Abstract: Nearshore Current Pattern Off South Texas--Interpretation from Aerial Photographs

R. E. Hunter, G. W. Hill

Current patterns in a zone 4 km wide along the South Texas coast were interpreted from aerial photographs taken by NASA on December 23, 1968, during a period of moderate northerly winds. An ebb-tidal plume of turbid water was developed unusually well at Aransas Pass. Another mass of turbid water along the coast south of Aransas Pass was probably the preceding ebb-tidal plume, which had become separated from the inlet and was drifting with the coastwise current; its position indicated a speed of 15 to 20 cm/sec.

Still farther southward, a linear pattern of turbid and less turbid bands suggested the development of Langmuir circulation cells whose axes were nearly parallel with shore. Lines of floating debris in a few of the less turbid bands probably defined the surface convergences of the circulation; the more turbid bands, therefore, probably represented water rising from near the bottom. The spacing between convergence lines was about 10 times the water depth; the cells thus were greatly flattened compared to cells in deep water.

Coverage of the nearshore zone on two flight lines showed that small features of the turbidity pattern remained recognizable after 25 minutes. The currents measured from the movements of these features were nearly parallel with shore, increasing from about 17 cm/sec in a zone 600 to 1,300 m from shore to about 37 cm/sec at 300 m from shore; the shoreward increase in the nearshore zone probably was caused by wave-driven longshore currents. Rip-current plumes, which extended to a distance of 600 m from shore and were migrating alongshore, were deformed by the longshore current shear so that they appeared to extend obliquely offshore in an updrift direction.

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