Abstract: Historical Shoreline Changes and Their Causes, Texas Gulf Coast

Robert A. Morton

Temporal and spatial variations in Gulf of Mexico shoreline changes were documented by sequential shoreline monitoring using vintage charts and aerial photographs. 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 3,500 years B.P.) shoreline is postulated with promontories at the Holocene Brazos-Colorado and Rio Grande deltas; a third promontory probably was related to a Pleistocene delta system and the Sabine arch. The interdeltaic areas were the locations of littoral drift cells and the sites of accretionary shoreline topography primarily on barrier islands and peninsulas. Historical records (125 years) indicate that the deltaic mainlands have experienced long-term erosion at relatively high rates. With changes in littoral-drift cells, natural net-shoreline accretion supplied by updrift erosion generally has been restricted to Matagorda Island and central Padre Island in the extant zone of convergence. Short-term (last 5 to 10 years) changes are predominantly erosional with more than 70% of the shoreline experiencing land losses totaling about 400 acres (160 ha.) annually.

Shoreline erosion is largely natural and 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. The available data indicate that most of the Texas coast will continue to retreat landward as part of a long-term erosional trend.

AAPG Search and Discovery Article #90967©1977 GCAGS and GC Section SEPM 27th Annual Meeting, Austin, Texas