Field observations of currents and circulation in the Houston Ship Channel.




Ward, G.H., Jr.

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The Houston Ship Channel is a dredged canal traversing Galveston Bay and linking Houston with the Gulf of Mexico. The lower reach of the confined portion of the Houston Ship Channel (that above Morgans Point) follows the main riverine system of the San Jacinto River. In this 17 km reach, during the period 13-19 September 1976 a series of detailed hydrographic measurements were executed continuously for several tidal cycles, with the objective of characterizing the low-flow tidal-mean equilibrium circulation regime. The measurments consisted of current velocity profiles, salinity and temperature profiles, and profiles of flourescent dye concentration from a continuous release at Morgans Point for the specific purpose of tracing water movement. The current structure in the Channel was processed to expose its various components, viz. tidal and short-period currents, tidal flows (resulting from the long-term rise and fall of water level in the system), and density currents. The density current, driven by the longitudinal gradient in salinity is most important from the standpoint of long-term transport, since it is a persistant component of the current structure, present throughout the tidal cycle. Behavior of the currents during the study period is reviewed particularly with respect to hydrometeorological influences. The tidal current is found to dominate the current speed, though the density current approaches the speed of the ebb race and near slack forces a vertical reversal in current. The throughflow is at least an order of magnitude less than the tidal component and virtually negligible insofar as current speeds are concerned. Responses of the currents to transient events (an intense thunderstorm and a forced external wave) are noted.


39 p.


navigational channels, dredging, ship canals, water currents, water circulation, hydrography