The Role of Flow in the Everglades 

Ridge and Slough Landscape

Science Coordination Team 

South Florida Ecosystem Restoration Working Group 

(Approved by the SCT: January 14, 2003) 

Executive Summary 

The Everglades has at the core of its identity the slow movement of water across the vast, low 

gradient, wetland landscape. Marjory Stoneman Douglas eloquently immortalized this identity in 

her descriptions of the “River of Grass” (Douglas 1947). Drainage and compartmentalization 

efforts during the 20th century for flood control and water supply purposes interrupted this flow, 

as well as altering water levels, distribution, and seasonal timing. Water flows are closely linked 

to water levels, and their alterations have caused environmental damage. Efforts to restore the 

Everglades have focused on re-establishing more natural hydropatterns – the appropriate water 

levels, and the location, timing, and duration of these water levels. While these natural 

hydropatterns are widely recognized as being extremely important, much less attention has been 

paid to the importance of the actual movement of water, the physical and ecological roles that 

movement of this water plays, and how management activities have altered that flow. Thus, the 

Science Coordination Team has chosen understanding the science of the role of flow in the 

Everglades as one of its priorities. The purpose of this paper is to provide a stimulus for 

increasing the level of understanding and awareness of the role of flow in restoration activities, 

and to highlight the urgent need for research in this area. 

Pre-drainage Everglades hydrology was dominated by a remarkable flow regime – a 30-milewide expanse of water moving down the low-gradient wetland landscape from north to south. 

Surprisingly, although Everglades hydrology has flow as one of its defining characteristics, most 

discussions of hydrology in the Everglades exclude mention of the role of water movement. The 

movement of water in aquatic ecosystems such as wetlands is a fundamental construct of 

ecosystem structure and function, and its ecosystem role is well-established. It is likely that water 

movement plays a similar vital role in the Everglades. 

The ridge and slough landscape, one of several major habitat types in the Everglades, originally 

consisted of a peat-based system of dense sawgrass ridges interspersed with adjacent and 

relatively open sloughs. These parallel ridges and sloughs existed in an organized pattern, 

oriented parallel to the flow direction, on a slightly sloping peatland. Unfortunately, 

compartmentalization and related water management activities are resulting in the loss of this 

ridge and slough landscape. This loss is evidenced by replacement of the characteristic ridge and 

slough landscape with a landscape that is more topographically and vegetationally uniform. It is 

clear that 1) the Everglades ridge and slough landscape has changed, and is continuing to change 

significantly; and 2) the landscape changes are having detrimental ecological effects on 

Everglades plants and animals. It is likely that these changes are the result of altered water flow 

and hydropattern caused by human-made barriers and shunts, interacting with corresponding 

changes in water depth and water level fluctuations. 
The role of flow (continued) Page 2 

The mechanisms causing the loss of ridge and slough landscape likely are complex, are 

occurring over a time scale of decades or more, and restoration decisions will have to be made on 

a time frame shorter than decades. A number of mechanisms for the formation and maintenance 

of the ridge and slough landscape are proposed, including: sediment transport; changes in water 

depth under managed conditions; differential rates of peat accumulation and decomposition; 

erosional formation; extreme hydrological events; fire; underlying bedrock patterns; and 

microhabitat differences in water chemistry. The presence of flow is necessary for almost all of 

these mechanisms to operate, and it is likely that a combination of several of these mechanisms 

operating together is responsible for formation and maintenance of the ridge and slough 

landscape. 

The mechanisms of ridge and slough landscape degradation are not fully understood. However, it 

is likely that barriers to flow, including levees and canals, contribute significantly to the 

conversion of the ridge and slough wetland mosaic to more uniform stands of sawgrass. 

Conversion of the ridge and slough landscape pattern to uniform sawgrass stands has had, and 

will continue to have, deleterious impacts on Everglades plants and animals. An Everglades 

landscape increasingly dominated by dense sawgrass stands supports fewer numbers of animals 

and a lower diversity of animals. The control of vegetation over wading bird ecology is strong 

enough that Kushlan (1989) states, “Whatever determines vegetation patterns will also, to a large 

degree, determine bird use of wetlands.” Wading birds are an important component of the 

Everglades ecosystem. Their foraging and nesting success often are used as indicators of the 

overall health of the system, and they are one of the most visible and highly regarded fauna of 

the Everglades. The conversion of ridge and slough landscape to dense sawgrass stands has had a 

negative impact on wading birds and other important birds of the Everglades. Negative impacts 

of these landscape changes extend throughout the Everglades food web, including fish, which are 

important food for wading birds. In addition to altering flow patterns and wetland landscape 

patterns, barriers to flow serve as barriers to movement of aquatic animals. 

Very few research studies have been conducted specifically to determine the role of flow in the 

Everglades ecosystem. Most of the research projects from which data are presented in this paper, 

while relevant to the role of flow, were not designed to determine the role of flow. It is precisely 

for this reason that the Science Coordination Team chose the topic of flow as one of its priorities. 

Recommendations for future research are prioritized, and include: a multidisciplinary 

paleoenvironmental study; a thorough geomorphic review; sediment transport studies; synoptic 

and time series measurements of flow; development of a carbon balance model; remote sensing; 

and others. 

Finally, additional performance measures are recommended for the ridge and slough landscape 

for the monitoring and assessment of the Comprehensive Everglades Restoration Plan (CERP) 

progress. These measures, largely based on expanded collection and analysis of remotely sensed 

images, include: aerial extent and temporal trends of sawgrass ridge, slough, and tree island 

polygons; edge-to-area ratios for landscape types; average length-to-width ratio and temporal 

trends of sawgrass ridges or sloughs for a defined area; and spatial orientation of the three 

landscape types as compared to their historic orientations. 
The role of flow (continued) Page 3 

Background 

The Everglades, referred to as the “River of Grass” by Marjory Stoneman Douglas in her famous 

book of the same title (Douglas 1947), has at the core of its identity the slow movement of water 

across the vast, low gradient, wetland landscape. Drainage and compartmentalization activities 

for flood control and water supply purposes during the 20th century caused unintended 

environmental impacts. As restoration of the Everglades has proceeded to reverse these impacts, 

most of the attention to restoring more natural hydropatterns has focused on water levels, and the 

timing, duration, and distribution of water levels. Much less attention has been paid to the 

importance of the actual movement of water through the Everglades, and how management 

activities have altered that flow. The Science Coordination Team (SCT) has provided this paper 

as a stimulus for increasing the level of understanding and awareness of the role of flow in 

restoration activities, and to highlight the urgent need for research in this area. 

The SCT, formed in 1997 as a successor to the Science Sub-Group by the South Florida 

Ecosystem Restoration Task Force, consists of scientists and managers from federal, state, and 

local government, and two Indian tribes. The SCT’s Charter (SCT Charter 1997) charges the 

team with ensuring the highest level of communication, coordination, and cooperation in the 

application of scientific disciplines to the south Florida restoration effort. In 1999, the SCT 

revised its work plan to more narrowly focus on scientific topics most relevant to present 

ecosystem restoration efforts. The SCT membership chose five priorities, one of which was to 

examine the role of flow in the Everglades ecosystem. This priority addresses a specific SCT 

responsibility stated in the SCT Charter – to identify key gaps in management information and 

propose research and data collection to address these needs. 

As the first step toward examining the role of flow, the SCT sponsored a flow workshop at the 

Greater Everglades Ecosystem Restoration Science Conference, held in December, 2000, in 

Naples, Florida (http://conference.ifas.ufl.edu/everglades). This workshop included panel 

presentations, discussions, audience questions, and solicitation of one and five-year research 

priorities from the 100+ persons in the audience. A summary of that workshop was produced 

(http://sofia.usgs.gov/geer) and contains an overview of the panel presentations and the research 

priorities that were developed. 

As a second step, the SCT prepared this paper, which builds on the flow workshop by examining 

the role of flow in the ridge and slough landscape. While the focus of this paper is on the ridge 

and slough physiographic region, the SCT recognizes that flow also occurs widely throughout 

the freshwater and downstream estuarine regions of the greater Everglades. In general, ideas 

about the role of flow in these other regions are much less well developed, and are not addressed 

comprehensively in this paper. 

There are two main purposes of this paper: 1) to increase awareness among scientists and 

resource managers of the importance of flow to Everglades restoration, and 2) to provide 

scientists with background information and data to stimulate further discussion and research, and 

to recommend specific areas for future research. This paper does not attempt to prove or disprove 

the various mechanisms proposed for creation and maintenance of the ridge and slough 

landscape. In fact, the paper highlights the current lack of scientific data needed for proof. 
The role of flow (continued) Page 4 

Rather, it attempts to lay the groundwork for the type of data and research needed, to provide a 

thoughtful and scientifically sound foundation upon which to better understand the ridge and 

slough landscape type, and to ensure that it is protected and restored. The SCT envisions that this 

information will be useful at all levels of restoration effort, including the Comprehensive 

Everglades Restoration Plan (CERP), the Modified Water Deliveries Project, and other 

restoration programs at the regional and local levels. 

It should be noted that under ideal circumstances, water flow, water levels, and all aspects of the 

Everglade’s natural hydropattern should be restored via implementation of CERP. Because 

anthropogenic alterations of the historic system are so extensive, it may be difficult to achieve all 

aspects of hydropattern restoration simultaneously. This difficulty may force tradeoffs when 

restoration decisions are made. Understanding more about the significance of flows to 

Everglades restoration will make these resulting tradeoffs easier to evaluate. 

Flow is defined as the continuous motion of a fluid (Morris 1992). For the purposes of this paper, 

flow is the actual movement of water across the Everglades wetland landscape. The time rate of 

flow is velocity, which is a vector quantity whose magnitude is expressed in units of distance 

over time, such as inches per second (Morris 1992). In addition, the concept of flow in the 

Everglades includes consideration of the spatial distribution of that flow across the wetland 

landscape. It is important to distinguish this definition of flow from discharge (volume of water 

per unit time), and from the more general concepts of hydropattern, which include water levels, 

duration of water levels, timing of water levels, and distribution of water levels. 

Introduction 

The defining characteristics of the Everglades

The Everglades has much in common with other wetland ecosystems in the world, as well as 

some unique characteristics. The Everglades is characterized by the presence of peat, the 

importance of water flow, its location in a subtropical climate, and the nutrient limitation that 

exists, particularly for phosphorus. The presence of peat and nutrient limitation make the 

Everglades comparable to other peatlands in northern climates (e.g., Foster et al. 1983, Foster 

and Glaser 1986), as well as regionally specific types such as the Pocosins (Richardson 1981). 

The role of flow suggests that the Everglades might be viewed as fen (peat marsh with nonacidic soil) rather than an ombrotrophic peatland. However, its subtropical location, and, 

perhaps, its hydrological connection to Lake Okeechobee, are regional modifiers which 

distinguish it from other peatlands in the scientific literature. 

With respect to vegetation, many of the plant species present in the Everglades are found 

elsewhere along the Gulf Coast, including the Mississippi River Delta (Penfound and Hathaway 

1938). The delta of the Mississippi River also is characterized by moving water, and has plants 

common to the Everglades such as sawgrass (Cladium jamaicense) and maidencane (Panicum 

hemitomon). In addition, there are islands of bald cypress (Taxodium distichum) in the coastal 

marshes of the Mississippi Delta. 
The role of flow (continued) Page 5 

The role of moving water in wetlands

The movement of water in flowing water aquatic ecosystems is a fundamental construct of 

ecosystem structure and function, and its ecosystem role is well-established and studied. Flowing 

water has the ability to alter the landscape, which, in turn, has the ability to alter the landscape’s 

ecology. Although much less studied in Everglades wetlands, the flow of water across vast 

expanses of low-gradient marshes was one of the defining characteristics of the river of grass. 

The flow of water in streams and rivers has been the topic of much research, and stream 

ecologists are well-versed in the importance of flow. Although water flow is much slower in the 

river of grass (typically less than one inch per second under present managed conditions [Ray 

Schaffranek, USGS, unpublished data]), it may be just as important to the ecosystem. Water 

movement plays a number of roles, including transporting, mixing, and diluting dissolved and 

particulate materials, the removal of metabolites, and influencing the location and type of aquatic 

organisms (Allan 1995). Many aquatic organisms orient their bodies to flow and use flow to 

direct their movements in the flow channel either positively or negatively (Welch 1963, Hynes 

1970). The speed of the water flow also determines a number of physical features, including the 

size of eroded and suspended sediment particles, and the physical force that organisms 

experience in the water and on the bottom. 

Research has been conducted on flow in other wetland systems that bear many similarities to the 

Everglades (Gregory Pasternack, personal communication). For example, the role of flow in 

floodplains, river deltas, and tidal marshes has been examined, and they share several 

characteristics with the Everglades, such as low gradients, dense herbaceous vegetation, finegrained sediments, abundance of peat, and cohesive bottom substrates. These characteristics 

result in flow patterns that may be more complex than those of rivers and streams. Flow over a 

wide vegetated surface has dampened velocity fluctuations, higher turbulent dissipation, a 

complex vertical velocity profile, and significantly reduced lateral velocity profile relative to 

open channels. 

Historical flow patterns

The historic Everglades was part of a much larger drainage system, originating in south-central 

Florida in what is now known as the Upper Chain of Lakes near Kissimmee, Florida. The lake 

system formed the headwaters of the Kissimmee River, a 100-mile-long, meandering, lowgradient river that emptied into Lake Okeechobee (Fig. 1). The lake, much larger than its 

present-day surface area of 1,750 km2

, would spill over its southern rim during high water events 

into the northern part of the Everglades, dominated by vast sawgrass plains. Eventually, the 

southward movement of water through the sawgrass plains formed the source of water for the 

ridge and slough landscape. In this sense, the historic Everglades may be viewed as the lower 

reaches of the Kissimmee River. 

The central feature of the pre-drainage Everglades hydrology was a 30-mile-wide expanse of 

relatively shallow water moving downstream through the low-gradient wetland landscape. The 

pattern of water flow was remarkable for its regional uniformity across such a broad expanse, 

and for the absence of any central drainage channel or of any dendritic drainage pattern. Pine 

flatwoods formed most of the eastern boundary of this flow, and the western boundary was 
The role of flow (continued) Page 6 

defined by the Immokalee Rise and the relatively higher wetlands and uplands of what is now the 

Big Cypress National Preserve. Much of the flow discharged south and west through Shark River 

Slough, through the mangrove estuaries of the southwestern coast, into the Gulf of Mexico (Fig. 

1). South of, and including the New River (Ft. Lauderdale), the pine flatwoods were absent and 

the Atlantic Coastal Ridge became discontinuous, forming a series of islands separated by 

coastal rivers (Smith 1848). These rivers thus resulted in a portion of the flow being discharged 

eastward into Biscayne Bay and the Atlantic Ocean (MacGonigle 1896, Beard 1938). The 

remainder of the flow discharged southward through Taylor Slough into Florida Bay. Because of 

Florida’s porous geology dominated by limestone overlain by thick peat deposits, the boundaries 

between surface water and ground water flow are not always distinct. 

The Everglades ecosystem is thought to have been formed over the last 5,000 years as sea levels 

rose and precipitation increased, promoting water retention in a shallow inland basin, and the 

portion of the basin south of Lake Okeechobee filled in with peat (Gleason and Stone 1984). The 

result of peat accumulation in this bedrock basin was the formation of a peat surface, level in the 

east-west direction, and with a slight north-to-south downward slope. The concavity of the 

bedrock, coupled with the east-west levelness of the peat, resulted in thicker peat deposits in the 

middle of the basin and thinner deposits along the edges. By the 1880s, peat had accumulated to 

about 21 feet above sea level along the south shore of Lake Okeechobee (Meigs 1879), and had 

formed the northern edge of a north-to-south elevation gradient that is now less than 3 inches per 

mile. The southward flow of water down this gradient is thought to have formed and to maintain 

the ridge and slough pattern so characteristic of the Everglades (Kushlan 1993). 

Everglades plant and animal communities evolved under the conditions imposed by this flow, 

within a sub-tropical climate, and under the constraints of nutrient limitation. The habitat types 

that evolved included vast sawgrass plains south of Lake Okeechobee, in the region presently 

occupied by the Everglades Agricultural Area. South and east of the sawgrass plains was the 

ridge and slough habitat, including what are now Water Conservation Areas 1, 2, and 3, and 

Everglades National Park. Marl prairies – short hydroperiod marshes with marl sediments – 

occupied slightly higher elevations east and west of Shark River Slough. The mangrove zone 

was located from the Ten Thousand Islands south and east around the tip of Florida’s peninsula 

to the shores of Biscayne Bay. 

Surprisingly, most discussions of hydrology in the Everglades exclude mention of the role of 

water movement. For example, Kushlan (1997) notes that hydropattern in wetlands typically is 

defined as the depth, duration, timing, and periodicity of water, but does not include water 

movement. However, he does note that the wetland water regime can influence the fate of waterborne sediment. 

Historical ridge and slough landscape

Originally, the ridge and slough landscape consisted of a peat-based system of dense sawgrass 

ridges with soil surfaces roughly 2 to 3 feet higher than adjacent and relatively open sloughs 

(Wright 1912, Baldwin and Hawker 1915). The regular, approximately even spacing and the 

parallel arrangement of the ridges and sloughs, along with their alignment parallel with the 

direction of flow, formed a strongly organized pattern. Tree islands of various types formed a 
The role of flow (continued) Page 7 

third element of the landscape, rising slightly above the elevation of the sawgrass ridges. The 

orientation and streamlined shape of the larger tree islands formed a separate pattern, but with 

the same alignment parallel to the direction of flow. The organized pattern of parallel ridges and 

sloughs, oriented with flow direction, on a slightly sloping peatland partially resembled other 

patterned, slightly sloped peatlands such as the circumpolar string bogs (Gore 1983). 

Historically, the ridge and slough landscape was an extensive pre-drainage landscape, 

encompassing what are now the Arthur R. Marshall Loxahatchee National Wildlife Refuge, 

Water Conservation Areas 2A and 2B,Water Conservation Areas 3A and 3B, and Shark River 

Slough (Fig. 1). 

While seemingly small, the 2 to 3-foot difference in elevation between ridge surface and slough 

bottom was highly significant in the pre-drainage Everglades. During the typical annual rise and 

fall of wet and dry season water levels, this elevation difference allowed sloughs to remain 

water-filled throughout the year, while adjacent ridges would be exposed a few months of the 

year. In the pre-drainage system, native species were adapted to the multiple habitats provided by 

the tree islands, ridges, and sloughs. Aquatic organisms depended on the sloughs as extensive 

areas that would remain inundated throughout all but exceptionally dry years. 

Drainage and compartmentalization activities

The first major efforts to drain the Everglades came with Hamilton Disston. By the 1890s, he had 

drained over 50,000 acres of wetlands, opened the Kissimmee River for navigation, and linked 

the Caloosahatchee River to Lake Okeechobee (Light and Dineen 1994). In addition, he is 

credited with excavating the first 11 miles of canal south of Lake Okeechobee in the direction of 

Miami – the precursor to the Miami Canal. By 1917, four major muck-scalped canals transversed 

the Everglades from Lake Okeechobee to the Atlantic Ocean, short-circuiting the historic, northto-south pattern of flow and greatly accelerating the removal of water from the Everglades. 

Unfortunately, flow records prior to disruption of the entire drainage basin are not available. It 

has been hypothesized that flow magnitudes through the river of grass were significantly higher 

in the 1800s and early 1900s versus what has been monitored since 1939 (Parker et al. 1955, Jon 

Woolverton, USGS, unpublished data). Patterns of peat subsidence (Stephens and Johnson 

1951), water tables measured in 1915 (Baldwin and Hawker 1915), 1938 (Clayton 1938), and 

continuously between 1927 and 1939 (Parker et al. 1955), all suggest that these canals 

substantially lowered water levels in the northern Everglades, often below the peat surface. 

Local efforts to surround Lake Okeechobee with a levee began in the early 1900s and were 

completed with the construction of a levee completely encircling the lake by the mid 1900s. All 

surface water inflow and outflow points (except one at Fisheating Creek) are now controlled by 

pumps and/or water control structures. 

By the 1910s, Miami was expanding, and plans to drain and develop parts of the Everglades 

were pursued. Capt. Frank Jaudon, seeking to drain what is now called Northeast Shark Slough, 

successfully lobbied for creation of Tamiami Trail (Tamiami Trail Commissioners 1928). 

Objectors at the time (Tatum in Tamiami Trail Commissioners 1928) raised what turned out to 

be a legitimate concern, that the road bed would act as a dam, blocking the southward flow of 

water out of what is now Water Conservation Area 3B (c.f. Elliot in Graham 1951). 

Nevertheless, Tamiami Trail was completed in 1928. Photos from the 1930s show water 
The role of flow (continued) Page 8 

occasionally spilling over the top (Matlack 1939), but aerial photos from 1940 (USDA-SCS 

1940) suggest that in just 12 years, Tamiami Trail had created two separate landscape types, 

north and south, where once there had been a continuous landscape type. 

Since that time, the ridge and slough landscape has been further compartmentalized. The eastern 

perimeter levee, stretching from Palm Beach to Miami-Dade county, defined the eastern 

boundary of the Everglades, and was completed by 1954 (Light and Dineen 1994). This levee 

became the eastern boundary of Water Conservation Areas 1 and 2, preventing movement of 

water eastward to agricultural and developing urban areas. By 1959, the Everglades Agricultural 

Area was separated from the rest of the system by a series of levees, canals, and water control 

structures. Subsequent levee construction defined the western and northern boundaries of the 

three Water Conservation Areas, and all three areas were completely surrounded by levees by 

1963. A pair of parallel levees (L-67A and L-67C) divided Water Conservation Area 3 into two 

independent units. These levees, which run almost, but not quite perpendicular to the original 

sheet flow direction, were intended to reduce groundwater seepage through the highly porous 

Biscayne aquifer. The western unit, Water Conservation Area 3A, scheduled for higher water 

levels, serves as a major water supply reservoir. The eastern unit, Water Conservation Area 3B, 

with lower water levels, reduces the head difference to the developed areas to the east. In 1966, 

State Road 84 (now Alligator Alley), an east-west highway north of Tamiami Trail, was 

completed, adding another compartment to Water Conservation Area 3. Water conveyance was 

provided by bridges at one or more mile intervals. 

Although not associated with levees, the so-called “agricultural canals” (e.g., Blue Shanty, 

Cooperstown) to the north and south of Tamiami Trail created further breaks in the landscape. 

The Miami Canal, also not associated with a levee, degrades the landscape not as a cross-barrier 

to flow, but as a shunt concentrating water flow in the canal and short circuiting the landscape. 

Loss of ridge and slough landscape

It is clear that the compartmentalization and related water management activities, which have 

altered flow and other hydrological parameters such as water levels, are resulting in the loss of 

ridge and slough landscape. Loss is defined here in two ways: 1) a flattening of the landscape 

due to a decreased difference between ridge elevations and the elevations of the slough bottoms; 

and 2) an associated blurring of the distinct, directional pattern of ridge and slough vegetation. 

Evidence for this loss arises from alterations in vegetation patterns over time and indications of 

altered topography. Satellite images and aerial photography suggest subtle but definite changes 

in the extent and shape of sawgrass ridges. Where levees, canals, and roadways have separated 

the landscape into compartments, changes in the landscape are obvious. In areas where the 

original ridge and slough pattern still is evident, peat topography with identical patterning also is 

still evident. Where the vegetation pattern has been lost, the distinct topography also has 

disappeared. The post-drainage alterations in landscape topography show a clear trend from a 

highly organized, strongly directional pattern to a degraded, more random, and less directional 

pattern. 
The role of flow (continued) Page 9 

Causes of landscape change 

Based on these observations, it is apparent that: 1) the Everglades ridge and slough landscape has 

changed, and is continuing to change significantly; and 2) the landscape changes are having 

detrimental ecological effects on Everglades plants and animals. It is likely that these changes 

are the result of altered water flow caused by human-made barriers and shunts, interacting with 

corresponding changes in water depth and water level fluctuations. These observations can be 

broken down further, and are discussed in detail in the remainder of this paper: 

1. The ridge and slough landscape originally formed, under natural pre-drainage conditions, 

a continuous, directional, and patterned wetland mosaic. 

2. Flow occurred over the full width of this directional, patterned, wetland. 

3. The vegetation patterns of this landscape were influenced by water flow, water depth, and 

hydroperiod differences and their interactions with topographic variations in the peat 

surface. 

4. The original ridge and slough pattern has degraded to varying but substantial degrees 

throughout the landscape. 

5. The type of pattern degradation observed cannot be explained on the basis of altered 

water depths (or hydroperiods) alone – a change in directional, flow-related processes 

also must be implicated. 

6. Preservation of the ridge and slough pattern and potential restoration of degraded patterns 

require water movement across the landscape and in the original direction of flow. 

7. Conversion of ridge and slough habitat to a uniform, closed landscape of dense sawgrass 

is having significant, deleterious impacts on the ecology of Everglades plants and 

animals, including restrictions on dispersal and available habitat for aquatic animals, and 

limitations on foraging by wading birds and other top predators. 

8. If not reversed through restoration of flow, it is possible that the landscape endpoint 

suggested by current trends would be a uniform, closed landscape of sawgrass. 

Evidence of landscape change

Pre-drainage conditions of vegetation, topography, water depth, and water flow, coupled with 

observation of post-drainage changes, are summarized here from other research (Ingebritsen et 

al. 1999, Sklar et al.1999, Sklar et al. 2000, Sklar et al. 2001) and draw on diverse sources such 

as explorers’ journals, historic surveys and maps, and aerial photographs. The study of predrainage and pre-compartmentalization landscapes using historical information and indirect 

evidence might be called forensic ecology. When this type of study is combined with analysis of 

present-day aerial photographs and topography, natural and disturbed vegetative mosaics, and 

studies of peat-forming processes, the historical record can provide significant insight into the 

original, natural state of the ecosystem. 

Historical landscape condition 

At the regional scale, the peat-based Everglades included two landscapes, the sawgrass plains at 

the northern end, and the larger ridge and slough landscape in the central and part of the southern 
The role of flow (continued) Page 10 

portion (Fig. 1). The distinguishing differences between these two landscapes occur at the local 

scale, discussed in detail below. In the broader view, both of the landscapes were formed on a 

base of peat soil filling a bedrock basin. Although difficult to determine exactly, it appears that 

the pre-drainage elevation of the peat surface was about 3 feet below the elevation of the mineral 

soil-based edges of the basin, (e.g., the pine flatwoods east of the Everglades) (Van Zee et al. 

1998). This elevation difference suggests that the basin peat accumulation probably was linked 

to average water depth. 

The sawgrass plains and the ridge and slough landscape sloped very slightly from an elevation of 

about 21 feet above sea level at Lake Okeechobee (Meigs 1879) to sea level at Whitewater Bay 

100 miles south, a slope of less than 3 inches per mile. Viewed from east to west, the peat-based 

landscapes were either level or, in some locations, tipped slightly to the east, reflecting drainage 

toward the Atlantic coast. Overall, at the regional scale and in the direction perpendicular to 

flow, both landscapes appear to have been very close to level over distances of more than 30 

miles. 

Sawgrass plains landscape

While the sawgrass plains and ridge and slough landscapes likely had similarly level surfaces at 

the regional scale, they differed markedly in topography at the local scale. The sawgrass plains 

formed a remarkably uniform, dense, and nearly monotypic stand of sawgrass, 8 to 12 feet tall. 

An 1883 expedition sponsored by the New Orleans Times Democrat did manage to penetrate and 

cross the sawgrass plains, but only by burning the sawgrass ahead of their progress. 

“...all jump overboard to begin the usual work of pushing boats through the sawgrass [stubble]... No material change is found in the country through which we 

travel this day. It is the same through which we have traveled for seven days. 

Nothing but sawgrass, a little water, plenty of soft, black, slimy mud, and with not 

a single tree or bush in sight...” (Wintringham 1964). 

The uniform sawgrass vegetation and the apparent absence of woody vegetation may reflect a 

very level peat surface. 

Typical water depths in the sawgrass plains can be estimated from actual recorded water levels, 

from the nature of the soils and vegetation, and from studies of soil cores. The descriptions of a 

stringy peat with noticeable roots and sufficient structure to resist collapse (Stewart 1907, 

Harshberger 1914, Baldwin and Hawker 1915) suggest what would now be classified as a Fibric 

Histosol – a partially decomposed peat (McCollum et al. 1976). The partial decomposition may 

have resulted from nutrient limitation in the oligotrophic Everglades, and/or from oxygen 

limitation because the soil was covered with water most of the year. Surface ponding for most, 

but not all, of the year also would be consistent with the optimal sawgrass growth conditions 

suggested by the great density and height of the sawgrass canopy. 

“[Sawgrass] seems to grow best where water covers the ground for a large portion 

of the year, but where the water table sinks below the ground late in the dry 

season. Once established, sawgrass can withstand rather deep water for extended 

periods, but gradually thins out as water of 3 feet or more is held for periods of 2 - 

3 years without drawdown.” (Andrews 1957). 
The role of flow (continued) Page 11 

Andrews’ observations are consistent with recorded pre-drainage water depths in areas of 

sawgrass growing on peat (i.e., the sawgrass plains and the peat transverse glades). Water depths 

in the 6 to 18-inch range, as well as the 24 to 36-inch range, were recorded in these areas. On the 

basis of pre-drainage soil and vegetation, and from the recorded historical water depths (Meigs 

1879, Stewart 1907, Wintringham 1964), we estimate a typical annual variation in pre-drainage 

water depths between approximately 6 inches below ground surface at the end of the dry season, 

rising to a typical annual maximum of approximately 1.5 feet above ground at the end of the wet 

season. As historical descriptions suggest that sawgrass density and canopy height were similar 

on the ridges of the ridge and slough landscape, the water depth estimates from the sawgrass 

plains likely are applicable to sawgrass ridges of the ridge and slough landscape as well. 

Ridge and slough landscape

In contrast to the uniform vegetation, topography, and hydrology of the uniform sawgrass plains, 

the ridge and slough landscape formed a distinctly non-uniform, systematically patterned 

peatland. The local and regional scale of these patterns were recognized clearly during early 

explorations of the Everglades. 

“The surface of the Everglades, taken as a whole, appears to be a level plain, 

having a slope of three inches per mile toward the south and east, yet this 

statement is subject to slight modification. Throughout the entire [ridge and 

slough] area there are numerous winding shallow depressions or channels 100 to 

500 feet wide, and one to three feet lower than the land through which they pass. 

These depressions, locally called 'Strands,' [i.e., sloughs] wind through the 'Glades 

in all directions, though their general trend is from north to south. In other places 

there are slight depressions, like ponds or lagoons, covering one to forty acres. The 

muck in these depressions is usually less firm than the land on either side. These 

irregularities of the surface also affect the depth of muck at these points, as the 

underlying hard material is no lower in these surface depressions than under the 

adjacent land. These low places are usually filled with water, while the general 

surface of the Everglades is comparatively dry.” (Wright 1912, p.18-19). 

Soil scientists who field-surveyed a 180-square-mile swath through the sawgrass plains and the 

ridge and slough landscape during the dry season of 1915 introduced the term “ridges and 

sloughs” to the scientific literature and found substantial differences in elevation between them. 

“[The landscape seen to the east and west of the North New River Canal] is very 

gently undulating or hummocky, owing to a series of ridges and sloughs with local 

differences of 2 to 3 feet in elevation, having a general northwest-southeast 

direction. ...” (Baldwin and Hawker 1915, p. 752). 

Earlier, in 1907, members of a west to east survey across the Everglades also encountered 

alternating sawgrass ridges and open water sloughs which showed the same southeastward 

orientation later noted by Baldwin and Hawker (1915). 
The role of flow (continued) Page 12 

“...Chadwick mentioned saw-grass ridges alternating with open leads of water 

running approximately in a southeastern direction.” (Harshberger 1914). 

The photographs reproduced in Figs. 2 and 3 illustrate the ridge and slough landscape described 

above. They were taken in March, 1917, several months into the dry season. The photographer 

and explorer, John King, indicated that the Everglades already was drier than they had been prior 

to drainage. The open sloughs and distinct sawgrass ridges in these photographs are consistent 

with early descriptions of canoe travel. Col. Harney, and numerous others during the 19th

century, found sufficient channels of open water to not only cross the Everglades by canoe, but 

to do so rapidly (Ives 1856, Dix and MacGonigle 1905, Dimock 1907, Marchman 1947, Church 

1949, Anonymous 1960 [1841]). These open sloughs allowed canoe travel, much of it using 

paddles, rather than the poles more commonly used in shallower waters. The Baldwin and 

Hawker survey conducted in 1915, a year of apparently normal rainfall, between January and 

March showed that even during the dry season, water levels apparently were high enough to 

cover both sloughs and ridges. 

“At the time of the survey a few of the higher ridges were above water, but in 

general the entire surface was inundated. The water in the sloughs in many cases 

was 2 to 3 feet deep.” (Baldwin and Hawker 1915, p. 788). 

The photographs also emphasize a remarkable aspect of early narrative descriptions of the ridge 

and slough landscape – common pre-drainage observations of a directional, downstream 

orientation. These early observations are remarkable because the large size of ridges and sloughs 

makes it difficult to perceive a directional pattern when actually on the ground in the landscape 

(c.f. Figs. 2 and 3). Present-day helicopter experience suggests that the regional pattern, although 

partially apparent at lower altitudes, only becomes visibly obvious at altitudes greater than 800-

1000 feet. Figure 4 shows an oblique aerial view taken from a dirigible in the 1930s. The altitude 

is not known, but the pattern of elongated sawgrass ridges and open water sloughs is clearly 

visible and is very similar to present day oblique aerial views of well-preserved portions of the 

landscape. The many pre-drainage observations of clear directionality in the landscape suggest 

that observers perceived the orientation either through the process of traveling through the 

landscape, or by the visible direction of water flow, often remarked upon. 

Having the benefit of aerial views and aerial photographs, hydrogeologist Garald Parker 

suggested that the directional orientation of the ridge and slough landscape was a natural result 

of water flow over a peat soil substrate. 

“The linear arrangement of this pattern is most noticeable from the air, from 

which, as Dickerson (1942, p.136-139) says, ‘They reveal a decided ‘grain’ to a 

broad sweep of country ... as if a great coarse broom had been rudely brushed over 

the low-lying Everglades region.’ 

... The ‘grain’ of the Everglades ... is believed to be developed entirely on freshwater peat and muck... It ... represents a drainage pattern produced on a very gentle 

sloping surface of organic deposits. The ‘grain’ is composed of tree islands and 

swales [sloughs] that trend parallel to the regional slope, just as one would expect 

in an area of consequent drainage.” (Parker et al. 1955). 
The role of flow (continued) Page 13 

The ridge and slough pattern is strikingly regular, with evenly spaced ridges (centerline to 

centerline), and only moderate variation in ridge width. Also striking is the absence of any 

indication of either a central drainage channel or of any dendritic, hierarchical drainage network. 

Instead, flow seems to have occurred quite evenly across the full 30-mile width of the 

Everglades, distributed quite equally across all the numerous sloughs. All of these observations 

support the regional impression of an unusually level peat surface in the cross-flow (east-west) 

direction. 

The grain mentioned by Parker can be used to create a map of landscape directionality. Figure 5 

shows the result of superimposing a 2-mile by 2-mile grid on the earliest available, 

comprehensive aerial photographs of the Everglades (USDA-SCS 1940), and then visually 

assigning a landscape direction to each grid cell. The uniformity of the landscape and flow 

directionality is striking, and reinforces the impression that peat accumulated in equilibrium with 

a regional water surface that was very level in the cross-flow (approximately east-west) 

direction. The mapping exercise also reinforces the impression of sheet flow distributed evenly 

across the full landscape width. 

Figure 6 is a stylized depiction (exaggerated vertical scale) of the pre-drainage ridge and slough 

landscape illustrating the close relation between vegetation and elevation of the underlying peat 

substrate. Figure 6 helps illustrate the diversity of observations found in different narrative 

accounts of the pre-drainage Everglades. In particular, descriptions of the Everglades as a “vast 

lake” on the one hand can be reconciled with other descriptions of an alternating landscape of 

open water and boggy land on the other hand. At the end of the dry season, there could still be 

water in sloughs, yet the peat of the ridges could be slightly exposed, yielding boggy conditions 

on the ridges. In contrast, during the high water at the end of the wet season, water could cover 

both sloughs and ridges, yielding a continuous water surface – a lake – with emergent sawgrass 

stems.

Such a range of water depths is consistent with pre-drainage observed depths, soil characteristics, 

hydrologic preferences of the vegetation, and with hypothesized frequencies of peat fires. 

Several lines of evidence suggest that under natural, pre-drainage conditions, the water remained 

in sloughs throughout typical dry seasons. While there certainly is pre-drainage evidence of at 

least some sloughs drying out, such drying occurred infrequently. Also, there is evidence for 

year-round presence of surface water within sloughs during typical years, including ability to 

travel quickly by canoe (Smith 1848), lack of dry camping sites (Sprague 1848, Willoughby 

1898, Dimock 1907), and absence of widespread peat fires (Gifford 1911, Cohen 1984). 

Water flow

There are many qualitative observations of water flow in the pre-drainage ridge and slough 

landscape. The majority of sources specifically noted the current of the water in the Everglades, 

making it clear that they did not observe stagnant areas and most also mentioned the direction of 

the flow. 

“The water is pure and limpid and almost imperceptibly moves, not in partial 

currents, but, as it seems, in a mass, silently and slowly to the southward.” (Smith 

1848). 
The role of flow (continued) Page 14 

Soil surveyors working in the spring of 1915 noted a visible current in sloughs, even in the dry 

season. 

“There is a marked current of the water in the sloughs...” (Baldwin and Hawker 

1915, p. 788). 

The botanist John Davis noted evidence of a current, even in the 1940s. 

“The more common aquatic plants are the bonnets, Nuphar, swamp-lily, Crinum 

americanum L., white water-lily, Nymphaea, and a number of "slough grasses" 

that bend in the water before the current.” (Davis 1943, p. 266). 

Current landscape condition 

Post-drainage changes and vegetation patterns in the remaining ridge and slough landscape have 

been assessed using a variety of remote sensing data, including Landsat Thematic Mapper 

imagery, infrared aerial photographs, 1940s aerial photographs, and detailed vegetation maps. 

Float helicopter trips were used to examine the landscape at altitudes up to 1000 feet. GPS-linked 

photography was used to map particular observations within the overall landscape pattern. At 

this point, spatial analyses primarily are qualitative. As detailed vegetation mapping presently 

underway by the South Florida Water Management District is completed for Water Conservation 

Area 3A, it is expected that quantitative spatial analyses of vegetation polygon attributes will be 

helpful. The present lack of specific quantitative data at the landscape scale, however, does not 

negate the overwhelming degree of changes that are recognized easily by visual observation of 

aerial photographs, digital images, and maps. 

Well-preserved landscape

With a template of the original ridge and slough landscape morphology in mind, it is possible to 

evaluate the condition of the currently remaining landscape. Figure 7 shows a present-day 

oblique aerial view of central Water Conservation Area 3A. Comparison with pre-drainage 

descriptions and with 1940s aerial photographs suggests that the original pattern has been well 

preserved in this area south of Alligator Alley and west of the Miami Canal. The exception to 

this pattern is a distinct band of altered vegetation immediately south of the Alley. Otherwise, 

this photograph is remarkable for its similarity with Fig. 4, the dirigible photo from the 1930s. 

Figure 7 and the area it represents provide our best estimate of an original ridge and slough 

landscape pattern. Figure 8, a vertical color infrared aerial, also is from central Water 

Conservation Area 3A. The directional pattern of entire, elongated ridges shown here serves as a 

good example of well-preserved ridge and slough landscape. 

Degraded landscape

In contrast, Figs. 9-14 show oblique and plan view images and maps of degraded ridge and 

slough landscape. In each case, it is significant that comparison with the well-preserved pattern 
The role of flow (continued) Page 15 

suggests a transformation from narrow, linear, and strongly directional polygons, to a postdrainage pattern of more randomly oriented, amorphous, and less directional polygons. 

In Fig. 9, the landscape apparently has stayed wet enough to maintain open water and water lily 

sloughs, but the sawgrass ridges have disintegrated into many small, randomly oriented patches 

of sawgrass. In an aerial photo of the same region (larger area), faint traces of former sawgrass 

ridges are apparent (Fig. 10), as in much of the landscape north of Alligator Alley (I-75), and 

clearly show how much the landscape pattern has disintegrated in this area. 

The degradation of the original ridge and slough pattern in this area and along the full length of 

Alligator Alley illustrates the impact of Alligator Alley construction and related water 

management practices. As can be seen in Figure 10, extra care was taken with this road to 

minimize the impacts of a hydrological barrier. Two canals were dredged adjacent to the road, 

one on each side to provide fill for the road. At every 2.5-mile interval (1-mile intervals, in some 

places), a small bridge underlies the roadway to connect the two canals and to attempt to make 

Alligator Alley “hydrologically transparent” within the Everglades landscape to the north and 

south. 

However, despite the conveyance of water across the Alley at discrete intervals, the ridge and 

slough landscape has degraded substantially (Fig. 10). Negative landscape effects associated 

with the road have been even more severe farther west, between the Miami and L-28 Canals. The 

Alligator Alley experience is instructive, particularly given the efforts at maintaining hydrologic 

connectivity. The degraded ridge and slough landscape suggests that something more than 

hydrologic conveyance at discrete intervals is needed. 

Figures 11 and 12 show a different form of ridge and slough landscape degradation, in which the 

sawgrass ridges appear to have remained intact. The sloughs, however, appear to be 

disintegrating, apparently by sawgrass invasion. The random orientation of the invading 

sawgrass contrasts with the original linear orientation of the ridges and sloughs. Although 

quantitative data have not been collected, it is possible that the sloughs are filling in with 

depositional sediments, as well as with vegetation. This process would result in severe 

degradation of the ridge and slough landscape, with the slough elevation eventually approaching 

that of the sawgrass ridges. 

Figure 13 shows such an example of severe degradation of ridge and slough landscape in which 

the sloughs almost have been replaced completely by sawgrass. This degradation is typical for 

much of Water Conservation Area 3B. The pre-drainage expeditions that passed through Water 

Conservation Area 3B could not have traversed the landscape in its present condition. Figure 14 

shows the same information as an excerpt from a vegetation map. A trace of the original 

directionality can be made out from the aligned remnants of sloughs. Even more complete 

replacement of ridge and slough landscape by uniform sawgrass has been observed in western 

Water Conservation Area 2A. Two peat transects (one-half mile each) measured in Water 

Conservation Area 3B show almost no discernible elevation differences (Chris McVoy, 

unpublished data). These transects support the relationship between flattening of the peat surface 

and loss of the characteristic ridge and slough vegetative pattern. 
The role of flow (continued) Page 16 

A 1980 vegetation map of part of Shark River Slough (Fig. 15) suggests that the process of ridge 

and slough landscape degradation and replacement by less directional, more amorphous 

landscapes also has occurred within Everglades National Park. The contrast in spatial pattern 

between the old and the new sawgrass is strikingly apparent. 

Figure 16 is a satellite image of the western ridge and slough landscape which includes the 

locations represented in previous figures. This image provides the best available summary 

indication of the location of well-preserved versus degraded ridge and slough landscape pattern. 

Flow in other regions of the greater Everglades

Surface flow obviously occurs in the freshwater and mainland estuarine wetlands of south 

Florida, and is not restricted to the Everglades ridge and slough system. For example, Tabb 

(1990) described flow in the broad marl prairies that border the southeastern flank of Shark River 

Slough. Tabb suggested that this flow occurred primarily during wet seasons when surface water 

levels in Shark River Slough were elevated enough to carry moving water onto and across the 

higher elevation prairies. Duever et al. (1979) showed possible flow patterns and directions 

during periods of high water for the entire Big Cypress National Preserve. 

Flows from the Everglades to coastal estuaries are moderated by a coastal topography that has 

been shaped by water flow. The eastern fringe of the Everglades is bounded by a coastal ridge, 

interrupted by coastal rivers. On the lower southeast fringe, depressions in the ridge, called 

transverse glades, once carried fresh water to coastal wetlands, from where it was transported to 

Biscayne Bay by coastal creeks. Canals and levees lowered the water table, drained the 

transverse glades, and interrupted the flow of fresh water to coastal creeks. By analyzing aerial 

photography and sediment cores, Meeder et al. (2000) documented a substantial alteration in 

coastal creek topography that occurred sometime after 1940. The presence of small, buried 

oyster reefs near the mouths of these former creeks indicate that nearshore salinities at these sites 

were seldom greater than 20 ppt before 1940. Meeder et al. (2000) found that the creek bed area, 

once a topographic low that facilitated the transport of water, is now a topographic high that 

would retard water flow if water were available. Apparently, the flow of fresh water maintained 

these coastal creeks, acting as positive feedback that allowed future flow. When flow was 

redirected, a major landscape change took place. Observations by Glenn Simmons, reported in 

Simmons and Ogden (1998), suggest that a similar filling in of creeks that had previously 

facilitated freshwater flow to the coast across a low coastal berm (the Buttonwood Embankment 

described by Craighead [1971]) may have occurred on the coast bounding northern Florida Bay. 

Although it is beyond the scope of this paper to provide a detailed review of the role of flow in 

these other regions, it should be noted that much less attention has been given to flow in these 

landscapes than has been the case for the ridge and slough landscape. 

Possible mechanisms of ridge and slough formation and maintenance 

The mechanisms that are causing the loss of ridge and slough landscape likely are complex. 

These changes are occurring over a time scale of decades, and restoration decisions will be made 
The role of flow (continued) Page 17 

on a shorter time scale. Data collected before compartmentalization activities began, such as 

continuous time series records of pre-drainage stage, flow direction, and flow velocity, would 

have been extremely helpful. Unfortunately, the individuals observing the Everglades one 

hundred years ago had neither the capacity, the foresight, or the inclination to conduct such 

measurements. This situation forces the use of all available pre-drainage information, including 

recorded, narrative information, to the fullest. Also, due to the lack of a comprehensive 

paleoenvironmental study, valuable information that may be contained in the sediment layers is 

not available at the present time. 

The central geomorphological issues regarding the pre-compartmentalized ridge and slough 

landscape are the mechanisms by which the landscape pattern arose, and the dynamics of 

landscape pattern over time. While the first issue certainly is of importance, the immediate needs 

of restoration planning draw attention primarily to the second. It will be necessary to ascertain 

whether or not landscape patterns naturally shifted over time, and if so, what temporal patterns 

existed. Also, it will be important to know how human-induced changes in the landscape have 

altered the natural temporal pattern of landscape dynamics. Regardless of the long-term 

dynamics, maintenance of the remaining ridge and slough pattern, particularly preventing 

sloughs from becoming dense stands of sawgrass, is critical for sustaining habitat and dispersal 

pathways for aquatic animals. 

The key geomorphological characteristics of the Everglades are: its peatland base; outcroppings 

of limestone; a highly cohesive substrate with high clay and organic content; and a floc layer that 

is more commonly associated with muddy estuaries. These characteristics are in contrast to 

alluvial systems that have no near-surface bedrock control, very low organic content of 

sediments, and that beds and banks composed of unconsolidated sand and silt (Gregory 

Pasternack, personal communication). In addition, the role of vegetation in shaping landscape 

pattern is important, as well as the feedback mechanisms that likely exist between topography 

and vegetation. 

As in classical geomorphology, there is almost certainly a physical and biological explanation for 

the particular landscape patterns found in the pre-drainage Everglades and topography in the 

present Everglades, and they are tied to physical driving forces. On one hand, it is possible that 

the mechanisms may never be known for certain, particularly given their likely complexity and 

the long time scale over which they may operate. On the other hand, geomorphic theories have 

provided reasonable explanations for landscape processes over the full range of time scales, from 

raindrop erosion to mountain building (Gregory Pasternack, personal communication). 

It also is possible that alterations in the ridge and slough landscape result from changes in water 

quality. In fact, CERP’s underlying premise includes water quality as a very important 

component of Everglades restoration. However, this paper focuses on the hydrological rather 

than the water quality aspects of ridge and slough formation and maintenance. CERP assumes 

that restoration of natural flows and levels will be accomplished with water that is not poorer in 

quality than that of the unimpacted ecosystem. 

In the following sections, possible mechanisms of ridge and slough formation and maintenance 

are presented and discussed. Note that flow is an important component of almost all of them. As 
The role of flow (continued) Page 18 

mentioned previously, it is not possible to prove or disprove any of these mechanisms, given the 

present lack of data and analysis. The possible mechanisms are presented to stimulate discussion 

and future research. In addition, although the possible mechanisms are presented in separate 

sections, it is likely that a combination of several of these mechanisms operating together is 

responsible for formation and maintenance of the ridge and slough landscape. 

Sediment transport 

One possible mechanism of slough maintenance is net downstream transport of sediments, 

primarily floc, by water flow prior to compartmentalization. For the purposes of this discussion, 

floc is defined as loosely consolidated particles that are larger than 0.45 μm in diameter, that are 

largely organic in nature, and that have densities very close to 1.0. Such a transport mechanism is 

consistent with the landscape directionality, the shape of ridge outlines, and preliminary 

indications of floc movement. 

Sediment transport by water flow is responsible for maintaining many types of flowing systems. 

Flows can take multiple paths down gradient and these paths form in the areas of least resistance. 

As flows increase, these paths widen and there is a velocity distribution across each flow path, 

with higher velocities in the central (deeper) area and slower velocities on the sides due to 

friction. Suspended sediments fall out at the slower velocity edges – thus the formation of ridges. 

The next flow event adds to the process and flow deepens in the center and the ridges grow 

more. During really large hydrological events, the flow can even be horizontal as the banks 

overflow and recede, also trapping sediments in the ridge area. As the ridges build, the channel 

depth increases and the deeper flooding tends to kill off vegetation, making the slough more 

efficient for water transport and the ridges relatively less efficient. 

In the Everglades, because of the normally slow moving water and the peat substrate, floc is 

likely to make up the bulk of transported sediments. The floc layer can be up to 12 inches thick 

and is nearly structureless, especially in comparison with the peat soil substrate. Pre-drainage 

observations of floc in sloughs are available. 

“The top soil [of the ridges] is a turf composed largely of saw-grass roots, except 

in the leads and shallow basins [i.e., sloughs], where the saw-grass does not grow. 

Here [sloughs] the vegetation is more completely decayed and [the soil] is so loose 

when saturated with water that one sinks to the bottom sand, or rock.” 

(Harshberger 1914, p. 159). 

Downstream transport of floc presently found in the remaining ridge and slough landscape might 

occur either on a slow continual basis, incrementally with individual local storms, or as 

infrequent high-energy events. Bill Loftus (unpublished data) observed that after Hurricane 

Andrew in 1992, the floc layer, the periphyton/Utricularia mat, and dead vascular plant stems 

were blown into the sawgrass ridges from the adjacent sloughs. Ridges apparently acted as traps 

to capture the material. This observation demonstrates how infrequent high-energy events may 

serve to distribute and deposit materials on the ridges. 
The role of flow (continued) Page 19 

In any of these cases, unrestricted flow paths (sloughs) would be critical for uninterrupted 

downstream transport. The density of floc is very close to that of water, giving floc a low settling 

velocity. Considering how easily floc is resuspended by physical and biological processes such 

as gas bubble flotation, bioturbation, and temperature/density effects, it is possible for floc to be 

carried long distances downstream. 

Sedimentation within sloughs subsequent to compartmentalization

Net accumulation in sloughs of organic sediments such as floc might be the process most 

responsible for the disappearance of open-water habitat, and the increase in the area of dense 

sawgrass. The shift from net transport of floc prior to compartmentalization to net accumulation 

of floc subsequent to compartmentalization could be caused by a number of mechanisms, acting 

separately or together. For example, lowering average water surface elevations decreases water 

depths, which in turn promotes emergent plant species. Increased emergent growth increases 

hydrologic resistance to flow, decreasing velocities and floc transport. Increased emergent 

growth, more so if periphyton coatings are present, also increases filtering of suspended floc. 

Both decreased water velocities and increased filtering will tend to increase in situ accumulation, 

further decreasing water depths and promoting increased plant growth and stem density. 

Together, these effects could lead to vegetative as well as topographic filling-in of sloughs. 

The onset of such filling-in processes was remarked upon almost fifty years ago. The following 

is from a Florida Game and Freshwater Fish Commission progress report regarding the then new 

Water Conservation Areas 2 and 3. 

"Prior to intensive drainage much of the Glades area was dissected by relatively 

deep open water "sloughs.” These natural drainage channels permitted traverse into 

the interior of the Glades by "pole-boat" [probably dugout cypress canoes]. 

Journey by "pole-boat" for example from Dania on the east coast to the Big 

Cypress, forty miles to the west, or from Ft. Pierce south through the Glades to Ft. 

Lauderdale was not uncommon. A "pole-boat" trip such as this would be a 

remarkable feat indeed at the present time even during periods of high water. The 

major portion of these open water "sloughs" have now reverted to Rhynchospora

spp. or maidencane or have been invaded by sawgrass, making navigability 

possible only by airboat and then only during the wet season. 

On the heels of the [State] drainage program and the general drying up of the 

Everglades came the airboat. The "pole-boat" days were over and a new era was 

beginning. The development of the airboat permitted entry into any portion of the 

Glades where the sawgrass was not too dense and a few inches of water could be 

found. This is the situation in the sawgrass country today. Unless a hunter or a 

fisherman possesses an airboat he does not venture far into the interior of the 

Glades [i.e., far away from the canals].” (Wallace 1955, p. 2). 

Influence of barriers on flow and sediment transport

Barriers such as roads and levees disrupt continuous flow paths. Perforation by culverts or 

bridges can connect some sloughs, but the majority of sloughs remain completely blocked, 

forcing water and sediment laterally across ridges. Areas of stagnation can result between 

culverts. Suspended sediments likely are deposited in these areas of stagnation upstream and 
The role of flow (continued) Page 20 

downstream of the barrier. Higher density sediments would be picked up in the area of 

accelerated flow velocities upstream of the culverts and that these sediments would be deposited 

immediately downstream as the water slows and spreads out. For example, this mechanism 

might explain the pockets of unnatural woody vegetation immediately downstream of the 

culverts under Tamiami Trail. 

Along a linear flow barrier, creation of discrete drainage points connecting upstream and 

downstream wetland fragments also results in the creation of backwater regions between these 

discrete points. A backwater wetland receives inflow as water rises, and discharges water as the 

water surface falls, but backwater wetlands largely are disconnected from their sediment and 

nutrient sources, and also have reduced flushing. Linear flow barriers with discrete cross 

connections (e.g., culverts) will develop backwater lobes between these discrete points extending 

to a distance away from the barrier. 

Influence of canals

Canals intercept continuous flow paths and provide short-circuits that connect flow paths that 

would otherwise have been isolated. Satellite images of areas around canals that do not have 

associated levees (e.g., Miami Canal, agricultural canals) demonstrate that vegetative shifts do 

occur across canal boundaries. Canals that are not exactly perpendicular to the flow direction 

provide preferential flow paths that divert water and cause different hydrologic conditions on 

either side of the canal. Canals also act to reduce the surface water gradient, and therefore reduce 

water velocities in adjacent wetlands. 

Changes in water levels due to the water management system 

Construction of Florida’s extensive water management system altered other hydrological 

parameters in addition to flow. For example, it is possible that unusually high water levels in 

Water Conservation Area 3A resulting from water management operations upstream caused the 

loss of most of the tree islands and resulted in the expansion of sawgrass, and that degradation of 

vegetation patterns in many areas are due to changes in water quality (Terry Rice, personal 

communication). Regardless of which possible mechanism(s) for ridge and slough formation are 

correct, it is likely that flow interacts with water depth, hydroperiod, and other hydrological 

parameters in maintaining landscape heterogeneity in the Everglades. 

Although extended periods of unnaturally high water levels can be detrimental, water levels that 

are too low also can have negative consequences. In shallower waters, emergent species, 

particularly Eleocharis cellulosa, species of Rhynchospora, and short and mid-sized sawgrass, 

replace the floating and submerged slough community. This sequence of wetland plant 

communities with changing depths is a familiar one found throughout the world. The emergent 

communities, besides being associated with shallower depths, experience shorter hydroperiods 

and are subject to increased fire frequencies, as evidenced by the frequency of charcoal in 

sediments cores. Collectively, these are environmental conditions unfavorable for peat 

accumulation and consequently this wetland plant guild usually is associated with marl deposits 

formed by the abundant periphyton found in the same habitat rather than with peat. 
The role of flow (continued) Page 21 

The water depths needed to sustain Nymphaea-dominated slough communities are hard to define 

precisely in a variable environment such as the Everglades because water flow and low nutrientlevels also are important factors. However, when water levels began to regularly exceed 2.5 feet 

in the central Everglades, Nymphaea communities began replacing the emergent wet prairies 

(Goodrick 1984). Cohen et al. (1984) and Herdendorf et al. (1986) suggest that Nymphaea is 

characteristic where year-round water depths range from 1.0 - 3.3 feet and 0.8 - 3.3 feet, 

respectively. In Shark River Slough, Olmsted and Armentano (1997) and Ross et al. (2001) 

found that the wettest sites were occupied by Eleocharis stands and that slough vegetation was 

too rare to be mapped. Insights into the influence of water depths can be gained from knowing 

what depths are too shallow for floating plant communities. Ross et al. (2001) found that in the 

Eleocharis stands, the greatest water depths in the study areas averaged 1.3 - 1.8 feet year-round 

in an average rainfall year of the 1990s, with maximum 30-day depths being 2.0 - 2.6 feet. In the 

wetter years, of course, depths were higher. 

Variations in water depth also can influence decomposition rates. If peat on ridges experience 

shorter hydroperiods due to changes in water management, the ability of fungi to serve as the 

dominant agents of vascular plant decomposition may increase. Fungi are important 

decomposers of vascular plant material in terrestrial habitats, and are less important in 

submerged freshwater habitats. Because fungi possess enzyme systems necessary for decay of 

structural plant material such as lignin, they may out-compete bacteria in these circumstances, 

and increase the rate of plant decomposition on ridges. This increased rate may contribute to the 

flattening of the ridge and slough landscape under altered water depth patterns (also, see 

following section on differential rates of peat accumulation and decomposition). 

Although changes in water depth under managed conditions have been suggested as an 

alternative explanation for decreases in the ridge and slough landscape, changes in water depth 

alone are not sufficient to account for the observed landscape changes. Comparison of the 

original and current patterns suggests that a directionally neutral change, such as changes in 

water depth due to water management practices, while certainly important, would not be 

sufficient alone to explain the observed changes. Ridges and sloughs exhibit a regional pattern 

that corresponds with the surface gradient in the Everglades, and the direction and extent of predrainage flow patterns. This pattern alone is strong evidence for the role of water movement. 

In addition, an examination of water level and vegetation in Shark River Slough and Water 

Conservation Area 1 suggest that degradation of landscape pattern is not related to changes in 

water levels. A similar increasing trend of amorphous, non-directional polygons is illustrated in 

Plate 9 of Davis et al. (1994), both in Shark River Slough and in Water Conservation Area 1 

between 1968 and 1984. The vegetation transformations observed in both of these locations are 

not due to changes in managed water depth; nearby stage gauges indicate no change in water 

depth patterns or mean water depth over the observed period. All of these examples illustrate a 

transformation from an originally flowing, directional system to a presently non-flowing, or 

insufficiently flowing, impounded system. 
The role of flow (continued) Page 22 

Differential rates of peat accumulation and decomposition 

Peat is created by the accumulation of organic matter over time as organic matter production 

exceeds decomposition. Labile plant material decays quickly, while refractory plant material 

decays more slowly. Peat is composed of refractory components of the source vegetation 

material. If sawgrass decomposes more slowly than water lily and other slough species, this 

difference alone could account for maintenance of the elevations of the ridges and the lower 

elevations of the sloughs. Other physical and biological processes interact to control increases in 

peat elevation. White (1994) uses his process-oriented landscape description to show that peat 

elevation largely is a consequence of increases from peat accumulation balanced by decreases 

from fire. 

Numerous decomposition studies have been conducted in the peatlands of North America and 

Europe. Northern bogs are dominated usually by Sphagnum mosses, which create the peat of 

these wetlands. Although different Sphagnum species are closely related, they differ in both net 

primary production and in decay potential. Species that grow in the hollows, the lower elevation 

and wetter microhabitats, produce biomass at rates up to twice that of mosses growing on the 

higher, dryer hummocks (Nungesser 1997, Table 2, p. 35). Johnson and Damman (1991) report 

that in transplant studies, Sphagnum moss species that inhabit elevated positions decay more 

slowly than those that grow in the wetter microhabitats. Labile fractions of Sphagnum mosses 

range from 18% in hummock species to 28% in hollow species (Clymo 1983, Table 4.7, p. 177). 

The different decay rates reinforce the differences in microhabitat peat depths because peat 

accumulates faster in the hummocks in spite of a two-fold higher net primary production in the 

hollows. Therefore, under identical conditions, the hummock species decompose more slowly 

than the hollow species, producing greater peat accumulation for the same unit of biomass 

produced, in spite of lower net primary production. 

Other peatland research has shown similar results – species that grow in the lower, wetter 

microhabitats decay at rates two to six times that of species that grow in the elevated, dryer 

microhabitats (Heal et al. 1978, Rochefort et al. 1990, van Dierendonck 1992, Johnson and 

Damman 1993). A peatlands microtopography model developed to predict hummock and hollow 

features indicates that the differences between production and decay of the Sphagnum species 

contributes greatly to generating bog microtopography (Nungesser 1997, Nungesser in press). 

Under equilibrium conditions, the higher decomposition of the hollow species accumulates less 

peat than the hummocks species with lower decomposition rates in spite of substantially different 

productivities. Innate differences in decay rates of peatland species have been reported for other 

peatlands, as well (Rosswall 1973, Clymo 1983, Morris and Lajtha 1986, Johnson and Damman 

1991, Harris et al. 1995). 

In the Everglades, similar processes may produce the distinct differences between the ridge and 

slough microtopography. The dominant ridge species, sawgrass (C. jamaicense), is highly 

resistant to decay relative to the slough species Nymphaea odorata. Sawgrass contains much 

higher proportions of lignin than the floating and submerged slough species. In field litterbag 

studies, 60% of sawgrass litter in unenriched areas remained after one year (Davis 1991), 

whereas the Nymphaea litter disintegrates within a few months (Shili Miao, personal 

communication). Harris et al. (1995) reported much lower annual loss of sawgrass mass, 8.7% to 
The role of flow (continued) Page 23 

10.8%, in contrast to higher annual loss rates of other plant species found in sloughs (E. 

cellulosa, 45.7% - 84.0%; P. repens 36% - 46.5%). These differences would enhance peat 

accumulation on the ridges relative to the sloughs. 

In addition, the presence of unimpeded flow in the pre-drainage Everglades could increase the 

oxygen concentrations in the bottom of sloughs. More stagnant conditions resulting from 

decreases in flow could decrease oxygen concentrations in the bottoms. Increased oxygen 

concentrations would further enhance the rate of decomposition of the more labile submerged 

vegetation in the slough, resulting in increased differences between ridge and slough bottom 

elevations. Also, decomposition release nutrients into solution. Increased availability of soluble 

nutrients and the transport of those nutrients in the presence of unimpeded flow could further 

increase decomposition rates of slough vegetation (Newman et al. 2001). 

Erosional formation of ridge and slough habitat 

In contrast to the effects of flow on deposition of organic matter such as floc, it is possible that 

the ridge and slough habitat was formed originally via erosional processes occurring on a 

recently uplifted surface (Gregory Pasternack, personal communication). This possibility was 

first raised by Parker et al. (1955) in a quote appearing previously in this paper. 

“... The ‘grain’ of the Everglades ... is believed to be developed entirely on freshwater peat and muck... It ... represents a drainage pattern produced on a very gentle 

sloping surface of organic deposits. The ‘grain’ is composed of tree islands and 

swales [sloughs] that trend parallel to the regional slope, just as one would expect 

in an area of consequent drainage.” (emphasis added in bold) 

The emphasized text contains very important ideas, particularly regarding the term “consequent.” 

It is a term that originates with W. Davis, a forefather of geomorphology, in his classic essay 

entitled, “The Geographical Cycle” (Davis 1909). While Davis’ ideas about landscape origins 

and evolution recently have been displaced by the Gilbert/Hack dynamic equilibrium theorem 

(Hack 1960), Davis’ ideas did dominate the early and middle 20th century. His ideas still are 

viewed as useful, though not generally correct. It is possible that Parker et al. were using their 

Davisian point of view to suggest a specific hypothesis about the origin and processes at work in 

the ridge and slough landscape. 

A consequent stream is one that forms in proto-troughs on a recently uplifted (or in this case, 

perhaps, on a peninsula recently exposed by sea level drop) fresh surface. According to Davis, 

“all the changes which directly follow the guidance of the ideal initial forms may be called 

consequent; thus a young form would possess consequent divides, separating consequent slopes, 

which descend to consequent valleys, the initial troughs being changed to consequent valleys in 

so far as their form is modified by the action of the consequent drainage.” Thus, Parker et al. 

(1955) were suggesting that the regional surface had an initial roughness of non-aligned prototroughs that, through the action of water-induced erosion, became connected to form sloughs 

directed down the regional gentle gradient. It is central to this possible mechanism that the ridge 

and slough landscape is of an erosional origin, not a depositional origin. 
The role of flow (continued) Page 24 

Extreme hydrological events 

The Everglades, as are most ecosystems, is influenced by extreme hydrological events. The 

subtropical setting guarantees occasional impacts from hurricanes, tropical storms, and tropical 

waves, all of which are capable of producing rainfall events in excess of 20 inches over a 

relatively short period of time. Because these events typically occur during Florida’s wet season 

(May through September), their impacts may be exacerbated by already saturated soils and 

existing high water levels. As an example of the potential magnitude of such events, Taylor 

Alexander relates part of an oral history taken from Fred Dayhoff – an Everglades hunter and 

angler who later became an Everglades National Park ranger. 

“One unique adventure Fred described to me concerned the ’47 hurricane, when 

flood waters as deep as a foot were still running over the Tamiami Trail. Not yet 8 

years old, he and his older brother sat on opposite fenders of their ’37 Packard, their 

legs around the fender-mounted headlights, as their father drove slowly. Fred 

recalled that giant whirlpools marked the submerged north ends of the culverts that 

passed under the road, and that the floodwater over the road was swift. With their 

rifle, they took turns shooting bass that were running over the road against the 

current. Upon each hit, the other brother would jump off and attempt to run the fish 

down. They had to be quick because the current was fast enough that the fish would 

be quickly carried into deep water over the sawgrass south of the road. He said the 

bass were most abundant about where the L-67 levee hits the trail today, in the 

middle of the Shark River Slough. They ended that day’s adventure on Loop Road 

about eight and a half miles westward from the Trail’s ‘Fortymile Bend.’ The flow 

there was too swift and deep – about 2 feet he recalled – for them to go farther.” 

(Lodge, in preparation; excerpted with permission of CRC Press) 

These extremes in flow and water depths likely had a profound impact on the Everglades 

landscape. Increased flow volumes and rates undoubtedly transported particulate and dissolved 

materials, affecting both upstream source areas and downstream receiving areas. The impact of 

these events is difficult to assess, particularly without data from a detailed paleoenvironmental 

study. However, it is certain that following construction of the water management system in the 

mid-1900s, the magnitude and frequency of extreme hydrological events was decreased. What 

role these water management changes have on the impact of extreme events is unknown, but 

worthy of further attention. 

Fire 

Fire was an important component of the pre-impacted Everglades. Drainage in the Everglades 

beginning in the late 1800s resulted in a substantial increase in the occurrence of fire in the ridge 

and slough landscape. It is possible that the linear slough pattern was created by tongues of fire 

that followed dryer (overdrained) peat lines in a sawgrass-dominated landscape (Craighead 

1971). These fires burned out sawgrass rhizomes and peat to create linear pools (sloughs) 

throughout the ridge and slough system. Fire may explain the sharp separation in vegetation 

between ridge and sloughs, and the current differences in elevation between ridges and sloughs. 

More recently, sawgrass is re-invading sloughs where ponded water (levees) has reduced fires. 
The role of flow (continued) Page 25 

“Remains of saw grass peat indicate that as late as 1900 saw grass communities 

may have covered much of the area between the tree islands.” (Craighead 1971; p. 

162). 

“Accompanying the recent drainage in the dry years, fires burned in long tongues, 

following the drier peat. Here rhizomes of the saw grass were killed. New plants 

revegetate slowly, and a sharp line of demarkation [between ridge and slough] 

remains for many years. Thus, much peat is removed... During the rainy season 

ponds form in these depressions...” (Craighead 1971; p. 164). 

“Ponds in the Shark Slough... large shallow basins floored with marl and flooded 

in the wet seasons with 18 to 24 inches of water...are the result of fires burning 

off the peat above the marl base.” (Craighead 1971; p. 169). 

Underlying bedrock patterns 

Another mechanism that has been suggested is related to changes in sea level. During the past 

interglacial epoch, when the sea level was higher than present, flow from the Gulf of Mexico 

likely crossed the southern peninsula of Florida, thus leaving “ripple” deposits. These deposits 

eventually, through sediment deposition, could have led to elongated ridges in the bedrock. It is 

possible that underlying bedrock undulations are the base upon which peat deposits are built. 

Surface geophysics can provide conclusive evidence regarding bedrock configuration and its role 

in ridge formation and maintenance. Regardless of the specific mechanism(s), the regularity of 

the ridge and slough pattern suggests the presence of some organizing force acting over the full 

breadth of the landscape. 

Preliminary measurements of peat and underlying bedrock elevations have been made in several 

transects conducted in ridge and slough and sawgrass plain habitats (Chris McVoy, personal 

communication). McVoy compared measurements of peat and bedrock elevations to aerial 

images of the landscape. As expected, peat elevations were higher in areas that would be visually 

described as sawgrass ridges, based on the presence of sawgrass stands. Conversely, peat 

elevations were lower in areas that would be visually described as sloughs, based on the presence 

of open water habitat having sparse emergent vegetation. However, bedrock elevations 

underneath the peat were variable but generally flatter than peat elevations, and did not 

correspond to changes in peat elevation. It is possible that bedrock elevations directly beneath 

the transects would not necessarily correspond to peat elevations along the transects. It may be 

that, in the presence of unimpeded flow, the bedrock pattern is manifested in the peat pattern at 

some distance downslope. While these preliminary data do not support the possible mechanism 

of underlying bedrock influence, more data need to be collected across a broader range of 

habitats, including degraded and undegraded ridge and slough habitat, to confirm the initial 

results. 

Microhabitat differences in water chemistry due to differences in flow 

Anecdotal evidence from northern peatlands suggest the possibility that microhabitat differences 

in flow may result in microhabitat differences in water chemistry, thereby influencing 
The role of flow (continued) Page 26 

Everglades vegetation patterns. The majority of the remaining ridge and slough habitat in the 

Everglades is in areas in which water quality has not been degraded by inflows from the north. 

Therefore, small differences in water chemistry could have large effects on biology. 

A common form of northern peatlands are raised bogs (the lowest nutrient peatlands), in which 

the surface is elevated slightly above the surrounding landscape. This elevation results in a very 

nutrient-poor wetland, with precipitation providing the only water source. In contrast, seepage 

areas often are found on bogs, and these areas exhibit vegetation tolerant of more eutrophic 

conditions than vegetation of the main bog expanse. Vegetation in these seepage areas is more 

typical of nutrient-enriched peatlands than of the raised bogs, but the source water for the seeps 

is exclusively the upslope parts of the bog. Nutrients are elevated in these seeps (Malmer and 

Sjors 1955, Heinselman 1963, Ingram 1967, Siegel 1992). Ingram (1964) reported that 

phosphorus levels in a water track (seep) were 0.148 g m-2 compared to 0.057 g m-2 from the 

source bog expanse (upslope). Similarly, potassium was 1.51 g m-2 in the water track and 0.99 g 

m-2 in the mire expanse. Malmer and Sjors (1955) similarly reported water tracks that contained 

higher potassium and calcium levels than the source drainage area of the bog. Ingram (1967) 

concluded that moving water supports poor fen vegetation while the same water when still 

supports only bog vegetation. Kulczynski (1949) reported similar findings. Similar relationships 

were reported by Ingram (1967), who found that the fluctuation of bog water levels is significant 

in determining site quality; the relationship of his site index with maximum water fluctuations 

was r = 0.73. 

These observations suggest that water movement in peatlands provides a means to transport 

nutrients and to support a richer vegetation type than still water. If this mechanism operates in 

the Everglades ridge and slough habitat, the slight nutrient enrichment of moving slough water 

may contribute both to faster growth of slough species and more rapid decomposition of slough 

litter. Enrichment may occur for a variety of reasons, including groundwater seepage, contact 

with mineral soils or bedrock, and scavenging of nutrients from decaying peat. Davis (1991) 

showed that nutrient enrichment in the Everglades increases the decomposition rates of both 

sawgrass and cattail. With higher decomposition rates of slough species, this slight nutrient 

enrichment may be one of the feedbacks increasing slough/ridge differentiation. Such a potential 

mechanism can be tested readily through controlled experiments in slough habitats that examine 

nutrient levels in flowing water versus still water. 

 

Ecological impacts of ridge and slough degradation

Even though the mechanisms of ridge and slough landscape degradation are not fully known, 

barriers to flow are resulting in the conversion of the ridge and slough wetland mosaic to more 

uniform stands of sawgrass. It is likely that this conversion is related to the elimination of flow 

across the broad expanse in which it once existed. Even though culverts were constructed as part 

of Alligator Alley, Tamiami Trail, U.S. 27, and other levees to convey water past these barriers, 

landscape degradation has occurred probably due to the elimination of flow, changes in quantity 

and distribution of water conveyed, and associated physical and biological components. 

Conversion of the ridge and slough landscape pattern to uniform sawgrass stands has had, and 

will continue to have, deleterious impacts on Everglades plants and animals. 
The role of flow (continued) Page 27 

Flow may be essential for tree island formation and survival

In addition to the disappearance of the ridge and slough landscape, barriers to flow may have a 

negative impact on tree islands – an important component of the Everglades landscape. Tree 

islands now are known to be biodiversity hotspots and critical nesting and foraging habitats for 

numerous species. Tree islands are tear-shaped islands in the ridge and slough landscape whose 

long axis normally runs more or less north-south (i.e., upstream-downstream). Both their shape 

and orientation suggest that water flow has played a major role in their development. The two 

basic kinds of tree islands in the Everglades are floating tree islands and fixed tree islands. 

Floating tree islands primarily are found in the Arthur R. Marshall Loxahatchee National 

Wildlife Refuge and occasionally in other areas with deep peats. Fixed tree islands are found 

south of the Refuge in Water Conservation Areas 2A, 3A, 3B, and Everglades National Park. 

Floating tree islands originate when a large piece of peat, known as a battery, detaches from the 

bottom during a period of high water and floats to the surface. This new island eventually 

becomes colonized by a variety of shrubs and trees. The role of flow in this process is completely 

unknown. 

Although there are known exceptions (Loveless 1959), the majority of fixed tree islands are 

believed to develop because of topographic highs in the limestone bedrock underlying the 

Everglades. The small bedrock pinnacles or platforms, associated with the heads of the islands, 

are typically the highest part of a fixed tree island. The tallest trees and shrubs are found on the 

heads of tree islands. Tails are long, linear mounds of peat that form behind the heads. The 

elevation of a tail gradually drops from that of the head to that of the surrounding wetland. The 

vegetation of the tail ranges from tall trees and shrubs immediately downstream of the head, 

through ever shorter and sparser shrub communities, to a mix of tall sawgrass, ferns, and cattail 

just before it becomes indistinguishable from the surrounding vegetation. This combination of 

head and tail gives fixed tree islands a characteristic, elongated tear shape. 

Two hypotheses have been proposed to explain the formation of tails – the hydrodynamic and 

chemo-hydrodynamic hypotheses (Sklar and van der Valk in press). According to the 

hydrodynamic hypothesis, the tail develops due to litter from the head (or other sources) being 

deposited in its lee by water currents. According to the chemo-hydrodynamic hypothesis, the tail 

develops due to the release of nutrients from the head. These nutrients are leached from the head 

by surface water or shallow groundwater. This leaching creates a plume of nutrients behind the 

head that increases plant growth and a differential build-up of peat in the plume area when 

compared to nearby areas outside the plume. Both hypotheses require water flow. 

In a study of the size, shape, orientation, and distribution of tree islands in the Arthur R. Marshall 

Loxahatchee National Wildlife Refuge, Brandt et al. (2000) found that tree islands decreased in 

size, and that the overall area of tree islands decreased between 1950 and 1991. Photo plots in 

the interior of the wetland demonstrate a tendency for tree islands to become irregularly shaped, 

possibly due to the loss of water flow, reduction of pulse magnitude, and ponding of water along 

the wetland perimeter levees. Pristine tree islands have been described as being small and 

circular (Loveless 1959) or large and orientated in the direction of water flow (Gleason et al. 

1984). It has been hypothesized that the elongated tree islands are found in areas with higher 
The role of flow (continued) Page 28 

flow rates, and that reductions in these flows due to compartmentalization have resulted in 

changes in tree island shape and reduction in size. 

When viewed from space, the Everglades is clearly a landscape of large-scale hydrologic 

gradients. Fixed tree islands are not distributed randomly across the landscape. They seem to be 

associated with the ridge and slough topography of the Everglades. Although flows are 

hypothesized to be critical to tree island formation and sustainability (Stone et al. in press, 

Wetzel in press), the nature of the relationship between the ridge and slough pattern and tree 

islands is not clear. 

The alterations described above in the ridge and slough landscape and in tree islands already 

have caused major ecological impacts to Everglades ecosystem structure and function. The 

importance of major landscape features to Everglades ecology and the ecological impacts that 

result from changes to these features, particularly the loss of open water habitat such as sloughs 

and wet prairies, are described below. 

Sloughs and wet prairies are species rich 

Although sawgrass marsh is the predominant wetland plant association in the Everglades, 

sawgrass marshes in unimpacted regions are interspersed with open water sloughs and wet 

prairies. An Everglades landscape increasingly dominated by sawgrass, which may exceed 10 

feet in height and form an impenetrable mass (Kushlan 1990), will support fewer numbers of 

animals and a lower diversity of animals. Sawgrass habitats in the southern Everglades are the 

poorest habitat in both the number of fish species inhabiting them (Loftus and Kushlan 1987) 

and in the numbers of individuals of those species (Bill Loftus, unpublished data). In contrast, 

adjacent wet prairie/slough habitats have twice the number of species (Loftus and Kushlan 1987) 

and much higher densities of organisms (Trexler et al. 2002). 

Wet prairies and wet meadows, such as those found in the ridge and slough environment, are 

wetland types that are associated with high biological diversity. Keddy (2000) notes that in 

shoreline communities, wet meadows are the least studied community type and most at risk from 

changes in hydrology. Also, there seems to be a general lack of appreciation among wetland 

ecologists for how much higher plant diversity is in infertile (nutrient limited) wet prairies and 

wet meadows than in other wetland habitats. Moore et al. (1989) demonstrate that infertile wet 

meadows had vastly more species, and more rare species, than other wetland types. 

A diverse landscape mosaic is important to the Everglades animal community. Trexler et al. 

(2002) find that wet prairies and sloughs interspersed among sawgrass ridges are important 

sources of refugia, particularly for small fishes, during periods of dry down. Periods of dry down 

are normal features of Everglades hydrology, and Trexler et al. (2002) note that hydrology is a 

major factor in shaping fish communities. Benefits to the fish community from restoration of 

more natural hydrology by CERP implementation may be offset by the lack of availability of 

suitable refugia during dry periods if there are fewer sloughs. 

In a study of prawn, crayfish, and small fish distribution in the Arthur R. Marshall Loxahatchee 

National Wildlife Refuge, Jordan (1996) shows that the wetland is composed of a mosaic of 
The role of flow (continued) Page 29 

habitat structure, and that decapod crustaceans and fishes respond to this mosaic. These 

organisms are important prey of higher trophic levels, and his research indicates that vegetation 

structure, along with hydropattern and other factors, govern the availability of prey. With 

reference to sawgrass stands, Jordan (1996) found fewer prawns and fishes than adjacent wet 

prairies or sloughs. 

Chick and Trexler (in review) find that the large-fish community of Water Conservation Area 3A 

is dominated by large-bodied predators, such as Florida gar and largemouth bass, whereas the 

Shark River Slough community consists primarily of less piscivorous species such as lake 

chubsucker and spotted sunfish. The density of smaller fishes, of the size consumed by many 

wading bird species, is greater in Shark River Slough than in Water Conservation Area 3A, 

possibly because of the larger community of predatory fishes in Water Conservation Area 3A. 

These data suggest that the longer hydroperiod marshes of Water Conservation Area 3A, 

particularly at its southern end just north of Tamiami Trail, seemed to promote growth of large 

predatory fish, which, in turn, limit the abundance of small fishes. They suggest that restoration 

may be best achieved by increasing the spatial extent of long hydroperiod marshes, such as Shark 

River Slough, to improve marsh quality for wading bird prey. 

In summary, the importance of elevation changes in the ridge and slough habitat to the biological 

community is very important. One of the most dramatic features of wetlands is the degree to 

which small changes in elevation can allow large numbers of species to coexist (Paul Keddy, 

personal communication). In one study of coastal plain vegetation in Nova Scotia (vegetation 

that shares many genera with the Everglades), the distribution of each of more than 30 wetland 

species was centered upon slightly different elevations along a gradient of less than 5 feet 

(Keddy 1984). If the topographical variation of the Everglades landscape was lost, there is no 

doubt that biological diversity of both plants and animals would dramatically decline. 

Wading birds need a mosaic of wetland habitats 

Wading birds are an important component of the Everglades ecosystem. Their foraging and 

nesting success often are used as indicators of the overall health of the system. Wading birds also 

are one of the most visible and highly regarded parts of the Everglades. In fact, the overall 

decline of wading birds over the last century – to less than one-fifth of their abundance during 

the 1930s (Davis and Ogden 1994) – has been one of the major factors galvanizing public 

support for Everglades restoration. Scientists understand the central role that wading birds play 

in Everglades restoration – so much so that wading bird ecology is being used to define 

hydrologic targets for restoration, and their population responses to hydrologic restoration will 

be used as measures of restoration success. 

The conversion of ridge and slough landscape to dense sawgrass stands will have a negative 

impact on wading birds and other important birds of the Everglades. In a study of the factors 

affecting foraging behavior of wading birds in the Everglades, Peter Frederick (personal 

communication) states that his researchers did not even attempt to include moderately dense to 

dense sawgrass habitat in their sampling scheme because they never saw birds in this habitat. 

The control of vegetation over wading bird ecology is strong enough that Kushlan (1989) states, 
The role of flow (continued) Page 30 

“Whatever determines vegetation patterns will also, to a large degree, determine bird use of 

wetlands.” 

Wet prairie habitat is dominated by spikerush, although other plant species include maidencane, 

beakrush, and arrowheads, with bladderworts and periphyton mats interspersed among the 

emergent species (Loftus and Eklund 1994). Although these open water habitats do not occupy 

as much of the unimpacted Everglades as sawgrass marshes, sloughs and wet prairies are more 

heavily utilized by fish and wading birds (Hoffman et al. 1994). 

In a review of systematic reconnaissance flight data collected in the late 1980s, Hoffman et al. 

(1994) demonstrate that Great Egrets, Great Blue Herons, and White Ibises almost never were 

associated with dense grass habitats. These types of dense grass habitats only tended to support 

wading birds when water levels were high, and then only in relatively small numbers. Hoffman 

et al. (1994) go on to recommend that to improve wading bird habitat, particularly in the Water 

Conservation Areas, managers should promote the interspersion of slough and wet prairie 

habitats into areas of dense grass. In addition, Bancroft et al. (1994) suggest that loss of natural 

connectivity from compartmentalization might have resulted in a reduction of fish prey for 

wading birds. They hypothesize that levee construction increased the duration of flooding caused 

by dry season rainfall events, which ultimately hindered the concentration of prey items that 

occurs during the dry season. 

Kushlan (1989) shows that vegetation structure affects wading bird and waterfowl use of 

wetlands, because different species have different habitat requirements. For example, longlegged species such as Great Blue Herons and Great Egrets feed by wading in shallow open 

water marsh. Waterfowl that swim require deeper zones without emergent marsh vegetation. 

Coots, Gallinules, and Grebes feed in open water but remain near the cover of emergent 

vegetation which they use for nesting (Kushlan 1989). Resident water bird species that nest in 

swamp forest vegetation depend on nearby marshes for foraging (Kushlan 1990). 

The mechanisms by which vegetation structure affects wading birds are the subject of ongoing 

research. There is strong evidence to suggest that nesting wading birds in the Everglades are 

limited by prey availability (Gawlik 2002). This hypothesis, termed the Everglades preyavailability hypothesis (Figure 17), was first proposed as an explanation for the decline of the 

Wood Stork population in south Florida (Kahl 1964), but it has wide support today for several 

other species of wading birds (Frederick and Spalding 1994, Gawlik 2002). Based on 

experimental studies, this hypothesis was modified to focus specifically on the occurrence of 

high-quality landscape patches, or patches with a high availability of prey (Gawlik 2002). 

Although there have been no studies examining the influence of flow rates on wading birds in the 

Everglades, it is hypothesized that water flow may affect the occurrence of high-quality 

landscape patches indirectly by affecting hydroperiod and characteristics of the environment 

such as topography and vegetation structure (Figure 17). If water flow is necessary for 

maintaining the ridge and slough mosaic, then flow could affect high-quality feeding patches via 

effects on vegetation structure and topography. Fish are most vulnerable to capture by birds 

where vegetation has an open structure (Surdick 1998). During the wet season, dense sawgrass 

ridges in the Arthur R. Marshall Loxahatchee National Wildlife Refuge provide habitat for many 
The role of flow (continued) Page 31 

fish (Frank Jordan, unpublished data), but they are protected from wading bird predation, which 

is probably why wading birds avoid that habitat (Hoffman et al. 1994). However, as the dry 

down progresses and water levels decline, fish on sawgrass ridges are forced to move into more 

open sloughs where they are vulnerable to capture by wading birds. Also, the concentration of 

fish from higher elevation ridges to lower elevation sloughs during the drydown increases fish 

density 20-150 times in the remaining pools of water (Carter et al. 1973, Kushlan 1974, Kushlan 

1976, Loftus and Eklund 1994, Howard et al. 1995). Not surprisingly, densities of some wading 

bird species are highest where slough habitat is most abundant, even after accounting for the 

effect of water depth (Bancroft et al. 2002). Species that seem to require both high prey densities 

and vulnerable prey (i.e., Wood Stork, White Ibis, and Snowy Egret) have declined the most 

since the 1930s (Ogden 1994). 

Collectively, these patterns suggest that the interaction of topography, vegetation structure, 

hydroperiod, water depth, and draw-down rate can determine the quality of feeding patches for 

wading birds. Changes to this interaction, from flow or other processes, could alter the timing 

and magnitude of high-quality prey patches resulting from the seasonal drydown. Coincidentally, 

two major changes in wading bird populations since the 1930s have been the timing and 

magnitude of nesting effort (Ogden 1994). Frederick et al. (2001) note considerable degradation 

of active or former wading bird colony substrate in Water Conservation Areas 2 and 3, and 

hypothesize that this trend imposes limits on available nesting substrates for wading birds. It is 

known that compartmentalization has resulted in an increase in ponding in the Water 

Conservation Areas, especially just upstream of levees. 

A diverse wetland mosaic is important to birds other than wading birds. The endangered Snail 

Kite is a highly specialized bird of prey that depends almost exclusively on one species of 

aquatic snail (apple snail). The presence of relatively sparse emergent vegetation in open-water 

areas is an important component of Snail Kite foraging habitat, and kites are unable to forage 

effectively in dense emergent vegetation (Bennetts et al. 1994). Open water habitats also may be 

important habitat for foraging by the apple snail population. Therefore, suitable Snail Kite 

foraging habitat is best represented by a mix of emergent vegetation with open-water 

communities, which includes the ridge and slough habitat type. 

Barriers to fish migration 

In addition to altering flow patterns and wetland landscape patterns, barriers to flow serve as 

barriers to movement of aquatic animals. Joel Trexler (unpublished data) conducted analyses of 

the population structure of three aquatic species (mosquitofish, spotted sunfish, and grass 

shrimp). These analyses were conducted by examining relative gene flow, which is a measure of 

the average number of fish in a generation that move from one area to another and successfully 

reproduce. Relative gene flow was estimated by comparing gene frequencies from fishes 

collected in different areas of the Everglades and applying standard population genetics theory to 

interpret the differences observed (Slatkin 1985, Beerli and Felsenstein 1999, Beerli and 

Felsenstein 2001). Trexler found that the Tamiami Trail limits migration by mosquitofish 

between Water Conservation Area 3A and Shark River Slough. A comparison of migration 

within Water Conservation Area 3A and Shark River Slough and between these two regions 

suggests that migration within these areas is greater than migration between them (Fig. 18). 
The role of flow (continued) Page 32 

An ongoing study of aquatic animal use of shallow, peripheral Everglades marshes is beginning 

to demonstrate how those animals move over the landscape in response to flow direction and rate 

(Loftus et al. 2001). Even at very slow flows, it is evident that fishes and decapod crustaceans 

can detect and use flow in their dispersal, and that their orientation to flow appears to be species 

specific. 

Research and data collection recommendations

Very few research studies have been conducted specifically to determine the role of flow in the 

Everglades ecosystem. Most of the research projects from which data were presented in this 

paper, while relevant to the role of flow, were not designed to determine the role of flow. It is 

precisely for this reason that the SCT chose the topic of flow as one of its priorities. Because 

compartmentalization and drainage of the Everglades almost certainly had a major impact on 

flow patterns, it is important that appropriate research and data collection occur to best guide 

future management and restoration decisions. It is with that goal in mind that the following 

research and data collection recommendations are provided. 

It should be noted that listing of these recommendations does not eliminate the need for a 

thorough science plan for ridge and slough research. It is important that such a plan be 

developed, with participation by all stakeholders, including restoration managers. The plan 

should clearly develop priorities for research, so that limited funding can be applied in the most 

effective manner possible to develop new information. The plan should be revised on a regular 

basis as new information and knowledge is obtained. Also, because multiple mechanisms of 

ridge and slough formation and maintenance likely operate, research projects should specifically 

address the relative importance of the various mechanisms. 

The recommendations below are separated into 3 general priorities – higher, medium, and lower 

– based upon the degree of consensus among the contributors and the reviewers of earlier drafts 

of this manuscript. 

Higher priority

1. A multidisciplinary study of Everglades paleoenvironmental history is essential to determine 

the historical extent of ridge and slough habitat, the long-term dynamics of this and other 

landscape types, and more recent dynamics based on impacts from water management activities, 

barriers to flow, and other disturbance events such as fire. Measurements needed include: 

sediment stratigraphy; sediment dating; pollen analysis; peat charcoal detection; isotope 

geochronology; grain size analysis, bulk density measurements; carbon/nitrogen analysis; C3 vs 

C4 photosynthetic pathways; sediment geochemistry; macrofossil analysis; nitrogen isotope 

analysis; analysis of lipid biomarker compounds that reveal the origin of organic matter; and 

analysis of authigenic minerals such as iron sulfides to determine past redox changes. 

2. A thorough and broad geomorphic review is necessary to develop competing conceptual 

models of how the ridge and slough landscape formed and how it is maintained. This review 

should provide lists of specific questions and hypotheses that would have to be addressed to 
The role of flow (continued) Page 33 

evaluate each possible mechanism of formation and maintenance. The review should lead to the 

selection of a few of the conceptual models that would provide a better foundation for large-scale 

scientific inquiry. The review should evaluate processes of peat formation and vertical accretion 

of organic material, as these processes are fairly well understood and relevant. 

3. Sediment transport distributions (spatially and temporally) should be quantified as a possible 

mechanism of ridge and slough formation and maintenance. Measurements needed include: 

distribution of particle size and density in suspended sediments, including floc; thickness and 

other specific characteristics of the floc layer, including changes over time; interception of 

suspended sediment by vegetation; the velocity at which suspended sediments will be deposited 

(sedimentary velocity); the velocity at which sediments are resuspended (erosive velocity); 

sediment deposition and decomposition rates in sloughs and sawgrass stands; and the typical 

elevation differences between ridges and sloughs. Collection of suspended sediments under 

variable flow regimes, both before, during, and after restoration is needed to support these 

objectives. 

4. Synoptic measurements of flow should be conducted over short time scales and large space 

scales in order to quantify ranges of flow velocity and direction and to delineate major flow 

pathways. Flow measurements should be made in both intact and degraded ridge and slough 

habitat, and should include surface and ground water. Vertical profiling of flow should be 

conducted at specific times and locations to quantify details of the flow in order to understand 

the processes involved in sediment transport, erosion, deposition, mixing, and transport, and to 

correlate point measurements to vertical means. Time series measurements of flow should be 

conducted over long time scales at a limited number of locations in order to quantify the effect of 

infrequent events, such as the passage of storms, and the effect of low frequency phenomena, 

such as seasonal variations. Individual flow measurements, coupled with ecological surveys, 

should be designed to study the specific processes that are hypothesized to most likely alter the 

landscape and affect transport and mixing. Examples include flows around tree islands, near 

culverts, in fire-impacted areas, and in the vicinity of canals. 

Medium priority

1. Develop a simple carbon balance model as a basis for understanding the biological and 

geomorphological processes that may differ between ridge and slough habitats, and to address 

the possible mechanism of differential rates of peat accumulation and decomposition. Model 

parameters would include: primary productivity; decomposition; carbon inputs and exports, both 

dissolved and particulate; and methane export. Obviously, the data collection and research 

necessary to provide these types of inputs to the model would have to be conducted, and 

coordinated with the collection of hydrological data suggested elsewhere. From this model 

development, a thorough, data-based, carbon budget could be established. Such an approach 

would illustrate any differences that may exist between ridges and sloughs, and would provide 

insight into factors that control carbon flow. 

2. Continued collection and analysis of remotely sensed images, either fixed wing or satellite, is 

required to track trends in ridge and slough landscape patterns, and to track restoration progress, 

particularly when barriers to flow are removed. Field studies, remote sensing techniques, and 
The role of flow (continued) Page 34 

system models also should be coordinated to provide a thorough understanding of the 

mechanisms involved. For instance, remote sensing and surface geophysics could be used to 

identify areas with strong or weak ridge and slough characteristics and depths of sediment 

deposition on bedrock, and field research could attempt to quantify environmental conditions 

leading to both landscape types. Field studies should be able to provide the parameters required 

by the system models. 

3. Develop a seasonal water balance for the entire Everglades, illustrating the relative 

contribution of regional groundwater, direct precipitation, and surface inflows from the north. 

This balance would allow estimation of flow availability, quantity, and timing to the ridge and 

slough landscape prior to and after the water management system was constructed. Even if this 

water balance is available only as a first-order analysis, it would be useful in assessing the 

historical and present role of flow in creating and maintaining the ridge and slough landscape 

pattern. 

Lower priority

1. Numerical and analytic techniques, including modeling, are needed to determine the 

mechanisms of ridge and slough formation and degradation. Numerical modeling of water and 

sediment flows should be conducted at a variety of temporal and spatial scales in order to 

provide a physics-based interpolation of the flow field on scales of ecological interest. Modeling 

also is required to evaluate restoration alternatives. System models that investigate the 

interactions of important landscape mechanisms would improve our understanding of the relative 

importance of the environmental factors. These models could also assess potential feedback 

processes between vegetation and hydrology. A specific example of a model is a ridge and 

slough patterning model. This model is a simple, grid-based simulation model that has been 

partially developed by South Florida Water Management District staff (Martha Nungesser, 

personal communication) but not yet implemented. Another possible approach to understanding 

the nature of flow and these landscape patterns is to build a simple physical model that tracks 

how slowly flowing water interacts with a peat-type material. 

2. Studies should be conducted to assess the potential for recovery from dense sawgrass stands 

back to a more diverse wetland mosaic once uninterrupted flow patterns are restored. These 

studies would address whether the system is resilient enough to recover on its own, or further 

intervention would be required. 

3. Research should be conducted to determine steps that must be taken to ensure that existing 

ridge and slough landscape can be sustained even in compartmentalized areas of the Everglades. 

4. The responses of Everglades animals to flow should be studied, particularly how they may use 

flow to disperse seasonally to recolonize the system and how flow barriers affect that process. 

5. Because of the lack of pre-drainage data, additional historical information concerning predrainage vegetation conditions should be sought. In particular, interviews should be conducted 

with individuals having direct experience in the Everglades prior to the majority of humaninduced changes. For example, there may be Miccosukee Tribal elders who lived in the 

Everglades prior to the construction of the Tamiami Trail. 
The role of flow (continued) Page 35 

6. Regular workshops, focused on the ecological effects of flow in the Everglades, should be 

held. These workshops should involve wide participation of hydrologists and ecologists. 

Additional recommendations for future research, both at the one and five-year time horizons, are 

contained in the flow workshop summary, accessible at http://sofia.usgs.gov/geer. 

Performance measure development 

A centerpiece of the overall south Florida restoration effort is CERP. As a restoration priority, 

CERP includes re-establishment of pre-drainage hydrological parameters shown by a natural 

systems model. Science is to serve as the foundation of CERP, and CERP managers have chosen 

to use adaptive assessment as the underlying principle during the three-plus decades of the 

restoration implementation. Adaptive assessment provides the scientific feedback loop to 

restoration managers to change direction if desired outcomes are not being realized. A 

Monitoring and Assessment Plan is under development to provide this feedback during the 

restoration program, and includes conceptual ecosystem models (including a ridge and slough 

conceptual model) and performance measures as indicators of restoration success. 

During the development of CERP, restoration of water levels, rather than water flows, dominated 

the consideration of performance measures. Water levels, their distribution, and their timing are 

vital to the Everglades. Water flow played a lesser role during the Restudy planning process 

because accurate modeling of water flows is much more difficult than that of water levels, and 

the consensus view regarding the role of flow presented in this paper was not available to the 

Restudy planning teams. Understanding of the relationship between water flow and water level is 

complicated by the presence of flow barriers in the Everglades, which have made interpretations 

of empirical observations difficult in a compartmentalized system. Because the consensus view 

presented in this paper now is available and should result in new flow-related research, flow 

performance measures should be developed accordingly. 

Future improvements in performance measures related to flow will depend on additional research 

as suggested above to expand our knowledge of the role of flow. Several possible performance 

measures have been explored, but their interpretation is limited by the availability of fieldverified quantitative measures. Additional research will allow resource managers to make better 

decisions when trade-offs between flow and hydroperiod (and any other hydrological 

parameters) may have to be considered. 

Remote sensing provides one of the best tools from which to continually assess trends in ridge 

and slough landscape characteristics. Possible performance measure metrics to be used from 

image analysis include: aerial extent and temporal trends of tree island, sawgrass ridge, and 

slough polygons; edge-to-area ratios for landscape types; average length-to-width ratio and 

temporal trends of sawgrass ridges or sloughs for a defined area; and spatial orientation of the 

three landscape types as compared to the historic spatial orientation. Surface geophysics at set 

transects over time will demonstrate movement of surficial sediments, and enhance performance 

assessment as restoration measures are implemented. 
The role of flow (continued) Page 36 

Refinement of hydrologic models to provide velocity vectors (both magnitude and direction) and 

water depths would help predict where erosive and sedimentary velocities might occur, where 

flow directions differ from the natural direction, and where depths might be expected to alter 

landscape features. Spatial assessments can involve calculating suitability indices to indicate 

areas with: unnaturally high or slow velocities; unnaturally broad or narrow annual ranges in 

water depth; unnaturally high peak water levels (or low minimum water levels); and unnatural 

deviation in flow direction. 

Acknowledgements

The SCT expresses its sincere gratitude to all of the contributors and reviewers listed below that 

participated in the preparation of the many drafts of this document. Those listed as contributors 

wrote one or more sections of the paper, and/or contributed specific text. Those listed as 

reviewers reviewed one or more of the drafts, and provided written comments. The SCT thanks 

Chris McVoy for playing a pivotal role in bringing attention to the role of flow in the ridge and 

slough landscape. We also are indebted to Garth Redfield and the South Florida Water 

Management District for funding and conducting an independent peer review of this document 

by seven, independent experts listed below. Their contributions, and the contributions of all of 

the reviewers, were invaluable in improving the quality of the paper. 

Editor

Nicholas G. Aumen, Everglades National Park 

Contributors: 

Tom Armentano, Everglades National Park 

Nicholas G. Aumen, Everglades National Park 

Joan Browder, National Oceanographic and Atmospheric Administration 

Elizabeth Crisfield, Everglades National Park 

Peter Frederick, University of Florida 

Dale Gawlik, South Florida Water Management District 

Harry Jenter, US Geological Survey 

Jim Kushlan, Smithsonian Institution 

Chris McVoy, South Florida Water Management District 

Martha Nungesser, South Florida Water Management District 

John Ogden, South Florida Water Management District 

Gregory Pasternack, University of California - Davis 

Mike Ross, Florida International University 

Fred Sklar, South Florida Water Management District 

Joel Trexler, Florida International University 

Jon Woolverton, US Geological Survey 
The role of flow (continued) Page 37 

Individual and agency reviewers from which comments on earlier drafts were received: 

Sydney Bacchus, public 

Ronnie Best, US Geological Survey 

Gwen Burzycki, Miami-Dade County 

James Duck, compiled comments from the US Army Corps of Engineers, Jacksonville District 

Chris Farrell, public 

Matt Harwell, US Fish and Wildlife Service 

Harry Jenter, US Geological Survey 

Brian Keller, National Oceanographic and Atmospheric Administration 

Tom Lodge, public 

Bill Loftus, US Geological Survey 

John Marshall, public 

Paul McCormick, Everglades National Park 

Jack Moller, public 

Mitch Murray, US Geological Survey 

John Ogden, South Florida Water Management District 

Peter Ortner, National Oceanographic and Atmospheric Administration 

Peter Rauch, public 

Terry Rice, Miccosukee Tribe of Indians of Florida 

Eric Swain, US Geological Survey 

Ken Tarboton, South Florida Water Management District 

Mike Waldon, US Fish and Wildlife Service 

Jeff Walters, Virginia Polytechnic Institute and State University 

Independent peer review panel 

Barbara L. Bedford, Senior Research Associate, Department of Natural Resources, Cornell 

University 

Thomas S. Bianchi, Associate Professor, Department of Earth and Ecosystem Sciences, Tulane 

University 

James G. Gosselink, Professor Emeritus, Center for Wetland Resources, Louisiana State 

University 

Paul A. Keddy, Professor of Environmental Sciences, Department of Biological Sciences, 

Southeastern Louisiana University 

Barbara W. Leyden, Professor, Department of Geology, University of South Florida 

William H. McDowell, Professor, Department of Natural Resources, University of New 

Hampshire 

Gregory B. Pasternack, Associate Professor, Department of Land, Air, and Water Resources, 

University of California – Davis 
The role of flow (continued) Page 38 

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Figure 1. General locations of the major landscape types in the Everglades prior to human intervention. 
The role of flow (continued) Page 49 

Figure 2. Ridge and slough landscape in its pre-drainage condition. Note sharp, distinct edges on most sawgrass 

ridges, and the open water of sloughs, with few emergent plants. Location: present Northeast Shark Slough area. 

Figure 3. Ridge and slough landscape in its pre-drainage condition. Note large extent of open water slough. 

Location: southwest corner of present Water Conservation Area 3B. 
The role of flow (continued) Page 50 

Figure 4. Ridge and slough landscape in its pre-drainage condition (approximate). Oblique aerial view of 

Everglades from a dirigible, 1930s, looking west. Location: west of Miami, probably south of Tamiami Trail. Note 

linear pattern of elongated sawgrass ridges (dark) and intervening sloughs (light) (Matlack 1939). 
The role of flow (continued) Page 51 

Figure 5. Landscape directionality and estimated pre-drainage flow directions within the western ridge and slough 

landscape. Mapped from aerial photographs from 1940 (USDA-SCS 1940). Published in Sklar et al. (2001), Fig. 2-

9. Note continuous flow lines through Water Conservation Areas 3A, 3B, and Northeast Shark Slough. Red line 

indicates portion of Tamiami Trail between Dade Corners and the intersection of L-67. 
The role of flow (continued) Page 52 

Figure 6. Ridge and slough landscape: artist’s reconstruction of pre-drainage condition. Note relation of landscape 

pattern (plan view) to underlying peat microtopography (vertical profile). Scale: length = 1.5 miles; width = 1.0 

mile.
The role of flow (continued) Page 53 

Figure 7. Ridge and slough landscape, considered to be well preserved in its present condition, as seen in a June 

2001 aerial view from central Water Conservation Area 3A. Image size approximately 1.5 X 2 miles; North is to 

left. Gray-green strips are sawgrass ridges; intervening lighter areas are open-water sloughs. 

Figure 8. Ridge and slough landscape considered to be well preserved in its current condition, as seen in a 1991 

color infrared aerial photo from central Water Conservation Area 3A. Image size approximately 2.5 X 3.75 miles; 

North is to left. Red indicates woody vegetation; gray strips are sawgrass ridges; darker areas are sloughs, except for 

two recently burned ridges. An east-west transect through image would cross 15-20 sawgrass ridges. Note welldefined, elongated shape of ridges. 
The role of flow (continued) Page 54 

Figure 9. Ridge and slough landscape in its current, degraded condition as seen in a June, 2001 oblique aerial view 

from the southeast corner of northern Water Conservation Area 3A, north of Alligator Alley (I-75). Gray-green is 

sawgrass; other areas are slough-like. Note breaking up of sawgrass into numerous, small patches. Photo taken from 

an altitude of 300-500 feet. 
The role of flow (continued) Page 55 

Figure 10. Ridge and slough landscape in its current, degraded condition as seen in a 1991 color infrared aerial 

photo of the eastern side of Water Conservation Area 3A (intersection of Alligator Alley and US 27) Traces of 

original NNW-SSE orientation of sawgrass ridges still are visible, but the pattern is unclear, and ridges are 

breaking up into individual sawgrass patches. 

Figure 11. Ridge and slough landscape in its current, degraded condition, as seen in an April 6, 2001, oblique aerial 

view from northern Water Conservation Area 3A, north of Alligator Alley, looking south. Yellowish-green is 

sawgrass; gray-green indicates former sloughs, now grown over with wet prairie species. Photo taken from an 

altitude of about 1000 feet. 
The role of flow (continued) Page 56 

Figure 12. Ridge and slough landscape in its current, degraded condition as seen in detail from a vegetation map of 

Water Conservation Area 3A, north of Alligator Alley, west of Miami Canal. North is to left. Green indicates 

sawgrass; blue indicates sloughs. Note breaking up of sloughs, resulting in “moth-eaten” appearance in plan view. 
The role of flow (continued) Page 57 

Figure 13. Ridge and slough landscape in its current, degraded condition as seen in Water Conservation Area 3B. 

Landscape is almost completely covered by sawgrass; slough areas are reduced to minor isolated remnants and 

directional pattern largely obscured. 
The role of flow (continued) Page 58 

Figure 14. Ridge and slough landscape in its current, degraded condition, as seen in a vegetation map of western 

Water Conservation Area 3B, along L-67A and L-67C canals. The original pre-drainage NNW-SSE directionality 

(arrow) still is recognizable faintly (hold at arm’s length; rotate image). However, the typical pattern of clear ridges 

and sloughs has been almost completely obscured, primarily by sawgrass overgrowing the sloughs. 
The role of flow (continued) Page 59 

Figure 15. 1980 vegetation map of area within Shark Slough, Everglades National Park (Olmsted and Armentano 

1997). Area approximately 3.75 miles wide. Green indicates stands of tall sawgrass, usually very dense and 

monotypic, slightly elevated above surrounding marsh; yellow indicates sawgrass marsh, with sparse, low stature 

sawgrass; orange indicates wet prairies; red is bayhead swamp forest. Middle panel shows only tall, dense sawgrass 

polygons; bottom panel shows sawgrass marsh polygons only. Note contrast in directionality between panels: 

polygons in middle are directional, with consistent orientation; polygons in bottom panel are amorphous, with 

random orientation. Middle panel is thought to map original, pre-drainage sawgrass ridge geometry, while bottom 

panel thought to map post-drainage sawgrass which has randomly colonized sloughs. Random colonization suggests 

post-drainage absence of a strong directional process. 
The role of flow (continued) Page 60 

Disintegrating 

sloughs 

 Disintegrating 

 ridges 

 

Well-conserved 

ridge and slough 

landscape 

Ridge and slough 

pattern weak; 

overgrown by 

sawgrass 

Close to predrainage condition 

Likely approximate 

location of photo in 

Figure 4 

Sloughs being 

invaded by 

sawgrass 

Figure 16. Satellite image of the western ridge and slough landscape, including Water Conservation Areas 3A and 

3B, and the Shark Slough/Northeast Shark Slough portions of Everglades National Park. Largest circle indicates 

portion of landscape which most closely resembles original pattern of ridges and sloughs. Smallest circles show 

location of 1917 photographs that closely resemble pre-drainage descriptions. Other circles indicate various 

degraded conditions of present day ridge and slough landscape. 
The role of flow (continued) Page 61 

 

Figure 17. Everglades prey-availability hypothesis (Gawlik in press). 
The role of flow (continued) Page 62 

Figure 18. Estimates of migration rate within Shark River Slough and Water Conservation Area 3A, and between 

the two areas. Sites were chosen to have separations of approximately equal distances within each slough, and 

between the two sloughs. 

0

0.5

1

1.5

2

2.5

3

SRS WCA-3A Between

Relative Gene Flow

A A/B B

P < 0.02