Prepared in cooperation with the Broward County Environmental Planning 

and Resilience Division

Potential for Increased Inundation in Flood-Prone Regions 

of Southeast Florida in Response to Climate and Sea-Level 

Changes in Broward County, Florida, 2060–69

Scientific Investigations Report 2018–5125

U.S. Department of the Interior

U.S. Geological Survey
Cover. Photograph showing S-13 structure. Photograph by Jeremy D. Decker, U.S. Geological Survey.
Potential for Increased Inundation in 

Flood-Prone Regions of Southeast 

Florida in Response to Climate and 

Sea-Level Changes in Broward 

County, Florida, 2060–69

By Jeremy D. Decker, Joseph D. Hughes, and Eric D. Swain

Prepared in cooperation with the Broward County Environmental Planning and 

Resilience Division

Scientific Investigations Report 2018–5125

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DAVID BERNHARDT, Acting Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2019

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment—visit https://www.usgs.gov or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, 

visit https://store.usgs.gov.

Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Decker, J.D., Hughes, J.D., and Swain, E.D., 2019, Potential for increased inundation in flood-prone regions of 

southeast Florida in response to climate and sea-level changes in Broward County, Florida, 2060–69: U.S. Geological 

Survey Scientific Investigations Report 2018–5125, 106 p., https://doi.org/10.3133/sir20185125.

ISSN 2328-0328 (online)
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................2

Description of Study Area ...................................................................................................................2

Related Studies .....................................................................................................................................4

Approach................................................................................................................................................4

Simulation of the Hydrologic System for Historical Conditions During 1990–99.................................5

Conceptual Hydrologic Flow Model ..................................................................................................5

Precipitation and Evapotranspiration.......................................................................................7

Groundwater Pumping................................................................................................................7

Canal System................................................................................................................................8

Regional Groundwater Flow ......................................................................................................8

Simulation Codes ..................................................................................................................................9

Model Fit to Historical Conditions....................................................................................................10

Simulated Groundwater Levels Within the County-Scale Model......................................11

Simulated Groundwater Levels Within the Local-Scale Model.........................................11

Simulated Stages and Flows at Surface-Water Control Structures Within the

County-Scale Model ...................................................................................................11

Simulated Stages and Flows at Surface-Water Control Structures Within the

Local-Scale Model ......................................................................................................16

Summary of Model Fit to Historical Conditions ....................................................................16

Effects of Climate Changes and Sea-Level Rise on Groundwater Levels, Canal Stages, 

and Flows at Coastal Structures..................................................................................................17

Simulation of Climate Conditions During 1990–99 and 2060–69 ..................................................19

Simulation of the Hydrologic System for Future Climate and Sea-Level Conditions 

During 2060–69.......................................................................................................................23

County-Scale Model Scenario Results ..................................................................................23

Comparison of CCSM and HadCM3 Base-Case Scenarios to the Historical

Simulation.............................................................................................................23

Comparison of Sea-Level Rise and Wetter or Drier Future Scenarios With

Base-Case Scenarios.........................................................................................23

Local-Scale Model Scenario Results.....................................................................................34

Comparison of Base-Case Climate Scenarios to the Historical Simulation ...........34

Comparison of Sea-Level Rise and Wetter or Drier Future Scenarios With

Base-Case Scenarios.........................................................................................35

Simulation of Hypothetical Mitigation Strategies ..................................................................................37

Adapting Pumping Operations at S–13 to Maintain Upstream Stages......................................38

Pumping Groundwater to Reduce Potential for Inundation ........................................................43

Model Limitations.........................................................................................................................................46

Groundwater-Model Properties .......................................................................................................46

Western Groundwater Head Boundaries .......................................................................................47

Tidal Boundaries .................................................................................................................................47

Canal Representation.........................................................................................................................47

Precipitation and Potential Evapotranspiration.............................................................................48

Future Climate and Sea-Level Projections .....................................................................................48

Summary........................................................................................................................................................48
iv

References Cited..........................................................................................................................................50

Appendix 1. Simulated Groundwater Response to Individual Precipitation Events.........................54

Appendix 2. Numerical Model Construction ...........................................................................................60

References Cited...............................................................................................................................101

Appendix 3. Sensitivity Testing of Numerical Models .........................................................................102

Reference Cited.................................................................................................................................106

Figures

1. Map showing location of the study area, Broward County, Florida.....................................3

2. Map showing county-scale model area and local-scale model boundaries,

Broward County, Florida..............................................................................................................6

3. Map showing local-scale model area, Broward County, Florida .........................................7

4. Graph showing averaged annual precipitation and potential evapotranspiration 

for the county-scale model area................................................................................................8

5. Graph showing total groundwater-pumping rate in the county-scale simulated 

area for all simulations ................................................................................................................8

6. Hydrograph showing groundwater levels in Water Conservation Areas and tidal

stage during the study period 1990–99......................................................................................9

7. Graph showing projected sea-level rise for the 21st century...............................................9

8. Map showing groundwater-level observation locations and transects ...........................12

9. Hydrographs showing simulated and measured groundwater levels for

county-scale model transects 1 and 2 during 1990–99 ........................................................13

10. Hydrographs showing simulated and measured groundwater levels for

county-scale model transects 3, 4, and 5 during 1990–99 ...................................................14

11. Hydrographs showing simulated and measured groundwater levels for three

observation locations within the local-scale model during 1990–99 .................................15

12. Hydrographs showing simulated and measured upstream stage and flow at

primary active structures G–54 and S–33 during 1990–99 for the county-scale 

model ............................................................................................................................................17

13. Hydrographs showing simulated and measured upstream stage and flow at

primary active structure S–13 during 1990–99 for the county-scale model .....................18

14. Hydrographs showing simulated and measured upstream stage and flow at

primary active structure S–9 during 1990–99 for the county-scale model .......................18

15. Hydrographs showing simulated and measured headwater stage and flow at

structures G–54 and S–13 for the local-scale model during 1990–99................................19

16. Graphs showing mean rainfall, in inches, for the county-scale model area....................20

17. Graph showing cumulative difference in rainfall between the Community 

Climate System Model climate simulation during 2060–69 and the CCSM 

climate simulation during 1990–99, and between the Hadley Centre Coupled 

Model version 3 climate simulation during 2060–69 and the HadCM3 climate 

simulation during 1990–99, averaged spatially for the county-scale 

model area ...................................................................................................................................21

18. Graphs showing mean potential evapotranspiration, in inches, for the 

county-scale model area...........................................................................................................22

19. Profiles showing west-east continuous transect of average wet-season

groundwater levels for base-case and wetter and drier future sea-level rise

scenarios for 2060-69 .................................................................................................................27
v

20. Hydrographs showing structure S–13 spillway flow for low, intermediate, and 

high sea-level rise scenarios, and pump flow for the high sea-level rise scenarios 

for 1990-99 or 2060-69.................................................................................................................28

21. Hydrographs showing upstream stage at structure S–13 for low, intermediate, 

and high sea-level rise and wetter and drier future climate scenarios for 1990-99 

or 2060-69 .....................................................................................................................................29

22. Hydrographs showing upstream stage at primary structures G–54, S–33, and

S–9 for high sea-level rise and wetter and drier future climate scenarios for

1990-99 or 2060-69.......................................................................................................................30

23. Maps showing percentage of sea-level rise reflected in increased average

wet-season groundwater levels for low sea-level rise, intermediate sea-level

rise, and high sea-level rise, for wetter future climate scenarios within the

county-scale model....................................................................................................................31

24. Maps showing percentage of sea-level rise reflected in increased average

wet-season groundwater levels for low sea-level rise, intermediate sea-level

rise, and high sea-level rise, for drier future climate scenarios within the

county-scale model....................................................................................................................32

25. Maps showing average wet-season groundwater levels within the county-scale

model for Community Climate Systems Model base case; wetter future, high

sea-level rise; and drier future, high sea-level rise, future scenarios...............................33

26. Maps showing average wet-season depth to groundwater for base-case and

the wetter future high sea-level rise scenarios within the county-scale model .............34

27. Hydrographs showing simulated upstream stage at the G–54 and S–13 

structures for future climate and sea-level rise scenarios for the local-scale 

model for 1990-99 or 2060-69.....................................................................................................37

28. Hydrographs showing spillway and pump flow for structure S–13 for wetter

future and drier future climate and sea-level rise scenarios for the local-scale

model for 1990-99 or 2060-69.....................................................................................................38

29. Maps showing average wet-season groundwater-level increases in the 

local-scale model for wetter future low, intermediate, and high sea-level 

rise scenarios..............................................................................................................................39

30. Maps showing average wet-season groundwater-level increases in the 

local-scale model for drier future low, intermediate, and high sea-level 

rise scenarios..............................................................................................................................40

31. Maps showing average wet-season groundwater level for base-case and 

high sea-level rise, wetter, and drier future climate scenarios for the 

local-scale area ..........................................................................................................................41

32. Maps showing average wet-season depth to groundwater in the local-scale 

model for wetter future low, intermediate, and high sea-level rise scenarios ................42

33. Hydrograph showing upstream stage at structure S–13 for wetter and drier 

high sea-level rise scenarios with original and altered S–13 pump operations 

for 1990-99 or 2060-69.................................................................................................................43

34. Map showing difference in average wet-season groundwater levels between

original and altered S–13 pump operations for the wetter future high sea-level 

rise scenario................................................................................................................................44

35. Map showing Areas 1 and 2 for wetter future pumped adaptation strategy 

simulation.....................................................................................................................................45

36. Graphs showing monthly averaged groundwater being removed from Area 1

and Area 2 during drainage scenarios with drainage elevations set to levels

zero, 1 foot, and 2 feet above base-case scenario wet-season averages within

each cell.......................................................................................................................................46
vi

Tables

1. County-scale and local-scale model comparison...................................................................7

2. Fit statistics for groundwater levels of 14 selected well locations for historical

county-scale model simulation ................................................................................................10

3. Fit statistics for groundwater levels at three monitoring locations and upstream

stage and flow through primary active control structures for historical 

local-scale model simulation....................................................................................................16

4. Fit statistics for upstream stage and flow through primary active control 

structures for historical county-scale model simulation.....................................................16

5. Project modeling scenarios incorporating sea-level rise and climate change

predictions ...................................................................................................................................23

6. Groundwater levels and primary structure flows for the historical simulation and

differences in groundwater levels and primary structure flows between Community

Climate System Model and Hadley Centre Coupled Model version 3

Base-Case scenarios and the historical simulation at groundwater-well

locations shown in figure 8 and surface-water structures shown in figure 2 .................24

7. Community Climate System Model Base-Case groundwater levels and

primary structure flows and mean differences in groundwater levels and primary

structure flows between base-case and wetter future sea-level rise simulations 

for the county-scale model .......................................................................................................25

8. Hadley Centre Coupled Model version 3 Base-Case groundwater levels and 

primary structure flows and mean differences in groundwater levels and primary 

structure flows between base-case and drier future sea-level rise simulations for 

the county-scale model .............................................................................................................26

9. Groundwater levels and primary structure flow and changes for historical and

base-case Community Climate System Model and Hadley Centre Coupled Model 

version 3 simulations for the local-scale model....................................................................35

10. Simulated groundwater levels and primary structure flows and mean differences

in groundwater levels and primary structure flows for climate and sea-level rise

scenarios using the local-scale model ...................................................................................36
vii

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2) 

Flow rate

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3/s)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Hydraulic conductivity

inch per hour (in/h) 2.54 centimeter per hour (cm/h)

foot per day (ft/d) 0.3048 meter per day (m/d)

Conductance

square foot per day (ft2/d) 0.09290 square meter per day (m2/d)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as 

°F = (1.8 × °C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as 

°C = (°F – 32) / 1.8.

Datum

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Elevation, as used in this report, refers to distance above the vertical datum.
viii

Abbreviations

AR4 Intergovernmental Panel on Climate Change Fourth Assessment Report

BAS6 MODFLOW Basic package

CCSM Community Climate System Model

COAPS Center for Ocean-Atmospheric Prediction Studies

DRN MODFLOW Drain package

EDEN Everglades Depth Estimation Network

ET evapotranspiration

EVT MODFLOW Evapotranspiration package 

GCM global circulation model

GFDL Geophysical Fluid Dynamics Laboratory

GHB MODFLOW General-Head Boundary package

HadCM3 Hadley Centre Coupled Model version 3

HPM Hydrologic Process Module

IPCC Intergovernmental Panel on Climate Change

LECsR Lower East Coast sub-Regional Model

lidar light detection and ranging

LPF MODFLOW Layer-Property Flow package

MD mean difference

NOAA National Oceanic and Atmospheric Administration

NRC National Research Council

PEST parameter estimation

PEV percent explained variance

RCH MODFLOW Recharge package

RIV MODFLOW River package

RMSD root-mean-square difference

SWR1 MODFLOW Surface-Water Routing process

URO MODFLOW Urban Runoff process

USACE U.S. Army Corps of Engineers

USGS U.S. Geological Survey

WCA Water Conservation Area

WEL MODFLOW Well package
Potential for Increased Inundation in Flood-Prone Regions 

of Southeast Florida in Response to Climate and Sea-Level 

Changes in Broward County, Florida, 2060–69

By Jeremy D. Decker, Joseph D. Hughes, and Eric D. Swain

Abstract

The U.S. Geological Survey, in cooperation with 

Broward County Environmental Planning and Resilience 

Division, has developed county-scale and local-scale 

groundwater/surface-water models to study the potential for 

increased inundation and flooding in eastern Broward County 

that are due to changes in future climate and sea-level rise. 

These models were constructed by using MODFLOW 2005, 

with the surface-water system represented by using the 

Surface-Water Routing process and a new Urban Runoff 

process. The local-scale model allowed the use of finer 

grid resolution in a selected area of the county, whereas 

the county-scale model provided boundary conditions 

for the local-scale model and insight into the hydrologic 

behavior of the larger system. The aquifer layering, 

properties, and boundaries relied heavily on a previous 

three-dimensional variable-density solute-transport model 

of the same area developed by the U.S. Geological Survey. 

The surface-water system within these new models actively 

simulates a part of the extensive canal network by using 

level-pool routing and active structure operations within 

the Surface-Water Routing process. These models were 

used to simulate a historical base-case period (1990–99) 

by using measured data and regional climate model rainfall 

and potential evapotranspiration output. The simulated flow 

and water-level results generally captured the behavior 

of the hydrologic system. A future period (2060–69) was 

simulated by using regional climate model rainfall and 

potential evapotranspiration output representing a wetter and 

drier future and low, intermediate, and high sea-level rise 

projections. The results were used to evaluate the potential 

effects on the surface-water drainage system, coastal-structure 

operation, and wet-season groundwater levels.

Future period simulations using the county-scale model 

indicate that (1) the effects of the changing climate and sea 

level are much more evident in eastern and coastal areas of 

Broward County compared to western areas, with increases 

in groundwater level nearly equivalent to sea-level rise; 

(2) coastal groundwater-level increases are distributed farther 

inland in the wetter future scenarios than in the drier future 

scenarios; (3) water levels at the westernmost groundwater 

station locations exhibited little change caused by sea-level 

rise and showed more dependence on changes in precipitation; 

(4) there was a reduced west-to-east groundwater gradient 

with increasing sea-level rise; and (5) increased downstream 

tidal stage at the S–13 structure resulted in increased reliance 

on the pump to control upstream inland canal stages. Future 

simulations using the local-scale model indicate similar 

behavior as seen in the county-scale model: (1) the coastal 

areas exhibited the largest impacts in groundwater levels in the 

future scenarios; (2) the westernmost, interior areas exhibited 

little change during the future scenarios; and (3) there was an 

increased reliance on the pump at the S–13 coastal structure 

but to a lesser extent than indicated in the county-scale model 

because of the reduced temporal scale of the local-scale model.

Possible adaptation and mitigation strategies were 

simulated to evaluate the county-scale and local-scale 

models’ ability to simulate hydrologic changes. Alterations 

to S–13 pump operations within the county-scale model were 

tested, and results indicate a reduced effect of sea-level rise 

inland of the control structure, but the affected area is spatially 

limited. The concept of using pumps to reduce the local 

groundwater levels in two neighborhood-sized areas was tested 

by using the local-scale model. The MODFLOW 2005 Drain 

package was used to remove groundwater by using drainage 

elevations set to zero, 1 foot, and 2 feet above average 

wet-season groundwater levels. Area 1 was well connected 

to coastal boundaries, and a high rate of groundwater 

removal was required, whereas the rate of groundwater 

removal required was greatly reduced in Area 2, which is less 

connected to tidal boundaries. Water for these scenarios was 

assumed to be pumped to tide with no downstream effects.

Introduction

Southeast Florida is highly susceptible to flooding because 

of its low topography and porous, highly permeable aquifer. 

Flood risk may be intensified by climatic variations and sea-level 

rise. Flood management and mitigation strategies for high-density 

coastal populations in the region are likely to be complicated by 

projected changes in sea-level rise and climate change. 
2 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

The potential effects of sea-level rise and climate change 

have become a primary concern for Broward County, Fla., as 

well as for neighboring communities. The National Oceanic 

and Atmospheric Administration (NOAA) reports a historical 

mean sea-level rise for Key West, Fla., of 9 inches (in.) based 

on monthly mean sea-level data from 1913 to 2013. The 

unified sea-level rise projections for southeast Florida adopted 

by the Southeast Florida Regional Climate Change Compact 

predict an accelerated rate of sea-level rise producing 3-7 in. of 

additional rise by 2030 and 9-24 in. of rise by 2060 (Southeast 

Florida Regional Climate Change Compact Technical Ad Hoc 

Work Group, 2011). Higher tidal stages may result in reduced 

capacities at the gravity-controlled coastal structures, limiting 

their abilities to drain inland canals. Additionally, sea-level rise 

can increase regional groundwater levels, resulting in reduced 

coastward hydraulic gradients and available groundwater 

storage and increasing the likelihood and duration of 

inundation events within inland neighborhoods. 

Changes in precipitation amounts that are due to climate 

change can also increase the vulnerability of southeast 

Florida’s coastal and inland neighborhoods to flooding. 

More intense rainfall events coupled with reduced drainage 

capacity and soil storage could lead to increased ponding and 

inundation. Currently (2018), agreement is poor among the 

multitude of global and regional climate models concerning 

projected changes in precipitation amounts; therefore, future 

planning for flood management and mitigation needs to 

consider the potential effects of a range of climate model 

predictions and sea-level rise trends.

To assess the current infrastructure and assist in the 

development of possible adaptation and mitigation strategies, 

the U.S. Geological Survey (USGS), in cooperation with the 

Broward County Environmental Planning and Resilience 

Division, has developed test-case models at two spatial 

scales within Broward County by using MODFLOW 2005 

(Harbaugh, 2005) the Surface-Water Routing (SWR1) 

process (Hughes and others, 2012), and a new method—the 

Urban Runoff (URO) process. Two MODFLOW-2005-based 

groundwater-flow models were developed for this study. 

The MODFLOW 2005 countywide model provided regional 

simulations and was used to establish the boundary conditions 

for a finer-scale local model for the central part of the county, 

including the city of Fort Lauderdale. The local-scale model 

was used in this study to develop a more detailed spatial 

and temporal analysis of the hydrologic system and canal 

response to sea-level rise. These models are used to simulate 

the effects of sea-level rise and variations of climate on 

groundwater levels and discharge from drainage canals. The 

results can then be used to help quantify the effectiveness 

of proposed management and infrastructure changes for 

various climate-change and sea-level rise scenarios.

Purpose and Scope

The purpose of this report is to provide information that 

can be used to help evaluate the increased potential for risk 

of inundation for various sea-level rise rates and changes in 

precipitation patterns attributed to climate change in parts of 

Broward County. Information and model output providing 

insight into the hydrologic behavior within the county can be 

used by county managers to inform future decision making 

and long-term (multidecadal) planning. After completion, 

additional scenarios and management strategies can be tested 

to further evaluate the system’s response to proposed or 

expected changes. 

This report documents the construction, testing, 

and application of numerical hydrologic models used for 

the analysis. The study area extends east from the water 

conservation areas to the Atlantic coastline, and from 

north-central Broward County into northern Miami-Dade 

County in the south (fig. 1). Input data from two downscaled 

climate models were tested and evaluated for two periods: a 

historical period, 1990–99; and a future period, 2060–69, for 

which predicted sea-level rise was also applied. With a focus on 

the potential for landscape inundation in the future, the changes 

in the potential risk for inundation during precipitation events 

were quantified based on projected shallower groundwater 

levels and the resulting decreased storage capacity between 

the water table and land surface (in the unsaturated zone). 

This report includes descriptions of the hydrologic system, a 

conceptual flow model, and model parameter estimation. The 

results of several sea-level rise and climate-change scenarios 

are presented herein, as well as some evaluation of possible 

adaptation strategies. Additionally, the structure, equations, 

and input requirements of the URO process are documented. 

The study’s associated data release contains the model’s 

executable and required input files, URO input instructions and 

description, as well as post-processing executables that can be 

used to reproduce simulation results (Decker, 2018).

Description of Study Area

Broward County has a total land area of 1,225 square 

miles (mi2) and is situated on the southeast coast of Florida 

(fig. 1). As of 2017, Broward County had a population of 

1.9 million, making it the second-most populated county in 

Florida with approximately 9 percent of the State population 

(U.S. Census Bureau, 2018). The highly urbanized eastern 

part comprises approximately one-third of the county, and the 

remaining undeveloped western part encompasses much of 

the water conservation areas (WCAs) managed by the South 

Florida Water Management District (Broward County, 2009). 

The majority of Broward County is low and flat, with 

most land-surface elevations between 2 and 10 feet (ft) above 

the North American Vertical Datum of 1988 (NAVD 88). The 

highest natural elevations within the county are approximately 

30 ft above NAVD 88 along the Pine Island Ridge in the 

city of Davie (Broward County, 2009). The Biscayne aquifer 

in Broward County is shallow and composed of highly 

transmissive limestone. The groundwater and surface-water 

systems are closely connected. The area has distinct wet and 

dry seasons with an average annual rainfall between 45 to 

60 in., with three-fourths of the rain falling between May and 

November (Broward County, 2009). Year-to-year variability 

can be high with periodic dry and wet years.
Introduction 3

C–11 East

Dania Cut-Off

Canal

C–11 West

North New River Canal

C–10

ATLANTIC OCEAN

North Fork

New River

C–12

Water Conservation

Area 2B

Water Conservation

Area 2A

Water Conservation

Area 3B

Water Conservation Area 3A

95

75

595

MIAMI-DADE COUNTY

BROWARD COUNTY

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

G–54

S–13 S–13a

S–9

S–33

S–34

G–54

S–13 S–13a

S–9

S–33

S–34

FLL

Southwest

Ranches

Plantation

Fort Lauderdale

Pompano

Beach

Hollywood

Davie

EXPLANATION

Offshore

Active model domain

Tidal general head boundary

Western general head boundary

Surface-water structure and identifier

Fort Lauderdale-Hollywood International

 Airport (FLL) 

G–54

Study area

FLORIDA

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 1. Location of the study area, Broward County, Florida.
4 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

The existing surface-water management system is used 

to control groundwater levels and is designed and operated 

to accomplish several objectives. The system is used to 

route excess water to the WCAs and to the coast to prevent 

flooding during the wet season; it is used to route water 

from the conservation areas to the urban area to recharge the 

groundwater system to meet supply demands during the dry 

season; and the system can provide environmental flows when 

required. The current drainage system includes 1,700 miles 

of canals, gravity control structures, and pumps (Broward 

County, 2009). Despite the complexities and capabilities of 

the system, several areas within Broward County are prone 

to flooding. In particular, low-lying coastal areas east of the 

salinity control structures and poorly drained areas in western 

Broward County near the WCAs have flooding problems.

Related Studies

The construction of the hydrologic models described 

in this report rely heavily on a previous study that involved 

the development of a variable-density, solute-transport 

groundwater-flow model of central and southern Broward 

County, Fla. (Hughes and others, 2016). The model was 

calibrated to conditions from 1970 to 2012 by using automated 

parameter estimation (PEST) techniques. The model was 

then used to simulate historical conditions from 1950 to 

2012, evaluate the sensitivity of the salinity distribution in 

groundwater to sea-level rise and groundwater pumping, and 

estimate the possible effects on future salinity distribution in 

the aquifer attributed to changes in groundwater pumping, 

sea-level rise, and changes to the hydrologic system. The 

vertical layering used within the model was based on a 

composite of lithostratigraphic and conceptual hydrogeologic 

models. The model was calibrated by using the PEST software 

to estimate model parameters so as to reasonably replicate 

measured head and salinity values. The software-estimated 

parameters at discrete pilot-point locations and then the 

cell-by-cell parameter values were spatially interpolated 

from these points. A combination of coarse and fine pilot 

points was used with increased pilot-point coverage near the 

saltwater/freshwater interface.

The central and southern Broward County model 

relied upon the input datasets from two other existing 

groundwater-flow models during model construction: 

(1) the Lower East Coast sub-Regional Model (LECsR) 

(Giddings and others, 2006) and (2) a groundwater-flow 

and surface-water-flow model developed for the urbanized 

areas within Broward County using the MIKE SHE and 

MIKE 11 simulators (referred to hereinafter as the “MIKE 

SHE/MIKE 11 model”; Islam and Dunn, 2006). The LECsR 

model was composed of smaller subregional flow models 

and was used to assist with regional water supply issues and 

the Comprehensive Everglades Restoration Plan. The MIKE 

SHE/MIKE 11 model was used to aid Broward County in 

evaluating water management plans and practices. 

The SWR1 process of MODFLOW was developed 

for and first applied to a study area within neighboring 

Miami-Dade County (Hughes and others, 2016). The 

groundwater/surface-water model for this area was used to 

evaluate the movement of the saltwater/freshwater interface 

in response to changes in groundwater pumpage and sea-level 

rise. Additionally, the model was used to evaluate changes in 

canal leakage in the area during these future scenarios. The 

study concluded that the model effectively represented the 

interconnectivity between the extensive surface-water and 

underlying groundwater systems. 

There have been several other groundwater models 

developed for the area or that include parts of the area: 

(1) Langevin and Zygnerski (2013) developed a model for 

the northern part of coastal Broward County to evaluate 

the effects of well-field pumping and sea-level rise on the 

salinity distribution; (2) a model was developed to simulate 

the salinity distribution and effects of well-field management 

for areas near Hallandale Beach (Andersen and others, 1988); 

and (3) a three-dimensional model was constructed by Guha 

and Panday (2012) to predict the effect of sea-level rise on 

the distribution of salinity in southern Broward and northern 

Miami-Dade Counties.

The development of the methods used to simulate 

infiltration, recharge, and unsaturated zone storage within 

the URO process was based on concepts used by the South 

Florida Management District in the Regional Simulation 

Model’s Hydrologic Process Modules (HPMs) for different 

land-use types. In one such HPM, infiltration and recharge 

rates are calculated based on maximum rates and watercontent-dependent relationships. Excess rainfall is routed to 

adjacent features or stored, which is similar in concept to the 

URO handling of rainfall, evapotranspiration (ET), and runoff, 

in which infiltration and recharge rates are water-content 

dependent and based on maximum rates; however, water can 

be stored in the unsaturated zone and stored as surface water.

Approach

Two hydrologic flow models, together henceforth called 

the inundation models, were created using MODFLOW 2005 

and the URO MODFLOW process, developed for this 

study. The larger of the two models, henceforth called the 

county-scale model, covers 450 mi2 in areal extent and uses a 

relatively coarse 500-ft grid. The smaller of the two models, 

henceforth called the local-scale model, lies within the 

boundaries of the county-scale model, uses a relatively fine 

166.7-ft grid resolution, and uses output from the county-scale 

model as boundary conditions. The local-scale model provides 

output at a finer grid resolution and incorporates a more 

detailed representation of the surface-water system. 

The county-scale model is a modified version 

of a SEAWAT-based (Langevin and others, 2008) 

saltwater-intrusion model developed to simulate the effects 

of hydrologic changes on the distribution of groundwater 

salinity within central and southern Broward County (Hughes 
Simulation of the Hydrologic System for Historical Conditions During 1990–99 5

and others, 2016). Changes made to the saltwater-intrusion 

model for the county- and local-scale models include 

converting to MODFLOW 2005 from SEAWAT, such that 

variable-density transport is not simulated. Neglecting the 

approximate 2.5-percent difference in density between fresh 

and saltwater reduces computational time with limited impact 

on model results. The number of hydrogeologic model layers 

was reduced from 12 vertical layers to 3 vertical layers, thus 

simplifying the groundwater component of the inundation 

models. Canal stages and flows were simulated using active 

level-pool routing in the central part of the county-scale 

model and in all areas of the local-scale model, as opposed to 

non-dynamic, specified stage reaches (fig. 2). Additionally, 

rather than using the MODFLOW 2005 Evapotranspiration 

(EVT) and Recharge (RCH) packages, the URO process 

was used to represent ET, precipitation, infiltration, and 

recharge within the county- and local-scale models. The 

MODFLOW 2005 stress period length was shortened from 

monthly to daily periods with hourly URO and groundwater 

time steps and 15-minute SWR1 time steps. These changes 

were necessary for increased SWR1 model stability and to 

increase the temporal resolution of the surface-water output. 

The local-scale model extent was chosen to include both 

a coastal area, which is directly exposed to sea-level rise and 

an inland area that may experience decreases in groundwater 

storage and reduced drainage capacities associated with an 

increase in sea level (fig. 2). Compared to the county-scale 

model, the temporal and spatial scales were reduced for a 

more detailed analysis of the hydrologic system (table 1). 

Groundwater levels predicted from the county-scale model 

were specified along the local-scale model’s perimeter by 

using head-dependent flow boundaries within MODFLOW 

(general head boundaries, GHBs) (figs. 2 and 3). The canal 

network from the county-scale model was supplemented with 

additional secondary and some tertiary features. All canals 

within the local-scale model were simulated as level-pool 

reach groups. Canal inflows and outflows obtained from the 

county-scale model were added to the local-scale model using 

specified lateral flows within the SWR1 process. A more 

refined topography was incorporated into the local-scale model 

than was used in the county-scale model, derived using light 

detection and ranging (lidar) data at a spatial discretization of 

166.7 ft compared to the 500 ft used in the county-scale model 

(South Florida Water Management District, 2009). Aquifer 

properties, including hydraulic conductivity, vertical hydraulic 

conductivity, specific storage, and porosity were calculated 

from the county-scale model property fields by using bilinear 

interpolation. The areal extent of the local-scale model 

was 61.5 mi2. 

The inundation models were used to simulate changes 

in groundwater levels and canal operations that are due to 

sea-level rise and changes in predicted future precipitation, 

which could lead to increased inundation and flooding events. 

The climate model projections were provided by the Center 

for Ocean-Atmospheric Prediction Studies (COAPS) for 

a historical period from 1968 to 1999 and a future period 

from 2038 to 2069 (Stefanova and others, 2012). Output 

from a regional-scale climate model of the Southeast United

States developed by COAPS was used with three alternative 

general circulation models providing boundary conditions: the 

Community Climate System Model (CCSM), the Geophysical 

Fluid Dynamics Laboratory (GFDL) model, and the Hadley 

Centre Coupled Model version 3 (HadCM3). The CCSM and 

HadCM3 model projections showed the most variability and 

were used for this study. The projections correspond to the 

Intergovernmental Panel on Climate Change (IPCC) Fourth 

Assessment Report (AR4) A2 emissions scenario representing 

a heterogeneous world with continuously increasing world 

population (IPCC, 2007). The latest 10-year periods of the 

historical and future projections simulations were used for this 

study. Predicted sea-level rise input was calculated by using 

the methods described by the U.S. Army Corps of Engineers 

(USACE) and the modified National Research Council 

(NRC) sea-level rise Curves I and III (USACE, 2011). A 

more conservative scenario was included that used the current 

linear rate of sea-level rise estimated from historical tidal 

measurements. These sea-level rise scenarios represent low, 

intermediate, and high predictions. 

Several scenarios were evaluated by using combinations 

of these sea-level rise and climate-change model inputs, as 

well as a historical scenario using measured potential ET, 

rainfall, and observed tidal stage, which were used for model 

validation. Potential adaptation and mitigation strategies 

were tested to gauge the model’s ability to predict hydrologic 

alterations, and the results were analyzed. Additionally, 

groundwater levels within the local-scale model following 

a historical precipitation event and two future scenario 

precipitation events were evaluated and are presented 

in appendix 1.

Simulation of the Hydrologic System for 

Historical Conditions During 1990–99

The inundation models were designed to simulate 

groundwater levels, canal stages, and canal structure flows 

within the central and southern parts of Broward County. 

Historical simulation inputs were prepared and run to 

represent the hydrologic conditions of 1990–99. Details of 

model construction are provided in appendix 2. The sensitivity 

of these models to changes in model parameters were 

tested (appendix 3). No formal calibration was completed 

and parameters for the model were derived primarily from 

existing, calibrated models. The resulting models were then 

used to simulate base-case and future scenarios by using 

climate model output and sea-level rise estimates. 

Conceptual Hydrologic Flow Model

Inflows into the study area’s surface-water system 

include precipitation, groundwater discharge within inundated 

areas, aquifer-to-canal discharge, and canal inflows from the 

western control structures. Surface-water outflows consist 
6 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Active model domain

Tidal general head boundary

Western general head boundary

Specified stage canal reach within cell

Active canal reach within cell

Local-scale model general head boundary

West-to-east groundwater transect

G–54 Primary active structure and identifier

G–54

S–13 S–13a

S–9

S–33

S–34

G–54

S–13 S–13a

S–9

S–33

S–34

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2. County-scale model area and local-scale model boundaries, Broward County, Florida.
Simulation of the Hydrologic System for Historical Conditions During 1990–99 7

Table 1. County-scale and local-scale model comparison.

[mi2, square mile; ft, foot; SWR1, surface-water routing]

County-scale model Local-scale model

Columns/rows 501/411 531/159

Active spatial extents 450 mi2 61.5 mi2

Groundwater layers 3 3

Spatial discretization 500 ft 166.7 ft

MODFLOW stress period/time step 1 day/1 hour 1 day/1 hour

Canal representation Active level-pool routing and specified stage Active level-pool routing

SWR1 time step/tidal level update 15 minutes/1 day 10 minutes/1 hour

Historical/ base-case simulation period 1/1/1990–12/31/1999 1/1/1990–12/31/1999

Future simulation period 1/1/2060–12/31/2069 1/1/2060–12/31/2069

0 1 2 3 4 MILES

0 2 31 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Active model domain

Tidal general head boundary

Generated general head boundary

Active canal reach within cell

G–54 Primary active structure and identifier

Area enlarged

County-scale

model area

G–54

S–13a S–13

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

Figure 3. Local-scale model area, Broward County, Florida.

of ET, groundwater recharge, canal-to-aquifer leakage, and 

canal discharge through the coastal/western control structures. 

Aquifer inflows include recharge from the unsaturated zone, 

canal leakage, and boundary influxes from the western 

interior and the eastern tidal zone. Aquifer outflows consist of 

groundwater discharge to canals, ET, groundwater pumping, 

boundary outflows to the western interior, and submarine 

discharge along the coast. 

Precipitation and Evapotranspiration

A spatially variable rainfall time series was created for the 

historical simulations using data from 18 measurement locations 

within the county-scale model area (appendix 2). During the 

historical study period (January 1, 1990, to December 31, 1999), 

the average of these rainfall time series varied between 

52.6 inches per year (in/yr) and 76.2 in/yr, with an average of 

62.5 in/yr. A spatially uniform potential evapotranspiration rate 

was created for the historical simulations using data from two 

measurement locations near the study area (appendix 2). During 

the historical study period, the average value of this potential 

ET time series varied between 63.2 in/yr and 86.9 in/yr, with an 

average of 73.6 in/yr (fig. 4).

Groundwater Pumping

Groundwater is removed from the system as the Biscayne 

aquifer is the primary water supply for Broward County. The 

1990–99 monthly groundwater pumpage values and locations 

from the pre-existing variable-density model were used for 

base-case, historical, and future model simulations (fig. 5) 

(Hughes and others, 2016). The total pumping from the study 

area has an average removal of 199.5 million gallons per day 

(Mgal/d) for the historical study period (1990–99). 
8 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

55.9

76.2

56.6

52.6

71.1

67.4

55.8

66.2

62.2 60.8

85.6

80.9 80.9

73.0

63.3

67.1

86.9

63.2

67.9 67.0

Date

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

Averaged annual precipitation, in inches

Potential evapotranspiration, in inches

0

10

20

30

40

50

60

70

80

90

100

0

10

20

30

40

50

60

70

80

90

100

EXPLANATION

Precipitation—Value above bar is averaged annual 

 precipitation, in inches per year (in/yr)

Potential evapotranspiration (ET)—Value above 

 bar is averaged annual potential ET, in in/yr

Figure 4. Averaged annual precipitation and potential evapotranspiration for the county-scale model area.

Day of simulation

0 500 1,000 1,500 2,000 2,500 3,000 3,500

Total groundwater-pumping rate,

 in million gallons per day

0

50

100

150

200

250

300

Figure 5. Total groundwater-pumping rate in the county-scale simulated 

area for all simulations.

Canal System

The extensive canal system constructed in Broward 

County is operated to prevent inland flooding while 

maintaining groundwater levels and salinity gradients to 

protect well-field water quality. The system has evolved 

over the course of many decades and now includes primary, 

secondary, and tertiary canal and drainage features, gravity-fed 

and pumped structures near the coast, as well as gravity-fed 

and pumped structures at the western extent of the urban 

area, which can be used to recharge the system or discharge 

flows west to the WCAs. Conceptually, leakage from the 

canal system can recharge the groundwater aquifer when 

surface-water stages are maintained at higher levels than 

groundwater levels or can discharge water coastward from the 

aquifer when groundwater levels are higher than surface-water 

stages. A recent hydrologic study in adjacent Miami-Dade 

County indicates that the surface-water system discharges 

more water from the aquifer than it recharges to the aquifer 

(Hughes and White, 2014). The directionality of these 

groundwater/surface-water interactions depend upon seasonal 

conditions and water management practices.

Regional Groundwater Flow

The study area is bound to the west by the WCAs, 

which maintain high groundwater elevations, and to the east 

by the Atlantic Ocean (fig. 1). Land-surface elevation and 

groundwater levels are generally higher to the north than to the 

south, which results in a historical potentiometric surface that 

generally slopes from the northwest to the southeast. Localized 

cones of depression, which form around major production-well 

locations, are superimposed on a low-gradient potentiometric 

surface (Renken and others, 2005). The northwest-to-southeast 

groundwater-flow gradient is illustrated by comparing daily 

measurements from three representative WCA stations with 
Simulation of the Hydrologic System for Historical Conditions During 1990–99 9

tidal stage observations (fig. 6). From north to south, the 

average daily stage of the WCA sites are 10.98 ft, 9.23 ft, and 

6.44 ft above NAVD 88 for sites 2-17 (WCA2), 3-63 (WCA3), 

and 3-76 (WCA3), respectively. Daily averaged tidal levels 

during the study period vary between -2.167 ft and 0.849 ft 

above NAVD 88, with an average of -0.848 ft above NAVD 88.

Future changes in tidal levels could substantially alter 

the regional groundwater levels, gradients, and the resulting 

groundwater/surface-water flows. Sea-level rise projections for 

the 21st century, calculated by using methods described by the 

USACE and the modified NRC sea-level rise Curves I through 

III, range from 6.77 to 17.05 in. for 2050 and from 20.04 to 

58.4 in. for 2100 (USACE, 2011). The 2017 local estimated 

rate of sea-level rise of 2.24 millimeters per year (mm/yr) 

(0.088 in/yr) projects out to 3.53 in. for 2050 and 7.93 in. 

for 2100 (fig. 7).

Simulation Codes

Both the county- and local-scale models were 

constructed by using MODFLOW 2005 (Harbaugh, 2005). 

MODFLOW 2005 is a three-dimensional finite-difference 

groundwater model based on Darcy’s Law and conservation 

of mass principles that simulates steady-state or transient 

flow in a confined or unconfined aquifer system. Model 

applications can include external stresses such as specified 

fluxes, specified heads, and head-dependent flows. The 

simulations described in this report include the use of the 

Basic (BAS6), Layer-Property Flow (LPF), Well (WEL), and 

the General-Head Boundary (GHB) packages, the SWR1 

process and a new process, URO (Harbaugh, 2005; Decker 

and Hughes, 2013). Required input for the model simulations 

Date

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

Water level, in feet above

North American Vertical Datum

of 1988 (NAVD 88) -4

-2

0

2

4

6

8

10

12

14

16

EXPLANATION

Groundwater level in western Water Conservation Areas (WCA)

 Site 2–17 (WCA2), (26.2867 ̊, -80.4108 ̊)

 Site 3–63 (WCA 3), (26.1883 ̊, -80.5311 ̊)

 Site 3–76 (WCA 3), (26.0078 ̊, -80.4825 ̊)

Tidal stage in eastern tidal areas

 Haulover Pier (tide), (25.7317 ̊, -80.1617 ̊)

 Virginia Key (tide), (25.9033 ̊, -80.1200 ̊)

Figure 6. Groundwater levels in Water Conservation Areas and tidal stage during the study period 1990–99. 

Western groundwater levels include sites 2–17, 3–63, and 3–76. Eastern tidal locations include Haulover Pier 

and Virginia Key. Location of sites in latitude and longitude included in explanation.

Future

scenario

period

(2060–69)

2010 2020 2030 2040 2050 2060 2070 2080 2090 2100

Date

0

10

20

30

40

50

60

Sea-level rise (SLR), in inches

EXPLANATION

Current (2017) SLR rate

National Research Council SLR projection

 Curve I

 Curve II

 Curve III

Figure 7. Projected sea-level rise for the 21st century.
10 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

included aquifer layering elevations, vertical and horizontal 

hydraulic conductivity, specific yield of layer 1, specific 

storage of all groundwater layers, withdrawal rates at 

pumping locations within the model area, groundwater levels 

and conductance values along boundaries, canal locations, 

canal connectivity, canal cross-sectional information, 

canal leakance values, water control structure locations 

and operations or height settings, specified canal flows or 

specified canal stages at several locations, rainfall rates, 

potential ET rates, maximum infiltration, and maximum 

recharge rates. 

The SWR1 process (Hughes and others, 2012) simulates 

surface-water stages and flows and surface-water/groundwater 

interactions. Surface-water features can be represented as 

specified stages or actively simulated by using level-pool 

or diffusive wave routing. The SWR1 process can simulate 

several water-control structure types and simple structure 

operations. The SWR1 process is implicitly coupled to 

MODFLOW 2005.

The MODFLOW 2005 process, URO, was created 

and used to simulate additional surface-water processes. 

The URO process can represent two-dimensional overland 

flow by using a diffusive wave approach, precipitation, ET, 

infiltration, and recharge. Like the SWR1 process, the URO 

process is implicitly coupled to MODFLOW 2005 (Decker 

and Hughes, 2013). The equations and input data used for the 

URO process are included in appendix 2. 

Model Fit to Historical Conditions

Simulated groundwater levels, canal stages, and structure 

flows were compared to measured values, and model-fit 

statistics were calculated to evaluate the ability of county-scale 

and local-scale models to reproduce historical conditions.

 The mean difference (MD), root-mean-square difference 

(RMSD), and the percent explained variance (PEV) were 

calculated for simulated and measured values of groundwater 

level, upstream stage at surface-water control structures, 

and flow rate through structures at selected observation 

sites with available continuous monitoring (table 2). The 

MD describes how evenly the simulated observation values 

are distributed between greater than or less than measured 

observation values, where positive values of MD indicate 

that the simulated values are, overall, greater than measured, 

and negative values indicate that simulated values are 

less than measured. The MD was calculated by using the 

following equation:

MD

n

X X s

i

m

i

i

n

    



1

1

(1)

where

n is the number of simulated/measured values 

Xs

i is the i th simulated value; and

X m

i is the i th measured value.

Table 2. Fit statistics for groundwater levels of 14 selected well 

locations for historical county-scale model simulation.

Station name

Mean 

difference

(foot)

Root-meansquare 

difference

(foot)

Explained 

variance 

(percent)

G–2031 0.567 0.733 28.8

G–1316 0.359 0.513 59.0

G–853 -1.605 2.141 27.2

G–2033 -0.056 0.449 24.3

G–2395 6.661 6.829 50.1

G–1220 -0.206 0.459 70.7

G–617 -0.105 0.514 10.5

G–1221 0.265 0.639 33.7

G–561 -0.172 0.496 55.2

G–2034 -0.055 0.536 29.8

G–1225 0.376 0.653 67.8

F–291 -0.637 0.804 61.6

G–970 0.005 0.343 55.4

G–3571 0.045 0.617 47.1

Mean of all stations 0.389 1.123 44.4

Mean excluding 

G–2395 and 

G–853

0.032 0.563 45.3

The RMSD indicates the magnitude of the error of 

simulated values relative to measured values, where a larger 

value indicates a larger error, and a smaller value indicates 

a smaller error, and thus relatively closer fit of simulated 

to measured values of the observations. The RMSD was 

calculated by using the following equation:

RMSD

n

X X s

i

m

i

i

n

    



1 2

1

(2)

The PEV indicates how closely the model simulates the 

variance represented in the measured observation values, 

where the closer the value is to 1.0, the more similar are the 

variances of simulated and measured values. The PEV was 

calculated by using the following equation:

PEV

X X X X

X X

s

i

s m

i

m

i

n

m

i

m

i

n  

       

 

  









1

2

1

2

1

(3)

where

Xs is the mean simulated value, and

X m is the mean measured value. 
Simulation of the Hydrologic System for Historical Conditions During 1990–99 11

Simulated Groundwater Levels Within the 

County-Scale Model

Time series of simulated and measured daily mean 

groundwater levels were compared, and fit statistics 

were calculated for 15 observation sites throughout the 

county-scale model area. The 15 chosen observation sites 

form 5 east-to-west transects (fig. 8). Simulated groundwater 

levels exhibit similar trends and peaks to measured values 

at monitoring locations. The simulated hydrographs at 

groundwater wells G–853 and G–2395 display the largest 

deviations from measured values, likely caused by the 

nearby presence of production well fields, which may be 

over- or under-represented in the model because of the 

scale of model discretization (figs. 9 and 10). Time-series 

comparisons for G–2294 were created, but fit statistics were 

not calculated because of the limited number of observations 

at this location.

The MD varied from -1.605 ft to 6.661 ft for observations 

in the county-scale model near pumping wells (G–853 and 

G–2395, respectively). The mean MD for all observation 

locations within the county-scale model area was 0.389 ft; 

however, the mean MD is reduced to 0.032 ft when the two 

locations near pumping wells (G–2395 and G–853) are 

excluded. The RMSD varied from 0.343 ft to 6.829 ft, with 

a mean of 1.123 ft for all observation locations within the 

county-scale model area or a mean of 0.563 ft if G–2395 and 

G–853 were excluded. The PEV ranged from 10.5 percent 

to 70.7 percent, with an average of 45.3 percent for all 

observation locations (table 2).

Simulated Groundwater Levels Within the LocalScale Model

Model fit was evaluated for the three groundwaterobservation locations within the local-scale model area. Like 

the county-scale model, local-scale simulation results showed 

qualitatively similar mean groundwater-level values and 

lower peak values as compared to measured (fig. 11). The 

mean MD for the three groundwater-observation locations 

in the local-scale model is 0.125 ft, and the mean RMSD is 

0.630 ft. The highest difference in PEV occurred at G–617, 

the westernmost well. Within this observation location, the 

calculated PEV was -16.9 percent in the local-scale model, 

compared to 10.5 percent in the county-scale model. The 

reason for this difference in PEV can be attributed to the 

higher variability of the groundwater levels within the 

local-scale model, coupled with small differences in timing. 

Qualitatively, the local-scale model shows an improved 

ability to capture the magnitude of the peaks within the 

simulated and measured groundwater levels, whereas the 

PEV is substantially lower than calculated in the county-scale 

model because of the shift in the timing of the peak water 

levels. Smaller differences in PEV were seen at the other two 

locations (table 3).

Simulated Stages and Flows at Surface-Water 

Control Structures Within the County-Scale 

Model 

Time series of simulated and observed daily upstream 

stages and flows through the primary active structures 

within the county-scale model were compared, and error 

statistics were calculated for these structures (G–54, S–13, 

S–9, and S–33; fig. 1). In the models, the surface-water 

control structures are simulated according to operational 

rules, which generally establish thresholds at which specified 

actions are implemented. In practice, operations of the 

structures are more complex and ad hoc, operational rules 

are commonly overridden and manual adjustments are made 

to address specific conditions. Each of the surface-water 

control structures has a unique set of operating instructions. 

Differences between the control structure operation rules and 

actual operations result in differences between simulated and 

measured upstream stages and structure flows, which are 

reflected in resulting model-fit statistics. Furthermore, the 

county-scale model utilizes mean daily tidal stage input, and 

the local-scale model utilizes mean hourly tidal stage input, 

compared to actual continually changing tidal stage, which 

affects the simulated structure operations. 

The structure at G–54 (fig. 1) is a gated spillway that 

was designed to open when upstream stage on the North 

New River Canal rises above 2.899 ft NAVD 88 and to close 

when upstream stage declines to 1.899 ft above NAVD 88. 

For much of the study period, actual operations followed the 

operating rules closely, as shown by the similarity between 

county-scale model-simulated and measured upstream stage 

values (fig. 12A). During several periods starting in mid-1995, 

measured stage dropped below the lower threshold for a 

variety of possible reasons. The magnitude and timing of 

simulated flow through this structure is generally similar to 

the measured flows (fig. 12B). The simulated flow shows 

a base level of flow of approximately 200 cubic feet per 

second (ft3/s), which generally drops to zero when upstream 

stages drop below the lower operating threshold. This base 

level of simulated flow is likely an artifact of a continuous 

contribution to the North New River Canal from the model 

boundary condition at the southern edge of the WCA2, where 

groundwater is leaking into the canal because of a hydraulic 

gradient at that boundary. The controlling head at this model 

boundary is taken from the Everglades Depth Estimation 

Network (EDEN) (Telis, 2006), which tends to overestimate 

water levels at this location because it is at the edge of the area 

defined by EDEN. This base level of simulated flow is also 

evidenced in the generally higher simulated than measured 

flows during high-flow (>1,000 ft3/s) periods. The MD 

between simulated and measured upstream stage is 0.029 ft, 

indicating that the simulated stage is generally slightly 

higher than the measured stage (table 4). The RMSD of 

upstream stage is indicative of the magnitude of the difference 

between the simulated and measured flows, and is 0.461 ft. 

The large negative value of the PEV (-50.1 percent) for the 
12 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983 EXPLANATION

Active model domain

Tidal general head boundary

Western general head boundary

Line of section

Groundwater station and identifier

 Westernmost

 Interior

 Easternmost

G–970

G–2395

G–2294

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

G–2031

G–2033

G–617

G–2034

G–970

G–1316

G–2395

G–1221

G–1225

G–3571

G–2294

F–291

G–561

G–1220

G–853

Transect 1

Transect 2

Transect 3

Transect 4

Transect 5

Figure 8. Groundwater-level observation locations and transects.
Simulation of the Hydrologic System for Historical Conditions During 1990–99 13

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

Date

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

Groundwater level, in feet above North American Vertical Datum of 1988 (NAVD 88) -3

-2

-1

0

1

2

3

4

5

6

7

8

9

10

-1

-2

0

1

2

3

4

5

6

7

8

9

-13

-12

-11

-16

-15

-14

-10

-9

-8

-7

-6

-5

-4

-3

-2

-1

0

A. Transect #1

B1. Transect #2

B2. Transect #2

EXPLANATION

Groundwater level, by site

 and method

 G–2031 (Simulated)

 G–2031 (Measured)

 G–1316 (Simulated)

 G–1316 (Measured)

 G–853 (Simulated)

 G–853 (Measured)

EXPLANATION

Groundwater level, by site

 and method

 G–2033 (Simulated)

 G–2033 (Measured)

 G–1220 (Simulated)

 G–1220 (Measured)

EXPLANATION

Groundwater level, by site

 and method

 G–2395 (Simulated)

 G–2395 (Measured)

Figure 9. Simulated and measured groundwater levels for county-scale model 

transects 1 and 2 during 1990–99.
14 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

Date

Groundwater level, in feet above North American Vertical Datum of 1988 (NAVD 88) -2

-1

0

1

2

3

4

5

6

-1

0

1

2

3

4

5

6

7

-2

-1

0

1

2

3

4

5

6

7

-2

A. Transect #3

B. Transect #4

C. Transect #5

EXPLANATION

Groundwater level, by site

 and method

 G–617 (Simulated)

 G–617 (Measured)

 G–1221 (Simulated)

 G–1221 (Measured)

 G–561 (Simulated)

 G–561 (Measured)

EXPLANATION

Groundwater level, by site

 and method

 G–2034 (Simulated)

 G–2034 (Measured)

 G–1225 (Simulated)

 G–1225 (Measured)

 F–291 (Simulated)

 F–291 (Measured)

EXPLANATION

Groundwater level, by site

 and method

 G–970 (Simulated)

 G–970 (Measured)

 G–3571 (Simulated)

 G–3571(Measured)

 G–2294 (Simulated)

 G–2294 (Measured)

Figure 10. Simulated and measured groundwater levels for county-scale model 

transects 3, 4, and 5 during 1990–99.

upstream stage is a result of the differences in simulated 

structure operations and discharge timing/rates compared to 

the actual operations, which cause subsequent differences in 

upstream stage increases and decreases. The higher values 

of MD (106.1 ft3/s) and RMSD (209.8 ft3/s) of the simulated 

G–54 structure flow can be attributed to the aforementioned 

base-level flow. The larger positive value of PEV of structure 

flow, 49.5 percent, indicates that the mean of the simulated 

error/variance is closer to the mean of the measured 

error/variance.

The S–33 structure on the C–12 Canal/North Fork New 

River (fig. 1) is a gated spillway that was designed to open 

when the upstream stage on the C–12 Canal rises above 

2.5 ft above NAVD 88 and close when the stage falls to 1.5 ft 

above NAVD 88 (fig. 12C). In general, the actual operations 

of the control structure closely followed the operating rules, 

as indicated by the similarity between the county-scale 

model-simulated and measured stages. Likewise, the simulated 

and measured flows at the structure are similar (fig. 12D). 

The MD between simulated and measured upstream stage 

is -0.070 ft, indicating that the simulated stage is very near 

measured values (table 4). The RMSD (0.400 ft) is indicative 

of the magnitude of the difference between the simulated 

and measured upstream stages. The large negative value of 

the PEV (-33.4 percent) of upstream stages again indicates 

differences in simulated structure operations compared to the 

actual operations, resulting in changes in upstream stages with 

varying discharge timing and rates. The MD of the structure 

flow is 10.2 ft3/s; the RMSD is 32.9 ft3/s. The large negative 

value of the PEV of structure flow (-44.7 percent) can be 

attributed to the differences in simulated structure operation 

and resulting discharge timing and rates.
Simulation of the Hydrologic System for Historical Conditions During 1990–99 15

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

Date

Groundwater level, in feet above North American Vertical Datum of 1988 (NAVD 88)

0

1

2

3

4

5

6

-1

0

1

2

3

4

5

6

-1

0

1

2

3

4

5

6

-2

A

B

C

EXPLANATION

G–617 Simulated

G–617 Measured

EXPLANATION

G–1221 Simulated

G–1221 Measured

EXPLANATION

G–561 Simulated

G–561 Measured

Figure 11. Simulated and measured groundwater levels for three observation 

locations (A, G–617; B, G–1221; and C, G–561) within the local-scale model during 

1990–99.

The S–13 structure on the C–11 Canal (fig. 1) consists 

of both a gated spillway and a pump. During 1990–99, the 

structure was designed to operate by opening the spillway 

when upstream stage rose above 0.2 ft and close when 

the stage declined to -0.2 ft. The pump was designed to 

pump water from the upstream side of the structure to the 

downstream side (to tide) based on a linear stage-discharge 

function. The stage-discharge function begins pumping water 

at 0.7 ft and reaches a maximum rate of 540 ft3/s at 1.7 ft. 

Results from the county-scale model simulation indicate that 

actual operations at the S–13 structure diverged frequently 

from operational rules during 1990–99. During the study 

period, the upstream stage was frequently allowed to drop 

below the lower control elevation of -0.2 ft above NAVD 88 

(fig. 13A), often to between -1.5 and -2.0 ft above NAVD 88. 

During the study period, actual pumping also occurs more 

frequently than operating rules would indicate (fig. 13C). 

Measured periods of pumping correspond well with periods 

when the upstream stage dropped below 0.0 above NAVD 88, 

indicating that the lower upstream stages were not largely due 

to natural causes, such as drought, but more likely due to some 

other decisional factors to move water out of the canal upstream 

of the structure (for example, to reduce the potential for flooding 

during precipitation events or pluvial periods). The MD between 

simulated and measured upstream stage is 0.168 ft, indicating 

that the simulated stage is generally larger than the measured 

stage (table 4). The RMSD (0.379 ft) is indicative of the 

magnitude of the difference between the simulated and measured 

upstream stages. The negative value of the PEV (-15.6 percent) 

of upstream stages again indicates the differences in the timing 

of simulated structure operations compared to actual gate 

operations during this period. The MD of the structure flow is 

-3.3 ft3/s; the RMSD is 107.9 ft3/s. The negative value of PEV 

(-15.6 percent) of structure flow indicates timing and flow rate 

differences in the simulated structure operations but shows more 

similar variance than simulated stage.

The S–9 structure near the intersection of the L–37 Canal, 

the L–33 Canal, and the western part of the C–11 Canal (fig. 1) 

was designed to route water from the western part of the C–11 

Canal westward into WCA 3 during 1990–99. The structure 

is represented as a linear stage-discharge function that begins 

pumping water at 1.5 ft and reaches a maximum rate of 
16 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

Table 3. Fit statistics for groundwater levels at three monitoring 

locations and upstream stage and flow through primary active 

control structures for historical local-scale model simulation.

[ft, foot; ft3/s, cubic foot per second]

Groundwater levels at monitoring locations

Station 

name

Mean 

difference

(ft)

Root-meansquare 

difference

(ft)

Explained 

variance 

(percent)

G-617 -0.050 0.577 -16.9

G-1221 0.413 0.771 16.7

G-561 0.011 0.541 39.1

Mean 0.125 0.630 NA

Upstream stage

Structure

Mean 

difference

(ft)

Root-meansquare 

difference

(ft)

Explained 

variance

(percent)

G–54 0.135 0.479 -49.3

S–13 0.135 0.351 -5.4

Simulated structure flow

Structure

Mean 

difference

(ft3

/s)

Root-meansquare 

difference

(ft3

/s)

Explained 

variance

(percent)

G–54 104.4 208.4 49.9

S–13 (spillway) 11.1 98.6 -11.8

Table 4. Fit statistics for upstream stage and flow through 

primary active control structures for historical county-scale 

model simulation.

[ft, foot; ft3/s, cubic foot per second]

Upstream stage

Structure

Mean 

difference

(ft)

Root-meansquare 

difference 

(ft)

Explained 

variance

(percent)

G–54 0.029 0.461 -50.1

S–13 0.168 0.379 -15.6

S–33 -0.070 0.400 -33.4

S–9 0.116 0.897 -8.3

Simulated structure flow

Structure

Mean 

difference

(ft3

/s)

Root-meansquare 

difference

(ft3

/s)

Explained 

variance

(percent)

G–54 106.1 209.8 49.5

S–13 (spillway) -3.3 107.9 -0.1

S–33 10.2 32.9 -44.7

S9 -30.0 299.0 29.7

1,000 ft3/s at 2.0 ft above NAVD 88 (fig. 14A). During the study 

period, results from the county-scale model show that measured 

stages and flows differed substantially from operational controls 

(figs. 14A, B), indicating that actual operations commonly 

diverged from the specified operational rules. The MD between 

simulated and measured upstream stage is 0.116 ft, indicating 

that the simulated stage is generally larger than the measured 

stage (table 4). The RMSD is indicative of the magnitude of 

the difference between the simulated and measured upstream 

stages, and is 0.897 ft. The small negative value of the PEV 

(-8.3 percent) of upstream stages indicates differences in the 

timing of structure flows and resulting stage values. The MD of 

the structure flow is -30.0 ft3/s, the RMSD is 299.0 ft3/s, and the 

value of PEV is 29.7 percent.

Simulated Stages and Flows at Surface-Water 

Control Structures Within the Local-Scale Model 

Time series of simulated and observed daily upstream 

stages and flows through G–54 and S–13 were also compared 

for the local-scale model, and error statistics were calculated 

for these structures (fig. 3). Differences between local-scale 

simulated and measured upstream stages and structure flows at 

G–54 and S–13 (fig. 15) were similar to differences between 

the county-scale simulated and measured upstream stages and 

structure flows for the study period (figs. 12A, B, and 13). Fit 

statistics for these structures generated from the results of the 

local-scale model (table 3) are also similar to the fit statistics 

generated from the results of the county-scale model (table 4). 

Summary of Model Fit to Historical Conditions

Both models produce similar overall groundwater levels 

compared to measured levels, with MDs of 0.032 ft (when 

excluding two observation sites near production wells) and 

0.125 ft for the county- and local-scale models, respectively. 

The county- and local-scale models produced qualitatively 

similar groundwater-level time series to those measured. 

Both models tend to simulate lower peak values than those 

measured, with the local-scale model capturing higher 

peaks than the county-scale model because of the finer grid 

resolution. There are small shifts in the timing of peak values 

evidenced in the time-series plots and the PEV statistics. 

The county- and local-scale models produced similar 

results to one another for the primary structure flows. The 

mean upstream stage values at these structures were similar 

to measured values, with ranges of MDs of -0.070 - 0.168 ft 

and values of 0.135 ft for the county- and local-scale models, 

respectively. The timing and values of discharges through 

these structures vary from measured values because of 

the models’ use of operational rules that vary from actual 

operations. The behavior and intent of the drainage system 

are captured by using the specified operational rules and 

were used to operate the structure when testing various future 

scenarios. 
Effects of Climate Changes and Sea-Level Rise on GroundwaterLevels, Canal Stages, and Flowsat Coastal Structures 17

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

Date

Upstream stage, in feet

above North American

Vertical Datum of 1988

(NAVD 88)

Upstream stage, in feet

above NAVD 88

Flow to tide, in cubic feet

per second

Flow to tide, in cubic feet

per second

0

1

2

3

4

0

500

1,000

1,500

2,000

2,500

0

1

2

3

4

0

100

200

300

400

500

600

A. Structure G–54

B. Structure G–54

D. Structure S–33

C. Structure S–33

EXPLANATION

Simulated

Measured

EXPLANATION

Simulated

Measured

EXPLANATION

Simulated

Measured

EXPLANATION

Simulated

Measured

Figure 12. Simulated and measured upstream stage and flow at primary active structures G–54 

(A, B) and S–33 (C, D) during 1990–99 for the county-scale model.

Although no formal calibration was performed and 

parameters were derived primarily from existing models, 

the groundwater and surface-water results indicate that 

the overall behavior of the hydrologic system, under 

historical conditions, is well represented by the inundation 

models. Using these models as a tool to simulate changes 

in groundwater levels and surface-water drainage that are 

due to projected future climate and sea-level changes would 

provide insight into how the system may respond under these 

new conditions. As with most models, more focus should be 

placed on the qualitative effects within the output rather than 

exact quantitative results. The comparison of output from 

various scenarios and differences between these scenarios will 

provide the most insight. 

Effects of Climate Changes and 

Sea-Level Rise on Groundwater

Levels, Canal Stages, and Flows

at Coastal Structures

To evaluate effects of climate changes, specifically 

changes in precipitation and ET, and sea-level rise on the 

potential for inundation in Broward County, scenarios 

were simulated by using the county-scale and local-scale 

models, representing two different climates and three rates 

of sea-level rise, for a future 10-year period. First, two 

climate model output datasets were used to generate climate 
18 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

Date

Upstream stage, in feet

above North American

Vertical Datum of 1988

(NAVD 88)

Flow to tide, in cubic feet

per second

Flow to tide, in cubic feet

per second

-2

-1

0

1

2

0

250

500

750

1,000

0

250

500

750

1,000

A. Structure S–13

B. Structure S–13 (spillway)

C. Structure S–13 (pump)

EXPLANATION

Simulated

Measured

EXPLANATION

Simulated

Measured

EXPLANATION

Simulated

Measured

Figure 13. Simulated and measured upstream stage and flow at primary active structure S–13 

during 1990–99 for the county-scale model.

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

Date

Upstream stage, in feet

above North American

Vertical Datum of 1988

(NAVD 88)

Flow to Water

Conservation Area,

in cubic feet per second

-2

-1

0

1

2

3

4

0

500

1,000

1,500

2,000

2,500

A 

B

EXPLANATION

Simulated

Measured

EXPLANATION

Simulated

Measured

Figure 14. Simulated and measured upstream stage and flow at primary active structure S–9 

during 1990–99 for the county-scale model.
Effects of Climate Changes and Sea-Level Rise on GroundwaterLevels, Canal Stages, and Flowsat Coastal Structures 19

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

Date

Upstream stage, in feet

above North American

Vertical Datum of 1988

(NAVD 88)

Flow to tide, in cubic feet

per second

Flow to tide, in cubic feet

per second

-2

-1

0

1

2

3

4

0

200

400

600

800

1,000

1,200

0

500

1,000

1,500

2,000

2,500

A. Structures G–54 and S–13

B. Structure G–54

C. Structure S–13

EXPLANATION

G–54 Simulated

G–54 Measured

S–13 Simulated

S–13 Measured

EXPLANATION

G–54 Simulated

G–54 Measured

EXPLANATION

S–13 Simulated

S–13 Measured

Figure 15. Simulated and measured headwater stage and flow at structures G–54 (A, B) and 

S–13 (C) for the local-scale model during 1990–99.

conditions during 1990–99 and during 2060–69, which 

corresponded to the latest period of the available output. 

Precipitation and potential ET output from these climate 

simulations were then used as input for the county-scale and 

local-scale models, and hydrologic conditions were simulated 

by using combinations of climate and sea-level variations 

during 1990–99 and 2060–69. 

Simulation of Climate Conditions 

During 1990–99 and 2060–69

Two global circulation models (GCMs), the CCSM 

and the HadCM3, were selected and applied by COAPS to 

their regional-scale climate model to generate estimates and 

projections of precipitation and potential ET for base-case 

and future periods for the study area. The AR4 A2 emissions 

scenarios, which were used for these simulations, assume a 

more heterogeneous developing world with increasing global 

population (IPCC, 2007). The COAPS regional climate 

model has a resolution of 10 kilometers (km) by 10 km and 

simulates a historical period from 1968–99 and a future period 

from 2038–69. At this resolution, the county-scale study 

area used output from approximately 56 climate model cells, 

and the local-scale study area used output from 3 of those 

climate model cells (appendix 2). The downscaled climate 

model output was provided as daily values of bias-corrected 

precipitation and potential ET. A truncated 10-year 

simulation period was used because of computational time 

limitations, and the furthest projected available climate data 

period, 2060–69, was used. These future condition scenarios 

are just two of a multitude of possible realizations of future 

climate and weather. 

Regional model precipitation output for 1990–99 within 

the county-scale study area varied between 39.2 in/yr and 

65.0 in/yr, with an average of 53.4 in/yr, for the CCSM climate 

simulation and varied between 31.7 in/yr and 72.6 in/yr, with 

an average of 54.9 in/yr, for the HadCM3 climate simulation 

(fig. 16A). Both climate simulations represent drier conditions 

during 1990–99 when compared to the measured average of 

62.5 in/yr during this time. Despite drier simulated average 

conditions during 1990–99, the two climate simulations had 

wet-season totals similar to measured 1990–99 wet-season 

totals, where the wet season is defined as May 1 to October 31. 
20 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

55.9

76.2

56.6

52.6

71.1

67.4

55.8

66.2

62.2 60.8

51.5 51.9

49.1

39.2

57.4 55.3 57.3

65.0

61.5

45.5

67.0

45.3

41.1

72.6

67.0

59.5 58.2

53.0 53.3

31.7

61.8

55.5

64.4 64.0

52.5

57.2

65.1

48.0

61.4

52.2

45.5

56.1

48.8 49.6

37.2

60.6

37.8

59.2

50.8

61.5

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

2060 2061 2062 2063 2064 2065 2066 2067 2068 2069

Year

Year

0

10

20

30

40

50

60

70

80

90

Rainfall, in inches Rainfall, in inches

0

10

20

30

40

50

60

70

B. Future scenario

A. Historical and base case

EXPLANATION

Simulated, by climate simulation—Value

 above bar is mean annual precipitation, 

 in inches per year (in/yr)

 Community Climate System Model

 base case (CCSM)

 Hadley Centre Coupled Model

 version 3 base case (HadCM3)

Measured—Value above bar is mean

 annual precipitation, in in/yr

Simulated, by climate simulation—Value

 above bar is mean annual precipitation,

 in in/yr

 CCSM—Wetter

 HadCM3—Drier

EXPLANATION

Figure 16. Mean rainfall, in inches, for the county-scale model area. A, measured and simulated values for the 

Community Climate System Model (CCSM) and Hadley Centre Coupled Model version 3 (HadCM3) climate simulations 

during 1990–99, and B, simulated values for the CCSM and HadCM3 climate simulations during 2060–69. 
Effects of Climate Changes and Sea-Level Rise on GroundwaterLevels, Canal Stages, and Flowsat Coastal Structures 21

The percentage of total wet-season precipitation relative to 

total annual precipitation was 72.5 percent for the CCSM 

climate simulation and 75.0 percent for the HadCM3 

climate simulation compared with 68.8 percent for measured 

precipitation during 1990–99. The average wet-season 

precipitation total was 38.7 in. for the CCSM climate 

simulation and 40.0 in. for the HadCM3 climate simulation 

during 1990–99 compared to an average measured wet-season 

total of 43.0 in. during that period. 

Regional climate-model-predicted precipitation for 

the county-scale model during 2060–69 varied between 

48.0 in/yr and 65.1 in/yr, with an average of 58.2 in/yr, for 

the CCSM climate simulation, and varied between 37.2 in/yr 

and 61.5 in/yr, with an average of 50.7 in/yr, for the HadCM3 

climate simulation (fig. 16B). The average yearly precipitation 

represents a 9.1-percent increase for the CCSM climate 

simulation during 2060–69 compared to the 1990–99 CCSM 

climate simulation and a 7.6-percent decrease in average yearly 

rainfall for the HadCM3 climate simulation during 2060–69 

compared to the 1990–99 HadCM3 climate simulation. The 

distinction between the wetter conditions of the CCSM climate 

simulation and drier conditions of the HadCM3 climate 

simulation are further illustrated in the cumulative differences 

in rainfall between each climate simulation during 2060–69 

and each climate simulation during 1990–99 (fig. 17). 

Henceforth, the future hydrologic scenarios that use the CCSM 

precipitation will be referred to as “wetter future,” and future 

hydrologic scenarios using the HadCM3 precipitation output 

will be referred to as “drier future.” 

Potential ET output within the county-scale study 

area for the CCSM climate simulation during 1990–99

varied between 73.5 in/yr and 76.3 in/yr, with an average of 

74.5 in/yr; potential ET for the HadCM3 climate simulation 

during 1990–99 varied between 68.1 in/yr and 74.1 in/yr, 

with an average of 71.8 in/yr (fig. 18A). These values are 

similar to the average yearly potential ET of 73.6 in/yr 

measured during the 1990–99 time period within the study 

area. Regional climate model potential ET output for CCSM 

climate simulations during 2060–69 varied between 79.4 in/yr 

and 84.5 in/yr, with an average of 81.4 in/yr; potential ET 

output for the HadCM3 climate simulations during 2060–69 

varied between 76.3 in/yr and 82.5 in/yr, with an average 

of 78.9 (fig. 18B). The CCSM climate simulation results 

during 2060–69 represent a 9.2-percent increase relative 

to the 1990–99 CCSM climate simulation average yearly 

potential ET and the HadCM3 climate simulation results 

during 2060–69 represent a 10.0-percent increase relative 

to the 1990–99 HadCM3 climate simulation average yearly 

potential ET. The effects of the 9.1-percent increase in wetter 

future scenario precipitation could be partially dampened by 

the increase in wetter future potential ET, but the differences 

in timing of the two model inputs reduce this interaction. By 

the same reasoning, the effects of the 7.6-percent decrease in 

drier future scenario precipitation is likely exacerbated by the 

increase in drier future increase potential ET. 

The uncertainty of these projections was not considered 

as a part of this analysis. These scenarios are not meant to 

represent an exact expectation of future conditions. The 

uncertainty of these types of projections, especially this far 

into the future, is likely high, but the projections represent 

feasible possibilities of future conditions. 

0 500 1,000 1,500 2,000 2,500 3,000 3,500

Day of simulation

-150

-100

-50

0

50

100

150

Difference in cumulative rainfall, in inches

Drier

Wetter

EXPLANATION

Simulated, by climate simulation

 Community Climate System Model

 base case (CCSM)

 Hadley Centre Coupled Model

 version 3 base case (HadCM3)

Figure 17. Cumulative difference in rainfall between the Community 

Climate System Model (CCSM) climate simulation during 2060–69 and the 

CCSM climate simulation during 1990–99, and between the Hadley Centre 

Coupled Model version 3 (HadCM3) climate simulation during 2060–69 

and the HadCM3 climate simulation during 1990–99, averaged spatially 

for the county-scale model area.
22 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

85.6

80.9 80.9

73.0

63.3

67.1

86.9

63.2 67.9 67.0

74.2 73.8 74.3 74.0 73.9 75.2 76.3 74.7 73.5 75.7 73.8 73.3

70.9 68.1 70.1 70.6 70.5

73.6 72.8 74.1

81.3 84.5 81.3 81.7 81.5 82.3 80.7 79.4 80.0 81.4 78.4 76.3

81.2 77.9 77.9

82.5

77.3 76.3

81.6 79.7

Year

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

2060 2061 2062 2063 2064 2065 2066 2067 2068 2069

Year

0

10

20

30

40

50

60

70

80

90

100

Potential evapotranspiration, in inches Potential evapotranspiration, in inches

0

10

20

30

40

50

60

70

80

90

100

B. Future

A. Historical and base case

EXPLANATION

Simulated, by climate simulation—Value above bar

 is mean annual potential evapotranspiration (ET),

 in inches per year (in/yr)

 Community Climate System Model

 base case (CCSM)

 Hadley Centre Coupled Model

 version 3 base case (HadCM3)

Measured—Value above bar is mean annual 

 potential ET, in in/yr

Simulated, by climate simulation—Value above bar

 is mean annual potential ET, in in/yr

 CCSM

 HadCM3

EXPLANATION

Figure 18. Mean potential evapotranspiration, in inches, for the county-scale model area. A, measured and 

simulated for the Community Climate System Model (CCSM) and Hadley Centre Coupled Model version 3 (HadCM3) 

climate simulations during 1990–99, and B, simulated for the CCSM and HadCM3 climate simulations during 2060–69.
Effects of Climate Changes and Sea-Level Rise on GroundwaterLevels, Canal Stages, and Flowsat Coastal Structures 23

Simulation of the Hydrologic System for 

Future Climate and Sea-Level Conditions 

During 2060–69

Base-case (1990–99) and future (2060–69) conditions 

were simulated using the county- and local-scale models 

and compared to examine the hydrologic system’s response. 

First, base-case hydrologic conditions were established for 

comparison purposes for the county-scale and local-scale 

models, representing conditions during 1990–99, by replacing 

the precipitation and potential ET used in the historical 

simulation with output from the CCSM and HadCM3 climate 

simulations for that time period (table 5). These conditions 

are called the CCSM Base-Case and HadCM3 Base-Case 

scenarios, respectively. Then, 2060–69 hydrologic conditions 

were simulated for the county-scale and local-scale models 

by using CCSM and HadCM3 climate simulation output and 

sea levels as predicted by three sea-level rise rate functions for 

2060–69 (table 5). Sea-level rise scenarios were implemented 

to represent (1) a sustained linear sea-level rise trend derived 

from current and historical tidal measurements, designated 

as “Low Sea-Level Rise”; (2) the NRC Curve I, designated 

as “Intermediate Sea-Level Rise”; and (3) NRC Curve III, 

designated as “High Sea-Level Rise” (table 5), based on 

methodology established by the USACE (appendix 2). The 

resulting mean sea-level rise projections for the period 2010 

to 2060–69 using these three sea-level rise rates are 6.2 in. 

(0.52 ft), 11.9 in. (0.99 ft), and 29.9 in. (2.49 ft), respectively 

(fig. 7). Results of simulations representing different climate and 

sea-level scenarios during 2060–69 were compared with results 

of the base-case scenarios to evaluate changes in groundwater 

levels, surface-water stages, and surface-water flows in response 

to projected changes in precipitation, potential ET, and sea level. 

County-Scale Model Scenario Results

Results from the CCSM and HadCM3 Base-Case 

scenarios were compared to the results from the historical 

simulations and to scenarios representing each of the sea-level 

rise conditions (table 5). Differences in average wet-season 

groundwater levels, primary structure flows, and percentage 

of sea-level rise reflected in increased groundwater levels 

were calculated to evaluate the effects of potential climate and 

sea-level rise on the hydrologic system. 

Comparison of CCSM and HadCM3 Base-Case Scenarios 

to the Historical Simulation

The means of the MDs in groundwater levels at the 

groundwater-observation locations (fig. 8) between the 

CCSM and HadCM3 Base-Case scenarios and the historical 

simulation were -0.045 ft and -0.015 ft, respectively (table 6). 

The negative values indicate that, in general, both base-case 

scenarios simulate lower groundwater levels than the historical 

simulation. The largest MDs occurred at G–853 located near 

a well pumping location, which, with the drier base-case 

conditions, would lead to larger decreases in groundwater 

levels. The means of the MDs in primary structure flows 

between the CCSM and HadCM3 Base-Case scenarios 

and the historical simulation were -11.0 ft3/s and -6.4 ft3/s, 

indicating that the base-case scenarios generally simulate 

smaller structure flows than does the historical simulation. 

The largest difference in mean flow rates through a primary 

active structure between the CCSM and HadCM3 BaseCase scenarios and the historical simulation occurred at S–9 

and G–54 and were -19.2 ft3/s and -10.8 ft3/s, respectively 

(table 6). These large differences are likely due to the drier 

base-case conditions and the larger drainage areas that 

discharge through the S–9 pump and G–54 gated spillway. 

Comparison of Sea-Level Rise and Wetter or Drier Future 

Scenarios With Base-Case Scenarios

Simulation results show that the largest effects on 

groundwater levels attributed to changes in sea-level rise and 

precipitation occur in areas closest to the coast. For the wetter 

future scenarios, the five easternmost groundwater-station 

locations (G–853, G–1220, G–561, F–291, and 

G–2294; fig. 8) indicate average groundwater-level increases 

Table 5. Project modeling scenarios incorporating sea-level rise and climate change predictions.

[ET, evapotranspiration; CCSM, Community Climate System Model; NRC, National Resource Council; HadCM3, Hadley Centre Coupled Model version 3]

Designation Time frame Precipitation/ET source Sea-level rise source

Historical simulation 1/1/1990–12/31/1999 Historical data Historical tidal gage data 

CCSM Base-Case scenario 1/1/1990–12/31/1999 CCSM (1990–99) Historical tidal gage data

Wetter future, low sea-level rise scenario 1/1/2060–12/31/2069 CCSM (2060–69) Historical linear sea-level rise trend

Wetter future, intermediate sea-level rise scenario 1/1/2060–12/31/2069 CCSM (2060–69) NRC Curve I projection

Wetter future, high sea-level rise scenario 1/1/2060–12/31/2069 CCSM (2060–69) NRC Curve III projection

HadCM3 Base-Case scenario 1/1/1990–12/31/1999 HadCM3 (1990–99) Historical tidal gage data

Drier future, low sea-level rise scenario 1/1/2060–12/31/2069 HadCM3 (2060–69) Historical linear sea-level rise trend

Drier future, intermediate sea-level rise scenario 1/1/2060–12/31/2069 HadCM3 (2060–69) NRC Curve I projection

Drier future, high sea-level rise scenario 1/1/2060–12/31/2069 HadCM3 (2060–69) NRC Curve III projection
24 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

Table 6. Groundwater levels and primary structure flows for the historical simulation and differences in groundwater levels and 

primary structure flows between Community Climate System Model (CCSM) and Hadley Centre Coupled Model version 3 (HadCM3) 

Base-Case scenarios and the historical simulation at groundwater-well locations shown in figure 8 and surface-water structures shown 

in figure 2. 

[Wells grouped as westernmost, interior, and easternmost; positive values indicate an increase in groundwater levels from the historical simulation. ft, foot; 

CCSM, Community Climate System Model; HadCM3, Hadley Centre Coupled Model version 3; ft3/s, cubic foot per second]

Station name

Historical simulation mean 

groundwater level

(ft)

CCSM Base-Case scenario

mean difference

(ft)

HadCM3 Base-Case scenario 

mean difference

(ft)

Westernmost

G–2031 6.631 -0.001 0.008

G–2033 5.149 -0.013 -0.002

G–617 2.263 0.000 0.038

G–2034 2.161 -0.203 -0.157

G–970 1.387 -0.032 -0.009

Interior

G–1316 6.612 -0.025 -0.003

G–2395 -3.828 -0.098 -0.037

G–1221 1.096 -0.119 -0.087

G–1225 1.374 -0.046 -0.005

G–3571 1.426 0.022 0.055

Easternmost

G–853 0.794 0.035 0.055

G–1220 0.202 -0.067 -0.029

G–561 0.340 -0.087 -0.037

F–291 -0.414 -0.020 -0.010

G–2294 -0.593 -0.015 -0.010

Mean 1.640 -0.045 -0.015

Structure

Historical simulation 

mean flow

(ft3

/s)

CCSM Base-Case 

mean difference

(ft3/s)

HadCM3 Base-Case

mean difference

(ft3/s)

G–54 319.6 -12.5 -10.8

S–13 (spillway) 94.0 -6.7 -4.0

S–33 20.5 -5.4 -3.7

S–9 288.5 -19.2 -7.2

Mean 180.7 -11.0 -6.4

of 0.525 ft, 0.909 ft, and 2.085 ft for the low, intermediate, 

and high sea-level rise scenarios, respectively (table 7). Drier 

future scenarios for the five easternmost groundwater-station 

locations (G–853, G–1220, G–561, F–291, and G–2294) 

result in average groundwater-level increases of 0.329 ft, 

0.716 ft, and 1.911 ft for the low, intermediate, and high 

sea-level rise scenarios, respectively (table 8). These five 

groundwater-station locations are the closest observation 

locations to the sea-level boundary conditions, and thus, the 

resulting simulated groundwater levels are more strongly 

controlled by the effects of elevated sea level in the scenarios 

than at the interior and westernmost station locations. 

The groundwater level at the least affected easternmost 

station, G–853, increased by 1.566 ft and 1.390 ft for the 

high sea-level rise scenario for the wetter and drier future 

scenarios, respectively (tables 7 and 8). Station G–853 is the 

northernmost coastal station and is the closest to both SWR1 

specified-stage reach boundary conditions and a specified 

flow-pumping location. The proximity of a pumping center to 

this well keeps groundwater levels low, while the increased 

coastal groundwater levels associated with sea-level rise is 

reduced by the specified-stage reaches. 

The westernmost groundwater station locations 

(G–2031, G–2033, G–617, G–2034, and G–970; fig. 8) 

are least affected by increasing sea level and changes in 

precipitation compared to the easternmost and interior 

observation locations. Average groundwater-level differences 

between the wetter future and base-case scenarios were 
Effects of Climate Changes and Sea-Level Rise on GroundwaterLevels, Canal Stages, and Flowsat Coastal Structures 25

Table 7. Community Climate System Model (CCSM) Base-Case groundwater levels and primary structure flows and mean differences 

in groundwater levels and primary structure flows between base-case and wetter future sea-level rise simulations for the county-scale 

model.

[Wells grouped as westernmost, interior, and easternmost; positive values indicate an increase in groundwater levels and flows from the base-case simulation. 

CCSM, Community Climate System Model; ft, foot; ft3/s, cubic foot per second]

Station name

CCSM Base-Case mean 

groundwater level

(ft)

Wetter future, low 

sea-level rise mean 

difference

(ft)

Wetter future, 

intermediate sea-level 

rise mean difference

(ft)

Wetter future, 

high sea-level rise 

mean difference

(ft)

Westernmost

G–2031 6.630 0.010 0.012 0.016

G–2033 5.137 0.035 0.041 0.052

G–617 2.263 0.033 0.037 0.053

G–2034 1.958 0.021 0.025 0.034

G–970 1.355 0.005 0.007 0.010

Mean 3.469 0.021 0.024 0.033

Interior

G–1316 6.587 0.041 0.043 0.049

G–2395 -3.926 0.104 0.119 0.163

G–1221 0.977 0.147 0.298 0.963

G–1225 1.328 0.217 0.296 0.545

G–3571 1.448 0.083 0.089 0.105

Mean 1.283 0.118 0.169 0.365

Easternmost

G–853 0.829 0.401 0.691 1.566

G–1220 0.135 0.572 0.985 2.221

G–561 0.254 0.632 1.050 2.354

F–291 -0.433 0.506 0.887 2.067

G–2294 -0.608 0.513 0.931 2.217

Mean 0.035 0.525 0.909 2.085

Structure

CCSM Base-Case 

mean flow

(ft3

/s)

Wetter future, 

low sea-level rise 

mean difference

(ft3

/s)

Wetter future, 

intermediate sea-level 

rise mean difference

(ft3

/s)

Wetter future, 

high sea-level rise 

mean difference

(ft3

/s)

G–54 307.1 6.9 12.2 21.5

S–13 (spillway) 87.3 11.6 6.7 -86.5

S–13 (pump) 0.4 0.3 4.0 86.5

S–33 15.1 6.6 8.9 15.2

S–9 269.3 4.6 5.9 12.5

0.021 ft, 0.024 ft, and 0.033 ft in the five westernmost 

groundwater-station locations for the low, intermediate, and 

high sea-level rise scenarios, respectively. In comparison, 

the average groundwater-level differences between drier 

future and base-case scenarios were -0.064 ft, -0.060 ft, 

and -0.051 ft in the five westernmost groundwater-station 

locations for the low, intermediate, and high sea-level 

rise scenarios, respectively (tables 7 and 8). This result 

indicates that precipitation totals have a stronger influence 

on groundwater levels at these westernmost station locations 

than tidal boundary conditions.

With increasing sea levels represented by the low, 

intermediate, and high sea-level rise scenarios, the west-toeast groundwater gradient during the wet season is reduced 

relative to historical conditions, east of the S–13a structure 

for both the wetter predicted climate conditions (fig. 19A) and 

drier predicted climate conditions (fig. 19B), as shown on a 

transect that passes through the local-scale model area (fig. 2). 

For all scenario simulations, structure S–13a effectively 

acts as an east-west divide of the C–11 Canal drainage 

area. Groundwater levels west of this structure change little 

relative to historical conditions with different magnitudes of 
26 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

Table 8. Hadley Centre Coupled Model version 3 (HadCM3) Base-Case groundwater levels and primary structure flows and mean 

differences in groundwater levels and primary structure flows between base-case and drier future sea-level rise simulations for the 

county-scale model.

[Wells grouped as westernmost, interior, and easternmost; positive values indicate an increase in groundwater levels and flows from base-case simulation. 

HadCM3, Hadley Centre Coupled Model version 3; ft, foot; ft3/s, cubic foot per second]

Station name

HadCM3 Base-Case 

mean 

groundwater level

(ft)

Drier future, 

low sea-level rise 

mean difference

(ft)

Drier future, intermediate sea-level rise mean 

difference

(ft)

Drier future, 

high sea-level rise 

mean difference

(ft)

Westernmost

G–2031 6.640 -0.015 -0.012 -0.006

G–2033 5.148 -0.022 -0.016 -0.003

G–617 2.301 -0.081 -0.076 -0.061

G–2034 2.004 -0.114 -0.110 -0.101

G–970 1.378 -0.088 -0.086 -0.082

Mean 3.494 -0.064 -0.060 -0.051

Interior

G–1316 6.609 -0.051 -0.049 -0.042

G–2395 -3.864 -0.066 0.050 0.003

G–1221 1.009 -0.029 0.122 0.796

G–1225 1.369 -0.041 0.044 0.331

G–3571 1.481 -0.102 -0.095 -0.078

Mean 1.321 -0.058 -0.006 0.201

Easternmost

G–853 0.849 0.217 0.508 1.390

G–1220 0.173 0.321 0.743 2.034

G–561 0.303 0.305 0.733 2.073

F–291 -0.423 0.373 0.754 1.935

G–2294 -0.603 0.428 0.842 2.119

Mean 0.060 0.329 0.716 1.911

Structure

HadCM3 Base-Case 

mean flow

(ft3

/s)

Drier future, 

low sea-level rise 

mean difference

(ft3

/s)

Drier future, intermediate sea-level rise mean 

difference

(ft3

/s)

Drier future, 

high sea-level rise 

mean difference

(ft3

/s)

G–54 308.8 -5.5 -1.6 8.8

S–13 (spillway) 90.0 -5.3 -9.4 -89.1

S–13 (pump) 0.3 0.3 3.4 74.6

S–33 16.8 -1.7 0.7 8.0

S–9 281.3 -27.5 -26.0 -19.6

sea-level rise because, within the model, canal stages west of 

S–13a are controlled by the S–9 structure operations. Changes 

in precipitation and potential ET from base-case to the future 

predicted climate conditions have minimal effects, as shown by 

slight differences between groundwater levels along the transect 

(figs. 19A, B). Subsequently, flow through the S–9 structure is 

reduced during the drier future scenario and is increased in the 

wetter future scenario relative to historical conditions effectively 

controlling C–11 Canal levels west of S–13a. 

East of the S–13a structure, operations at the 

S–13 structure change for the different sea-level rise scenarios 

(figs. 20 and 21). The S–13 structure has a gravity spillway 

and a pump, and generally operates as follows: when upstream 

stages are rising, the gates for the spillway are opened at an 

upstream stage of 0.199 ft above NAVD 88 to release water to 

tide; when upstream stages are falling, the spillway begins to 

close at an upstream stage of -0.210 ft above NAVD 88. The 

S–13 pump is represented as a stage-discharge structure in 

the SWR1 process with a linear stage-discharge relationship, 

which begins to discharge to tide at an upstream stage of 0.7 ft 

above NAVD 88 and reaches its maximum pumping rate 

of 540 ft3/s at an upstream stage of 1.7 ft above NAVD 88. 

For the low and intermediate sea-level rise scenarios, the 

spillway is the primary source of discharge (figs. 20A, B), 
Effects of Climate Changes and Sea-Level Rise on GroundwaterLevels, Canal Stages, and Flowsat Coastal Structures 27

State Plane Easting, in feet

836,800 856,800 876,800 896,800 916,800 936,800

836,800 856,800 876,800 896,800 916,800 936,800

Groundwater level, in feet above North American Vertical Datum of 1988

-1.0

1.0

3.0

5.0

7.0

9.0

11.0

-1.0

1.0

3.0

5.0

7.0

9.0

11.0

S–13a S–13

S–13a S–13

A. Wetter future precipitation and evapotranspiration (ET)

B. Drier future precipitation and ET

EXPLANATION

Hadley Centre Coupled Model

 version 3 base case

Low sea-level rise

Intermediate sea-level rise

High sea-level rise

EXPLANATION

Community Climate System 

 Model base case

Low sea-level rise

Intermediate sea-level rise

High sea-level rise

Figure 19. West-east continuous transect of average wet-season groundwater levels 

for base-case and wetter and drier future sea-level rise scenarios for 2060-69.

and the pump does not discharge. During these simulations, 

the upstream stage at S–13 is similar to the base-case 

scenarios (figs. 21A, B). 

For the high sea-level rise scenarios, operation of the 

S–13 spillway and pump structures changes notably from 

historical conditions as sea level rises. The elevated tidal 

levels increase the spillway’s downstream stage and reduce 

the structure’s capacity to discharge to the coast. With the 

high sea-level rise scenario average tidal level of 1.65 ft 

above NAVD 88 during 2060–69, the spillway daily average 

downstream stage is nearly always greater than the upstream 

stage (fig. 21C), precluding discharge by gravity flow and 

requiring instead the S–13 pump to discharge nearly all of the 

structure flow (fig. 20D). Under these conditions, the spillway 

is inoperable for large portions of the simulation period 

(figs. 20C, D; tables 7 and 8). When pumping is required 

to transport the majority of the S–13 discharge because of 

the linear stage-discharge relationship that sets the pumping 

controls, the average upstream stages increase, resulting in 

higher canal and groundwater levels, as seen between the 

S–13a and S–13 structures in figure 19. For the high sea-level 

rise scenarios, the upstream stage at S–13 becomes elevated 

by an average of 0.744 ft for the wetter and 0.721 ft for the 

drier future precipitation scenarios. In contrast to conditions 

at S–13, the other primary active structures (G–54, S–33, and 

S–9) maintain upstream levels similar to base-case scenarios 

for the high sea-level rise scenarios (fig. 22). 

The effects of sea-level rise on groundwater levels within 

the eastern coastal part of the model area are further illustrated 

by evaluating the percentage of increased sea-level rise that 

is reflected in the increased average wet-season groundwater 

levels (figs. 23 and 24). For example, if wet-season 

groundwater levels reflected 100 percent of the average 

sea-level rise, groundwater levels would rise 0.514 ft, 0.99 ft, 

and 2.49 ft for the low, intermediate, and high sea-level rise 

scenarios, respectively. In contrast, if wet-season groundwater 

levels reflected 0 percent of sea-level rise for any scenario, 

groundwater levels would not rise at all. For all scenarios, 

the groundwater levels in coastal areas reflect increases 

nearly equivalent to sea-level rise, whereas in much of the 

simulated area away from the coast, groundwater levels do 

not reflect any effects of sea-level rise. The effect of sea-level 
28 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 5 6 7 8 9 10

0 1 2 3 4 5 6 7 8 9 10

0 1 2 3 4 5 6 7 8 9 10

0 1 2 3 4 5 6 7 8 9 10

Simulation year

Flow, in cubic feet per second

0

50

100

150

200

250

300

350

400

0

50

100

150

200

250

300

350

400

0

50

100

150

200

250

300

350

400

0

50

100

150

200

250

300

350

400

EXPLANATION

Community Climate System

 Model (CCSM) base case

Wetter future

Drier future

EXPLANATION

CCSM base case

Wetter future

Drier future

EXPLANATION

CCSM base case

Wetter future

Drier future

EXPLANATION

CCSM base case

Wetter future

Drier future

A. S–13 Spillway, low sea-level rise

B. S–13 Spillway, intermediate sea-level rise

C. S–13 Spillway, high sea-level rise

D. S–13 Pump, high sea-level rise

Figure 20. Structure S–13 spillway flow, for A, low; B, intermediate; and C, high sea-level rise 

scenarios, and D, pump flow for the high sea-level rise scenarios for 1990-99 or 2060-69. 
Effects of Climate Changes and Sea-Level Rise on GroundwaterLevels, Canal Stages, and Flowsat Coastal Structures 29

Simulation year

0 1 2 3 4 5 6 7 8 9 10

0 1 2 3 4 5 6 7 8 9 10

0 1 2 3 4 5 6 7 8 9 10

Upstream stage, in feet above North American Vertical Datum of 1988

-0.50

0

0.50

1.00

1.50

2.00

2.50

3.00

3.50

-0.50

0

0.50

1.00

1.50

-0.50

0

0.50

1.00

1.50

A. Low sea-level rise

B. Intermediate sea-level rise

C. High sea-level rise

EXPLANATION

Community Climate System 

 Model (CCSM) base case

Wetter future

Drier future

EXPLANATION

CCSM base case

Wetter future

Drier future

EXPLANATION

CCSM base case

Wetter future

Drier future

Daily tide

Figure 21. Upstream stage at structure S–13 for A, low; B, intermediate; and C, high 

sea-level rise and wetter and drier future climate scenarios for 1990-99 or 2060-69. 
30 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

Simulation year

0 1 2 3 4 5 6 7 8 9 10

0 1 2 3 4 5 6 7 8 9 10

0 1 2 3 4 5 6 7 8 9 10

Upstream stage, in feet above North American Vertical Datum of 1988

0

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

0

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0

0.50

1.00

1.50

2.00

2.50

A. G–54

B. S–33

C. S–9

EXPLANATION

Community Climate System 

 Model (CCSM) base case

Wetter future

Drier future

EXPLANATION

CCSM base case

Wetter future

Drier future

EXPLANATION

CCSM base case

Wetter future

Drier future

Figure 22. Upstream stage at primary structures A, G–54; B, S–33; and C, S–9 for high 

sea-level rise and wetter and drier future climate scenarios for 1990-99 or 2060-69. 

rise on groundwater levels for the drier future scenarios is 

less extensive (fig. 24) than for the wetter future scenarios 

(fig. 25) because of the relatively lower precipitation. The 

general northwest-to-southeast groundwater-level gradient 

within the model area persists for all scenarios, even with the 

average sea-level rise of 2.49 ft from the high sea-level rise 

scenarios (fig. 25). 

The coastal areas also exhibit the largest increase in 

extents of groundwater cells, with average wet-season depth 

to groundwater of less than 1 ft because of sea-level rise and 

precipitation variations (fig. 26). These coastal areas have 

a much higher likelihood of becoming inundated during 

moderate precipitation events because of the shallow depth to 

groundwater. For the wetter future scenarios, the low sea-level 

rise simulation resulted in a 2.484-mi2

 (+3.0 percent) increase 

in inundated area; the intermediate simulation resulted in a 

3.757-mi2 (+4.6 percent) increase; and the high simulation 

scenario resulted in a 12.106-mi2 (+14.8 percent) increase 

in inundated coastal area. With the decreased precipitation 

in the drier future scenarios, the total area where the depth 

to groundwater was less than 1 ft decreased by 3.085 mi2

(-3.7 percent) and 1.668 mi2 (-2.0 percent) for the low and 

intermediate sea-level rise scenarios, respectively, and increased 

by 5.69 mi2 (+6.9 percent) for the high sea-level rise scenario.
Effects of Climate Changes and Sea-Level Rise on GroundwaterLevels, Canal Stages, and Flowsat Coastal Structures 31

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

G–54

S–13a S–13

S–9

S–33

S–34

G–54

S–13a S–13

S–9

S–33

S–34

G–54

S–13a S–13

S–9

S–33

S–34

EXPLANATION

Percentage of sea-level rise

 100

 50

 0

Surface-water structure and identifier G–54

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

A. Wetter future, low sea-level rise B. Wetter future, intermediate sea-level rise

C. Wetter future, high sea-level rise

Figure 23. Percentage of sea-level rise reflected in increased average wet-season groundwater levels for A, low sea-level 

rise; B, intermediate sea-level rise; and C, high sea-level rise, for wetter future climate scenarios within the county-scale 

model.
32 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

G–54

S–13a S–13

S–9

S–33

S–34

G–54

S–13a S–13

S–9

S–33

S–34

G–54

S–13a S–13

S–9

S–33

S–34

EXPLANATION

Percentage of sea-level rise

 100

 50

 0

Surface-water structure and identifier G–54

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

A. Drier future, low sea-level rise B. Drier future, intermediate sea-level rise

C. Drier future, high sea-level rise

Figure 24. Percentage of sea-level rise reflected in increased average wet-season groundwater levels for A, low sea-level 

rise; B, intermediate sea-level rise; and C, high sea-level rise, for drier future climate scenarios within the county-scale model.
Effects of Climate Changes and Sea-Level Rise on GroundwaterLevels, Canal Stages, and Flowsat Coastal Structures 33

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

G–54

S–13a S–13

S–9

S–33

S–34

G–54

S–13a S–13

S–9

S–33

S–34

G–54

S–13a S–13

S–9

S–33

S–34

EXPLANATION

Groundwater level, in feet above North

 American Vertical Datum of 1988

 8

 3

 -2

Surface-water structure and identifier G–54

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

A. Community Climate System Model base case B. Wetter future, high sea-level rise

C. Drier future, high sea-level rise

Figure 25. Average wet-season groundwater levels within the county-scale model for A, Community Climate Systems Model 

base case; B, wetter future, high sea-level rise; and C, drier future, high sea-level rise, future scenarios.
34 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 2 31 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983 EXPLANATION

Inundated in base case

Depth to groundwater, in feet

Greater than 1

1

0.5

Less than 0

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

A. Community Climate System Model base case B. Wetter future, high sea-level rise

Figure 26. Average wet-season depth to groundwater for base-case, A, and the wetter future high sea-level rise, B, scenarios 

within the county-scale model.

Local-Scale Model Scenario Results

The scenarios representing future conditions that were 

applied to the county-scale model were also applied to the 

local-scale model. These conditions included combinations of 

low, intermediate, and high sea-level rise rates and wetter and 

drier future climate conditions. The local-scale model’s results 

are more spatially refined with 166.7-ft grid spacing compared 

to the 500-ft grid spacing used for the county-scale model. 

Additionally, the local-scale model uses the SWR1 process 

time step of 10 minutes, compared to the 15 minutes used in 

the county-scale model, and uses hourly tidal-level data instead 

of the daily averaged tidal levels used in the county-scale 

model. Differences in average wet-season groundwater levels, 

primary structure flows, and increases in groundwater levels 

were used to evaluate the effects of potential climate conditions 

and sea-level rise on the hydrologic system. 

Comparison of Base-Case Climate Scenarios to the 

Historical Simulation

Local-scale, model-simulated base-case groundwater 

levels and structure flow rates deviate more from the historical 

scenario results than results from the county-scale model. For 

the three groundwater-observation locations in the localscale model, the simulated mean base-case groundwater level 

was 0.379 ft and 0.339 ft lower for the CCSM and HadCM3 

scenarios, respectively, than for the historical simulation 

(table 9). Similarly, the mean simulated flow rates through 

the G–54 and S–13 (spillway) structures were 23.0 ft3/s 

and 19.1 ft3/s lower for the CCSM and HadCM3 scenarios, 

respectively, compared to the historical simulation. The 

time-series results from the local-scale base-case scenarios for 

both groundwater levels and structure flow have similar peaks 

and trends when compared to the results from the historical 
Effects of Climate Changes and Sea-Level Rise on GroundwaterLevels, Canal Stages, and Flowsat Coastal Structures 35

Table 9. Groundwater levels and primary structure flow and 

changes for historical and base-case Community Climate System 

Model (CCSM) and Hadley Centre Coupled Model version 3 

(HadCM3) simulations for the local-scale model.

[Positive values indicate an increase in groundwater levels and flows from 

historical simulation. ft, foot; CCSM, Community Climate System Model; 

HadCM3, Hadley Centre Coupled Model version 3; ft3/s, cubic foot per 

second]

Station name

Historical 

simulation

mean groundwater level

(ft)

CCSM 

Base-Case

mean difference

(ft)

HadCM3 

Base-Case

mean difference

(ft)

G–617 2.318 -0.261 -0.222

G–1221 1.244 -0.505 -0.474

G–561 0.527 -0.372 -0.322

Mean 1.363 -0.379 -0.339

Structure

Historical 

simulation

mean flow

(ft3

/s)

CCSM 

Base-Case

mean difference

(ft3

/s)

HadCM3 

Base-Case

mean difference

(ft3

/s)

G–54 317.9 -23.9 -18.8

S–13 (spillway) 107.8 -22.0 -19.3

Mean 212.8 -23.0 -19.1

scenario and the corresponding county-scale base-case 

scenarios. These differences are likely associated with the 

increased resolution within the groundwater model and 

increased density in SWR1-represented surface-water features. 

Comparison of Sea-Level Rise and Wetter or Drier Future 

Scenarios With Base-Case Scenarios

Similar to the results from the county-scale model, 

simulation results from the local-scale models show that the 

largest effects on groundwater levels caused by changes in 

sea-level rise and precipitation occur in areas closest to the 

coast. In the wetter future climate scenarios for the local-scale 

model, the mean precipitation increased 18.8 percent from 

56.9 in/yr during the 1990–99 CCSM Base-Case scenario to 

67.6 in/yr during the 2060–69 future simulation period. This 

increase in precipitation, coupled with increased sea level, 

resulted in average groundwater-level increases of 0.710 ft, 

1.133 ft, and 2.423 ft at the easternmost groundwater station 

location, G–561, for the low, intermediate, and high sea-level 

rise scenarios, respectively. The westernmost groundwater 

well, G–617, displayed minimal increases of 0.037 ft, 0.034 ft, 

and 0.036 ft for the low, intermediate, and high sea-level rise 

scenarios, respectively, whereas the centrally located well, 

G–1221, exhibited increases of 0.238 ft, 0.397 ft, and 1.074 ft 

for the same scenarios, respectively (table 10). 

In the drier future climate scenarios for the local-scale 

area, precipitation decreased 7.0 percent from 58.6 in/yr 

during the 1990–99 HadCM3 Base-Case scenario to 54.5 in/yr 

during the 2060–69 future simulation period. The decrease in 

precipitation, coupled with increasing sea level, resulted in 

increasing groundwater levels in the easternmost well, G–561, 

by 0.345 ft, 0.777 ft, and 2.103 ft for the low, intermediate, 

and high sea-level rise scenarios, respectively. Simulated 

groundwater levels decreased at the westernmost well, G–617, 

relative to the baseline simulation by 0.116 ft, 0.121 ft, and 

0.121 ft for the low, intermediate, and high sea-level rise 

scenarios, respectively. Simulated groundwater levels at 

well G–1221 increased relative to the baseline simulation by 

0.048 ft, 0.205 ft, and 0.898 ft for the low, intermediate, and 

high sea-level rise scenarios, respectively (table 10).

The upstream stage at structure G–54 was maintained 

within the same gate-operating range of 2.899 to 1.899 ft 

above NAVD 88 for all wetter and drier future scenarios, 

as was maintained in both base-case scenarios. For the 

wetter future scenarios, the MD in the mean flow through 

the G–54 structure was 11.8 ft3/s, 14.9 ft3/s, and 21.4 ft3/s 

for the low, intermediate, and high sea-level rise scenarios, 

respectively. For the drier future scenarios, the MD in the 

mean flow through the G–54 structure was -7.5 ft3/s, -4.8 ft3/s, 

and 3.6 ft3/s for the low, intermediate, and high sea-level rise 

scenarios (table 10). 

In contrast, the upstream stage and flow rates at structure 

S–13 change substantially at different sea levels in the future 

scenarios, compared to the small differences in upstream stage 

and flow rates at structure G–54 (fig. 27). The future scenarios 

result in higher and more frequent peaks in upstream stages 

at structure S–13 than those seen in the base-case scenarios as 

the downstream stages increase with the low, intermediate, and 

high sea-level rise scenarios (figs. 27B, C). For the high sealevel rise future scenarios, the upstream stage is consistently 

above base-case scenario stages, with average increases of 

0.693 ft and 0.671 ft for the wetter and drier future scenarios, 

respectively (figs. 27B, C). The S–13 pump rarely operates in 

the base-case scenarios, and there are only marginal increases 

for the low and intermediate sea-level rise scenarios (table 10). 

In the high sea-level rise scenarios, there is a shift to rely 

more on the S–13 pump than the spillway, with 71.2 percent 

of the structure flow being pumped in the wetter scenario 

and 68.7 percent being pumped in the drier scenario. This is 

less reliance on the pump than required in the county-scale 

model, which was 99 percent for the wetter and drier high 

sea-level rise future scenarios. The difference can be attributed 

to the temporal resolution of the tidal stage inputs used in 

the county- and local-scale simulations. The county-scale 

model uses daily tidal stage values, whereas the local-scale 

model uses hourly tidal stage values. During the daily low tide 

periods of the local-scale model, the spillway can operate if 

the downstream stage falls below the upstream stage, which 

does not occur when using averaged daily tidal stages. As the 

average tidal stage levels continue to increase throughout the 

high sea-level rise simulation, the number of times when the 
36 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

Table 10. Simulated groundwater levels and primary structure flows and mean differences in groundwater levels and primary 

structure flows for climate and sea-level rise scenarios using the local-scale model. 

[Positive values indicate an increase in groundwater levels and flows from the base-case simulation. CCSM, Community Climate System Model; ft, foot; ft3/s, 

cubic foot per second; HadCM3, Hadley Centre Coupled Model version 3]

CCSM/wetter future

Station name

Base-case mean 

groundwater level

(ft)

Future, low 

sea-level rise mean 

difference 

(ft)

Future, intermediate 

sea-level rise mean

difference

(ft)

Future, high sea-level 

rise mean difference

(ft)

G–617 2.057 0.037 0.034 0.036

G–1221 0.739 0.238 0.397 1.074

G–561 0.156 0.710 1.133 2.423

Structure

Base-case

mean flow

(ft3

/s)

Future, low 

sea-level rise 

mean difference

(ft3

/s)

Future, intermediate 

sea-level rise

mean difference

(ft3

/s)

Future, high sea-level 

rise mean difference

(ft3

/s)

G–54 293.9 11.8 14.9 21.4

S–13 (spillway) 85.8 14.1 13.9 -59.9

S–13 (pump) 0.0 0.4 2.2 64.0

S–13 percent flow spillway/pump 100.0/0.0 99.6/0.4 97.8/2.2 28.8/71.2

HadCM3/drier future

Station name

Base-case mean 

groundwater level

(ft)

Future, low 

sea-level rise 

mean difference

(ft)

Future, intermediate 

sea-level rise

mean difference

(ft)

Future, high sea-level 

rise mean difference

(ft)

G–617 2.096 -0.116 -0.121 -0.121

G–1221 0.770 0.048 0.205 0.898

G–561 0.206 0.345 0.777 2.103

Structure

Base-case

mean flow

(ft3

/s)

Future, low 

sea-level rise 

mean difference

(ft3

/s)

Future, intermediate 

sea-level rise

mean difference

(ft3

/s)

Future, high sea-level 

rise mean difference

(ft3

/s)

G–54 299.1 -7.5 -4.8 3.6

S–13 (spillway) 88.4 -3.8 -2.9 -64.5

S–13 (pump) 0.0 0.3 1.7 52.6

S–13 percent flow spillway/pump 100.0/0.0 99.6/0.4 98.0/2.0 31.3/68.7

downstream stage falls below the upstream stage decreases, 

and there is more reliance on the pump (fig. 28). As in the 

county-scale model, the stage-discharge curve representing the 

pump causes the upstream stage to increase when the spillway 

is no longer able to operate.

The increased precipitation for the wetter future scenarios 

has a substantial effect on the increased average wet-season 

groundwater levels for the three sea-level rise scenarios 

(fig. 29). Compared to the drier future scenarios results 

(fig. 30), the average wet-season groundwater-level maps 

indicate increased mounding of water in interior areas between 

surface-water features, as well as higher overall groundwater 

levels. While some interior areas of the eastern part of 

the model area have only minor increases in groundwater 

levels for the drier future low and intermediate sea-level 

rise scenarios, the wetter future model results indicate 

groundwater-level increases that are greater than the increases 

in sea level. The results from the drier scenarios show less 

interior mounding (fig. 30). Despite these differences, the 

groundwater-level maps exhibit the same general patterns 

for each scenario: increases in groundwater levels near the 

coast are nearly equal to the sea-level rise; groundwater tends 

to mound in areas between surface-water features, such as 

canals, and this becomes more pronounced in the wetter future 
Simulation of Hypothetical Mitigation Strategies 37

Simulation year

0 1 2 3 4 5 6 7 8 9 10

0 1 2 3 4 5 6 7 8 9 10

0 1 2 3 4 5 6 7 8 9 10

Simulated upstream stage, in feet above North American Vertical Datum of 1988

1.50

2.00

2.50

3.00

3.50

-0.50

0

0.50

1.00

1.50

-0.50

0

0.50

1.00

1.50

A. Structure G–54, high sea-level rise

B. Structure S–13, wetter future

C. Structure S–13, drier future

EXPLANATION

Community Climate System 

 Model (CCSM) base case

Wetter future

Drier future

EXPLANATION

Hadley Centre Coupled Model

 version 3 base case

Low sea-level rise

Intermediate sea-level rise

High sea-level rise

EXPLANATION

CCSM base case

Low sea-level rise

Intermediate sea-level rise

High sea-level rise

Figure 27. Simulated upstream stage at the A, G–54; and B, C, 

S–13 structures for future climate and sea-level rise scenarios for the localscale model for 1990-99 or 2060-69.

scenarios; and groundwater increases less in the western part 

of the model than in the eastern part. Pump operations at 

S–13 effectively lower the groundwater levels between the 

S–13 and S–13a structures for the high sea levels and limit 

the groundwater increases in the western part of the model 

(figs. 29, 30, and 31). 

The average wet-season depths to groundwater for each 

of the local-scale model future scenarios indicate a larger area 

of potential inundation in the eastern model area relative to 

the western part (fig. 32), as was shown by using results from 

the county-scale model (fig. 26). For the CCSM scenarios, 

the current rate of sea-level rise simulation had an increased 

area of 1.33 mi2 (+12.0 percent) with a water table of less 

than 1 ft, whereas the NRC Curve I and NRC Curve III 

simulations had increased areas of 2.13 mi2 (+13.0 percent) 

and 5.79 mi2 (+14.0 percent).

Simulation of Hypothetical Mitigation 

Strategies

The results of this study indicate that projected 

future climate change and, in particular, sea-level rise will 

increase groundwater levels in Broward County, with the 

largest increases occurring along the eastern coastline and 

diminishing inland. Because of the highly permeable aquifer, 

shallow depths to the water table, and flat groundwater 

gradients, the projected rise in sea level will contribute 

to widespread increases in groundwater levels and will 

exacerbate the challenges of adapting to or mitigating the 

negative effects of sea-level rise and climate change. The 

increased groundwater levels exhibited in the various future 

scenarios result in newly inundated areas and increase the 
38 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 5 6 7 8 9 10

0 1 2 3 4 5 6 7 8 9 10

Simulation year

Flow, in cubic feet per second

0

50

100

150

200

250

300

350

400

0

50

100

150

200

250

300

350

400

EXPLANATION

S–13 (spillway) Community Climate

 System Model base case

S–13 (pump) High sea-level rise

S–13 (spillway) High sea-level rise

EXPLANATION

S–13 (spillway) Hadley Centre Coupled

 Model version 3 base case

S–13 (pump) High sea-level rise

S–13 (spillway) High sea-level rise

B. Drier future 

A. Wetter future 

Figure 28. Spillway and pump flow for structure S–13 for A, wetter future, and B, drier future climate and 

sea-level rise scenarios for the local-scale model for 1990-99 or 2060-69.

areal extent of flood-prone lands because of reduced soil 

storage capacity. Possible mitigation strategies include 

alterations to coastal structure operations or locations, changes 

to building foundation and roadway elevation requirements, 

and neighborhood-scale flood control using pumps. Using the 

local-scale and county-scale models, scenarios using these 

types of mitigation strategies were simulated with the primary 

goal of maintaining historical simulation groundwater levels.

Adapting Pumping Operations at S–13 to 

Maintain Upstream Stages

The coastal S–13 spillway operations in response to rising 

downstream stages during the high sea-level rise scenarios 

resulted in increased upstream stage (figs. 21 and 27). 

According to the linear stage-discharge operational function 

of the pump, pumping starts as the upstream stage rises 

0.70 ft above NAVD 88 and increases linearly to a peak rate 

of 540 ft3/s when the upstream stage reaches 1.7 ft above 

NAVD 88. Operating along this stage-discharge curve resulted 

in average increases of 0.744 ft and 0.721 ft in upstream stage 

for the wetter and drier high sea-level scenarios, respectively. 

Pump operations were modified to maintain S–13 upstream 

stages at 0.11 ft above NAVD 88, which is the average stage 

for both base-case scenarios. The resulting stage-discharge 

operational function starts as the upstream stage rises above 

0.0 ft NAVD 88, increases linearly to a rate of 85 ft3/s at a stage 

elevation of 0.11 ft above NAVD 88, and then increases linearly 

to a peak rate of 540 ft3/s when the upstream stage reaches 0.7 ft 

above NAVD 88. This modified stage-discharge operation was 

simulated by using the county-scale model with the highest 

projected sea level and resulted in average S–13 upstream 

stages of 0.15 ft and 0.13 ft for the wetter and drier future 

scenarios, respectively (fig. 33). The model-simulated 

average flow through the structure increased from 90.0 ft3/s to 

116.9 ft3/s for the wetter future scenario and increased from 

74.8 ft3/s to 103.6 ft3/s for the drier future scenario using the 

altered pump operation. The S–13 model-simulated spillway 

flow was 0.0 ft3/s for each of the altered pump operation 

future scenarios because of the reduced upstream stage and 

increased downstream stage due to sea-level rise. The effect 

on groundwater levels was limited to the area between the 

S–13 and S–13a structures, extending north to the North New 

River Canal and south toward the C–9 Canal, with a maximum 

decrease in average groundwater of 0.70 ft (fig. 34).
Simulation of Hypothetical Mitigation Strategies 39

0 1 2 3 4 MILES

0 2 31 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

1.00

0

2.50

Average wet-season groundwater-level increases, in feet

Area enlarged

County-scale

model area

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

C. Wetter future, high sea-level rise

B. Wetter future, intermediate sea-level rise

A. Wetter future, low sea-level rise

Figure 29. Average wet-season groundwater-level increases in the local-scale model 

for wetter future A, low; B, intermediate; and C, high sea-level rise scenarios.
40 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 2 31 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

1.00

Less than 0

2.50

Average wet-season groundwater-level increases, in feet

Area enlarged

County-scale

model area

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

C. Drier future, high sea-level rise

B. Drier future, intermediate sea-level rise

A. Drier future, low sea-level rise

Figure 30. Average wet-season groundwater-level increases in the local-scale model 

for drier future A, low; B, intermediate; and C, high sea-level rise scenarios.
Simulation of Hypothetical Mitigation Strategies 41

0 1 2 3 4 MILES

0 2 31 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

1.50

-1.00

4.00

Groundwater level, in feet above North American Vertical Datum of 1988

Area enlarged

County-scale

model area

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

C. Drier future, high sea-level rise

B. Wetter future, high sea-level rise

A. Community Climate System Model base case

Figure 31. Average wet-season groundwater level for A, base-case and high sealevel rise; B, wetter; and C, drier future climate scenarios for the local-scale area.
42 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 2 31 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Inundated in base case

Depth to groundwater, in feet

Greater than 1

1

0.5

Less than 0

Area enlarged

County-scale

model area

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

C. High sea-level rise

B. Intermediate sea-level rise

A. Low sea-level rise

Figure 32. Average wet-season depth to groundwater in the local-scale model for 

wetter future A, low; B, intermediate; and C, high sea-level rise scenarios.
Simulation of Hypothetical Mitigation Strategies 43

0 1 2 3 4 5 6 7 8 9 10

Simulation year

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

Stage, in feet above NAVD 88

EXPLANATION

Upstream stage, in feet above North American 

 Vertical Datum of 1988 (NAVD 88), at structure

 S–13, by scenario

 Community Climate System Model base case

 Original operations (wetter)

 Original operations (drier)

 Altered operations (wetter)

 Altered operations (drier)

Figure 33. Upstream stage at structure S–13 for wetter and drier high sea-level rise scenarios with original and 

altered S–13 pump operations for 1990-99 or 2060-69.

Pumping Groundwater to Reduce Potential 

for Inundation

Additional adaptation strategies were simulated by using 

the local-scale model to examine the concept of using pumps 

to reduce the local groundwater levels in neighborhood-sized 

areas and to thereby reduce the potential for inundation from 

sea-level rise and precipitation events. For these scenarios, 

pumping of groundwater to maintain three specified control 

elevations was simulated in two areas of interest (fig. 35). 

For these scenarios, the excess groundwater was assumed to 

be removed from the area. The magnitude of the average and 

peak pumping rates required to maintain groundwater levels 

at the control elevations provide city planners and water 

resource managers an indication of the potential effort required 

to prevent inundation in these areas. A major limitation to 

these results is the uncertainty in localized soil and aquifer 

properties in the areas, which would have a substantial effect 

on required pumping rates to prevent inundation. Additionally, 

local surface-water control features such as drains, piped 

connections, and direct runoff connections are not explicitly 

simulated, and in reality, these features could have an effect on 

drainage rates. 

The two selected areas were each composed of 

21 columns and 21 rows within the local-scale model, 

representing 0.439 mi2 each (fig. 35). The pumping of excess 

groundwater was simulated by using the MODFLOW 2005 

Drain package (DRN). The conductance used for DRN 

features representing the pumping of excess groundwater 

was uniformly set to 25,000 square feet per day. Area 1 is 

a coastal site that showed an increase of 2.50 ft in average 

wet-season groundwater levels during the wetter high 

sea-level rise scenario. Area 1 has strong connections 

to tidal boundaries. The specified groundwater-control 

elevations were set to values that would allow increases in 

groundwater levels of zero, 1 ft, and 2 ft above the average 

wet-season levels from the base-case simulation for each 

cell. The resulting average groundwater-control elevations 

for Area 1 were -0.61 ft, 0.39 ft, and 1.39 ft above NAVD 88. 

Area 2 is west of Area 1 and east of the S–13 and G–54 

control structures; Area 2 showed an increase of 2.36 ft in 

average wet-season groundwater levels during the wetter 

high sea-level rise scenario (fig. 35). Area 2 was farther 

removed from tidal boundaries than Area 1 but was strongly 

hydraulically connected to canal reaches within the area. 

Conditions representing the wetter high sea-level rise inputs 

were simulated by using three groundwater-control elevations: 

zero, 1 ft, and 2 ft above the base-case average wet-season 

groundwater levels within each cell. This simulation resulted 

in average groundwater-control elevations for Area 2 of 

0.08 ft, 1.08 ft, and 2.08 ft above NAVD 88.

The average simulated wet-season groundwater levels 

within Area 1 were 0.54 ft, 1.07 ft, and 1.78 ft above 

NAVD 88 for the three scenarios, with groundwater-control 

elevations representing zero, 1 ft, and 2 ft of groundwater-level 

increase from base conditions, respectively. When compared 

to the base-case average level of -0.61 ft above NAVD 88, 

these values result in average wet-season groundwater-level 

increases of 1.15 ft, 1.68 ft, and 2.39 ft for the zero, 1 ft, and 

2 ft groundwater-control elevation scenarios, respectively. 

The average rates of groundwater pumping required to 

maintain the control groundwater elevations in Area 1 were 

2,220.0 ft3/s, 1,262.5 ft3/s, and 346.6 ft3/s for the zero, 1-ft, 

and 2-ft control elevations, respectively (fig. 36). Because of 
44 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

ATLANTIC OCEAN

C–9

North New River Canal

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

S–13a S–13

EXPLANATION

Inactive model area

Active model area—

 No change in

 groundwater

 levels

Difference, in feet, in average wet-season groundwater levels between original

 and altered S–13 operations—Negative values indicate a decrease in average

 groundwater levels compared to original S–13 pump operations

Surface-water structure

S–13 and identifier

0

-0.35

-0.70

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 34. Difference in average wet-season groundwater levels between original and altered S–13 pump operations 

for the wetter future high sea-level rise scenario. Negative values indicate a decrease in average groundwater levels 

compared to original S–13 pump operations.
Simulation of Hypothetical Mitigation Strategies 45

0 1 2 MILES

0 1 2 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Active model domain

Tidal general head boundary

Area with drains applied

Active canal reach within cell

Area enlarged

County-scale

model area

80°10' 80°07'30"

26°07'30"

26°05'

Area 1

Area 2

Figure 35. Areas 1 and 2 for wetter future pumped adaptation strategy simulation.

the strong connection of Area 1 to general head boundaries 

(GHBs) representing the Intracoastal Waterway and the high 

conductivity used to characterize the aquifer, a large volume 

of water was removed, which caused considerable increases 

in groundwater levels despite the established drainage control 

elevations. The discharge of the large volumes of water 

removed in these scenarios represents an additional problem. 

As modeled, the water is assumed to be pumped to tide and 

is simply removed from the model. Some strategies could be 

devised to store and release water during low tidal periods, but 

such strategies were not addressed during these simulations 

and were beyond the scope of this study. 

The average model-simulated wet-season groundwater 

levels within Area 2 were 0.31 ft, 1.17 ft, and 1.71 ft above 

NAVD 88 for the three scenarios with drainage elevations 

representing zero, 1 ft, and 2 ft of groundwater level increase 

from base conditions, respectively. When compared to the 

base-case average level of 0.08 ft above NAVD 88, these 

values are average wet-season groundwater-level increases of 

0.23 ft, 1.09 ft, and 1.63 ft. The average rates of groundwater 

pumping required to maintain the control groundwater 

elevations in Area 2 were 636.0 ft3/s, 271.5 ft3/s, and 28.6 ft3/s 

for the zero, 1-ft, and 2-ft control elevations, respectively 

(fig. 36). These volumes are substantially less than those 

removed from Area 1 but still represent a considerable volume 

because of the high conductivity used to characterize the 

aquifer and the connection to canal reaches that pass through 

the same area.
46 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . . Monthly averaged groundwater removed, in cubic feet per second

0

200

400

600

800

1,000

1,200

0

1,000

2,000

3,000

4,000

Date

2060 2061 2062 2063 2064 2065 2066 2067 2068 2069

2060 2061 2062 2063 2064 2065 2066 2067 2068 2069

A. Area 1

B. Area 2

EXPLANATION

Groundwater-level increase from base-case scenario, in feet

0 1 2 

Figure 36. Monthly averaged groundwater being removed from A, Area 1, and B, Area 2 during 

drainage scenarios with drainage elevations set to levels zero, 1 foot, and 2 feet above basecase scenario wet-season averages within each cell.

Model Limitations

The general limitations of the numerical models include 

the following:

• A hydrologic model’s ability to mimic past hydrologic 

conditions does not necessarily guarantee ability to 

predict future conditions. When hydrologic forcings 

move further away in time or magnitude from forcings 

for which the model was calibrated, the model is less 

likely to accurately represent the conditions of the 

hydrologic system.

• Models are limited by their spatial and temporal 

resolutions. Processes and responses that occur 

on shorter temporal and spatial scales than those 

represented in the model may not be captured accurately.

• The model is limited by the necessarily simplified 

representation of natural processes. The conceptual 

model used to represent the hydrologic flow system 

and the numerical methods used to solve the 

mathematical model representation of this conceptual 

model are both only approximations of the actual 

hydrologic flow system.

There are more specific limitations of the model listed 

in the following sections that should be considered when 

analyzing the results.

Groundwater-Model Properties

• Groundwater properties for the inundation models were 

derived from the southern and central Broward County 

saltwater-intrusion model, which was calibrated 

with the primary focus of history matching salinity 

concentrations. Any uncertainties and errors introduced 

by the saltwater-intrusion model are propagated into 

the inundation models. These values were averaged 

to obtain composite parameters for the three vertical 

layers used for the county-scale model and interpolated 

to obtain the parameters for the local-scale model, 

potentially accumulating more error.
Model Limitations 47

Western Groundwater Head Boundaries

• The western boundaries near the WCAs are represented 

by data obtained from EDEN. These designated GHB 

values appear to be higher than expected and are often 

higher than ground elevations at the boundary. This 

may allow more water to enter the system through this 

boundary, which may result in greater groundwater 

discharge into the North New River Canal than 

actually occurs (appendix 3).

• Future groundwater levels at the model boundaries 

are uncertain but likely differ from current elevations, 

particularly as any changes are made to management of 

the Everglades or to the WCAs. For this study, historical 

GHB input values are used in future scenarios.

Tidal Boundaries

• Groundwater head boundaries representing tidal levels 

were created by using a combination of two tide 

measurement locations (Haulover Pier and Virginia Key 

tidal stations; described in detail in appendix 2) and 

NOAA’s tidal generator/predictor. Neither of these tidal 

gages is within the model’s geographic domain, and 

there is a data gap of approximately 515 days, which is 

populated by using the tidal generator. No attempt was 

made to correct for tidal stage or timing differences due 

to geographical location. If actual tidal levels are higher 

or lower than implemented in the model, the resulting 

groundwater levels would alter the depth to water and 

soil storage capacities within base-case and future 

scenarios. Additionally, coastal structure operations 

would be affected by changes in tidal inputs.

• GHBs representing the Intracoastal Waterway are 

approximated by using the same tidal data series, 

and changes in available data would affect local 

groundwater levels. The representation of sea-level rise 

involves adding the projected rise for each scenario to 

the historical time series and does not account for shifts 

in the daily series or any imbedded natural cycles. 

• The county-scale model uses daily tidal levels for both 

the surface-water and groundwater boundaries, whereas 

the local-scale model uses hourly tidal levels. The 

difference in results is evident in pumped versus spillway 

flow at structure S–13 in future simulations. Without 

the representation of daily low tidal levels within the 

county-scale models, the pump must be operated more 

often because of averaged downstream stage conditions.

Canal Representation

• Active canal representation in the county-scale model 

is limited to only a central part of the county that 

encompasses the local-scale model area. The active 

part was chosen on the basis of location and connection 

types to neighboring canal sections to best represent 

the behavior of the system within the local-scale area. 

The remaining parts of the canal system have specified 

stages throughout the simulation that remain unchanged 

for all scenarios and may act to dampen or conceal 

changes in adjacent areas during future simulations.

• Active canal segments are represented as level pools. 

Given the low surface-water gradients seen west of 

the coastal control structures, this assumption may not 

significantly affect model accuracy.

• Surface-water control structures within the model are 

represented with the intent to capture the system’s 

behavior and may deviate from the actual systems. 

For example, pumps are operated as stage-discharge 

relationships, gates may use opening and closing speeds 

that differ from documented values, and some gates 

are implemented as fixed-crest weirs. Additionally, the 

operation of these structures is governed by specific 

rules within the models, which are frequently and 

randomly not followed in actual operation, and these 

ad hoc operations were not simulated. The resulting 

simulated hydrologic conditions should and do differ 

from measured hydrologic conditions.

• The limited or generic cross-sectional data available 

for some parts of the canal system can have an 

effect on the accuracy of the calculated canal storage 

and flow for historical and future simulations. For 

example, a canal reach with an overestimated top 

width would have a lower increase in stage change 

for a given volume, and conversely, a canal with an 

underestimated top width would have a higher increase 

in stage for the same given volume.

• Frictional coefficients specified for the canal system 

and structures were generated from standard values and 

may deviate from actual characteristics. Overestimated 

frictional coefficients between reach groups would 

cause increased stage differences between the 

groups to achieve the same flow rates. Conversely, 

underestimated frictional coefficients would cause 

decreased stage differences between the reach groups 

to achieve the same flow rates. 

• Canal leakance coefficients were calculated by using 

calibrated leakage values from the MODFLOW 2005 

River package (RIV) used in the central and southern 

Broward County saltwater-intrusion model (Hughes 

and others, 2016). As mentioned, this model was 

calibrated with the primary focus of history matching 

of saltwater transport and canal leakance values derived 

from the cited model may not be the optimum values 

for the current simulations; however, the leakance 

values are within the range of standard values.
48 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

Precipitation and Potential Evapotranspiration

• Potential ET for the historical simulation was assumed 

to be uniform over the model extent. Actual potential 

ET may have varied spatially and would differ from 

the actual water volume removed from the model. 

Potential ET for the baseline and future scenarios was 

applied on the basis of the 10-km climate model grid 

while potential ET may vary at a smaller scale and 

could cause similar differences.

• The baseline and future scenario precipitation was 

applied based on the 10-km climate model grid. For 

consistency, historical precipitation calculated from 

various measured rainfall stations was applied based 

on the same 10-km grid. Actual precipitation may 

have finer-scale spatial variability and could cause 

differences in simulated model output. 

Future Climate and Sea-Level Projections

• Projections of sea-level change and climate change are 

generally highly uncertain. They represent the outcome 

of complex systems with complicated interactions. 

The further into the future, the more uncertain the 

projections become. The scenarios presented within 

this report do not represent the exact expectation 

of future conditions but rather represent possible 

combinations of conditions. More extreme projections 

exist but typically have a lower chance of occurrence 

and were not considered.

Summary

A county-scale MODFLOW 2005 groundwater/

surface-water model of the urban areas of southern and 

central Broward County was developed to simulate the 

possible effects of potential changes in precipitation, 

evapotranspiration, and sea level on groundwater levels. 

The primary data source for model construction and 

hydraulic parameters was an existing saltwater-intrusion 

model of the same area. The aquifer layering was vertically 

simplified to represent upper, production, and lower zones. 

The representation of the extensive canal network was 

accomplished using dynamic canal stages computed using 

level-pool routing with dynamic structure flows for the 

central portion of the study area. The remaining northern 

and southern parts used observed, specified stages within the 

reaches. Precipitation, evaporation, infiltration, recharge, and 

surface-water and unsaturated zone storages were represented 

by using a newly developed Urban Runoff process. The 

temporal scale was modified from monthly to daily stress 

periods. Additionally, a local-scale model was developed with 

more refined spatial and temporal scales, and additional detail 

was added to the active canal network. 

Simulations were run by using observed rainfall, potential 

evapotranspiration, and tidal levels from 1990 to 1999 to 

gauge the model’s ability to capture the historical behavior 

of the hydrologic system. Fit statistics and time-series data 

were calculated and analyzed for several groundwater station 

locations and the primary active canal structures. Projected 

future scenarios were constructed for the years 2060–69 by 

using regional climate model output derived from two general 

circulation models and three different sea-level rise curves. 

The precipitation and potential evapotranspiration from the 

Community Climate System Model (CCSM) and Hadley 

Centre Coupled Model version 3 (HadCM3) regional climate 

model scenarios represented possible wetter and drier futures, 

respectively, with a 9.1-percent increase and a 7.6-percent 

decrease in average yearly precipitation totals, respectively, 

for the county-scale model area. Low, intermediate, and 

high sea-level rise curves were created that represented the 

currently measured linear rate of increase and the National 

Research Council Curves I and III; these resulted in average 

tidal level increases of 6.2 inches (in.), 11.9 in., and 29.9 in. 

for the 2060–69 time period relative to 2010. Base-case 

simulations using regional climate model precipitation and 

potential evapotranspiration for the CCSM and HadCM3 

scenarios and measured tidal observations from 1990 to 1999 

were run and used for comparison to the future scenarios. 

For the county-scale model area, the base-case CCSM 

and HadCM3 regional climate model output underestimated 

averaged precipitation values for 1990–99 with totals of 

53.4 inches per year (in/yr) and 54.9 in/yr, respectively, 

compared to an observed 62.5 in/yr. Wet-season precipitation 

totals were also underestimated but less so, with averages of 

38.7 in. and 40.0 in. for the base-case CCSM and HadCM3, 

respectively, compared to a measured average of 43.0 in. The 

base-case scenario groundwater-level results were compared 

to the historical scenario model results with mean differences 

in groundwater levels of -0.045 feet (ft) and -0.015 ft in the 

15 groundwater station locations for the CCSM and HadCM3 

Base-Case scenarios, respectively. When compared to the 

historical simulation, the mean differences in discharge at the 

four primary flow structures (G–54, S–13, S–33, and S–9) 

during the CCSM and HadCM3 Base-Case simulations were 

-11.0 cubic feet per second (ft3/s) and -6.42 ft3/s, respectively. 

When analyzing and comparing the simulation results by 

using future projections, it is important to focus more on the 

qualitative effects evidenced in the output rather than exact 

quantitative results. Important findings include direction and 

range in magnitude of changes in simulated results under 

projected future scenarios and determining the primary cause 

of these changes. On the basis of the simulations using future 

sea-level rise and climate projections, several observations 

were made analyzing the results of the county-scale model:

• The effects of the future scenarios are much more 

evident in eastern and coastal areas, which show 

groundwater level increases nearly equivalent to 
Summary 49

the tidal level increases. These groundwater level 

increases are distributed further inland in the wetter 

future scenarios than in the drier future scenarios. 

This finding indicates the primary driver for increased 

groundwater levels and subsequent reductions in soil 

storage is sea-level rise for these coastal areas, and 

projected climate can enhance or reduce these effects.

• Average groundwater levels at the easternmost 

groundwater wells increased 0.525 ft and 0.329 ft for 

the low sea-level rise scenarios for the wetter and drier 

future scenarios, respectively. The average sea-level 

rise for these scenarios was 0.514 ft.

• Average groundwater levels at the easternmost 

groundwater wells increased 0.909 ft and 0.716 ft for 

the intermediate sea-level rise scenarios for the wetter 

and drier future scenarios, respectively. The average 

sea-level rise for these scenarios was 0.991 ft.

• Average groundwater levels at the easternmost 

groundwater wells increased 2.085 ft and 1.911 ft for 

the high sea-level rise scenarios for the wetter and drier 

future scenarios, respectively. The average sea-level 

rise for these scenarios was 2.491 ft.

• The westernmost groundwater station locations 

exhibited little change caused by sea-level rise and 

showed more dependence on changes in precipitation 

but with a much-reduced overall effect compared to the 

coastal wells. The averaged groundwater levels within 

these wells for the wetter future scenarios increased 

0.021 ft, 0.024 ft, and 0.033 ft for the low, intermediate, 

and high sea-level rise scenarios, respectively. 

The same westernmost wells exhibited average 

groundwater-level decreases of 0.064 ft, 0.060 ft, and 

0.051 ft for the drier future low, intermediate, and high 

sea-level rise scenarios, respectively.

• There was a lessened west-to-east groundwater gradient 

through the central part of the county-scale model, 

which also crosses through the local-scale model area, 

for the future scenarios relative to historical conditions. 

These groundwater levels and gradients change very 

little west of structure S–13a on the C–11 Canal, which 

acts as a divide. Canal levels in the western part of the 

C–11 Canal are controlled by the western discharge of 

water through the S–9 pump structure. Groundwater 

levels east of S–13a are controlled by the eastern part 

of the C–11 Canal and structure S–13 and increase 

with increased sea-level rise, particularly in the high 

sea-level rise scenario. In this scenario, the increased 

downstream stage at structure S–13 from sea-level 

rise reduces the spillway capacity, and coastal flows 

must be maintained through pump operations. The 

stage-discharge relationship that represents the S–13 

pump operates at a higher upstream stage and increases 

the local groundwater levels.

• Results obtained by using the wetter future inputs show 

an increase of 2.484 square miles (mi2) (+3.0 percent), 

3.757 mi2 (+4.6 percent), and 12.106 mi2

(+14.8 percent) in areas with less than a 1-ft depth to 

average wet-season groundwater level. These areas are 

considered to have a high likelihood of inundation and 

extended flooding during precipitation events.

• Alterations to S–13 pump operations within the model 

can be used to reduce the effects of sea-level rise, but 

the affected area is spatially limited.

Groundwater levels and canal flows from the 

county-scale model were used as boundary conditions and 

inputs for the local-scale model. The results and observations 

from the local-scale model were similar to those from the 

larger, coarser county-scale model with similar fit statistics 

and qualitative fits for the historical and base-case scenarios. 

Based on the simulations using future sea-level rise and 

climate projections, several observations were made by 

analyzing the results of the local-scale model:

• The effects of the underestimated yearly precipitation 

totals for the historical period by the regional climate 

models were more pronounced in the local-scale model 

area than in the county-scale model. The CCSM and 

HadCM3 Base-Case regional climate model output 

scenarios respectively had average yearly precipitation 

that was 18.3 percent and 15.9 percent lower than 

measured totals. The three groundwater station locations 

in the local-scale area were an average of 0.379 ft and 

0.339 ft lower for the CCSM and HadCM3 Base-Case 

scenarios, respectively, than for the historical scenario. 

The two primary structure flows, G–54 and S–13, were a 

mean of 23.0 ft3/s and 19.1 ft3/s lower for the CCSM and 

HadCM3 scenarios, respectively, when compared to the 

historical scenario. The time series for the groundwater 

levels and structure flows had similar peaks and trends 

to the historical scenario results and the county-scale 

model’s base-case scenarios.

• Similar to the county-scale model results, the coastal 

areas exhibited the largest effects in groundwater 

levels in the future scenarios. Yearly precipitation 

totals increased 18.8 percent within the local-scale 

area in the wetter future scenario and resulted in 

average groundwater-level increases of 0.710 ft, 

1.133 ft, and 2.423 ft in the easternmost groundwater 

well for the low, intermediate, and high sea-level 

rise scenarios, respectively. The drier future scenario 

had a 7.0-percent decrease in rainfall, and the results 

show average groundwater-level increases of 0.345 ft, 

0.777 ft, and 2.103 ft in the same groundwater wells 

for the low, intermediate, and high sea-level rise 

scenarios, respectively.

• As seen in the county-scale model, the westernmost 

interior areas exhibited little change during the 

future scenarios. The westernmost monitoring 

location had average groundwater-level increases of 
50 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0.037 ft, 0.034 ft, and 0.036 ft for the wetter future 

low, intermediate, and high sea-level rise scenarios, 

respectively. The westernmost monitoring location 

had average groundwater-level decreases of 0.116 ft 

and 0.121 ft for the drier future low and intermediate 

sea-level rise scenarios, respectively, and a decrease of 

0.121 ft for the drier future high sea-level rise scenario.

• Similar operational changes were seen at structure 

S–13 in the local-scale simulations as in the 

county-scale simulations; however, there was less 

reliance on the pump during the high sea-level rise 

scenarios because of the hourly tidal stage inputs used 

in the local-scale model. The county-scale model 

used daily tidal levels, which neglected the daily 

low tide levels that allowed intermittent operation 

of the gated spillway at S–13 in the local-scale area. 

As a result, reliance on pumped versus spillway flow 

shifted from 99 percent in the county-scale model to 

approximately 71.2 percent in the local-scale model. 

Upstream stage at S–13 was increased during the high 

sea-level rise scenarios because of the operational 

rules of the stage-discharge relationship. Upstream 

levels increased 0.693 ft and 0.670 ft for the wetter 

and drier high sea-level rise scenarios, respectively, 

compared to increases of 0.744 ft and 0.721 ft for the 

wetter and drier sea-level rise scenarios, respectively, 

for the county-scale model. The concept of using 

pumps to reduce the local groundwater levels in 

two neighborhood-sized areas was tested by using 

the local-scale model. Area 1 was coastal, with 

strong connections to the general-head boundaries 

representing the tidal fluctuations. Area 2 was more 

inland but still east of the coastal water-control 

structures and had only limited connection to a 

simulated tidal reach. Drainage elevations were 

set to zero, 1 ft, and 2 ft above average wet-season 

groundwater levels for each area. The amount of 

groundwater removed from Area 1 varied from 

2,220.0 ft3/s to 346.6 ft3/s for the three drainage 

elevation scenarios. The amount of groundwater 

removed from Area 2 varied from 636.0 ft3/s to 

28.6 ft3/s for the three drainage elevation scenarios. 

References Cited

Andersen, P.F., Mercer, J.W., and White, H.O., Jr., 1988, 

Numerical modeling of salt-water intrusion at Hallandale, 

Florida: Groundwater, v. 26, no. 5, p. 619–630.

Broward County, 2009, Broward county-wide integrated water 

resource plan report: Broward County, 156 p., accessed 

January 14, 2015, at http://www.broward.org/IWRP

/Documents/IntergratedWaterResourcePlan.pdf.

Decker, J.D., 2018, MODFLOW 2005 data sets for the simulation of potential increased inundation in flood-prone regions 

of Southeast Florida in response to climate and sea-level 

changes in Broward County, Florida, 2060-69: U.S. Geological Survey data release, https://dx.doi.org/10.5066/

P9E6INWZ. 

Decker, J.D., and Hughes, J.D., 2013, Urban runoff (URO) 

process for MODFLOW 2005—Simulation of sub-grid 

scale urban hydrologic processes in Broward County, 

Florida, in MODFLOW and More 2013—Translating 

Science into Practice Proceedings: Golden, Colo., Colorado 

School of Mines, Integrated Groundwater Modeling Center, 

p. 216–221.

Giddings, J.B., Kuebler, L.L., Restrepo, J.I., Rodberg, K.A., 

Montoya, A.M., and Radin, H.A., 2006, Lower east coast 

subregional (LECsR) MODFLOW model documentation: 

South Florida Water Management District draft report, 

213 p., accessed May 19, 2016, at http://www.sfwmd.gov/

portal/page/portal/xrepository/sfwmd_repository_pdf/

lec_sr_draft_documentation.pdf.

Guha, H., and Panday, S., 2012, Impact of sea level rise on 

groundwater salinity in coastal community of south Florida: 

Journal of the American Water Resources Association, v. 48, 

no. 3, p. 510–529.

Harbaugh, A.W., 2005, MODFLOW-2005, The U.S. 

Geological Survey modular groundwater model—The 

groundwater flow process: U.S. Geological Survey Techniques and Methods, book 6, chap. A16.

Hughes, J.D., Sifuentes, D.F., and White, J.T., 2016, Simulated 

effects of alterations to the hydrologic system on the 

distribution of salinity in the Biscayne aquifer in Broward 

County, Florida: U.S. Geological Survey Scientific Investigations Report 2016–5022.

Hughes, J.D., and White, J.T., 2014, Hydrologic conditions 

in urban Miami-Dade County, Florida and the effect of 

groundwater pumpage and increased sea level on canal 

leakage and regional groundwater flow: U.S. Geological Scientific Investigations Report 2014–5162, 175 p., 

accessed August 1, 2018, at http://dx.doi.org/10.3133/

sir20145162.

Hughes, J.D., Langevin, C.D., Chartier, K.L., and White, 

J.T., 2012, Documentation of the Surface-Water Routing 

(SWR1) process for modeling surface-water flow with 

the U.S. Geological Survey modular groundwater model 

(MODFLOW-2005): U.S. Geological Survey Techniques 

and Methods, book 6, chap. A40.

Intergovernmental Panel on Climate Change (IPCC), 2007, 

Climate change 2007—Synthesis report in Core Writing 

Team, Pachauri, R.K., and Reisinger, A., eds., Contribution 

of working groups I, II and III to the Fourth Assessment 

Report of the Intergovernmental Panel on Climate Change: 

IPCC, Geneva, Switzerland, 104 p.
References Cited 51

Islam, N., and Dunn, D., 2006, Recalibration and 

consolidation of integrated surface water and groundwater 

models for Broward County: Broward County 

Environmental Protection Department, Water Resources 

Division, 40 p.

Langevin, C.D., and Zygnerski, M., 2013, Effect of 

sea-level rise on saltwater intrusion near a coastal well 

field in south-eastern Florida: Ground Water, v. 51, no. 5, 

p. 781–803.

Langevin, C.D.; Thorne, D.T., Jr.; Dausman, A.M.; Sukop, 

M.C.; and Guo, W., 2008, SEAWAT version 4—A computer 

program for simulation of multi-species solute and heat 

transport: U.S. Geological Survey Techniques and Methods, 

book 6, chap. A22, 39 p.

Renken, R.A., Dixon, J., Koehmstedt, J., Lietz, A.C., and 

others, 2005, Impact of anthropogenic development on 

coastal ground-water hydrology in southeastern Florida, 

1900–2000: U.S. Geological Survey Circular 1275, 77 p.

Stefanova, L., Misra, V., Chan, S.C., Griffin, M., O’Bren, J.J., 

and Smith T.J., 2012, A proxy for high-resolution regional 

reanalysis for the southeast United States—Assessment 

of precipitation variability in dynamically downscaled 

reanalyses: Climate Dynamics, v. 38, p. 2449–2466, 

accessed July 1, 2016, at http://dx.doi.org/10.1007/

s00382-011-1230-y.

Southeast Florida Regional Climate Change Compact 

Technical Ad hoc Work Group, 2011, A unified sea level 

rise projection for southeast Florida: Document prepared for 

the Southeast Florida Regional Climate Change Compact 

Steering Committee, 27 p.

South Florida Water Management District, 2009, 2007 

Broward 10-ft DEM in NAVD 1988, Release Version 1, 

accessed March 8, 2012, at http://sfwmd.maps.arcgis.com/

home/item.html?id=98b7f5def64345a3a7060b21b500dcf5.

Telis, P.A., 2006, The Everglades Depth Estimation Network 

(EDEN) for support of ecological and biological assessments: U.S. Geological Survey Fact Sheet 2006–3087, 4 p.

U.S. Army Corps of Engineers (USACE), 2011, Water 

Resources Policies and Authorities Incorporating Sea-Level 

Change Considerations in Civil Works Programs, 

EC 1165-2-211, U.S. Army Corps of Engineers, Department 

of Army, Washington, D.C.

U.S. Census Bureau, 2018, Annual estimates of the resident population—April 1, 2010 to July, 2017: U.S. Census Bureau website accessed September 19, 2018, at 

https://factfinder.census.gov/faces/tableservices/jsf/pages/

productview.xhtml?src=CF.

U.S. Department of Agriculture, Natural Resource 

Conservation Service, 2007, Part 630—Hydrology, in

National Engineering Handbook: Washington D.C., U.S. 

Department of Agriculture.

Appendixes 1–3
54 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

Appendix 1. Simulated Groundwater Response to Individual Precipitation Events

The local-scale groundwater/surface-water model was 

used to evaluate the response of groundwater levels and 

potential for inundation to individual precipitation events 

for historical and projected wetter climate conditions for 

both high and low sea-level rise scenarios. A measured 

precipitation event that occurred on November 15, 1994, 

was used to evaluate the response of groundwater levels for 

historical conditions. Comparing the measured groundwater 

levels to simulated levels during the same time period 

demonstrates the local-scale model’s ability to capture 

the effect of precipitation on the groundwater levels. The 

measured groundwater levels are displayed with the measured 

precipitation from the nearest rainfall gauge used to create 

the historical scenario input, while the simulated groundwater 

levels are displayed with the historical scenario precipitation 

input data (fig. 1.1A–F). The averaging method used to create 

the historical scenarios’ precipitation input tends to spatially, 

and sometimes temporally, smooth out localized precipitation 

events; therefore, the model data precipitation inputs often 

have lower maximums but more frequent non-zero values. 

The precipitation in the easternmost (coastal) areas during 

this selected time period had a maximum rainfall of 3.1 and 

5.0 inches (in.) for the model data input and measured data, 

respectively (fig. 1.1E, F), and the simulated and measured 

groundwater levels showed similar trends. The simulated 

groundwater levels have a lower peak and occur later than 

the measured groundwater levels, which could be attributed 

to spatial and temporal resolution and spatially averaged 

groundwater levels calculated in numerical models, as well as 

the average precipitation model input. The greatest magnitude 

of measured and model input precipitation occurs at the 

westernmost site, G–617 (fig. 1.1A, B), but the simulated 

groundwater response is lower and later than measured, 

compared with sites G–1221 and G–561. 

The local-scale model was then used to analyze the 

simulated groundwater levels following two different 

precipitation events within the wetter-future Community 

Climate System Model scenarios. The wetter future, 

projected-precipitation time series in the easternmost (coastal) 

climate model cell within the local-scale model was used 

to identify two representative events. The first precipitation 

event had a maximum daily total of 3.4 in. projected to occur 

hypothetically on August 16, 2068 (fig. 1.2A–C). The second 

event was more extreme, with a maximum daily rainfall of 

14.6 in. projected to occur on April 4, 2066 (fig. 1.3C). It 

is important to note that these dates are representative of 

hypothetical conditions that could occur during projected 

future climate conditions and are not intended to represent a 

prediction of actual events occurring on these dates. 

The resulting groundwater effects from these 

two precipitation model inputs show similar increases 

during both the high sea-level rise and low sea-level rise 

scenarios (fig. 1.2). The differences between the minimum 

and maximum daily groundwater levels, or the rises 

in groundwater levels, during this time period for the 

westernmost well, G–617, are 0.39 and 0.67 foot (ft) for the 

low and high sea-level rise scenarios, respectively (fig. 1.2A). 

The groundwater-level rise values during the 2060–69 future 

simulation period at G–1221 were similar for both sea-level 

rise scenarios, with changes of 0.665 and 0.667 ft for the low 

and high sea-level rise scenarios, respectively (fig. 1.2B). 

Lastly, the groundwater-level rises were 1.58 and 1.43 ft at 

the easternmost well, G–561, for the low and high sea-level 

rise scenarios, respectively (fig. 1.2C). The high sea-level rise 

scenario tended to reach the maximum groundwater levels 

later when compared to the low sea-level rise scenario. This 

remained true even at G–561 where the groundwater-level rise 

for the high sea-level rise scenario (1.43 ft) was less than that 

of the low sea-level rise scenario (1.58 ft; fig. 1.2C). 

The groundwater-level rises during the more extreme 

precipitation event on April 4, 2066, were higher (fig. 1.3) than 

those for the previously described event on August 16, 2068. 

At G–617, the high sea-level rise scenario exhibited a larger 

groundwater-level rise, with an increase of 2.1 ft compared 

to 1.5 ft occurring during the low sea-level rise scenario 

(fig. 1.3A). The maximum simulated groundwater level for 

G–617 of 3.95 ft above the North American Vertical Datum 

of 1988 (NAVD 88) and a land elevation of 4.98 ft above 

NAVD 88 resulted in a minimum depth to water of 1.03 ft 

for the high sea-level rise scenario during this time period. 

The groundwater-level rises at G–1221 were changes of 

2.45 and 2.27 ft for the low and high sea-level rise scenarios, 

respectively (fig. 1.3B). The maximum simulated groundwater 

level for G–1221 of 3.44 ft above NAVD 88 and a land 

elevation of 4.82 ft above NAVD 88 resulted in a minimum 

depth to water of 1.38 ft for the high sea-level rise scenario 

during this time period. The low sea-level rise scenario 

produced a larger increase at G–561 (4.9 ft) than the high 

sea-level rise scenario (4.4 ft; fig. 1.3C). The maximum 

groundwater level during this time period was 6.126 ft above 

NAVD 88 for the high sea-level rise scenario. The land 

elevation of the cell containing this well used in the model is 

6.86 ft above NAVD 88, resulting in 0.73 ft depth to water. 

These maximum groundwater levels were reached later during 

the high sea-level rise scenario than during the low sea-level 

rise scenario. In general, the groundwater-level response was 

more subdued and delayed farther west, which is possibly 

due to the increased density of drainage features and reduced 

model input precipitation farther west. 

The effects of the larger precipitation event on possible 

increases in inundation were also assessed. The model cell 

was designated as “inundated” when the groundwater level 

exceeded the land-surface elevation. Using this criterion, there 

were 4.74 square miles (mi2

) within the local-scale model 

that became newly inundated because of the precipitation. 

The maximum depth within these newly inundated areas was 

2.18 ft and varied spatially (fig. 1.4). The smaller precipitation 

event led to only 0.30 mi2 of newly inundated areas.
Appendix 1. Simulated Groundwater Response to Individual Precipitation Events 55

11/6/1994 11/11/1994 11/16/1994 11/21/1994 11/26/1994 12/1/1994 12/6/1994

11/6/1994 11/11/1994 11/16/1994 11/21/1994 11/26/1994 12/1/1994 12/6/1994

Date

11/6/1994 11/11/1994 11/16/1994 11/21/1994 11/26/1994 12/1/1994 12/6/1994

11/6/1994 11/11/1994 11/16/1994 11/21/1994 11/26/1994 12/1/1994 12/6/1994

Groundwater level, in feet above North American Vertical Datum of 1988 (NAVD 88)

Daily precipitation, in inches

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

0

1

2

3

4

5

6

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

0

1

2

3

4

5

6

D. G–1221 (Measured)

C. G–1221 (Simulated)

B. G–617 (Measured)

A. G–617 (Simulated)

G–617 Groundwater level—Measured Precipitation—Measured

EXPLANATION

G–617 Groundwater level—Simulated Precipitation—Model input

EXPLANATION

G–1221 Groundwater level—Measured Precipitation—Measured

EXPLANATION

G–1221 Groundwater level—Simulated Precipitation—Model input

EXPLANATION

Figure 1.1. Simulated and measured groundwater levels at three groundwater stations (A, B, G–516; 

C, D, G–1221; and E, F, G–617) preceding and following a precipitation event.
56 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

Date

11/6/1994 11/11/1994 11/16/1994 11/21/1994 11/26/1994 12/1/1994 12/6/1994

11/6/1994 11/11/1994 11/16/1994 11/21/1994 11/26/1994 12/1/1994 12/6/1994

Groundwater level, in feet above North American

Vertical Datum of 1988 (NAVD 88)

Daily precipitation, in inches

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

0

1

2

3

4

5

6

F. G–561 (Measured)

E. G–561 (Simulated)

EXPLANATION

G–561 Groundwater level—Measured Precipitation—Measured

EXPLANATION

G–561 Groundwater level—Simulated Precipitation—Model input

Figure 1.1. Simulated and measured groundwater levels at three groundwater stations (A, B, G–516; 

C, D, G–1221; and E, F, G–617) preceding and following a precipitation event.—Continued
Appendix 1. Simulated Groundwater Response to Individual Precipitation Events 57

Date

8/6/2068 8/11/2068 8/16/2068 8/21/2068 8/26/2068 8/31/2068 9/5/2068

8/6/2068 8/11/2068 8/16/2068 8/21/2068 8/26/2068 8/31/2068 9/5/2068

8/6/2068 8/11/2068 8/16/2068 8/21/2068 8/26/2068 8/31/2068 9/5/2068

Groundwater level, in feet above North American Vertical Datum of 1988

Daily precipitation, in inches

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0

1

2

3

4

5

0

1

2

3

4

5

0

1

2

3

4

5

A. G–617

B. G–1221

C. G–561

EXPLANATION

G–561 Simulated groundwater level

 High sea-level rise

 Low sea-level rise

Precipitation

EXPLANATION

G–1221 Simulated groundwater level

 High sea-level rise

 Low sea-level rise

Precipitation

EXPLANATION

G–617 Simulated groundwater level

 High sea-level rise

 Low sea-level rise

Precipitation

Figure 1.2. Simulated groundwater levels at three groundwater stations (A, G–617; B, G–1221; and C,

G–516) preceding and following a 3.4-inch daily precipitation event.
58 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

Date

3/25/2066 3/30/2066 4/4/2066 4/9/2066

4/9/2066

4/9/2066

4/14/2066 4/19/2066 4/24/2066

3/25/2066 3/30/2066 4/4/2066 4/14/2066 4/19/2066 4/24/2066

3/25/2066 3/30/2066 4/4/2066 4/14/2066 4/19/2066 4/24/2066

Groundwater level, in feet above North American Vertical Datum of 1988 (NAVD 88)

Daily precipitation, in inches

0

1

2

3

4

5

6

7

-1 0

2

4

6

8

10

12

14

16

0

1

2

3

4

5

6

7

-1 0

2

4

6

8

10

12

14

16

0

1

2

3

4

5

6

7

-1 0

2

4

6

8

10

12

14

16

A. G–617

B. G–1221

C. G–561

EXPLANATION

G–561 Simulated groundwater level

 High sea-level rise

 Low sea-level rise

Precipitation

EXPLANATION

G–1221 Simulated groundwater level

 High sea-level rise

 Low sea-level rise

Precipitation

EXPLANATION

G–617 Simulated groundwater level

 High sea-level rise

 Low sea-level rise

Precipitation

Figure 1.3. Simulated groundwater levels at three groundwater stations (A, G–617; B, G–1221; and C,

G–516) preceding and following a 14.6-inch daily precipitation event.
Appendix 1. Simulated Groundwater Response to Individual Precipitation Events 59

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

Study area

Area enlarged

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

G–617

G–1221

G–561 Transect 3

EXPLANATION

Inundated before event

Depth, in feet, of newly inundated area after event

0

2.18

Line of section

Groundwater station and identifier

 Westernmost

 Interior

 Easternmost

G–617

G–1221

G–561

Figure 1.4. Depth of newly inundated areas following a 14.6-inch daily 

precipitation event.
60 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

Appendix 2. Numerical Model Construction

County-Scale Numerical Model Construction

The variable-density flow model developed for central 

and southern Broward County (Hughes and others, 2016), 

henceforth called the “saltwater-intrusion model,” was 

used as the basis to construct the county-scale model. The 

saltwater-intrusion model was the primary source for the 

extent, discretization, and the calibrated hydrologic parameters 

used for the county-scale model. This section documents 

the construction of the county-scale model and describes 

in detail the parts of the model that were modified from the 

saltwater-intrusion model. The study’s associated data release 

contains the input files described herein as well as the required 

executables to reproduce simulation results (Decker, 2018).

Extent and Discretization

The county-scale model extent was unchanged from 

the central and southern Broward County saltwater-intrusion 

model. The spatial discretization was maintained at 500 feet 

(ft) by 500 ft for all 411 rows and 501 columns. The original 

saltwater-intrusion model was vertically discretized into 

12 layers by using a combination of lithostratigraphic 

and hydrogeologic models for the surficial aquifer. 

During the calibration of that model, these 12 layers were 

redistributed and assigned to 3 layers: (1) the upper (UPR), 

(2) production (PRD), and (3) lower (LWR) model layers. 

These three designations are described in detail in Hughes 

and others (2016). Layers 1 and 2 are combined into the 

UPR layer, layers 3–10 are combined to form the PRD layer, 

and layers 11 and 12 represent the LWR layer. The model 

consists of 50,179 active cells per vertical layer for a total of 

150,537 active groundwater cells covering a spatial extent of 

450 square miles (mi2).

The simulation period for the original saltwater-intrusion 

model was from January 1, 1950, to May 31, 2012, and used 

a monthly MODFLOW 2005 stress period and time step. The 

base-case and historical simulation periods were shortened 

to January 1, 1990, to December 31, 1999, and used a daily 

MODFLOW stress period and hourly time steps to obtain 

better temporal resolution. Fifteen-minute time steps are used 

for the Surface-Water Routing (SWR1) and Urban Runoff 

(URO) processes. Shortened MODFLOW time steps reduced 

the number of outer MODFLOW iterations and overall run 

times of the model because of the implicit coupling of the 

URO and SWR1 processes. The future simulation period 

represents predicted values of sea-level rise and climate 

forcing for January 1, 2060, to December 31, 2069. The stress 

period and time-step lengths remain the same as with the 

base-case and historical simulations.

Land Surface and Layer-Bottom Elevations

The top of layer 1, which corresponds to land surface, 

ranged from -1.98 to 20 ft above North American Vertical 

Datum of 1988 (NAVD 88), with an average elevation of 

6.24 ft above NAVD 88 (fig. 2.1). These values are the same 

land-surface elevations found within the central and southern 

Broward County saltwater-intrusion model, which was 

developed by using 3-ft resolution light detection and ranging 

(lidar) data (Hughes and others, 2016). The saltwater-intrusion 

model layer-bottom elevations from layers 2, 10, and 12 were 

used for the bottoms of the three layers of the county-scale 

model (figs. 2.2 to 2.4). The elevations of the bottom of layer 1 

varied between -71.81 ft and -22.83 ft above NAVD 88, 

with an average elevation of -50.34 ft above NAVD 88. The 

elevations of the bottom of layer 2 varied between -137.83 and 

-48.58 ft above NAVD 88, with an average elevation of 

-103.64 ft above NAVD 88. The elevations of the bottom 

of layer 3 varied between -319.28 and -193.22 ft above 

NAVD 88, with an average elevation of -248.29 ft above 

NAVD 88.

Hydraulic Parameters

The hydraulic parameters used for the county-scale 

model were calculated by using the calibrated parameters 

from the saltwater-intrusion model (Hughes and others, 2016). 

The properties of layers 1 and 2, 3–10, and 11 and 12 were 

averaged to produce the county-scale model parameter fields 

for layers 1, 2, and 3, respectively.

Horizontal and Vertical Hydraulic Conductivity

The horizontal hydraulic conductivity (Kh) for each layer 

in the county-scale model was calculated from the 12-layer 

saltwater-intrusion model by using the layer-thickness 

weighted arithmetic mean:

K

b K

b h

i i i

n

i i

n  







1

1

, (1)

where

Kh is the mean horizontal hydraulic conductivity 

for groundwater cell;

bi is the thickness of layer i within the 

groundwater cell; and

Ki is the horizontal hydraulic conductivity for 

layer i within the groundwater cell (L/T).
Appendix 2. Numerical Model Construction 61

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Offshore

Inactive county-scale model area

Active county-scale model area—Top of layer 1, in feet

 above North American Vertical Datum of 1988

20.00

-1.98

9.00

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.1. County-scale model top of layer 1.
62 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Offshore

Inactive model area

Active model area—Bottom of layer 1, in feet above

 North American Vertical Datum of 1988

-22.83

-71.81

-47.32

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.2. County-scale model bottom of layer 1.
Appendix 2. Numerical Model Construction 63

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Offshore

Inactive model area

Active model area—Bottom of layer 2, in feet above

 North American Vertical Datum of 1988

-48.58

-137.83

-93.21

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.3. County-scale model bottom of layer 2.
64 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Offshore

Inactive model area

Active model area—Bottom of layer 3, in feet above

 North American Vertical Datum of 1988

-193.22

-319.28

-256.25

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.4. County-scale model bottom of layer 3.
Appendix 2. Numerical Model Construction 65

The horizontal hydraulic conductivity in layer 1 varied from 

220.5 feet per day (ft/d) to 32,000 ft/d, with an average 

of 1,905.8 ft/d. The horizontal hydraulic conductivity in 

layer 2 varied from 245 ft/d to 29,400 ft/d, with an average of 

3,060.3 ft/d. The horizontal hydraulic conductivity in layer 3 

varied from 185.5 ft/d to 25,624 ft/d, with an average of 

743.3 ft/d (figs. 2.5 to 2.7).

The vertical hydraulic conductivity (Kv) for each layer 

in the county-scale model was calculated from the 12-layer 

saltwater-intrusion model by using the layer-thickness 

weighted harmonic mean:

K

b

b

K

v

i i

n

i

vi

i

n

 







1

1

, (2)

where

Kv is the mean vertical hydraulic conductivity for 

the groundwater cell (L/T); and

Kvi is the vertical hydraulic conductivity for layer 

i within the groundwater cell (L/T).

The vertical hydraulic conductivity in layer 1 varied from 

1.1 ft/d to 39.5 ft/d, with an average of 6.9 ft/d. The vertical hydraulic conductivity in layer 2 varied from 2.0 ft/d to 

21.2 ft/d, with an average of 10.1 ft/d. The vertical hydraulic 

conductivity in layer 3 varied from 2.8 ft/d to 9.1 ft/d, with an 

average of 5.2 ft/d (figs. 2.8 to 2.10).

Specific Yield and Specific Storage

The specific yield of the top layer, which was specified 

as convertible, and the specific storage of all three layers 

used the layer-thickness weighted arithmetic mean from the 

12-layer saltwater-intrusion model and the UPR, PRD, and 

LWR designations. The specific yield for layer 1 ranged from 

0.03 to 0.4, with an average of 0.24. The specific storage of 

layer 1 ranged from 6.43×10-6 to 1.33×10-5, with an average 

of 1.03×10-5. The specific storage of layer 2 ranged from 

7.20×10-6 to 1.21×10-5, with an average of 1.03×10-5. The 

specific storage of layer 3 ranged from 8.65×10-6 to 1.18×10-5, 

with an average of 1.02×10-5 (figs. 2.11 to 2.14).

Head-Dependent Boundaries at Model Extents

The northern, southern, and western general head 

boundaries (GHBs) from the saltwater-intrusion models 

were used for the county-scale model (fig. 1 in main body 

of report). The western head values were generated by using 

data from the Everglades Depth Estimation Network (EDEN), 

whereas the northern and southern head values were calculated 

by using nearby groundwater-monitoring wells (Hughes 

and others, 2016). The monthly stress period heads of the 

saltwater-intrusion model were linearly interpolated to daily 

stress period values. 

Tidal Boundaries

The county-scale model used MODFLOW GHBs to 

represent the tidal boundaries (fig. 1 in main body of report). 

The locations of these boundaries were taken from the 

saltwater-intrusion model (Hughes and others, 2016). The 

tidal head values for the historical and base-case simulations 

were generated from daily averaged tidal measurements from 

nearby gages when available and estimations using National 

Oceanic and Atmospheric Administration (NOAA) tide 

predictions when values were missing. Hourly data from the 

Haulover Pier tidal station were used for January 1, 1990, to 

August 31, 1992; NOAA tide predictions for Virginia Key 

using the NOAA Tide Prediction algorithm (NTP4) were 

used for September 1, 1992, to January 28, 1994; and hourly 

measured tide for the Virginia Key tidal station was used for 

the remainder of the simulation period. Any gaps in measured 

values were filled with the NOAA tide predictions. When 

predicted values were used rather than actual measurements, 

the weather component of the tidal levels was missing, which 

typically led to reduced daily fluctuations (fig. 2.15).

Three future tidal-level scenarios representing high, 

intermediate, and low projections were calculated by adding 

sea-level rise estimates to the historical and base-case 

tidal GHB levels. The three sea-level rise scenarios were 

constructed by using an estimated current sea-level rise rate of 

2.24 millimeters per year (mm/yr) (0.088 inch per year [in/yr]) 

and the National Research Council (NRC) Curve I and Curve 

III sea-level rise predictions, which use an acceleration term 

(b, eq. 6). The NRC projections were calculated by using the 

equation and methodology described by the U.S. Army Corps 

of Engineers (USACE, 2011):

E t E t a t t b t t 212 1 2

2

1

2              , (3)

where

E(t) is the sea-level rise expected since 1992, in 

meters;

t

1 is the time between the projection start date 

and 1992; 

t

2 is the time between the projection end date 

and 1992; 

a is the local current linear sea-level rise rate, in 

meters; and

b is a constant depicting the acceleration of 

sea-level rise.

The current linear rate of sea-level rise (a) used to 

calculate the NRC predictions was 0.00224 meter per year 

(m/yr) (0.088 in/yr), and the acceleration constants (b) used 

for Curve I and Curve III predictions were 0.0000271 and 

0.000113, respectively. The resulting projections of sea-level 

rise from current tidal levels for the beginning and end of 

the 2060–69 simulation were 0.478 ft and 0.551 ft using the 

linear rate (low), 0.888 ft and 1.091 ft using NRC Curve I 

(intermediate), and 2.189 ft and 2.803 ft using the NRC 

Curve III (high) (fig. 2.15). 
66 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Active model area—Horizontal hydraulic conductivity of layer 1, in feet per day

10,000

15,000

32,000

1,000

220

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.5. Horizontal hydraulic conductivity of layer 1 in the county-scale model.
Appendix 2. Numerical Model Construction 67

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983 EXPLANATION

Inactive model area

Active model area—Horizontal hydraulic conductivity of layer 2, in feet per day

10,000

20,000

29,400

1,000

245

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.6. Horizontal hydraulic conductivity of layer 2 in the county-scale model.
68 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

10,000

20,000

25,625

1,000

185

Active model area—Horizontal hydraulic conductivity of layer 3, in feet per day

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.7. Horizontal hydraulic conductivity of layer 3 in the county-scale model.
Appendix 2. Numerical Model Construction 69

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

20.3

39.5

1.1

Active model area—Vertical hydraulic conductivity of layer 1, in feet per day

EXPLANATION

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.8. Model input showing vertical hydraulic conductivity of layer 1 in the county-scale model.
70 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Active model area—Vertical hydraulic conductivity of layer 2, in feet per day

11.1

21.2

2.0

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.9. Model input showing vertical hydraulic conductivity of layer 2 in the county-scale model.
Appendix 2. Numerical Model Construction 71

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Active model area—Vertical hydraulic conductivity of layer 3, in feet per day

2.8

6.0

9.1

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.10. Model input showing vertical hydraulic conductivity of layer 3 in the county-scale model.
72 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Active model area—Specific yield of layer 1

0.4

0.03

0.22

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.11. Specific yield of layer 1 in the county-scale model.
Appendix 2. Numerical Model Construction 73

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Active model area—Specific storage of layer 1

1.33 × 10−5

9.86 × 10−6

6.43 × 10−6

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.12. Specific storage of layer 1 in the county-scale model.
74 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Active model area—Specific storage of layer 2

1.21 × 10−5

9.65 × 10−6

7.20 × 10−6

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.13. Specific storage of layer 2 in the county-scale model.
Appendix 2. Numerical Model Construction 75

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Active model area—Specific storage of layer 3

1.18 × 10−5

1.03 × 10−5

8.65 × 10−6

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.14. Specific storage of layer 3 in the county-scale model.
76 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

Day of simulation

0 500 1,000 1,500 2,000 2,500 3,000 3,500

Tidal level, in feet above

National American Vertical Datum of 1988

-3

-2

-1

0

1

2

3

4

5

6

EXPLANATION

Historical base-case scenario

Current (2017) sea-level rise (SLR) rate—Low SLR

National Research Council SLR projection

 Curve I—Intermediate SLR

 Curve III—High SLR

Figure 2.15. Historical and future tidal levels used for base-case and sea-level rise scenarios.

Groundwater Pumpage

Groundwater pumpage within the model was represented 

by using the MODFLOW 2005 Well package (WEL). 

The locations and pumping rates were taken from the 

saltwater-intrusion model (Hughes and others, 2016). Pumping 

rates for layers 1 and 2 in the 12-layer saltwater-intrusion 

model were assigned to layer 1 of the county-scale 

model. Pumping rates for layers 3–10 in the 12-layer 

saltwater-intrusion model were assigned to layer 2 of the 

county-scale model. Any pumping rates for layers 11 and 12 

in the 12-layer saltwater-intrusion model were assigned to 

layer 3 of the county-scale model. The pumping rates from 

the historical period within the saltwater-intrusion model were 

used for all future scenarios and varied between 160.9 million 

gallons per day (Mgal/d) and 260.7 Mgal/d, with an average 

value of 199.5 Mgal/d (fig. 5 in main body of report). 

Initial Conditions

Initial conditions for the county-scale model were 

based on results from the saltwater-intrusion model. The 

average groundwater elevations for January 1, 1990, within 

the 12 layers were assigned to the 3 groundwater layers 

within each groundwater cell. The specified canal stages for 

January 1, 1990, used in the saltwater-intrusion model were 

used as the initial canal elevations for the county-scale model. 

Initial flow rates, gate openings, and discharge rates of SWR1 

structures were assumed to be zero.

Canal Representation Using the Surface-Water 

Routing Process

The extensive canal network throughout Broward 

County was represented by using the SWR1 process. Primary 

and most secondary drainage features were included with 

locations and parameters taken from the saltwater-intrusion 

model (Hughes and others, 2016), which was based on the 

MikeSHE/Mike11 model developed for Broward County 

(Islam and Dunn, 2006). The central part of the county-scale 

model’s canal network, which encompasses the local-scale 

model, was dynamically simulated by using active level-pool 

reach groups connected through weirs, stage-discharge curves, 

and gate operations (fig. 2.16 and fig. 2 in main body of 

report). The northern and southern parts of the county’s canal 

network were represented as specified stage reaches, with 

stage values taken from the saltwater-intrusion model.

The central active canal network includes representation 

of 19 water-control structures using SWR1 weir structure 

types, 9 water-control structures using stage-discharge 

relationships, 3 gated spillway SWR1 structure types, 

and 1 structure represented as a specified inflow 

(fig. 2.16, tables 2.1 and 2.2). Weir invert elevations and 

stage-discharge curves, representing pumps, were based 

on the MikeSHE/Mike11 model parameters and the South 

Florida Water Management District (SFWMD) structures 

handbook (SFWMD, 2016). The gate opening and closing 

rules for the gated spillway structures were also taken 

from the SFWMD structures handbook. Discharge through 

stage-discharge structures begin at various upstream stages 
Appendix 2. Numerical Model Construction 77

0 1 2 3 4 MILES

0 2 31 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

G–87

G–86S

G–86N

S–9XN

S–9XS

PA C6

PA C1

PA C2

PA C3

PA C4

PA C5

S–125

3L3WES

SBDD_S–8

OPWCD PS4

S–13a

S–124

S–32

S–30

S–13 P1

OPWCD PS1

OPWCD PS2

OPWCD PS3

Weston PS2 Weston PS1

Sunrise PS1

Sunrise PS8

S–9

S–33

G–54

S–13S

S–34

EXPLANATION

Active model domain

General head boundary

Specified stage canal reach within cell

Active canal reach within cell

Weir and identifier

Gated spillway and identifier

Stage-discharge curve and identifier

Specified inflow and identifier

G–54

S–13a

Weston PS1

S–34

County-scale

model area

Area enlarged

80°25' 80°20' 80°15' 80°10'

26°10'

26°05'

26°00'

Figure 2.16. Representation of water-control structures in the county-scale model by using the 

Surface-Water Routing (SWR1) process.
78 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

Table 2.1. Structures represented in the active part of the 

canal network by using a weir or specified inflow within the 

surface-water routing (SWR1) process.

[ft, foot; NAVD 88, North American Vertical Datum of 1988; °, degree; ft3/s, 

cubic foot per second]

Represented using weir structure type

Designation Latitude Longitude

Invert 

elevation 

(ft above 

NAVD 88)

S–125 26.1643° -80.2980° 4.501

PA C6 26.1568° -80.2982° 3.002

3L3WES 26.1498° -80.2972° 1.000

PA C5 26.1495° -80.2980° 3.002

PA C4 26.1422° -80.2978° 3.002

OPWCD PS4 26.1355° -80.2345° 2.000

PA C3 26.1349° -80.2979° 3.002

S–124 26.1294° -80.3653° 6.201

PA C2 26.1276° -80.2979° 3.002

PA C1 26.1203° -80.2979° 3.002

S–13a 26.0645° -80.2815° 3.000

S–9XN 26.0621° -80.4431° 7.500

G–86N 26.0619° -80.4347° 3.999

SBDD S–8 26.0617° -80.3785° 4.199

S–9XS 26.0601° -80.4432° 5.500

G86S 26.0594° -80.4346° 3.999

G–87 26.0295° -80.3130° 8.000

S–30 25.9568° -80.4317° 4.500

S–32 25.9422° -80.4397° 4.500

Represented using specified inflow

Designation Latitude Longitude

Average flow 

into model 

(ft3

/s)

S–34 26.1496° -80.4423° 180.3

(table 2.2) and discharge linearly, increasing to the maximum 

discharge rate at 1.0 ft above the start elevation for all 

stage-discharge structures except S–9. The maximum rate 

of discharge of 1,000 cubic feet per second (ft3/s) for S–9 

occurs at an upstream stage 0.5 ft above the discharge start 

elevation of 1.5 ft above NAVD 88. Measured daily average 

inflows through S–34 taken from the historical period were 

used as specified inflows to represent S–34 within the model 

because of unclear or inconsistent operating rules during the 

simulation period. The average measured flow rate during the 

historical period (January 1, 1990, to December 30, 1999) was 

180.3 ft3

/s, with a maximum value of 822.6 ft3/s (fig. 2.17). 

Table 2.2. Structures represented in the active part of the canal 

network by using a gated spillway or stage-discharge curve within 

the surface-water routing (SWR1) process.

[ft, foot; NAVD 88, North American Vertical Datum of 1988; °, degree; ft3/s, 

cubic foot per second]

Designation

Represented using gated spillway

Latitude Longitude

Gate open 

elevation

(ft above 

NAVD 88)

Gate close 

elevation

(ft above 

NAVD 88)

S–33 26.1357° -80.1945° 2.422 1.422

G–54 26.0948° -80.2298° 2.899 1.899

S–13 Spillway 26.0661° -80.2089° 0.199 -0.011

Designation

Represented using stage-discharge curve

Latitude Longitude

Discharge 

start 

elevation1

(ft above 

NAVD 88)

Maximum 

discharge 

rate 

(ft3

/s)

Sunrise PS1 26.1383° -80.2282° 3.999 98

Sunrise PS8 26.1214° -80.3380° 3.999 98

OPWCD PS3 26.1082° -80.2817° 2.650 300

OPWCD PS2 26.1043° -80.2658° 2.650 300

OPWCD PS1 26.0984° -80.2334° 2.650 400

S–13 Pump 26.0661° -80.2089° 0.700 540

Weston PS1 26.0633° -80.3786° 3.000 180

Weston PS2 26.0627° -80.4013° 3.000 360

S–9 26.0615° -80.4435° 1.500 1,000

1

Maximum discharge occurs at 1 ft above discharge start elevation for all 

stage-discharge structures except S–9 which occurs 0.5 ft above discharge 

start elevation.

Representation of Additional Drainage Features

Within the saltwater-intrusion model, the tertiary drainage 

features were represented by using the MODFLOW 2005 

Drain package (DRN). Drainage elevations within this 

package were defined by using the watershed-management 

plans developed for the drainage districts (Hughes and 

others, 2016). The county-scale model used this approach 

in representing the detailed drainage features in parts of 

the northern and southern model area that correspond to 

specified-head SWR1 canal reaches. Areas where the canal 

network was modeled by using SWR1 level-pool routing 

and active structures did not incorporate the DRN package 

(fig. 2.18). The drainage elevations were defined as those 

used in the saltwater-intrusion model and varied from 2.1 ft to 

16.0 ft above NAVD 88, with the highest elevations used in 

the northern part of the model area.
Appendix 2. Numerical Model Construction 79

Date

1/1/1990 1/1/1992 12/31/1993 12/31/1995 12/30/1997 12/30/1999

Flow, in cubic feet per second

0

200

400

600

800

1,000

Figure 2.17. Measured flow through structure S–34. Flows greater than 0.0 correspond to flow into 

the Surface-Water Routing (SWR1) canal network.

Representation of Additional Hydrologic 

Processes Using the Urban Runoff Process

The remaining hydrologic processes within the 

county-scale model were represented by using the newly 

developed Urban Runoff (URO) process. These hydrologic 

processes include precipitation, evapotranspiration, 

infiltration, and recharge (fig. 2.19). The URO process 

represents unsaturated zone and surface-water storage for 

each cell; overland flow; rainfall; evaporation from the surface 

water and the unsaturated and saturated zones; infiltration 

from the surface-water storage into the unsaturated zone; 

recharge from the unsaturated zone into the MODFLOW 

groundwater cell; and when necessary, groundwater discharge 

from the MODFLOW groundwater cell into the surface-water 

storage (Decker and Hughes, 2013). The county- and 

local-scale models were initially setup to simulate overland 

flow; however, the predominantly low surface-water depths 

throughout the urban areas did not necessitate its inclusion 

into the final setup, which helped to reduce model runtimes. 

The values for the frictional coefficients and detention depths 

developed for the model are included in this section despite 

not being used in producing the final results.

Precipitation and Evapotranspiration

For each time step within the URO process, the 

precipitation and evapotranspiration (ET) volumes are 

calculated by multiplying the specified rate by the time-step 

length. First, precipitation is added to the surface-water 

storage. Evaporation is then removed from the surface-water 

storage first at the full potential rate; if the potential rate is 

not satisfied, any remaining volume is then removed from the 

unsaturated zone storage at a reduced rate, dependent on the 

water content, and lastly, any remaining volume is removed 

from the groundwater cell at a linearly reduced rate down to a 

user-defined extinction depth (Decker and Hughes, 2013). 

The precipitation and potential ET values used 

for model simulations were provided by the Center for 

Ocean-Atmospheric Prediction Studies (COAPS). The output 

for two general circulation models, Community Climate 

System Model (CCSM) and Hadley Centre Coupled Model 

version 3 (HadCM3), were used to provide the boundary 

conditions for a regional climate model that encompasses the 

southeastern United States. The regional climate model had 

a 10-kilometer (km) by 10-km grid resolution and simulated 

a historical period (January 1, 1968, to December 31, 1999) 

and a future period (January 1, 2038, to December 31, 2069). 

Precipitation and potential ET outputs were provided as 

daily values. The precipitation output was bias-corrected by 

COAPS for the entire climate model simulation period by 

using the quantile matching approach, which utilizes monthly 

cumulative distribution functions (Wood and others, 2002). 

This approach ensures that the bias-corrected regional climate 

model output for precipitation has the same mean and variance 

as the observation dataset.

Twenty-two 10-km by 10-km climate cells cover the 

county-scale model’s active domain (fig. 2.20). The rainfall 

and potential ET input for each cell was specified as the output 

from the surrounding regional climate model cell, creating 

22 rainfall and ET cells. The average rainfall for each month 

of the year for the CCSM model ranged from 2.2 inches (in.) 

for February to 9.6 in. for June during the base-case simulation 

period and from 1.65 in. for January to 12.3 in. for August 

during the future simulation period. The average rainfall for 

each month of the year for the HadCM3 model ranged from 

1.7 in. for December to 10.0 in. for June during the base-case 

simulation period and from 1.66 in. for February to 7.6 in. for 

October during the future simulation period (fig. 2.21). The 

CCSM yearly rainfall varied from 40.3 in. to 67.0 in., with an 

average of 56.4 in. during the base-case simulation period. The 

HadCM3 yearly rainfall varied from 31.9 in. to 73.7 in., with 

an average of 57.5 in. during the base-case simulation period 

(fig. 16A in main body of report). The CCSM yearly rainfall 

varied from 54.0 in. to 77.4 in., with an average of 66.3 in. 

during the future simulation period. The HadCM3 yearly 

rainfall varied from 39.4 in. to 64.7 in., with an average of 

53.5 in. during the future simulation period (fig. 16B in main 
80 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983 EXPLANATION

Drainage elevation, in feet above North American Vertical Datum of 1988

16.0

2.1

County-scale model area boundary

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.18. Drainage elevations used in county-scale model construction to simulate tertiary and detailed drainage 

features in areas using specified-head Surface-Water Routing (SWR1) canal reach types.
Appendix 2. Numerical Model Construction 81

Modflow grid cell 

Unsaturated zone storage

Groundwater recharge

Surface water storage

Infiltration

Precipitation

Evaporation

Groundwater discharge

Figure 2.19. Hydrologic processes represented by the 

Urban Runoff process.

body of report). These average yearly rainfall totals represent 

a 17.6-percent increase in the CCSM output compared to the 

base-case simulation period and a 7.0-percent decrease in the 

HadCM3 output compared to the base-case simulation period. 

The CCSM future scenarios were therefore referred to as 

“wetter future,” whereas the HadCM3 future scenarios were 

referred to as “drier future.”

The maximum daily rainfall was 3.54 in. and 9.95 in. for 

the CCSM base-case and future periods, respectively, when 

analyzing daily rainfall averaged over the active county-scale 

model area. The maximum daily rainfall was 3.66 in. and 

5.43 in. for the HadCM3 base-case and future periods, 

respectively, when analyzing daily rainfall averaged over the 

active county-scale model area. The 1-day rainfall totals of 

7.5 in., 10.75 in., and 13.0 in. represented 5-year, 25-year, 

and 100-year precipitation events within the model area. The 

future scenario CCSM was the only simulation to include 

a day when the daily rainfall total averaged over the entire 

active area reached a 5-year precipitation event of 7.5 in. 

(fig. 2.22). The two base-case scenarios included no individual 

climate cell output locations that reached any of these 

thresholds either. The CCSM future scenario output included 

9 days when the 5-year event threshold was reached, 2 days 

when the 25-year threshold was reached, and 1 day when the 

100-year threshold was reached by at least 1 cell within the 

active county-model area. The HadCM3 future scenario output 

included 3 days when the 5-year threshold was reached, 1 day 

when the 25-year threshold was reached, and zero days when 

the 100-year precipitation threshold was reached by at least 

1 cell within the active county-model area. 

The average annual potential ET totals were 78.2 in. 

and 85.7 in. for the CCSM base-case simulation and future 

scenario periods, respectively. The average annual potential 

ET totals were 74.1 in. and 86.4 in. for the HadCM3 base-case 

simulation and future scenario periods, respectively (fig. 18 

in main body of report). The average potential ET for each 

month of the year for the CCSM model ranged from 4.4 in. for 

December to 8.5 in. for July during the base-case simulation 

period and from 4.67 in. for December to 9.3 in. for July 

during the future simulation period. The average potential ET 

for each month of the year for the HadCM3 model ranged 

from 4.3 in. for December to 7.7 in. for July during the 

base-case simulation period and from 4.4 in. for December to 

9.0 in. for July during the future simulation period (fig. 2.23).

Infiltration and Groundwater Recharge

Within the URO process, infiltration into and recharge 

out of the conceptualized unsaturated zone represented within 

the top layer of each groundwater column is controlled by 

using a linear water-content-dependent relationship:

h k t inf i   nf 0   1   , (4)

h k t rec r  ec0 , (5)

  L

L

UZS

UZSmx

, (6)

where

hinf is the infiltration depth (L);

kinf0 is the maximum infiltration rate (L/T);

	 θ	 is the water content;

	 Δt	 is the URO time step (T);

hrec is the recharge depth (L);

krec0 is the maximum recharge rate (L/T);

LUZS is the current unsaturated zone storage within 

the cell (L); and

LUZSmx is the maximum storage depth of the 

unsaturated zone (L).

The values of kinf0 used in the model were calculated by 

using a combination of land-use coverage, soil classification 

coverage, and typical dry soil infiltration rates. The values 

of krec0

 used in model were calculated on the basis of the soil 

classification coverage and typical saturated soil hydraulic 

conductivities (kss). The land-use coverage was generated by 

the SFWMD from 2008–9 aerial photographs (fig. 2.24). The 

coverage within the county-scale model area was simplified to 

include 17 types of land use, and the impervious area (IA) for 

each type was estimated by using published data (table 2.3) 

(USDA, 1986; Kluitenberg, 1994; Cappiella and Brown, 2001; 

Dougherty and others, 2004).
82 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983 EXPLANATION

Regional climate model output cell

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.20. Regional climate model output cells coverage of the county-scale model.
Appendix 2. Numerical Model Construction 83

1 2 3 4 5 6 7 8 9 10 11 12

1 2 3 4 5 6 7 8 9 10 11 12

Month of year

Average rainfall, in inches

0

2

4

6

8

10

12

0

2

4

6

8

10

12

14

Base-case period

EXPLANATION

Future period

Base-case period

Future period

EXPLANATION

A. Community Climate System Model (wetter future)

B. Hadley Centre Coupled Model version 3 (drier future)

Figure 2.21. Regional climate model average precipitation by month during base-case and future 

simulation periods for A, the Community Climate System Model (CCSM) wetter future, and B, the 

Hadley Centre Coupled Model version 3 (HadCM3) drier future scenarios.

A soil classification coverage derived from the SFWMD 

Natural Soils Landscape Position (NSLP) database was 

generated by the SFWMD and used to calculate kinf0 and krec0

(fig. 2.25) (Zahina and others, 2001). On the basis of the 

NSLP description, each category within the soil classification 

coverage was assigned a corresponding hydrologic group code 

and soil drainage class code. Typical dry soil infiltration rates 

and saturated hydraulic conductivity for the corresponding soil 

descriptions were estimated for each hydrologic group code 

(tables 2.4 and 2.5) (Akan, 1993).

From the data coverages, the area of each land-use 

category and soil type within each URO model cell was 

calculated. The kinf0 for each cell was calculated by multiplying 

the area-weighted arithmetic mean of the impervious 

area by the area-weighted harmonic mean of the dry soil 

infiltration rate:

k

al IA

al

as

as

k

j j j

m

j j

m

i i

n

i

dsi

i

n inf 0

1

1

1

1











































, (7)

where

alj is the area within the cell-designated land-use 

category j (L2);

IAj is the estimated impervious area for land-use 

category j;

asi is the area within the cell-designated soil 

classification i (L2); and

kdsi is the dry soil infiltration rate for soil 

classification i (L/T).

The resulting values of kinf0 within the county-scale model 

varied from 0.4 ft/d to 10 ft/d, with a mean of 3.94 ft/d 

(fig. 2.26). The krec0 for each cell was calculated by finding the 

area-weighted harmonic mean of the saturated soil hydraulic 

conductivity:

k

as

as

k

rec

i i

n

i

ssi

i

n 0

1

1

 





 , (8)

where

kssi is the saturated soil hydraulic conductivity for 

soil classification i (L/T).
84 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

Date

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

2060 2061 2062 2063 2064 2065 2066 2067 2068 2069

2060 2061 2062 2063 2064 2065 2066 2067 2068 2069

Daily rainfall, in inches

0

2

4

6

8

10

0

2

4

6

8

10

0

2

4

6

8

10

0

2

4

6

8

10

B. Hadley Centre Coupled Model version 3 (HadCM3) base-case period

D. HadCM3 future period

A. Community Climate System Model (CCSM) base-case period

C. CCSM future period

Figure 2.22. Regional climate model daily rainfall averaged over active county-model area during basecase and future simulation periods for A, C, the Community Climate System Model (CCSM) wetter future, 

and B, D, the Hadley Centre Coupled Model version 3 (HadCM3) drier future scenarios.
Appendix 2. Numerical Model Construction 85

1 2 3 4 5 6 7 8 9 10 11 12

Month of year

Average potential evapotranspiration,

 in inches

0

2

4

6

8

10

12

EXPLANATION

Community Climate System Model 

 (CCSM) base-case period

Hadley Centre Coupled Model version 3

 (HadCM3) base-case period

CCSM future period HadCM3 future period

Figure 2.23. Regional climate model average potential evapotranspiration by month during basecase and future simulation periods for the Community Climate System Model (CCSM) wetter future 

and Hadley Centre Coupled Model version 3 (HadCM3) drier future scenarios.

This method resulted in values of krec0 within the county-scale 

model that varied from 0.14 ft/d to 10 ft/d. The lower values 

of krec0 within the urban areas of the county-scale model did 

not adequately transfer water from the unsaturated zone to 

the underlying MODFLOW cell during early testing, and a 

minimum krec0 of 1.00 ft/d was specified for all simulations 

described in this report (fig. 2.27). The resulting mean value of 

krec0 was 3.79 ft/d.

Overland Flow

The URO process has the ability to simulate 

two-dimensional overland flow by using the Manning’s 

equation. After initial testing, it was determined that the low 

ponding depths within the urban area did not necessitate 

the inclusion of this option. The required coefficients were 

calculated and included in this section but were not used. The 

Manning’s n values used for the model were calculated on 

the basis of the land-use coverage (fig. 2.24) and Manning’s 

n values used by the SFWMD in previous studies for similar 

land-use types (tables 2.6 and 2.7) (SFWMD, 2005). The 

composite Manning’s n value for each cell was calculated as 

the area-weighted arithmetic mean of the Manning’s n of all 

the land-use types within a cell:

n

al n

al

i i i

n

i i

n  







1

1

, (9)

where

ali is the area within the cell-designated land-use 

category i (L2); and

ni is the estimated Manning’s n for the land-use 

category i (T/L1/3).

Detention depth values for these same land-use types were 

used to calculate an area-weighted arithmetic mean similar 

to equation 12 in the main body of this report. No overland 

flow occurs below this value. The resultant composite 

Manning’s n values and detention depth values are shown in 

figures 2.28 and 2.29.

Local-Scale Numerical Model Construction

The local-scale model relied heavily on the 

variable-density model developed for central and southern 

Broward County (saltwater-intrusion model; Hughes and 

others, 2016) for the hydraulic parameters and layering. 

The precipitation, ET, maximum infiltration rate, and 

maximum recharge rates were calculated by using the same 

methodology used to calculate those same parameters in the 

county-scale model.

Extent and Discretization

The local-scale model’s extent was designed to include 

areas of interest within southern and central Broward 

County (figs. 2 and 3 in main body of report). The spatial 

resolution was increased with horizontal cell dimensions 

of 166.7 ft by 166.7 ft, resulting in three columns and rows 

within each county-scale model row and column. The same 

layering scheme used in the county-scale model was used 

in the local-scale model. The calibrated parameters used 

for the 12-layer saltwater-intrusion model also were used to 

construct three layers using the upper, production, and lower 

layer designations. The local-scale model has 531 columns 

and 159 rows, with 63,445 active cells per model layer 

covering 63.24 mi2

. 
86 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Land-use coverage—Generated by South Florida Water Management District used

 to calculate maximum infiltration rates for use in the Urban Runoff process

Residential, low density

Residential, medium density

Residential, high density

Commercial

Industrial

Institutional

Recreational

Open land

Agriculture

Upland non-forested

Upland forested

Water

Wetlands

Disturbed land

Transportation

Communications

Utilities

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.24. Land-use coverage generated by the South Florida Water Management District and used to calculate 

maximum infiltration rates for use in the Urban Runoff process.
Appendix 2. Numerical Model Construction 87

Table 2.3. Published estimated percentage of impervious area for land-use categories found in Broward County, Florida.

[USDA, U.S. Department of Agriculture; IA, impervious area; %, percent]

Land-use category Dougherty and 

others (2004)

Cappiella and 

Brown (2001)

Kluitenberg, 

(1994) USDA (1986) IA value used 

Low-density residential 5–10% 11–14% 19% 12–20% 14%

Medium-density residential 20–25% 21–28% 38% 25–38% 29%

High-density residential 35–45% 33% 51% 65% 47%

Commercial 35–55% 72% 56% 85% 64%

Industrial 35–55% 53% 76% 72% 62%

Institutional 35–55% 34% No value given No value given 40%

Recreational

2–7%

(Agriculture, 

forest, golf, idle 

land)

5–12%

(Parks, golf) No value given No value given 7%

Open land (urban) 9% 11% No value given 8%

Cropland/pasture, tree crops, nurseries, 

farms

2%

(Agriculture)

2%

(Agriculture) No value given 3%

Open land (rural) No value given 2% No value given 2%

Upland forested No value given 2% No value given 2%

Upland nonforested No value given No value given No value given 2%

Water No value given No value given 51%

(Water, wetlands)

No value given 0%

Wetland No value given No value given No value given 2%

Disturbed land 50–70% No value given No value given No value given 60%

Transportation 50–70% No value given 53% No value given 57%

Communications/utilities No value given No value given No value given No value given 62%

The simulation periods and MODFLOW stress periods 

and time steps used in the local-scale model were the same 

as those used in the county-scale model. The historical 

simulation period was January 1, 1990, to December 31, 1999, 

and the future simulation period was January 1, 2060, to 

December 31, 2069. The model used a daily MODFLOW stress 

period and hourly time steps (table 1 in main body of report). 

Land Surface and Layer-Bottom Elevations

The top of layer 1, which corresponds to land surface, 

ranged from -2.2 ft to 114.1 ft above NAVD 88, with 

an average of 5.05 ft above NAVD 88 (fig. 2.30). The 

land-surface elevations were created by using the 2007–8 

Florida Division of Emergency Management lidar data 

prepared by the SFWMD. The tops of layer 1 were calculated 

as the mean of the 10-ft resolution lidar values within each 

grid cell. The layer bottoms were calculated through the 

bilinear interpolation of the corresponding bottoms of the 

county-scale model. The elevations of the bottom of layer 1 

varied between -71.8 ft and -36.40 ft above NAVD 88, with 

an average elevation of -54.13 ft above NAVD 88 (fig. 2.31A). 

The elevations of the bottom of layer 2 varied between 

-133.6 ft and -67.5 ft above NAVD 88, with an average 

elevation of -108.73 ft above NAVD 88 (fig. 2.31B). The 

elevations of the bottom of layer 3 varied between -220.2 and 

-148.6 ft above NAVD 88, with an average elevation of 

-189.32 ft above NAVD 88 (fig. 2.31C).

Hydraulic Parameters

The hydraulic parameters used for the local-scale model 

were calculated by using the parameters calculated for the 

county-scale model (figs. 2.5 to 2.14), which were derived 

from the calibrated parameters used in the saltwater-intrusion 

model (Hughes and others, 2016). The values used in the 

local-scale model were calculated through the bilinear 

interpolation of the values used in the county-scale model.

Horizontal and Vertical Hydraulic Conductivity

The calculated values of horizontal hydraulic 

conductivity for layer 1 of the local-scale model varied 

from 411.8 ft/d to 2,439.2 ft/d, with a mean of 862.4 ft/d 

(fig. 2.32A). The calculated values of horizontal hydraulic 

conductivity for layer 2 of the local-scale model 

varied from 341.8 ft/d to 25,932.3 ft/d, with a mean of 

3,141.9 ft/d (fig. 2.32B). The calculated values of horizontal 

hydraulic conductivity for layer 3 of the local-scale 

model varied from 241.1 ft/d to 1,727.6 ft/d, with a mean 

of 722.1 ft/d (fig. 2.32C). 

The calculated values of vertical hydraulic conductivity 

for layer 1 of the local-scale model varied from 4.9 ft/d to 

14.2 ft/d, with a mean of 8.26 ft/d (fig. 2.33A). The calculated 

values of vertical hydraulic conductivity for layer 2 of the 

local-scale model varied from 5.4 ft/d to 15.8 ft/d, with a mean 

of 10.6 ft/d (fig. 2.33B). The calculated values of vertical 

conductivity for layer 3 of the local-scale model varied from 

3.7 ft/d to 6.1 ft/d, with a mean of 5.00 ft/d (fig. 2.33C). 
88 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Soil classification—Generated by South Florida Water Management District and

 used to calculate maximum infiltration rates and maximum recharge rate

No data

Water

Tidal soils

Marl and rocky soils

Everglades peat

Muck depressions

Sand depressions

Flat soils

Flatwood soils

Knolls

Central ridge and dunes

Urban/made lands

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.25. Soil classification coverage generated by the South Florida Water Management District and used to 

calculate maximum infiltration rates and maximum recharge rate.
Appendix 2. Numerical Model Construction 89

Table 2.4. Hydrological group codes used in soil classification completed by the South Florida Water Management District.

[in/h, inch per hour; %, percent; >, greater than; <, less than; ≤, less than or equal to]

Hydrologic 

group code Description1

Saturated hydraulic 

conductivity,1 kss

(in/h)

Dry soil infiltration 

rate,2 kds

(in/h)

A High infiltration rates; low runoff potential; typically less than 10% 

clay and more than 90% sand or gravel kss > 5.67 5.0 < kds < 10.0

(Dry sandy soils)

B Moderate infiltration rates; moderately low runoff potential; typically 

10–20% percent clay and 50–90% sand 1.42 < kss ≤ 5.67

3.0 < kds < 6.0

(Dry loam soils)

C Slow infiltration rates; moderately high runoff potential; typically 

20–40% clay and less than 50% sand 0.14 < kss ≤ 1.42

D Very slow infiltration rates; high runoff potential; typically greater 

than 40% clay and less than 50% sand kss ≤ 0.14 1.0 < kds < 2.0

(Dry clay soils)

1

Descriptions and typical kss values from “National Engineering Handbook” (U.S. Department of Agriculture, 2007).

2

Typical kds values for soil types from “Urban Stormwater Hydrology: A Guide to Engineering Calculations” (Akan, 1993).

Table 2.5. Natural Soils Landscape Position classifications and associated hydrological group codes found within Broward County 

soil sample sites and corresponding infiltration and conductivity values used in model parameter development (based on Zahina and 

others, 2001).

[NSLP, Natural Soils Landscape Position; Hydrological group code descriptions can be found in table 2.4; in/h, inch per hour]

NSLP description Associated hydrological 

group code

Saturated hydraulic 

conductivity used 

for model, kss

(in/h)

Dry soil infiltration rate 

used for model, kds

(in/h)

Water Not applicable 10.0 10.0

Tidal soils D 0.14 2.0

Marl and rocky D 0.14 2.0

Everglades peat D 0.14 2.0

Muck depressions D 0.14 2.0

Sand depressions D 0.14 2.0

Flats soils D 0.14 2.0

Flatwood soils D 0.14 2.0

Knolls A–C 5.0 6.5

Central ridge and dunes A 6.0 7.5

Urban or made lands Not applicable 5.0 6.5
90 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Calculated maximum infiltration rates, in feet per day—Used by the Urban Runoff process

0.4 

10.0

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.26. Calculated maximum infiltration rates used by the Urban Runoff process within the county-scale model 

area.
Appendix 2. Numerical Model Construction 91

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Calculated maximum recharge rates, in feet per day—Used by the Urban Runoff process

1.0 

10.0

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.27. Calculated maximum recharge rates used by the Urban Runoff process within the county-scale model 

area.
92 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

Table 2.6. Manning’s n values based on land-use types used 

to calculate composite Manning’s n values for the county-scale 

model (South Florida Water Management District, 2005).

[ft, foot]

Land-use description Manning’s n

 Detention 

depth 

(ft)

Urban/low density 0.20 0.60

Urban/medium density 0.14 0.55

Urban/high density 0.08 0.50

Agriculture 0.23 0.10–0.50

Wetland1 0.75–1.25 0.10

Forest/forested wetlands1 0.35 0.10

Water 0.01 0.10

Forests/forested uplands 0.85 0.10

1

Manning’s n value actually calculated by using N = n (h)b, where h = 

depth, b = -0.77; values shown are for h = 1 ft.

Table 2.7. Estimated Manning’s n and detention depth for 

land-use categories found in Broward County, Florida.

[ft, foot]

Land-use category Manning’s n

Detention 

depth 

(ft)

Low-density residential 0.20 0.60

Medium-density residential 0.14 0.55

High-density residential 0.14 0.55

Commercial 0.08 0.50

Industrial 0.14 0.55

Institutional 0.14 0.55

Recreational 0.20 0.60

Open land (urban) 0.14 0.55

Cropland/pasture, tree crops, 

nurseries, farms

0.23 0.30

Open land (rural) 0.23 0.30

Upland forested 0.85 0.10

Upland nonforested 0.23 0.30

Water 0.03 0.10

Wetland 1.00 0.10

Disturbed land 0.20 0.60

Transportation 0.08 0.10

Communications/utilities 0.08 0.10

Specific Yield and Specific Storage

The specific yield of the top layer, which was specified 

as convertible, was calculated from the values used in the 

county-scale model by using bilinear interpolation. The 

calculated specific yield used in layer 1 of the local-scale 

model varied from 0.16 to 0.4, with a mean value of 0.29 

(fig. 2.34). The specific yield is the volume of water released 

from storage by the unconfined aquifer per unit area per 

groundwater head change and is therefore unitless. The 

specific storage for all layers was set to a constant value of 

1.00×10-5 ft-1. The specific storage is the volume of water 

released from a confined aquifer per volume of aquifer per unit 

head change and therefore has units of per foot. 

Groundwater Pumpage

Groundwater pumpage within the local-scale model 

was represented by using the MODFLOW WEL package. 

The locations and pumping rates were taken from the 

saltwater-intrusion model (Hughes and others, 2016). The layer 

from which the water was removed was determined the same 

way as in the county-scale model. The pumping rates from 

within the local-scale model from the historical period were 

used for all future scenarios and varied between 8.3 Mgal/d and 

17.9 Mgal/d, with an average value of 11.9 Mgal/d (fig. 2.35). 

Canal Representation Using the Surface-Water 

Routing Process

The canal network within the local-scale model area 

was represented by using the SWR1 process. Primary and 

most secondary drainage features were included, as well as 

some tertiary drainage features (fig. 3 in main body of report). 

Locations and parameters for the primary and secondary 

features were the same as those used in the county-scale 

model. The locations and parameters used for the tertiary 

drainage features were taken from a dataset produced by 

Florida Atlantic University (Hindle, 1992). All canals within 

the local-scale model were represented as active level-pool 

reach groups. The parts of the canal network east of the 

coastal control structures were divided into 10 reach groups 

connected by using basic weir structure types. The lengths 

of these groups varied from 255 ft to 27,971 ft, with a mean 

length of 13,901 ft. The weir crest elevations were specified as 

the canal bottom elevations, and weir widths were specified as 

canal widths. The equivalent weir flow coefficients for these 

structures were calculated by using the Manning’s equation 

with average canal depth, Manning’s friction, and connected 

reach group lengths. The equivalent weir flow coefficients 

varied from 0.23 to 0.46, with a mean of 0.31. 

Represented Canal Structures

Three structures from the county-scale model were also 

represented in the local-scale model: G–54, S–13, and S–13a 

(fig. 2.16). The G–54 and S–13 structures were represented as 
Appendix 2. Numerical Model Construction 93

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

0.03 

1.00

Calculated Manning’s n value

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.28. Calculated Manning’s n for the county-scale model area.
94 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 1 2 3 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Calculated detention depth, in feet

0.1

0.6

80°25' 80°20' 80°15' 80°10' 80°05'

26°15'

26°10'

26°05'

26°00'

25°55'

Figure 2.29. Calculated detention depth for the county-scale model area.
Appendix 2. Numerical Model Construction 95

0 1 2 3 4 MILES

0 2 31 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

G–54 Primary active structure and identifier -2.2

114.1

EXPLANATION

Active local-scale model area—Top of layer 1, in feet

 above North American Vertical Datum of 1988

Area enlarged

County-scale

model area

G–54

S–13a S–13

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

Figure 2.30. Local-scale model top of layer 1.

gated spillways with the same structure parameters as those 

used in the county-scale model (table 2.2). The S–13 pump 

station was represented with the same stage-discharge curve as 

that used in the county-scale model. The S–13a structure was 

represented as a fixed crest weir with the same parameters as 

was used in the county-scale model (table 2.1).

Linkage to County-Scale Model and 

Tidal Boundaries

The local-scale model used head-dependent boundaries 

created from the simulated county-scale model (figs. 2 and 

3 in main body of report). Simulated daily groundwater levels 

for each scenario were used as GHBs along the local-scale 

model’s perimeter. The GHBs representing tidal areas (fig. 3 in 

main body of report) used the same daily tidal input as used in 

the county-scale model.

Specified flows into the western ends of the SWR1 canal 

network were generated by county-scale model output and 

represented the flows into each of the canals that enter the 

local-scale model area (fig. 3 in main body of report). The 

tidal boundary into the SWR1 canal network was represented 

by an hourly updated specified stage at the easternmost end 

of each of the two primary coastal canals in the local-scale 

model. The hourly tidal data were the same data used to create 

the daily tidal stage used as GHB input for the local- and 

county-scale models.

Representation of Conceptualized 

Surface-Water Processes Using 

the Urban Runoff Process

As in the county-scale model, the remaining hydrologic 

processes were represented by using the URO process. 

These processes include precipitation, evapotranspiration, 

infiltration, and recharge.

Precipitation and Evapotranspiration

The same daily precipitation and potential ET volumes 

that were specified for the county-scale model were also 

used in the local-scale model. The precipitation and ET 

volume for each grid cell was specified as the volume from 

the corresponding 10-km by 10-km regional climate model 

cell (fig. 2.20).

Infiltration and Groundwater Recharge

The same methodology used to calculate the maximum 

infiltration and recharge rate in the county-scale model 

was used for the local-scale model. These parameters were 

recalculated by using the same land-use and soil coverages 

(figs. 2.24 and 2.25). The calculated values of maximum 

infiltration rate varied from 0.4 ft/d to 10.0 ft/d (fig. 2.36A). 

The calculated values of maximum recharge rate varied from 

0.1 ft/d to 10.0 ft/d (fig. 2.36B).
96 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 2 31 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Elevation, in feet above NAVD 88

EXPLANATION

Elevation, in feet above North American

Vertical Datum of 1988 (NAVD 88)

EXPLANATION

Elevation, in feet above NAVD 88

-148.6

-220.2

-67.5

-133.6

-36.4

-71.8

Area enlarged

County-scale

model area

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

C. Layer 3 bottom elevations

B. Layer 2 bottom elevations

A. Layer 1 bottom elevations

Figure 2.31. Local-scale model A, bottom of layer 1; B, bottom of layer 2; and 

C, bottom of layer 3.
Appendix 2. Numerical Model Construction 97

0 1 2 3 4 MILES

0 2 31 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Horizontal hydraulic conductivity,

in ft/d

EXPLANATION

Horizontal hydraulic conductivity,

in feet per day (ft/d)

EXPLANATION

Horizontal hydraulic conductivity,

in ft/d

2,439.2

411.8

25,932.3

341.8

1,727.6

241.1

Area enlarged

County-scale

model area

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

C. Layer 3 horizontal hydraulic conductivity

B. Layer 2 horizontal hydraulic conductivity

A. Layer 1 horizontal hydraulic conductivity

Figure 2.32. Horizontal hydraulic conductivity used for A, layer 1; B, layer 2; and 

C, layer 3 in the local-scale model.
98 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 2 31 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Vertical hydraulic conductivity,

in ft/d

EXPLANATION

Vertical hydraulic conductivity,

in feet per day (ft/d)

EXPLANATION

Vertical hydraulic conductivity,

in ft/d

14.2

4.9

15.8

5.4

6.1

3.7

Area enlarged

County-scale

model area

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

C. Layer 3 vertical hydraulic conductivity

B. Layer 2 vertical hydraulic conductivity

A. Layer 1 vertical hydraulic conductivity

Figure 2.33. Vertical hydraulic conductivity used for A, layer 1; B, layer 2; and 

C, layer 3 in the local-scale model.
Appendix 2. Numerical Model Construction 99

0 1 2 3 4 MILES

0 2 31 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Specific yield of layer 1

0.4

0.16

Area enlarged

County-scale

model area

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

Figure 2.34. Specific yield of layer 1 used in the local-scale model.

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999

Date

Groundwater-pumping rate,

in million gallons per day

0

5

10

15

20

Figure 2.35. Total groundwater-pumping rate in the local-scale model 

area for all simulations.
100 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

0 1 2 3 4 MILES

0 2 31 4 KILOMETERS

Base modified from U.S. Geological Survey digital data

Universal Transverse Mercator, zone 17

North American Datum of 1983

EXPLANATION

Maximum recharge rate,

in feet per day

EXPLANATION

Maximum infiltration rate,

in feet per day

10.0

0.4

10.0

0.14

Area enlarged

County-scale

model area

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

80°20' 80°17'30" 80°15' 80°12'30" 80°10' 80°07'30"

26°07'30"

26°05'

B. Maximum recharge rate

A. Maximum infiltration rate

Figure 2.36. Maximum infiltration rate, A, and maximum recharge rate, B, for the 

local-scale model.
Appendix 2. Numerical Model Construction 101

References Cited

Akan, O.A., 1993, Urban stormwater hydrology—A guide to 

engineering calculations: Boca Raton, Fla., CRC Press, LLC.

Cappiella, K., and Brown, K., 2001, Impervious cover and 

land use in the Chesapeake Bay watershed: Ellicott City, 

Md., Center for Watershed Protection, 51 p.

Decker, J.D., 2018, MODFLOW 2005 data sets for 

the simulation of potential increased inundation in 

flood-prone regions of Southeast Florida in response 

to climate and sea-level changes in Broward County, 

Florida, 2060-69: U.S. Geological Survey data release, 

https://dx.doi.org/10.5066/P9E6INWZ. 

Decker, J.D., and Hughes, J.D., 2013, Urban runoff (URO) 

process for MODFLOW 2005—Simulation of sub-grid 

scale urban hydrologic processes in Broward County, 

Florida, in MODFLOW and More 2013—Translating 

Science into Practice Proceedings: Golden, Colo., Colorado 

School of Mines, Integrated Groundwater Modeling Center, 

p. 216–221.

Dougherty, M., Dymond, R.L., Goetz, S.J., Jantz, C.A., 

and Goulet, N., 2004, Evaluation of impervious 

surface estimates in a rapidly urbanizing watershed: 

Photogrammetric Engineering and Remote Sensing, v. 70, 

no. 11, p. 1275–1284.

Hindle, T. and Restrepo, J., 1999, Broward County 

hydrographic survey report: Boca Raton, Fla., Florida 

Atlantic University Department of Geography & Geology. 

Hughes, J.D., Sifuentes, D.F., and White, J.T., 2016, 

Simulated effects of alterations to the hydrologic system 

on the distribution of salinity in the Biscayne aquifer in 

Broward County, Florida: U.S. Geological Survey Scientific 

Investigations Report 2016–5022.

Islam, N., and Dunn, D., 2006, Recalibration and consolidation 

of integrated surface water and groundwater models for 

Broward County: Broward County Environmental Protection 

Department, Water Resources Division, 40 p.

Kluitenberg, E., 1994, Wayne County Rouge Program office 

memorandum—Determination of impervious area and 

directly connected impervious area: Rouge Program Office.

South Florida Water Management District, 2005, 

Documentation of the South Florida Water Management 

Model Version 5.5: West Palm Beach, Fla., South Florida 

Water Management District Final Peer Review Report. 

South Florida Water Management District (SFWMD), 

2016, Structure books: West Palm Beach, Fla., accessed 

May 19, 2016, at ftp://ftp.sfwmd.gov/pub/hehmke/AsBuilts/

Other%20Reports/OCC%20Structure%20Book.pdf.

U.S. Army Corps of Engineers (USACE), 2011, Water 

resources policies and authorities incorporating sea-level 

change considerations in civil works programs: Washington, 

D.C., Department of Army, U.S. Army Corps of Engineers, 

EC 1165-2-211.

U.S. Department of Agriculture (USDA), Natural Resource 

Conservation Service, 1986, Urban hydrology for small 

watersheds: Washington D.C., U.S. Department of 

Agriculture Technical Release 55.

Wood, A.W., Maurer, E.P., Kumar, A., and Letternmaier, D.P., 

2002, Long-range experimental hydrologic forecasting 

for the eastern United States: Journal of Geophysical 

Research, v. 107, p. 4429. [Also available online at 

https://doi.org/10.1029/2001JD000659.]

Zahina, J., Liudahl, K., Liebermann, T., Saari, K., 

Krenz, J., and Mullen, V., 2001, Soil classification database—

Categorization of county soil survey data within the SFWMD 

including natural soils landscape positions: West Palm Beach, 

Fla., South Florida Water Management District, Water Supply 

Planning Department, Technical Publication WS-06. 
102 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

Appendix 3. Sensitivity Testing of Numerical Models

A sensitivity analysis was completed to evaluate the 

influence of the primary parameters on the behavior of the 

system. Of particular interest are the uncertain parameter 

influences on groundwater levels, active canal stages, and active 

structure flows. The canal leakances, general head boundary 

(GHB) conductivities, horizontal and vertical hydraulic 

conductivities, and the maximum infiltration and recharge rates 

were varied, and the results are presented in this appendix.

Horizontal and Vertical Hydraulic Conductivity

The original horizontal and vertical conductivity fields 

varied from 186 feet per day (ft/d) to 32,000 ft/d and from 

1.1 ft/d to 39.5 ft/d, respectively. The mean and standard 

deviation of the log transformed hydraulic conductivity values 

were calculated, and three uniform parameter fields for each 

conductivity, horizontal and vertical, were created for the 

analysis: (1) the log-transformed mean conductivity, (2) one 

standard deviation greater than the log-transformed mean 

conductivity, and (3) one standard deviation less than the logtransformed mean conductivity. These transformations resulted 

in values of 1,057 ft/d, 2,376 ft/d, and 470 ft/d for the horizontal 

conductivity and values of 6.9 ft/d, 10.1 ft/d, and 4.7 ft/d for 

the vertical conductivity. The model’s sensitivities to these 

parameters were tested independently from one another.

The effect of horizontal hydraulic conductivities on 

groundwater levels varied spatially, with maximum differences 

of 2.850 feet (ft), -2.010 ft, and 5.357 ft occurring at G–2395 

for uniform conductivity values of 1,057 ft/d, 470 ft/d, and 

2,376 ft/d, respectively (table 3.1). In general, the groundwater 

wells nearest to the GHBs exhibited the least sensitivity to 

horizontal conductivities, with mean differences of -0.044 ft, 

-0.001 ft, and -0.071 ft for conductivity values of 1,057 ft/d, 

470 ft/d, and 2,376 ft/d, respectively. The interior wells were 

the most sensitive, with mean differences of 0.615 ft, -0.231 ft, 

and 1.006 ft for conductivity values of 1,057 ft/d, 470 ft/d, 

and 2,376 ft/d, respectively. Structure flow rates generally 

decreased with lower conductivity values and increased with 

higher values, except for structure S–33 (table 3.1). The largest 

differences in flow rates occurred at S–9, with a decrease of 

22 percent for a conductivity of 470 ft/d and an increase of 

24 percent for a conductivity of 2,370 ft/d.

The sensitivity analysis of the vertical conductivity 

revealed a general insensitivity in most locations. The 

average difference in mean groundwater levels for the 

comparison wells was 0.037 ft, 0.055 ft, and 0.025 ft for 

vertical conductivity values of 6.9 ft/d, 4.7 ft/d, and 10.1 ft/d, 

respectively. The location with the highest sensitivity was 

G–2395, which is near a pumping-well location. The mean 

flow rate from the primary structures was also generally 

insensitive to changes in vertical conductivity, with a 

maximum difference of 3.3 percent at structure S–33 for a 

vertical conductivity of 4.7 ft/d (table 3.2). 

Conductance at Western Groundwater 

Boundary

The western groundwater boundaries were generated 

by using the Everglades Depth Estimation Network (EDEN) 

data. Although the EDEN data tended to overestimate the 

local groundwater levels near the boundaries of the model, 

they provided good estimates for the interior parts of the 

Water Conservation Areas. The original boundary conductance 

(C) values associated with these boundaries were calculated 

by using the calibrated horizontal conductivity from the 

saltwater-intrusion model discussed in appendix 2 and the 

main body of the report, the vertical cell thickness and width 

to calculate the flow area, and an assumed 10-cell width 

(0.95 mile) as the horizontal connection distance:

C H A

X

k   , (1)

where

Hk is the horizontal hydraulic conductivity of the 

connection;

A is the flow area perpendicular to the 

connection; and

ΔX is the horizontal distance parallel to the flow 

connection.

Two sensitivity simulations were run by using conductance 

values of 25 percent and 200 percent of the originally 

calculated values, which represented horizontal-flow 

connection distances of 40-cell widths (3.78 miles) and 5-cell 

widths (0.47 mile), respectively. The resulting groundwater 

levels at the 15 groundwater observation sites showed general 

insensitivity to the boundary conductance, which produced a 

maximum mean difference in the average groundwater level of 

-0.042 ft at G–2034 for the 25-percent conductance simulation 

(table 3.3). The average groundwater-level difference for 

the 15 observation sites was -0.006 ft and 0.004 ft for the 

25- and 200-percent conductance simulations, respectively. 

This insensitivity can be explained through examination of the 

change in flow rate through the primary structures. Structures 

G–54 and S–9 exhibited the largest percentage differences, 

with decreases of 15.6 percent and 29.3 percent, respectively, 

in average structure flow for the 25-percent conductance 
Appendix 3. Sensitivity Testing of Numerical Models 103

Table 3.1. Sensitivity results for variations of horizontal conductivities using uniform parameter fields within the county-scale model.

[ft, foot; Hk, horizontal hydraulic conductivity; ft/d, foot per day; ft3/s, cubic foot per second; %, percent]

Station name

Mean groundwater level 

(ft)

Original Hk field

Mean difference (ft)

Hk = 1,057 ft/d

Mean difference (ft) 

Hk = 470 ft/d

Mean difference (ft) 

Hk = 2,370 ft/d

G–2031 6.628 -0.037 0.051 -0.125

G–1316 6.580 -0.146 -0.145 -0.192

G–853 0.781 0.227 -0.075 0.434

G–2033 5.136 -0.147 0.087 -0.352

G–2395 -3.952 2.850 -2.010 5.357

G–1220 0.184 0.579 1.377 0.103

G–617 2.232 0.025 0.022 0.037

G–1221 1.066 0.071 0.335 -0.078

G–561 0.310 0.118 0.993 -0.359

G–2034 1.894 -0.022 -0.088 0.075

G–1225 1.307 0.357 0.499 0.144

F–291 -0.422 0.520 1.114 0.225

G–970 1.366 -0.038 -0.079 0.009

G–3571 1.399 -0.058 0.165 -0.201

G–2294 -0.598 -0.106 -0.136 -0.073

Structure Mean flow (ft3

/s)

Original Hk field

% Difference 

Hk = 1,057 ft/d

% Difference

Hk = 470 ft/d

% Difference

Hk = 2,370 ft/d

G–54 312.5 1.3% -7.1% 9.7%

S–13 (spillway) 91.6 -6.2% -22% 15.3%

S–33 19.9 11.5% 7.3% 3.1%

S–9 258.9 -0.8% -22.4% 24.0%

Table 3.2. Sensitivity results for variations of vertical conductivities using uniform parameter fields for county-scale model.

[ft, foot; Vk, vertical hydraulic conductivity; ft/d, foot per day; ft3/s, cubic foot per second; %, percent]

Station name Mean stage (ft)

Original Vk field

Mean difference (ft)

Uniform Vk = 6.9 ft/d

Mean difference (ft) 

Uniform Vk = 4.7 ft/d

Mean difference (ft) 

Uniform Vk = 10.1 ft/d

G–2031 6.628 0.000 0.006 -0.006

G–1316 6.580 -0.015 -0.038 0.008

G–853 0.781 0.011 0.028 0.001

G–2033 5.136 0.001 0.028 -0.022

G–2395 -3.952 0.403 0.264 0.585

G–1220 0.184 0.028 0.155 -0.079

G–617 2.231 -0.003 -0.001 -0.005

G–1221 1.066 0.044 0.116 -0.022

G–561 0.310 0.076 0.191 -0.019

G–2034 1.894 -0.003 0.015 -0.020

G–1225 1.307 -0.003 0.014 0.017

F–291 -0.422 0.000 0.002 -0.002

G–970 1.366 0.002 0.004 0.003

G–3571 1.399 0.005 0.046 -0.033

G–2294 -0.598 0.002 0.000 0.002

Structure Mean flow (ft3

/s)

Original Vk field

% Difference 

Uniform Vk = 6.9 ft/d

% Difference

Uniform Vk = 4.7 ft/d

% Difference

Uniform Vk = 10.1 ft/d

G–54 312.5 -0.2% -2.6% 1.9%

S–13 (spillway) 91.6 -1.2% 2.8% 1.9%

S–33 19.9 0.2% 3.3% -1.0%

S–9 258.9 -0.3% 2.4% 0.5%
104 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

Table 3.3. Sensitivity results for variations in conductance along western general head boundaries (GHBs) within county-scale model.

[ft, foot; %, percent; ft3/s, cubic foot per second]

Station name Mean groundwater level (ft)

Original conductances 

Mean difference (ft)

25% of original conductances

Mean difference (ft)

200% of original conductances

G–2031 6.628 0.001 0.000

G–1316 6.580 -0.002 0.001

G–853 0.781 0.001 0.000

G–2033 5.136 -0.029 0.020

G–2395 -3.952 0.000 0.000

G–1220 0.184 0.001 0.000

G–617 2.232 -0.033 0.019

G–1221 1.066 0.001 -0.001

G–561 0.310 0.001 0.000

G–2034 1.894 -0.042 0.022

G–1225 1.307 0.000 0.000

F–291 -0.422 0.000 0.000

G–970 1.366 0.005 -0.003

G–3571 1.399 0.004 -0.002

G–2294 -0.598 0.000 0.000

Structure Mean flow (ft3

/s)

Original conductances 

% Difference 

25% of original conductances

% Difference

200% of original conductances

G–54 312.5 -15.6% 8.7%

S–13 (spillway) 91.6 -0.2% 0.2%

S–33 19.9 0.5% -0.8%

S–9 258.9 -29.3% 16.4%

simulation and increases of 8.7 percent and 16.4 percent, 

respectively, for the 200-percent conductance simulation. 

These results illustrate the canal system’s ability to effectively 

control the groundwater elevations within their surrounding 

areas. Structures S–13 and S–33 showed little change in 

average flows with the values used at the boundaries for the 

sensitivity tests, but these structures were more distant from 

these boundaries and separated by additional inland structures, 

such as S–13a (fig. 1 in main body of report).

Maximum Infiltration and Recharge Rates

The spatially variable maximum infiltration rates 

within the model varied from 10 to 0.4 ft/d, with an average 

value of 2.7 ft/d and a standard deviation of 1.7 ft/d. The 

spatially variable maximum recharge rates varied from 

10 ft/d to 1 ft/d, with an average value of 2.9 ft/d and a 

standard deviation of 2.0 ft/d. Sensitivity simulations were 

run with uniform maximum infiltration and recharge fields by 

using average values and values one standard deviation higher 

and lower than the averages. These tests resulted in paired 

maximum infiltration and recharge rates of 2.7 and 2.9 ft/d, 

4.4 and 5.0 ft/d, and 1.0 and 0.9 ft/d for the three sensitivity 

simulations. Groundwater levels at the 15 observation site 

locations were generally insensitive to these changes, with 

mean changes in groundwater levels of 0.003 ft, -0.013 ft, 

and 0.006 ft for the average, lower, and higher infiltration 

and recharge values, respectively (table 3-4). The flow rates 

through the primary structures also did not substantially vary 

with changes in the maximum infiltration and recharge rates. 

The maximum change of -4.8 percent was seen at S–33 for 

the lower values tested. The remaining changes in flows were 

1.5 percent or less (table 3.4).
Appendix 3. Sensitivity Testing of Numerical Models 105

Table 3.4. Sensitivity results for variations in maximum infiltration, Kinf, and recharge, Krec, rates for county-scale model.

[ft/d, foot per day; ft3/s, cubic foot per second; %, percent]

Station name Mean stage (ft/d)

Original Kinf and Krec fields

Mean difference (ft/d)

Kinf = 2.70, Krec = 2.91

Mean difference (ft/d) 

Kinf = 1.02, Krec = 0.87

Mean difference (ft/d) 

Kinf = 4.37, Krec = 4.95

G–2031 6.628 0.003 -0.005 0.005

G–1316 6.580 0.005 -0.007 0.009

G–853 0.781 -0.003 -0.016 0.001

G–2033 5.136 0.006 -0.006 0.009

G–2395 -3.952 0.002 -0.018 0.009

G–1220 0.184 0.006 -0.029 0.011

G–617 2.232 0.014 -0.005 0.021

G–1221 1.066 0.004 -0.013 0.009

G–561 0.310 -0.005 -0.030 0.003

G–2034 1.894 0.005 -0.002 0.007

G–1225 1.307 -0.001 -0.023 0.006

F–291 -0.422 -0.002 -0.011 0.000

G–970 1.366 0.003 -0.001 0.005

G–3571 1.399 0.001 -0.020 0.008

G–2294 -0.598 -0.002 -0.007 0.000

Structure Mean flow (ft3

/s)

Original Kinf and Krec fields

% Difference 

Kinf = 2.70, Krec = 2.91

% Difference

Kinf = 1.02, Krec = 0.87

% Difference

Kinf = 4.37, Krec = 4.95

G–54 312.5 0.1% -0.9% 0.5%

S–13 (spillway) 91.6 0.6% -1.1% 1.2%

S–33 19.9 -0.7% -4.8% 0.8%

S–9 258.9 1.1% -0.3% 1.5%

Canal Leakance Coefficient

The canal leakance coefficient values used in the model 

were derived from the saltwater-intrusion model (Hughes 

and others, 2016). The calibrated riverbed conductance for 

each reach was divided by the length and average wetted 

parameter from the historical scenario to obtain the leakance 

coefficient. The resulting leakance coefficient values varied 

from 0.17 day-1 to 17.27 day-1, with an average of 3.66 day-1. 

Sensitivity simulations were run with coefficient values 

modified to 50 percent and 200 percent of the original values, 

resulting in averages of 1.83 day-1 and 7.33 day-1, respectively. 

The effect of these changes on the groundwater levels at the 

15 observation sites were average changes of 0.064 ft and 

-0.042 ft for the 50- and 200-percent leakance coefficient 

values, respectively. The largest difference occurred at 

G–2395, which is near a well field, with a mean difference of 

-0.463 ft and 0.404 ft for the 50- and 200-percent leakance 

coefficient values, respectively. In general, an increase in 

leakance coefficient led to decreased groundwater levels, 

whereas an increase in the leakance coefficient resulted in 

increased groundwater levels (table 3.5). Flow at primary 

structure S–13 was the most sensitive to canal leakance 

coefficient, with a decrease of 14.7 percent and an increase 

of 13.9 percent in flows for the 50- and 200-percent leakance 

coefficient values, respectively. Flow at structure G–54 was 

the least sensitive to canal leakance coefficient, with decreases 

of 0.1 percent and -1.7 percent for the 50- and 200-percent 

leakance coefficient values, respectively (table 3.5).
106 Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .

Table 3.5. Sensitivity results for variations in canal leakance coefficient, GLK within county-scale model.

[ft, foot; %, percent; ft3/s, cubic foot per second]

Station name Mean groundwater level (ft)

Original leakances

Mean difference (ft)

50% of original leakances

Mean difference (ft)

200% of original leakances

G–2031 6.628 0.055 -0.034

G–1316 6.580 0.224 -0.272

G–853 0.781 -0.025 0.021

G–2033 5.137 0.079 -0.018

G–2395 -3.952 -0.463 0.404

G–1220 0.184 0.104 -0.057

G–617 2.232 0.293 -0.223

G–1221 1.066 0.208 -0.157

G–561 0.310 0.047 -0.027

G–2034 1.894 0.117 -0.063

G–1225 1.307 0.018 0.001

F–291 -0.422 0.027 -0.018

G–970 1.366 0.090 -0.067

G–3571 1.399 0.171 -0.117

G–2294 -0.598 0.009 -0.004

Structure Mean flow (ft3

/s)

Original leakances 

% Difference 

50% of original leakances

% Difference

200% of original leakances

G–54 312.5 -0.1% -1.7%

S–13 (spillway) 91.6 -14.7% 13.9%

S–33 19.9 -6.2% 2.9%

S–9 258.9 -7.8% 6.8%

Conductance of General Head Boundary 

Adjacent to North New River Canal

A separate simulation demonstrated the sensitivity of 

the structure flow at G–54 to the GHB adjacent and parallel 

to the westernmost part of the North New River Canal. 

Although the EDEN data used for the boundary levels were 

higher than reasonably expected, they represented a good 

estimation of water-level depth farther within the Water 

Conservation Area. As a result, the conductance (C) of the 

part of the GHB adjacent to the North New River Canal was 

reduced to represent a distance of 40-cell widths (3.78 miles) 

between the boundary and the connected cell. As with the 

previously described sensitivity simulation, this test resulted in 

conductance values that were 25 percent of the original values. 

The result was a decrease of 80.2 cubic feet per second (ft3/s), 

which reduced the mean difference from 114.0 ft3/s to 

35.2 ft3/s. This finding indicates that further refinements to 

the representation of the western boundaries could lead to 

enhanced model results.

Reference Cited

Hughes, J.D., Sifuentes, D.F., and White, J.T., 2016, 

Simulated effects of alterations to the hydrologic system 

on the distribution of salinity in the Biscayne aquifer in 

Broward County, Florida: U.S. Geological Survey Scientific 

Investigations Report 2016–5022.
For more information about this publication, contact

Director, Caribbean-Florida Water Science Center

U.S. Geological Survey

4446 Pet Lane, Suite 108

Lutz, FL 33559

(813) 498-5000

For additional information visit 

https://www2.usgs.gov/water/caribbeanflorida/index.html

Publishing support provided by

Lafayette Publishing Service Center
Decker and others—Potential for Increased Inundation in Flood-Prone Regions of Southeast Florida in Response to Climate . . .—Scientific Investigations Report 2018–5125

ISSN 2328-0328 (online)

https://doi.org/10.3133/sir20185125