chapter  9
17 Pages

Geomorphic Processes and Land use Planning, South Texas Barrier Islands

WithChristopher C. Mathewson, William F. Cole

Barrier islands are active geomorphic areas that are also highly desirable development sites. Two basic classes of processes affect these areas: (a) hurricanes and storms, which are irregular, intermittent events; and (b) shoreline and aeolian processes, which are regular, daily processes. The intermittent events can drastically alter the island in a short time period, whereas the daily processes gradually modify the island. Land use planners and developers rarely consider the active processes or the impact of altering the geomorphology of the island. Studies conducted along separate areas of Padre Island, Texas, suggest that active geomorphic processes are different for each site. A study of the natural alteration of a part of the Padre Island Natural Seashore, using historical aerial photographs, shows that the island geomorphology follows a predictable cycle. The cycle is initiated when a hurricane breaches the foredune ridge. The resulting major foredune breach gradually heals as isolated dunes coalesce except at the downwind end where an aeolian chute forms. The chute funnels aeolian sand through the foredune ridge, forming an aeolian fan and back-island dune field. This aeolian transport system may exist for as long as 30 years. Eventually the chute closes and the island returns to pre-hurricane conditions. Land use decisions should contend with both irregular events and daily processes. It is impossible to predict where the next hurricane will strike, thus structures should either be designed to withstand the storm or as sacrifice structures. Once a hurricane breach forms, however, the location of the resulting aeolian fan can be predicted and the effect of aeolian transport can be incorporated into land use plans. Historical air photography of South Padre Island shows that hurricanes alter island geomorphology predictably and that daily processes do not effectively change this alteration. Hurricane hazard zones could easily be considered in land use plans to ensure responsible development of the area. To date, development on South Padre has disregarded the active coastal processes: residential zones have been built in washover channels, portions of the foredune ridge have been removed for hotel construction, construction siting has disregarded shoreline erosion, and aeolian sand is being removed for fill on the mainland. To maximize protection: from storm surge and scour, commercial structures should be founded on deep piles and located behind the foredune ridge; from washover channel erosion, channel sites should be maintained to relieve erosive pressure from the foredune ridge; from flooding, residential structures should be located on back-island areas away from washover channels. With low cost and little effort, geologic input can be incorporated into any plan and can make the barrier island a safer place to live.