COASTAL MORPHOLOGICAL CHANGES RESULTING 

 FROM HURRICANE "AUDREY" 



by 



James P. Morgan 

 Louisiana State University 



Tropical hurricane "Audrey" crossed the Louisiana -Texas coastline 

 during the morning of June 27, 1957. The storm had winds in excess of 100 

 m.p.h. and raised tides of 12 feet in some areas. More than 500 people lost 

 their lives and property damage exceeded 150 million dollars. It was a major 

 hurricane by any standard. Considerable field work has been done in the 

 storm area by Coastal Studies Institute personnel over the past several years. 

 The Geography Branch, Office of Naval Research, sponsoring the field pro- 

 gram cooperated further by obtaining strip aerial photographs of the storm- 

 affected coastal region on July 15, 1957. 



Detailed comparison of before -and -after aerial photographs has made 

 possible an evaluation of hurricane induced morphological changes in this low 

 coastal region. More specific data have come from a series of nineteen sur- 

 vey stations located along the shoreline within the storm area. Beach profiles 

 made at these stations before the storm have been duplicated one or more times 

 since "Audrey's" passage. 



Morphological changes resulting from the storm are due both to effects 

 of wind and water but the latter is by far the most important agent. During 

 the height of the storm, Gulf waters inundated over 3000 square miles of salt 

 to brackish marshlands including the higher standing abandoned beaches of 

 the Chenier Plain of western Louisiana. Most morphological changes resulted 

 from wave action during the height of storm inundation. Shell -sand beach 

 ridges were eroded and flattened. Their sediments were reworked and re- 

 deposited in a low, flat band upon the marsh some distance inland. Average 

 figures are difficult to determine but a landward movement of the beach crest 

 amounting to 200-300 feet was not abnormal. Wave action was extremely 

 effective in reworking the shell-sand beach deposits, but not nearly so effect- 

 ive in eroding the finer-grained tidal marsh deposits underlying the beach 

 ridges. After the stornn a strip of re -exhumed marsh was left seaward from 

 the beach ridge. Immediate post-hurricane surveys indicated beach profiles 

 out of equilibrium with normal wave action. Resurveys at intervals of several 

 months establish that wave activity is causing gradual erosion of the re -exhumed 

 marsh deposits. As wave erosion continues, the shoreline retreats toward the 

 shell-sand beach material redeposited by the storm. The ultimate result, bar- 

 ring additional major storms, will be re -establishment of an equilibrium pro- 

 file between the shell-sand beach deposits, the underlying tidal nnarsh and 

 normal wave conditions. When such equilibrium is attained the shoreline in 

 the hurricane affected area will have retreated some 200-400 feet. 



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