ABSTRACT

Nearly 1,500 acres of prime coastal real estate and productive wetlands are destroyed each year in Texas along the Gulf shoreline, near bay margins, and within alluvial valleys primarily as a result of erosion and submergence. Wetland losses constitute about 75 % of the total land losses. Historical analyses of maps and aerial photographs indicate that land losses are accelerating and that human activities are either directly or indirectly responsible for the increased losses. Natural decreases in sediment supply have been exacerbated by (1) river basin projects that reduce the volume of sediment transported to the coast and (2) coastal structures and navigation projects that prevent redistribution of littoral sediments along the coast. Erosion, caused by high wave and current energy and an inadequate supply of sediment, is responsible for higher local rates of land loss than submergence. Erosion losses are also more perceptible, especially after major storms when the greatest losses occur. Boat traffic causes substantial erosion along some navigation channels. The principal components of submergence are subsidence and the eustatic rise in sea level. Submergence converts uplands to wetlands and wetlands to open water. These surficial changes occur mostly on the coastal plain, but are also observed on barrier islands, on bayhead deltas, and within entrenched valleys. Recent accelerated submergence is induced by extraction of shallow ground water or production of hydrocarbons at moderate depths. Faults activated by the withdrawal of these fluids concentrate the subsidence near fault planes. Coastal land losses directly caused by dredging (marinas, subdivisions, canals, rig locations) are less than those caused by erosion and submergence, but they constitute a growing percentage of total land losses in Texas.