Numerical Model Development
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.
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
SMAST's Finite Volume Model
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.
Like any computer application, the effectiveness of
the MHBNL numerical model is highly dependent on the quality of data used
for the model. Below are some examples of data that are used to initialize
and drive the computer simulation.
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.
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.
Figure 5: Initial
conditions used for MHBNL model runs.
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.
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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