The Coastal Resources Commission has incorporated updated long-term average annual erosion rates into its oceanfront development rules. The new rates are represented on maps prepared by the Division of Coastal Management. The new rules took effect April 1, 2004.
Rule text (in PDF format; requires Adobe Acrobat Reader)
What is a long-term average annual erosion rate?
A long-term average annual erosion rate is the average amount of erosion that occurs each year over a period of about 50 years. By measuring movement of the ocean shoreline over a long period of time, Coastal Management is able to get a more accurate representation of the net shoreline change, taking into account normal shoreline movement, beach nourishment and storms.
How was this rate measured?
The shoreline change was measured by comparing the shoreline in aerial photographs from 1998 with photographs, topographic surveys (T-sheets) and other shoreline data from the 1940s. The measurements were put through several computerized processes designed to reduce errors and increase accuracy. The result is the most accurate erosion rates the state has ever had.
How does the Division of Coastal Management use these erosion rates?
DCM uses long-term average annual erosion rates in determining setback distances for oceanfront construction. Setbacks are measured from the first line of stable, natural vegetation. For small structures and single-family residences of any size, the setback distance is determined by multiplying the average annual erosion rate by 30. For example, on a property where the erosion rate is 3 feet a year, the setback is a minimum of 90 feet from the vegetation line. In areas that are naturally gaining sand or have an erosion rate of 2 feet a year or less, the setback distance is a minimum of 60 feet.
For multi-family residences, such as condominiums, and commercial structures larger than 5,000 square feet, the setback distance is determined by multiplying the average annual erosion rate by 60. For example, on a property where the erosion rate is 3 feet a year, the setback is a minimum of 180 feet from the vegetation line. In areas where the erosion rate is greater than 3.5 feet a year, the setback for large structures is determined by multiplying the erosion rate by 30 and adding 105 feet. In areas that are naturally gaining sand or have an erosion rate of 2 feet a year or less, the setback distance is a minimum of 120 feet.
I own property on the oceanfront. How will the change in erosion rates affect my setback?
If you own a lot platted by Jan. 29, 2004, and obtain a CAMA permit to build on it after the new erosion rates take effect, you must meet a setback based on the new rates to the maximum extent feasible. If you cannot meet a setback based on the new erosion rates, the setback distance will be based on the erosion rate in effect at the time your lot was created.
On lots platted after Jan. 29, 2004, the distance of the construction setback will be based on the new erosion rates.
If the average annual erosion rate in front of my property has decreased, can I build closer to the ocean?
Not necessarily. Your setback distance will still be based on the erosion rate in effect at the time your lot was created. However, you can build closer to the ocean if the first line of stable natural vegetation on your lot has moved seaward. Remember, the setback is measured from this vegetation line.
When will the rule changes using the new rates take effect?
The new rules take effect April 1, 2004.
Where can I find the new erosion rate maps?
The new maps are available at www.nccoastalmanagement.net/Maps/ER_1998/SB_Factor.htm.
The new maps show low erosion rates in front of some properties that clearly are threatened by erosion. Why?
The rates and maps were calculated using photographs taken in 1998. In communities such as North Topsail Beach and Emerald Isle, sudden shifts by inlets since 1998 have eroded the beach in front of some houses. DCM recognizes that dramatic changes in shoreline can occur – whether because of shifting inlets or major storms – in a short amount of time. The division’s staff is working on methods to reflect shoreline-change rates over a shorter period of time.
Why was there a lag between when the photos were taken in 1998 and the rate calculations?
The lag between when the 1998 photographs were taken and when the rates were calculated was the result of changing the method and technology used in updating the rates. Future updates should be accomplished more quickly.
What’s so special about the new erosion rate maps?
Because the new maps were created in a geographic information systems, or GIS, format, they are more accurate, more detailed and easier to use than previous erosion rate maps. In addition, DCM is developing an interactive online mapping tool that will allow visitors to the agency’s Web site to look at a variety of erosion information pertaining to oceanfront communities. This new feature will be available later this year.
How was the update done, and who funded it?
Coastal Management contracted with the state Department of Transportation to take the aerial photos in 1998. DCM then contracted with Surdex Corp. to digitize the photographs and conduct a process using global-positioning technology to correct for errors in scale. The rectified photos, known as ortho-photographs, then were sent to the Kenan Natural Hazards Mapping Program at N.C. State University, where the shoreline-change calculations were conducted. DCM used this data to produce the shoreline-change rate maps.
Funding for the project came from the Federal Emergency Management Agency, the N.C. Division of Emergency Management and the National Oceanic and Atmospheric Administration.