100-foot-wide strip. 



(b) A 2-£oot plant spacing with high transplant survival 

 (76 percent) gave a very uniform, tall, but narrow- 

 based dune. 



(c) Rows 4 feet apart with intermediate transplant survival 

 (36 or 18 percent if based on 2-foot rows) gave a less 

 uniform, lower elevation, but broader based dune than 

 the dune part constructed from 2-foot transplant 

 spacing. 



The longitudinal survey (Fig. 19) indicates that the effective 

 height of dune is considerably less for the south 600 feet of the 

 dune constructed with the 4- foot row spacings. Yet, the base of 

 this part of the dune varies from 65 to 100 feet (20 to 30 meters) 

 compared to a more uniform 75 -foot (23 meters) width for the north 

 600 feet. Effectiveness of the more variable, but broader based, 

 more "ragged topped" dune may be as good as the narrower more uniform, 

 taller north segment. If transplant survival of 40 percent or 

 greater is expected, there is no reason to double the plant material 

 required by using 2- foot row spacing. However, the 40 percent 

 survival is uncertain, so a safer way would be to stay with the 

 2-foot spacings. 



A more effective way to extend dune width than making an 

 initially wide planting is to allow a more narrow planting to grow 

 to some predetermined height, e.g., 12 feet (3.7 meters), then make 

 a second planting in front (seaward) . The dune-width extension area 

 was initially planted with bitter panicum in 1969. In April 1973, 

 a 50-by 400- foot strip of bitter panicum was planted immediately 

 gulfward of the earlier established dune. Figure 14 shows that 

 this dune has a base at least 125 feet wide and a mean elevation 

 of about 14 feet (4.3 meters). Figures 20 and 21 show that the 

 effective height is probably only 10 feet but the wider base should 

 allow this dune to be more effective in withstanding severe surges 

 with prolonged wave attack than the taller more narrow-based dunes. 



2. Rate of Sand Accumulation and/or Loss . 



Since beach sand volumes were not specifically measured during 

 the first phase of this study (Dahl, et al . , 1975) , several years 

 of data on which to determine rate of accretion or erosion was 

 unavailable. However, the net sand accumulation from August 1975 

 to August 1976 should provide an indication. For the study locations 

 monitored, the average new sand per linear foot of beach, at a 

 655 -foot distance inland, was 5.7 cubic yards. This was 1.4, 

 0.2, 11.0, 8.9, and 7.0 cubic yards (1.1, 0.2, 8.4, 6.8, and 5.4 

 cubic meters) for the unplanted, 1,200- foot sea oats, dune-width 

 extension, 1,100-foot bitter panicum, and 1,200-foot bitter 



50 



