The first lift of fencing was constructed in each plot in April 1970. 

 Eight months after installation, sand accumulation was slightly higher in the 

 straight fence plot (plot 4). In January and April 1971, lifts two and three 

 were installed. By October 1971 the straight fence plot had trapped about 20 

 percent more material and its crest elevation had increased 10 percent more 

 than the spur plot (plot 2). This inequity between plots may not be the 

 direct result of fence performance. Note in Figure 13 that a secondary dune 

 line formed landward of the spur fence plot. It is likely that the secondary 

 dune reduced the volume of sand available from the landward beach. 



In October 1971, the spur fence plot was damaged by overwash, whereas the 

 straight fence remained intact. Comparison of the performance of the two 

 fence schemes is meaningful only during the 18-month period before the damage 

 occurred. During this period, there was no evidence that side spurs improved 

 trapping efficiency or fence stability, but use of the side spurs did increase 

 construction cost of the fence by about 20 percent. 



A fourth lift of fencing was added to both plots in January 1972, and both 

 plots were planted with American beachgrass in April 1972. By September 1975, 

 5 yeai;s and 5 months after installation, the straight fence plot had trapped 

 48.8 cubic meters per meter. This represents an annual accumulation rate of 

 9.0 cubic meters. Between 1975 and 1977, a slight loss of material occurred 

 due to shoreline recession. By 1977, crest elevation in the straight fence 

 plot had increased 3.0 meters or an average annual growth rate of 0.4 meter. 



3. Comparison of American Beachgrass and Sand Fence . 



Sand accumulation was negligible in the three American beachgrass plots 

 during the first growing season (Tables 3, 5, and 7). The 20 cubic meters per 

 meter of accumulation in plot 3 resulted from the migration of the storm berm 

 into the planting area. Sand accumulation in the fenced plots was very high 

 during the first year, averaging 11.9 cubic meters. 



The undamaged straight fence plot trapped sand at a rapid rate of 9.0 

 cubic meters per year for the first 5.5 years. Though initially slow, the 

 beachgrass plots trapped an average of 8.3 cubic meters per meter per year 

 over seven growing seasons. These observations support conclusions by Savage 

 and Woodhouse (1968): (a) Sand fences initially trap more sand than newly 

 established stands of beachgrass, (b) multiple lifts of sand fencing can sus- 

 tain dune growth, and (c) once established beachgrass stands trap sand at 

 rates comparable to multiple lifts of sand fence. 



There are two striking differences between the sand fence and beachgrass 

 dunes — final base width and crest growth (Tables 3 to 7). Base width of the 

 fence dunes was only 30 to 37 meters. The beachgrass dunes were 61 to 96 

 meters, two to three times the width of the fence dunes. However, crest 

 growth was 1 meter greater in the straight fence plot than in the most suc- 

 cessful beachgrass plot. 



4. Comparison with Previous Studies . 



Table 11 provides a comparison of annual sand accumulation and dune growth 

 rates observed in this study and rates observed in previous studies at Ocracoke 

 Island, North Carolina, Padre Island, Texas, and Clatsop Plains, Oregon. Cape 



