Recent Rates of Shoreline Erosion at Sargent Beach Matagorda County, Texas

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Date

1991

Authors

Morton, Robert A.

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The Gulf shoreline at Sargent Beach, Texas, is the most rapidly eroding open coast shoreline in the State and one of the most rapidly retreating beaches in the Gulf of Mexico. Because the Gulf Intracoastal Waterway (GIWW) is so close to the Gulf shoreline along this ten-mile coastal segment, continued erosion will breach the Waterway in the near future and preclude navigation through the GIWW unless preventive action is taken. Protecting the Waterway is of paramount importance considering the large negative economic impacts that would occur if the Waterway were even temporarily closed. A study was conducted to determine the recent rates of erosion at Sargent Beach and to evaluate the factors that control erosion of this beach. Results of the study demonstrate that erosion at Sargent Beach accelerated after 1930, and recent rates of erosion generally are consistent with the higher rates recorded after 1930. Erosion rates increase from northeast to southwest, and the highest erosion rates since 1965 consistently occur in the developed area east and west of State Road 457. Within this segment of rapid beach erosion, the highest measured rates between 1987 and 1991 ranged from 51.6 to 67.3 ft/yr, where the Gulf shoreline intercepted a dredged canal and encountered a former artificial inlet between the Gulf and the GIWW. Since 1974, the width of land between the high water line of the Gulf of Mexico and the south bank of the GIWW has rapidly decreased at some sites as a result of both beach erosion and bank erosion along the GIWW. Recent rates of beach erosion along the Gulf shoreline have depended on storm frequency and intensity as well as on changes in the volume of sediment transported by waves and currents in the Gulf of Mexico. Future erosion rates will probably be similar to the most recent rates unless a major hurricane strikes the area causing a rapid increase in erosion or the sand supply is altered by human activities. Placing sand directly on the beach (beach nourishment) or bypassing sand around the San Bernard River would likely reduce erosion at Sargent Beach, whereas interception of the littoral material by dredging at the San Bernard River mouth or by placing structures perpendicular to the Gulf shoreline would prevent sand from reaching the downdrift coastal segment and would increase erosion at Sargent Beach.

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