| Abstract: | The effect of storms on long-term dynamics of barrier islands was evaluated on Core Banks, a series of barrier islands that extend from Cape Lookout to Okracoke Inlet in the Cape Lookout National Seashore, North Carolina. Shoreline and elevation changes were determined by comparing 77 profiles and associated reference markers established by the U.S. Army Corps of Engineers (USACE) on Core Banks from June 1960 to July 1962 to a follow-up survey by Godfrey and Godfrey (G&G) in 1971 and a survey by the Department of Geology at East Carolina University (ECU) in 2001, in which 57 of the original 77 profiles were located.
Evaluation of the baseline data associated with the USACE study supplies an important record of barrier island response to two specific storm events - Hurricane Donna in September 1960 and the Ash Wednesday extra-tropical cyclone in March 1962. The 1962 USACE survey was followed by 9 years characterized by no major storms; this low-energy period was captured by the G&G survey in 1971. The G&G survey was followed by 22 years characterized by occasional small to moderate storms. Starting in 1993, however, and continuing through 1999, the North Carolina coast experienced a major increase in storm activity, with seven major hurricanes impacting Core Banks.
Both the USACE 1960-1962 and G&G 1962-1971 surveys produced short-term data sets that reflected very different sets of weather conditions. The ECU 2001 survey data were then compared with the USACE 1960 survey data to develop a long-term (41 years) data set for shoreline erosion on Core Banks. Those resulting long-term data were compared with the long-term (52 years) data sets by the North Carolina Division of Coastal Management (NCDCM) from 1940-1992 and 1946-1998; a strong positive correlation and very similar rates of average annual erosion resulted. However, the ECU and NCDCM long-term data sets did not correlate with either of the USACE and G&G short-term survey data and had very different average annual erosion rates.
The average annual long-term rate of shoreline erosion for all of Core Banks and for both the ECU 1960-2001 and the NCDCM 1946-1998 surveys was -5 feet per year (ft/yr). These long-term rates of shoreline recession are in strong contrast with the short-term, storm-dominated rates of shoreline erosion for all of Core Banks developed by the USACE 1960-1961 and USACE 1961-1962 surveys, which have average annual erosion rates of -40 ft/yr and -26 ft/yr, respectively, and range from -226 feet (ft) to +153 ft. The combined short-term, storm-dominated shoreline erosion rate for the USACE surveys (1960-1962) was -36 ft/yr. In contrast, the average annual short-term, non-stormy period G&G 1962-1971 survey demonstrated shoreline accretion for all of Core Banks with an average annual rate of +12 ft/yr. In general, North Core Banks has higher erosion and accretion rates than South Core Banks.
In the 1961 survey, the USACE installed 231 reference markers (RM-0 is closest to the ocean and RM-2 is farthest from the ocean) along the 77 profiles, as well as 33 reference markers labeled RM-4, RM-6, and RM-8 in the wider portions of the islands. The G&G survey recovered a total of 141 reference markers (61 percent), and the ECU survey recovered a total of 83 reference markers (36 percent) of the RM-0, RM-1, and RM-2 markers. The average ground elevation measured by the USACE in 1961 was RM-0 = +5.8 ft, RM-1 = +5.2 ft, and RM-2 = +4.8 ft. The G&G 1970 survey measured average ground elevations of RM-0 = +6.7 ft, RM-1 = +6.4 ft, and RM-2 = +6.1 ft, and the average ground elevation measured by ECU in 2001 was RM-0 = +10.1 ft, RM-1 = +9.1 ft, and RM-2 = +8.5 ft. The latter numbers represent approximately an overall 72-percent increase in island elevation from 1961 to 2001. Based on aerial photographic time-slice analyses, it is hypothesized that this increase in island elevation occurred during the post-1962 period with storm overwash systematically raising t |
| Genre: | USGS Numbered Series |
| ProdID: | 80453 |
| Citation Author: | Riggs, Stanley R.; Ames, Dorothea V. |
| Citation Contributing Office: | USGS Woods Hole Science Center |
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| Citation Language: | ENGLISH |
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| Citation Phsyical Description: | viii, 45 p. |
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| Citation Public Comments: | Prepared in cooperation with the National Park Service and East Carolina University |
| Citation Publisher: | Geological Survey (U.S.) |
| Citation Series: | Scientific Investigations Report |
| Citation Series Code: | SIR |
| Citation Series Number: | 2006-5309 |
| Citation Search Results Text: | Effect of Storms on Barrier Island Dynamics, Core Banks, Cape Lookout National Seashore, North Carolina, 1960-2001; 2007; SIR; 2006-5309; Riggs, Stanley R.; Ames, Dorothea V. |
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| Citation Year: | 2007 |
| Type: | citation/reference |
| Text: | Effect of Storms on Barrier Island Dynamics, Core Banks, Cape Lookout National Seashore, North Carolina, 1960-2001; 2007; SIR; 2006-5309; Riggs, Stanley R.; Ames, Dorothea V. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/usgs_thumb.jpg |
| URL (INDEX PAGE): | http://pubs.usgs.gov/sir/2006/5309/ |
| Date Other: | Fri, 28 Sep 2007 00:00 -0500 |
| Publisher: | Geological Survey (U.S.) |
