Prepared as part of the U.S. Geological Survey Greater Everglades Priority 

Ecosystem Science

Analysis of Changes in Water-Level Dynamics 

at Selected Sites in the Florida Everglades

Scientific Investigations Report 2012–5286

U.S. Department of the Interior

U.S. Geological Survey
Cover photographs. Left: Drillers from the North Carolina Department of Environment and Natural Resources, Division of Water 

Quality, collecting core samples (photograph by Charles G. Pippin, North Carolina Department of Environment and Natural Resources, 

Division of Water Quality). Right: Data-collection platform at well cluster MW-2 at the Allison Woods research station (photograph by 

Joju Abraham, North Carolina Department of Environment and Natural Resources, Division of Water Quality). Background: Well cluster 

MW-4 at the Allison Woods research station (photograph by Joju Abraham).

Cover : Vegetation at the 3A-15 field site

in Water Conservation Area 3A.

Photograph: U.S. Geological Survey, 

June 26, 2002
Analysis of Changes in Water-Level Dynamics at 

Selected Sites in the Florida Everglades

By Paul A. Conrads and Stephen T. Benedict

Prepared as part of the U.S. Geological Survey Greater Everglades Priority 

Ecosystem Science

Scientific Investigations Report 2012–5286

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2013

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Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Conrads, P.A., and Benedict, S.T., 2013, Analysis of changes in water-level dynamics at selected sites in the 

Florida Everglades: U.S. Geological Survey Scientific Investigations Report 2012–5286, 36 p.
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................3

Description of Study Area ...................................................................................................................3

Approach.........................................................................................................................................................3

Cumulative Z-Score..............................................................................................................................5

Site Selection.........................................................................................................................................7

Period of Analysis.................................................................................................................................8

Results of Analysis of Water-Level Data....................................................................................................8

Analysis for Period of Record ............................................................................................................8

Water Conservation Area 1........................................................................................................8

Water Conservation Area 2......................................................................................................11

Water Conservation Area 3......................................................................................................16

Everglades National Park.........................................................................................................18

Analysis of Concurrent Period..........................................................................................................18

Comparison of Time Series Water-Level Data Among Sites .......................................................24

Summary........................................................................................................................................................27

Selected References...................................................................................................................................28

Appendix. Overview of the Z-scores for Everglades Breakpoint Analysis Application...................29

Figures

1. Map showing locations of Water Conservation Areas and National Parks, 

Refuges, and Preserves in the Florida Everglades .................................................................2

2. Vegetation map of southern Florida, circa 1943 ......................................................................4

3. Map showing locations of water-level gages used in this study with 

respect to the Aquatic Cycling of Mercury in the Everglades sites.....................................6

4. Daily water-level data at Site 64 in Water Conservation Area 3A for 

the period April 6, 1962, to December 31, 2011 ........................................................................7

5. Cumulative Z-score curve and daily water-level data and cumulative 

water-level frequency distribution curves for Site 64 in Water 

Conservation Area 3A for the period April 6, 1962, to December 31, 2011 ..........................7

6. Cumulative Z-score curve and daily water-level data and cumulative 

water-level frequency distribution curves for Site 7 in Water 

Conservation Area 1 for the period January 1, 1954, to December 31, 2011.....................10

7. Cumulative Z-score curve and daily water-level data and cumulative 

water-level frequency distribution curves for Site 17 in Water 

Conservation Area 2A for the period June 10, 1952, to December 31, 2011......................13

8. Cumulative Z-score curve and daily water-level data and cumulative 

water-level frequency distribution curves for Site 99 in Water 

Conservation Area 2B for the period July 12, 1991, to December 31, 2011 .......................15
iv

 9. Cumulative Z-score curve and daily water-level data and cumulative 
v

Tables

1. List of ACME sites and corresponding water-level gages used to 

assess historical changes in hydrologic behavior..................................................................8

2. Selected statistics for the cumulative water-level frequency 

distribution curves for selected time periods at Site 7 in Water 

Conservation Area 1 in the Florida Everglades........................................................................9

3. Selected statistics for the cumulative water–level frequency 

distribution curves for selected time periods at Site 17 in Water 

Conservation Area 2A in the Florida Everglades...................................................................12

4. Selected statistics for the cumulative water–level frequency 

distribution curves for selected time periods at Site 99 in Water 

Conservation Area 2B in the Florida Everglades...................................................................14

5. Selected statistics for the cumulative water–level frequency 

distribution curves for selected time periods at Site 3ANE in Water 

Conservation Area 3A in the Florida Everglades...................................................................16

6. Selected statistics for the cumulative water–level frequency 

distribution curves for selected time periods at Site 64 in Water 

Conservation Area 3A in the Florida Everglades...................................................................19

7. Selected statistics for the cumulative water–level frequency 

distribution curves for selected time periods at station P37 in Water 

Conservation Area 3A in the Florida Everglades...................................................................20

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

mile (mi) 1.609 kilometer (km)

square mile (mi2

) 2.590 square kilometer (km2)

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

Vertical coordinate information is referenced to North American Datum of 1988 (NAVD 88) 

or National Geodetic Vertical Datum of 1929 (NGVD 29).

Analysis of Changes in Water-Level Dynamics at Selected 

Sites in the Florida Everglades

By Paul A. Conrads and Stephen T. Benedict

Abstract

The historical modification and regulation of the hydrologic patterns in the Florida Everglades have resulted in 

changes in the ecosystem of South Florida and the Florida 

Everglades. Since the 1970s, substantial focus has been given 

to the restoration of the Everglades ecosystem. The U.S. Geological Survey through its Greater Everglades Priority Ecosystem Science and National Water-Quality Assessment Programs 

has been providing scientific information to resource managers to assist in the Everglades restoration efforts. The current 

investigation included development of a simple method to 

identify and quantify changes in historical hydrologic behavior within the Everglades that could be used by researchers to 

identify responses of ecological communities to those changes. 

Such information then could be used by resource managers 

to develop appropriate water-management practices within 

the Everglades to promote restoration. The identification of 

changes in historical hydrologic behavior within the Everglades was accomplished by analyzing historical time-series 

water-level data from selected gages in the Everglades using 

(1) break-point analysis of cumulative Z-scores to identify 

hydrologic changes and (2) cumulative water-level frequency 

distribution curves to evaluate the magnitude of those changes. 

This analytical technique was applied to six long-term waterlevel gages in the Florida Everglades. The break-point analysis 

for the concurrent period of record (1978–2011) identified 

10 common periods of changes in hydrologic behavior at the 

selected gages. The water-level responses at each gage for 

the 10 periods displayed similarity in fluctuation patterns, 

highlighting the interconnectedness of the Florida Everglades 

hydrologic system. While the patterns were similar, the analysis also showed that larger fluctuations in water levels between 

periods occurred in Water Conservation Areas 2 and 3 in 

contrast to those in Water Conservation Area 1 and the Everglades National Park. Results from the analysis indicate that 

the cumulative Z-score curve, in conjunction with cumulative 

water-level frequency distribution curves, can be a useful tool 

in identifying and quantifying changes in historical hydrologic 

behavior within the Everglades. In addition to the analysis, a 

spreadsheet application was developed to assist in applying 

these techniques to time-series water-level data at gages within 

the Everglades and is included with this report. 

Introduction

From the mid-1800s to the late 1900s, the hydrologic 

conditions of the Florida Everglades (hereinafter, referred to as 

the Everglades) have been substantially altered by the extensive draining of wetlands, diversion of natural flows, and regulation of natural flow patterns (fig. 1). These altered hydrologic patterns have produced commensurate environmental 

effects, such as lowered water tables, saltwater intrusion into 

freshwater aquifers, land subsidence, and altered water quality 

associated with agriculture and urban land-use practices. Of 

particular concern are the shifts in select populations of native 

and non-native plant and animal communities (McPherson 

and others, 1995). Since the 1970s, focus has been given to 

mitigate these adverse effects and, where possible, to begin 

restoration of the ecosystem and ecological communities of 

the Everglades. The U.S. Geological Survey (USGS) through 

its USGS Priority Ecosystem Science Program (http://access.

usgs.gov/, accessed August 25, 2012) and National WaterQuality Assessment (NAWQA) Program (http://water.usgs.

gov/nawqa/, accessed August 25, 2012) has been involved 

in data collection, data management, and field investigations 

within the Everglades, with a primary objective to provide 

scientific information to resource managers to assist in the 

mitigation and restoration process. A description of USGS 

activities in the Everglades can be found at the South Florida 

Information Access Web page: http://sofia.usgs.gov/index.html

(accessed July 9, 2012).

The ecological communities of the Everglades are 

influenced by the current and historical hydrologic conditions. 

Small changes in seasonal and annual water levels can cause 

changes within those communities. The Everglades were originally a precipitation-driven hydrologic system, but the system 

is now heavily regulated. To promote restoration within the 

Everglades, it is important to understand how ecological communities respond to temporal and spatial changes in hydrology 

so that regulatory patterns can be used to promote hydrologic 

conditions that yield favorable responses. One method to 

evaluate the response of ecological communities to changes 

in hydrologic behavior is by review of historical responses. 

If periods of similar hydrologic behavior can be identified in 

historical gage records and associated with responses from 

ecological communities, then insights regarding hydrologic 

conditions that promote favorable or adverse responses 

can be identified and used in restoration efforts. A primary 

task of this investigation was to develop a simple method 

to identify changes in historical hydrologic behavior within 

the Everglades that could be used by researchers to identify 

responses of ecological communities to those changes. 
2 Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades Florida Management

South

boundary

District

Everglades Protection Area

Rotenberger and Holey Land

 Wildlife Management Areas

Stormwater Treatment Areas

Indian Reservation

EXPLANATION

Boundary of Water Conservation 

 Area (WCA)

Lake

Kissimmee

Lake

Okeechobee

Kissimmee River

Caloosahatchee

Florida Bay

River

Florida Panther

National Wildlife

Refuge

Seminole

Miccosukee

Everglades

National

Park

WCA-3A

WCA-2A

WCA-1

ARM

Loxahatchee

National

Wildlife

Refuge

Big

Cypress

National

Preserve

Boynton

Beach

Everglades

agricultural

area

0 10 20 30

N

40 MILES

0 10 20 30 40 KILOMETERS

WCA-2B

WCA-3B

Water

Figure 1. Locations of Water Conservation Areas and National Parks, Refuges, and Preserves in the

Florida Everglades (modified from U.S. Fish and Wildlife Service, 2000).

FLORIDA

Map

area

Figure 1. Locations of Water Conservation Areas and National Parks, Refuges, and Preserves in the 

Florida Everglades (modified from U.S. Fish and Wildlife Service, 2000).
Approach 3

Purpose and Scope

The purpose of this report is to present the techniques and 

results of an investigation that included analyses of historical 

water-level (gage height) dynamics at six sites in the Florida 

Everglades in order to identify changes in historical hydrologic behavior. The geographical extent of the report is 

from Water Conservation Area 1 to the Everglades National 

Park (fig. 1). The analytical techniques included break-point 

analysis associated with cumulative Z-score curves to identify 

changes in hydrologic behavior and cumulative water-level 

frequency distribution curves to quantify those changes. Additionally, this report documents the Z-scores for Everglades 

Breakpoint Analysis (ZEBRA), a spreadsheet application 

developed to assist in applying the analytical techniques used 

in the investigation that also can be used to analyze other 

gages within the Everglades.

An important role of the USGS mission is to provide 

scientific information for the effective management of the 

Nation’s water resources. The techniques presented in this 

report demonstrate how existing databases of continuous timeseries data can be compiled and analyzed to assist researchers 

and resource managers to better understand complex natural 

systems and, therefore, better manage the resources of those 

systems. In particular, these techniques demonstrate how 

break-point analysis with cumulative Z-scores in combination with cumulative frequency distribution curves can be 

used to assess historical changes in a hydrologic system and 

the magnitude of those changes. The techniques are readily 

applicable to other natural systems for evaluation of historical 

time-series data.

Description of Study Area

The Everglades is a vast wetland consisting of approximately 2.9 million acres covering much of southern Florida 

(fig. 1). The Everglades primarily consists of peat soils and tall 

sawgrass that are interspersed with slightly raised tree islands 

covered by shrubs and woody vegetation (fig. 2; McPherson and others, 1995). Historically, the Everglades were an 

uninterrupted wetland that extended from Lake Okeechobee 

and flowed to the southwestern tip of Florida (Richardson 

and others, 1990). During the annual wet season (May or 

June to September or October), water levels would rise and 

inundate most of the land, producing seasonal flows into the 

Florida Bay and the Gulf of Mexico. In contrast, during the 

dry season, water levels declined and were near land surface 

(McPherson and others, 1995). This hydrologic pattern helped 

produce and sustain the unique ecosystem of the Everglades.

From the mid-1800s to the late 1900s, the flow patterns, 

and thus the ecosystem, of the Everglades have been substantially altered. Beginning in the mid-1800s, wetlands began 

to be drained and used for agricultural purposes and urban 

development such that by the early 1990s, about 50 percent 

of the historic Everglades had been drained (McPherson and 

others, 1995). With population growth and increased agricultural production, flood mitigation and water use in South 

Florida became prominent concerns. To address those concerns, Water Conservation Areas (WCAs) 1, 2, and 3 (fig. 1) 

were constructed by the U.S. Army Corps of Engineers in the 

1940s with the goal of regulating water through an extensive 

series of levees and canals. In general, the WCAs store water 

during the wet season and supply water during the dry season. 

The combined effect of drained wetlands and water regulation 

introduced during the 1800s and 1900s diverts an estimated 

40 percent of the water originally flowing through the Everglades (McPherson and others, 1995). The substantial changes 

in land use and flow patterns within the Everglades have had 

adverse environmental effects on the hydrology, water quality, 

and native plant and animal communities (McPherson and others, 1995). Since the late 1900s, through the collaboration of 

Federal, State, and private agencies, substantial focus has been 

given to mitigate these adverse effects and, where possible, to 

begin restoration of the ecosystem and ecological communities 

of the Everglades.

Approach

Correlating the response of ecological communities to 

changes in hydrologic behavior is requisite for evaluating 

best-management practices for water regulation and restoration efforts within the Everglades. The focus of this investigation was to develop a simple method to identify and quantify 

historical hydrologic changes that, in turn, could be used by 

researchers to make such correlations. The primary data source 

for evaluating historical changes in hydrologic behavior within 

the Everglades is the extensive water-level gage networks in 

WCAs 1, 2, and 3, Big Cypress National Preserve, and the 

Everglades National Park (fig. 1) maintained by State and Federal Agencies. Some of the gages have data from as long ago 

as the 1930s. The data from the water-level monitoring sites 

used in this report are part of the Everglades Depth Estimation 

Network (EDEN), a subset of more than 250 water-level gages 

maintained by Big Cypress National Preserve, Everglades 

National Park, South Florida Water Management District, and 

the USGS (Telis, 2006). 

Changes in hydrologic behavior within the Everglades 

can be subtle and difficult to discern within these water-level 

data; therefore, analytical tools must be used to identify such 

changes. A proven technique for identifying subtle changes, 

or break points, in time-series data is the use of the cumulative Z-score curve (Buishand, 1982; Rodionov, 2005; Briceño 

and others, 2010). While there are more rigorous mathematical techniques to investigate changes in time-series data 

(Buishand, 1982; Rodionov, 2005), the cumulative Z-score 

curve provides a simple graphical method in which abrupt 

changes in the slope (break points) of the cumulative curve 

indicate potential changes in the behavior of the system. 

This analytical technique, in conjunction with cumulative 
4 Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades

Base modified from U.S. Geological Survey State base, 1933

Originally printed 1943, 1:400,000

0 10 20 30 40 MILES

0 10 20 30 40 KILOMETERS

FLORIDA GEOLOGICAL SURVEY BULLETIN TWENTY-FIVE—FIGURE 71

EXPLANATION

General vegetation

Scrub forest

Hammock

forest

Bay tree forest

Inland swamp

Cypress forest

Cypress heads

or domes

Pine flatwood

forest

High pine forest

Miami Rockland

pine forest

Miami open

pine forest

Mangrove

swamp

Mangrove

swamp and

saltwater marsh

Saltwater

marsh

Salt Prairie

(Cape Sable area)

Freshwater marsh

(outside of E.)

Wet prairies

Saw palmetto

or Dry Prairies

Southern coast

marsh prairie

Coastal beach 

and dune

vegetation

Saw-grass marsh (medium dense 

to sparse)

Saw-grass marsh

(with wax-myrtle thickets)

Saw-grass marsh

(dense)

Willow and elderberry zone

(mostly cultivated)

Custard-apple zone (mostly cultivated)

Saw-grass marsh 

(with abundant ferns and cattails)

Tree island, bay tree forest

Tree island, hammock forest

Marsh prairie, southern E.

Slough, pond, and lake

(with aquatic plants)

Main Everglades (E.) vegetation

Figure 1. Vegetation map of southern Florida circa 1943 (modified from Davis, 1943). The Arthur R. Marshall Loxahatchee Wildlife 

FLORIDA

Map

area

Figure 2. Figure 2. Vegetation map of southern Florida circa 1943 (modified from Davis, 1943). Vegetation map of southern Florida, circa 1943 (modified from Davis, 1943).
Approach 5

frequency distribution curves (Iman and Conover, 1983), was 

applied to time-series water-level data from selected gages in 

the Everglades in order to identify and quantify changes in 

hydrologic behavior. A spreadsheet application was developed 

to assist in applying the technique and is documented in the 

appendix. A description of this technique and example of its 

application follows. 

Cumulative Z-Score

For a given set of data with n measurements, a Z-score 

(Zi; eq. 1) is the measured value (Xi) minus the mean value 

( ; eq. 2) divided by the standard deviation (s; eq. 3) and 

defines how many standard deviations the measured value is 

above or below the mean (Iman and Conover, 1983). 

 (1)

(2)

 

(3)

The cumulative Z-score curve is determined by calculating a cumulative total of the Z-scores with respect to time 

and represents the cumulative sum of the deviations from the 

mean. Changes in the slope of the cumulative Z-score curve 

indicate that the mean for a subset of the dataset deviates from 

the mean for the period of record and thus indicates a change 

in the behavior, or dynamics, of the time-series data. Positive 

slopes along the cumulative Z-score curve represent a subset 

of the data that has a mean greater than the mean for the 

period of record. Similarly, negative slopes represent a subset 

of the data that has a mean lower than the mean for the period 

of record. Slopes with a value of zero represent a subset of the 

data that has a mean equal to the mean for the period of record 

(Buishand, 1982). 

For example, a 50-year daily water-level time series for 

Site 64 (fig. 3) is shown in figure 4. One can see that there is 

a difference in the hydrologic behavior before and after 1990, 

but changes within these periods are more difficult to discern. 

The Z-score for each day was computed and the cumulative 

Z-score curve plotted (fig. 5A). The cumulative Z-score curve 

shows eight substantial breaks (marked by red vertical lines), 

or changes, in the slope of the line occurring in the following 

years: 1966, 1971, 1977, 1988, 1992, 2000, 2001, and 2006. 

(The small annual changes are due to wet- and dry-season 

water-level differences.) The break points in the cumulative 

Z-score curve are indicative of changes in the hydrologic 

behavior at Site 64 resulting from changes in climatic and 

(or) water regulation patterns. A comparison of the mean 

water level to the time-series water-level data between break 

points (also called periods) in figure 5A demonstrates how 

the slope of the cumulative Z-score curve indicates whether 

the mean water-level data for that period is above, below, or 

near the mean for the period of record. For the period of 1962 

to 1966, the slope of the cumulative Z-score curve is negative, and most of the data for that period are below the mean 

water level. For the period of 1977 to 1988, the slope of the 

cumulative Z-score curve is relatively flat, and the data for that 

period are scattered about the mean water level. For the period 

of 1992 to 2000, the slope of the cumulative Z-score curve 

is positive, and most of the data for that period are above the 

mean water level. 

To evaluate the relative differences of water levels during 

the nine periods identified by the break-point analysis, cumulative water-level frequency distribution curves can be developed for each period (fig. 5B). Selected statistical values, such 

as the mean, standard deviation, 50th percentile, and the average of the 5th to 95th percentiles associated with the cumulative 

frequency distribution curves of figure 5B can be computed 

in order to evaluate the relative change in water level between 

the periods. (Note: The average of the 5th to 95th percentiles 

was calculated by taking percentiles for the data in each period 

in 1-percent increments and then averaging the percentiles 

between 5 and 95, inclusive.) Tabulations of these statistics are 

presented as part of the analysis for each gage.

Z X X s i i = − ( ) /

Z X X s i i = − ( ) /

X X

i n

n

i = =

∑

1

s

X X

i n

n

i = − ∑=1 −

2

1

( )

( )
6 Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades

Figure 3. Locations of water-level gages used in this study with respect to the Aquatic Cycling of Mercury in the

Everglades (ACME) sites.

Lake

Okeechobee

BROWARD

COLLIER

GLADES

HENDRY

MIAMI-DADE

MONROE

PALM

BEACH

Islamorada

Key

Biscayne

Miami

LOX

F1

U3

2BS

3A-33

3A-15

TS-7

TS-9

Site 7

Site 17

Site 99

Site 64

3ANE

P37

WCA-1

BIG CYPRESS

NATIONAL

PRESERVE

EVERGLADES

NATIONAL PARK

WCA-2A

WCA-2B

WCA-3A

WCA-3B

81° 80°30'

26°30'

26°

25°30'

EXPLANATION

Water Conservation Area

(WCA) and identifier

ACME site

Water-level gage

Base From ESRI® Data & Maps, 2008

Albers Equal-Area Conic projection;

Standard parallels 29°30’ N and 45°30’ N

Central meridian –81°00’

GULF OF MEXICO

EVERGLADES

AGRICULTURAL

AREA (EAA)

ATLANTIC OCEAN

WCA-2A

0 5 10 15 20 MILES

0 5 10 15 20 KILOMETERS

TS-7

Figure 3. Locations of water-level gages used in this study with respect to the Aquatic Cycling of Mercury in the 

Everglades (ACME) sites.
Approach 7

4

5

6

7

8

9

10

11

12

13

14

Jan. 1962Jan. 1967Jan. 1972Jan. 1977Jan. 1982Jan. 1987Jan. 1992Jan. 1997Jan. 2002Jan. 2007Jan. 2012

Water level, in feet NGVD 29

Water level (Site 64)

EXPLANATION

Figure 4. Daily water-level data at Site 64 in Water

Conservation Area 3A for the period April 6, 1962,

to December 31, 2011.

Figure 4. Daily water-level data at Site 64 in Water 

Conservation Area 3A for the period April 6, 1962, to 

December 31, 2011.

Site Selection

Long-term water-level gages close to sampling sites for 

the Aquatic Cycling of Mercury in the Everglades (ACME) 

Project were identified for inclusion in the analysis. In 1994, 

a consortium of agencies lead by the USGS began the ACME 

Project to study the factors contributing to high levels of mercury in the Everglades (http://sofia.usgs.gov/projects/index.

php?project_url=evergl_merc, accessed June 25, 2012). The 

overall objective is to understand mercury cycling well enough 

to create management strategies that will minimize bioaccumulation in the Everglades (Krabbenhoft and others, 2000). 

One aspect of the ACME investigation is the assessment of 

how changes in hydrologic behavior may affect the mercury 

cycle within the Everglades. To assist the ACME investigation with this assessment, the current investigation included 

analyses of changes in hydrologic behavior at six long-term 

water-level gages in close proximity to the ACME sampling 

sites (fig. 3; table 1). Sites having longer periods of record 

were given a higher preference in the selection process. Often, 

monitoring stations in the Everglades have been maintained 

under different, although similar, station names. In this report, 

the water-level station names are consistent with those used in 

the EDEN network.

5

6

7

8

9

10

11

12

13

14

Water level, in feet NGVD 29

Period 1 (1962–1966)

Period 2 (1966–1971)

Period 3 (1971–1977)

Period 4 (1977–1988)

Period 5 (1988–1992)

Period 6 (1992–2000)

Period 7 (2000–2001)

Period 8 (2001–2006)

Period 9 (2006–2011)

EXPLANATION

Figure 5. (A) Cumulative Z-score curve and daily waterlevel data and (B) cumulative water-level frequency

distribution curves for Site 64 in Water Conservation

Area 3A for the period April 6, 1962, to December 31, 2011.

B

–4,500

–4,000

–3,500

–3,000

–2,500

–2,000

–1,500

–1,000

–500

0

500

4

5

6

7

8

9

10

11

12

13

14

Jan. 1962Jan. 1967Jan. 1972Jan. 1977Jan. 1982Jan. 1987Jan. 1992Jan. 1997Jan. 2002Jan. 2007Jan. 2012

Cumulative Z-score

Water level, in feet NGVD 29

Cumulative Z-score (Site 64)

Water level (Site 64)

Mean water level

Period Number

EXPLANATION

A

0 10 20 30 40 50 60 70 80 90 100

Cumulative percent

1 2 3 4 5 6 7 8 9

1

Figure 5. (A) Cumulative Z-score curve and daily 

water-level data and (B) cumulative water-level 

frequency distribution curves for Site 64 in Water 

Conservation Area 3A for the period April 6, 1962, 

to December 31, 2011.
8 Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades

Table 1. List of ACME sites and corresponding water-level gages used to assess historical changes in 

hydrologic behavior.

[ACME, Aquatic Cycling of Mercury in the Everglades project; DMS, degrees, minutes, and seconds; WCA, Water Conservation Area; ENP, Everglades National Park]

ACME site 

(see fig. 3 for 

site location)

Basin *Corresponding 

water-level gage

Latitude 

of gage, 

in DMS

Longitude 

of gage, 

in DMS

Period of record for gage

Start date 

(year)

End date 

(year)

LOX WCA-1 Site 7 263111 802049 1954 2011

F1 WCA-2A Site 17 261712 802439 1952 2011

U3 WCA-2A Site 17 261712 802439 1952 2011

2BS WCA-2B Site 99 260821 802202 1991 2011

3A-33 WCA-3A 3ANE 261644 803617 1978 2011

3A-15 WCA-3A Site 64 255832 804009 1962 2011

TS-7 ENP P37 251703 804118 1953 2011

TS-9 ENP P37 251703 804118 1953 2011

*

Often, monitoring stations in the Everglades have been maintained under different, although similar, station names. In this 

report, the station names are consistent with those used in the Everglades Depth Estimation Network (EDEN; Telis, 2006).

Period of Analysis

The selected water-level gages for this investigation 

have periods of record ranging from 21 to 60 years (table 1). 

In order to understand the hydrologic trends at each site, the 

break-point analysis associated with the cumulative Z-score 

curves was applied to each of the six water-level gages for 

the period of record. Additionally, to discern the differences 

and similarities in hydrologic behavior between the selected 

gages, the break-point analysis was applied to each gage 

for a concurrent period of time between October 12, 1978, 

and December 31, 2011. The period of record for Site 99 is 

from July 12, 1991, to December 31, 2011; while this record 

is shorter than that used in the concurrent period analysis 

(October 12, 1978, to December 31, 2011), it was still 

included in that analysis for information.

Results of Analysis of Water-Level 

Data

Data for the selected water-level gages were compiled in 

the spreadsheet application, ZEBRA, in order to develop the 

cumulative Z-score curves for each gage. Each curve for the 

respective water-level gage was reviewed to identify changes 

in the slope (break points) of the cumulative curve indicating potential changes in the hydrologic behavior. Some slope 

break points were more pronounced than others requiring 

judgment in the selection of some of the break points. The 

cumulative Z-score curves for the respective gages often had 

common break points, and where possible, the same break 

points were chosen to allow comparisons between gages. In 

some cases, the slope change in the cumulative Z-score curve 

was less pronounced at a given gage than at the other gages, 

but the same break point was still chosen. The ZEBRA spreadsheet application only allows nine break points; therefore, 

nine or fewer break points were identified for each curve. 

Having identified break points for the cumulative Z-score 

curve for each gage, cumulative frequency distribution curves 

for water level were developed for the time periods between 

the break points. (Note: The break-point dates were entered 

into ZEBRA, and the cumulative frequency distribution 

curves for a given period were automatically generated in the 

spreadsheet.) This process was applied to the water-level data 

at each gage for both the period of record and for the concurrent period of October 12, 1978, to December 31, 2011, and 

results are presented in the following sections.

Analysis for Period of Record 

The cumulative Z-score curves and cumulative frequency 

distribution curves for the period of record associated with the 

water-level gages listed in table 1 are presented in this section 

in upstream to downstream order.

Water Conservation Area 1

Site 7 is located in WCA-1 (fig. 3) and has a 58-year 

period of record from 1954 to 2011 (table 1) with a mean 

water level of 16.12 ft (table 2). For the period of record, 

water levels were lowest during period 6 (1988–1991) with 

a mean of 15.41 ft, and highest during period 7 (1991–2000) 

with a mean of 16.55 ft (fig. 6; table 2). The largest increasing shift in water levels between subsequent periods occurred 

between periods 6 and 7 (1988–1991 and 1991–2000, respectively) with a value of 1.14 ft based on the mean (table 2). The 

largest decreasing shift in water levels between subsequent 

periods occurred between periods 5 and 6 (1982–1988 and 

1988–1991, respectively) with a value of –0.97 ft based on the 

mean (table 2). 
Results of Analysis of Water-Level Data 9

Table 2. Selected statistics for the cumulative water-level frequency distribution curves for selected time periods at Site 7 in Water 

Conservation Area 1 in the Florida Everglades.

[NGVD 29, National Geodetic Vertical Datum of 1929]

Period Start date End date Number of 

observations

Standard 

deviation, 

in feet

Mean, 

in feet 

NGVD 29

50th Percentile water 

level, 

in feet 

NGVD 29

Average 

5th–95th 

percentile 

water level, 

in feet 

NGVD 29

Change from previous period

Mean, 

in feet

50th Percentile water 

level, 

in feet

Average 

5th–95th 

percentile 

water level, 

in feet 

Period of Record—Janurary 1, 1954, to December 31, 2011

1 January 1, 1954 August 1, 1964 3,353 0.50 15.66 15.68 15.66

2 August 1, 1964 June 1, 1970 2,131 0.57 16.20 16.21 16.21 0.54 0.53 0.55

3 June 1, 1970 August 1, 1973 1,158 0.70 15.63 15.70 15.65 –0.57 –0.51 –0.56

4 August 1, 1973 May 1, 1982 3,196 0.44 15.96 15.93 15.96 0.33 0.23 0.31

5 May 1, 1982 March 1, 1988 2,132 0.38 16.38 16.35 16.37 0.42 0.42 0.41

6 March 1, 1988 January 1, 1991 848 0.62 15.41 15.53 15.43 –0.97 –0.83 –0.94

7 January 1, 1991 January 1, 2000 3,220 0.47 16.55 16.51 16.54 1.14 0.99 1.10

8 January 1, 2000 December 31, 2011 4,378 0.47 16.38 16.43 16.39 –0.17 –0.08 –0.15

Record January 1, 1954 December 31, 2011 20,410 0.61 16.12 16.15 16.13

Concurrent Period—October 12, 1978, to December 31, 2011

1 October 12, 1978 December 1, 1980 782 0.46 16.07 15.91 16.06

2 December 1, 1980 June 1, 1982 548 0.33 15.76 15.76 15.75 –0.31 –0.15 –0.30

3 June 1, 1982 November 1, 1988 2,346 0.38 16.34 16.32 16.34 0.58 0.56 0.58

4 November 1, 1988 July 1, 1991 717 0.65 15.34 15.42 15.34 –1.00 –0.90 –0.99

5 July 1, 1991 August 1, 1994 1,128 0.38 16.34 16.33 16.34 1.00 0.91 1.00

6 August 1, 1994 January 1, 1996 519 0.52 16.79 16.80 16.77 0.45 0.47 0.42

7 January 1, 1996 February 1, 2000 1,493 0.44 16.65 16.60 16.64 –0.14 –0.20 –0.12

8 February 1, 2000 August 1, 2001 548 0.49 16.15 16.13 16.14 –0.50 –0.48 –0.50

9 August 1, 2001 March 1, 2004 944 0.35 16.62 16.63 16.62 0.47 0.50 0.48

10 March 1, 2004 December 31, 2011 2,857 0.47 16.34 16.39 16.36 –0.28 –0.24 –0.26

Record October 12, 1978 December 31, 2011 11,873 0.55 16.31 16.35 16.32
10 Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades Water level, in feet NGVD 29

Period 1 (1954–1964)

Period 2 (1964–1970)

Period 3 (1970–1973)

Period 4 (1973–1982)

Period 5 (1982–1988)

Period 6 (1988–1991)

Period 7 (1991–2000)

Period 8 (2000–2011)

EXPLANATION

Figure 6. (A) Cumulative Z-score curve and daily waterlevel data and (B) cumulative water-level frequency

distribution curves for Site 7 in Water Conservation

Area 1 for the period January 1, 1954, to December 31, 2011.

B

EXPLANATION

A

0 10 20 30 40 50 60 70 80 90 100

16

15

17

18

19

20

10

11

12

13

14

Jan. 1952Jan. 1957Jan. 1962Jan. 1967Jan. 1972Jan. 1977

Jan. 1982

Jan. 1987Jan. 1992

Jan. 1997

Jan. 2002Jan. 2007Jan. 2012

Water level, in feet NGVD 29

Cumulative Z-score (Site 7)

Water level (Site 7)

Mean water level (Site 7)

Period number

EXPLANATION

13

14

15

16

17

18

19

Cumulative percent

1

1

2 3 4 5 6 7 8

–4,500

–4,000

–3,500

–3,000

–2,500

–2,000

–1,500

–1,000

–500

0

500

Cumulative Z-score

Figure 6. (A) Cumulative Z-score curve and daily water-level 

data and (B) cumulative water-level frequency distribution 

curves for Site 7 in Water Conservation Area 1 for the period 

January 1, 1954, to December 31, 2011.
Results of Analysis of Water-Level Data 11

Water Conservation Area 2

Site 17 is located in WCA-2A (fig. 3) and has a 60-year 

period of record from 1952 to 2011 (table 1) with a mean 

water level of 12.41 ft (table 3). For the period of record, 

water levels were lowest during period 1 (1952–1957) with 

a mean of 11.31 ft, and highest during period 5 (1975–1980) 

with a mean of 13.59 ft (fig. 7; table 3). The largest increasing shift in water levels between subsequent periods occurred 

between periods 2 and 3 (1957–1962 and 1962–1970, respectively) with a value of 1.51 ft based on the mean (table 3). The 

largest decreasing shift in water levels between subsequent 

periods occurred between periods 5 and 6 (1975–1980 and 

1980–1994, respectively) with a value of –1.79 ft based on 

the mean (table 3). It is interesting to note that Sites 7 and 17 

have a similar period of record (1954–2011 and 1952–2011, 

respectively), but the periods of high and low water levels 

occur at different periods of time.

Site 99 is located in WCA-2B (fig. 3) and has a 21-year 

period of record from 1991–2011 (table 1) with a mean water 

level of 9.84 ft (table 4). For the period of record, water 

levels were lowest during period 1 (1991–1992) with a mean 

of 8.55 ft, and highest during period 3 (1994–1997) with a 

mean of 10.55 ft (fig. 8; table 4). The largest increasing shift 

in water levels between subsequent periods occurred between 

periods 6 and 7 (2006–2008 and 2008–2011, respectively) 

with a value of 1.38 ft based on the mean (table 4). The 

largest decreasing shift in water levels between subsequent 

periods occurred between periods 7 and 8 (2008–2011 and 

January 2011–December 2011, respectively) with a value 

of –1.36 ft based on the mean (table 4). 
12 Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades

Table 3. Selected statistics for the cumulative water-level frequency distribution curves for selected time periods at Site 17 in Water 

Conservation Area 2A in the Florida Everglades.

[NGVD 29, National Geodetic Vertical Datum of 1929]

Period Start date End date Number of 

observations

Standard 

deviation, 

in feet

Mean, 

in feet 

NGVD 29

50th Percentile water 

level, 

in feet 

NGVD 29

Average 

5th–95th 

percentile 

water level, 

in feet 

NGVD 29

Change from previous period

Mean, 

in feet

50th Percentile water 

level, 

in feet

Average 

5th–95th 

percentile 

water level, 

in feet 

Period of Record—June 10, 1952, to December 31, 2011

1 June 10, 1952 May 1, 1957 1,423 0.76 11.31 11.35 11.32

2 May 1, 1957 July 1, 1962 1,740 0.61 11.95 11.81 11.93 0.64 0.46 0.61

3 July 1, 1962 September 1, 1970 2,985 0.77 13.46 13.44 13.45 1.51 1.63 1.52

4 September 1, 1970 February 1, 1975 1,615 0.95 12.57 12.58 12.59 –0.89 –0.86 –0.86

5 February 1, 1975 December 1, 1980 2,131 0.64 13.59 13.59 13.62 1.02 1.01 1.03

6 December 1, 1980 March 1, 1994 4,839 0.75 11.80 11.71 11.80 –1.79 –1.88 –1.81

7 March 1, 1994 April 1, 1996 763 1.08 12.96 12.80 12.92 1.16 1.09 1.12

8 April 1, 1996 December 31, 2011 5,729 0.86 12.24 12.16 12.23 –0.72 –0.64 –0.69

Record June 10, 1952 December 31, 2011 21,218 1.06 12.41 12.29 12.40

Concurrent Period—October 12, 1978, to December 31, 2011

1 October 12, 1978 December 1, 1980 782 0.67 13.80 13.73 13.80

2 December 1, 1980 June 1, 1982 548 0.57 11.61 11.52 11.60 –2.19 –2.21 –2.20

3 June 1, 1982 November 1, 1988 2,346 0.68 11.88 11.72 11.86 0.27 0.21 0.26

4 November 1, 1988 July 1, 1991 973 0.75 11.33 11.41 11.35 –0.55 –0.31 –0.50

5 July 1, 1991 August 1, 1994 1,128 0.67 12.18 12.15 12.17 0.85 0.74 0.82

6 August 1, 1994 January 1, 1996 519 0.92 13.47 13.38 13.47 1.29 1.23 1.29

7 January 1, 1996 February 1, 2000 1,493 0.84 12.35 12.28 12.33 –1.12 –1.10 –1.14

8 February 1, 2000 August 1, 2001 548 0.59 11.86 11.80 11.84 –0.49 –0.48 –0.49

9 August 1, 2001 March 1, 2006 1,674 0.84 12.37 12.21 12.34 0.51 0.41 0.51

10 March 1, 2006 December 31, 2011 2,108 0.89 12.14 12.13 12.15 –0.23 –0.08 –0.20

Record October 12, 1978 December 31, 2011 12,110 0.97 12.21 12.05 12.19
Results of Analysis of Water-Level Data 13

Water level, in feet NGVD 29

Period 1 (1952–1957)

Period 2 (1957–1962)

Period 3 (1962–1970)

Period 4 (1970–1975)

Period 5 (1975–1980)

Period 6 (1980–1994)

Period 7 (1994–1996)

Period 8 (1996–2011)

EXPLANATION

Figure 7. (A) Cumulative Z-score curve and daily waterlevel data and (B) cumulative water-level frequency

distribution curves for Site 17 in Water Conservation

Area 2A for the period June 10, 1952, to December 31, 2011.

B

EXPLANATION

A

0 10 20 30 40 50 60 70 80 90 100

–3,000

–2,000

–1,000

0

1,000

3,000

2,000

4,000

16

18

4

6

8

10

12

14

Jan. 1952Jan. 1957Jan. 1962Jan. 1967Jan. 1972Jan. 1977

Jan. 1982

Jan. 1987Jan. 1992

Jan. 1997

Jan. 2002Jan. 2007Jan. 2012

Cumulative Z-score

Water level, in feet NGVD 29

Cumulative Z-score (Site 17)

Water level (Site 17)

Mean water level (Site 17)

Period number

EXPLANATION

Cumulative percent

8

9

10

11

12

13

14

15

16

1

1

2 3 4 5 6 7 8

Figure 7. (A) Cumulative Z-score curve and daily water-level 

data and (B) cumulative water-level frequency distribution 

curves for Site 17 in Water Conservation Area 2A for the period 

June 10, 1952, to December 31, 2011.
14 Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades

Table 4. Selected statistics for the cumulative water-level frequency distribution curves for selected time periods at Site 99 in Water 

Conservation Area 2B in the Florida Everglades.

[NGVD 29, National Geodetic Vertical Datum of 1929]

Period Start date End date Number of 

observations

Standard 

deviation, 

in feet

Mean, 

in feet 

NGVD 29

50th Percentile water 

level, 

in feet 

NGVD 29

Average 

5th–95th 

percentile 

water level, 

in feet 

NGVD 29

Change from previous period

Mean, 

in feet

50th Percentile water 

level, 

in feet

Average 

5th–95th 

percentile 

water level, 

in feet 

Period of Record—July 12, 1991, to December 31, 2011**

1 July 12, 1991 September 1, 1992 389 1.59 8.55 9.17 8.68

2 September 1, 1992 August 1, 1994 684 0.76 9.86 9.96 9.88 1.31 0.79 1.19

3 August 1, 1994 January 1, 1997 870 0.57 10.55 10.63 10.54 0.69 0.67 0.66

4 January 1, 1997 January 1, 2001 1,399 0.82 10.31 10.58 10.37 –0.24 –0.05 –0.17

5 January 1, 2001 March 1, 2006 1,876 1.26 9.87 10.29 9.98 –0.44 –0.29 –0.39

6 March 1, 2006 August 1, 2008 879 1.39 8.88 9.18 8.98 –0.99 –1.11 –1.00

7 August 1, 2008 January 1, 2011 884 0.81 10.26 10.37 10.33 1.38 1.19 1.35

8 January 1, 2011 December 31, 2011 365 2.07 8.90 9.43 8.99 –1.36 –0.93 –1.35

Record July 12, 1991 December 31, 2011 7,339 1.28 9.84 10.19 9.97

** The period of record for the water-level gage at Site 99 is from July 12, 1991, to December 31, 2011. While this record is shorter than that used in the concurrent 

period analysis (October 12, 1978, to December 31, 2011), it was still included in the analysis for information.
Results of Analysis of Water-Level Data 15

Water level, in feet NGVD 29

Period 1 (1991–1992)

Period 2 (1992–1994)

Period 3 (1994–1997)

Period 4 (1997–2001)

Period 5 (2001–2006)

Period 6 (2006–2008)

Period 7 (2008–2011)

Period 8 (2011–2011)

EXPLANATION

Figure 8. (A) Cumulative Z-score curve and daily waterlevel data and (B) cumulative water-level frequency

distribution curves for Site 99 in Water Conservation

Area 2B for the period July 12, 1991, to December 31, 2011.

B

EXPLANATION

A

0 10 20 30 40 50 60 70 80 90 100

–600

–400

–200

0

2000

400

600

800 16

4

2

6

8

10

12

14

Jan. 1990Jan. 1992Jan. 1994Jan. 1996Jan. 1998

Jan. 2000Jan. 2002Jan. 2004Jan. 2006Jan. 2008

Jan. 2010

Jan. 2012

Cumulative Z-score

Water level, in feet NGVD 29

Cumulative Z-score (Site 99)

Water level (Site 99)

Mean water level (Site 99)

Period number

EXPLANATION

Cumulative percent

5

4

3

6

7

8

9

10

11

12

13

1

1

2 3 4 5 6 7 8

Figure 8. (A) Cumulative Z-score curve and daily water-level 

data and (B) cumulative water-level frequency distribution 

curves for Site 99 in Water Conservation Area 2B for the period 

July 12, 1991, to December 31, 2011.
16 Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades

 Water Conservation Area 3

Water-level gage 3ANE is located in WCA-3A (fig. 3) 

and has a 34-year period of record from 1978–2011 (table 1) 

with a mean water level of 10.59 ft (table 5). The period of 

record (January 1, 1978, to December 31, 2011) and the concurrent period (October 12, 1978, to December 31, 2011) are 

similar, so only the concurrent period of analysis is presented. 

For the concurrent period of record, water levels were lowest during period 4 (1988–1991) with a mean of 8.84 ft, and 

highest during period 6 (1994–1996) with a mean of 12.05 ft 

(fig. 9; table 5). The largest increasing shift in water levels 

between subsequent periods occurred between periods 4 and 5 

(1988–1991 and 1991–1994, respectively) with a value of 

1.98 ft based on the mean (table 5). The largest decreasing 

shift in water levels between subsequent periods occurred 

between periods 3 and 4 (1982–1988 and 1988–1991, respectively) with a value of –1.90 ft based on the mean (table 5).

Site 64 is located in WCA-3A (fig. 3) and has a 50-year 

period of record from 1962 to 2011 (table 1) with a mean 

water level of 9.68 ft (table 6). For the period of record, water 

levels were lowest during period 1 (1962–1966) with a mean 

of 8.63 ft, and highest during period 6 (1992–2000) with a 

mean of 10.49 ft (fig. 5; table 6). The largest increasing shift 

in water levels between subsequent periods occurred between 

periods 5 and 6 (1988–1992 and 1992–2000, respectively) 

with a value of 1.70 ft based on the mean (table 6). The 

largest decreasing shift in water levels between subsequent 

periods occurred between periods 2 and 3 (1966–1971 and 

1971–1977, respectively) with a value of –1.15 ft based on the 

mean (table 6). 

Table 5. Selected statistics for the cumulative water-level frequency distribution curves for selected time periods at Site 3ANE in Water 

Conservation Area 3A in the Florida Everglades.

[NGVD 29, National Geodetic Vertical Datum of 1929]

Period Start date End date Number of 

observations

Standard 

deviation, 

in feet

Mean, 

in feet 

NGVD 29

50th Percentile water 

level, 

in feet 

NGVD 29

Average 

5th–95th 

percentile 

water level, 

in feet 

NGVD 29

Change from previous period

Mean, 

in feet

50th Percentile water 

level, 

in feet

Average 

5th–95th 

percentile 

water level, 

in feet 

Concurrent period—October 12, 1978, to December 31, 2011

1 October 12, 1978 December 1, 1980 729 0.42 10.44 10.54 10.46

2 December 1, 1980 June 1, 1982 370 1.30 9.08 9.57 9.13 –1.36 –0.97 –1.34

3 June 1, 1982 November 1, 1988 2,146 0.66 10.74 10.78 10.77 1.66 1.22 1.64

4 November 1, 1988 July 1, 1991 940 1.30 8.84 9.00 8.86 –1.90 –1.79 –1.91

5 July 1, 1991 August 1, 1994 1,128 0.70 10.82 10.88 10.85 1.98 1.89 1.99

6 August 1, 1994 January 1, 1996 519 0.94 12.05 12.06 12.05 1.23 1.18 1.20

7 January 1, 1996 February 1, 2000 1,493 0.81 10.96 11.06 10.97 –1.09 –1.00 –1.09

8 February 1, 2000 August 1, 2001 466 0.51 10.39 10.47 10.39 –0.57 –0.60 –0.57

9 August 1, 2001 March 1, 2006 1,674 0.72 11.05 10.94 11.05 0.66 0.48 0.66

10 March 1, 2006 December 31, 2011 2,009 0.73 10.48 10.45 10.43 –0.57 –0.49 –0.62

Record October 12, 1978 December 31, 2011 11,465 1.06 10.59 10.67 10.64
Results of Analysis of Water-Level Data 17

Water level, in feet NGVD 29

Period 1 (1978–1980)

Period 2 (1980–1982)

Period 3 (1982–1988)

Period 4 (1988–1991)

Period 5 (1991–1994)

Period 6 (1994–1996)

Period 7 (1996–2000)

Period 8 (2000–2001)

Period 9 (2001–2006)

Period 10 (2006–2011)

EXPLANATION

Figure 9. (A) Cumulative Z-score curve and daily waterlevel data and (B) cumulative water-level frequency

distribution curves for station 3ANE in Water Conservation

Area 3A for the period October 12, 1978, to December 31, 2011.

B

EXPLANATION

A

0 10 20 30 40 50 60 70 80 90 100

–2,500

–2,000

–1,5000

–1,000

–500

0

500 17

5

7

9

11

13

15

Jan. 1977

Jan. 1982Jan. 1987Jan. 1992Jan. 1997Jan. 2002

Jan. 2007

Jan. 2012

Cumulative Z-score

Water level, in feet NGVD 29

Cumulative Z-score (3ANE)

Water level (3ANE)

Mean water level (3ANE)

Period number

EXPLANATION

Cumulative percent

4

6

8

10

12

14

16

1

1

2 3 4 5 6 7 8 9 10

Figure 9. (A) Cumulative Z-score curve and daily water-level 

data and (B) cumulative water-level frequency distribution 

curves for station 3ANE in Water Conservation Area 3A for the 

period October 12, 1978, to December 31, 2011.
18 Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades

Everglades National Park

Water-level gage P37 is located in the Everglades 

National Park (fig. 3) and has a 59-year period of record from 

1953 to 2011 (table 1) with a mean water level of 1.28 ft 

(table 7). For the period of record, water levels were lowest 

during period 2 (1955–1957) with a mean of 0.70 ft, and 

highest during period 3 (1957–1961) with a mean of 1.57 ft 

(fig. 10; table 7). The largest increasing shift in water levels 

between subsequent periods occurred between periods 2 and 

3 (1955–1957 and 1957–1961, respectively) with a value of 

0.87 ft based on the mean (table 7). The largest decreasing 

shift in water levels between subsequent periods occurred 

between periods 1 and 2 (1953–1955 and 1955–1957, respectively) with a value of –0.73 ft based on the mean (table 7). 

Analysis of Concurrent Period

The cumulative Z-score curves and cumulative frequency distribution curves for the concurrent period of record, 

October 12, 1978, to December 31, 2011, associated with 

the water-level gages listed in table 1 are presented in this 

section. Using a concurrent period of record between the six 

gages allows for comparison of water levels in the WCAs and 

Everglades National Park. The period of record for Site 99 

(fig. 3) extends from 1991 to 2011 (table 1), which is shorter 

than the concurrent period of analysis. Therefore, the only 

analysis at this site was for the period of record as presented 

previously in this report (fig. 8; table 4). The period of record 

(January 1, 1978, to December 31, 2011) for water-level gage 

3ANE (fig. 3; table 1) is similar to the concurrent period of 

analysis, October 12, 1978, to December 31, 2011. Therefore, 

it was decided to only analyze the concurrent period of record 

as presented previously in this report (fig. 9; table 5). Plots 

of the cumulative Z-score and daily water-level and cumulative water-level frequency curves for Site 7, Site 17, Site 64, 

and station P37 are shown in figures 11–14, respectively. The 

means, standard deviations, 50th percentiles, and averages of 

the 5th to 95th percentiles associated with the cumulative frequency distribution curves for Site 7, Site 17, station 3ANE, 

Site 64, and station P37 are listed in tables 2, 3, 5, 6, and 7, 

respectively, along with the change in the values of the mean, 

50th percentile, and average of the 5th to 95th percentiles from 

the previous period.
Results of Analysis of Water-Level Data 19

Table 6. Selected statistics for the cumulative water-level frequency distribution curves for selected time periods at Site 64 in Water 

Conservation Area 3A in the Florida Everglades.

[NGVD 29, National Geodetic Vertical Datum of 1929]

Period Start date End date Number of 

observations

Standard 

deviation, 

in feet

Mean, 

in feet 

NGVD 29

50th Percentile water 

level, 

in feet 

NGVD 29

Average 

5th–95th 

percentile 

water level, 

in feet 

NGVD 29

Change from previous period

Mean, 

in feet

50th Percentile water 

level, 

in feet

Average 

5th–95th 

percentile 

water level, 

in feet 

Period of Record—April 6, 1962, to December 31, 2011

1 April 6, 1962 May 1, 1966 1,276 0.78 8.63 8.67 8.68

2 May 1, 1966 January 1, 1971 1,663 0.75 9.92 9.99 9.95 1.29 1.32 1.28

3 January 1, 1971 July 1, 1977 2,289 0.96 8.77 8.74 8.81 –1.15 –1.25 –1.14

4 July 1, 1977 December 1, 1988 4,172 0.73 9.68 9.80 9.72 0.91 1.06 0.91

5 December 1, 1988 January 1, 1992 1,127 0.80 8.79 8.73 8.78 –0.89 –1.07 –0.94

6 January 1, 1992 February 1, 2000 2,901 0.85 10.49 10.49 10.46 1.70 1.76 1.69

7 February 1, 2000 August 1, 2001 546 0.49 9.52 9.42 9.52 –0.97 –1.08 –0.95

8 August 1, 2001 January 1, 2006 1,598 0.79 10.44 10.44 10.45 0.92 1.03 0.93

9 January 1, 2006 December 31, 2011 2,163 0.83 9.89 9.91 9.90 –0.55 –0.53 –0.55

Record April 6, 1962 December 31, 2011 17,727 1.03 9.68 9.74 9.69

Concurrent Period—October 12, 1978, to December 31, 2011

1 October 12, 1978 December 1, 1980 782 0.39 9.90 9.87 9.91

2 December 1, 1980 June 1, 1982 548 0.78 8.99 8.98 8.99 –0.91 –0.89 –0.92

3 June 1, 1982 November 1, 1988 2,346 0.75 9.78 9.94 9.82 0.79 0.96 0.83

4 November 1, 1988 July 1, 1991 973 0.58 8.56 8.61 8.56 –1.22 –1.33 –1.26

5 July 1, 1991 August 1, 1994 1,128 0.56 10.13 10.21 10.15 1.57 1.60 1.60

6 August 1, 1994 January 1, 1996 500 0.94 11.34 11.50 11.36 1.21 1.29 1.20

7 January 1, 1996 February 1, 2000 1,459 0.75 10.44 10.57 10.41 –0.90 –0.93 –0.95

8 February 1, 2000 August 1, 2001 546 0.49 9.52 9.42 9.52 –0.92 –1.16 –0.89

9 August 1, 2001 March 1, 2006 1,657 0.78 10.44 10.43 10.45 0.92 1.02 0.93

10 March 1, 2006 December 31, 2011 2,104 0.84 9.88 9.88 9.88 –0.56 –0.56 –0.56

Record October 12, 1978 December 31, 2011 12,034 0.94 9.93 9.98 9.93
20 Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades

Table 7. Selected statistics for the cumulative water-level frequency distribution curves for selected time periods at station P37 in Water 

Conservation Area 3A in the Florida Everglades.

[NGVD 29, National Geodetic Vertical Datum of 1929]

Period Start date End date Number of 

observations

Standard 

deviation, 

in feet

Mean, 

in feet 

NGVD 29

50th Percentile water 

level, 

in feet 

NGVD 29

Average 

5th–95th 

percentile 

water level, 

in feet 

NGVD 29

Change from previous period

Mean, 

in feet

50th Percentile water 

level, 

in feet

Average 

5th–95th 

percentile 

water level, 

in feet 

Period of Record—January 15, 1953, to December 31, 2011

1 January 15, 1953 January 1, 1955 717 0.51 1.43 1.48 1.48

2 January 1, 1955 June 1, 1957 883 0.77 0.70 0.87 0.74 –0.73 –0.61 –0.74

3 June 1, 1957 January 1, 1961 1,311 0.42 1.57 1.55 1.58 0.87 0.68 0.84

4 January 1, 1961 January 1, 1970 3,288 0.72 1.12 1.23 1.17 –0.45 –0.32 –0.40

5 January 1, 1970 January 1, 1977 2,557 0.77 0.96 1.17 1.03 –0.16 –0.06 –0.14

6 January 1, 1977 January 1, 1989 4,250 0.46 1.34 1.40 1.36 0.38 0.23 0.33

7 January 1, 1989 January 1, 1992 1,096 0.80 0.84 1.05 0.87 –0.50 –0.35 –0.49

8 January 1, 1992 January 1, 2004 4,384 0.49 1.55 1.60 1.57 0.71 0.55 0.70

9 January 1, 2004 December 31, 2011 2,922 0.64 1.39 1.47 1.43 –0.16 –0.13 –0.14

Record January 15, 1953 December 31, 2011 21,400 0.66 1.28 1.38 1.32

Concurrent Period—October 12, 1978, to December 31, 2011

1 October 12, 1978 December 1, 1980 782 0.42 1.37 1.46 1.40

2 December 1, 1980 June 1, 1982 516 0.48 1.20 1.23 1.20 –0.17 –0.23 –0.20

3 June 1, 1982 November 1, 1988 2,244 0.48 1.38 1.45 1.40 0.18 0.22 0.19

4 November 1, 1988 July 1, 1991 973 0.76 0.71 0.97 0.75 –0.67 –0.48 –0.64

5 July 1, 1991 August 1, 1994 1,128 0.41 1.44 1.48 1.46 0.73 0.51 0.71

6 August 1, 1994 January 1, 1996 519 0.37 1.88 1.90 1.88 0.44 0.42 0.42

7 January 1, 1996 February 1, 2000 1,493 0.46 1.61 1.67 1.63 –0.27 –0.23 –0.25

8 February 1, 2000 August 1, 2001 548 0.55 1.20 1.27 1.21 –0.41 –0.40 –0.42

9 August 1, 2001 March 1, 2006 1,674 0.64 1.47 1.57 1.51 0.27 0.30 0.30

10 March 1, 2006 December 31, 2011 2,132 0.59 1.43 1.51 1.47 –0.04 –0.06 –0.04

Record October 12, 1978 December 31, 2011 12,000 0.59 1.39 1.47 1.42
Results of Analysis of Water-Level Data 21

Water level, in feet NGVD 29

Period 1 (1953–1955)

Period 2 (1955–1957)

Period 3 (1957–1961)

Period 4 (1961–1970)

Period 5 (1970–1977)

Period 6 (1977–1989)

Period 7 (1989–1992)

Period 8 (1992–2004)

Period 9 (2004–2011)

EXPLANATION

Figure 10 . (A) Cumulative Z-score curve and daily waterlevel data and (B) cumulative water-level frequency

distribution curves for station P37 in the Everglades National

Park for the period January 15, 1953, to December 31, 2011.

B

EXPLANATION

A

0 10 20 30 40 50 60 70 80 90 100

–3,000

–2,500

–2,000

–1,500

–1,000

–500

0

500 6

–8

–2

–4

–6

0

2

4

Jan. 1952

Jan. 1957Jan. 1962Jan. 1967Jan. 1972Jan. 1977Jan. 1982Jan. 1987Jan. 1992Jan. 1997

Jan. 2002Jan. 2007

Jan. 2012

Cumulative Z-score

Water level, in feet NGVD 29

Cumulative Z-score (P37)

Water level (P37)

Mean water level (P37)

Period number

EXPLANATION

Cumulative percent

–3

–2

–1

0

1

2

3

4

1

1

2 3 4 5 6 7 8 9

Figure 10. (A) Cumulative Z-score curve and daily water-level 

data and (B) cumulative water-level frequency distribution 

curves for station P37 in the Everglades National Park for the 

period January 15, 1953, to December 31, 2011.
22 Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades

Water level, in feet NGVD 29

Period 1 (1978–1980)

Period 2 (1980–1982)

Period 3 (1982–1988)

Period 4 (1988–1991)

Period 5 (1991–1994)

Period 6 (1994–1996)

Period 7 (1996–2000)

Period 8 (2000–2001)

Period 9 (2001–2004)

Period 10 (2004–2011)

EXPLANATION

Figure 11. (A) Cumulative Z-score curve and daily waterlevel data and (B) cumulative water-level frequency

distribution curves for Site 7 in Water Conservation Area 1

for the period October 12, 1978, to December 31, 2011.

B

EXPLANATION

A

0 10 20 30 40 50 60 70 80 90 100

–2,500

–2,000

–1,500

–1,000

–500

0

500 20

8

14

12

10

16

18

Jan. 1978

Jan. 1983Jan. 1988Jan. 1993Jan. 1998

Jan. 2003Jan. 2008

Jan. 2013

Cumulative Z-score

Water level, in feet NGVD 29

Cumulative Z-score (Site 7)

Water level (Site 7)

Mean water level (Site 7)

Period number

EXPLANATION

Cumulative percent

13

14

15

16

17

18

19

1

1

2 3 4 5 6 7 8 9 10

Figure 11. (A) Cumulative Z-score curve and daily 

water-level data and (B) cumulative water-level frequency 

distribution curves for Site 7 in Water Conservation Area 1 

for the period October 12, 1978, to December 31, 2011.

Figure 12. (A) Cumulative Z-score curve and daily 

water-level data and (B) cumulative water-level frequency 

distribution curves for Site 17 in Water Conservation Area 2A 

for the period October 12, 1978, to December 31, 2011.

Water level, in feet NGVD 29

Period 1 (1978–1980)

Period 2 (1980–1982)

Period 3 (1982–1988)

Period 4 (1988–1991)

Period 5 (1991–1994)

Period 6 (1994–1996)

Period 7 (1996–2000)

Period 8 (2000–2001)

Period 9 (2001–2006)

Period 10 (2006–2011)

EXPLANATION

Figure 12 . (A) Cumulative Z-score curve and daily waterlevel data and (B) cumulative water-level frequency

distribution curves for Site 17 in Water Conservation Area 2A

for the period October 12, 1978, to December 31, 2011.

B

EXPLANATION

A

0 10 20 30 40 50 60 70 80 90 100

–1,500

–1,000

–500

0

500

1,000

1,500 16

4

10

8

6

12

14

Jan. 1978

Jan. 1983Jan. 1988Jan. 1993Jan. 1998

Jan. 2003Jan. 2008

Jan. 2013

Cumulative Z-score

Water level, in feet NGVD 29

Cumulative Z-score (Site 17)

Water level (Site 17)

Mean water level (Site 17)

Period number

EXPLANATION

Cumulative percent

8

10

9

11

12

13

14

15

16

1

1

2 3 4 5 6 7 8 9 10
Results of Analysis of Water-Level Data 23

Figure 13. (A) Cumulative Z-score curve and daily waterlevel data and (B) cumulative water-level frequency 

distribution curves for Site 64 in Water Conservation Area 3A 

for the period October 12, 1978, to December 31, 2011.

Water level, in feet NGVD 29

Period 1 (1978–1980)

Period 2 (1980–1982)

Period 3 (1982–1988)

Period 4 (1988–1991)

Period 5 (1991–1994)

Period 6 (1994–1996)

Period 7 (1996–2000)

Period 8 (2000–2001)

Period 9 (2001–2006)

Period 10 (2006–2011)

EXPLANATION

Figure 13 . (A) Cumulative Z-score curve and daily waterlevel data and (B) cumulative water-level frequency

distribution curves for Site 64 in Water Conservation Area 3A

for the period October 12, 1978, to December 31, 2011.

B

EXPLANATION

A

0 10 20 30 40 50 60 70 80 90 100

–3,000

–2,500

–2,000

–1,500

–1,000

–500

0

500 13

6

10

9

8

7

11

12

Jan. 1978

Jan. 1983Jan. 1988Jan. 1993Jan. 1998

Jan. 2003Jan. 2008

Jan. 2013

Cumulative Z-score

Water level, in feet NGVD 29

Cumulative Z-score (Site 64)

Water level (Site 64)

Mean water level (Site 64)

Period number

EXPLANATION

Cumulative percent

5

7

6

8

9

11

10

12

13

14

1

1

2 3 4 5 6 7 8 9 10

Water level, in feet NGVD 29

Period 1 (1978–1980)

Period 2 (1980–1982)

Period 3 (1982–1988)

Period 4 (1988–1991)

Period 5 (1991–1994)

Period 6 (1994–1996)

Period 7 (1996–2000)

Period 8 (2000–2001)

Period 9 (2001–2006)

Period 10 (2006–2011)

EXPLANATION

Figure 14 . (A) Cumulative Z-score curve and daily waterlevel data and (B) cumulative water-level frequency

distribution curves for station P37 in the Everglades National

Park for the period October 12, 1978, to December 31, 2011.

B

Cumulative Z-score

EXPLANATION

A

0 10 20 30 40 50 60 70 80 90 100

–1,600

–1,400

–1,200

–1,000

–800

–600

–400

–200

0

200 6

–3

2

1

0

–2

–1

3

4

5

Jan. 1978

Jan. 1983Jan. 1988Jan. 1993Jan. 1998

Jan. 2003Jan. 2008

Jan. 2013

Water level, in feet NGVD 29

Cumulative Z-score (P37)

Water level (P37)

Mean water level (P37)

Period number

EXPLANATION

Cumulative percent

–2.0

–1.0

–1.5

–0.5

0

1.5

0.5

1.0

2.0

2.5

3.0

3.5

1

1

2 3 4 5 6 7 8 9 10

Figure 14. (A) Cumulative Z-score curve and daily 

water-level data and (B) cumulative water-level 

frequency distribution curves for station P37 in Water 

Conservation Area 3A for the period October 12, 1978, 

to December 31, 2011.
24 Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades

Comparison of Time Series Water-Level Data 

Among Sites

Figure 15A shows the cumulative Z-score curves for the 

six water-level gages for the concurrent period of analysis 

along with the break points used in the analyses (vertical red 

lines). As can be seen, the cumulative Z-score curves have 

similar shape and break points. While the change in the slope 

may be less pronounced in some curves compared to others, 

the general response for all the curves is similar. Because the 

six water-level gages are part of an interconnected system 

within the Everglades, it is reasonable to expect similar 

responses among the gages. The time-series water-level data 

for all gages for the concurrent period of analysis are shown in 

figure 15B along with the same break points from figure 15A. 

The break points provide a visual aid to help identify changes 

within the water-level behavior, in particular some of the more 

subtle changes. While each set of gage data has unique features, the response patterns are similar. It is interesting to note 

that the response patterns of the water level at the northernmost gage, Site 7 in WCA-1, and the southernmost gage, station P37 in the Everglades National Park, although separated 

by approximately 90 miles, are similar. Again, this pattern 

highlights the interconnectedness of the Everglades system. 

To better compare the general patterns between the 

water-level gages during the concurrent period of analysis, 

the average 5th to 95th percentile water levels based on the 

10 periods (periods between break points) associated with the 

cumulative frequency distribution curves (tables 2–7) were 

plotted in several ways. Figure 16 shows the values for the 

average 5th to 95th percentile water levels at five of the gages 

with respect to the 10 periods. (Note: The analysis at Site 99 

was not included in the following comparisons because the 

period of record [1991–2011] did not encompass the concurrent period.) The general patterns between the gages are similar, with the lowest and highest values at each gage occurring 

in periods 4 and 6, respectively. An exception to this occurs at 

Site 17 where the largest water level occurs in period 1. 

While the general shape for each curve is similar, there is 

a larger range in water-level fluctuation at Site 17, station 

3ANE, and Site 64 located in WCAs 2 and 3 (fig. 3), than at 

Site 7 and station P37 located in WCA-1 and the Everglades 

National Park (fig. 3), respectively. 

To more readily compare the trends of the data presented 

in figure 16, it is possible to standardize the average 5th to 

95th percentile water levels to provide a common comparison 

scale. In figure 17, the data were standardized by taking the 

difference between the average 5th to 95th percentile water 

level for each of the 10 periods of analysis and that of the 

full concurrent period (1978–2011). These standardized data 

show the relative difference in water level for the 10 periods with respect to the mean for the full concurrent period 

(1978–2011). The common scale in figure 17 highlights the 

patterns observed in figure 16 including the similarity in 

curve patterns for all the gages, the occurrence of the low and 

high extremes in periods 4 and 6, respectively, and the larger 

variability at Site 17, station 3ANE, and Site 64. It also is 

possible to standardize the data in figure 16 using the Z-score 

(eqs. 1–3). The individual Z-score at a given gage and period 

is computed by taking the average 5th to 95th percentile 

water level for a given period, subtracting the mean of the 

average 5th to 95th percentile water level for the 10 periods, 

and dividing by the standard deviation of the average 5th to 

95th percentile water level for the 10 periods. The Z-score 

values represent the number of standard deviations that the 

average 5th to 95th percentile water level for a given period is 

above or below the mean of the average 5th to 95th percentile 

water level for the 10 periods. (Note: The individual Z-score 

described above should not be confused with the cumulative 

Z-score used in the break-point analysis.) Figure 18 shows the 

Z-scores at each gage for the average 5th to 95th percentile 

water levels for the 10 periods and confirms the general patterns observed in figures 16 and 17 with the exception that the 

larger variabilities at Site 17, station 3ANE, and Site 64 are 

less pronounced. 
Results of Analysis of Water-Level Data 25

Site 7

Site 17

Site 99

3ANE

Site 64

P37

EXPLANATION

Figure 15 . (A) Cumulative Z-score curves and and (B) waterlevel data for selected water-level gages in the Florida

Everglades for the period October 12, 1978, to December 31, 2011.

B

A

–3,000

–2,500

–2,000

–1,500

–1,000

–500

0

500

1,000

1,500

2,000

Cumulative Z-score

–2

2

6

10

14

18

22

Jan. 1978

Jan. 1983Jan. 1988Jan. 1993Jan. 1998

Jan. 2003Jan. 2008

Jan. 2013

Water level, in feet NGVD 29

Figure 15. (A) Cumulative Z-score curves and 

(B) water-level data for selected water-level 

gages in the Florida Everglades for the period 

October 12, 1978, to December 31, 2011.

Site 7

Site 17

3ANE

Site 64

P37

EXPLANATION

Figure 16 . Relation of the average 5th to 95th percentile water

level with respect to the 10 periods of analysis for selected

gages in the Florida Everglades for the period October 12, 1978,

to December 31, 2011.

0

2

4

6

8

10

12

14

16

18

0 1 2 3 4 5 6 7 8 9 10 11

Average 5th to 95th percentile water level,

in feet NGVD 29

Period

Figure 16. Relation of the average 5th to 95th percentile 

water levels with respect to the 10 periods of analysis for 

selected gages in the Florida Everglades for the period 

October 12, 1978, to December 31, 2011.

Site 7

Site 17

3ANE

Site 64

P37

EXPLANATION

0 1 2 3 4 5 6 7 8 9 10 11

Period

–2.0

–1.5

–1.0

–0.5

0

0.5

1.0

1.5

2.0

Difference between the average 5th to 95th percentile

water level for the partial period and the full

concurrent period, in feet 

Figure 17 . Relation of the difference between the average 5th to

95th percentile water level for the 10 periods of analysis and

that of the full concurrent period (1978–2011) for selected gages

in the Florida Everglades.

Figure 17. Relation of the difference between the average 

5th to 95th percentile water level for the 10 periods of 

analysis and that of the full concurrent period (1978–2011) 

for selected gages in the Florida Everglades.
26 Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades

Site 7

Site 17

3ANE

Site 64

P37

EXPLANATION

0 1 2 3 4 5 6 7 8 9 10 11

Period

Figure 18 . Relation of the Z-score for the average 5th to

95th percentile water levels with respect to the 10 periods

of analysis for selected gages in the Florida Everglades.

–2.5

–2.0

–1.5

–1.0

–0.5

0

0.5

1.0

1.5

2.0

2.5

Z-score for the average 5th to

95th percentile water level 

Figure 18. Relation of the Z-score for the average 5th to 

95th percentile water levels with respect to the 10 periods 

of analysis for selected gages in the Florida Everglades.

Figures 19, 20, and 21 respectively show the ranges of 

the water-level fluctuations, the largest water-level increases 

between consecutive periods, and the largest water-level 

decreases between consecutive periods for each gage. These 

figures show the larger variability in water-level fluctuations at 

Site 17, station 3ANE, and Site 64. Figures 20 and 21 indicate 

that the largest increases and decreases in water level between 

consecutive periods occur during the same consecutive periods 

(from period 4 to 5 and from period 3 to 4, respectively) at all 

gages except Site 17, highlighting the similarity in response 

patterns at each gage. The largest increase in water level 

between consecutive periods at Site 17 occurs from periods 5 

to 6, which is close chronologically to the consecutive periods, 

from period 4 to 5, in which the other gages display the largest 

increase. The largest decrease in water level between consecutive periods at Site 17 occurs from period 1 to 2 and is caused 

by the unusually high water levels at the beginning of period 1 

(fig. 12A). 

Figure 19 . Range of water-level fluctuation based on the average

5th to 95th percentile water levels for the 10 periods of analysis

at selected gages in the Florida Everglades.

Site 7 Site 17 3ANE Site 64 P37

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Range in the average 5th to 95th percentile

water level, in feet

Figure 19. Range of water-level fluctuation based on the 

average 5th to 95th percentile water levels for the 10 periods 

of analysis at selected gages in the Florida Everglades.

Figure 20 . Largest increase in water-level between consecutive

periods based on the average 5th to 95th percentile water

levels for the 10 periods of analysis at selected gages in the

Florida Everglades.

0

0.5

1.0

1.5

2.0

2.5

Largest increase in the average 5th to 95th percentile water

level between consecutive periods, in feet

From

Period 4 to 5

From

Period 5 to 6

From

Period 4 to 5

From

Period 4 to 5

From

Period 4 to 5

Site 7 Site 17 3ANE Site 64 P37

Figure 20. Largest increase in water level between 

consecutive periods based on the average 5th to 

95th percentile water levels for the 10 periods of analysis 

at selected gages in the Florida Everglades.
Summary 27

Figure 21 . Largest decrease in water-level between consecutive

periods based on the average 5th to 95th percentile water

levels for the 10 periods of analysis at selected gages in the

Florida Everglades.

Largest decrease in the average 5th to 95th percentile

water level between consecutive periods, in feet

From

Period 3 to 4

From

Period 1 to 2

From

Period 3 to 4

From

Period 3 to 4

From

Period 3 to 4

–2.5

–2.0

–1.5

–1.0

–0.5

0

Site 7 Site 17 3ANE Site 64 P37

Figure 21. Largest decrease in water level between 

consecutive periods based on the average 5th to 

95th percentile water levels for the 10 periods of analysis 

at selected gages in the Florida Everglades.

Summary

The U.S. Geological Survey, through its Greater 

Everglades Priority Ecosystem Science and National WaterQuality Assessment Programs, has been involved in data 

collection, data management, and field investigations within 

the Florida Everglades with a primary objective of providing scientific information to assist resource managers in 

the Everglades restoration efforts. A primary task of the 

current investigation was to develop a simple method to 

identify changes in historical hydrologic behavior within 

the Everglades that could be used by researchers to identify 

responses of ecological communities to those changes. Such 

information could in turn be used by resource managers to 

develop appropriate water-management practices within the 

Everglades to promote the restoration and health of the Everglades ecosystem. The identification of historical hydrologic 

behavior within the Everglades was accomplished by analyzing historical time-series water-level data from selected gages 

in the Everglades using (1) break-point analysis of cumulative Z-scores to identify changes in hydrologic behavior and 

(2) cumulative water-level frequency distribution curves to 

evaluate the magnitude of those changes. This analytical 

technique was applied to six long-term water-level gages 

in the Florida Everglades located near the U.S. Geological 

Survey Aquatic Cycling of Mercury in the Everglades Project 

sampling sites so that results from the investigation could be 

used to support the research efforts in those areas. The cumulative Z-score analysis was applied for the period of record 

at each individual gage as well as for the concurrent period 

of October 12, 1978, to December 31, 2011. The break-point 

analysis for the concurrent period of record (1978–2011) identified 10 common periods of changes in hydrologic behavior 

at the selected gages. The water-level responses at each gage 

for the 10 periods displayed similarity in fluctuation patterns, 

highlighting the interconnectedness of the Florida Everglades 

hydrologic system. While the patterns were similar, the 

analysis also showed that larger fluctuations in water levels 

occur in Water Conservation Areas 2 and 3 in contrast to those 

in Water Conservation Area 1 and the Everglades National 

Park. Results from the analysis indicate that the cumulative 

Z-score curve in conjunction with cumulative water-level 

frequency distribution curves can be a useful tool in identifying and quantifying changes in historical hydrologic behavior 

within the Everglades. In addition to the analysis, a spreadsheet application, the Z-scores for Everglades Breakpoint 

Analysis (ZEBRA), was developed to assist in applying these 

techniques to time-series water-level data at other gages within 

the Everglades.
28 Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades

Selected References

Briceño, H.O., Boyer, J.N., and Harlem, P.W., 2010, Proposed 

methodology for the assessment of numeric nutrient criteria 

for South Florida estuaries and coastal waters, Report to the 

National Park Service, Everglades National Park, Cooperative Agreement Number: H5000-06-0104, 44 p.

Buishand, T.A., 1982, Some methods for testing the homogeneity of rainfall records: Journal of Hydrology, v. 58, 

no. 1–2, p. 11–27.

Davis, J.H., Jr., 1943, Vegetation map of Southern Florida: 

Florida Geological Survey, Bulletin 25, figure 71, 1 sheet, 

1:400,000 scale.

Florida Department of Environmental Protection, 2011, Mercury in aquatic ecosystems in Florida, accessed June 25, 

2012, at http://www.dep.state.fl.us/water/sas/mercury/index.

htm.

Iman, R.L., and Conover, W.J., 1983, A modern approach to 

statistics: John Wiley and Sons, Inc., 497 p.

Krabbenhoft, D.P., Gilmour, C.C., Orem, W.H., Aiken, G.R., 

Kendall, Carol, Olsen, M.L., and DeWild, John, 2000, 

Aquatic Cycling of Mercury in the Everglades (ACME) 

Project—Synopis of Phase I Studies and Plans for Phase 

II Studies, in Eggleston, J.R., Embry, T.L., Mooney, R.H., 

Wedderburn, Leslie, Goodwin, C.R., Henkel, H.S., Pegram, 

K.M.H., and Enright, T.J., 2001, Presentations made at 

the Greater Everglades Ecosystem Restoration (GEER) 

Conference, December 11–15, 2000, Naples, Florida: U.S. 

Geological Survey Open-File Report 00-449, p. 62–63.

McPherson, B.F., Higer, A.L., Gerould, S., and Kantrowitz, 

I.H., 1995, South Florida Ecosystem Program of the U.S. 

Geological Survey: U.S. Geological Survey Fact Sheet 

FS-134-95, accessed June 19, 2012, at http://sofia.usgs.gov/

publications/fs/134-95/index.html.

Richardson, J.R., Bryant, W.L., Kitchens, W.M., Mattson, J.E., 

and Pope, K.R., 1990, An evaluation of the refuge habitats 

and relationships to water quality, quantity, and hydroperiods—A synthesis report: Gainesville, Fla., Florida Cooperative Fish and Wildlife Research Unit, University of Florida.

Rodionov, S.N., 2005, A brief overview of the regime shift 

detection methods, in Velikova, V., and Chipev, N., eds.,

Large-scale disturbances (regime shifts) and recovery 

in aquatic ecosystems—Challenges for management 

toward sustainability: Varna, Bulgaria, June 14–16, 2005, 

UNESCO-ROSTE/BAS Workshop on Regime Shifts, 

p. 17–24.

South Florida Water Management District, 2011, DBHYDRO 

Browser user documentation, accessed July 9, 2012, at 

http://www.sfwmd.gov/portal/page/portal/xweb%20environmental%20monitoring/dbhydro%20application.

Telis, P.A., 2006, The Everglades Depth Estimation Network 

(EDEN) for support of ecological and biological assessments: U.S. Geological Survey Fact Sheet 2006-3087, 4 p.

U.S. Fish and Wildlife Service, 2000, Arthur R. Marshall 

Loxahatchee National Wildlife Refuge Comprehensive 

Conservation Plan, accessed September 13, 2010, at http://

loxahatchee.fws.gov.
Appendix. Overview of the Z-Scores for Everglades Breakpoint 

Analysis Application

Figures

Screen captures showing—

1-1. ZEBRA title sheet..................................................................................................................31

1-2. ZEBRA worksheet showing water-level data for selected gages ...............................33

1-3. ZEBRA worksheet showing computation tables or the cumulative Z-score 

and cumulative water-level frequency distribution curves.........................................34

1-4. ZEBRA worksheet for selecting break points for the cumulative Z-score 

curve and plots of the cumulative water-level frequency distribution curves 

for the periods between the selected break points.......................................................35

1-5. ZEBRA worksheet for tabulation of basic statistics for each cumulative 

water-level frequency distribution curve........................................................................36

Table

1−1. Description of worksheets and applications included in ZEBRA.......................................32
30 Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades
Appendix 31

Appendix. Overview of the Z-Scores for Everglades Breakpoint 

Analysis Application

A break-point analysis using the cumulative Z-score and 

cumulative frequency distribution curves, as briefly described 

in the body of this report, is a simple technique to apply to 

a given dataset. However, the application can become challenging for large datasets, such as daily average water-level 

data associated with gages in the Everglades that often have 

long periods of record extending over decades. To minimize 

this difficulty, a spreadsheet application called the Z-scores 

for Everglades Breakpoint Analysis (ZEBRA) (fig. 1–1), was 

developed to assist in applying the analytical techniques. 

ZEBRA provides a means to (1) store selected water-level 

data, (2) compute the cumulative Z-score for the selected 

data, (3) plot the selected cumulative Z-score curve so that 

break points can be visually identified, and (4) manually enter 

break-point data that will be used to automatically generate 

the cumulative water-level frequency distribution curves. 

The worksheets that compose ZEBRA are listed in table 1–1. 

A brief description of ZEBRA follows.

Figure 1-1. Screen capture of ZEBRA title sheet. Figure 1-1. Screen capture of ZEBRA title sheet.
32 Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades

Table 1−1. Description of worksheets and applications included in ZEBRA.

[ZEBRA, Z-scores for Everglades Breakpoint Analysis]

Worksheet Name Description

Title Sheet Title sheet for ZEBRA.

ReleaseNotes Selected information associated with ZEBRA and a description of each 

worksheet.

TABLE Basic statistics for each cumulative water-level frequency distribution 

curve are automatically calculated and tabulated. 

BREAK POINTS Graphs displaying the water-level, cumulative Z-score curve, and the 

cumulative water-level frequency distribution curves for the gage of 

interest. The user can enter selected break points into the break-point 

table, and the cumulative water-level frequency distribution curves will 

be automatically computed and plotted. (Note: Dropdown menus allow 

the user to select the gage of interest for display.) 

COMPUTATIONS Computations for the cumulative Z-score curve and the cumulative waterlevel frequency distribution curves are made on this sheet. Data from 

this worksheet are used in the spreadsheet graphs.

WATER-LEVEL 

DATA

Tabulation of water-level data at selected gages in the Florida Everglades.

Cum Z-Score 

Curve

Full graph of cumulative Z-score curve, water-level data, and break points 

for the selected gage.

Freq Curve Full graph of cumulative water-level frequency distribution curves for the 

selected gage.
Appendix 33

Water-Level Data and Computation 

of Cumulative Z-Scores and Frequency 

Distribution Curves

The DBHYDRO database (South Florida Water Management District: http://www.sfwmd.gov/portal/page/portal/

xweb%20environmental%20monitoring/dbhydro%20application, accessed July 9, 2012) is the hydrometeorologic, 

water-quality, and hydrogeologic data retrieval system for the 

South Florida Water Management District. The database is 

maintained through a cooperative effort of various agencies 

including the U.S. Geological Survey, Everglades National 

Park, the U.S. Army Corps of Engineers, Lake Worth Drainage 

District, and the U.S. Department of Agriculture and includes 

more than 30,000 station-years of data, collected at more than 

6,000 stations (South Florida Water Management District, 

2011). Water-level data for gages in the Florida Everglades 

can be queried and retrieved through the DBHYDRO Browser 

located at the previously mentioned Web page. The data can 

be downloaded in a spreadsheet format allowing the transfer 

of the data into ZEBRA through a simple “copy and paste” 

command. The water-level data at a given gage in DBHYDRO 

is often broken into several records that must be manually 

combined in order to obtain a complete record. In some cases, 

there may be overlap and slight differences between the 

broken records, and judgment must be applied to decide which 

data to use in compiling the complete record. Once a complete 

water-level data record is compiled for a gage of interest, the 

data can be copied into ZEBRA. Figure 1–2 shows a screen 

capture of the ZEBRA worksheet “WATER-LEVEL DATA,” 

which contains the water-level data for the gages analyzed in 

this report. Dates corresponding with the water-level data are 

in the first column of the worksheet, and the water-level data 

are entered to correspond with those dates. The header cells 

above the water-level data provide information on the gage 

location, the period of record, and basic statistics associated 

with the dataset. 

Figure 1-2. Screen capture of ZEBRA worksheet showing water-level data for selected gages. Figure 1-2. Screen capture of ZEBRA worksheet showing water-level data for selected gages.
34 Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades

Figure 1–3 shows a screen capture of the ZEBRA worksheet “COMPUTATIONS,” which computes the cumulative 

Z-score and cumulative water-level frequency distribution 

curves for the gage of interest. The header cells above the 

frequency distribution curves provide information about the 

period of analysis between break points and basic statistics 

associated with each of the periods. The gage of interest 

can be selected from the dropdown menu near the upper left 

corner of the worksheet, and the gage data and user-defined 

break points for the selected gage will be automatically 

retrieved from the “WATER-LEVEL DATA” and “BREAK 

POINTS” worksheets, respectively. The cumulative Z-score 

and cumulative water-level frequency distribution curves 

are then automatically computed. Data contained in the 

COMPUTATIONS worksheet are used to produce the graphs 

found in ZEBRA. 

Figure 1-3. Screen capture of ZEBRA worksheet showing computation tables for the cumulative Z-score and cumulative

water-level frequency distribution curves.

Figure 1-3. Screen capture of ZEBRA worksheet showing computation tables for the cumulative Z-score and cumulative 

water-level frequency distribution curves.
Appendix 35

Selection of Break Points for the Cumulative 

Z-Score Curve

Figure 1–4 shows a screen capture of the ZEBRA worksheet “BREAK POINTS.” This worksheet allows the user to 

visually identify and manually enter break points for a given 

cumulative Z-score curve that in turn are used to develop the 

cumulative water-level frequency distribution curves for the 

gage of interest. The gage of interest can be selected from 

the dropdown menu near the upper left corner of the worksheet. (Note: The dropdown menu on this worksheet is linked 

to the dropdown menu on the “COMPUTATIONS” worksheet.) The water-level data and cumulative Z-score curves 

for the selected gage are automatically plotted on the graph 

at the bottom right of this worksheet (fig. 1–4), allowing the 

user to visually identify break points where the slope of the 

cumulative Z-score curve changes. The dates associated with 

these break points can then be entered into the Break-Point 

Table located near the top of the worksheet. The column in 

the Break-Point Table associated with the selected gage is 

highlighted in green indicating where the break-point dates 

should be entered. ZEBRA can accommodate a maximum of 

nine break points. These break points are automatically plotted as red vertical lines on the cumulative Z-score curve. The 

cumulative water-level frequency distribution curves for the 

periods between the selected break points are automatically 

computed on the “COMPUTATIONS” worksheet and plotted on the graph located on the bottom left of the “BREAK 

POINTS” worksheet (fig. 1–4). 

Figure 1-4. Screen capture of ZEBRA worksheet showing computation tables for selecting break points for the

cumulative Z-score curve and plots of the cumulative water-level frequency distribution curves for the periods

between the selected break points.

Figure 1-4. Screen capture showing ZEBRA worksheet for selecting break points for the cumulative Z-score curve and 

plots of the cumulative water-level frequency distribution curves for the periods between the selected break points.
36 Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades

Basic statistics for each cumulative water-level frequency 

distribution curve are automatically calculated and tabulated 

on the “TABLE” worksheet (fig. 1–5). Additionally, the start 

and end dates for the periods between the selected break 

points along with the number of days within the period and 

the percentage of available data in that period are tabulated in 

the Frequency Curve Periods table in the upper right corner 

of the “BREAK POINTS” worksheet (fig. 1–4). A larger 

plot of the two graphs shown at the bottom of the “BREAK 

POINTS” worksheet can be viewed on the worksheets labeled 

“Cum Z-Score Curve” and “Freq Curve.” 

Using ZEBRA with Other Data

It is possible to use ZEBRA to analyze water-level data 

at other gages in the Everglades; however, caution must be 

used to not exceed the cell ranges built into the spreadsheet 

algorithms. To analyze data at another gage, the existing data 

in the spreadsheet can be overwritten. The cell ranges used to 

store the existing data should not be exceeded by the new data, 

however, and the new data must be entered in the appropriate cell to correspond with the dates in the first column of the 

“WATER-LEVEL DATA” worksheet. Additionally, the identification data in the column headers of the “WATER-LEVEL 

DATA” worksheet must be changed to reflect the new gage.

Figure 1-5. Screen capture of ZEBRA worksheet for tabulation of basic statistics for each cumulative water-level

frequency distribution curve.

Figure 1-5. Screen capture showing ZEBRA worksheet for tabulation of basic statistics for each cumulative water-level 

frequency distribution curve.

For additional information regarding this 

publication, contact:

Director

USGS South Carolina Water Science Center

Stephenson Center, Suite 129

720 Gracern Road

Columbia, SC 29210-7651

(803) 750-6181

email: dc_sc@usgs.gov

Or visit the USGS South Carolina Water 

Science Center Web site at:

 http://sc.water.usgs.gov

Prepared by:

USGS Science Publishing Network

Raleigh Publishing Service Center

3916 Sunset Ridge Road

Raleigh, NC 27607

Conrads and Benedict—Analysis of Changes in Water-Level Dynamics at Selected Sites in the Florida Everglades—Scientific Investigations Report 2012–5286