3. Dune Crest Elevation . 



Longitudinal surveys that paralleled the beach were made along the 

 crests of all the planted dunes. No definable dune existed in the unplanted 

 study area prior to 1981; therefore, no longitudinal survey was made until 

 that year. Figure 13 graphically shows the crest survey data. The 

 longitudinal figures are more revealing than the cross-sectional figures for 

 ascertaining the effective height of dunes. It is also easier to show where 

 relatively more sand is accumulating. The profiles also provide an instant 

 evaluation of the effectiveness of the overall dune-building research. 

 Although some low areas through the dunes begin to heal in time, some are 

 quite persistent and may require mechanical repair to completely heal", e.g., 

 most deep cuts present in March 1975 were still evident in August 1976 and 

 some were even still present in 1981. The repair of these low areas should be 

 further researched. Stacking bales of hay in the cuts and tying the bales to 

 the canyon walls with netting to reduce the wind velocity may help these areas 

 fill with sand. Some low areas have filled in naturally through time. The 

 one major breach occurring in the experimental dunes from Hurricane Allen 

 (Fig. 13) occurred in a relatively high area in the dune ridge. This would 

 suggest that changes in the beach and offshore zone during a storm may be more 

 important than the dune crest elevation in determining the location of 

 overwash events. 



4. Shoreline Changes . 



Hurricane activity has resulted in minimal long-term changes on the 

 shoreline protected by the study dunes as evidenced by total sand volumes. 

 However, immediately following a major hurricane, such as Hurricane Anita in 

 1977, 31.5 cubic meters per meter of beach was eroded from the beach segment 

 of the study dunes (Table 2). A part of the eroded beach sand was deposited 

 higher on the foredune segment, but most of it was transported seaward into 

 the gulf (Figs. 8 to 12). The wave and tide action apparently redeposited 

 this sand on the beach within a few months. Undoubtedly, Hurricane Allen 

 transported even more sand from the beach into the gulf than Hurricane Anita, 

 but the 7-month period between the hurricane and the survey allowed 

 redeposition of most of the eroded beach sand (Table 6). 



5. Naturally Formed Dunes versus Experimental Dunes . 



In studies made over the past 10 years, the existing dunes that survived 

 the hurricanes in the 1960 's were not monitored. However, a survey was made 

 on one cross section of a naturally formed dune in 1974 and remeasured in 1981 

 (Fig. 14). This cross section is about 91 meters north of the entrance to the 

 beach from the Ranger Station access road. Also, the Padre Island National 

 Seashore had a number of cross sections surveyed on north Padre Island on 3 

 August 1980, only a few days before Hurricane Allen. Although these latter 

 measurements do not include the landward side of the dunes, they do provide a 

 way to further estimate the meters accreted in naturally formed dunes. 

 Remeasurement was made of three of the transects that ran perpendicular to the 

 pedestrian segment of the beach, but having no vehicular use (Fig. 14; 

 Table 7). 



The 108-meter beach segment differed little in sand volume on 

 experimental dune areas with 123 cubic meters per meter and natural dune areas 



33 



