Table 55 



Sand accumulation for south Padre Island dunes. 













Month of survey 



Location 



1969 



1970 



1971 



1972 



1973 



1974 





June 



Dec. 



Apr. 



Sept. 



Jan. 



Mar. 



July 



Dec. 



Apr. 



Dec. 



May 



Jan. 



Sea oats beach planting, 



February 1969 



(south 400-foot north section) 



-1.5 



2.2 



4.0 



5.9 



7.5 



7.2 



8.1 



10.8 



11.8 



15.9 



16.9 



17.2 



2-foot-high picket fence 

 (four parallel rows) 

 Pass No. 3 2 





















3.1 



3.1 



5.4 



4-foot-high picket fence 

 (two tiers) 

 North Section Fence 

 1,200 to 1,600 feet 3 



-1.0 



2.7 



3.3 



4.6 



6.2 



5.8 



7.3 



10.8 



11.0 



11.0 



11.8 



12.7 



1. Sand accumulation in cubic yards per linear foot of beach; each is the mean of two profiles. Data courtesy of 

 U.S. Army Engineer District, Galveston. Sand-fence data part of a separate Corps of Engineers study. 



2. Fence constructed in November 1971 was filled with sand by winter 1972—73; planted with sea oats and 

 bitter panicum in monthly increments from November 1972 to July 1973. 



3. Barren dune planted February 1973 after fences were filled. Sand accumulation in this section was above 

 average for the 1-mile long North Section fence experiments. 



potential capacity. These authors concluded that where annual sand movement was 3 cubic 

 yards per linear foot of beach per year, a 35- to 40-foot-wide planting would trap all the 

 available sand. 



The 1,200-foot dune-width bitter panicum planting showed that the main limitation to 

 dune growth in this area was not the capacity of the plants to trap sand, but the amount of 

 blowing sand available to be trapped. For some reason, this amount was variable, even 

 within similar areas of the same planting. For example, the north 400 feet of the 1,200-foot 

 sea oats dune received considerably less sand than the middle and south 400-foot sections, 

 and consequently grew at a slower rate (Fig. 46). The north half of the 1,100-foot bitter 

 panicum dune initially grew faster than the south half, but now both are nearly equal 

 (Fig. 47). The dune-width panicum plot is growing at a more uniform rate, despite 

 differences in survival between the north and south halves. 



A longitudinal profile along the crest of a section of the 1,200-foot sea oats dune 

 (Fig. 48) shows the relative uniformity. This profile was surveyed in July 1974, and 

 continued sand accumulation has resulted in increased elevations compared with previous 

 figures and text from a March 1974, survey. In early stages of growth, this dune exltibited a 

 tendency toward hummocks (peaks and troughs) which now have largely filled. Tliis was a 

 characteristic of monospecific sea oats plantings with relatively low survival, whereas bitter 

 panicum dunes usually had a more uniform longitudinal profile even in early growth stages. 



c. Dune Growth: Lateral Spread of Vegetation. Cross-sectional profiles of an American 

 beachgrass dune in North Carolina (Savage and Woodhouse, 1968) showed that most sand 

 was trapped at the front of the dune, and vegetation expanded 40 feet shoreward and 20 



151 



