U.S. Department of the Interior 

 U.S. Geological Survey 

 Fact Sheet 2004-3130

October 2004 

 Development of Coastal Flow and Transport Models in 

Support of Everglades Restoration 

By 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 

Printed on recycled paper

 Introduction 

 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 hydrologic 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. 

 The U.S. Geological Survey is actively involved in science 

support for Everglades restoration. This paper summarizes 

the development and application of two integrated surfacewater/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. 
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. 

Figure 1. Map of southern Florida showing the active model domains 

of SICS and TIME and the SFWMM grid.

 Surface-Water/Ground-Water Interactions 

 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 Overland/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.

Figure 3. 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 TIME Model 

 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 

aquifer

Sediment layer

Surface-water

system

Ground-water

system

Land

surface

Seawater Brackish water Fresh water

0 1

0 1 2 3 4 5 KILOMETERS

2 3

0.2 0.1 0.05 0.01 0 -0.01 -0.05 -0.1 -0.2

EXPLANA AVERAGE SIMULA GE SIMULATED LEAKA TED LEAKAGE RATE, IN CENTIMETERS PER TE, IN CENTIMETERS PER DAY

C-111

Levee 31W 27

Road Park Main

Old Ingraham Highw

Taylor

Slough

Bridge

Royal Palm

Ranger

25°25 80°50 ́ 80° 45 ́ 80° 40 ́ 80° 35 ́ 80° 30 ́ 80°25 ́

25°10

25° 

25° 

81°30 ́ 81°00 ́ 80°30 ́ 80°00 ́

25°00 ́

25°30 ́

26°00 ́

26°30 ́

27°00 ́

0 25 MILES

0 25 KILOMETERS

Lake

Okeechobee

GULF OF MEXICO

ATLANTIC OCEAN

Florida

Bay

Base from South Florida Water Management District, Landsat TM Mosaic 1992-94

Universal Transverse Mercator projection, Zone 17, Datum NAD 27

SICS ACTIVE

MODEL DOMAIN

SFWMM

GRID

TIME ACTIVE

MODEL DOMAIN Shark River

Slough

Taylor

Slough
Figure 4. Example of simulated water depths from the TIME model.

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. 

Figure 5. Schematic showing the relation between the SICS and TIME 

models and the SFWMM, ALFISHES, and Florida Bay models.

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. Application of SICS and TIME for Everglades 

Restoration 

 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, 

WATER DEPTH, IN METERS TER DEPTH, IN METERS

EXPLANATION

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

0

0 10 KILOMETERS

10 MILES

REGIONAL

HYDROLOGIC MODEL

(SFWMM)

COASTAL FLOW

AND TRANSPORT MODELS

(TIME/SICS)

HYDRODYNAMIC

ESTUARY MODEL

(FLORIDA BAY MODEL)

ATLSS

ECOLOGICAL MODEL

(ALFISHES)

Freshwater flows and coastal

salinities for northeastern Florida Bay

used as input for Florida Bay model

Stages and salinities from SICS

used as hydrologic input for ATLSS

ALFISHES model (Cline and others,

2004)

Stages from SFWMM used to assign

boundary conditions for TIME and

SICS (Wolfert and others, 2004)

ws and coastal

est Florida

coast used as input for Florida Bay

model
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. 

 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, Twodimensional 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-scienceplan/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. 

 References 

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. 

 Concluding Discussion 

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. 

Figure 6. General structure of the Across Trophic Level Systems Simulation (ATLSS) modeling system showing the importance of landscape 

hydrology to ecological models.

 For more information, contact: 

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 

GENERAL STRUCTURE OF ATLSS EVERGLADES MODELING SYSTEM

TYPE OF MODEL

Individual-Based Models

(Individuals can move

between spatial cells)

Age/Size

Structured Models

Local Models for

Each Spatial Cell

Process Models

Abiotic Conditions

Models

Wading

Birds Alligators Snail

Kites

Florida

Panthers

White-Tailed

Deer

Cape Sable

Sparrows

Piscivorous

Fish

Planktivorous

Fish

Apple

Snails

Herps: frogs,

lizards, snakes,

turtles,

salamanders

Crayfish/

Prawns

Zooplankton

Periphyton

Benthic

Insects

Detritus/

Microbes

Aquatic/Estuarine

Macrophytes

Terrestrial Insects

Terrestrial

Vegetation

Mercury Nutrients Landscape Hydrology

Model

Landscape

Disturbance Models

(Photograph by Lori Oberhofer, 

courtesy National Park Service)