Mixing Salt Water with Fresh
Using Sensor Technology to Understand Estuarine Turbulence
The Mobile Array for Sensing Turbulence (MAST), a state-of-the-art sensor, designed to directly measure the turbulent characteristics of coastal and estuarine flows. Scully, with funding from The Beacon Institute, conducted a six-day field experiment in the Hudson River near Spuyten Duyvil in October, 2006.
What happens when salt water mixes with fresh water in an estuary?
Malcolm E. Scully, Ph.D., the Beacon Institute's first postdoctoral research fellow, is investigating answers to that question through a research fellowship at the Woods Hole Oceanographic Institution (WHOI) in Applied Ocean Physics and Engineering under advisor Rocky Geyer, Ph.D. Scully's research has focused on the physical processes that transport salt into an estuary, and direct measurement of the turbulence as salt water meets and mixes with fresh river water.
"This research helped to highlight how turbulent mixing can impact the basic circulation patterns of an estuary," notes Scully. "Understanding when and where mixing occurs is of fundamental importance to many estuarine processes, including contaminant exchange, nutrient availability, sediment transport and larval dispersal."
Scully combined numerical modeling with a six-day field study in the Hudson River using a newly developed turbulence sensor. The Hudson River modeling work built strongly on previous research by John Warner of the United States Geological Survey (USGS) and has been key to Scully's analysis of the physical mechanisms that drive the circulation.
The Hudson River-based field study employed the Mobile Array for Sensing Turbulence (MAST) - new, state-of-the-art sensor technology jointly developed by Rocky Geyer and John Trowbridge at WHOI. The MAST is equipped with instruments that measure the velocity and salinity of the water at high sampling rates and is deployed from a research vessel on a vertical 10-meter pole. Says Scully, "Our preliminary results from MAST suggest it will provide the unique ability to measure turbulent processes and improve our understanding of mixing in the Hudson and other estuarine systems."
Scully reports that despite its fundamental importance to estuarine research, few studies that directly measure turbulent mixing have been conducted in the estuarine environment. His preliminary results help to provide validation for the results obtained using the Regional Ocean Modeling System (ROMS), a three-dimensional numerical model for simulating oceanographic changes. Scully's research demonstrates the spatial and temporal variability of mixing and highlights the importance of mixing during the ebb tide. Scully's research has yielded several manuscripts currently being readied for publication in scientific journals.
Scully concludes, "The integration of innovative observational technologies with advanced numerical models should significantly improve our understanding of estuarine systems, vastly improving our ability to manage these valuable resources."
Rocky Geyer, Ph.D. of Wood's Hole Oceanographic Institute (WHOI) oversees the postdoctoral fellowship program with support from The Beacon Institute. Geyer was a sailor before he was a scientist, and he was long baffled by the complex swirls of currents that often wrecked havoc with his attempts at precision navigation. He had the good fortune to turn this fascination into a vocation, and has subsequently worked in many estuarine and coastal environments, including the Amazon outflow, the Po River outflow in Italy, the fjords and estuaries of the Pacific Northwest, the tidal channels of New England and Singapore, the Hudson River, the Eel River plume in northern California, and the western Gulf of Maine. Geyer's research includes a blend of observational process-studies and numerical modeling, directed both at basic research questions and applied problems of societal concern, such as harmful algal blooms and contaminant transport.
