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N.C. Department of Environment and Natural Resources

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Coastal Management - CRC approves draft updated oceanfront erosion rates for public hearings this summer

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CRC approves draft updated oceanfront erosion rates for public hearings this summer

The N.C. Coastal Resources Commission has approved a draft proposal to incorporate updated long-term average annual erosion rates into the state’s oceanfront development rules. The proposed rule change would use the updated erosion rates for determining setback distances for oceanfront construction.

The CRC will hold public hearings in each of the eight oceanfront counties over the summer. Dates and locations for those hearings will be announced when they are scheduled. If adopted by the CRC this fall and approved by the state Rules Review Commission, the updated erosion rates would become part of coastal development rules in early 2012.

North Carolina first evaluated long-term average annual erosion rates for the state’s 300-mile ocean shoreline in 1979. DCM evaluates these erosion rates about every five to ten years. The last update went into effect in 2003.

Draft erosion rate maps, a copy of the complete report, and a data summary are available for download.

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, the Division of 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?
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. This update uses aerial photos taken in the summer of 2009.

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, and then its position (relative to a fixed shoreline baseline) is added to an existing database.
The shoreline change was measured by comparing the shoreline in the 2009 aerial photographs with early photographs (1940 and 1962) and National Ocean Survey Topographic sheets (NOS T-sheets). The measurements were calculated utilizing computerized processes designed to analyze erosion rates and map results. This work yields thousands of numbers. For practical purposes, DCM groups the data into continuous blocks, or segments, along the oceanfront, with each block having approximately the same erosion rate.

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, or static vegetation line where applicable. For structures of less than 5,000 square feet, 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 per year, the setback is 90 feet from the vegetation line. In areas that are naturally gaining sand or have an erosion rate of 2 feet per year or less, the setback distance is 60 feet.

The setback factor for all structures between 5,000 and 10,000 square feet is 60 times the erosion rate. The setback factor increases incrementally with structure size, reaching a maximum setback of 90 times the erosion rate for structures 100,000 square feet and larger. 

I own property on the oceanfront. How will the change in erosion rates affect my property?
The 2011 draft erosion rates are not substantially different from the rates adopted in 2003, as 99.8 percent of the oceanfront shoreline demonstrated consistent erosional or accretional characteristics when compared to results from the previous study. In other words, if a location on the shoreline demonstrated erosional characteristics in the 2003 study, it also continued an erosional trend based on results from the 2011 study.  From a regulatory standpoint, the new erosion rates, or setback factors, did not change for 64 percent of the shoreline. These rates will be used in determining setback distances on lots created on or after June 1, 1979. If you own a lot that was platted prior to that date, and cannot meet the current setback, you may be eligible to use a reduced setback rate, which must be at least 60 feet landward of the vegetation line.

When will the rule changes using the new rates take effect?
If the CRC adopts the new rates this fall, they will likely be incorporated into the state’s coastal development rules in early 2012.

When will the erosion rate maps be available?
The new maps are available onDCM’s website. They will also be available for review at each of the public hearings this summer.

How was the update funded?
Improvements in Geographic Information Systems (GIS) technology allowed Division of Coastal Management staff to perform the update in-house for the first time. Previous updates have been done through outside contracts, which had a cost of about $250,000. Performing this update in-house proved to be a significant cost savings for the state.

Last Modified:May 24, 2011

 

N.C. Division of Coastal Management . 400 Commerce Ave. Morehead City, NC 28557
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