Numerical Modeling

Numerical Model Development

 




Introduction


Figure 1:  Conceptual schematic of the MHBNL modeling system.

  • A major component of the Mt. Hope Bay Natural Laboratory (MHBNL) is the integration of models of the physical environment, ecosystem, and fish populations together with existing historical data sets, real-time data, and other data sets, to model the total Mount Hope Bay system.  The resulting Natural Laboratory Information System (NALIS) will allow MHBNL Scientists to conduct scenario testing of the impact of different stressors and natural sources of variation on Mt. Hope Bay.
 


Figure 2: Components of the MHBNL physical model.

  • An initial version of the model structure has been developed, along with algorithms for tidal forcing at the boundaries, initial conditions, and river and power plant discharges.  Calibration and sensitivity testing for these components is ongoing.
  • The MM5 meteorological model, which will provide more accurate wind forcing, and air-sea heat exchange to the main model, and the water quality model are currently under initial development.
 

SMAST's Finite Volume Model
Model Grid
Figure 3: Grid mesh for initial MHBNL model runs.

  • The MHBNL numerical model is constructed using the smast finite volume modeling system (chen et al, 2003).
  • This modeling system uses triangular grids to more accurately conform to complex coastlines.
  • The grid shown in Figure 3 has its finest horizontal resolution (on the order of 100 meters) within Mt. Hope Bay, with close to 7,000 grid points in the horizontal across the entire domain.  We are currently working towards increasing horizontal resolution in certain regions of Mt. Hope Bay to on the order of 10 meters.
  • Vertical structure is represented within the model by 20 grid points in the vertical at each horizontal grid point location.  The spacing of the vertical grid points varies across the domain as a function of the local water depth.
 

Input Data

Like any computer application, the effectiveness of the MHBNL numerical model is highly dependent on the quality of data used as input for the model.  Below are some examples of data that are used to initialize and drive the computer simulation.

PORTS map

PORTS data
Figure 4: Location of NOAA Physical Oceanographic Real Time Systems (PORTS) moorings that supply real time updates of hydrographic and meteorological data (top), and examples of available data. Note that wind data are taken from the Prudence Island station, and the remainder of the data are taken from the Fall River station.

  • Data from these stations and other locations (e.g., T.F. Green Airport in Warwick, RI, Buzzards Bay meteorological buoy NOAA NDBC Station BUZM3, etc.) are used to provide boundary conditions for the numerical model.The PORTS data is only available after late 1999, as shown in Figure 4, so other sources must be used for simulations of earlier periods.
  • Use of the MM5 meteorological model will provide a better system for incorporation of the wind and air temperature data into the MHBNL numerical model.
  • More information on the PORTS program can be found at the PORTS website.
 

Initial Conditions
Initial Conditions
Figure 5: Initial conditions used for MHBNL model runs.

The initial conditions shown in Figure 5 were based on salinity and temperature  transects performed by Hicks (1959) during the 1950s, a decade prior to the first unit of the Brayton Point Power Station going online.
 

Scenario Testing: Preliminary Results

  • Once operational, the model will be used to simulate alternative conditions in the Bay and to answer “what if” questions.
  • Here we show the difference in temperature resulting from the heated power plant discharge during late summer conditions.
  • Keep in mind that these results are preliminary, and should be taken as qualitative only. These results were generated with a preliminary version of the numerical model that, among other things, does not include air-sea heat exchange, and does not resolve processes within Mt. Hope Bay at horizontal scales comparable to that of the plume. Nevertheless the results provide a great qualitative representation of the effect of the heated discharge in various regions of the Bay.
Heat added by power plant.

Figure 6: Temperature and velocity difference between model runs with and without powerplant, using late summer conditions. Left panel shows surface difference, right panel represents bottom difference. Color scale represents temperature added by power plant, and arrows show the vector difference between velocities for each of the scenarios. Black line represents location of vertical transect shown in Figure 7. Click on image to open animation.

Figure 7: Vertical transect through temperature data of Figure 6. Click on image to open animation.


 

Looking forward . . .

The example above demonstrates the power of the modeling system that lies at the heart of the Mt. Hope Bay Natural Laboratory. This system can be an effective tool for probing answers to difficult questions through the use of scenario testing. As we move forward and continue development of the model, we will incorporate water quality parameters, and eventually biological parameters as well. This will allow us to ask “what-if” questions of ever increasing complexity. 

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The School for Marine Science and Technology
University of Massachusetts Dartmouth
706 South Rodney French Blvd, New Bedford, MA 02744-1221
(508) 910-8193 • FAX (508) 910-6371
Brian Rothschild, P.I: brothschild@umassd.edu
Changsheng Chen, MHBNL Modeling Program Manager: c1chen@umassd.edu

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