d. Average annual sand accumulation in 15-meter-wide plantings of 

 American beachgrass was 8.3 cubic meters per linear meter during seven growing 

 seasons. Dune height increased an average of 0.25 meter per year. These are 

 similar to growth rates reported for North Carolina. 



e. A 15-meter-wide planting, three to five sprigs per hill and 90 cen- 

 timeters between hills, formed a dune 2.0 meters high and 96 meters wide at 

 the base in seven growing seasons. The 90-centimeter spacing is both econom- 

 ical and effective. 



f. Foot and vehicular traffic can damage American beachgrass plantings 

 and prohibit growth in footpaths and wheel tracks, thereby reducing or pre- 

 venting sand accumulation. 



2. Sand Fence . 



a. Multiple lifts of sand fence are effective for dune building on Cape 

 Cod. 



b. Four lifts of straight sand fence trapped sand at an annual rate of 

 9.0 cubic meters per meter of beach over a 5-year and 5-month observation 

 period. 



c. Four lifts of straight fence formed a dune 3.0 meters high and 30.2 

 meters wide in 7 years. 



d. Adding side spurs to straight fencing does not measurably improve 

 long-term fence performance and increases construction costs by about 20 

 percent. 



3. American Beachgrass Versus Sand Fencing . 



a. American beachgrass plantings trap little sand during the first 

 growing season. Sand fences initially trap sand at a high rate, about 11.9 

 cubic meters per meter. 



b. American beachgrass plantings, once established, trap sand at a rate 

 comparable to multiple lifts of sand fence. 



33 



