Abstract: LANDSAT Study of Nearshore Circulation Off Aransas Pass, Texas

Robert J. Finley, Robert Baumgardner, Jr.

LANDSAT multispectral-scanner images in the visible red band readily reveal variations in suspended-sediment concentration in coastal waters. Using this turbidity as a natural tracer, the nearshore surface-water circulation in the Gulf of Mexico off Aransas Pass, Texas, was examined for 14 scenes from 1972 through 1976, and correlated with tide-gauge records, wind-velocity and direction data, wave observations, and predicted tidal-current velocities.

Aransas Pass is a stabilized inlet with jetties extending 1.25 km seaward on either side. These structures control the observed turbid plumes by: (1) limiting expansion of ebb-tidal effluent to beyond the zone of inshore wave-generated turbidity, and (2) diverting inshore turbid waters seaward to be mixed with the ebb-tidal flow. Bay-derived ebb water may be as turbid or much less turbid than inshore water and, in the latter case, plumes up to 6 km long result from entrainment by the ebb flow of turbid jetty-diverted inshore water. The best developed plumes of turbid-inlet effluent form clockwise gyres up to 8.1 km long and correlate with the greatest tidal elevation drops (0.64 m) and effective northerly winds. During times of weak or flood currents only small patches of low turbidit were observed in the gulf.

These results indicates that LANDSAT imagery offers a synoptic overview from which the circulation of inlet effluent and jetty-diverted inshore waters can be inferred for an area rarely covered by aerial photography. Such data can supplement as well as aid in the planning of environmental-impact studies at sites of hydrocarbon production and transportation.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC