion.