project 

Evaluation 

Report

SFNRC Technical Series

2010:1

Tamiami Trail Modifications:

Next Steps Project 

Summary of Findings and 

Draft Environmental Impact Statement

National Park Service

U.S. Department of the Interior

South Florida Natural Resources Center

Everglades National Park 

Tamiami Trail Modifications:

Next Steps Project

Summary of Findings and 

Draft Environmental Impact Statement

Project Evaluation Report

SFNRC Technical Series 2010:1

South Florida Natural Resources Center

Everglades National Park

Homestead, Florida

National Park Service

U.S. Department of the Interior

Cover photograph courtesy of ©Rick Cruz, Rick Cruz Photography
Tamiami Trail Modifications: Next Steps Project i

EXECUTIVE SUMMARY

Introduction

The need to eliminate barriers to overland flow of water in the 

Everglades is now considered one of the indisputable tenets 

of restoration. Much scientific information in support of this 

requirement has been amassed in recent decades indicating 

the importance of removing these barriers to flow in order to 

restore natural marsh connectivity. Science informs us that it 

is not sufficient to simply provide a particular volume of water 

to these wetlands to attain restoration. Flows must mimic the 

natural water depths and flooding durations, be distributed 

across this landscape in a manner that best approximates historical flow patterns, and travel at sufficient velocities to promote the maintenance of ridge and slough landscape characteristics. Sufficient water quality must also be achieved. Only 

when all of these conditions are met will the natural system 

respond in a manner that will promote marsh conditions capable of supporting the unique flora and fauna characteristic 

of the Everglades.

The Tamiami Trail (U.S. Highway 41) has long been recognized as one of the primary barriers to flow of water through 

the ecosystem. While the 1992 General Design Memorandum 

for the Modified Water Deliveries to Everglades National Park 

Project (16 U.S.C. § 410r-S) recommended a plan that only 

included minor modifications to Tamiami Trail, subsequent 

analyses conducted by the U.S. Army Corps of Engineers 

recognized this design deficiency and resulted in recommendations that were either too expensive or provided too little 

restoration benefit. Indeed, the final plan currently being constructed as part of the implementation of the Modified Water 

Deliveries Project is recognized as a first step for the modifications to Tamiami Trail that are needed for full restoration. 

In recognition of this, the 2009 Omnibus Appropriations 

Act (Act) (H.R. 1105; P.L. 111-008, March 11, 2009), directed the Department of the Interior and the National Park 

Service to evaluate the feasibility of additional bridging for 

the Tamiami Trail necessary to improve the ecological connectivity within the remaining natural Everglades, including 

Everglades National Park and the State of Florida Water 

Conservation Areas. The Act further directed that more natural water flow and habitat restoration within the Everglades be 

achieved. This report responds to the direction set forth in the 

Act and summarizes the findings in the Draft Environmental 

Impact Statement (DEIS), for which a 60-day public comment 

period will begin with publication of the Notice of Availability 

in the Federal Register. 

The key finding is that an additional 5.5 miles of bridging 

and raising the balance of the 10.7-mile highway corridor are 

necessary to achieve the Act’s restoration objectives. When 

combined with the 1-mile bridge presently under construction, 6.5 miles of the 10.7-mile stretch of the Tamiami Trail 

that is the focus of this evaluation would be bridged should 

Congress authorize and fund the roadway modifications. 

This level of bridging would eliminate historical hydrologic 

constraints and allow for more natural sheetflow patterns, 

improving ecological conditions throughout much of the 

southern Everglades, including the Water Conservation Areas 

and Everglades National Park. The increased water volumes 

and flow distributions would reestablish the seasonal water 

depths and flooding durations that are critical to the survival 

of fish and wildlife species, including many endangered species. The National Park Service evaluation now underway for 

the Tamiami Trail responds directly to the 2008 findings of the 

National Academy of Sciences in its Biennial Report to the 

Congress which warned that unless near-term progress with 

respect to restoration benefits is achieved, the Everglades 

would experience irreversible loss of natural resource values 

and function.

Tamiami Trail Modifications: Next Steps 

Project – Key Findings and Summary of 

Draft Environmental Impact Statement

The 2009 Omnibus Appropriations Act direction and recent 

science on restoration requirements, including science conducted by the State of Florida, provided the framework for 

the National Park Service’s analysis of the question of how 

much additional bridging is needed and the benefits and impacts associated with the six alternatives that are the subject 

of the current evaluation. Eight separate factors were assessed 

by a project delivery team that included representatives of the 

National Park Service, the U.S. Fish and Wildlife Service, the 

U.S. Army Corps of Engineers, the South Florida Water Management District, the Florida Department of Environmental 

Protection, the Florida Department of Transportation, and 

the Miami-Dade County Department of Environmental Resource Management. These factors included marsh connectivity and flow velocity, reconnection of the ridge and slough 

landscape, and vehicular wildlife mortality, as well as preserTamiami Trail Modifications: Next Steps Project 

Summary of Findings and Draft Environmental Impact Statement

Project Evaluation Report

SFNRC Technical Series 2010:1
ii South Florida Natural Resources Center Technical Series (2010:1)

vation of cultural resources and wetland loss. Analysis of the 

alternatives found a strong positive correlation between the 

amount of bridge span and the benefits provided and culminated in the selection of Alternative 6E as the preferred alternative as set forth in the Draft Environmental Impact Statement that is available for public comment and summarized 

in this publication. This alternative, consisting of four spans 

of bridging totaling 5.5 miles and road raising, provides the 

greatest environmental benefits. In addition to analyses conducted by the National Park Service, the U.S. Army Corps of 

Engineers evaluated the alternatives and affirmed the National Park Service’s selection of an additional 5.5 miles of bridging for the Tamiami Trail as the preferred alternative.

Although a similar project to bridge the Tamiami Trail is 

included in the Comprehensive Everglades Restoration Plan 

and is authorized for implementation by the U.S. Army Corps 

of Engineers in the Water Resources Development Act of 

2000, the National Park Service lacks authority to build the 

5.5 miles of additional bridging that it has determined to be 

necessary for restoration. However, if this project is authorized, funded, and implemented in conjunction with other 

planned restoration projects, ecological connectivity between 

the marshes located in the Water Conservation Areas and 

Everglades National Park will be substantially improved. 

Further, it will also be possible to move larger volumes of 

water through the Water Conservation Areas to Everglades 

National Park in a more natural sheetflow pattern, improving ecological conditions throughout the park and within 

the Water Conservation Areas. The increased water volumes 

and improved flow distributions will reestablish seasonal 

water depths and flooding durations that are critical to the 

survival of many fish and wildlife species, including the federally endangered Wood Stork, Everglade Snail Kite, and Cape 

Sable Seaside Sparrow, and state listed Roseate Spoonbill. 

Alternative 6E will also enable the reconnection of Water 

Conservation Area 3 to Everglades National Park, reducing 

the severity and duration of dry-down events in one compartment of this region (Water Conservation Area 3B) and the 

prolonged deep-water conditions associated with loss of tree 

islands in the southern portion of Water Conservation Area 

3A. Achievement of the many ecological benefits through the 

implementation of Alternative 6E will not adversely affect 

Native American Indian camps located on the Tamiami Trail, 

as it provides for a one-half-mile set-aside on either side of existing Native American Indian camps. The proposed location 

of the bridge spans also maintains access to existing airboat 

tour operations.

The total cost for implementation of Alternative 6E is $330 

million. The itemized cost breakdown is as follows:

Construction: $260 million

Land Acquisition: $24 million

Compensable Business Costs: $30 million

Demolition: $16 million

Although the Draft Environmental Impact Statement 

was prepared in response to the language contained in the 

2009 Omnibus Appropriations Act, the Department and the 

National Park Service note that a similar proposal for bridging the Tamiami Trail is contained in the Comprehensive 

Everglades Restoration Plan authorized by the Water 

Resources Development Act of 2000. That proposal includes 

10 1,000-foot bridge spans which would be cost shared equally between the U.S. Army Corps of Engineers and the South 

Florida Water Management District. The project included 

in the Comprehensive Everglades Restoration Plan is different in both its legislative origins and scope and size from the 

preferred Alternative 6E selected by the National Park Service 

and evaluated in its DEIS and summarized in this report. It is 

worth noting that the framework authorization contained in 

the Comprehensive Everglades Restoration Plan was planned 

over a decade ago. Since that time, significant new scientific information indicates the importance of historic flow 

to fully restore and maintain the ridge and slough landscape 

of the park and the Water Conservation Areas. Further, it is 

important to note that the directive to which the National 

Park Service is responding — to more fully restore more 

natural water flow to Everglades National Park and Florida 

Bay and the ecological connectivity of the park and the Water 

Conservation Areas — is distinct from the legislative mandate 

that directed the U.S. Army Corps of Engineers to prepare the 

Comprehensive Everglades Restoration Plan with its planning 

assumption for the Tamiami Trail. 

If the additional bridging and raising of the Tamiami Trail 

is authorized by the Congress, construction would be located 

predominantly within Everglades National Park, south of the 

alignment of the existing Tamiami Trail corridor, and would 

require 48.1 acres of lands currently within the park. The 

National Park Service would utilize current law to provide a 

highway easement deed to allow the use of these lands to construct the necessary bridging, and would ultimately seek authorization to exchange these lands with the State of Florida 

for an equal amount of state lands adjacent to the current 

park boundary. This approach is the same as was utilized for 

the implementation of the 1-mile bridge for the Tamiami Trail 

as part of the Modified Water Deliveries Project. 

Ridge and slough habitat. Photo by William Perry, NPS.
Tamiami Trail Modifications: Next Steps Project iii

Table of Contents

Contributing Authors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

foreword. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

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

Legislative Mandate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Existing Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

restoration and the tamiami trail. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

tamiami trail modifications: next steps project. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Purpose and Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Evaluation of Project Alternatives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Summary of Findings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
iv South Florida Natural Resources Center Technical Series (2010:1)

Please reference this report as follows: 

Boler, R. B. and D. A. Sikkema. 2010. Tamiami Trail Modifications: Next Steps Project. Summary of Findings and Draft Environmental Impact 

Statement. South Florida Natural Resources Center, Everglades National Park, Homestead, FL. Project Evaluation Report. SFNRC Technical 

Series 2010:1. 17 pp.

Contributing authors

R. Bruce Boler and David A. Sikkema

South Florida Natural Resources Center, Everglades National Park, 950 N. Krome Avenue, Homestead, FL 33030-4443

Comments and Questions: Bruce_Boler@nps.gov or Dave_Sikkema@nps.gov

ACKNOWLEDGEMENTS

The authors are indebted to the following for their technical and project management support: Alicia LoGalbo and Gregg Reynolds (Everglades National Park, National Park Service), Bradley Foster, Ernest Clarke, Gwen Nelson, Susan Connor, Kevin Wittman (U.S. Army Corps of Engineers, Jacksonville District), and Kevin Palmer (U.S. Fish and Wildlife Service).

The following reviewers provided thoughtful comments and much appreciated edits: Donald Jodrey (Department of the Interior), Dan Kimball, Robert Johnson, Carol Mitchell, and Jerome Krueger (Everglades National Park, National Park Service). 

Our thanks go as well to Everglades National Park staff who played a role in the production of this report: Alice Clarke, editor; 

Brandon Gamble, graphics production; and Joy Brunk, design and desktop publishing. The final version of this document is much 

improved as a result of these contributions.

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

this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted material 

contained within this report.

Pursuant to the legislative direction contained in the 2009 Omnibus Appropriations Act, the National Park Service has prepared a Draft Environmental Impact Statement (DEIS) analyzing alternatives for additional bridging in the Tamiami Trail to fully restore more natural water flow to 

Everglades National Park and Florida Bay and the ecological connectivity between the park and the Water Conservation Areas. The DEIS, which 

provides significantly more detail than summarized in this report, is provided on a CD attached to the back cover of this document. When the 

Notice of Availability of the DEIS is published in the Federal register, a 60-day public comment period will commence. If you wish to provide 

comment on the DEIS during the public comment period, or access the DEIS online, you may do so at the National Park Service’s Planning, Environment, and Public Comment website at: http://parkplanning.nps.gov after the Federal Register publication date. To access the DEIS on this site 

select Everglades National Park from the drop down box and follow the links for the Tamiami Trail Modifications: Next Steps Project.
Tamiami Trail Modifications: Next Steps Project v

FOREWORD

In March 2009, Congress directed the National Park Service to complete a report evaluating additional bridging for the Tamiami 

Trail beyond what is being undertaken as part of the Modified Water Deliveries to Everglades National Park Project (16 U.S.C. 

§ 410r-S) to fully restore more natural water flow to Everglades National Park and Florida Bay and to restore the ecological 

connectivity between the park and the Water Conservation Areas. This directive by Congress was an acknowledgement that major 

modifications of the Tamiami Trail are essential both to restoration of Everglades National Park and to restoration of the Greater 

Everglades Ecosystem. 

This publication summarizes the work done during a year-long collaboration between federal, state, and local agencies and the 

general public. The National Park Service’s preferred alternative is that an additional 5.5 miles of bridging of the Tamiami Trail is 

necessary to achieve the ecological restoration objectives as directed by the Congress. This preferred alternative is science-based and 

represents the first time that the National Park Service science staff has articulated what is needed to set the stage for full restoration. 

Consultation with the Miccosukee Tribe of Indians of Florida was conducted at numerous junctures during the development of the 

Draft Environmental Impact Statement (DEIS). The DEIS finds that an additional 5.5 miles of bridging and raising the unbridged 

portion of the highway corridor is necessary to achieve restoration and reflects the preferred alternative (Alternative 6E) that is 

presently undergoing public notice and comment pursuant to the National Environmental Policy Act and which is anticipated to 

be final in October 2010. This additional bridging is beyond the current plan being implemented by the Modified Water Deliveries 

Project, and is larger than plans developed by the U.S. Army Corps of Engineers in the late 1990s and included in the framework 

authorization for the Comprehensive Everglades Restoration Plan, and would increase the ecological connectivity between 

Everglades National Park and the upstream Water Conservation Areas by approximately 500 percent.

The single most important accomplishment that would be gained through the implementation of this project, should it ultimately 

be authorized and funded by the Congress, is the ability to pass unconstrained water flows under Tamiami Trail and into the historic 

eastern flowway of Northeast Shark River Slough in Everglades National Park. The cost to provide the additional bridging and 

roadway improvements is currently estimated at $330 million. This plan is considerably more cost effective than previous plans 

associated with bridging and raising the Tamiami Trail and provides considerably more environmental benefits.

In carrying forward the continued development of recommendations for the Tamiami Trail through this process to respond to the 

direction in the 2009 Omnibus Appropriations Act, the Department of the Interior will work with its other federal and non-federal 

restoration partners to ensure that the Water Conservation Area 3 Decompartmentalization and Sheetflow Enhancement Project 

and the Everglades National Park Seepage Management Project are implemented in a manner that complements the ongoing work 

on Tamiami Trail. Addressing these related projects concurrently with the proposed Tamiami Trail improvements would reestablish 

flow patterns that are reminiscent of the historical flows that sculpted and sustained the ridge and slough landscape, and provide 

adequate freshwater flows to reduce the frequency and severity of hypersaline events in Florida Bay. The additional bridging for 

Tamiami Trail, in conjunction with ongoing efforts to improve water quality and enhance water storage opportunities, provides the 

ability to pass substantially larger volumes of clean water to the Everglades. This in turn will lead to improved ecological conditions 

for all of the remaining natural Everglades, both north and south of the Trail, and is an imperative if we are to see a restored 

Everglades in our lifetime. As the National Academy of Sciences has warned, if ecological resilience is not restored soon, the possibility 

exists that negative environmental changes to habitats and populations could precipitate rapid deleterious landscape-level changes 

that might be difficult to reverse. 

Once the public comment period for the Draft Environmental Impact Statement ends, the National Park Service will respond to 

the comments and prepare the Final Environmental Impact Statement, which is expected to be available late in 2010. Subsequent 

to that, the National Park Service and the Department will report those findings to the Congress as directed in the 2009 Omnibus 

Appropriations Act.

 

Jonathan B. Jarvis

Director

National Park Service

May 2010
vi South Florida Natural Resources Center Technical Series (2010:1)
Tamiami Trail Modifications: Next Steps Project 1

INTRODUCTION

Legislative Mandate

The Omnibus Appropriations Act of 2009 (H.R. 1105; P.L. 

111-008, March 11, 2009) directed the Department of the 

Interior and the National Park Service to evaluate what additional modifications to the Tamiami Trail roadway are necessary beyond the features currently being constructed under 

the Modified Water Deliveries to Everglades National Park 

authority for the purpose of restoring ecological connectivity 

between the Everglades National Park and the Water Conservation Areas and to restore more natural water flow to Everglades National Park and Florida Bay.

Specifically, the Omnibus Appropriations Act of 2009 

(Act) states the following:

Provided further, That the Secretary of the Interior, 

acting through the National Park Service, is directed to 

immediately evaluate the feasibility of additional bridge 

length, beyond that to be constructed pursuant to the 

Modified Water Deliveries to Everglades National Park 

Project (16 U.S.C. § 410r-S), including a continuous 

bridge, or additional bridges or some combination thereof, for the Tamiami Trail (U.S. Highway 41) to restore 

more natural water flow to Everglades National Park 

and Florida Bay and for the purpose of restoring habitat 

within the Park and the ecological connectivity between 

the Park and the Water Conservation Areas. The feasibility study and the recommendation of the Secretary shall 

be submitted to the Congress no later than 12 months 

from the date of enactment of this Act.

This publication summarizes the National Environmental 

Policy Act process that the National Park Service is utilizing 

to develop recommendations to respond to the requirements 

set forth in the Act. Through the analysis conducted to date, 

the National Park Service has selected a preferred alternative as set forth in a Draft Environmental Impact Statement, 

for which a 60-day public comment period will commence 

with publication of the Notice of Availability in the Federal 

Register. The National Park Service finds that an additional 

5.5 miles of bridging is necessary beyond the present 1 mile 

under construction (for a total of 6.5 miles of bridging) to 

fully restore more natural water flow to Everglades National 

Park and Florida Bay and to restore the ecological connectivity between the park and the Water Conservation Areas. If authorized and funded, and assuming implementation of other 

planned restoration projects further upstream, the additional 

bridging would allow for unconstrained flow to Northeast 

Shark River Slough. The resulting flow patterns would closely 

resemble historical flows that sculpted and sustained the ridge 

and slough landscape and would provide adequate freshwater flows to reduce the frequency and severity of hypersaline 

events in Florida Bay.

Existing Conditions

In 1928, the Tamiami Trail roadway and the Tamiami canal 

were constructed across the entire width of the Everglades 

(Fig. 1). While photos from the 1930s show water occasionally spilling over the top of the road, by 1940 aerial photos indicate that, in just 12 years, the construction of Tamiami Trail 

had resulted in the formation of two separate and distinct 

landscape types, a wetter, more preserved ridge and slough 

habitat north of the trail, in what is now Water Conservation 

Area 3A, and a much drier, degraded sawgrass-dominated 

habitat south of the trail, in what is now Everglades National 

Park. Tamiami Trail forms the northern boundary of the park 

and acts as a dam, preventing water from freely flowing from 

north to south along its historical and natural path. This alteration has effectively deprived the park of vital water, resulting 

in the deterioration of the park’s unique ecosystems, and also 

hindering restoration of the Everglades. 

 In 1948, Congress authorized the Central and Southern 

Florida Project in part to provide for regional water supply 

and flood protection for the lower east coast of Florida. The 

Central and Southern Florida Project diverted much of the 

water historically flowing south out of Lake Okeechobee to 

the east and west coasts, allowing the creation of over 700,000 

acres of agricultural lands in the heart of the Everglades 

ecosystem and eliminating overland flows south from the 

lake to the central and southern Everglades (see inside cover 

map). Over the next 20 years, a network of canals and levees 

constructed by the U.S. Army Corps of Engineers (Corps) 

increased the diversion of water from the Everglades to meet 

the expanding needs of agricultural and urban development. 

Some 1,800 miles of canals and levees, 200 water-control 

structures, and 16 major pumping stations were eventually 

constructed that altered flow patterns, fragmented the central 

Everglades into a set of compartments, and drained 1.7 million acres of wetlands, comprising almost half of the historical 

Everglades ecosystem (Fig. 2).

The ecological effects of the Central and Southern Florida 

Project on the Everglades, including Everglades National 

Park and the State’s Water Conservation Areas, have been 

devastating. During drier periods the upstream Water 

Conservation Areas retain water to meet urban and agricultural water supply needs. During wetter periods excess water 

is released to the park; however, it does not follow the historic 

eastern flowway of Northeast Shark River Slough and causes 

flooding problems in Water Conservation Area 3A and in the 

marl prairies in Western Shark River Slough. Because of these 

hydrologic changes, entire populations of some endangered 

species, including the West Indian manatee, the Cape Sable 

Seaside Sparrow, the Everglade Snail Kite, the Wood Stork, 

and the Florida panther, are at risk of disappearing. Exotic 

non-native plants such as Melaleuca, Brazilian pepper, and 

Australian pine have invaded natural areas, choking out native plants and altering habitats. Massive algal blooms and 

die-offs of seagrass beds in Florida Bay have been followed 

by extensive losses of coastal wading birds, sportfish, shrimp, 
2 South Florida Natural Resources Center Technical Series (2010:1)

and sponges. Slough habitat, the unique Everglades wetland 

complex immortalized as the “river of grass” by Marjory 

Stoneman Douglas, is among the most adversely impacted 

habitats by reduction in water flow.

While the entire Greater Everglades ecosystem has been 

negatively impacted by certain aspects of the Central and 

Southern Florida Project, the unique subtropical habitat of 

Everglades National Park, located at the southern end of this 

compartmentalized system, is at risk due to the reduced water 

volumes and altered flow distributions. Research on water 

flow characteristics in the pre-drainage Everglades suggests 

that the average annual volume of water reaching the park has 

been reduced by approximately 1.3 million acre-feet, approximately a 65-percent reduction in historical flow volumes. In 

addition to the reduction in volume, research indicates there 

has also been a concurrent change in the distribution of the 

flow within the Shark River Slough drainage basin. Prior to 

implementation of the Central and Southern Florida Project, 

more than 60 percent of average annual flows to the park 

ran through Northeast Shark River Slough, with less than 

40 percent flowing through the area to the west, commonly 

referred to as Western Shark River Slough. For example, data 

from 1959, a wet year prior to compartmentalization of Water 

Conservation Area 3, had a distribution of 29 percent of the 

annual flows to Western Shark River Slough and 71 percent 

to Northeast Shark River Slough. In comparison, in 2005, 

also a wet year, this distribution was reversed to 89 percent of 

Figure 1. Location of the Tamiami Trail in south Florida. The road was constructed in 1928 to connect the city of Miami on the east coast 

to Tampa on the west coast. The segment of the road that is the subject of this study (Project Area) is also depicted. 

Wood Stork. Photo by Darlene Harris, NPS volunteer. 
Tamiami Trail Modifications: Next Steps Project 3

Figure 2. The historic, free-flowing, south Florida landscape, including the boundary of the Greater Everglades (left), compared to the 

highly compartmentalized landscape of today (right) with the historic boundary overlaid (red). The map of the current landscape illustrates how much of the historic landscape has been lost to agricultural and urban development. The barriers to sheetflow, due to the 

construction of Central and Southern Florida Project levees and canals, have resulted in the loss of natural marsh connectivity (adapted 

from a 2007 South Florida Water Management District map). State Water Conservation Areas (WCA) lie to the north of Everglades 

National Park.

the annual flows to Western Shark River Slough and only 11 

percent to Northeast Shark River Slough (Fig. 3). Clearly, the 

managed system resulting from construction of the Tamiami 

Trail and the Central and Southern Florida Project significantly re-routes water flowing through the system to the detriment 

of the natural resources of Everglades National Park, as well as 

the State’s Water Conservation Areas.

Flow reductions to the Everglades resulted in dramatic 

alterations to the landscape. Historically, sloughs in the 

Northeast Shark River Slough area experienced water depths 

of 3 to 4 feet during the wet season and were numerous and 

interconnected, allowing early human inhabitants to travel by 

pole boats across the breadth of the area (Fig. 4). Over time 

the loss of water flow through Water Conservation Area 3B 

and Northeast Shark River Slough caused the organic peat 

soils to oxidize, and the flow-sculpted ridge and slough 

landscape began to flatten, as open-water slough communities were replaced by emergent vegetation (primarily dense 

sawgrass). The U.S. Environmental Protection Agency reports 

that over 3 vertical feet of soil in approximately 30,000 acres in 

Northeast Shark River Slough have been lost through oxidation following severe dry-down events and destructive peat 

fires.1

 These peat fires have also burned hardwood hammocks 

that are hotspots of biological diversity.

1

 Scheidt, D., J. Stober, R. Jones, and K. Thornton. 2000. South 

Florida Ecosystem Assessment: Everglades Water Management, Soil

Loss, Eutrophication and Habitat. Report No. 904-R-00-003, United 

States Environmental Protection Agency, West Palm Beach, Florida.
4 South Florida Natural Resources Center Technical Series (2010:1)

 The reduction in water flow to Everglades National Park 

has not only resulted in the loss of slough habitat with its 

richness and diversity of wildlife, but has also translated into 

wholesale loss of landscape and ecosystem function. Deepwater sloughs are nearly nonexistent now in Northeast Shark 

River Slough, and shallow waters are filled in by a monoculture of sawgrass. This loss of habitat heterogeneity reduces 

the ability for Northeast Shark River Slough to recover from 

periodic extreme events, such as droughts and hurricanes. If 

ecological resilience is not restored soon, the possibility exists that environmental changes to habitats and populations 

within localized areas of the Everglades could precipitate 

rapid and deleterious landscape-level changes that might be 

difficult or impossible to reverse.2

The sloughs functioned as nursery grounds for aquatic 

species during the rainy season and as refuges for many 

Everglades species during the dry season. The successful 

rearing of young wading birds is dependent on the availability 

of adequate numbers of prey species (fish and invertebrates) 

found primarily in the shallow waters of the sloughs during 

the early months of the dry season. As water depths slowly 

recede with the onset of each dry season, prey is concentrated in remaining pools, providing the foraging conditions 

needed for young birds to prosper. In addition, these sloughs 

once maintained some surface water year round, allowing 

for the growth of periphyton (a mixture of algae, cyanobacteria, and other micro-organisms) that supported a complex 

web of invertebrates and fish even during the driest months. 

However, as water flow to the system diminished, the primary 

food sources became reduced, and wading bird populations 

declined by 90 to 95 percent. 

Figure 3. Water depths and flow distributions for two wet years (1959 and 2005) when more than 1 million acre-feet of water was 

discharged to Shark River Slough, Everglades National Park. These two years correspond to the period prior to compartmentalization 

(1959) and post-compartmentalized Water Conservation Area (WCA) 3 (2005). Prior to compartmentalization, the higher water depths 

and flow volumes were more confined to the eastern flowway through Northeast Shark River Slough. Today, as depicted in 2005, the 

deeper water and greater flows are more confined to Water Conservation Area 3A and Western Shark River Slough.

2 National Research Council. 2008. Progress towards restoring the 

Everglades: The second biennial review – 2008. National Academies 

Press: Washington D.C. 324 pp.
Tamiami Trail Modifications: Next Steps Project 5

3 King, John W. 1917. Report of exploration, examination and 

reconnaissance of the lands of the Tamiami Trail in Dade County, 

Florida. Unpublished report found in the Jaudon Collection, 

Historical Museum of South Florida, Miami. 

Figure 4. Ridge and slough landscape in Northeast Shark River Slough, 1917, prior to the drainage of the Everglades. The ridge and 

slough habitat was once the most dominant and diverse habitat in the central and southern Everglades. Most of the open-water 

sloughs in this area have been replaced with sawgrass, or lost entirely, due to persistent lower water depths in the region. Original 

mounted photograph and survey notes by King, 1917.3

While the adverse effects of the Tamiami Trail on the 

Water Conservation Areas and Everglades National Park are 

well-documented, its location makes it the focal point of a 

complex water management system. The Tamiami Trail north 

of Northeast Shark River Slough is bounded by water control 

structure S-333 on the west and S-334 on the east (Fig. 5). The 

delivery of water to Northeast Shark River Slough is controlled 

by the operation of these two structures which maintain water 

levels in the L-29 Canal within strict limits for protection of 

the roadway. The relatively small amount of water that does 

enter Northeast Shark River Slough is conveyed through 19 

outlets under the 10.7-mile section of roadway, each outlet 

having three culverts ranging from 41 inches to 59 inches in 

diameter. The L-29 Canal is currently managed at a stage of 

7.5 feet National Geodetic Vertical Datum (NGVD). Since the 

land surface elevation in Northeast Shark River Slough just 

south of the road is similar to the canal stage, there is an insufficient water-level gradient to allow any more than minimal 

flows into Northeast Shark River Slough during much of the 

year (Fig. 6). 

Snowy Egret. Photo by William Perry, NPS.
6 South Florida Natural Resources Center Technical Series (2010:1)

Figure 6. Current configuration of Water Conservation Area (WCA) 3B, L-29 Levee, L-29 Canal, existing Tamiami Trail, and Northeast 

Shark River Slough. Water levels in the L-29 Canal are maintained at 7.5 ft NGVD to prevent damage to the sub-base of the road, precluding the ability to transfer substantial volumes of surface water to Northeast Shark River Slough through a series of culverts (not 

depicted) to the south side where marsh ground surface elevations are only slightly lower than canal stage (see also Fig 7.).

Figure 5. The project area for this study consists of a 10.7-mile section of the Tamiami Trail bounded by S-333 on the west and S-334 on 

the east. Also depicted is the relationship between this section of Tamiami Trail and Water Conservation Area (WCA) 3B, the L-29 levee 

and road, the L-29 Canal, and Everglades National Park. Today, water flows from the L-29 Canal into Northeast Shark River Slough, 

Everglades National Park, occur through a series of 19 outlets containing 3 culverts per outlet under the Tamiami Trail.
Tamiami Trail Modifications: Next Steps Project 7

RESTORATION AND THE TAMIAMI TRAIL

The Tamiami Trail roadway not only acts as a physical barrier 

and marks the geographic division between the Water Conservation Areas and Everglades National Park, but also serves 

as a boundary between differing water management practices 

that have altered the natural flow of water and made some areas too wet and other areas too dry. Prior to the implementation of the Central and Southern Florida Project, the natural 

flow of water within the Everglades had the greatest volume 

of water entering Everglades National Park through Northeast Shark River Slough (Fig. 3). The water would flow to the 

southwest and periodically overflow the Rocky Glades, providing additional water into Taylor Slough and Florida Bay. 

In contrast, the majority of the flow into the park now enters 

farther to the west via the S-12 structures due to modifications 

to this section of the road corridor in the 1960s as part of the 

Central and Southern Florida Project construction to create 

Water Conservation Area 3A and 3B (L-29, L-67A, L-67C, 

and L-67 Extension) (Fig. 3 and Fig. 7). Recognition that these 

flows are unnatural and have caused ecological damage to the 

park was the impetus for authorization of the Modified Water 

Figure 7. Significant differences exist between the sections of Tamiami Trail corresponding to Western Shark River Slough (west of the 

project area boundary or S-333) and the road corridor within the project area (east of S-333). When compartmentalization of Water 

Conservation Area (WCA) 3 was completed in the 1960s, the western section of Tamiami Trail was raised and the high-capacity S-12 

water control structures were added to allow increased flow capacity to Western Shark River Slough (see Photo 1). In contrast, the 

portion of Tamiami Trail east of S-333 was not raised and has retained the culvert design until now. This eastern portion corresponds 

to the project area (see Photo 2).
8 South Florida Natural Resources Center Technical Series (2010:1)

Deliveries Project in 1989. The purpose of the Modified Water Deliveries Project is to restore the natural timing, volume, 

and distribution of flows to Everglades National Park to the 

extent practicable, necessitating modifications to the Tamiami 

Trail north of Northeast Shark River Slough.

Earlier federal planning by the U.S. Army Corps of 

Engineers to meet the restoration targets for the Modified 

Water Deliveries Project included the 1992 General 

Design Memorandum, 2003 General Reevaluation Report 

and Supplemental Environmental Impact Statement, 

2005 Revised General Reevaluation Report and Second 

Supplemental Environmental Impact Statement: Tamiami 

Trail Modifications, and the 2008 Limited Reevaluation 

Report (Fig. 8). All of these plans contained proposals for 

how to address flows through the Trail; however, no one plan 

was comprehensive in addressing the need for ecological 

connectivity between the park and the Water Conservation 

Areas. The last report recommended a plan that allows the 

water level in the L-29 Canal to increase to as much as 8.5 feet 

NGVD, an improvement from the current operating level of 

7.5 feet NGVD, but insufficient to meet the Modified Water 

Deliveries Project target of 4,000 cubic feet per second (Fig. 

9). In addition, this alternative provides only a portion of the 

hydrologic connectivity needed to restore ridge and slough 

landscape characteristics. Nonetheless, the one-mile bridge 

plan set forth in the 2008 Limited Reevaluation Report is a 

first step in Tamiami Trail modifications that are required for 

full restoration of more natural water flow. 

 While each of these previous efforts required modifications to the Tamiami Trail, the 2009 Omnibus Appropriations 

Act that directed the preparation of this study establishes 

well-defined ecological restoration targets associated with 

these modifications, including restoration of ecological connectivity between marshes severed by the road and restoration of natural marsh flow patterns. 

Figure 8. Timeline of project planning for modifications to the 

Tamiami Trail project area, 1992 to present. Significant planning 

efforts occurred throughout the time period; however, the first 

significant modifications to this portion of the road corridor did 

not take place until December 2009, when construction of the 

2008 Limited Reevaluation Report (LRR) Project features was initiated.

Figure 9. Revised configuration of Tamiami Trail following the implementation of the 2008 Limited Reevaluation Report (LRR) project. 

Modifications include the addition of a 1-mile bridge (not depicted) and the addition of asphalt to raise the road surface elevation. 

Modifications will allow water levels to increase to a maximum of 8.5 feet NGVD but will be operated to maintain a 7.8 feet NGVD level 

as a precaution to prevent damage to the unbridged portion of the highway.

MWD General Design 

Memorandum (GDM) 1992

MWD General Reevaluation 

Report (GRR) 2003

Omnibus Appropriations Act 2009

2005

MWD Revised General 

Reevaluation Report (RGRR)

MWD Limited Reevaluation

Report (LRR) 2008
Tamiami Trail Modifications: Next Steps Project 9

TAMIAMI TRAIL MODIFICATIONS: NEXT 

STEPS PROJECT

Acknowledging the need to restore more historical flow conditions in Northeast Shark River Slough, as well as overcoming legal challenges to raising the Tamiami Trail, Congress, in 

the 2009 Omnibus Appropriations Act, directed the Corps 

to immediately build the 2008 Limited Reevaluation Report 

plan. Implementation of the 2008 Limited Reevaluation Report plan will raise the road to allow L-29 Canal stages to occasionally rise to 8.5 feet; however, constraints associated with 

highway safety will require that the stage in the L-29 Canal be 

operated on a sustained basis at no higher than 7.8 feet (Fig. 

9). This translates into only a 0.3-foot increase over the existing operational maximum canal stage (7.5 feet) and does not 

produce the water flow needed to restore the characteristic 

ridge and slough topography in Northeast Shark River Slough. 

The Act also directed the National Park Service to complete 

a study that identifies additional modifications to the Tamiami 

Trail (e.g., bridging and road-raising) required to fully restore 

the ecological conditions in Northeast Shark River Slough and 

the Water Conservation Areas and establish the foundation 

for future restoration efforts in the Everglades. This initiative 

is referred to as the Tamiami Trail Modifications: Next Steps 

Project. The Tamiami Trail Modifications: Next Steps Project 

would modify the road to allow water stages in the L-29 Canal 

to rise to 9.7 feet, providing the capability to convey the historical volumes of water that once passed into Everglades 

National Park. Importantly, meeting the structural roadbed 

requirements for the 9.7-foot stage within this project would 

preclude the need for expensive future modifications to the 

Tamiami Trail when related projects that store and distribute 

the water required for full restoration are implemented. 

To meet the Act’s mandate, the National Park Service, as 

lead agency pursuant to the requirements of the National 

Environmental Policy Act, formed a project delivery team 

consisting of representatives from federal, state, and local 

agencies to develop project objectives, screen and evaluate the 

benefits and costs of alternatives, and assist in the alternative 

evaluations leading to the National Park Service’s selection 

of a preferred alternative. The National Park Service invited 

the Miccosukee Tribe of Indians of Florida to participate as 

a member of the project delivery team. Although representatives of the Tribe attended most meetings, they indicated that 

they were not a member of the interagency team.

Purpose and Objectives 

The purpose of the Tamiami Trail Modifications: Next Steps 

Project is to comply with the Act that directs the Secretary of 

the Interior, acting thorough the National Park Service

“to immediately evaluate the feasibility of additional 

bridge length, beyond that to be constructed pursuant 

to the Modified Water Deliveries to Everglades National 

Park Project (16 U.S.C. § 410r-S), including a continuous bridge, or additional bridges or some combination 

thereof, for the Tamiami Trail (U.S. Highway 41) to 

restore more natural water flow to Everglades 

National Park and Florida Bay and for the purpose 

of restoring habitat within the Park and the ecological connectivity between the Park and the Water 

Conservation Areas.” (emphasis added) 

Based on the specific language in the Act, the project delivery team developed the following project objectives: 

1. Improve flows to and ecological conditions in 

Everglades National Park by bridging the Tamiami 

Trail to provide for unconstrained flows to Northeast 

Shark River Slough and Florida Bay

2. Restore the natural pathways for species movements 

(ecological connectivity) by removing obstructions to 

sheetflow between Water Conservation Area 3B and 

Northeast Shark River Slough 

3. Improve historic flow patterns between Water 

Conservation Area 3B and Northeast Shark River 

Slough by reconnecting remnant sloughs, allowing natural re-contouring of the ridge and slough 

landscape 

4. Improve ecological habitats in Everglades National 

Park, including ridge and slough, the Rocky Glades, 

and coastal estuaries 

5. Ensure compatibility with pre-Comprehensive 

Everglades Restoration Plan (CERP) and CERP 

projects.

In undertaking the required evaluation, Department and 

National Park Service staff determined that it was necessary 

to: (1) complete an Environmental Impact Statement for 

National Environmental Policy Act (NEPA) compliance, (2) 

include all real estate costs for acquisition of remaining properties in Northeast Shark River Slough authorized by the 1989 

Everglades National Park Protection and Expansion Act, (3) 

continue to provide access to commercial airboat operators 

and Native American Indian camps located on the Tamiami 

Trail, (4) rely heavily on earlier studies that analyzed bridging 

alternatives for the Trail, particularly the alternatives and analyses conducted by the U.S. Army Corps of Engineers in the 

2005 Revised General Reevaluation Report, (5) use existing 

technical information, (6) design the canal stage in the project 

to allow for unconstrained flow (later verified to be the same 

as the canal stage value used in the 2005 Revised General 

Reevaluation Report and equal to 9.7 feet NGVD), and (7) 

provide a 0.5-mile buffer between all bridge approaches and 

Native American Indian camps located within the project 

area as requested by these camps and the Miccosukee Tribe 

of Indians of Florida. 

In addition, public scoping provided information and 

identified areas of support and concern. Approximately 97 

percent of public comments strongly favored the project. 
10 South Florida Natural Resources Center Technical Series (2010:1)

No Action Alternative (includes the Limited Reevaluation 

Report 1.0-mile bridge). The 10.7- mile causeway alternative 

was screened out due to potential impacts to Native American 

Indian camps (i.e., bridging over the two Native American 

Indian camps would result in both impacts to native customs 

and practices). No alternatives specifying features other than 

additional bridge spans were considered in this study due 

to the specificity of the language authorizing the study. This 

initial screening resulted in the selection of six conceptual 

action alternatives and their variations to carry forward into 

the Tamiami Trail Modifications: Next Steps Project for more 

detailed engineering analysis (Table 1). 

After completion of the Preliminary Engineering Report, 

the six action alternatives were further modified. Alternative 

2B was removed because Alternative 2A would provide greater benefits at similar costs. Alternative 3 was removed after 

the engineering analysis indicated this alternative would be 

similar in bridge length to Alternative 5. Because Alternative 6 

was the alternative in which the project delivery team sought 

to maximize bridging, this alternative went through several 

iterations. Alternative 6A and 6B, the first two iterations, both 

included 5.05 miles of bridging. Alternative 6A was removed 

from further consideration because it did not provide access 

to two commercial airboat facilities. Alternative 6B was modified to remove a 0.66-mile easternmost bridge due to seepage management concerns expressed during an inter-agency 

workshop, creating Alternative 6C with a total of 4.39 miles of 

bridging. Updated real estate information, received after the 

inter-agency workshop, indicated that acquisition and complete removal of two radio towers, in lieu of providing flood 

protection to the facilities, was the preferred course of action. 

Alternative 6C was subsequently modified to provide bridging 

instead of access roads to the radio towers, increasing total 

bridging to 4.75 miles and resulting in Alternative 6D. Finally, 

it was also decided that the eastern 0.66-mile bridge, removed 

from Alternative 6B, should be included for consideration 

with the understanding that adequate seepage management 

would have to be provided to address concerns associated 

with the location of this particular bridge. This modification 

resulted in the identification of Alternative 6E with 5.5 miles 

of bridging. In addition to the No Action Alternative, Figure 

10 depicts the final alternatives evaluated. 

Comments in favor of the project included the need for restoration of the Everglades in general, restoration of sheetflow 

conditions, restoration of habitat for wildlife, protection of 

threatened and endangered species, and preservation of the 

Everglades for future generations. Those respondents in opposition to the project voiced concerns about project costs, 

the planning process, and potential unforeseen environmental impacts (i.e., flood potential, socioeconomic, and cultural 

impacts). The Miccosukee Tribe of Indians of Florida expressed concerns about costs, safety issues with higher water 

levels, floodplain impacts, and the planning process. Further, 

the Tribe continued to express its opposition to the implementation of the 1-mile bridge presently under construction.

Evaluation of Project Alternatives

This publication summarizes information contained in the 

National Park Service’s Draft Environmental Impact Statement on this project which is presently out for the 60-day 

public comment period that will begin with publication of 

the Notice of Availability in the Federal Register. A copy of 

the Draft Environmental Impact Statement may be obtained 

at: http://parkplanning.nps.gov and is also included on CD at 

the back of this report. A summary of the process that is described in greater detail in the Draft Environmental Impact 

Statement follows.

Screening Project Alternatives

Acknowledging the aggressive schedule needed to complete the evaluation and report to Congress as called for in the 

Act, the National Park Service relied upon project alternatives 

developed for the 2005 Revised General Reevaluation Report 

and modified to meet Tamiami Trail Modifications: Next Steps 

Project objectives. All of the alternatives in the 2005 Revised 

General Reevaluation Report elevated the roadway to allow 

stages in the L-29 Canal to be raised to 9.7 feet (consistent 

with this project); however, bridging lengths for the alternatives ranged from less than 1.0 mile to a 10.7-mile causeway. 

The bridging alternatives shorter than 1.0 mile were screened 

out of this project due to minimal improvements above the 

Alternative Alternative Variations and Total Bridge Lengths

Alternative 1 2.15 miles (No other variations)

Alternative 2 2A. 3.33 miles 2B. 2.68 miles

Alternative 3 1.39 miles (No other variations)

Alternative 4 1.01 miles (No other variations)

Alternative 5 1.52 miles (No other variations)

Alternative 6 6A. 5.05 miles 6B. 5.05 miles 6C. 4.39 miles 6D. 4.75 miles 6E. 5.50 miles

Table 1. Six conceptual action alternatives and variations of these alternatives for both the amount and location of bridging.
Tamiami Trail Modifications: Next Steps Project 11

Figure 10. Final suite of alternatives evaluated in this study. The No Action Alternative consists of the road corridor modifications associated with the approved 2008 Limited Reevaluation Report (LRR) and includes only 1 mile of bridging. Alternatives evaluated in this 

study add to the LRR plan and have additional total span lengths ranging from 1.01 miles to 5.5 miles.
12 South Florida Natural Resources Center Technical Series (2010:1)

Benefits of Alternatives

The project delivery team used the National Park Service 

Choosing by Advantages process to evaluate the benefits of 

each of the project alternatives and determine the preferred 

alternative based on both benefits and construction costs. The 

Choosing by Advantages process assists the agency in making 

its decision by evaluating the relative benefits of alternatives 

based both on the objectives of the project (e.g., ecological 

restoration) and National Park Service mission (e.g., protection of both natural and cultural resources). Critical to the 

Choosing by Advantages process is selection of performance 

measures (called factors in the Choosing by Advantages 

process) used to evaluate the relative importance of each 

alternative in meeting the objectives/mission of the project. 

The factors selected were (1) potential ecological connectivity between the marshes in Water Conservation Area 3B and 

Northeast Shark River Slough in Everglades National Park, 

(2) natural marsh flow conditions (velocity), (3) reconnection 

of sloughs fragmented by construction of Tamiami Trail, (4) 

restoration of sheetflow conditions, (5) reduction in vehicular wildlife mortality, (6) impacts to historic properties, (7) 

impacts to other cultural resources, and (8) direct wetland 

impacts. 

 While the Tamiami Trail Modifications: Next Steps Project 

alternatives ranged in bridging lengths from 1.01 to 5.5 miles, 

all of the action alternatives would raise Tamiami Trail to allow the stage in the L-29 Canal to be raised to 9.7 feet—the 

water level that the inter-agency team agreed would provide 

for the natural, unregulated flows between marshes to the 

north and marshes in the park essential to full restoration of 

both Everglades National Park and the Greater Everglades 

ecosystem. Increasing the stage in the L-29 Canal provides 

hydraulic head to push water from the L-29 Canal into Shark 

River Slough and to allow water to flow through the existing 

culverts and future bridges. Without a stage increase, a sufficient hydraulic gradient would not exist to push the water 

to the south. The greater the L-29 Canal stage increase, the 

greater the water availability to Northeast Shark River Slough 

and the greater the water depths and corresponding restoration benefit to the downstream ridge and slough community. 

The current canal stage of 7.5 feet was established to prevent 

damage to the sub-base of the road. Therefore, it is a fundamental assumption that the entire section of road will have 

to be raised or replaced with bridging to accommodate the 

increase in canal stage.

 As reflected in Figure 11, numerical values were assigned 

to factors based on their importance in achieving the objectives of the project. The factor, restoring sheetflow conditions, 

was given the greatest importance value by the project delivery team for two reasons. First, this factor used distribution 

of flows across the 10.7-mile project area and topography 

to identify those areas where bridging would most enhance 

volumes of water flows and ecological benefits over the largest area in Northeast Shark River Slough. Second, modeling 

from the 2005 Revised General Reevaluation Report clearly 

indicated that bridges located in the western portion of the 

10.7-mile project corridor provided greater volumes of flows 

to Everglades National Park, with fewer seepage concerns, 

than bridges located farther to the east. The next-highest 

scoring factors were, in order, increasing ecological connectivity, reconnecting sloughs, and restoring marsh flow (velocity) conditions. Alternative 6E scored demonstrably higher in 

the total importance scores (402) than the other alternatives 

(Fig. 11). 

Costs of Alternatives

Total implementation costs for all alternatives were estimated and included the following (see Table 2 for detailed 

cost figures):

6 Construction costs — includes all costs for materials and 

labor for construction of bridges and road improvements 

to the portion of the project area not containing bridges

6 Real estate costs — includes all costs for the in-fee acquisition of three commercial airboat facilities, two commercial radio towers currently operating within the park, the 

relocation of a radio tower facility operated by the South 

Florida Water Management District, a flowage easement 

for a private airboat facility, as well as additional costs associated with business impacts and required demolition

6 Management Costs — includes engineering and design 

(estimated at 10 percent of the construction costs), construction management (estimated as 10 percent of the 

construction costs), and contingency or potential error in 

the cost estimate (estimated at 25 percent of the construction costs). 

The Preferred Alternative

Alternative 6E, which has been identified as the preferred 

alternative in the Draft Environmental Impact Statement, 

most closely meets the project objectives and the National 

Park Service mission by having the highest total importance 

value after summing the importance scores for each of the 

eight factors for each alternative (Fig. 11). While Alternative 

6E has the highest benefit, this alternative also has the highest cost. After quantifying the importance (i.e., benefits) for 

all alternatives using the Choosing by Advantages method, 

the alternatives were further evaluated using the cost-to-importance analysis prescribed by the Choosing by Advantages 

based on the importance scores in Figure 11 and the total 

project costs in Table 2. 

 When the total project cost is plotted against the importance scores for all alternatives (Fig. 12), the results produce 

a somewhat linear relationship between the variables, indicative of similar benefit-to-cost ratios; however, an inflection 

point for Alternative 2A indicates this alternative may provide 

the best cost-to-benefit value. Since it was unclear whether 
Tamiami Trail Modifications: Next Steps Project 13

Alternative Construction 

Duration (yrs)

Construction 

Costs (M $)

Management 

Costs (M $)a

Total 

Construction 

Costs (M $)b

RE Costs (M $)c

Total 

Project Cost 

(M $)d

Alt 4: 1.01 mi 3.8 $59 $27 $85 $70 $155

Alt 5: 1.52 mi 3.6 $71 $32 $103 $70 $173

Alt 1: 2.15 mi 3.6 $89 $40 $129 $70 $199

Alt 2A: 3.33 mi 3.2 $103 $46 $149 $70 $219

Alt 6E: 5.50 mi 3.7 $185 $75 $260 $70 $330

Table 2. Construction durations and unescalated (2010) costs including construction, construction management, total construction, real 

estate, and total project costs for final alternatives evaluated. The alternative having the highest importance (Alternative 6E) has a 

total project cost of $330 million.

Figure 11. Importance scores for final alternatives using the Choosing by Advantages value analysis. This 

methodology resulted in Alternative 6E scoring the highest degree of importance, an indication of benefit. 

a

Costs estimated by the Corps to manage the construction contracts

b

Total construction costs equal the summation of the construction costs and the management costs

c

Includes fee acquisition, relocation, and management costs (estimated at $24 M), compensable business costs (estimated at $30 M), and relocation and demolition of South Florida Water Management District telemetry tower and demolition of two commercial radio towers (estimated at 

$16 M)

d

Total project costs equal the summation of the total construction costs and the real estate costs
14 South Florida Natural Resources Center Technical Series (2010:1)

Table 3. Results of Cost-Benefit Analysis performed by the Corps. These results indicated that Alternative 6E had the best value for the 

environmental benefits provided in relation to costs. Alternative 6E was the only alternative exhibiting most efficient cost performance 

when compared to the other alternatives examined in the study.

Alternative Total Cost (M $)1 Importance Score Lift over no-action Cost per lift (M $) Cost Effective

No Action 0 70

Alt 4: 1.01 mi $149.6 121 51 $2.9 Yes

Alt 5: 1.52 mi $167.0 168 98 $1.7 Yes

Alt 1: 2.15 mi $192.8 207 137 $1.4 Yes

Alt 2A: 3.33 mi $213.2 281 211 $1.0 Yes

Alt 6E: 5.50 mi $324.1 402 332 $0.97 Most Efficient

Alternative 2A was a true best value, or simply an artifact of the 

Choosing by Advantages scoring methodology, the National 

Park Service requested that the Corps apply the cost-benefit 

analysis technique commonly used in its project assessments. 

These results are depicted in Table 3 and resulted in all alternatives being characterized as cost effective, but Alternative 

6E was determined to be a better value (most efficient) when 

compared to the other alternatives, including Alternative 2A. 

Therefore, the National Park Service Choosing by Advantages 

Importance Analysis, coupled with the Corps cost-benefit 

analysis, resulted in the decision to identify Alternative 6E as 

the preferred alternative (Fig. 13). 

Alternative 6E, in combination with the 1.0-mile bridge to 

be constructed under the 2008 Limited Reevaluation Report 

plan, would restore a total of 6.5 miles of ecological connectivity between Everglades National Park and marshes to 

the north, reconnecting 10 sloughs that have been severed 

since 1928, and restoring marsh flow patterns across much 

of Northeast Shark River Slough. The increased connectivity results from the construction of the new bridges coupled 

y = 1.5607x - 100.01

R2 = 0.9544

0

50

100

150

200

250

300

350

400

450

145 170 195 220 245 270 295 320

Importance Valu

e

Total Project Cost (Million $)

Importance vs Total Project Cost

Alt 4: 1.01 mi

Alt 5: 1.52 mi

Alt 1: 2.15 mi

Alt 2A: 3.33 mi

Alt 6E: 5.50 mi

Figure 12. Total cost versus importance as prescribed by the Choosing by Advantages value analysis methodology. 

Alternative 6E had the highest importance but also the highest cost. 

1

The Total Cost values in this table, and reflected in Figure 12, were completed by the Corps prior to NPS receiving additional demolition cost 

estimates reflected in the Total Cost values in Table 2.
Tamiami Trail Modifications: Next Steps Project 15

with the removal of the existing Tamiami Trail roadway corresponding to the bridge locations. The greater expanse of 

bridging allows for improved distribution and timing of water 

flows at velocities of 0.08 foot per second similar to historical 

conditions (0.05 foot per second). The removal of 6.5 miles of 

roadway will also reduce wildlife mortality and reconnect a 

large swath of the historic ridge and slough landscape, restoring breeding and foraging conditions for many aquatic and 

terrestrial species. Alternative 6E would provide the conveyance capacity to meet the original Modified Water Deliveries 

Project target water flow of 4,000 cubic feet per second and 

also accommodate future projects, including those of the 

Comprehensive Everglades Restoration Plan and recent State 

of Florida restoration initiatives. Importantly, the increased 

bridging of Alternative 6E will allow stages in the L-29 Canal 

to be raised to 9.7 feet. Hydrologic analysis conducted for 

the 2005 Revised General Reevaluation Report indicated 

that substantial bridging, as in Alternative 6E, was needed for 

the higher volumes of flows to Northeast Shark River Slough 

without adversely impacting ecologically and culturally important tree islands in Water Conservation Area 3B.

Alternative 6E would result in impacts to cultural resources and more direct wetland impacts than other alternatives 

considered. In order to maintain traffic flow during bridge 

and road construction and avoid impacts to state lands north 

of the existing highway, Alternative 6E would be constructed 

south of the existing highway in Everglades National Park. 

The construction easement for the 5.5 miles of bridges extends 50 linear feet south of the existing highway right-of-way, 

while the road-raising easement extends 30 linear feet south. 

The total wetland impact area would be 48.1 acres; however, 

the long-term benefits of the improved flow patterns and 

ecological connectivity outweighed these impacts. It was 

also determined that Alternative 6E would adversely impact 

two cultural resources—the existing Tamiami Trail roadway 

and the Coopertown airboat facility; however, these impacts 

could be adequately mitigated and were justified on the basis 

of the substantial environmental benefits of Alternative 6E 

compared to the other alternatives.

Regional Benefits

Two technical documents developed between 2002 

and 2006 provide valuable insights into the broader ecological benefits of Alternative 6E: the 2005 Revised General 

Reevaluation Report, used extensively in the development 

and assessment of alternatives evaluated in this report, and 

the Modified Water Deliveries Project Combined Structural 

and Operational Plan, drafted by the Corps in 2006, but never 

finalized. 

WCA-3B S355A

G69

S355B

S334

S356

G70

S333 L-29

L-31N

Northeast Shark River Slough

Everglades National Park 2008 LRR Bridge

Road Raising

Proposed Bridges

Tamiami Trail

Everglades

Safari

Osceola Camp

Airboat

Association

Tigertail

Camp

Gator Park Coopertown Frog City 1-mile

1.77

mile

Radio 

Tower

Radio 

Tower

2.6 mile .38-mile .66-mile

Figure 13. Alternative 6E had the highest importance score, consists of 5.5 miles of bridging, and would also maintain access to the 

commercial airboat facilities and the Native American Indian camps.
16 South Florida Natural Resources Center Technical Series (2010:1)

Regional modeling for the Combined Structural and 

Operational Plan, using the South Florida Water Management 

Model (36-year period of record from 1965-2000), was conducted concurrently with development of the 2005 Revised 

General Reevaluation Report and made similar assumptions 

that were later confirmed through technical analysis by the 

Corps and the Florida Department of Transportation. One 

of the major assumptions was that the eastern Tamiami Trail 

would require expansive bridging (culverts by themselves 

would not suffice) to allow unimpeded, unregulated flows 

between the marshes in Water Conservation Area 3 and 

Northeast Shark River Slough. It was determined that to provide these natural flow conditions in the marshes, the higher 

L-29 Canal stage of 9.7 feet was required. This stage value is 

the same assumption used in the Tamiami Trail Modifications: 

Next Steps Project.

In addition, the Combined Structural and Operational 

Plan regional modeling indicated substantial ecological benefits to Northeast Shark River Slough and Water Conservation 

Area 3 would result from a combination of higher stages (9.7 

feet in L-29 Canal) and greater bridging lengths in the 10.7-

mile section of the eastern Tamiami Trail. Bridging options, 

similar to those in Alternative 6E, would substantially improve 

the volume, distribution, and timing of flows to Northeast 

Shark River Slough, even under current conditions where 

flow volumes to Everglades National Park have been reduced 

by greater than one million acre-feet per year. The Combined 

Structural and Operational Plan modeling indicated that flow 

distributions following implementation of expansive bridging, such as the 5.5 miles of bridging provided by Alternative 

6E, would improve from the current annual average distribution of 78 percent to Western Shark River Slough and 22 percent to Northeast Shark River Slough to 45 percent to Western 

Shark River Slough and 55 percent to Northeast Shark River 

Slough. This distribution is more indicative of the desired distributions following restoration and would be achievable with 

Alternative 6E. Combined Structural and Operational Plan 

modeling also indicated that the improved timing of flows 

achievable with an alternative such as Alternative 6E would 

reduce damaging high volume discharges to Western Shark 

River Slough through the S-12 structures, reducing the loss 

of wet prairie habitat in this area. In addition, the improved 

capacity to move greater volumes and better distributions of 

flows to Northeast Shark River Slough would reduce the number and severity of dry-down events (when water levels drop 

below the ground surface) and peat fires in both Northeast 

Shark River Slough and Water Conservation Area 3B. 

Combined Structural and Operational Plan modeling also 

indicated that modifications to Tamiami Trail, such as those 

prescribed in Alternative 6E, would improve conditions for 

fish and wildlife species by providing improved average water depths and recession rates in all of Northeast Shark River 

Slough and areas of Water Conservation Area 3. These longer 

and more natural hydroperiods would begin the process of 

restoring ridge and slough landscape patterns and the peat 

soils that are the foundation of the ridge and slough habitat 

in Northeast Shark River Slough. Modeling indicated that 

improving the flows and ecological conditions in Everglades 

National Park would also result in improved ecological 

conditions in Water Conservation Area 3. Alternative 6E 

could allow for both a reduction in the severity and duration of dry-down events in Water Conservation Area 3B 

and the prolonged deep-water conditions in southern Water 

Conservation Area 3A associated with loss of tree islands. 

The improved hydrologic changes resulting from the implementation of Alternative 6E are expected to translate into 

substantially improved ecological conditions in the region, 

benefiting threatened and endangered species, including the 

Wood Stork, Everglade Snail Kite, and the Cape Sable Seaside 

Sparrow. 

In summary, Alternative 6E will remove major impediments to the natural, unregulated flow of water over greater 

than one million acres of the central and southern Everglades, 

providing the foundation for full restoration of the Greater 

Everglades ecosystem. 

Wood Stork colony near Tamiami Trail. Photograph by Lori 

Oberhofer, NPS.
Tamiami Trail Modifications: Next Steps Project 17

SUMMARY OF FINDINGS

The 2009 Omnibus Appropriations Act directed the Department of the Interior and National Park Service to immediately 

evaluate the feasibility of additional bridging of the Tamiami 

Trail, beyond the Modified Water Deliveries to Everglades 

National Park Project, for purposes of restoring habitat within the park and the ecological connectivity between the park 

and the Water Conservation Areas. This study is ongoing. The 

Draft Environmental Impact Statement, which will be finalized later this year, is presently out for the 60-day public comment period that will begin with publication of the Notice 

of Availability in the Federal Register. Based upon the work 

completed to date, the Department of the Interior and the 

National Park Service have selected Alternative 6E, consisting 

of an additional 5.5 miles of bridging and road raising within 

a critical 10.7-mile portion of the Tamiami Trail, as the preferred alternative that best achieves the goals and purposes of 

the Act.. Implementation of Alternative 6E, when combined 

with the ongoing work to implement the 1-mile bridge under 

the Modified Water Deliveries Project would allow for the 

natural, unimpeded flow of water between Water Conservation Area 3 and Northeast Shark River Slough. This segment 

of the Tamiami Trail would no longer function as a barrier to 

the restoration of Everglades National Park and the Greater 

Everglades ecosystem and would set the stage for full restoration of the remaining 4 million acres of Everglades that is set 

aside and protected under federal and state law for conservation purposes. 

Alternative 6E, in conjunction with other planned restoration projects, would provide more than five times the connectivity between upstream and downstream marshes when 

compared to the modifications currently being constructed 

under the Modified Water Deliveries Project. This heightened degree of marsh connectivity would also allow for unconstrained flow patterns to Northeast Shark River Slough. 

In addition, ten of the historical sloughs that once flowed 

unobstructed within this portion of the Everglades would be 

reconnected. Altogether, this broad expanse of bridges would 

re-establish sheetflow conditions in the historic eastern flowway of Shark River Slough that closely approximate those of 

the natural marsh.

The total cost of Alternative 6E is $330 million, which 

includes a total construction cost of $260 million and real estate, business, and demolition costs of $70 million. Real estate 

costs include the purchase of three commercial airboat facilities, two radio towers, and a flowage easement to a private 

recreational airboat facility. The locations of the bridges in 

Alternative 6E are designed to maximize environmental benefits in Everglades National Park by increasing sheetflow conditions, improving ecological connectivity, providing more 

natural marsh flow velocities, and reducing wildlife fatalities 

associated with the roadway. The bridge locations would also 

provide substantial buffers between the bridgeworks and all 

lands occupied by the Miccosukee Tribe of Indians of Florida 

and provide access to commercial and private airboat facilities 

located along the roadway. Should Alternative 6E be authorized and funded for implementation, current law provides 

for the use of the park lands for this project.

 In combination with an operational plan currently under 

development (the Combined Operational Plan), the benefits of this plan would result in immediate improvements 

to hundreds of thousands of acres of wetlands in Everglades 

National Park and Water Conservation Area 3. The 5.5 miles 

of bridging would allow for better distribution of existing 

flows to the park, improving conditions for endangered avian 

species, such as the Cape Sable Seaside Sparrow, Everglade 

Snail Kite, and the Wood Stork. This plan would also improve conditions for tree islands by reducing the duration 

of damaging water depths in Water Conservation Area 3A. 

These changes would also reduce the ongoing soil oxidation 

as well as the occurrence and severity of damaging peat fires 

in Everglades National Park and Water Conservation Area 3B. 

 The Department of the Interior and the National Park 

Service strongly endorse the preferred alternative presented 

in this publication as it would provide immediate and measurable benefits to both the upstream Water Conservation Areas 

and Everglades National Park. Upon receipt and analysis of 

the public comments, the National Park Service will work 

to finalize the study and issue a final Environmental Impact 

Statement and report to the Congress as required by the 2009 

Omnibus Appropriations Act.

Florida panther. Photo courtesy of ©Rick Cruz, Rick Cruz 

Photography.



South Florida Natural Resources Center

Everglades National Park

950 N. Krome Ave, 3rd Floor 

Homestead, FL 33030-4443

www.nps.gov/ever/naturescience/sfnrc.htm