frontage experiencing damaging erosion and artificial placement of fill 

 in their impounding areas, and that, if no fill is to be placed, the plan 

 should consist of 10 additional groins spaced 1,200 feet apart, con- 

 structing 4- groins the first year and two each year thereafter. 



At Hunting Island the possible sources of supply of beach material 

 are Harbor Island to the north, and the offshore bottom. Some material 

 crossing St. Helena Sound via the numerous shoals may reach Hunting 

 Island, but it appears that little new material reaches the problem 

 area. The north end of the island supplies material to the south end 

 and erosion of the dunes supplies sand to the beach. The rate of loss 

 exceeds the rate of supply for almost the entire ocean frontage, the 

 gireatest rate of loss being at the north end of the island where about 

 1.5 miles of the north end have been lost as shown by shore line changes 

 over the peirLod of record. The predominant direction of littoral drift 

 is southward, as indicated by minor southward migration of Fripp Inlet, 

 Material is moved by beach drifting, but strong tidal currents at the 

 entrance to St, Helena Sound probably cause frequent reversals in direc- 

 tion. The four groins built from 194-8 to 1950 have caused minor accumula- 

 tion of material in their immediate vicinity without adverse effects in 

 adjacent areas, but the evidence is not conclusive that they 7n.ll hold 

 sufficient material to result in permanent stabilization or widening of 

 the beachj in fact, erosion of the offshore bottom above elevation -9 

 feet mean low water, a condition which cannot be remedied economically 

 by the construction of groins, leads to the conclusion that groins alone 

 will not accomplish the desired stabilization. If wider beaches are 

 needed, or if prevention of erosion of the dunes becomes essential, 

 material must be provided by artificial means. The Board concluded 

 that probably the most economical method of complete protection is by 

 artificial placement alone. The estimated material requirements, on 

 an annual basis, are 275^000 cubic yards. However, the Board believed, 

 that at this locality, consideration should be given to planning develop- 

 ment and use of the shore in such manner that the detrimental effect of 

 continued recession would be minimized. 



The Board pointed out that the duJies constitute valuable protection 

 and that they should be preserved wlierever feasible. Excavation of 

 material in connection irith construction of buildings on or the cutting 

 of paths through the dunes materially lessens their protective value and 

 should not be permitted. Building should be permitted only in back of 

 the dunes. 



The Board noted that the groin details shown in the district engineer's 

 report included a triple thickness of 3-inch timber sheet piling. A 

 double thickness of sheet piling is ordinarily adequate for groin con- 

 struction. Although the triple thickness would theoretically have a 

 longer life than a double thickness of sheet piling, other parts of the 

 structure may limit the useful life of the entire groin, so that no value 

 will be secured from the extra thickness of sheeting. The Board was of 

 the opinion that modification of the struct\iral design of groins in this 



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