in which Qa-^ and S^^ are the standard deviation in (|) units of the 

 borrow and native materials (in tMs case 1.28 and 0.91, respectively) and 

 Mj)2) and Mx^ are the <j> means of the borrow and native materials (in 

 this case 0,88 and 1.69 respectively). The critical ratio was computed to 

 be 2.1, indicating that for every cubic yard of material on the active 

 profile in 1967, 2.1 cubic yards of borrow material should have been placed. 



In April 1965, approximately 2,632,000 cubic yards of borrow material 

 were placed along the 14,000 linear feet of shore fronting Carolina Beach. 

 (Vallianos, 1970.) Figure 6-21 shows the before-and-after conditions of 

 the beach. The fill consisted of a dune having a width of 25 feet at an 

 elevation of 15 feet above mean low water, fronted by a 50-foot wide berm 

 at an elevation of 12 feet above mean low water. Along the northern-most 

 3,700 feet of the project, (Figure 6-20), the berm was widened to 70 feet 

 to provide a beach-nourishment stockpile. 



Following construction, rapid erosion occurred along the entire length 

 of the beach fill. Initial adjustments were expected based on the use of 

 ^(hcrit ~ ^-^ which resulted in an excess of 1,350,000 cubic yards of fill 

 being placed on the beach to account for the unsuitability of part of the 

 borrow material. However, the actual rates of change, particularly those 

 evidenced along the onshore section of the project, were much greater than 

 originally anticipated considering that all of the fill had not been sub- 

 jected to winnowing by wave action. 



In the first 2 years, erosion persisted along the entire length of 

 fill. The erosion along the southern 10,000 feet of the project was less 

 than that along the northern 4,000 feet. 



During these years (1965-1967), approximately 712,000 cubic yards, of 

 the 1,652,000 cubic yards initially placed, were moved from the southern 

 10,000-foot section to depths seaward of the 22-foot contour. This loss 

 was about 43 percent of the total fill placed. Therefore, in terms of fill, 

 protection was reduced by 43 percent. Beach changes resulted in an 82-foot 

 recession of the high water line, and the loss of the horizontal berm of 

 the design profile. By the end of the second year, the southern 10,000 

 linear feet of project was stabilized, and remained in about the same 

 condition as of 1972. 



In the first 2 years after the placement of 980,000 cubic yards of 

 fill, erosion along the 4,000-foot northern section was greater than that 

 in the 10,000-foot southern section. About 550,000 cubic yards of fill 

 were lost from the active profile, amounting to a 56 percent reduction in 

 the total in-place fill. By March 1967, the high water line along this 

 section receded 140 feet, resulting in the complete loss of 1,500 linear 

 feet of original fill, and the severe loss of an additional 1,200 feet of 

 fill. This erosion progressed rapidly in a southward direction and threat- 

 ened the more stable southern section of the project. 



6-28 



