Flows, Stages, and Salinities: How Accurate is the SICS Integrated SurfaceWater/Ground-Water Flow and Transport Model?
Christian Langevin, Eric Swain, and Melinda Wolfert
U.S. Geological Survey, Center for Water and Restoration Studies, Miami, FL,
USA
The Southern Inland and Coastal Systems (SICS) model was developed by the
U.S. Geological Survey to simulate flows, stages, and salinities within the area
surrounding Taylor Slough and northeastern Florida Bay. The SICS model
consists of a two-dimensional hydrodynamic surface-water flow and transport
model coupled to a three-dimensional variable-density ground-water flow and
transport model. A description of the computer code used for the simulations is
described in a companion abstract included in these proceedings. The current
version of the model represents a 5-year period from January 1995 to December
1999. Comparisons between observed and simulated values of flow, stage, and
salinity suggest that the model provides a good representation of the physical
system; and that, with some additional effort, the model could be used to evaluate
the hydrologic effects of the Comprehensive Everglades Restoration Project
(CERP) on the coastal wetlands and northeastern Florida Bay.
Water-level hydrographs are useful ecological indicators because they can be used
to calculate hydroperiod, which is the number of days per year with standing
water. Within the Taylor Slough area, the SICS model seems to provide an
accurate description of water-level fluctuations. Figure 1 compares measured and
simulated stage for monitoring station TSH in central Taylor Slough. The mean
absolute error in simulated water level for the 5-year period is 0.06 meters. The
average hydroperiod at TSH calculated by the model (259 days) compares to
within 2 percent of the hydroperiod calculated using measured data (255 days).
Trout Creek is the major outlet for freshwater flow from the coastal wetlands into
northeastern Florida Bay. An advantage of using a fully hydrodynamic surfacewater model instead of a simplified model that neglects the effect of wind, for
example, is that volumetric discharge (and thus salinity) in complex coastal
environments can be represented. For example, figure 2 shows the comparison
between measured and simulated discharges for Trout Creek. Flow is positive for
most of the simulation period, indicating discharge into Florida Bay. During
periods of southerly winds, however, brackish water from Florida Bay is forced
inland into the coastal wetlands. Although the current version of the SICS model
simulates total discharge at Trout Creek that is slightly higher than measured
discharge, figure 2 suggest the model is capable of representing overall discharge
trends. The ability to represent transport, and thus salinity patterns, is another
advantage to using a fully hydrodynamic surface-water model. Figure 3 shows
the comparison between measured and simulated surface-water salinities at the
mouth of Trout Creek. The mean absolute difference in salinity is 4.6 parts per
thousand.
The SICS model has the potential for providing the important link between the
managed hydrologic system of southeastern Florida and the Florida Bay estuary.
One of the current plans is to complete the coupling of the SICS model with the
South Florida Water Management Model (2x2). The linked SICS model could
then be used to determine the effect of alternative water management scenarios on
coastal wetland salinities and freshwater flows to Florida Bay.
Christian Langevin, U.S. Geological Survey, 9100 NW 36th Street, Ste. 107,
Miami, FL, 33178,
Phone: 305-717-5817, Fax: 305-717-5801, langevin@usgs.gov
Figure 1. Measured and simulated stage at the TSH monitoring site, located in
central Taylor Slough.
Figure 2. Measured and simulated discharge values for Trout Creek.
Figure 3. Measured and simulated salinity values for Trout Creek.