Historical shoreline changes in Trinity, Galveston, West and East Bays, Texas Gulf Coast
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Changes in shoreline position occurring for more than a century provide estimates of the relative stability of shorelines and along the Texas coast, allow comparisons of shoreline changes before and after human modifications became significant. Documenting long-term shoreline movement in the Galveston Bay system (Trinity, Galveston, West, and East Bays), Texas Gulf Coast, included comparing topographic charts (dated 1850 to 1852) with aerial photographs (taken in 1930, 1956, 1974, and 1982), measuring shoreline movement, calculating the rates of change for particular time periods (1850-52 to 1982), and summarizing in tables and on maps the magnitude and rate of shoreline changes. Unprotected sediments forming the margins of the Galveston Bay system are modified by natural coastal processes and human activities, both of which can cause shoreline movement. These shorelines occur along steep clay bluffs, salt- and brackish-water marshes, and sand and shell beaches, at the base of moderate slopes composed mainly of sand, and in newly formed areas filled by dredged material. Despite the widespread use of shoreline protection measures, which began in some areas before 1930, approximately 78 percent of the shorelines within the Galveston Bay system retreated between the early 1850's and 1982. During this period, bay shorelines moved an average of 2.2 ft/yr landward, causing the loss of approximately 12.5 miles squared of land. Although the prevailing direction of shoreline movement remained the same through time, the rates of shoreline retreat increased from an average rate of 1.8 ft/yr before 1930 to 2.4 ft/yr after 1930. Shoreline attributes (orientation, wave fetch, and sediment type) determine shoreline response and consequent movement after changes in coastal conditions. Contributing to shoreline changes are (1) regional and worldwide climate, (2) local changes in relative sea level, (3) local alterations in sediment supply, (4) frequent and intense storms, and (5) human activities. Historical data indicate that increasing temperatures, rising sea level, subsiding land surface, decreasing sediment supply, recurring severe storms, and ongoing human activities all promote continued erosion of most Galveston Bay shore lines.