POSTHURRICANE SURVEY OF EXPERIMENTAL DUNES ON 

 PADRE ISLAND, TEXAS 



by 



B.E. Dahl, P.C. Cotter ^ D.B. Wester^ and D.D. Drbal 



I. INTRODUCTION 



Flood damage from hurricanes is a major concern to inhabitants of the 

 Texas gulf coast. Barrier islands, such as Padre Island, provide significant 

 protection against high water through the damming effect of foredunes, which 

 form parallel to the beach. Where these foredunes have eroded, storm surges 

 transport sand inland from the beach onto lowland vegetation and into lagoons, 

 where it accumulates on roads and in navigational channels adjacent to the 

 islands. After the severe flooding from Hurricane Carla in 1961, the mainland 

 residents requested restoration of these natural dunes on Padre Island. 



From 1968 to 1974 the U.S. Army Coastal Engineering Research Center 

 (CERC) supported research to define propagation' and transplanting techniques 

 with beach grass to construct and rehabilitate these coastal foredunes (Dahl, 

 et al. , 1975). The data collected included information on changes in dune 

 dimensions and beach topography, encroachment of indigenous flora, and 

 comparisons with naturally occurring foredunes. During these studies, several 

 foredunes were shaped from test plantings on the north and south ends of Padre 

 Island (Fig. 1). On completion of the initial contracts, CERC continued 

 monitoring the foredunes formed from the beach-grass plantings on north Padre 

 Island beaches in 1975 and 1976 to evaluate the long-term performance and 

 effects of the foredunes (Dahl and Goen, 1977). 



Hurricane Anita struck the coast of northern Mexico in August 1977, 

 causing substantial foredune erosion on south Padre Island. The storm caused 

 significant reorientation of sand even on north Padre Island beaches, but it 

 did not damage the experimental foredunes of north Padre Island. This was the 

 only major storm affecting Padre Island beaches since the original test 

 plantings were made from 1969 to 1973 and the cross-sectional profiles were 

 resurveyed in September 1977. On 9 and 10 August 1980, Hurricane Allen 

 violently struck the Texas coast, entering the mainland between the Mansfield 

 Channel and Kingsville (Fig. 1). South Padre Island, which has lower 

 elevations than north Padre Island, was dramatically altered with frequent 

 overwash channels. The storm substantially damaged the Padre Island National 

 Seashore Malaquite Beach facilities on north Padre Island, significantly 

 altering beach vegetation and eroding the beach face of foredunes, with the 

 hurricane-generated waves breaching the island's dunes in many instances. 

 This report summarizes the impact of Hurricane Allen on the dune 

 configuration, sand yardage accretion or erosion, and changes in the 

 vegetation on four experimental foredune sections and one unplanted section 

 within the boundaries of the Padre Island National Seashore. This was 

 accomplished by comparing the 1981 posthurricane surveys with those of 

 1975-77. 



