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. For all structures less than 5,000 square feet (regardless of whether it is single-family, multi-family or commercial) the minimum setback factor is 30 times the annual erosion rate, with a minimum setback of 60 feet.
The setback factor for all structures between 5,000 and 10,000 square feet is 60 times the erosion rate and increases incrementally with structure size, reaching a maximum setback at 90 times the erosion rate for structures 100,000 square feet and greater. Development in communities with a static line exception is subject to a minimum setback factor of 60 times the erosion rate for all development greater than 10,000 square feet total floor area. In all cases, the minimum erosion rate is considered to be two feet per year.
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 produces small-scale maps that will give you an idea of what erosion is like in your area. Because of their small size, these maps are not considered technically accurate. But they can give you a general picture of long-term shoreline changes.
To find out the erosion rate for your property, contact the CAMA local permit officer or Coastal Management district office nearest you. These personnel rely on large-scale aerial photographs for determining erosion rates.
For more information, contact:
N.C. Division of Coastal Management
For the name and address of the local permit officer in your area, click here.
Find out how to protect oceanfront property from erosion.