RAPID: Measuring Freshwater Exports from Galveston Bay After Hurricane Harvey-
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abstract
The unexpected and unprecedented flooding in Houston caused by Hurricane Harvey poses several human health and coastal ecosystem risks due to toxins remobilized by the floodwaters and severe modifications to salinity of regional coastal waters. Following the extreme flushing event, the salinity of Galveston Bay was set to near zero, an extreme condition that can impact the ecosystem and biodiversity of the area. The goal of this project is to understand how Galveston Bay and the adjacent coastal waters respond to this extreme freshwater forcing event. Time-critical measurements of currents, temperature and salinity will be undertaken at various locations within Galveston Bay and offshore, and at three different times following the flooding event. The measurements will allow: (1) quantification of residence time of Galveston Bay; (2) characterization of salinity structure within the bay; and (3) identification of the salinity structure and extend of the offshore plume from Galveston Bay. Analysis of the data will assist in establishing the time scales required for the reintroduction of salt into Galveston Bay, following the extreme flushing event that reset the Bay?s salinity to near zero. Through the new and timely observations generated by this proposal, a more accurate prediction of baroclinic circulation, which controls transport and fate of pollutants introduced into flood waters will be achieved. Thirteen superfund sites were flooded by this event; chemical plants were compromised; automobiles and households were inundated; and, unknown amounts of resuspension may have exposed buried contaminants. The results of this study will provide an understanding of the fate of these chemicals in the aquatic ecosystem. The data collected will be instrumental in testing and improving numerical models using extreme conditions, thus allowing for better and more accurate predictions. The observations in combination with a numerical modeling suite that will quantify and predict circulation and tracer concentrations in the region will serve as a template for coastal managers to create a nowcast/forecast system for future extreme events. Theory suggests that the net mixing that occurs across a near-field or tidal plume is scaled by the density difference between the outflow and receiving waters and is proportional to the discharge. These variables are also often confounded, since high discharge is associated with fresher estuarine outflow. Hence, a large density difference between the estuarine outflow and receiving waters is expected. Since there has been significant rainfall runoff throughout coastal watersheds up coast of Galveston Bay, and because of the position of the Mississippi/Atchafalaya plume, the receiving waters offshore of Galveston Bay are expected to be very fresh. At the same time, the discharge from the Bay is still quite high. This offers a unique opportunity to examine a large near-field, river plume (the outflow from Galveston Bay) dynamics, in a high discharge scenario with much smaller density anomalies than those typically observed. Such conditions will allow the discharge and density anomaly effects on the near-field mixing and tidal plume dynamics to be disentangled.
