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Lake Michigan Mass Balance
Hydrodynamics Model
The Princeton Ocean Model (POM; Blumberg and Mellor,
1980 and 1987) will be used to compute 3-dimensional current
fields in the lake. The POM will simulate large- and medium(km)-scale
circulation patterns, vertical stratification, and velocity distribution,
seiches, and surface waves. This model will also be used to simulate a
thermal balance for the lake, and will generate turbulent shear stresses
for the sediment transport model. The POM is a primitive equation,
numerical hydrodynamic circulation model that predicts 3-dimensional
water column transport in response to wind stress, temperature, barometric
pressure, and coriolis force. The POM has been demonstrated to accurately
simulate the predominant physics of large water bodies (Blumberg
and Mellor, 1983 and 1985; Blumberg and Goodrich, 1990). This
model will be used to develop year-long simulations on a 5-km horizontal grid with 15 sigma-coordinate vertical levels, at one-hour internals for Lake Michigan. Observed and simulated meteorological data will be used to define model forcing functions. Extensive measurements of temperature, transmissivity, and current distributions collected in Lake Michigan during 1982-83 will provide the necessary data for model confirmation; measurements of daily surface temperature (from satellite) and temperature, transmissivity, and current distributions will also be used to confirm hydrodynamic
simulations.
The hydrodynamic model is the appropriate transport foundation for an
accurate lake mass balance model, for a number of reasons. A confirmed
hydrodynamic model offers a credible basis for extrapolating transport,
in terms of forecasting the response to expected and extreme meteorological
forcing functions, that is desirable for a mass balance simulation. The
hydrodynamic model results are scaleable to provide transport predictions
at the desired spatial and temporal resolution. This is useful when considering
that the various processes incorporated in the mass balance are not
necessarily modeled at the same scale or resolution, yet all depend
upon a consistent transport simulation. In particular, the sediment
and contaminant transport model requires high resolution simulations of
current- and wave-induced shear stress to predict sediment transport.
Hydrodynamic models are also transportable, with little system-specific
parameterization in comparison to traditional water quality models. A
mass balance design based upon hydrodynamic transport is advantageous,
for instance, when considering applying the mass balance model for Lake
Michigan to the other Great Lakes.
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