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Historical Shoreline Changes and Their Causes, Texas Gulf Coast (1)
Robert A. Morton (2)
Sequential shoreline monitoring, using vintage charts and aerial photographs, documents temporal and spatial variations in historical Gulf shoreline changes. The regional distribution of shoreline erosion and accretion largely reflects changes in littoral drift cells, decreases in sediment supply, and continuing relative sea-level rise including compactional subsidence. A Late Quaternary (circa 3500 BP) shoreline is postulated with promontories at the Holocene Brazos-Colorado and Rio Grande deltas; a third promontory along the upper coast was probably related to a Pleistocene delta system and the Sabine Arch. The interheadland areas or bights were the locations of littoral drift cells and the sites of accretionary shoreline topography primarily on barrier islands and peninsulas. Historical records (past 125 years) indicate that the deltaic headlands have experienced long-term erosion at relatively high rates. With changes in littoral drift cells, natural net shoreline accretion, supplied primarily by updrift erosion, has been generally restricted to Matagorda Island and central Padre Island in the extant zone of convergence. Short-term (past 5 to 10 years) changes are predominantly erosional with more than 70 percent of the shoreline experiencing land losses totaling about 400 acres annually.
Shoreline erosion is caused by the complex interaction of climate, sediment budget, coastal processes, relative sea-level conditions, and human activities. Jettied inlets and navigation channels serve as the greatest sediment sink, and in certain areas major shoreline changes are clearly the result of human alterations. Rates of erosion and the total length of eroding shoreline have increased during historical time. Present data indicate that most of the Texas Coast will continue to retreat landward as part of a long-term erosional trend.
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