ABSTRACT: Coastal Land Loss in Texas--An Overview

Robert A. Morton, Jeffrey G. Paine

Each year in Texas more than 1500 acres of prime real estate and productive wetlands are destroyed along the Gulf shoreline and near the bay margins primarily as a result of coastal erosion and submergence. Wetland losses constitute about half of the total land losses. Historical analyses of maps and aerial photographs since the mid-1800s 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 since the modern sea-level stillstand 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 coas .

Erosion is primarily caused by high wave and current energy combined with an inadequate supply of sediment. Erosion is responsible for higher local rates of land loss than submergence, and the erosion losses are more perceptible, especially after major storms when the greatest losses occur.

The principal components of submergence are subsidence and the eustatic rise in sea level. Together these components are recorded by tide gauges as a relative 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 and bayhead deltas and within entrenched valleys. Although compactional subsidence is a natural process operating in the Gulf Coast basin, most of the accelerated land-surface subsidence in Texas is attributed to extraction of shallow ground water or production of hydrocarbons at moderate depths. Faults activated by the withdrawal of these fluids concentrate the subsidence near the fault planes.

Coastal land losses caused by dredging (marinas, canals, rig locations) are less than those caused by erosion and submergence, but they constitute a growing percentage of total land losses.

AAPG Search and Discovery Article #90999©1990 GCAGS and Gulf Coast Section SEPM Meeting, Lafayette, Louisiana, October 17-19, 1990