These were surveyed on 3 August 1980 just prior to Hurricane Allen by Chaney, 

 Williges, and Taylor (1980). The latter three surveys began at the crest of 

 the foredune and continued to the shoreline on the beach. Because the latter 

 surveys were not referenced to MSL, the crest elevations with respect to MSL 

 of the March 1981 survey were used to estimate the crest elevations of the 

 August 1980 survey. With this approximation the beach elevation (where the 

 surveys were terminated) was determined to be approximately 0.6 meter below 

 MSL. 



3. Vegetation . 



In August 1975, August 1976, and July 1981 vegetation transects were made 

 in the five experimental dune areas. The following transects were placed 

 paralleling the beach: a 60-plot transect on the seaward slope of the 

 foredune, a 60-plot transect on the landward slope of the foredune, a 40-plot 

 transect 8 meters landward of the dune, a 40-plot transect 38 meters landward 

 of the dune, and a 40-plot transect 69 meters landward of the dune. A 

 133-centimeter-diameter circular plot with an area of 1 square meter was used. 

 Frequency and cover data were recorded in each plot (App. B) . Cover 

 classes recorded were: 1, to 1 percent; 2, 1 to 5 percent; 3, 5 to 25 

 percent; 4, 25 to 50 percent; 5, 50 to 75 percent; 6, 75 to 90 percent; 7, 95 

 to 99 percent; and 8, 99 to 100 percent. An importance value (IV) was 

 computed by multiplying cover times frequency. 



IV. RESULTS 



Hurricane Allen's effect on north Padre Island's foredunes built from the 

 1969 to 1973 test plantings was less severe than expected. The storm caused 

 erosion of the seaward face of the dunes (including the naturally formed ones) 

 leaving a nearly vertical face, but it breached only one dune (the 335-meter 

 bitter panicum dune) (Fig. 5). A second hurricane impact was the total 

 destruction of the hummock dunes that had formed seaward of the experimental 

 foredunes (Fig. 6). Even major accumulations of sand due to vegetation 

 growing on a 6.5-kilometer segment of the beach reserved for pedestrians were 

 removed during the storm (Fig. 7). These were the more obvious hurricane 

 impacts. However, a comprehensive understanding of the beach and dune system 

 and its response to severe coastal storms can be gained from an analysis of 

 the long-term data available on this area. This report deals mainly with the 

 beach and dune changes over time, mostly during the past 6 years, and 

 particularly as affected by Hurricane Anita in 1977 and Hurricane Allen in 

 1980. 



1. Sand Volume. 



a. Mean Sea Level Inland 200 Meters . From the Padre Island surveys, 

 sand volumes were computed several ways to show the dynamics of the sand 

 accumulation and redistribution. First, consider the total sand volume from 

 MSL inland through that part of the beach normally occupied by the foredunes. 

 A 200-meter segment was used; the seaward side, 108 meters was designated the 

 beach segment, and a 108- to 200-meter segment was designated the foredune 

 segment (Table 2; Figs. 8 to 12). Because the March 1981 surveys were made 

 about 7 months after Hurricane Allen, only the 335-meter bitter panicum dune, 

 which was breached during the storm, showed a net loss of sand. Therefore, 

 for a hypothesis as to what actually occurs on a beach during a hurricane, the 



18 



