Final Report to
Lee County, Florida and the South Florida Water Management District
Scientific Evaluation and Simulation of the
Six Mile Cypress Watershed
John Murray (PI), Brenda Brooks-Solveson, Julianna da Frota, Jeff Key
Florida Gulf Coast University
December 31st, 2004
Table of Contents
1.0 Executive Summary………………………………..…………………………………………. 3
2.0 System Overview…………………………….…………………….…………………..……... 5
2.1 Scope of Study…….………….……..………….………...………...….………….…… 5
2.2 Landscape………………………………………………...……………….…….……... 5
3.0 Wetlands Ecology and Hydrology……………………..………..………………….………….. 7
3.1 Conceptual Model…………………….……………………….....……………....…….. 7
3.2 Research Methodology………………………….…………………..…………………. 10
3.3 Field Investigations and Ecological Impact Assessment…….……….………………... 11
4.0 System Simulation…………………………….…………………….…………………..……... 19
4.1 Simulation History…………………….…………………….……………………...…. 19
4.2 Simulation Results………….…………………….……………………………..…….. 20
5.0 Conclusions and Recommendations…….…………….……………………………………….. 25
6.1 Conclusions……………….…………………….………………………..…………….. 25
6.2 Recommendations…………….………………………………….………....………..… 25
6.0 Acknowledgements…………………..………………………………………..……………..… 26
7.0 References………………………………………………………………………………………27
8.0 DVDs/CD ROMs
8.1 DVD 1
8.1.1 Final Report
8.1.2 Transect Data: Vegetation Survey, PVC Latitude & Longitude, and Water Depths
8.1.3 Transect GIS Images
8.1.4 DB Hydro Data and Profile Spreadsheets
8.1.5 Watershed Permit Summaries
8.1.6 Built Structures and Photos
8.1.7 Six Mile Bibliography
8.2 DVD 2
8.2.1 MIKE SHE/MIKE 11 Files
8.3 CD ROM 1
8.3.1 System GIS Map, System Inputs & Outputs, Hydrological Database
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1.0 Executive Summary
A scientific study of the hydrology and ecology of Six Mile Cypress Slough, a subset of the Tidal
Caloosahatchee River Basin, was initiated by Lee County, the South Florida Water Management
District, and Florida Gulf Coast University. Six Mile Cypress Slough Preserve, the heart of the Six Mile
Cypress Watershed, is a 9-mile long, 0.5-mile wide cypress swamp encircled by residential and
commercial development, and crossed by 5 highways. The purpose of the study was to answer the
question, “Has Six Mile Cypress Slough Preserve been ecologically impacted by regional hydrological
changes?” Understanding the hydrology and ecology of the slough required that field investigations and
computer simulations of the slough be conducted.
Field investigations consisted of developing a conceptual system model and hydrological database of the
watershed, verifying the location and nature of the inputs and outputs, producing GIS maps of the study
area, accessing the SFWMD DB Hydro database for slough surface water level (stage) data over the last
15 years, and creating four 600-700 meter “paths” or transects across Six Mile Cypress Slough Preserve.
Measurements of plant community type, water level, and ground level (DGPS elevation) at 10 meter
intervals along each transect provided data essential in connecting ecology and hydrology in the slough.
An integrated, regional simulation model based on field investigations was developed for predicting
current and future hydrological behavior of the system. Impact assessment was performed by connecting
observed and simulated hydropatterns to plant communities along the transects. Pine, wet prairie,
cypress, and pond communities were considered since they interact in the slough in complex ways
related to hydrologic conditions, fire regimes, and soils. The simulation model encompasses the Tidal
Caloosahatchee River Basin, Six Mile Cypress Watershed, and the Six Mile Cypress Slough Preserve.
Surfacewater, groundwater, and atmospheric interactions are included in the model. DHI Water and
Environment’s MIKE SHE/MIKE 11 hydrological simulation software was employed. Predictive
scenarios included:
1. Simulation model calibration and refinement using observed inputs, output, and storages.
Topographical data, precipitation and evapotranspiration rates, surfacewater and groundwater levels
and flows, control structure operation, and geological parameters were included.
2. Simulations required in investigating ecological impact. These included simulations establishing
average wet season water levels and hydroperiods at specified locations along the slough.
3. Simulations and calculations investigating water transfer into the slough from external sources to
assure system restoration and long-term sustainability.
Scientific evidence resulting from the study suggests that Six Mile Cypress Slough Preserve is
ecologically impacted. The current hydropattern in the slough will not allow cypress communities
(dominant species = pond cypress, Taxodium ascends = T. distichum var. nutans) or swamp forest
communities (dominant species = bald cypress, Taxodium distichum) to be sustained. The term
“cypress” will be used to refer collectively to both species for the remainder of this report. The term
“hydropattern” encompasses three (3) ecologically critical parameters: average wet season water depth,
hydroperiod, and dry season water depth. Southwest Florida cypress hydropatterns and their associated
parameters are presented in Table 1.
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Table 1 - Southwest Florida Cypress Community Hydropatterns
Average Wet Season
Average Dry Season
Hydroperiod
Hydropattern
Water Depth
Water Depth
(Time
Parameters
Relative to Ground
Relative to Ground
Interval,
Wet Season = July 1(1, 10)**
Water Depth
October 1
Dry Season = April 1> Ground)
June 1
0.31m to 0.61m
-0.15m to –0.41m
6-10 mo
Sustainable
(12in to 24 in)
(-6in typ, -16in typ)
Range
(Southwest FL)
Range: 0.0in to12.0in
Range: -0.28m to -0.84m
Range: 4.6mo
Six Mile
(0.0 to 0.30m)
(-11in to –33in)***
to 6.7mo
Cypress Slough
Average: 0.15m (6.0in)
Average: -0.53m (-21in)
Average:
Preserve
From Highway 82 to Ten
Transect Data Not
5.7mo at
Range
Mile Canal (Observed and
Available (No Wells)
DB Hydro
Simulated)*
Stations
*Exception: Observed
** 1= Average Year Low
Notes
Data from Daniels
Water, 10 = One in Ten
Parkway to Ten Mile
Year Drought
Canal Not Available
*** Surface Water
(No Intermediate Surface
Monitoring Stations May
Water Monitoring Stations
Limit Range of Dry
or Wells)
Season Data Available
Research suggests that if one or more of the three (3) parameters listed above falls outside the
sustainable range, the system may be impacted. If the water is too shallow (depth < sustainable), other
plant species may, over time, displace the current cypress community, or it may be destroyed by fire. If
the water is too deep (depth > sustainable), germination may not take place. Other factors may also
indicate impact, such as the presence of invasive, exotic species, major disturbances (fire, hurricanes,
earthquakes), soil variations, logging, etc. As development progresses and climate change occurs, the
hydropattern may be further altered. These alterations may in turn feed back to affect future fire regimes,
flooding, soil composition, and ecological sustainability.
Given that the average wet season water level and hydroperiod for Six Mile Cypress Slough Preserve
fall outside the sustainable range for cypress, the dominant plant community, the slough is ecologically
impacted. The difference between the nominal average wet season water depth (18”) and the average
wet season water depth (6”) is 12” or 1ft. A second question arises as a result of this conclusion, “What
can be done to restore the system to its predevelopment state?” Answers to this question are critical in
achieving a dynamic equilibrium between natural and human systems in the region. In order to
ecologically restore and sustain Six Mile Cypress Slough Preserve for future generations, it is suggested
that high quality water be added to the system in such a way as to mimic natural system hydropatterns as
closely as possible. The volume of water required for slough restoration has been estimated at 1 million
cubic meters. Optimal methods for accomplishing this restoration process via sheetflow require further
investigation. Hydrological changes to the watershed resulting from anticipated land use changes over
the next 50 years should also be considered.
Extensions: Future efforts should be directed toward increasing our historical understanding of the
hydrology and ecology of Six Mile Cypress Slough, improving overall data acquisition and control
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capabilities (including the addition of wells), enhancing simulation resolution, developing restoration
strategies and tactics to assure sustainability, enhancing public understanding of complex dynamic
systems, and promoting hands-on involvement in restoration.
2.0 System Overview
2.1 Scope of Study
It is essential that humanity develop a collective appreciation for complex dynamic systems involving
multiple scales of space and time if the planet is to be sustained. Ornstein and Ehrlich [2000] have
suggested that although we did not originally evolve such an appreciation, it is imperative that we
move culturally toward a new paradigm of understanding, an inclusive, experiential framework in
which we perceive ourselves as a part of nature rather than apart from it. Wetlands, the subject of this
study, are complex, dynamic natural systems that require illumination through ecological study,
economic analysis, and application of the powerful, predictive lens of computer simulation. For the
population at large to appreciate such unfamiliar territory, we must communicate the value of wetlands
in an articulate, interdisciplinary manner, one that connects the arts and the sciences through metaphor,
analogy, and personal experience. Einstein’s statement, “we should make things as simple as possible,
but no simpler” applies to wetlands in the same way it does to relativistic mechanics.
This project consisted of an ecological and hydrological study of Six Mile Cypress Slough, a subset of
the Tidal Caloosahatchee River Basin. Complex interactions occur at multiple scales of space and time
among surface water, ground water, precipitation, evapotranspiration, development, and drainage
throughout this system, a diverse liquid landscape with little topographical relief. Ecological and
hydrological field investigations, differential GPS surveying, and computer simulations of regional and
local hydrological phenomena were required to understand the system. The interdisciplinary efforts of
a remarkable cast of scientific characters allowed us to answer the question, “Has Six Mile cypress
Slough Preserve been ecologically impacted as a result of regional hydrological changes?” The results
of the study suggest that the system is impacted and should be restored by adding water in a way that
closely emulates predevelopment processes.
2.2 System Landscape
Examination of the satellite image of South Florida shown in Figure 1 reveals that water dominates the
landscape. Wetland plants constitute the majority of the primary producers, the energy source for most
consumers. Since wetland vegetation is dependent on the quantity, quality, and timing of the water in
its immediate environment, changes in the landscape affecting water are often significant. Residential,
agricultural, and commercial development have altered the landscape and associated hydropatterns in
ways that are currently detrimental to wetland vegetation. Research by Duever [1975, 1978, 1984,
1986], Ewel [1986], Mitsch [2000, 2004], and Odum [1971, 1975, 1994, 1995, 2000] has provided a
detailed, quantitative understanding of the relationships between hydrology and vegetation in the
wetland ecosystems of Southwest Florida. The results of this research provided the intellectual
underpinnings for the current Six Mile Cypress study.
The first activity undertaken in the study was to become familiar with the six Mile Cypress Slough
landscape and its surroundings. Developing a sense of place proved critical in understanding the inputs
to, outputs from, and storages within the system. These activities also included GIS mapping and the
development of a system-wide hydrological database. They are documented in Appendix 8.2.1.
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Figure 1 - South Florida Landscape, Six Mile Cypress Slough Preserve
Three-dimensional landscape views of Six Mile Cypress Slough Preserve are shown in Figs 2 and 3.
Figure 2 – Slough 3-D Landscape with Cross Sections, Upstream View, MIKE 11 Simulation
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Figure 3 – Slough 3-D Landscape, Downstream View, MAYA Animation
3.0 Wetlands Ecology and Hydrology
3.1 Conceptual Model
The primary concern of this study was evaluating hydrological effects on cypress, the dominant plant
community in the slough. It was also necessary to consider the presence or absence of 31 other wetland
species to provide an overall context for analysis. Three factors strongly influence wetlands ecology in
Southwest Florida:
1. Water. The quantity, quality and timing of the water are critically important to wetlands and the
surrounding plant communities. The semi-tropical climate of South Florida produces distinct wet
and dry seasons. These seasonal processes can best be understood by an examination of the South
Florida water cycle as illustrated in Figure 2. Surfacewater and groundwater data obtained from the
6 automated monitoring stations located within Six Mile Cypress Slough Preserve are presented in
Figure 3. These stations have provided a continuous record of surfacewater and groundwater data
for fifteen years. In South Florida rainfall usually begins in June. The water level (water table)
gradually rises above ground, emerging at the surface between June and July. Water then moves
across the landscape as sheetflow. Water levels typically plateau in early July. In October, rainfall
often stops, followed by a period of decline in water level. When the water drops below the
surface, the water table declines rapidly through the unsaturated zone due to the limited volume
available for holding water between soil particles. Evapotranspiration, or evaporative water losses
from open water bodies and the water transpired by plants occurs year round, with the levels
varying according to season and other factors. It should be noted that too much water (on average)
might prevent germination of new cypress since the seeds may not grow enough during the dry
season and drown. Too little water suggests that other species might move into an otherwise wet
region and eventually displace the cypress. The water budget for the slough is also important to
understand. It states the “conservation of mass” principle that the sum of all the water inputs and
outputs to and from the slough, minus any water storage within the slough, must equal zero. This
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concept has important implications for system-wide or localized hydrological analysis.
Figure 4 – South Florida Water Cycle
Figure 5 - Six Mile Cypress Slough Preserve Surface Water and Groundwater Data (SFWMD)
It should be noted that the general shape of the six (6) water level plots in Figure 5 are similar to the plot
presented in Figure 4. Absolute water levels (elevations) in the slough decrease moving downstream.
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2. Fire regimes. Fires influence vegetation. During the wet season, when wetlands are inundated and
fires start, many wetland plants escape serious damage. Plants located a considerable distance
away from wetlands may be damaged or destroyed in this situation depending on the intensity of
the fire and the local fuel load. During the dry season, if fires exist in close proximity to wetland
plants, but do not consume them, species that might otherwise displace wetland plants over time
will be destroyed, preventing their succession. In environments in which excessive drainage has
occurred and water table levels are low, the succession of oak and wax myrtle may proceed. Fires
that move into drier, drained areas may also destroy young wetland plants.
3. Soils. Hydric soils, including peat, characterize wetlands. Soils will not be treated in this study
except to note that cypress size (DBH) correlates strongly with peat depth. Peat depth is also
influenced by the presence of bedrock. Wetland soils can only develop under inundated conditions.
Soils research contributed directly to the creation of predevelopment vegetation maps for
Southwest Florida. These maps provide restoration targets for altered or disturbed environments.
The conceptual model used to unite cypress swamp ecology and hydrology in this study is presented in
Figures 6 and 7. The research behind the model was performed by Duever [1975, 1978] starting in the
1970’s. Figure 6 illustrates optimal conditions for sustaining cypress in Southwest Florida. Optimal
wet season water depths for sustaining cypress range between 12’ and 24”. The optimal hydroperiod,
or time interval during which water exists above ground, ranges between 6 and 10 months. In Figure 7
optimal wet season water depths, dry season water depths, and hydroperiods are presented for a
spectrum of wetland plant communities [Duever, et. al. 2004].
Figure 6 – Hydroperiods and Average Wet Season Water Depth [Adapted from Duever, 2004]
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It is important to note that water levels in cypress communities typically drop below ground during the
dry season, a condition that, within limits, encourages the germination of cypress seeds. During an
average dry season, water depths in cypress communities are typically between –6 inches and –16
inches.
Figure 7 - Hydrologic Regimes of Major Southwest Florida Plant Communities [Duever, 2004]
3.2 Research Methodology
Research methods are summarized in Table 2. The key scientific activity necessary to determine
system impact was obtaining data about average wet season water depths in cypress communities.
Hydroperiods were also considered. If cypress was found to be present at specific sites along the
transects, or at sites along the length of the slough at the thalwegs (lowest point in MIKE 11 simulation
model cross sections), or at average ground levels, and the water depths proved too low (See Figure 7)
then it was deemed likely that these sites were impacted. A similar argument was applied regarding
dry season water levels. Uncertainties in the dry season water level measurement process precluded
any conclusions in this context. Hydroperiods (See Figure 7) established from data obtained from the
surface water monitoring sites also contributed to the impact evaluation process.
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Table 2 – Summary of Research Methods Used in Six Mile Cypress Slough Study
Activities & Resources
Data Acquisition/Processing
Data Acquisition/Processing Outcomes
(Step 1)
(Step 2)
(Step 3)
Six SFWMD DB Hydro
Surface Water Monitoring
Stations Along Slough
Yield: Observed Surfacewater
& (Limited) Groundwater Data,
Sampled @ 24hr, 4hr, &
15min Intervals for 15 yrs.
Processing Observed DB Hydro
Data Yields: Average Wet & Dry
Season Water Levels @ 6 Points
Along Slough
Transects:
Constructed from PVC Pipe
Inserted in Ground at 10 m
Intervals, Transects Yield
Spatial Reference Points (X, Y,
Z) for Recording Water Levels,
Depths & Plant Community
Data
Transect Vegetation Data Yields:
Presence or Absence of Plant
Communities (Pine, Wet Prairie,
Cypress, Pond) Along Transects.
Used in Conjunction with Water
Depth, Plant Presence or Absence
Data is Used in Evaluating Impact
@ PVC Transect Points
Differential GPS &
Conventional Surveying
Yield: Accurate Ground
Elevations and PVC Latitude
& Longitude Data Along
Transects
1990 Slough Survey
Yielded: MIKE 11 Simulation
Model Cross Section
Dimensional Data & Chainage
Point Data (X, Y, Z)
MIKE SHE/MIKE 11
Simulator: Allows User to Ask
“What if?” Questions About
Hydrological Behavior
Following Comparison of
Observed System Behavior &
Simulated Results (Model
Calibration /Verification)
Processed DGPS Survey Data
Yields Observed Ground Levels
(elevation, NAVD, m) Along
Transects
Sum of Time Intervals When Water
is Above Ground Yields: Data Used
in Calculating Hydroperiods @ 6
Points
Ground Levels at Low Points
(Thalwegs) on Each of 26 Slough
MIKE 11 Model Cross Sections
(Perpendicular to Water Flow)
Along Slough.
Processing MIKE 11 Simulator
Output Results Yields: Simulated
Average Wet & Dry Season Water
Levels @ 26 Cross Section
Thalwegs and Time Intervals
Between Ground Crossings
Subtracting Ground Levels from
Observed Average Wet and Dry
Season Water Levels Yields:
Observed Average Wet & Dry
Season Water Depths
Subtracting Ground Crossing Times
Yields:
Observed Hydroperiods
If Water
Depths <
Optimal
Avg Wet
Season
Water
Depths &
Cypress
Present
=> Impact
If Water
Depth >
Optimal
Avg Wet
Season
Water
Depths &
Cypress
Present
=> Impact
Limited Dry
Season Data
Precludes
Impact Eval
If Hydroperiods <
Optimum
=> Impact
Subtracting Thalweg Levels from
Simulated Average Wet and Dry
Season Water Levels Yields:
Simulated Average Wet & Dry
Season Water Depths
Subtracting Below Ground Times
Yields:
Observed Hydroperiods
3.3 Field Investigations and Ecological Impact Assessment.
It is instructive in field investigations to examine aerial photographs of the region under study. Images
illustrating Six Mile Cypress Slough transects, plus transect profiles showing water depth and
vegetation along each transect, and slough profiles showing water depth at the MIKE 11 Simulation
Model thalweg levels and at average cross section elevations are presented in Figures 8-19. Transverse
and longitudinal profiles of the slough are useful in evaluating impact from two perspectives.
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Figure 8 - Six Mile Cypress Slough Preserve Transects
Four 600-700m transects constructed across Six Mile Cypress Slough are shown in Figure 8. The
transects were chosen such that three examples of each of the four major plant communities present in
the slough were evaluated (pine, wet prairie, cypress, and pond), and as many plant communities as
possible were crossed and sampled along each transect. Red triangles are DB Hydro monitoring sites.
A transect is shown schematically in Figure 9. Following PVC pipe installation at ten (10) meter
intervals, the latitude and longitude of each PVC pipe was recorded via a hand-held GPS system.
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Water depth (relative to the water surface) and the height of each PVC pipe above ground were also
recorded. It was anticipated that a small number of differential GPS readings would be obtained at the
top of selected PVC pipes. Instead, Lee County provided extensive, highly accurate differential GPS
elevation and latitude & longitude measurements along all four transects. When tree canopy coverage
prevented DGPS satellite reception, surveyors developed elevation data between DGPS sites using rod
and level surveying techniques to achieve full transect coverage. Vegetation data indicating the
presence or absence of cypress plus 31 other species was collected between PVC pipes.
Figure 9 - Transect Oriented Perpendicular to Slough Water Flow Showing PVC Pipe Placement
An aerial view of Transect 1 (T1) is shown in Figure 10. Data from T1 is presented in Figure 11. Water
depth data suggests that water depths along this transect during the wet season are adequate to support
cypress, but only marginally at the outer edges. It should be noted that where water depth is much
greater than that associated with optimum conditions for cypress, little cypress was observed. This
phenomenon was observed at the edges of the two deep ponds. Wax myrtle was also present in many
locations across the transect, growing both from the ground and elevated on stumps and cypress knees
covered with detritus. This suggests water levels that may periodically be low enough to allow partial
succession to occur. In addition, since fire has been suppressed in the preserve, wax myrtle
concentrations have not been reduced by fire. Oak hammocks were located on elevated portions of T1.
Wet prairie communities adjacent to the cypress/oak communities contained a few small, “hat rack”
cypress that occurred in shallow soils. Time was not available to obtain peat samples, perform cypress
corings required for tree aging, or study herbaceous vegetation in detail.
Transect 3 (T3) is presented in Figure 12 with its associated data in Figure 13. Impact resulting from
lack of wet season water is clearly indicated across significant fractions of the transect bordering the
deep pond located (approximately) 425 meters along the transect. Note also that pine is only present in
the uplands. Cypress is also minimally present along the edges of the deep ponds.
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Figure 10 - Transect 1 Map Showing PVC Locations
Figure 11 - Transect 1 Profile: Vegetation, Ground Elevation, Water Depth, and Impact
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Figure 12 - Transect 3 Map Showing PVC Locations
Figure 13 -Transect 3 Profile: Vegetation, Ground Elevation, Water Depth, and Impact
An aerial view of Transect 6 is shown in Figure 14. Data from the transect is presented in Figure 15.
Areas both east and west of the large pond in T6 appear impacted. Informal observations of cypress
located at these sites indicate they are generally smaller than trees found on wetter sites.
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Figure 14 - Transect 6 Map Showing PVC Locations
Figure 15 - Transect 6 Profile: Vegetation, Ground Elevation, Water Depth, and Impact
An aerial view of Transect 7 is shown in Figure 16 with accompanying data in Figure 17. T7 presents an
16
opportunity to observe the effects of invasive exotic species on a localized cypress community. T7 exists
close to Ten Mile Canal, a canal installed in the 1930’s to remove water from the central portion of Fort
Myers, Florida to prevent flooding along the more populated coastal regions to the west. The canal
intersected Six Mile Cypress Slough and removed significant quantities of water from the southern or
Figure 16 - Transect 7 Map Showing PVC Locations
Figure 17 - Transect 7 Profile: Vegetation, Ground Elevation, Water Depth, and Impact
17
downstream end, lowering the water table, and creating a disturbed ecosystem in the process. Melaleuca
(Melaleuca quinquenervia) invaded the area along with Brazilian Pepper (Schinus terebinthifolius),
much to the detriment of many indigenous species. Wetter, less disturbed portions of the slough have
had modest infestations of these exotics, but the difference in number is apparent even to the casual
observer. Mitigation of this area will begin soon. Examination of T7 via Figure 17 shows impact to
cypress at several locations, but additional impact may be present between 75-125m and 200-300m into
the transect, possibly as a result of the large concentrations of melaleuca found there. Cypress is sparse
in these areas, an area that otherwise might be expected to support more cypress trees.
A profile view of the slough, presented in Figure 18, illustrates potential impact areas along the length of
the slough. Water depth is plotted as a function of distance down the slough. Horizontal lines
representing the limits of optimal water depth for cypress are also plotted. The (brown) ground reference
in this case represents the thalwegs or lowest points in the MIKE 11 Simulation Model cross sections.
These levels constitute a “best case” for cypress, due to the greater depths encountered there. It is
apparent from this figure that portions of the slough north of Penzance Road are impacted. In the upper
half of the graph, the observed average wet season water levels obtained from the SFWMD DB Hydro
database are shown with the simulated average wet season water levels, and the thalweg ground levels.
Numerical comparison of these water levels indicates the validity of the simulation model results.
Figure 18 – Slough Profile: Average Wet Season Water Depths @ Thalwegs & DB Hydro Stations
In order to evaluate potential impact at ground levels more representative of the dominant land levels
found within the surveyed cross sections, average values for cross section ground elevations were used
to calculate average wet season water depth. Elevations obtained in close proximity to highways and
other built structures located along the periphery of the slough were excluded from these calculations.
The results of these calculations are shown in Figure 19. It can be seen from the figure that impact due
to low water levels appears consistent and widespread from Daniels road northward, ranging from no
impact to an average water level 6” below the minimum level for sustaining cypress. This result is one
foot below the median level for optimal cypress growth and suggests that one foot of water be added to
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the slough. Hydroperiods calculated using data obtained from the six monitoring stations along the
slough also indicate impact. These values are shown in Figure 20.
Figure 19 – Slough Water Depths Calculated Using Average Cross Section Ground Elevations
Figure 20 - Six Mile Cypress Slough Preserve Hydroperiods and Average Dry Season Water Depths
Hydroperiods are also presented in Figure 21 as a function of distance along the slough at each of the
DB Hydro surface water monitoring stations and at the corresponding MIKE 11 model cross section
average ground levels. Longer hydroperiods result when cross section average ground levels are lower
than the ground levels at the associated monitoring stations.
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Figure 21 – Hydroperiods at Six DB Hydro Stations & Cross Section Average Ground Levels
4.0 System Simulation
4.1 History
The MIKE SHE/MIKE 11 Tidal Caloosahatchee River Basin (TCRB) Simulation Model used in this
research evolved over a period of years through the efforts of DHI Inc. and the South Florida Water
Management District. This large-scale simulation was needed to provide dynamic boundary conditions
for simulating the smaller-scale Six Mile Cypress Slough. The time frame defined for this study
precluded developing an independent, stand-alone small-scale hydrological model of the slough. It was
necessary to modify elements of the MIKE 11 slough model over the course of the project while the
larger-scale TCRB Model was being modified simultaneously. Reasons for the MIKE 11 modifications
included:
1. Assuring the correctness of dry season water levels. Inserting small slots in the MIKE 11 Model
cross sections allowed water levels to drop below ground level when appropriate. The simulation
algorithm used in calculating channel flow failed to work properly without these slots.
2. Including cross sections representing the four cross-slough transects constructed during the
research plus a new cross section required for increased model accuracy. These cross sections
allow micro-scale investigation of water dynamics across the slough and are useful in verifying
wet and dry season water levels and hydroperiods in specific plant communities located away
from the DB hydro stations.
4.2 Simulation Results
The results of representative simulations are included in the figures below. Examination of the results of
these dynamic simulations suggests that wet season water levels are primarily a function of surface
water inputs from the landscape surrounding the slough. Groundwater also provides a contribution
during the early part of the wet season. Outputs will occur from the slough during the dry season, until
there is little or no standing water in the slough, as groundwater flows into to the adjacent uplands. Lee
County surface water and groundwater data have provided independent verification of these
observations. A plot of water levels along the slough as a function of distance on October 10th, 1999
(end of wet season) is presented in Figure 21. When compared with DB Hydro station data, the values
obtained are, on average, accurate to within 5%. A similar plot for May 12, 1999 during the dry season
is shown in Figure 22. Note: The black line in the figures represents ground (bottom) level. It can be
seen from Figure 22 that the water levels at most locations along the slough are below ground. Useful
results obtained from Six Mile Cypress Slough simulations include the average wet season water levels
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at the 26 cross sections established along the length of the slough. Once the simulated water levels
closely matched the observed levels at the 6 DB Hydro stations, the simulation model could be used to
predict water levels at intermediate locations along the slough. This fact allowed average wet season
water levels to be calculated from simulation data and interpolated between cross section points to any
desired location. This information was critical for ecological impact assessment. Hydroperiods can also
be estimated from these results. Simulation model modifications to further improve overall predictive
accuracy are currently underway. These include the addition of new, essential model cross sections and
improvements in drainage and leakage parameters. Documented gate closing and opening information,
when available, should also prove valuable in improved stage prediction upstream of the Daniels weir.
Figure 22 – Simulation Results: End of Wet Season Water Levels, Six Mile Cypress Slough
Figure 23 – Simulation Results: Dry Season Water Levels in Six Mile Cypress Slough
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Observed water levels at the six DB Hydro surface water monitoring stations, and simulated water levels
at the corresponding MIKE 11 model cross sections are presented in Figures 23 through 28. Ground
levels at the monitoring station locations and average cross section ground levels are also included.
Differences between observed and simulated levels are noted in each figure. Figure 29 shows water
levels as function of time along the four transects that were constructed across the slough. It should be
noted that observed midstream and downstream water levels match simulated levels more closely than
upstream levels. Additional model refinements, including comprehensive DGPS and sonar-array based
ground elevation surveys, and digital signal processing of the resulting data may allow these differences
to be reduced.
Figure 24 – Observed & Simulated Water Levels, Highway 82 DB Hydro Station, 1998-2000
Figure 25 – Observed & Simulated Water Levels, I-75 DB Hydro Station, 1998-2000
Flow (discharge) along Six Mile Cypress Slough Preserve is shown in Figure 31. Note that flow levels
increase downstream in the watershed. The flow at Ten Mile Canal at the height of the wet season is five
cubic meters per second. This increases significantly when the Ten Mile weir gates are opened. Flow
monitoring at additional sites along the slough would be useful in achieving greater modeling accuracy.
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Figure 26 – Observed & Simulated Water Levels, Penzance Road DB Hydro Station, 1998-2000
Figure 27 – Observed & Simulated Water Levels, Daniels Pkwy HeadWtr DB Hydro Station, 1998-2000
Figure 28 – Observed & Simulated Water Levels, Daniels Pkwy TailWtr DB Hydro Station, 1998-2000
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Figure 29 – Observed & Simulated Water Levels, Ten Mile Canal DB Hydro Station, 1998-2000
Figure 30 – Simulated Water Levels, Six Mile Cypress Slough Transects, 1998-2000
Figure 31 – Simulated Flow (Discharge), Six Mile Cypress Slough, 1998-2000
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5.0 Conclusions and Recommendations
5.1 Conclusions
This study has demonstrated that Six Mile Cypress Slough Preserve is ecologically impacted over the
majority of the wetland landscape. Average wet season water depths and hydroperiods exist that are
suboptimal for cypress. The severity of the impact depends on slough topography, local drainage, and
regional development activities.
5.2 Recommendations
It is recommended that:
1. Studies should be undertaken to establish optimal methods for introducing high quality water
into Six Mile Cypress Slough in ways that emulate predevelopment hydropatterns as closely as
possible. Historically, this was accomplished via sheetflow during the wet season. The volume of
water required to raise the water level by one foot is approximately 1 million cubic meters.
Introduction of this volume of water may impact natural systems in the region, including those of
humanity.
2. Improvements in current water monitoring systems should be implemented, including additional
surface water monitoring stations in the slough between Daniels Parkway and Ten Mile Canal,
and deep ground water wells at selected sites within the preserve. Flow monitoring systems
should also be employed periodically at strategic locations along the slough.
3. An engineering survey of the slough should be completed using DGPS and/or sonar/radar
technology. Special attention should be given to precise surveying approaches and establishing
additional hydrological model cross sections, where needed, to achieve a more accurate
representation of the slough ground (bottom) topography. In addition, current geological,
hydrological and soils information should be obtained.
4. Gates (water control structures) associated the system should be fully automated and their
operation controlled to conform to established protocols. Operational data should be recorded.
5. Extensions to the current study should be considered. Objective of these extensions include:
a. Investigating the history of the slough to discover how it came to be impacted
b. Performing ecological research in Six Mile Cypress Slough focused on expanding our
understanding of the dynamic behavior of wetland flora (vegetation & peat studies) and
fauna over multiple scales of space and time, given the increasingly urban environment
surrounding the slough. Educational programs encouraging ecosystem restoration should
be developed in parallel with the scientific endeavors. A Web site should be constructed
to accommodate these efforts.
c. Developing an integrated, long-term ecological, hydrological, and water quality
monitoring program for the slough as a key element of the restoration process and to
assure sustainability.
d. Improving current simulation strategies to accommodate microscale hydrological studies
in Six Mile Cypress Slough.
e. Simulating the effects of land use changes anticipated over the next 50 years
f. Initiating an NSF proposal focusing on regional wetland, coastal, and urban ecosystem
restoration.
g. Publishing the results of this study in refereed scientific journals
h. Communicating the results of the current study to audiences outside the professional
scientific community.
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6.0 Acknowledgements
The authors would like to than the following individuals for their valuable contributions during the
course of this study:
1. Mr. Roger Clark, Lee County Parks & Recreation
2. Mr. Dan Calvert, Lee County Parks & Recreation
3. Mr. Mike Knight, Lee County Parks & Recreation
4. Mr. Clyde Dabbs, SFWMD
5. Dr. Mike Duever, SFWMD
6. Mr. Brian Turcotte, SFWMD
7. Mr. Tim Lieberman, SFWMD
8. Dr. Mike Bauer, SFWMD
9. Ms. Sally McPherson, SFWMD
10. Ms. Pat McGary, SFWMD
11. Mr. Anura Karuna-Muni, Lee County Department of Natural Resources
12. Mr. Allen Davies, Lee County Department of Natural Resources
13. Dr. Zia Hossenipour, DHI Inc.
14. Mr. Roger Copp, DHI Inc.
15. Mr. Peter de Golian, DHI, Inc.
16. Dr. Joseph Hughes, DHI Inc.
17. Ms. Marsha Hosner, DHI Inc.
18. Mr. Charles Kirsty, DHI Inc.
19. Dr. Bill Hammond, FGCU
20. Dr. Edwin Everham, FGCU
21. Ms. Mary Kay Cassani, FGCU
22. Ms. Donna Stremke, FGCU
23. Mr. Tom Roberts, FGCU
24. Mr. Bob Klein, FGCU
25. Ms. Barbara Gray, FGCU
26. Mr. Mark Dehus, FGCU
27. FGCU Student Volunteers
28. Mr. Clark Rhodes
29. Mr. Charles O’Connor, Lee County Schools
30. Ms. Joyce Sanders, Friends of Six Mile
31. Mr. Daryl Thomas, USFWS
32. Dr. Wendy Murray
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Duever, M.J., J.E. Carlson, L.A. Riopelle, and L.C., Duever. 1978. Corkscrew Swamp. In H.T. Odum,
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Odum, H.T. 1971. Environment, Power, and Society. Wiley Interscience, New York.
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Odum, H.T. 1994. Ecological and General Systems. University Press of Colorado, Niwot.
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