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Hurricane Allen caused erosion of the dune face of all the experimental 

 dunes, but caused a breach in only one dune. The beach elevations had returned 

 to approximately prehurricane heights by the time the area was resurveyed. The 

 unplanted control dune provided little resistance to waves generated by the 

 storm and a large quantity of sand was deposited inland. 



During the past 5 years the experimental dunes have accumulated sand at an 

 annual rate of 11.5 cubic meters per meter of beach compared with 9.3 cubic 

 meters per meter of beach for the unplanted control area. The higher annual 

 accumulation rate on the experimental dunes is due to the greater abundance of 

 vegetation. 



Vegetation on the experimental dunes apparently continues to spread seaward 

 at 1.5 to 1.8 meters per year. The total dune width has expanded 1.8 to 2.4 

 meters annually since 1976. There has been little invasion of other species 

 into the sea oats (Uniola paniautata) and bitter panicum {Paniawn amarum) 

 plantings, even after 8 to 10 years. Landward ground cover of the unplanted 

 control dune decreased from 28 percent in 1976 to 17 percent in 1981 due to 

 sand deposition on existing vegetation. Landward ground cover of experimental 

 dunes increased from 39 percent in 1976 to 56 percent in 1981, because the 

 foredune protected vegetation from storm waves and sand deposition. Also, 

 freshwater ponded behind the foredunes, creating a favorable habitat for 

 vegetation. The less salt-tolerant plants also benefited from the decreased 

 salt spray landward of the experimental foredunes. 



Vegetation on the backshore was eliminated during the storm, but rapidly 

 is becoming reestablished from residual perennial grass roots and rhizomes. 

 Foredunes on Padre Island dissipate hurricane-generated waves, thus lessening 

 water damage to the mainland; they are also major sand reservoirs, thereby 

 helping hold newly deposited sand. A large, midisland, unvegetated dune field 

 has migrated landward 27 meters per year since 1973. 



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