Table 5. Growth characteristics of American 

 beachgrass planting, plot 3 (60- 

 centimeter spacing), 1970-77. 



Parameter 



Time Interval by 

 growing season 



Value 



Sand accumulation 



One^ 

 Two 3 

 Seven 



20.0 m3/m 

 31.3 m3/m 

 51.3 m3/m 



Increase in 

 crest elevation 



1* 

 One 



Two 5 



Seven 



0.7 m 

 1.1 m 

 1.6 m 



Dune slope 

 Landward 

 Seaward 



Seven 

 Seven 



1 on 21.2 

 1 on 29.7 



5 

 Base width 



Seven 



81.7 m 



^Volume calculated for an area 23 meters landward and 

 seaward of plot centerllne for profile line 6; no data 

 available on profile line 5 for this survey period. 



^Volume calculated for an area 23 meters landward and 

 seaward of plot centerllne; average of profile lines 5 and 5. 



^Volume calculated for an area 30.5 meters landward and 

 seaward of plot centerllne; average of profile lines 5 and 6. 



Calculation based on profile line 6. 



^Average of profile lines 5 and 6. 



1972 (fourth lift). In April 1972 after the fourth lift had filled with sand, 

 the plot was planted with American beachgrass on 60-centimeter centers, three 

 to five sprigs per hill. This fence plot sustained little damage during the 

 experiment. 



b. Short-Term Dune Growth . The first lift of fence trapped approxi- 

 mately 12.5 cubic meters per meter by January 1971 when the second lift was 

 installed. After 1 year, a total of 21.3 cubic meters per meter had been 

 trapped by the first two lifts (Fig. 16). By May 1973 the four lifts of 

 fencing in combination with the beachgrass planted in April 1972 had trapped 

 42.5 cubic meters per meter. Figure 17 shows the plot in May 1973, 30 months 

 after initial installation. 



c. Long-Term Dune Growth . Figure 18 illustrates the continued growth of 

 the straight fence dune through November 1977. Although the crest elevation 

 continued to increase, there was little net accumulation after October 1972. 

 In general, the dune became progressively narrower due to erosion of the 

 shoreline. By 1977, crest elevation was 3.1 meters above the plot elevation 

 in 1970. Dune width was only an average of 30.1 meters and the landward and 

 seaward slopes of the dune were a steep 1 on 5.8 and 1 on 4.3, respectively. 

 The seaward shore retreated approximately 21.0 meters during the 8 years of 

 observation. 



d. Performance Summary. Table 6 summarizes dune development from 1970 to 



1977. 



24 



