1Christian D. Langevin,
1Eric D. Swain,
3John D. Wang,
1Melinda A. Wolfert,
2
Raymond W. Schaffranek, and
2Ami L. Riscassi
U.S. Geological Survey,
1Miami, FL,
2Reston, VA;
3Rosenstiel School of Marine and Atmospheric Science, Univ. of Miami, FL
The U.S. Geological Survey is actively involved in science
support for Everglades restoration. This paper summarizes
the development and application of two integrated surface-water/ground-water flow and transport models for the southern Everglades of Florida. Key points of this modeling effort
include the following:
•
The Southern Inland and Coastal Systems (SICS) model
represents hydrologic conditions for the Taylor Slough
area with 305-meter grid resolution.
•
The Tides and Inflows in the Mangroves of the
Everglades (TIME) model encompasses a larger area
than SICS, including both Taylor and Shark River
Sloughs, and uses 500-meter grid resolution.
•
The SICS model is fully operational and is being used
as part of the Florida Bay/Florida Keys Feasibility
Study (FBFKFS) to assess freshwater flows to
northeastern Florida Bay.
•
The TIME model is under calibration and is also being
used as part of FBFKFS to assess freshwater flows to the
Gulf of Mexico.
•
A procedure has been developed for running the coastal
flow and transport models with output from the South
Florida Water Management Model (SFWMM). This
procedure allows for the prediction of detailed coastal
wetland flows and salinities under various restoration
scenarios tested with the SFWMM.
•
Results from SICS and TIME are being used as input to
ecological models to predict the effects of Everglades
restoration on species populations.
Coastal wetlands are unique hydrologic environments
between inland freshwater systems and marine estuaries. The
development of methods and tools to understand and predict
hydrologic conditions within coastal wetlands has been limited
due to a lack of field data, and the complexity and number of
relevant hydrologic processes, such as tidal and wind forcing,
evapotranspiration, overland flow through emergent vegetation,
salinity-induced density-dependent flow, and surface-water/
ground-water interactions. In southern Florida, the need for
robust numerical methods to simulate coastal wetland hydro-logic processes, including the mixing of saltwater and freshwater within a coastal mangrove fringe, was motivated by the
ongoing effort to restore the Everglades and Florida Bay. In
response to the Comprehensive Everglades Restoration Plan
(CERP) to substantially increase flows through the Everglades,
the U.S. Geological Survey (USGS) and other agencies initiated
large research and data-collection programs to better understand coastal hydrologic processes and characterize baseline
pre-restoration conditions. One area that received considerable
attention was Taylor Slough—the main contributor of freshwater to northeastern Florida Bay. The large hydrologic database for the Taylor Slough area provided a unique opportunity
to characterize hydrologic processes through the development
of a numerical model.
In 1996, the USGS initiated development of the Southern
Inland and Coastal Systems (SICS) model (fig. 1). SICS was
originally developed to synthesize the large volume of field
data collected in the Taylor Slough area by improving upon
an existing hydrodynamic surface-water flow and transport
code; namely SWIFT2D (Leendertse, 1987), and using the
enhanced code (Schaffranek, 2004; Swain and others, 2004) to
characterize flow and salinity patterns in the coastal wetland
and adjacent Florida Bay estuary. As part of SICS development,
new algorithms were formulated for incorporating effects of
rainfall, evapotranspiration, wind sheltering, and the effect of
vegetation and microtopography on overland flow (Swain and
others, 2004). When applied to the Taylor Slough area, these
new methods substantially improved the ability of the model to
represent coastal hydrologic processes, particularly freshwater
discharges to northeastern Florida Bay and coastal wetland
salinities.
The USGS has continued to expand upon the initial SICS
modeling approach through: (1) scientific research to improve
the representation of hydrologic processes (for example,
surface- and ground-water interactions), (2) development
of the Tides and Inflows in the Mangroves of the Everglades
(TIME) model for Taylor and Shark River Sloughs (fig. 1),
and (3) application of SICS and TIME for Everglades restoration. The SICS and TIME models are continuously evolving as
new data are collected and the ability to represent hydrologic
processes improves. As the only hydrodynamic models capable
of simulating and predicting detailed flow and salinity patterns
in the southern Everglades, SICS and TIME show great promise
for the continued support of Everglades restoration.
U.S. Department of the Interior
U.S. Geological Survey
Printed on recycled paper
Fact Sheet 2004-3130
October 2004
Land
surface
Surface-water
system
81°30´
81°00´
80°30´
80°00´
Lake
Okeechobee
27°00´
Sediment layer
Ground-water
system
26°30´
aquifer
Seawater
Brackish water
26°00´
Fresh water
TIME ACTIVE
MODEL DOMAIN Shark River
Slough
SFWMM
GRID
25°30´
GULF OF MEXICO
OCEAN
Taylor
Slough
TLANTIC
area, but is also dependent on subsurface variations in fluid
density. Figure 3 indicates that leakage rates in some areas can
be similar in magnitude to rainfall, the primary source of water
within the SICS area. Daily average rainfall rate is about 0.4
centimeter per day. The magnitude of these exchanges supports
the general belief that surface-water and ground-water interactions in southern Florida must be accounted for in quantitative
hydrologic studies.
0 25 KILOMETERS
A
0 25 MILES
25°00´
Florida
Bay
SICS ACTIVE
MODEL DOMAIN
Base from South Florida Water Management District, Landsat TM Mosaic 1992-94
Universal Transverse Mercator projection, Zone 17, Datum NAD 27
R
oad
o
a
d
25°25
80°50´
80° ´
45
80° ´
40
80° ´
35
80° ´
30
80°25´
Map of southern Florida showing the active model domains
of SICS and TIME and the SFWMM grid.
P
a
r
k
M
ain
27
Levee 31W
ee 31W
In the southern Everglades of Florida, where the shallow
surficial aquifer system consists of highly permeable limestone,
interactions between surface water and ground water comprise
a large part of the water budget (Harvey and others, 2000a;
2000b). As part of the SICS and TIME modeling effort, a
method was developed for simulating the exchange of fluid and
salt between the wetland and underlying aquifer system (fig. 2).
The method was implemented by combining SWIFT2D with
the SEAWAT variable-density ground-water flow and transport
code (Guo and Langevin, 2002). The integrated code simulates
surface-water and ground-water interactions between a wetland
and aquifer, and is called Flow and Transport in a Linked Over-land/Aquifer Density Dependent System (FTLOADDS). The
mass-conserving approach for the explicit coupling between
SWIFT2D and SEAWAT, which is based on a variable-density
form of Darcy’s Law, is given in Langevin and others (2004).
FTLOADDS was applied to the SICS area to quantify the
importance of surface-water and ground-water exchanges and
to improve the original SICS model as a management tool
(Langevin and others, 2004). Results from the integrated model
demonstrate the importance of surface-water and ground-water
exchanges within the Taylor Slough area. Average annual
leakage rates between the wetland and aquifer for a 7-year
simulation period (1996-2002) indicate an alternating pattern of upward and downward flow (fig. 3). This pattern is
primarily related to topographic variations within the SICS
Figure 2.
Conceptual model for surface- and ground-water interactions as implemented in the Flow and Transport in a Linked Overland/
Aquifer Density Dependent System (FTLOADDS) computer code, which
is a coupled version of SWIFT1D and SEAWAT.
25°
Old Ingraham Highw
Taylor
Slough
Bridge
Royal Palm
Ranger
C-111
25°
25°10
2 3
EXPLANA
AVERAGE SIMULATED LEAKA
TED LEAKAGE RATE, IN CENTIMETERS PER
TE, IN CENTIMETERS PER DAY
0 1
0 1
5 KILOMETERS
2 3 4
0.2
0.1
0.05
0.01
-0.2
-0.1
-0.05
-0.01
0
Average annual surface-water budget for the coastal wetland
for the 7-year simulation period (1996-2002). Positive values indicate
downward flow into the aquifer (from Langevin and others, 2004).
The methodology used for the SICS model is being expanded
and improved for the development of the TIME model. TIME is
coarser in resolution (500 meters) than SICS (305 meters), but
covers a much larger area of the Everglades, including Shark
River and Taylor Sloughs to the Gulf of Mexico and northern
Florida Bay (fig. 1). Although TIME encompasses the SICS
model domain, the SICS model could be used in the future to
provide detailed simulations for the Taylor Slough area. The
TIME model also is being developed using the FTLOADDS
computer program, and thus, the type of output from both
models is similar and consists of flows, stages, and salinities in
the wetlands and underlying aquifer system.
An application of the TIME model as a tool to evaluate the
effects of CERP scenarios on freshwater flows to Florida Bay
and the Gulf of Mexico began in late 2003. Presently, the model
is being calibrated and verified with data collected from 1996 to
2002 in preparation for simulation of different scenarios. This
effort entails comparing computed and observed stages and
flows to elucidate model behavior and to develop measures of
model accuracy. An example of computed surface-water depth
during the wet season is shown in figure 4.
and thus, there is no direct way to predict the effects of
restoration scenarios on coastal wetland and aquifer salinities.
These limitations affect studies of Florida Bay, which require
accurate predictions of freshwater flows into the estuary. The
2-mile-square cell size of the SFWMM also yields inadequate
spatial resolution of hydrologic variability in the wetlands
for the development of accurate and representative ecological
species models. These species models are being used to guide
and evaluate restoration efforts by predicting future populations
of fish, alligators, and other organisms.
The SICS and TIME models are being applied to support Everglades restoration by bridging the gap between the
SFWMM, the Florida Bay hydrodynamic model, and the
ATLSS (Across Trophic Level System Simulation) ecological models (fig. 5). A key component in this application is the
method developed by Wolfert and others (2004), which allows
SICS model boundaries to be assigned based on stages from
a SFWMM baseline or restoration simulation. This link to the
SFWMM extends the capability of SICS to predict coastal flows
to Florida Bay and coastal wetland salinities under future restoration conditions. A similar link is planned for the TIME model.
There are two ongoing efforts related to simulating restoration conditions with SICS and TIME. The first effort is funded
under CERP as part of the Florida Bay/Florida Keys Feasibility Study (FBFKFS). A hydrodynamic model of Florida Bay
is currently being developed as part of the FBFKFS with a
primary objective of quantifying the effects of Everglades
restoration on the Florida Bay estuary (Hamrick and Moustafa,
2003). The USGS is playing an integral role in that study by
estimating past freshwater flows and predicting future flows
to northeastern Florida Bay (SICS model) and to the Gulf of
Mexico (TIME model). Future plans include the development of
a water-quality module for SICS and TIME that can be used to
predict nutrient loads to Florida Bay. The water-quality modeling will build on the work of Levesque (2004), which describes
water and nutrient fluxes along the southwestern Florida coast.
The second effort involves the use of SICS and TIME to
provide landscape hydrology input for the ATLSS ecological
models (fig. 6). A specific example of this application is the use
of SICS model output to drive the ATLSS ALFISHES model.
Numerical models of surface- and ground-water flow are
essential analysis tools in the Everglades restoration process.
Restoration alternatives are tested and evaluated prior to
implementation by simulating hydrologic conditions that would
result from proposed modifications to the existing system.
The South Florida Water Management Model (SFWMM),
or “2 by 2,” which refers to the 2- by 2-mile finite-difference
grid, was developed by the South Florida Water Management
District (SFWMD) to simulate the complex hydrologic conditions in southern Florida and to evaluate restoration alternatives
(MacVicar and others, 1984; South Florida Water Management
District, 1997). The SFWMM is an advanced and comprehensive management tool that covers most of southern Florida
(fig. 1) and represents canal, overland, and ground-water flows
and the interactions between them. As with any model, the
SFWMM has limitations. For example, the SFWMM is best at
simulating surface-water stage and ground-water head, but is
less reliable when it comes to simulating flow rates. Additionally, the SFWMM does not contain solute-transport capabilities,
0
10 MILES
0
10 KILOMETERS
WATER DEPTH, IN METERS
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Example of simulated water depths from the TIME model.
REGIONAL
HYDROLOGIC MODEL
(SFWMM)
COASTAL FLOW
AND TRANSPORT MODELS
(TIME/SICS)
ATLSS
ECOLOGICAL MODEL
(ALFISHES)
Stages from SFWMM used to assign
boundary conditions for TIME and
SICS (Wolfert and others, 2004)
HYDRODYNAMIC
ESTUARY MODEL
(FLORIDA BAY MODEL)
Stages and salinities from SICS
used as hydrologic input for ATLSS
ALFISHES model (Cline and others,
2004)
Freshwater flows and coastal
salinities for northeastern Florida Bay
used as input for Florida Bay model
ws and coastal
est Florida
coast used as input for Florida Bay
model
Schematic showing the relation between the SICS and TIME
models and the SFWMM, ALFISHES, and Florida Bay models.
ALFISHES is an extension of a preexisting ATLSS model
(ALFISH) for functional fish groups in freshwater marshes in
the Greater Everglades area of southern Florida. ALFISHES
was designed to evaluate the spatial and temporal patterns of
fish density in the Everglades mangrove zone of Florida Bay.
Each of the ALFISHES model cells is divided into two habitat types: flats that are flooded only during the wet season,
and creeks that are always wet and serve as refugia during
the dry season. Fish movement, production, and die-out are
a function of flooding and drying and salinity. Water-level
and salinity data generated by the SICS model are used as
input to the ALFISHES model to define these interactions
(Cline and others, 2004). With the development of restoration
scenario capabilities in the SICS model, the SICS/ALFISHES
coupling is an effective tool for evaluating the potential effect
of hydrologic changes on fish populations in the Everglades
mangrove zone. Future applications will be expanded to
include crocodiles and alligators.
GENERAL STRUCTURE OF
EVERGLADES MODELING SYSTEM
ATLSS
TYPE OF MODEL
Individual-Based Models
(Individuals can move
between spatial cells)
Wading
Birds Alligators
Snail
Kites
Florida
Panthers
White-Tailed
Deer
Cape Sable
Sparrows
Piscivorous
Fish
Planktivorous
Fish
Herps: frogs,
lizards, snakes,
turtles,
salamanders
Crayfish/
Prawns
Age/Size
Structured Models
Local Models for
Each Spatial Cell
Process Models
Abiotic Conditions
Models
Apple
Snails
Zooplankton
Periphyton
Benthic
Insects
Detritus/
Microbes
Aquatic/Estuarine
Macrophytes
Terrestrial Insects
Terrestrial
Vegetation
Mercury Nutrients
Landscape Hydrology
Model
Landscape
Disturbance Models
General structure of the Across Trophic Level Systems Simulation (ATLSS) modeling system showing the importance of landscape
hydrology to ecological models.
D evelopment of these coupled surface- and ground-water models by the USGS is serving to address key
restoration needs for Everglades restoration as identified in the U.S. Department of the Interior Science Plan
(2004). Models are needed that can address the response of coastal tidal creeks, estuaries, and embayments
to changes in freshwater inflows through the wetlands as affected and altered by restoration actions. New and
improved methods are needed for the assessment of restoration effects on critical estuarine environments and
threatened species. Moreover, linkages among models, as provided by SICS and TIME, are needed for the
detailed design and adaptive management of individual projects within the Greater Everglades ecosystem.
(Photograph by Lori Oberhofer,
courtesy National Park Service)
Levesque, V.A., 2004, Water flow and nutrient flux from five estuarine rivers
along the southwest coast of Everglades National Park, Florida: U.S.
Geological Survey Scientific Investigations Report 2004-5142.
MacVicar, T., Van Lent, T., and Castro, A., 1984, South Florida Water
Management Model documentation report: West Palm Beach, South Florida
Water Management District Technical Publication 84-3.
Schaffranek, R.W., 2004, Simulation of surface-water integrated flow and
transport in two dimensions: SWIFT2D user’s manual: U.S. Geological
Survey Techniques and Methods, book 6, chap.1, section B, 115 p.
South Florida Water Management District, 1997, DRAFT Documentation for
the South Florida Water Management Model: West Palm Beach, Florida,
South Florida Water Management District Report.
Swain, E.D., Wolfert, M.A., Bales, J.D., and Goodwin, C.R., 2004, Two-dimensional hydrodynamic simulation of surface-water flow and transport to
Florida Bay through the Southern Inland and Coastal Systems (SICS): U.S.
Geological Survey Water-Resources Investigations Report 03-4287, 56 p.
U.S. Department of Interior, 2004, Science Plan in Support of Ecosystem
Restoration, Preservation, and Protection in South Florida: Accessed
September 2004 at http://sofia.usgs.gov/publications/reports/doi-science-plan/DOI-SCIENCE-PLAN-04.pdf .
Wolfert, M.A., Langevin, C.D., and Swain, E.D., 2004, Assigning boundary
conditions to the Southern Inland and Coastal Systems (SICS) model using
the results from the South Florida Water Management Model (SFWMM):
U.S. Geological Survey Open-File Report 2004-1195, 30 p.
Cline, J.C., Lorenz, Jerome, and Swain, E.D., 2004, Linking hydrologic
modeling and ecologic modeling: An application of adaptive ecosystem
management in the Everglades mangrove zone of Florida Bay: International
Environmental Modelling and Software Society iEMSs 2004 International
Conference, 14-17 June 2004, University of Osnabrück, Germany.
Guo, Weixing, and Langevin, C.D., 2002, User’s guide to SEAWAT: A
computer program for simulation of three-dimensional variable-density
ground-water flow: U.S. Geological Survey Techniques of Water-Resources
Investigations, book 6, chap. A7, 77 p.
Hamrick, J.M., and Moustafa, M.Z., 2003, Florida Bay hydrodynamic and
salinity model analysis: 2003 Proceedings of the Greater Everglades and
Florida Bay Ecosystem Conference, Palm Harbor, Florida, April 13-18,
2003.
Harvey, J.W., Choi, J., and Mooney, R.H., 2000a, Hydrologic interactions
between surface water and ground water in Taylor Slough, Everglades
National Park, in U.S. Geological Survey Program on the South Florida
Ecosystem: 2000 Proceedings of the Greater Everglades Ecosystem
Restoration (GEER) Conference, December 11-15, 2000, edited by
Eggleston and others: U.S. Geological Survey Open-File Report 00-449,
p. 24-26.
Harvey, J.W., Jackson, J.M., Mooney, R.H., and Choi, J., 2000b, Interactions
between ground water and surface water in Taylor Slough and vicinity,
Everglades National Park, south Florida: Study methods and appendixes:
U.S. Geological Survey Open-File Report 00-483, 67 p.
Langevin, C.D., Swain, E.D., and Wolfert, M.A., 2004, Simulation of integrated
surface-water/ground-water flow and salinity for a coastal wetland and
adjacent estuary: U.S. Geological Survey Open-File Report 2004-1097, 30 p.
Leendertse, J.J., 1987, Aspects of SIMSYS2D, a system for two-dimensional
flow computation: Santa Monica, Calif., Rand Corporation Report R-3572-USGS, 80 p.
Christian Langevin, U.S. Geological Survey, Florida Integrated
Science Center—Water and Restoration Studies, 9100 NW
36th Street, suite 107, Miami, FL 33178, Phone: 305-717-5817,
Fax: 305-717-5801, Email: langevin@usgs.gov