HYDRODYNAMIC TRANSPORT IN A SHALLOW, MICRO-TIDAL SALT MARSH SYSTEM, BANGS LAKE, MS

During the summer of 2015, a NOAA led collaboration of state, federal, and academic institutions conducted a spill response exercise in Bangs Lake, MS, a shallow, stratified estuarine system with no river discharge that is a part of the Grand Bay National Estuarine Research Reserve (NERR). As a component of the exercise, an experiment simulating a phosphate spill was conducted by releasing fluorescein dye into surface waters and tracking the spread of the dye patch. In support of this effort, physical measurements of flow, temperature, and salinity were collected over a 3 day period and were used to develop and validate a numerical model of the system. The model was developed with the Environmental Fluid Dynamics Code and covers the Bangs Lake and Point aux Chenes Bay region of the system. Ebb flow patterns derived from the surface drifters were consistent with the modeling results, indicate a tidally dominated environment with highest velocities in Bangs Bayou, a narrow channel connecting Bangs Lake to Point aux Chenes Bay. The drifter clusters remained tightly grouped until they reached the bayou where clusters converged and formed a single line, suggestive of significant surface convergence, which was inconsistent with the expected secondary circulation patterns (i.e. differential advection generating surface divergence on an ebb tide). Furthermore, the model indicates that the tidal excursion associated with the ebb flow could allow material to exit the lake/bayou system, however weak dispersion in Point aux Chenes Bay results in significant portions of material re-entering the lake/bayou system. These findings have significant implications on short term (tidal time scale) spill response for shallow, micro tidal salt marshes as well as indicate that hazardous materials are like to have a long residence time in the local system where the spills occur.