APPENDIX B 



COMPARISON OF EXISTING BEACH AND POTENTIAL BORROW MATERIALS 

 AT OAK ISLAND, NORTH CAROLINA 



This example of using beach-fill models for hurricane-wave protection 

 and beach erosion control was reported in a General Design Memorandum (GDM) 

 for Yaupon Beach and Long Beach, Brunswick County, North Carolina [U.S. 

 Army Engineer District, Wilmington, 1973). These beaches extend east for 

 approximately 9 miles (14.5 kilometers) along Oak Island from Lockwood's 

 Folly Inlet (Fig. B-l, heavy line extending to profile 180). Long-term 

 erosion rates range from 5.7 feet (1.7 meters) per year at Yaupon Beach 

 at the western end of the project area to 3.6 feet (1.1 meters) at Long 

 Beach. 



1. Project Description . 



The GDM considered 19 plans of action for the area. Optimization 

 procedures were used to consider factors of shoreline and hurricane history, 

 wind and wave climate, shore processes, environmental impact, and recreation 

 and economic aspects of the area. In addition, 170 sand samples were col- 

 lected from along 10 beach profiles (Fig. B-l) and 750 samples were obtained 

 from 79 cores to describe native beach sediments and to evaluate potential 

 borrow materials for beach renourishment. Plan BTG in the GDM was selected 

 as the most cost effective to provide the needed protection from hurricanes 

 and beach erosion as well as being acceptable to State and local interests. 



Briefly, this plan consisted of an initial placement of 11,931,400 

 cubic yards (9,122,748 cubic meters) of fill plus additional fills of 

 1,055,400 cubic yards (806,959 cubic meters) placed every third year at 

 two feeder beach localities. The initial fill would be used to construct 

 a 25-foot-wide (7.6 meters) dune at +15 feet (4.0 meters) MSL, a 50-foot- 

 wide (15.2 meters) storm berm at +12 feet (3.7 meters) MSL, and a sloped 

 beach to close out with the existing bottom at approxiamtely -27 feet 

 (-8.2 meters) MSL. In addition to the beach fill, plan BTG called for 

 construction of a timber bulkhead at Yaupon Beach, a 900-foot (274 meters) 

 rock revetment at Long Beach, and groin fields at the east and west margins 

 of the project. The initial cost for plan BTG was estimated to be $11.6 

 million plus $1.2 million in annual maintenance costs. 



Nine potential borrow areas were considered and of these, sediments 

 from Lockwood's Folly Inlet and from the Yellow Banks area of the main- 

 land (Fig. B-l, area A) were determined most suitable. The criteria used 

 to select suitable borrow material were their similarity to native beach 

 sediments as determined by the SPM fill factor method, the environmental 

 impact of removing the materials, the cost per yard of material, and the 

 expense of mobilization and demobilization. Materials found in Middle 

 Ground shoal at the mouth of the Cape Fear River (Fig. B-l, area B) were 

 of the best quality for renourishment purposes but expensive in terms of 

 mobilization-demobilization expense estimates. Nevertheless, for this 

 example Middle Ground shoal and Yellow Banks sediments are evaluated as 



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