The average annual increment in elevation for 40 cross-sections on Ocra- 

 coke Island since 1964 is 1,01 feet. The average on Core Banks is less-- 

 0.17 feet for 18 cross-sections since 1965. The elevation increment for 

 20 cross sections on Clatsop Spit is 0.7 feet per year for 33 years. 

 Undoubtedly the latter average was much higher during the first 5 to 10 

 years, but survey information is lacking. For the first 3 years on Padre 

 Island, the average increase in elevation has been 2 feet per year. 



6.449 Cost Factors . Survival rate of transplants may be increased by 

 increasing the number of culms per transplant. This increase in survival 

 rate does not offset the increase in cost to harvest multiculm transplants. 

 It is less expensive to reduce plant spacing if factors other than erosion 

 (such as drought) affect survival rate. 



Harvesting, processing, and transplanting of sea oats requires one 

 man-hour per 130 hills, panic beach grass requires one man-hour per 230 

 hills. For example, a 50-foot wide, 1-mile long planting of sea oats on 

 24-inch centers requires about 500 man-hours for harvesting, processing, 

 and transplanting if plants are locally available. Using a mechanical 

 transplanter, 400 to 600 hills can be planted per man-hour. 



Nursery production of transplants is recommended unless, easily 

 harvested wild plants of quality are locally available. Nursery plants 

 are easier to harvest than wild stock. Commercial nurseries are now 

 producing American and European beach grass. 



6.5 SAND BYPASSING 



Several techniques have been used for mechanically bypassing sand at 

 littoral barriers. The type of littoral barriers--breakwaters and jetties 

 — determines the method of sand bypassing that should be employed. The 

 four types of littoral barrier where sand transfer systems have been used 

 are illustrated in Figure 6-42. The basic methods of sand bypassing are: 

 Fixed bypassing plants, floating bypassing plants, and land-based vehicles. 

 Various features combining types of littoral barriers and methods of bypass- 

 ing are illustrated by descriptions of selected projects. 



6.51 FIXED BYPASSING PLANTS 



Fixed bypassing plants have been used at the following Type I (Fig. 

 6-42) inlet improvements in the United States: Rudee Inlet, Virginia 

 Beach, Virginia; South Lake Work Inlet, Florida; and Lake Worth Inlet, 

 Florida. 



In other countries, fixed bypassing plants were used at Salina Cruz, 

 Mexico, (U.S. Army, Beach Erosion Board, 1951), Durban, Natal, South 

 Africa, (U.S. Army, Beach Erosion Board, 1956.) Both were located at 

 breakwaters on the updrift sides of harbor entrances. The Salina Cruz 

 plant rapidly became land-locked, and was abandoned in favor of other 

 methods of channel maintenance. (U.S. Army, Beach Erosion Board 1952, 



6-54 



