An SF₆ Tracer Experiment and Support Numerical Simulations in the Houston Ship Channel

NOAA's National Ocean Service (NOS) and Lamont-Doherty Earth Observatory of Columbia University, have designed and conducted a sulfur hexafluoride (SF₆) experiment in the Houston Ship Channel. SF₆ was released at the confluence of the HSC and Patrick Bayou, an EPA superfund site, to measure the dispersion characteristics of the upper Houston Ship Channel within the Port of Houston. Approximately 2 moles of SF₆ were released on 17 May and surface and vertical profiles were measured with a gas chromatograph over the period 17–26 May 2005. Initial measurements are provided and dispersion characteristics are presented. Numerical simulation results, which were performed prior to the experiment using the NOS Galveston Bay Operational Forecast System (GBOFS), were used to estimate the extent of tracer dispersion to plan the survey. The Bay and Channel hydrodynamic models within GBOFS were used to simulate the transport and dispersion of SF₆ over the ten day period, November 2–11, 2004, by adding two concentration algorithms to each model to simulate the movement of the passive tracer with and without surface gas transfer. The simulated water levels, currents, and density were compared with PORTS observations to quantify model accuracy. Model simulated tracer concentration distributions and the total tracer mass balance were studied. Residence time, turnover times of the injection cells, and exposure level and duration were computed. Areal extents of tracer concentration above background levels of 2 fmol L^–1 were determined to assist in the planning of the tracer release experiment. Surface gravity wave algorithms have been incorporated in both hydrodynamic models to simulate short period waves with and without wave-current interaction and indicate the feasibility of including the wave algorithms within GBOFS. In conclusion, plans for additional SF₆ data analysis and recommendations for additional SF₆ numerical simulations are discussed.