Thursday, August 5, 2010

A circulation model to investigate the movement of wastes from an Open ocean aquaculture site

David W. Fredriksson*, James D. Irish, Dale A. Kiefer, Jack Rensel, and Frank OBrien

Department of Naval Architecture and Ocean Engineering,
United States Naval Academy
590 Holloway Road 11D, Annapolis, MD 21402
USA A numerical circulation study of the western Gulf of Maine was conducted to investigate the movement of wastes from an open ocean aquaculture site. To examine the hydrodynamics of the region, a domain was built with the ADvance CIRCulation model with Gulf of Maine bathymetry, shoreline, island and open ocean boundary conditions. At the open boundaries, the model was forced with dominant tidal elevation components, including the M2, S2, N2, K1, O1 constituents, representing possible low flow conditions. These conditions are with no weather forced or geostrophic currents to further diffuse and advect material from the site, but just the regular tidal motions. Model predictions were compared with surface elevation and Acoustic Doppler Current Profiler (ADCP) measurements from a moored instrumentation platform at the aquaculture site. At the site, the ADCP collected velocity data sets oriented in the east-west, north-south and vertical directions at nineteen, 2 meter depth bins. The data sets were processed to obtain the velocity tidal components and reconstructed to form a time series. The reconstructed time series was then compared with the model results. Differences between the model and measured results were on the order of cm s-1

The numerical flow values from the large model domain were then used as input to the program AquaModel. AquaModel is a GIS tool that provides three-dimensional simulation of growth and metabolic activity of penned fish as well as the associated flow and transformation of nutrients, oxygen and particulate wastes in adjacent waters and sediments. AquaModel can be used to examine both the near and far field affects of individual or clusters of fish cages. The information can then be used to effectively site new farms, evaluate operation techniques, and plan monitoring programs.

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