A Comparison of the Near Bottom Current Velocity Characteristic at Two Gulf Brine Disposal Sites Based on Long Term Current Measurements

The Strategic Petroleum Reserve Office of the Department of Energy is currently disposing of brine at two sites in the Gulf of Mexico, one off Freeport, Texas and the other off Cameron, Louisiana. Texas A&M University has been collecting physical oceanographic data as part of a multidisciplinary environmental study of each site to determine the impact of the discharge of the brine. The monthly hydrographic surveys and the time series of current veolcity, temperature and salinity from in situ recording current meters now form the largest and longest running public domain data base of such measurements for the Texas and Louisiana inner continental shelf regions. This paper describes the data base which is available for each site, and as an example of the use of such data for pollution studies it characterizes the current regime in the near bottom layer at each site. The characteristics are quantified using the dimensionless parameters developed by Gaoury and Stolzenbach (1979) which indicate the relative importance of mean, residual and tidal advective transport processes to turbulent diffusion. Previous estimates of these parameters for these sites have had to utilize synthetic currents or currents from other coastal areas. The results show that in the near bottom layer at Bryan Mound the mean and residual components of current are generally large compared to the tidal component and to diffusion, while at West Hackberry they are smaller and the tidal component is larger. This implies that, in general, the pollutant plume can be expected to be more elongated at Bryan Mound and more radially symmetric at West Hackberry. Some less frequently occurring conditions, such as periods of stagnation and strong vertical stratification and their effect on the plume pattern are also discussed.