Water Budget and Water Quality of Ward Lake,

Flow and Water-Quality Characteristics of the

Braden River Estuary, and the Effects of

Ward Lake on the Hydrologic System,

West-Central Florida

Prepared in cooperation with the

CITY OF BRADENTON PUBLIC WORKS DEPARTMENT,

MANATEE COUNTY ENVIRONMENTAL MANAGEMENT DEPARTMENT,

and the SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 98-4251
Cover photo:

Photograph by B.R. Lewelling

Ward Lake outfall and gaging station
Water Budget and Water Quality of Ward Lake, Flow and

Water-Quality Characteristics of the Braden River

Estuary, and the Effects of Ward Lake on the Hydrologic

System, West-Central Florida

By J.T. Trommer, M.J. DelCharco, and B.R. Lewelling

U.S. Geological Survey

Water-Resources Investigations Report 98-4251

Prepared in cooperation with the

CITY OF BRADENTON PUBLIC WORKS DEPARTMENT

MANATEE COUNTY ENVIRONMENTAL MANAGEMENT DEPARTMENT

SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT

Tallahassee, Florida

1999
U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

Any use of trade, product, or firm names in this publication is for descriptive purposes only

and does not imply endorsement by the U.S. Geological Survey.

For additional information Copies of this report can be

write to: purchased from:

District Chief U.S. Geological Survey

U.S. Geological Survey Branch of Information Services

Suite 3015 Box 25286

227 N. Bronough Street Denver, CO 80225

Tallahassee, FL 32301 800-ASK-USGS
Contents III

CONTENTS

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

Introduction................................................................................................................................................................................ 2

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

Acknowledgments ........................................................................................................................................................... 3

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

Data Collection .......................................................................................................................................................................... 5

Water Budget for Ward Lake ..................................................................................................................................................... 9

Inflow ............................................................................................................................................................................. 10

Outflow........................................................................................................................................................................... 11

Budget Summary............................................................................................................................................................ 12

Water Quality ........................................................................................................................................................................... 13

Braden River near Lorraine............................................................................................................................................ 13

Tributaries to Ward Lake................................................................................................................................................ 16

Ward Lake Outfall.......................................................................................................................................................... 19

Constituent Load ............................................................................................................................................................ 22

Characteristics of the Braden River Estuary............................................................................................................................ 23

Inflows............................................................................................................................................................................ 23

Tidal Fluctuations........................................................................................................................................................... 23

Salinity .......................................................................................................................................................................... 24

Water Quality in the Tributaries that Drain to the Braden River Estuary ...................................................................... 28

Effects of the Reservoir on the Hydrologic System................................................................................................................. 29

Summary and Conclusions ...................................................................................................................................................... 30

Selected References ................................................................................................................................................................. 33

Figures

1-3. Maps showing:

1. Location of the study area in west-central Florida and the drainage area for the Braden River .............................. 2

2. Configuration of Ward Lake prior to 1985 and at present........................................................................................ 4

3. Ward Lake drainage basin and data-collection network........................................................................................... 6

4. Schematic of ground-water flow in the surficial aquifer system at the Linger Lodge, Lakewood Ranch,

and Lorraine Road well transects..................................................................................................................................... 8

5. Conceptual model of the cross-sectional flow nets used to calculate ground-water flow to Ward Lake......................... 9

6-8. Trilinear diagrams showing major cation and anion equivalent concentration percentages of:

6. Surface water at the Braden River near the Lorraine station and ground water at the Lorraine Road and

Lakewood Ranch surficial aquifer system well transects, and from the intermediate aquifer system and

the Upper Floridan aquifer ..................................................................................................................................... 15

7. Surface water from the tributaries to Ward Lake, and of ground water from the intermediate aquifer system

and the Upper Floridan aquifer .............................................................................................................................. 19

8. Water from Ward Lake, from the surficial aquifer system at the Linger Lodge well transect, and from the

intermediate aquifer system and the Upper Floridan aquifer................................................................................. 21

9-11. Graphs showing:

9. Duration curves of specific conductance at the Braden River near Elwood Park and the Braden River near

Bradenton stations .................................................................................................................................................. 25

10. Salinity profiles of the Braden River estuary.......................................................................................................... 26

11. Comparison of instantaneous discharge at the Ward Lake outfall with specific conductance at the Braden

River near Elwood Park and the Braden River near Bradenton stations, October 28 to November 20, 1995....... 27
IV Contents

Tables

1. Braden River streamflow station network ...........................................................................................................................7

2. Ground-water transect wells................................................................................................................................................7

3. Annual rainfall at the Bradenton 5 ESE and Verna FL41 weather stations and annual sum of weekly rainfall

averages used in the water budget for water years 1993-97..............................................................................................10

4. Surface-water inflow to Ward Lake, water years 1993-97 ................................................................................................11

5. Estimated water-budget for Ward Lake, water years 1993-97 ..........................................................................................11

6. Statistical summary of selected water-quality data from the Braden River near the Lorraine station and from

the surficial aquifer system at the Lakewood Ranch and Lorraine Road transect sites.....................................................14

7. Statistical summary of selected water-quality data from the tributaries draining into Ward Lake ...................................17

8. Statistical summary of selected water-quality data from Ward Lake and from the surficial aquifer system

transect site near Linger Lodge..........................................................................................................................................20

9. Estimated loads of selected chemical constituents to Ward Lake and to the Braden River estuary,

water years 1993-97...........................................................................................................................................................22

10. Statistical summary of selected water-quality data from the tributaries draining to the Braden River estuary,

water years 1995-97...........................................................................................................................................................28

CONVERSION FACTORS, VERTICAL DATUM, AND ADDITIONAL ABBREVIATIONS

Temperature can be converted between degrees Fahrenheit (o

F) and degrees celsius (oC) as follows: o

F = 9/5 (oC + 32) o

C = 5/9 (oF – 32)

Sea level: In this report “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)—a geodetic datum

derived from a general adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level

Datum of 1929.

Multiply inch-pound unit By To obtain

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

cubic foot per day (ft3/d) 0.02832 cubic meter per day

foot per mile (ft/mi) 0.1894 meter per kilometer

foot (ft) 0.3048 meter

foot squared (ft2

) 0.0929 square meter

foot per second (ft/s) 0.3048 meter per second

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

inch (in.) 25.40 millimeter

inch per day (in/d) 25.40 millimeter per day

inch per year (in/yr) 25.40 millimeter per year

mile (mi) 1.609 kilometer

million gallons (Mgal) 3,785 cubic meter

million gallons per day (Mgal/d) 0.43816 cubic meter per second

square mile (mi2

) 2.590 square kilometer

ton, short 0.9072 megagram

ton per year, (ton/yr) 0.9072 megagram per year
Contents V

ABBREVIATED WATER-QUALITY UNITS

mg/L = milligram per liter

(mg/L)/yr = milligram per liter per year

ppt = parts per thousand

μS/cm = microsiemens per centimeter at 25 degrees Celsius

(μS/cm)/yr = microsiemens per centimeter per year

ADDITIONAL ABBREVIATIONS

CCI = Conservation Consultants Inc.

FDEP = Florida Department of Environmental Protection

GCREC = Gulf Coast Research and Education Center

IFAS = Institute of Food and Agricultural Sciences

NADP/NTN = National Atmospheric Deposition Program/National Trends Network

NOAA = National Oceanic and Atmospheric Administration

ROMP = Regional Observation Monitoring Well Program

SWFWMD = Southwest Florida Water Management District

USEPA = U.S. Environmental Protection Agency

USGS = U.S. Geological Survey
VI Contents
Abstract 1

Water Budget and Water Quality of Ward Lake, Flow and

Water-Quality Characteristics of the Braden River

Estuary, and the Effects of Ward Lake on the Hydrologic

System, West-Central Florida

By J.T. Trommer, M.J. DelCharco, and B.R. Lewelling

Abstract

The Braden River is the largest tributary to

the Manatee River. The river was dammed in 1936

to provide the city of Bradenton a source of freshwater supply. The resulting impoundment was

called Ward Lake and had a storage capacity of

about 585 million gallons. Reconstruction in 1985

increased the size of the reservoir to about 1,400

million gallons. The lake has been renamed the

Bill Evers Reservoir and drains about 59 square

miles. The Braden River watershed can be subdivided into three hydrologic reaches. The upper

reach consists of a naturally incised free-flowing

channel. The middle reach consists of a meandering channel affected by backwater as a result of the

dam. The lower reach is a tidal estuary.

Water budgets were calculated for the 1993

through 1997 water years. Mean surface-water

inflow to Ward Lake for the 5-year period was 1,645

inches per year (equivalent depth over the surface of

the lake), or about 81.8 percent of total inflow.

Mean ground-water inflow was 311 inches per year,

or about 15.5 percent. A mean of 55 inches of rain

fell directly on the lake and accounted for only 2.7

percent. Mean surface-water outflow was 1,736

inches, or about 86.4 percent of total water leaving

the lake. There was no net ground-water outflow

from the lake. Mean surface-water withdrawal for

public supply was 229 inches per year, or about 11.4

percent. Mean evaporation was 45 inches and

accounted for only 2.2 percent of the mean outflow.

Change in lake storage on the budget was negligible.

Most chemical constituents contained in

water flowing to Ward Lake meet the standards

specified by the Florida Department of Environmental Protection and the U.S. Environmental

Protection Agency. Phosphorus is the exception,

exceeding the U.S. Environmental Protection

Agency limits of 0.10 milligram per liter in most

samples. However, the source of the phosphorus is

naturally occurring phosphate deposits underlying

the watershed. Organic nitrogen and orthophosphate are the dominant species of nutrients in the

streams and the lake. A major source of water to

the streams is the surficial aquifer system.

Mineralized water pumped from the intermediate

aquifer system and the Upper Floridan aquifer for

irrigation of agricultural areas or golf courses has

influenced the chemical composition of the

surficial aquifer and surface-water systems.

The Braden River estuary receives freshwater inflow from Ward Lake and from three

major streams discharging downstream from the

dam. Salinity levels in the estuary are affected by

freshwater flow from these sources and by antecedent conditions in the estuary prior to flow

events. The lowest salinity levels are often measured at the confluence with Williams and Gap

Creeks rather than at the outfall from the lake.
2 Water Budget and Water Quality of Ward Lake, Flow and Water-Quality Characteristics of the Braden River Estuary,

and the Effects of Ward Lake on the Hydrologic System, West-Central Florida

The chemical composition of water flowing

from the tributaries to the estuary is similar to the

chemical composition of water in the tributaries

flowing to Ward Lake and does not appear to be

affected by brackish water from high tides. Nitrogen concentrations in water from Glen Creek were

greater than in water from all other tributaries in

the watershed. Fertilizer from orange groves and

stormwater runoff from urban and industrial areas

affect the water quality in Glen Creek.

The effects of the reservoir on the hydrology

of the watershed were to change the middle reach

of the river from a brackish water estuary ecosystem to a freshwater lake ecosystem, raise water

levels in the surficial aquifer system adjacent to the

river, change water quality, and reduce freshwater

flow to the estuary during periods of low flow.

The lake acts as a sink for total organic carbon,

dissolved solids, calcium, chloride, and sulfate,

thereby decreasing loads of these constituents to

the estuary.

INTRODUCTION

The Braden River is the largest tributary to the

Manatee River (fig. 1). In 1936, the river was

dammed, forming Ward Lake. The reservoir provides

a source of freshwater supply for the city of Bradenton, a city with a population of more than 46,600

people (University Press of Florida, 1994). Ward Lake

drains an area of about 59 square miles (mi2).

Population growth and increasing land development within the watershed have caused rapid land-use

changes. Areas once used primarily for agricultural

and low-density residential purposes are rapidly being

developed for large medium-to-high density subdivisions with associated golf courses and shopping centers. These changes will affect the hydrology and

possibly the water quality of the watershed. Potential

environmental stresses related to the effects of modifying freshwater flows from Ward Lake to the downstream estuary are also a concern. The Southwest

Florida Water Management District (SWFWMD) is

regulating water-supply withdrawals from the lake and

is concerned that further withdrawals may affect the

27°40′

82°50′ 40′ 30′ 82°20′

30′

27°20′

Braden River

Tampa Bay

ver Ri ee at an

e Mltti L

re iv R ka ak My

re iv R

Manatee

PINELLAS

COUNTY

HILLSBOROUGH COUNTY

MANATEE COUNTY

SARASOTA COUNTY

Parrish

Lorraine

Sarasota

Bradenton

Elwood Park

0 5 10 KILOMETERS

0 5 10 MILES

Location of

study area

GULF OF MEXICO

Base from U.S. Geological Survey digital data, 1:100,000, 1983

Albers Equal-Area Conic projection

Standard Parallels 29ο 30′ and 45ο 30′, central meridian −83ο 00′

EXPLANATION

Basin boundary

Drainage area for Braden

 River estuary

Drainage area for Ward

 Lake

Ward

Lake

 275

75

75

64

62

675

301

301

301

41

41

Figure 1. Location of the study area in west-central Florida and the drainage area for the Braden River.
Description of the Study Area 3

downstream estuary. A detailed water budget and

information on the quality of water in the Braden

River watershed will be helpful for future resource

development and planning.

The U.S. Geological Survey (USGS) began a

study of the Braden River watershed in 1992.

This study was a cooperative effort with the city of

Bradenton Public Works Department, Manatee County

Environmental Management Department, and the

Southwest Florida Water Management District.

Streamflow data were previously collected between

1988 and 1992, at seven gaging stations above Ward

Lake, in cooperation with the Manatee County

Environmental Action Commission.

Purpose and Scope

The results of the study are presented in two

reports. The first report, published in 1997 (DelCharco

and Lewelling), provided (1) a hydrologic description

of the Braden River watershed and its major subbasins,

(2) a description of the data-collection network established to monitor surface drainage, and (3) a description

of the method used for measuring discharge at the Ward

Lake outfall. This is the second report and presents the

1993-97 water year water budgets for the lake, surfaceand ground-water quality, the characteristics of the

downstream estuary, and the effects of the reservoir on

the hydrologic system. Surface inflows from the

upstream tributaries to the lake, rainfall on the lake,

surface flows from the immediate area around the

lake, ground-water inflow and outflow, evaporation,

pumpage to the water plant, and discharge at the outfall are included in the water budget. Water-quality

data for Ward Lake, the upstream tributaries, the shallow ground water, and the Braden River estuary are

also presented. Water-quality data include specific

conductance and concentrations of major ions, nutrients, and total organic carbon. Estimates of chemical

loading, tide, and salinity data for the estuary are presented. The effects of the reservoir on the hydrologic

system are also discussed.

Acknowledgments

The authors gratefully acknowledge the cooperation and assistance from personnel with the city of

Bradenton, Manatee County, and the Southwest Florida

Water Management District. Special thanks are given to

the late Earl Crawley and to William Taylor, past

Directors of the Bradenton Public Works Department;

Keith McGurn and Clyde Crews, Bradenton Water

Treatment Plant; and to Robert Brown and Greg

Blanchard, Manatee County Department of Environmental Management, for their many contributions to the

study. Special thanks are given to C.D. Stanley at the

Gulf Coast Research and Education Center, Institute of

Food and Agricultural Sciences (IFAS), University of

Florida, for providing climatological data from the

Bradenton 5 ESE weather station.

DESCRIPTION OF THE STUDY AREA

In 1936, the Braden River was dammed about

6 miles (mi) upstream of the mouth to provide a freshwater source for the city of Bradenton’s water-supply

needs. The dam, an 838-foot (ft) broad-crested weir,

created a backwater condition within the banks of the

natural channel extending upstream for about 6 mi.

The resulting 167-acre reservoir was named Ward

Lake (fig. 2). The lake provided storage for about

585 million gallons (Mgal) and is the sole source of

freshwater for the city of Bradenton. An average of

5.7 million gallons per day (Mgal/d) was withdrawn

from the lake during the study period.

In 1985, a reservoir was constructed by expanding the lake, increasing storage capacity to about 1,400

Mgal. The reservoir was excavated to a depth of about

10 ft below sea level, from the dam to about 1 mi

upstream. A thick clay layer underlies the area at this

depth. The dam, constructed by driving concrete sheet

piles about 10 ft into the clay layer (to a depth of about

20 ft below sea level), was modified at this time to

minimize freshwater seepage losses to the estuary or

saltwater seepages to the lake that might occur during

high tides. Continuous, synthetic, membrane liners

were applied to both sides of the dam, extending out

along the riverbed and covered with fill material and

rip-rap. The crest of the dam ranges from 3.82 to 4.10 ft

above sea level. Ward Lake was renamed the Bill

Evers Reservoir after it was expanded. This report

refers to the reservoir as Ward Lake and refers to the

dam as the Ward Lake outfall based on current USGS

geographical naming convention.

DelCharco and Lewelling (1997) subdivided the

Braden River watershed into three hydrologic reaches

based on streamflow characteristics. These were

referred to as the upper, middle, and lower reaches.

The upper reach of the river consists of a naturally

incised channel that is free of any backwater effects
4 Water Budget and Water Quality of Ward Lake, Flow and Water-Quality Characteristics of the Braden River Estuary,

and the Effects of Ward Lake on the Hydrologic System, West-Central Florida

from Ward Lake. Land-surface elevations in this part

of the watershed range from about 100 ft above sea

level along the eastern watershed boundary to about

25 ft above sea level about 0.5 mi east of Interstate

Highway 75 (fig. 2). The middle reach of the river

consists of meandering channels with many oxbows

and is characteristic of streams having variable discharge and easily eroded banks. This is similar to the

structure of the river channel below the outfall and is

probably a remnant of estuarine conditions that existed

prior to construction of the dam. Backwater conditions

exist throughout the entire reach. This reach is synonymous with Ward Lake. Land-surface elevations in

this part of the watershed average about 25 ft above

sea level. The Ward Lake outfall forms the downstream boundary of the middle reach. The lower reach

of the river is brackish and tidal, extending from

below the outfall to the confluence with the Manatee

River. Land-surface elevations are commonly less than

15 ft above sea level in the watershed of the lower

reach of the river.

Daily mean discharge at the outfall, computed

for the study period (October 1992 to September

1997) was about 69 cubic feet per second (ft3/s), or

about 45 Mgal/d. Computed mean discharges are

strongly affected by high-flow events and are not

representative of typical flow patterns (Hammett,

1992). Daily mean discharge was reached or exceeded

only 20 percent of the time at the outfall. Median

discharge was only 6.5 ft3/s, or about 4 Mgal/d.

Discharges of 0.10 ft3/s or less occurred about 30 percent of the time. There were many days when no flow

occurred over the dam.

Climate in the area is subtropical and humid,

with an average annual temperature of 72 oF. Mean

annual rainfall from 1954 to 1993 was 56.0 in.

(National Oceanic and Atmospheric Administration,

1993). About 60 percent of all rainfall occurs during

intense, localized thunderstorms from June through

September. Winter frontal storms account for most of

the rainfall from December through March.

Thick sequences of carbonate rocks and clastic

deposits underlie the study area. A multilayered

ground-water flow system exists within these deposits

and has been divided into three hydrogeologic units:

the surficial, intermediate, and Floridan aquifer

systems.

 The surficial aquifer system is contiguous with

land surface and consists of unconsolidated sediments

composed mostly of quartz sand with some phosphatic

sand, clayey sand, clay, marl (carbonate sediments of

low permeability), organic debris, and phosphate that

Figure 2. Configuration of Ward Lake prior to 1985 and at present.

0 1/4 1/2 MILE

0 0.25 0.5 KILOMETER

Pumping

Station

EXPLANATION

Present configuration

Ground-water well and name

Configuration of Ward Lake

 prior to 1985

Ward Lake Outfall

ROMP

TR 7-4

Well

27°26′30′′

25′30′′

27°24′30′′

82°29′30′′ 28′30′′ 82°26′30′′

70

ver Ri

Linger Lodge

27′30′′

raden B

75

Braden 

River 

Estuary
Data Collection 5

range in age from Holocene to Pliocene. The deposits

become increasingly phosphatic and clayey with

depth. Discontinuous clay stringers interfinger the

unconsolidated materials and can restrict vertical

ground-water flow. Some of the wetlands in the watershed may be perched because of underlying clay

stringers. The thickness of the surficial aquifer system

is variable in the watershed, but is usually less than 40 ft.

At a SWFWMD Regional Observation and Monitoring Well Program (ROMP) well site adjacent to Ward

Lake (ROMP TR 7-4), the thickness was 21 ft, and at

a test site near Linger Lodge the thickness ranged

between 16 and 29 ft (fig. 2). The surficial aquifer

system is the principal hydrogeologic unit that

exchanges water with the surface-water system.

The intermediate aquifer system “includes all

rocks that lie between and collectively retard the

exchange of water between the overlying surficial

aquifer system and the underlying Floridan aquifer

system” (Southeastern Geological Society, 1986, p. 5).

Sediments in the intermediate aquifer system consist

of layers of limestone, dolostone, quartz and phosphatic sand, clayey sand, clay, and chert, ranging in

age from Pliocene to Oligocene (Barr, 1996, p. 10).

Many of these layers are thin and areally discontinuous. Three small water-bearing zones were identified

at the ROMP TR 7-4 site. The intermediate aquifer

system is a confined system with a seasonal upward

head gradient in the study area; therefore, the potential

for upward migration of water to the surficial aquifer

system exists. However, the intermediate aquifer

system acts as a single confining unit at the ROMP TR

7-4 site (Decker, SWFWMD, written commun.,1989),

restricting vertical ground-water flow to the surficial

aquifer system. The intermediate aquifer system is

about 350 ft thick.

The Floridan aquifer system consists of a vertically continuous sequence of carbonate rock of Tertiary age which is subdivided into the Upper Floridan

aquifer, the middle confining unit, and the Lower

Floridan aquifer. The middle confining unit and the

Lower Floridan aquifer contain saltwater. The Upper

Floridan aquifer contains freshwater and is the primary source of irrigation water in the watershed. Head

gradient in the Upper Floridan aquifer is also upwards

and may provide some recharge to the intermediate

aquifer system. However, because of the confining

characteristics of the intermediate aquifer system, the

Upper Floridan aquifer has little or no direct effect on

the surficial aquifer or surface-water systems in the

watershed.

DATA COLLECTION

Streamflow, lake-stage, ground-water level, climatological, and pumping data were necessary to construct a detailed water budget for Ward Lake. Waterquality data also were used to complete the evaluation

of the Braden River watershed. Data collection methods are summarized below.

Seventeen surface-water stations were established to characterize surface drainage in the Braden

River watershed. Thirteen stations were continuous

stations and four were partial-record stations (fig. 3,

table 1). Peak water-level elevations for high-flow

events were collected at the four partial-record stations

located on tributaries in the upper reach of the watershed. Discharge was computed at 11 of the continuous

stations using a stage/discharge relation developed

from a series of streamflow measurements made at

each station. Seven of the continuous stations were

located upstream of the Ward Lake outfall and were

used to measure inflow to Ward Lake. One continuous

station located at the outfall was used to measure outflow from the lake. Three continuous stations located

below the outfall on tributaries to the Braden River

estuary were used to estimate freshwater inflow to the

estuary from sources other than Ward Lake. The

remaining two continuous stations were used to collect

water-level and specific conductance data in the tidal

reach of the river. A detailed discussion of the gage

network and surface-drainage characteristics for each

of the subbasins can be found in the report by DelCharco and Lewelling (1997).

Three well transects were constructed to define

the ground-water component of flow to the river (fig. 3,

table 2). Each transect consisted of five or six wells

arranged in a line perpendicular to the river and completed into the surficial aquifer system. Two sets of

paired wells, one at the water table and one near the

bottom of the aquifer system, were placed at each end

of the transect to monitor head differences. The first

transect (T1) was located near Linger Lodge, an area

where the river is affected by backwater from the outfall and is representative of the ground-water flow

conditions around Ward Lake. The surficial deposits at

the Linger Lodge transect are relatively shallow (about

20 ft thick at the river). The river is incised through

these deposits to the underlying clay. All flow from the

surficial deposits is to the river (fig. 4a). The second

transect (T2) was located in the upper reach of the

river near Lakewood Ranch. Surficial deposits are

about 30 ft thick. The river is incised into, but not

through the surficial deposits in this area. Distribution
6 Water Budget and Water Quality of Ward Lake, Flow and Water-Quality Characteristics of the Braden River Estuary,

and the Effects of Ward Lake on the Hydrologic System, West-Central Florida

0 1 2 MILES

0 1 2 KILOMETER

301

301

683

64

675

75

Streamflow station and site number as  shown in table 1Weather stationGround-water transects

MANATEE COU

SARASOTA COU

82°30′ 25′ 82°20′

27°30′27°25′

EXPLANATION

Basin boundary. Subbasins are distinguished by shading

2

Ward Lake

T3

Gl en

Creek

Gap

Creek

Manatee

River

13 15

14

11

10

9 8

7

6

T2

T1

5 T3

4 3

2

1

16

17

Lorraine

Road

Transect

Lorraine Road

12

Lakewood

Ranch

Transect

Linger Lodge Transect

Bradenton 5 ESE

Williams Cree k

Braden River

Figure 3. Ward Lake drainage basin and data-collection network.
Data Collection 7

of hydraulic head indicates that all flow from the surficial aquifer system discharges to the river (fig. 4b).

The third transect (T3) was also located in the upper

reach of the river at Lorraine Road. Surficial deposits

are about 30 ft thick at this site. The river is not deeply

incised in this area and flow in the surficial aquifer

system is more regional with only partial discharge to

the river (fig. 4c).

Climatological data used in the water budget

were obtained from the Bradenton 5 ESE station,

operated by the Gulf Coast Research and Education

Center (GCREC), University of Florida, IFAS, and

from the Verna FL41 station, operated by the National

Atmospheric Deposition Program/National Trends

Network (NADP/NTN). Rainfall data from the

Bradenton 5 ESE and Verna FL41 stations (fig. 3)

were used as a watershed average in the water budget.

Pan-evaporation data used in the budget was collected

at the Bradenton 5 ESE station.

The quality of inflow to and outflow from the

lake was determined from samples collected at the

seven discharge stations upstream of the outfall, at the

outfall, and from wells at each of the transects. Samples were collected periodically at the outfall between

April 1966 and August 1997, from the upstream discharge sites between June 1993 and August 1997, and

from transect wells between September 1995 and

August 1997. Water-quality samples also were collected at the three discharge stations downstream from

the outfall and at the upper tidal station (fig. 3) to evaluate inflow to the estuary. Samples were collected at

the discharge stations between March 1995 and March

1997, and between June 1993 and February 1997 at

the tidal site. Samples were analyzed for specific conductance, major ions, nutrients, organic carbon, and

dissolved solids.

Table 2. Ground-water transect wells

Well

identification

Type

of

record

Depth of well

below land

surface

 (feet)

Length of

screen

(feet)

Transect No. 1 near Linger Lodge (T1)

272504082280501 periodic 14.7 2.0

272504082280502 periodic 9.2 2.0

272504082280503 periodic 10.3 9.5

272504082280504 periodic 21.4 2.0

272504082280505 periodic 6.8 2.0

Transect No. 2 at Lakewood Ranch (T2)

272517082250901 periodic 22.9 2.0

272517082250902 periodic 10.9 2.0

272517082250903 periodic 25.9 2.0

272517082250904 periodic 9.7 2.0

272517082250905 periodic 6.9 2.0

Transect No. 3 near Lorraine Road (T3)

272507082235901 periodic 21.6 2.0

272507082235902 periodic 6.3 2.0

272507082235903 periodic 19.6 2.0

272507082235904 periodic 7.1 2.0

272507082235905 periodic 11.3 9.5

272507082235906 periodic 1.5 1.5

Table 1. Braden River streamflow station network

1Site location shown on figure 3.

2Discharge station.

3Stage at Ward Lake has been recorded from 1942-47 and from 1976-present, discharge has been computed since 1992.

4Stage and conductivity (tidal station).

Site

number1

USGS

downstream

order number

Station

Type

of

record

Period of

record

(water

years)

Drainage

area

(square

miles)

1 02300024 Braden River near Verna partial 1993-97 6.8

2 02300025 Tributary No. 1 Braden River near Lorraine partial 1993-97 5.2

3 02300027 Tributary No. 2 Braden River near Lorraine partial 1993-97 3.8

4 02300031 Wolf Slough near Lorraine partial 1993-97 4.0

5 02300032 Braden River near Lorraine continuous2 1988-97 25.6

6 02300034 Hickory Hammock Creek near Lorraine continuous2 1988-97 2.4

7 023000355 Cooper Creek near Sarasota continuous2 1988-97 9.0

8 02300036 Tributary No. 1 to Cooper Creek near Lorraine continuous2 1994-97 4.4

9 02300037 Cedar Creek near Sarasota continuous2 1988-97 1.7

10 02300038 Rattlesnake Slough near Sarasota continuous2 1988-97 3.8

11 02300039 Nonsense Creek near Bradenton continuous2 1988-97 1.4

12 02300042 Ward Lake Outfall near Bradenton continuous2 1976-973 59.2

13 02300044 Braden River near Elwood Park continuous4 1992-97 60.0

14 02300050 Williams Creek near Bradenton continuous2 1994-97 2.7

15 02300056 Gap Creek near Bradenton continuous2 1995-97 7.2

16 02300062 Glen Creek near Bradenton continuous2 1995-97 2.5

17 02300064 Braden River near Bradenton continuous4 1994-97 83.0
8 Water Budget and Water Quality of Ward Lake, Flow and Water-Quality Characteristics of the Braden River Estuary,

and the Effects of Ward Lake on the Hydrologic System, West-Central Florida



LAND 

SURFACE

UNSATURATED ZONE

Braden

Screen River

20

10

10

20

10.0

9.0

8.0

7.0

6.0

5.0

Wells

Wells

02 01

02 01

05

05

04

04

03

03

0 250 500



LAND SURFACE

UNSATURATED ZONE

Braden 

River

Screen

Screen

SEA

LEVEL

SEA

LEVEL

SEA

LEVEL

0 250 500

10

10

20

30

DISTANCE, IN FEET

27.0

26.5

26.0

25.5

25.0

24.5

Wells

EXPLANATION

Water Table

Line of equal hydraulic head,

 In feet above sea level

Direction of ground-water flow

26.0

02 01

03 04 05



06

10

10

20

30

0 180 360

WATER LEVEL, IN FEET ABOVE OR BELOW SEA LEVEL

b. Lakewood Ranch surficial aquifer system well transect site

c. Lorraine Road surficial aquifer system well transect site

24

25

26

27

28

29

SEEPS

UNSATURATED

ZONE

LAND SURFACE

Braden 

River

CLAY

CLAY

CLAY

a. Linger Lodge surficial aquifer system well transect site

Figure 4. Ground-water flow in the surficial aquifer system at the (a) Linger

Lodge, (b) Lakewood Ranch, and (c) Lorraine Road well transects (transect

locations shown in fig. 3).
Water Budget for Ward Lake 9

WATER BUDGET FOR WARD LAKE

A water budget for a lake is an expression of the

conservation of water mass for the lake, and can be

simply stated as the inflow equals the outflow plus the

change in storage of the lake for a given period of time

(Lee and others, 1991, p. 14). The water budget for

Ward Lake is based on water years (October 1 through

September 30) for the 5-yr period from October 1,

1992, through September 30, 1997. Data used to construct the water budget were reported as daily values,

except for the rainfall data from the Verna FL41

weather station, which was reported as weekly values.

Subsequently, all daily value data were summarized to

correspond to the weekly Verna rainfall data, and the

water budget was calculated using a weekly time step.

The unit volume for each term is expressed as an

equivalent depth, in inches, over the surface of the

lake. A lake surface area of 14,525,500 ft2 (333 acres)

was used to convert all volumes to equivalent depths.

The specific components of the water budget used for

this study are shown in the following equation.

Rainfall + Surface-Water Inflow + Ground-Water Inflow =

Evaporation + Surface-Water Outflow +

Ground-Water Outflow + Withdrawal for

Water Supply + Storage Change (1)

Most components of a water budget are easily

measured or estimated. Ground-water flow is the

exception, and is an important and largely overlooked

component of water budgets because it is the most

difficult to quantify as it cannot be measured directly.

Cross-sectional flow-net analysis was used to estimate

ground-water flow for this study. Flow-net analysis is

a graphical technique that can be used to describe

steady-state, two dimensional ground-water flow in a

homogeneous, isotropic aquifer. A detailed discussion

of flow-net analysis can be found in Freeze and Cherry

(1979, p. 168-172). A conceptual model of the crosssectional flow nets used to estimate ground-water flow

to Ward Lake are shown on figure 5. For this report,

ground-water flow was calculated using the following

equation:

Q (2) mKH

n = ------------

where

Q is the inflow, in cubic feet per day;

m is the number of streamtubes, dimensionless;

K is the horizontal hydraulic conductivity, in feet

per day;

H is the head drop across the flow net, in feet; and

n is the divisions of head in the flow net,

dimensionless.

Flow nets were constructed using periodic head

measurements collected at each of the Linger Lodge

transect wells (T1, fig. 3). The Linger Lodge transect

was used because it is representative of the area

around the lake. Both inflow to the lake from the surficial aquifer system and outflow to the surficial aquifer

system from the lake were calculated using flow-net

analysis.

 Inflow to the lake occurs when ground-water

levels are greater than lake stage. Flow nets were constructed for inflow conditions that ranged from a lake

stage that was near a record low of 1.7 ft below sea

level and ground-water levels ranged from 0.6 ft

below sea level to 4.3 ft above sea level at each end of

the transect, to about a normal wet-season condition,

when the lake was about 4.3 ft above sea level and

ground-water levels ranged from 4.6 to 9.0 ft above

sea level at each end of the transect.

 Outflow to the surficial aquifer system occurs

when lake stage is greater than ground-water heads.

Five periodic head measurements made during the

study reflect these conditions. However, lake stages

only averaged about 0.2 ft higher than ground-water

levels for these measurements. Continuous groundwater head data are not available for evaluation, but

outflow conditions appear to be of limited extent and

duration.

EXPLANATION

Water surface

Line of Equal Hydraulic Head

H=h1-h2 z|

Lake

STREAMTUBE 1

STREAMTUBE 2

STREAMTUBE 3

h1

 h2

UNSATURATED 

 ZONE

Figure 5. Conceptual model of the cross-sectional flow

nets used to calculate ground-water flow to Ward Lake.
10 Water Budget and Water Quality of Ward Lake, Flow and Water-Quality Characteristics of the Braden River Estuary,

and the Effects of Ward Lake on the Hydrologic System, West-Central Florida

The horizontal hydraulic conductivity values of

the surficial aquifer system, calculated from slug tests

conducted by consultants for an aggregate mine

located in the Cooper Creek subbasin, were assumed

to be representative of the area around Ward Lake and

were used in the flow-net analysis. Estimated values

ranged from 0.77 to 3.6 ft/d (Environmental Affairs

Consultants, 1995), indicating variable lithology.

A value of 2.0 ft/d was used in all flow-net calculations and represents an average hydraulic conductivity.

Results indicate that flow from the surficial

aquifer system to the lake could range from 0.87 to

2.7 ft3/d per square foot of the area of discharge and

that flow from the lake to the surficial aquifer system

could average about 0.25 ft3/d per square foot of the

area of discharge. In most areas, the lake directly overlies the clay layer; therefore, there is little or no flow

through the lake bottom. A range of flow was then calculated by multiplying the discharge rate derived by

flow-net analysis by the length of the shoreline and the

effective depth of the lake. The length of the shoreline

is about 21 mi (110,880 ft). The effective depth is

dependent on the lake stage.

Inflow

Ward Lake receives water from precipitation

falling directly on the lake, surface-water inflow, and

ground-water inflow from ungaged areas around the

lake. Rainfall was measured at two nearby weather

stations. Surface inflow included direct runoff from

ungaged areas. Surface inflow was measured at seven

gaging stations and estimated for the ungaged areas

based on runoff-per-square-mile calculations from the

gaged areas. Ground-water inflow from the surficial

aquifer system was calculated using flow-net analysis.

Daily rainfall data from the Bradenton 5 ESE

and weekly rainfall data from the Verna FL41 weather

stations were used in the water budget. The Bradenton

5 ESE station is located near the northwestern watershed boundary, about 0.5 mi north of the Ward Lake

outfall, and the Verna FL41 station is located near the

Manatee-Sarasota County line, about 2 mi southeast of

the eastern watershed boundary (fig. 3). A weekly sum

of the daily rainfall data from the Bradenton 5 ESE

station was averaged with the Verna FL41 station data

and used as the watershed rainfall component of the

water budget. Annual rainfall at the Bradenton 5 ESE

and Verna FL41 weather stations and the annual sum

of weekly rainfall averages used in the water budget

for water years 1993-97 are listed in table 3.

Annual rainfall averages ranged from about 50

to about 61 in., with a mean of 55 in. Rainfall is the

smallest part of the inflow component of the water

budget.

Surface-water inflow to Ward Lake was measured at seven streamflow stations (fig. 3 and table 1)

and includes all ground-water inflow, rain falling

directly on the streams, and direct surface runoff to the

streams above the stations. Six stations were located

on tributaries, and one was located on the main stem

of the Braden River above Ward Lake. Eighty-two

percent of the drainage area to Ward Lake was monitored by this network. Surface-water inflow from the

ungaged area of each subbasin was estimated by calculating runoff-per-square-mile from the gaged area

and applying it to the remaining ungaged area.

A runoff-per-square-mile average for all the subbasins

was used to estimate runoff from the ungaged area

adjacent to the lake. Surface-water inflow calculations

for the water budgets were made using continuous

streamflow data collected during the period from

October 1992 through September 1997, except at Tributary No. 1 to Cooper Creek. Continuous streamflow

data were collected at this station from October 1994

through September 1997. Data used in the water

budget for the 1993 and 1994 water years, for this

subbasin, were estimated using average runoff-persquare-mile calculated from adjacent subbasins.

Discharge from each subbasin, the ungaged area

around Ward Lake, and the total surface-water inflow

to Ward Lake for each water year is shown in table 4.

Surface-water flow is the largest inflow component of the water budget. Total surface-water inflow to

Ward Lake for each water year ranged from 1,311 to

2,416 in/yr, with a mean value of 1,645 in/yr.

Table 3. Annual rainfall at the Bradenton 5 ESE and

Verna FL41 weather stations and annual sum of weekly

rainfall averages used in the water budget for water years

1993-97

Water year

Rainfall station

(inches)

Annual sum

of weekly

station

averages

(inches)

Bradenton 5

ESE

Verna

FL41

1993 46.13 53.21 49.67

1994 50.89 50.51 50.70

1995 61.23 61.47 61.35

1996 56.94 50.90 53.92

1997 61.17 58.21 59.69

Mean annual 55.27 54.86 55.07
11

Ground-water inflow to Ward Lake, estimated

using flow-net analysis, could range between 988,796

and 1,206,374 ft3/d or between 0.82 and 1.0 in/d. The

greatest inflow to the lake was calculated for the dry

period when the lake stage was about 1.7 ft below sea

level, indicating that lower lake stages induce groundwater inflow to the lake. Daily inflow corresponding to

a recorded lake stage was calculated by developing an

equation based on a linear relation between the calculated daily inflow for the highest and lowest lake

stages used in the flow nets. The result was multiplied

by seven to convert the daily inflow to a total weekly

inflow. The following equation was used:

(3)

where

Q is inflow, in inches per week;

Qh is the highest inflow to the lake calculated using

flow-net analysis, in inches per day;

Eh is the lake stage used in the high inflow analysis,

in feet;

Ec is the current lake stage, in feet; and

0.032 is the inflow per 0.01 ft of change in lake stage,

in inches per day.

The annual ground-water inflow component to

the lake ranged from 303 to 316 in/yr, with a mean of

311 in/yr. Ground-water inflow to the lake is the

second most significant part of the inflow component

and has largely been overlooked when comparing

inflow to and outflow from Ward Lake. Table 5 summarizes the inflow component of the water budget.

Outflow

Water from Ward Lake is lost to evaporation,

surface-water outflow, ground-water outflow, and

withdrawals for water supply. Evaporation from the

lake surface was estimated from pan-evaporation

measurements made at the Bradenton 5 ESE weather

station. Surface-water outflow was measured at the

Ward Lake outfall. Ground-water outflow was estimated as a residual of the water budget. Surface-water

withdrawals for public supply were reported by the

city of Bradenton.

Q Qh Eh Ec = ( ) + ( ) ( ) – × 0.032 × 7 Table 4. Surface-water inflow to Ward Lake, water years

1993-97

1Station location shown on figure 3 and described in table 1.

Station1

Water years

1993 1994 1995 1996 1997

Braden River near Lorraine 752 819 1,156 443 724

Hickory Hammock Creek 71 57 97 65 58

Cooper Creek 317 176 395 238 104

Tributary No. 1 to Cooper

Creek

137 115 218 107 86

Cedar Creek 70 51 99 100 92

Rattlesnake Slough 108 74 119 154 104

Nonsense Creek 38 32 98 77 77

Ungaged area around Ward

Lake

160 142 234 127 134

Total surface-water inflow to

Ward Lake

1,653 1,466 2,416 1,311 1,379

Table 5. Estimated water-budget for Ward Lake, water years 1993-97

[Unit volume is expressed as an equivalent depth, in inches, over the surface of the lake]

Water years

Mean

1993 1994 1995 1996 1997

Annual Inflow

Rainfall 50 51 61 54 0 55

Surface water 1,653 1,466 2,416 1,311 1,379 1,645

Ground water 313 316 313 303 311 311

Total 2,016 1,833 2,790 1,668 1,750 2,011

Annual Outflow

Evaporation 46 44 42 44 47 45

Surface water 1,551 1,310 2,492 1,351 1,977 1,736

Ground water 0 0 0 0 0 0

Withdrawal for water supply 232 231 220 225 237 229

Lake storage change -2 2 -3 -2 7 <1

Total 1,827 1,587 2,751 1,618 2,268 2,010

Residual 189 246 39 50 -518 1
12 Water Budget and Water Quality of Ward Lake, Flow and Water-Quality Characteristics of the Braden River Estuary,

and the Effects of Ward Lake on the Hydrologic System, West-Central Florida

The rate of evaporation depends on many

factors, including temperature, the amount of solar

radiation, vapor pressure, and wind speed. Lake evaporation is often estimated from regional pan-evaporation

data by applying a pan coefficient, defined as the ratio

of the theoretical free-water surface evaporation to pan

evaporation (Farnsworth and others, 1982). Lee and

Swancar (1997, p. 26) derived a pan-evaporation coefficient of 0.75 by comparing corrected energy-budget

evaporation values to observed pan-evaporation values

for a lake in central Florida. This coefficient agrees

closely with the long-term annual average coefficient

of 0.74 used by Farnsworth and others (1982).

An annual mean coefficient of 0.75 was applied to panevaporation data from the Bradenton 5 ESE weather

station to estimate evaporation from Ward Lake.

Annual evaporation losses ranged from 42 to 47 in.,

with a mean of 45 in.

All surface-water outflow from Ward Lake discharges at the outfall. Water-budget calculations were

made using continuous streamflow data collected at

the outfall during the period from October 1992

through September 1997. Surface-water outflow for

each water year ranged between 1,310 and 2,492 in/yr,

with a mean value of 1,736 in/yr (table 5).

Flow from the lake to the surficial aquifer system

occurs periodically, when ground-water heads are

lower than lake stage. Flow-net analysis indicates that

flow to the surficial aquifer system could average about

289,017 ft3/d, or about 0.25 in/d. Weekly outflow was

calculated by multiplying the average daily outflow

derived from flow-net analysis by seven, and entered

into the budget when measurements or storm conditions in the watershed indicated probable flow reversal

from the lake to the surficial aquifer system. However,

outflow from the lake is small and each annual water

budget reflects a net ground-water inflow to the lake;

therefore, flow from the lake to the ground-water

system was reported as zero for each annual budget.

Ground-water outflow can also occur as seepage

around or through the outfall. Two dye studies were

conducted to assess the extent of seepage. A network

of surficial aquifer system wells was installed around

both ends of the dam. Rhodamine dye was used as a

fluorescent tracer and traveltime between wells was

monitored. The results indicate small lateral seepage

losses of 0.0011 ft3/s to the surficial aquifer around the

west-end of the Ward Lake outfall. Rhodamine dye

was also placed along the length of the upstream side

of the dam at a time when the no flow over the dam

was occurring. Water samples were collected along the

length of the downstream side of the dam for a period

of 36 hours, with no detection of the dye. Thirty-six

hours was considered adequate to detect any significant leakage through or under the dam (DelCharco and

Lewelling, 1997). Outflow from seepage around the

outfall was not included in the water budgets because

it was less than 0.03 in/yr.

Ward Lake is the sole source of water supply for

the city of Bradenton. Permitted annual average withdrawals from the lake are 6.95 Mgal/d, with a peak

monthly withdrawal of 8.19 Mgal/d. The surfacewater withdrawal component for each of the annual

water budgets was calculated based on pumpage volumes supplied by the city of Bradenton. Withdrawals

ranged from 220 to 237 in/yr, with a mean value of

229 in/yr (2,073 Mgal). Table 5 summarizes the outflow component of the water budget.

Budget Summary

Components of a water budget, whether they are

measured or calculated variables, have associated

errors based on the degree of uncertainty of the measurements, limitations of methods, and the assumptions

made to calculate values. The rainfall, surface inflow

and outflow, and withdrawal for supply data used in

this study are considered to be reliable. The calculated

values of lake evaporation and lake storage can be considered less reliable because of the use of offsite panevaporation data and an estimated pan coefficient. Lake

stage also can be considered less reliable because of the

uncertainty associated with accurately assessing the

surface area of the lake. The least reliable component

of the budget is ground-water flow. When all the measured or calculated components were entered into each

annual water budget, residual values (the imbalance

between the inflow and outflow components) ranging

from -518 to +246 in/yr remained (table 5). The residual term in a water budget is an accumulation of all the

errors in the components of the budget.

Based on the total mean values from water years

1993-97, about 81.8 percent of the inflow to Ward Lake

comes from surface water. Ground water accounts for

15.5 percent of the mean total inflow, and rain falling

directly on the lake accounts for only 2.7 percent.

Surface-water outflow accounts for about 86.4 percent

of the total mean outflow from the lake during the

study period. Withdrawal for water supply accounts for

about 11.4 percent of the mean outflow, and about 2.2

percent was lost by evaporation. On average, the

change in lake storage was not significant.
Water Quality 13

WATER QUALITY

The quality of water in the Ward Lake watershed is important from a water-resource management

perspective because the lake provides the watersupply needs of the city of Bradenton. Water managers

are concerned that continuing development and land

use changes in the watershed could threaten the quality of water in the lake. This section of the report

assesses the quality of the surface and ground water

flowing to the lake and the quality of water in Ward

Lake. The Seasonal Kendall-Tau test (Kendall, 1975,

and Smith and others, 1982) was used to identify significant water-quality trends. Significance was based

on a two sided significance test (p value) of less than

0.10, or a greater than 90 percent likelihood that the

observed trend is real. Concentrations of many waterquality constituents vary with streamflow. To remove

the effects of this variation, a simple linear regression

analysis was used to adjust constituent concentrations

for streamflow. The flow-adjusted constituent concentration is calculated by subtracting the regression predictions from the measured concentrations (residuals).

The trend analysis was then conducted on these residuals (Hirsch and others, 1991). Water-quality and flow

data also were used to compute constituent loads from

the tributaries to the lake, and from the lake to the

Braden River estuary.

Surface-water samples were collected from the

river at the Braden River near Lorraine station, the six

tributaries that drain to Ward Lake, and at the Ward

Lake outfall (table 6, 7, and 8; and fig. 3). Samples

were collected at the streamflow sites that drain to

Ward Lake between June 1993 and August 1997.

Samples have been collected at the outfall since 1966.

Ground-water samples were collected from wells at

the transect sites (table 2 and fig. 3) between September 1995 and August 1997.

Braden River near Lorraine

The water in the river at the Braden River near

Lorraine station is a composite of all surface water and

ground-water baseflow to the tributaries above the station and is representative of the quality of water in the

upper one-third of the Braden River watershed. Some

rural, low density development exists along Lorraine

Road (fig. 3) and rapid, high density residential development is occurring in the immediate area of the

gaging station. However, most of the watershed

consists of pastureland, wetlands, forests, and agricultural areas, and is used primarily for the production of

cattle, hay, sod, and row crops. Water-quality samples

were collected from the river at the gaging station and

from surficial aquifer system wells at the nearby Lakewood Ranch transect site and at the upstream Lorraine

Road transect site for comparison with the surfacewater samples.

Specific conductance values for the surfacewater samples measured at the Braden River near

Lorraine station ranged from 172 to 917 microsiemens

per centimeter (μS/cm), with a mean value of

454 μS/cm (table 6). At the Lakewood Ranch transect

site (T2, fig. 3), specific conductance values of water

from the surficial aquifer system ranged from 66 to

529 μS/cm, with a mean of 210 μS/cm (table 6).

Specific conductance values for the samples from the

Lorraine Road transect site (T3, fig. 3) ranged from

403 to 573 μS/cm, with a mean value of 448 μS/cm

(table 6). Most conductance values measured at these

sites are higher than would be expected for an unconfined ground-water system recharged only by rainfall.

Samples collected at the Verna well field (fig 3.)

in 1992, as part of a previous study (Sacks and Tihansky, 1996, p. 57) reported specific conductance values

of 1,140 and 1,202 μS/cm for the intermediate aquifer

system and the Upper Floridan aquifer, respectively.

Mineralized water from these aquifers is the probable

source of the high specific conductance values measured in the surficial aquifer system. However,

because of the confining characteristics of the intermediate aquifer system, the higher conductance values

measured in the surficial aquifer system are probably

not the result of upwelling of water from the underlying aquifers, but rather the result of withdrawal from

these aquifers for agricultural irrigation.

Ground-water withdrawal for agricultural irrigation has occurred throughout the watershed for many

years. Mixing of rain water and irrigation water in the

surficial aquifer system is the probable cause of the

higher conductance values measured in the watershed.

Ground-water samples from the Lakewood Ranch site

have lower conductance values than samples from the

river or the Lorraine Road site because irrigation has

not occurred at the Lakewood Ranch site since 1993.

A significant trend in specific conductance was not

observed at the Braden River near Lorraine station

during the study.
14 Water Budget and Water Quality of Ward Lake, Flow and Water-Quality Characteristics of the Braden River Estuary,

and the Effects of Ward Lake on the Hydrologic System, West-Central Florida

Major cation and anion equivalent concentration

percentages were plotted on a trilinear diagram to

evaluate the chemical composition of surface water,

ground water from the surficial aquifer system, and

ground water from the intermediate aquifer system

and Upper Floridan aquifer (fig. 6). The major ions in

all samples collected at the Braden River near Lorraine station and the Lorraine Road and Lakewood

Ranch transects are dominated by either calcium sulfate or calcium bicarbonate and are very similar to the

major ions in samples previously collected from the

deeper aquifers. Ground water from the surficial aquifer system is, at times, the major source of water in the

river at the Lorraine station. Ground-water seeps have

been noted along many stretches of river bank in the

upper reach of the watershed. The high concentrations

of major ions in the river-water and shallow groundwater samples (table 6), particularly sulfate and strontium ions, and their distribution on the trilinear diagram (fig. 6), further indicates the surficial aquifer

system and the river have been influenced by water

from the deeper aquifer systems.

Significant trends in the concentration of the

major ions in the river water were not observed during

the study. With the exception of some sulfate samples,

all parameters were below the limits specified by the

FDEP (1994) for Class I waters and are within the

range commonly found in Florida streams (Friedmann

and Hand, 1989).

Table 6. Statistical summary of selected water-quality data from the Braden River near the Lorraine station and from the

surficial aquifer system at the Lakewood Ranch and Lorraine Road transect sites

[μS/cm, microsiemens per centimeter; mg/L, milligrams per liter, μg/L, micrograms per liter; --, no value; No. number]

1Mean value is estimated using a log-probability regression to predict the values below the detection limit.

Property

or constituent

No.

of

samples

Braden River near Lorraine

(02300032)

No.

of

samples

Lakewood Ranch

Transect

No.

of

samples

Lorraine Road

Transect

Max Mean Min Max Mean Min Max Mean Min

Specific conductance

(μS/cm)

 18 917 454 172 6 529 210 66 8 573 448 403

Nitrogen, ammonia, total

(mg/L as N)

 16 0.07 1 0.03 <0.01 4 0.03 -- 0.01 5 0.98 -- <0.01

Nitrogen, ammonia plus

organic, total

(mg/L as N)

 17 1.1 .65 .40 4 1.2 -- .22 5 2.1 -- .05

Nitrogen, nitrite, total

(mg/L as N)

 16 .01 1 .01 <.01 4 .01 -- <.01 5 .04 -- <.01

Nitrogen, NO2 +NO3, total

(mg/L as N)

 16 .14 1 .04 <.01 4 3.8 -- .28 5 .58 -- <.02

Phosphorus, total

(mg/L as P)

 17 .51 .25 .09 4 .30 -- <.02 5 .33 -- .02

Orthophosphorus, total

(mg/L as P)

 16 .48 .22 .08 4 .04 -- .01 5 .16 -- <.01

Organic carbon, total,

(mg/L as C)

 16 46 21 9.9 5 46 -- 3.9 5 70 -- 45

Dissolved solids

(mg/L)

 18 700 328 146 4 320 -- 82 4 390 -- 264

Calcium, dissolved

(mg/L as Ca)

 18 120 53 17 4 57 -- 5.5 5 98 -- 65

Magnesium, dissolved

(mg/L as Mg)

 18 43 18 5.70 4 25 -- 2.1 5 7.0 -- 3.6

Sodium, dissolved

(mg/L as Na)

 18 18 12 6.4 4 6.1 -- 2.0 5 12 -- 9.8

Potassium, dissolved

(mg/L as K)

 18 10 4.8 .90 4 11 -- 2.9 5 1.4 -- .50

Chloride, dissolved

(mg/L as Cl)

 20 29 20 10 10 15 7.4 1.8 11 21 15 6.1

Sulfate, dissolved

(mg/L as SO4)

 19 360 122 27 4 200 -- 7.7 5 130 -- <.20

Strontium, dissolved

(μg/L as Sr)

17 12,000 3,250 490 4 1,600 -- 470 5 840 -- 530

Fluoride, dissolved

(mg/L as F)

 18 .70 .27 .20 4 .10 -- <.10 5 .20 -- .10
Water Quality 15

Organic nitrogen was the dominant nitrogen

species in surface-water samples from the Braden

River near Lorraine station. Organic nitrogen can be

considered to be an indicator of pollution through disposal of sewage or organic waste (Hem, 1985, p. 124);

however, sewage is not disposed of in the watershed

upstream of the gaging station. Agriculture and cattle

grazing are major activities that occur in this area, and

are probably the major source of nitrogen in the river.

Inorganic nitrogen reaching the river is quickly taken

up by algae and aquatic vegetation, leaving mostly

organic nitrogen in the river water. Concentrations of

ammonia plus organic nitrogen ranged from 0.40 to

1.1 mg/L and concentrations of nitrite plus nitrate

nitrogen ranged from below detection limits to

0.14 mg/L (table 6).

Ground water from the surficial aquifer system

was sampled at the Lorraine Road site, located in an

area used to graze cattle (T3, fig. 3) and at the Lakewood Ranch site, located near the Braden River near

Lorraine station (T2, fig. 3). Ammonia was the dominant species of nitrogen in four of the five groundwater samples collected at the Lorraine Road site.

These samples were collected between July and

November 1996 during wet conditions when the water

table was relatively high. Concentrations of ammonia

nitrogen in these samples ranged from 0.53 to

0.98 mg/L. During wet conditions, organic nitrogen

from manure is converted anerobically to ammonia

and percolates to the water table during rainfall.

Nitrate nitrogen was the dominant source of nitrogen

in the fifth sample collected in January 1997, during

an extended dry period. The nitrate concentration was

about 0.54 mg/L and the concentration of ammonia

was below the detection limit, indicating that nitrification (the process by which the nitrogen in ammonia is

aerobically oxidized forming nitrite and then nitrate

nitrogen) had occurred. McNeal and others (1994)

Sulfate(SO )+Chloride(Cl) 4

Calcium(Ca)+Magnesium(Mg)

Carbonate(CO )+Bicarbonate(HCO ) 3

3

Sodium(Na)+Potassium(K)

Magnesium(Mg)

Sulfate(SO )4

Calcium (Ca) Chloride (Cl)

CATIONS ANIONS Equivalent concentration

percentages

EXPLANATION

20 20

40 40

60 60

20

40

60

80 20

40

60

80

80

20

40

60

80

80

20

40

60

80

20

40

60

80

80 60 40 20 20 40 60 80

20

40

60

80

Surficial aquifer system samples

Surface-water samples

Upper Floridan aquifer samples

Intermediate aquifer system samples

Figure 6. Major cation and anion equivalent concentration percentages

of surface water at the Braden River near the Lorraine station and

ground water at the Lorraine Road and Lakewood Ranch surficial aquifer

system well transects, and from the intermediate aquifer system and the

Upper Floridan aquifer.
16 Water Budget and Water Quality of Ward Lake, Flow and Water-Quality Characteristics of the Braden River Estuary,

and the Effects of Ward Lake on the Hydrologic System, West-Central Florida

observed that high nitrate levels occur in ground water

underlying vegetable fields during specific times of the

year, coinciding with pre- and post-planting activities

and that these conditions do not persist. Correlation

between the timing of the nitrate spikes observed by

McNeal and nitrate levels in samples collected during

this study could not be established.

Nitrate nitrogen was the dominant nitrogen

species at the Lakewood Ranch transect site. Concentrations of nitrite plus nitrate ranged from 0.28 to

3.8 mg/L and concentrations of ammonia plus organic

nitrogen ranged from 0.22 to 1.2 mg/L (table 6).

The area was used for row crops and cattle grazing

prior to 1994; however, rapid residential development

has occurred in this area since. Lawn and landscape

fertilization is probably the source of nitrate in the

ground water at the Braden River near Lorraine station.

Nitrogen concentrations in all samples from the

Braden River near Lorraine station and from the surficial aquifer system are below the limits specified by

the FDEP (1994) for Class I waters and the USEPA

(1986) for drinking water. A slightly increasing trend

of about 0.7 (mg/L)/yr, in the concentration of total

nitrogen was observed in samples collected from the

river at this station.

 Total phosphorus concentrations in samples

from the Braden River near Lorraine station ranged

from 0.09 to 0.51 mg/L. Total phosphorus concentrations in the ground-water samples collected at from

the surficial aquifer system ranged from below the

detection limit to 0.30 mg/L at the Lakewood Ranch

transect and from 0.02 to 0.33 mg/L at the Lorraine

Road transect. Orthophosphate was the dominant

species of phosphate in most samples and is the most

bioavailable form of phosphorus (table 6). Most total

phosphate concentrations were above the recommended upper concentration limit of 0.10 mg/L set by

the USEPA (1986) to control eutrophication; however,

these concentrations appear to be a natural condition.

Research conducted by the University of Florida,

Institute of Food and Agricultural Sciences (Stanley

and others, 1995) indicates that some orthophosphate

may move from vegetable production beds; however,

naturally occurring phosphate deposits appear to be

introducing considerable amounts of phosphorus into

the shallow ground- and surface-water systems in

west-central Florida. A significant trend in the concentration of phosphorus was not observed during this

study.

Total organic carbon can be a concern for water

managers when the concentration becomes great

enough to cause harmful disinfection byproducts to

form during treatment for water supply. Concentrations ranged from 9.9 to 46 mg/L, in samples from the

river at the Braden River near Lorraine station (table 6).

An increasing trend of about 5.7 (mg/L)/yr in the concentration of total organic carbon was observed in

samples collected at this station.

 Slight seasonal variations were observed in

specific conductance and in nutrient and major ion

concentrations in the river water. Specific conductance

and most major ion concentrations were higher in

samples collected during the dry season (October

through May) than in samples collected during the wet

season (June through September). However, concentrations of nutrients were slightly higher during the

wet season than during the dry season. Higher major

ion concentrations during the dry season are caused by

evaporation of river water, ground-water base flow to

the river, and less dilution by rainfall or stormwater.

Higher nutrient concentrations during the wet season

are caused by increased loading due to stormwater

runoff and drainage from wetlands, which may be significant sources of nitrogen (Conservation Consultants

Inc., 1983).

Tributaries to Ward Lake

The six tributaries that drain to Ward Lake

include Hickory Hammock Creek, Cooper Creek,

Tributary No. 1 to Cooper Creek, Cedar Creek, Rattlesnake Slough, and Nonsense Creek. Rapid, mediumto-high-density residential development has occurred

in the Hickory Hammock Creek, Tributary No. 1 to

Cooper Creek, and Cedar Creek subbasins, and residential development has been increasing in the northern and western part of the Cooper Creek subbasin.

Rattlesnake Slough drained improved pastureland, a

residential area, and a golf course for most of the

study. Currently the pastureland is being developed for

additional residential use. The Nonsense Creek subbasin, which was largely undeveloped for most of the

study, except for a commercial area near the intersection of Interstate Highway 75 and State Highway 70,

is also being developed with additional commercial

centers and medium-to-high-density residential areas.

Specific conductance values at the six stations

ranged from 181 to 894 μS/cm (table 7). The highest

specific conductance value was measured at the Cedar
Water Quality 17

Table 7. Statistical summary of selected water-quality data from the tributaries draining into Ward Lake

[μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms per liter; No., number]

1Mean value is estimated using a log-probability regression to predict the values below the detection limit.

Property

or constituent

No.

of

samples

Hickory Hammock Creek

(02300034)

No.

of

samples

Cooper Creek

(023000355)

No.

of

samples

Tributary 1 to Cooper Creek

(02300036)

Max Mean Min Max Mean Min Max Mean Min

Specific conductance

(μS/cm)

14 507 420 326 11 784 561 379 10 795 506 292

Nitrogen, ammonia, total

(mg/L as N)

18 0.08 10.04 <0.01 14 0.35 0.13 0.03 13 0.14 0.04 0.02

Nitrogen, ammonia plus

organic, total (mg/L as N)

18 1.1 .53 .26 14 1.7 .95 .53 13 1.50 .83 .51

Nitrogen, nitrite, total

(mg/L as N)

17 .02 1 .01 <.01 14 .04 1 .01 <.01 13 .03 1 .01 <.01

Nitrogen, NO2 + NO3, total

(mg/L as N)

17 .24 .10 .05 14 .24 1 .05 <.01 13 .33 1 .06 <.01

Phosphorus, total

(mg/L as P)

18 .36 .11 .04 14 .88 .27 .07 13 .73 1 .18 <.20

Orthophosphorus, total

(mg/L as P)

17 .15 .08 .05 14 .77 .23 .04 13 .57 .17 .02

Organic carbon, total

(mg/L as C)

18 49 21 7.9 14 57 22 7.9 13 80 33 14

Dissolved solids

(mg/L)

18 378 283 214 14 558 373 234 13 616 365 8

Calcium, dissolved

(mg/L as Ca)

18 78 57 36 14 120 78 52 13 120 74 41

Magnesium, dissolved

(mg/L as Mg)

18 21 10 7.0 14 21 10 6.0 13 27 13 4.7

Sodium, dissolved

(mg/L as Na)

18 19 14 11.0 14 21 15 11.0 13 29 18 11

Potassium, dissolved

(mg/L as K)

18 5.5 3.4 1.4 14 9.8 4.5 1.1 13 14 4.7 1.3

Chloride, dissolved

(mg/L as Cl)

18 31 23 18 14 29 21 13 13 36 26 14

Sulfate, dissolved

(mg/L as SO4)

18 140 66 39 14 230 105 39 13 260 102 31

Strontium, dissolved

(μg/L as Sr)

18 3,500 1,027 520 14 2,200 1,004 570 13 3,330 1,344 340

Fluoride, dissolved

(mg/L as F)

18 .30 .22 .20 14 .40 .253 .20 13 .50 .31 .20

Cedar Creek

(02300037)

Rattlesnake Slough

(02300038)

Nonsense Creek

(02300039)

Max Mean Min Max Mean Min Max Mean Min

Specific conductance

(μS/cm)

15 894 556 397 13 540 415 290 12 654 444 181

Nitrogen, ammonia, total

(mg/L as N)

16 4.7 .36 0.02 17 0.18 0.06 0.02 14 0.25 0.06 0.02

Nitrogen, ammonia plus

organic, total (mg/L as N)

16 5.4 1.0 .50 17 2.10 1.0 .39 14 1.5 .78 .41

Nitrogen, nitrite, total

(mg/L as N)

16 <.01 <.01 <.01 17 .07 1 .02 <.01 14 .01 .010 <.01

Nitrogen, NO2 + NO3, total

(mg/L as N)

16 6.1 .58 .08 17 .73 1 .18 <.01 14 <.01 <.01 <.01

Phosphorus, total

(mg/L as P)

16 .32 .15 .04 17 .62 .36 .12 14 .14 1 .06 <.20

Orthophosphorus, total

(mg/L as P)

16 .21 .11 .06 17 .56 .32 .12 14 .04 .03 .01

Organic carbon, total

(mg/L as C)

16 68 26 6.1 17 49 23 12 14 84 32 6.9

Dissolved solids

(mg/L)

16 594 379 272 17 1,060 312 206 14 412 285 152

Calcium, dissolved

(mg/L as Ca)

16 110 73 52 17 140 48 29 14 130 72 25

Magnesium, dissolved

(mg/L as Mg)

16 24 13 8.4 17 68 14 6.8 14 12 5.5 2.6

Dissolved solids

(mg/L)

16 594 379 272 17 1,060 312 206 14 412 285 152

Calcium, dissolved

(mg/L as Ca)

16 110 73 52 17 140 48 29 14 130 72 25

Magnesium, dissolved

(mg/L as Mg)

16 24 13 8.4 17 68 14 6.8 14 12 5.5 2.6

Sulfate, dissolved

(mg/L as SO4)

15 180 81 49 17 480 74 28 14 39 16 6.7

Strontium, dissolved

(μg/L as Sr)

15 3,300 1,358 690 17 19,000 1,669 360 14 700 375 140

Fluoride, dissolved

(mg/L as F)

16 .50 .39 .30 17 1.2 .56 .40 14 .40 .24 .10
18 Water Budget and Water Quality of Ward Lake, Flow and Water-Quality Characteristics of the Braden River Estuary,

and the Effects of Ward Lake on the Hydrologic System, West-Central Florida

Creek station and probably reflects the influence of

lawn and golf course irrigation water from the deeper

aquifers. The lowest conductance value was measured

at the Nonsense Creek station, on August 18, 1997,

during a period of heavy summer rainfall. The Nonsense Creek subbasin is the smallest of the six subbasins and is highly influenced by stormwater runoff

from the commercial areas and the major roads during

the summer wet season. Specific conductance values

at the Nonsense Creek station averaged about 298

μS/cm during the wet season. The mean specific conductance values measured at each of the six stations

ranged from 415 to 561 μS/cm (table 7). During the

dry season a large part of the water in the tributaries is

base flow from the surficial aquifer system. The high

specific conductance indicates that irrigation water

from the deeper aquifers has influenced the shallow

ground- and surface-water systems. An increasing

trend of about 18 (μS/cm)/yr, in specific conductance

was observed in samples from Hickory Hammock

Creek. Significant trends in specific conductance

values were not observed in samples from the

remaining tributaries during the study.

Major cation and anion equivalent concentration

percentages from samples collected at the six stations

and from the intermediate aquifer system and the

Upper Floridan aquifer collected at the Verna well

field, were plotted on a trilinear diagram. The major

ions in all samples are dominated by either calcium

sulfate or calcium bicarbonate (fig. 7). Ground water

from the surficial aquifer system, at times, is the major

source of water in the tributaries. The high concentrations of major ions in the surface-water samples

(table 7), particularly sulfate and strontium ions, and

the distribution of the plotted equivalent concentration

percentages on the trilinear diagram (fig. 7), indicates

the surficial aquifer system and the tributaries have

been influenced by water from the deeper aquifer systems, probably as a result of lawn, landscape, and golf

course irrigation. Increasing trends in the concentration of chloride and dissolved solids were observed in

samples from Hickory Hammock Creek. The increases

were about 1.7 and 8.4 (mg/L)/yr, respectively.

Increasing trends in the concentration of chloride and

dissolved solids also were observed in samples from

Cedar Creek. The increases were about 1.0 and 12

(mg/L)/yr, respectively. A decreasing trend in chloride

concentration was observed in samples from Rattlesnake Slough. The decrease was about 1.9 (mg/L)/yr.

Significant trends were not observed in the concentration of major ions in samples from the remaining tributaries. With the exception of the concentration of

sulfate in a sample collected at the Tributary No. 1 to

Cooper Creek station and a sample collected at the

Rattlesnake Slough station, all constituent concentrations were below the limits specified by the FDEP

(1994) for Class I waters and are within the range

commonly found in Florida streams (Friedmann and

Hand, 1989).

Organic nitrogen was the dominant nitrogen

species in surface-water samples collected at all six

stations. Cattle grazing has occurred in the Cooper

Creek, Tributary No. 1 to Cooper Creek, Rattlesnake

Slough, and Nonsense Creek subbasins at times during

the study and is a source of the nitrogen in these subbasins. Concentrations of ammonia plus organic nitrogen as nitrogen ranged from 0.26 to 5.4 mg/L (table 7).

Fertilizers applied to lawns, landscaping, or golf

courses is also a source of nitrogen in these subbasins,

as well as in the Hickory Hammock Creek and Cedar

Creek subbasins. Inorganic nitrogen reaching retention

ponds and the tributaries is quickly taken up by algae

and aquatic vegetation, leaving mostly organic nitrogen in water. Nitrogen concentrations were the highest

in the Cedar Creek subbasin and the lowest in the

Hickory Hammock Creek subbasin. A slightly

increasing trend of about 0.4 (mg/L)/yr, in the concentration of total nitrogen was observed in samples collected at the Cooper Creek station. Significant trends

in nitrogen concentrations were not observed in samples from the remaining tributaries to Ward Lake.

Nitrogen concentrations in all samples from the tributaries are below the limits specified by the FDEP

(1994) for Class I waters and the USEPA (1986) for

drinking water.

 Total phosphorus concentrations in samples

from the six tributaries ranged from below the detection limit at the Tributary No. 1 to Cooper Creek and

Nonsense Creek stations to 0.88 mg/L at the Cooper

Creek station. Orthophosphate was the dominant species of phosphate in most samples. Most sample concentrations were above the recommended upper

concentration limit of 0.1 mg/L set by the USEPA

(1986) to control eutrophication; however, the source

is from naturally occurring phosphate deposits.

Decreasing trends of about 0.02 and 0.06 (mg/L)/yr in

the concentration of total phosphorus were observed in

samples from Hickory Hammock and Cedar Creeks,

respectively. An increasing trend of about

0.05 (mg/L)/yr was observed in samples from Cooper
Water Quality 19

Creek, and may be related to the mining of sand and

shell in the subbasin. Trends were not observed in

samples from the remaining tributaries.

Total organic carbon concentrations ranged

from 6.1 to 84 mg/L in samples from the six tributaries. An increasing trend of about 3.1 (mg/L)/yr was

observed in the concentration of organic carbon in

samples collected from Hickory Hammock Creek

during the study. Significant trends were not observed

in the remaining tributaries.

The same seasonal variations observed in specific conductance, and in nutrient and major ion concentrations in the river water at the Braden River near

Lorraine station were observed in water from each

tributary. Specific conductance values and most major

ion concentrations were higher in samples collected

during the dry season than in samples collected during

the wet season, and concentrations of nutrients were

slightly higher during the wet season than during the

dry season.

Ward Lake Outfall

The water in Ward Lake is a composite of water

flowing from the upper reach of the Braden River, all

the tributaries to the lake, and from the surficial aquifer system near the lake. Continuing residential and

commercial development is also occurring in areas

surrounding Ward Lake.

Specific conductance values measured at the

outfall ranged from 150 to 1,000 μS/cm, with a mean

of 451 μS/cm (table 8). Ground-water samples from

the surficial aquifer system at the Linger Lodge well

transect site (fig. 3) are representative of the water in

the surficial aquifer system adjacent to Ward Lake.

Specific conductance values were less than those measured in the surficial aquifer system in the upper reach

of the watershed, in the river, or in Ward Lake, and

ranged from 49 to 70 μS/cm, with a mean value of

56 μS/cm (table 8). The surficial aquifer system in the

area around Ward Lake is not influenced by irrigation

from the deeper aquifers; it is recharged primarily by

Figure 7. Major cation and anion equivalent concentration percentages

of surface water from the tributaries to Ward Lake, and of ground water

from the intermediate aquifer system and the Upper Floridan aquifer.

Sulfate(SO )+Chloride(Cl) 4

Calcium(Ca)+Magnesium(Mg)

Carbonate(CO )+Bicarbonate(HCO ) 3 3

Sodium(Na)+Potassium(K)

Sulfate(SO )4

Magnesium(Mg)

Calcium (Ca) Chloride (Cl)

CATIONS ANIONS

Equivalent concentration

percentages

EXPLANATION

Surface-water samples

Intermediate aquifer system samples

Upper Floridan aquifer samples

20

20

20

20

20

20

20

20

20 20

40

40

40

40 40

40

40

40

40 40

60

60

60

60 60 60

60

60

60 60

80

80

80

80

80

80

80

80

80 80
20 Water Budget and Water Quality of Ward Lake, Flow and Water-Quality Characteristics of the Braden River Estuary,

and the Effects of Ward Lake on the Hydrologic System, West-Central Florida

rainfall, and periodically by lake water. A significant

trend in specific conductance values was not observed

in samples from Ward Lake collected near the outfall

during the study.

Major cation and anion equivalent concentration

percentages from samples collected at the Ward Lake

outfall, from the surficial aquifer system at the Linger

Lodge well transect site (T1, fig. 3), and from the

intermediate aquifer system and the Upper Floridan

aquifer at the Verna wellfield were plotted on a trilinear diagram. The major ions in most samples are dominated by either calcium sulfate or calcium bicarbonate

(fig. 8). Two of the six surficial aquifer ground-water

samples have a higher percentage of sodium and chloride ions, indicating a greater influence from rainfall.

The remaining four surficial aquifer ground-water

samples plot in an area of the diagram that is similar to

lake water samples and probably reflect recharge

conditions from the lake to the aquifer system.

Comparison of water from the deeper aquifers with

water in the surficial aquifer system and in the lake

indicates that the shallow ground- and surface-water

systems are not as influenced by pumpage from the

deeper aquifers as the water in the upper reaches of the

river or in the tributaries draining to the lake. Significant trends in the concentration of major ions were not

observed for samples from Ward Lake. Table 8 presents a summary of selected water-quality data for

samples from Ward Lake and from the surficial aquifer

system at the Linger Lodge transect site.

Organic nitrogen was the dominant nitrogen

species in samples from Ward Lake. Cattle grazing

and inflow from the upper reach of the river and from

the tributaries are the major sources of nitrogen in the

lake. Concentrations of ammonia plus organic nitrogen as nitrogen in samples from the lake ranged from

about 0.55 to about 1.5 mg/L. Nitrate nitrogen was the

dominant species of nitrogen in the ground-water

Table 8. Statistical summary of selected water-quality data from Ward Lake and from the surficial aquifer

system transect site near Linger Lodge

[μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms per liter; No., number]

1Mean value is estimated using a log-probability regression to predict the values below the detection limit.

Property or constituent

No.

of

samples

Ward Lake near Bradenton

(02300042)

No.

of

samples

Linger Lodge

Transect

Max Mean Min Max Mean Min

Specific conductance

(μS/cm)

93 1,000 451 150 9 70 56 49

Nitrogen, ammonia, total

(mg/L as N)

63 0.15 10.04 <0.01 6 0.02 -- <0.01

Nitrogen, ammonia plus organic, total

(mg/L as N)

62 1.5 .90 .55 6 <.20 -- <.20

Nitrogen, nitrite, total

(mg/L as N)

62 .04 1.01 <.01 6 <.01 -- <.01

Nitrogen, NO2 + NO3, total

(mg/L as N)

62 .30 1.03 <.01 6 .37 .21 .07

Phosphorus, total

(mg/L as P)

62 .49 .29 .08 6 .03 -- <.02

Orthophosphorus, total

(mg/L as P)

63 .45 .23 .05 6 .01 -- <.01

Organic Carbon, total,

(mg/L as C)

58 41 15 <.10 6 2.5 2.0 1.8

Dissolved solids

(mg/L)

10 542 296 142 6 48 36 24

Calcium, dissolved

(mg/L as Ca)

11 75 47 20 6 73 15 1.9

Magnesium, dissolved

(mg/L as Mg)

11 35 14 4.7 6 5.3 2.4 .60

Sodium, dissolved

(mg/L as Na)

11 29 16 6.6 6 11 4.4 1.8

Potassium, dissolved

(mg/L as K)

11 7.9 4.8 2.0 6 1.2 .65 .20

Chloride, dissolved

(mg/L as Cl)

11 44 26 11 6 8.3 3.4 .80

Sulfate, dissolved

(mg/L as SO4)

11 220 90 22 6 17 13 8.7

Strontium, dissolved

(μg/L as Sr)

10 12,000 2,664 520 13 300 111 20

Fluoride, dissolved

(mg/L as F)

11 .80 .34 .20 6 <.10 -- <.10
Water Quality 21

samples from the surficial aquifer system collected at

the Linger Lodge transect site. Fertilizer applied to

lawns and inflow from the surficial aquifer system

may also provide inorganic forms of nitrogen to the

lake. Concentrations of nitrite plus nitrate nitrogen in

ground-water samples ranged from 0.07 to 0.37 mg/L.

A significant trend in nitrogen concentration was not

observed during the study. Nitrogen concentrations in

all samples from the tributaries were below the limits

specified by the FDEP (1994) for Class I water and the

USEPA (1986) for drinking water.

 Total phosphorus concentrations from Ward

Lake ranged from 0.08 to 0.49 mg/L. Orthophosphate

was the dominant species of phosphate in most

samples. Most sample concentrations were above the

recommended upper concentration limit of 0.10 mg/L

set by the USEPA (1986) to control eutrophication;

however, the source is from naturally occurring phosphate deposits. A significant trend in the concentration

of phosphorus was not observed during the study.

Total organic carbon concentrations ranged

from below the detection limit to 41 mg/L in samples

from the lake. The concentration of total organic

carbon in samples from the surficial aquifer system at

the Linger Lodge site ranged from 1.8 to 2.5 mg/L.

Inflow from the tributaries and the upper reach of the

Braden River is the primary source of organic carbon

in the lake. Significant water-quality trends were not

observed in water from Ward Lake.

The same seasonal variations observed in specific conductance, nutrient, and major ion concentrations in the river water in the upper reach of the river

and at the tributaries were observed in water from the

lake. Specific conductance values and most major ion

concentrations were higher in samples collected

during the dry season than in samples collected during

the wet season, and concentrations of nutrients were

slightly higher during the wet season than during the

dry season.

Figure 8. Major cation and anion equivalent concentration percentages

of water from Ward Lake, from the surficial aquifer system at the Linger

Lodge well transect, and from the intermediate aquifer system and the

Upper Floridan aquifer.

Sulfate(SO )+Chloride(Cl)

4

Calcium(Ca)+Magnesium(Mg)

Carbonate(CO )+Bicarbonate(HCO ) 3 3

Sodium(Na)+Potassium(K)

Sulfate(SO )4

Magnesium(Mg)

Calcium (Ca) Chloride (Cl)

CATIONS ANIONS

Equivalent concentration

percentages

EXPLANATION

20 20

20 20

20

20

20

20 20

20

40 40

40 40

40

40

40

40

40

40

60 60

60 60

60

60

60

60

60

60

80

80 80

80 80

80

80 80

80 80

Surficial aquifer sytem samples

Surface-water samples

Intermediate aquifer sytem samples

Upper Floridan aquifer samples
22 Water Budget and Water Quality of Ward Lake, Flow and Water-Quality Characteristics of the Braden River Estuary,

and the Effects of Ward Lake on the Hydrologic System, West-Central Florida

Constituent Load

Constituent load is the amount of a constituent

transported by water during a specific time period.

In this report, the load is presented as tons per year

(tons/yr). Loads were calculated using the inflow

volume from the Braden River above Ward Lake, the

tributaries to the lake, runoff from ungaged areas surrounding the lake, ground water, and rainfall. Discharge

at the Ward Lake outfall was used to calculate loads to

the Braden River estuary. Flow volumes were multiplied by the mean concentration of selected constituents

for each flow source, and a conversion factor of

0.037795 to convert inches per year and milligrams per

liter to tons per year. Annual loads from each source

were then summed and reported as the load of selected

constituents to Ward Lake or to the estuary in table 9.

The following equation was used:

L = V x C x 0.037795 (4)

where

L is the calculated load, in short tons per year;

V is inflow volume, in inches per year, over the surface

of Ward Lake (from the water budget);

C is the average annual constituent concentration,

in milligrams per liter.

The greatest inflow to Ward Lake occurred

during the 1995 water year. The greatest loading of

nitrogen, phosphorus, chloride, and dissolved solids

also occurred in 1995. Calcium and sulfate loading to

the lake was greater in 1993, even though inflow to the

lake was less, and may be related to pumpage for agricultural irrigation in the upper reaches of the watershed. Loading of most constituents was the least

during the 1994 and 1996 water years. Both years

were dry, with rainfall and subsequent inflow to the

lake being less than during the 1993, 1995, and 1997

water years. Total organic carbon loads were higher in

the 1995, 1996, and 1997 water years.

 Inflows from the Braden River above Ward

Lake were similar to the combined inflows from the

six tributaries for most of the study period. Constituent

loading patterns also were similar. However, during

the 1996 water year, loading of selected constituents

from the tributaries was between 1.3 and 2.7 times

greater than loading from the Braden River above the

lake. Inflow from the tributaries was also greater than

inflow from the river and may be related to increased

landscape and golf course irrigation in the subbasins.

Constituent loading generally increased as inflow

increased; however, total organic carbon was the

exception. During the 1995, 1996, and 1997 water

years, total organic carbon loads increased unrelated to

inflow (table 9).

Table 9. Estimated loads of selected chemical constituents to Ward Lake and to the Braden River

estuary, water years 1993-97

[in/yr, inches per year; loads are in tons per year]

1Flow volumes are based on the water budget.

Water year

Inflow1 to

Ward Lake

(in/yr)

Total

nitrogen

Total

phosphorus

Total

organic

carbon

Dissolved

solids Calcium Chloride Sulfate

1993 1,827 51 11 931 25,559 4,411 1,516 9,468

1994 1,587 44 12 749 17,944 3,415 1,313 5,843

1995 2,751 99 29 1,481 28,008 4,290 1,957 8,544

1996 1,618 47 11 1,609 15,219 2,847 1,222 3,743

1997 2,268 54 11 1,636 17,957 3,114 1,420 5,279

Mean 2,010 59 15 1,281 20,937 3,615 1,486 6,575

Water year

Outflow1 to

the Braden

River

estuary

(in/yr)

Total

nitrogen

Total

phosphorus

Total

organic

carbon

Dissolved

solids Calcium Chloride Sulfate

1993 1,551 47 18 522 15,476 2,872 1,348 3,928

1994 1,310 52 13 629 15,745 2,674 1,337 4,803

1995 2,492 98 36 1,412 22,604 3,391 1,695 6,216

1996 1,351 41 13 919 13,429 2,196 1,225 3,166

1997 1,977 73 19 1,270 14,645 2,167 1,420 2,615

Mean 1,736 62 23 1,175 16,380 2,660 1,405 4,146
Characteristics of the Braden River Estuary 23

The greatest outflow from Ward Lake and the

greatest constituent loading to the Braden River estuary occurred during the 1995 water year. Loading of

constituents to the estuary also generally increased as

flow increased. The load of total organic carbon, dissolved solids, calcium, chloride, and sulfate being discharged to the estuary were less than those entering

the lake. Only a small amount of the difference can be

attributed to pumpage from the lake for water supply.

The lake appears to be a sink for these constituents.

Nitrogen loading to the estuary exceeded nitrogen

loading to the lake during the 1994 and 1997 water

years. Nitrogen loading to the estuary was less than

nitrogen loading to the lake during the remainder of

the study. The variability may be related to evaporation of lake water and to growth cycles of phytoplankton and aquatic vegetation in the lake and along

shallow shorelines. Phosphorus loading to the estuary

exceeded phosphorus loading to the lake during the

entire study. Naturally occurring phosphatic clay

deposits underlie west-central Florida, including the

Braden River watershed, and introduce considerable

amounts of phosphorus into the surface-water system

(Stanley and others, 1995). Dissolution of phosphorus

from clay deposits underlying the lake probably

account for the difference.

CHARACTERISTICS OF THE BRADEN

RIVER ESTUARY

The Braden River below the Ward Lake outfall

is brackish and is tidally influenced. The estuary

receives freshwater from four major sources: Ward

Lake, Williams Creek, Gap Creek, and Glen Creek

(fig. 3, and table 1). Freshwater flow to the estuary is

important for the ecological health of the system. The

SWFWMD has been charged by the State of Florida to

establish minimum levels of flow for rivers in westcentral Florida. Minimum flows will be based on various rates of freshwater flow that will provide a specific

range of fresh and saline waters in the estuary, and on

how these flow rates will affect existing water supplies

(SWFWMD, 1997, p. 1). Streamflow, specific conductance, and water-quality data have been collected by

the USGS to improve the understanding of the characteristics of the Braden River estuary.

Streamflow and water-quality data have been

collected at the Ward Lake outfall, Williams Creek,

Gap Creek, and Glen Creek. Continuous specific

conductance data have been collected at the Braden

River near Elwood Park and Braden River near

Bradenton sites, and quarterly specific conductance

measurements have been made at ten locations in the

river. A regression analysis was performed to derive

an equation that could be used to predict salinity in the

river. The quarterly measurements were used to construct salinity profiles.

Inflows

Flow from Ward Lake is the main source of

freshwater to the estuary. Annual mean flow from

Ward Lake, for water years 1993 through 1997, was

69.2 ft3/s; however, the median flow from the lake was

only 6.5 ft3/s. Median flows are about an order of magnitude smaller than mean flows. Flow events greater

than 200 ft3/s only occur about 10 percent of the time

and there are many days when there is no flow from

the lake. Williams Creek drains a small subbasin and

discharges to the upper part of the estuary, about 1 mi

downstream of the outfall. Annual mean flow at the

station is 2.5 ft3/s, but Williams Creek has a median

flow of only 0.5 ft3/s and periods of no flow. Gap

Creek is the second largest subbasin in the watershed

and is also the second largest source of freshwater to

the estuary. Annual mean flow is 11.2 ft3/s, and

median flow is about 3.5 ft3/s. Gap Creek had no zero

flow days during the study; it discharges to the river

near Williams Creek. Glen Creek is the third major

freshwater creek discharging to the river; it drains to

the lower part of the estuary and has an annual mean

flow of 3.2 ft3/s and a median flow of about 1.2 ft3/s.

Tidal Fluctuations

Analysis of elevation data from the two continuous tidal stations indicated there is about a 1-hour lag

between stations and that the tides occur as a progressive wave in the river. Spectral analysis (Sheng, 1994,

p. 59) of tidal data for both stations showed the strongest signal at 12.4 hours and two weaker, but broader

signals at 23.9 and 25.8 hours. These signals define the

tide as a mixed (semidiurnal and diurnal) tide. Tidal

elevations are also affected by an overlying seasonal

fluctuation due to increased freshwater flows. The

mean tidal elevation was 0.9 ft higher in the wet

season than in the dry season during the 1995 water

year, and 0.5 ft higher during the 1997 water year.
24 Water Budget and Water Quality of Ward Lake, Flow and Water-Quality Characteristics of the Braden River Estuary,

and the Effects of Ward Lake on the Hydrologic System, West-Central Florida

This effect precludes the use of tidal data collected

from estuaries or bays affected by freshwater flows for

the purpose of estimating “sea level rise.”

Elevation of the high tide in the river is normally several feet below the crest of the outfall; however, storm events on March 13, 1993, and October 7,

1996 caused tidal elevations to overtop the outfall,

impacting the city of Bradenton’s water supply with

brackish water. The high chloride concentrations were

quickly flushed out of the system by freshwater flows

from upstream. Peak tidal elevations during these

storms were 4.91 and 4.37 ft above sea level, respectively. Zero flow occurs at the outfall at an elevation of

3.82 ft above sea level.

Salinity

Salinity is difficult to measure in the field, but

specific conductance can easily be measured and salinity can be approximated from these measurements.

Therefore, specific conductance was used in this study

to approximate salinity. Conductance values of 1,000,

18,500, and 20,000 μS/cm are about 0.5, 6.0, and

12.0 parts per thousand (ppt) salinity, respectively.

Continuous specific conductance was recorded

at the Braden River near Elwood Park station between

1994 and 1997 and at the Braden River near Bradenton station between 1995 and 1997. The daily mean

conductance at the Elwood Park station exceeded

1,000 μS/cm, or about 0.5 ppt, more than 70 percent

of the time. This value was exceeded more than

99 percent of the time at the Bradenton station (fig. 9).

Median daily mean conductance at the Elwood Park

and the Bradenton stations was about 9,000 and

30,000 μS/cm (5.5 and 18.5 ppt salinity), respectively.

Simple linear regression analysis was performed

using the daily mean discharge from Ward Lake and

the daily mean specific conductance values from the

Elwood Park station. A strong relation between low

freshwater flow and high specific conductance exists;

however, the data show a great variability for flow

rates less than 100 ft3/s and did not result in a strong

regression equation. Monthly mean values of specific

conductance and flow at the outfall also were compared and showed similar results.

The freshwater/saltwater interface was considered to be 0.5 ppt salinity, for this report. The interface

can be estimated by observing the position of lines of

equal salinity, commonly referred to as isohaline lines.

Salinity profiles were constructed from 14 sets of

specific conductance measurements made between the

outfall and the mouth of the river. Measurements were

made between September 1993 and August 1997, and

were made at or near high tides to minimize tidal

effects on the data. Simple linear regression analysis

of the position of the measured isohaline lines and the

7-day flow over the outfall was used to derive equations that could be used to predict the position of the

isohaline lines. Similar to the results of the regression

analysis of the continuous data, the resulting equations

could not reliably predict the position when flows

were less than 100 ft3/s. Multiple linear regression

analysis of the position of the measured isohaline lines

and flows at the outfall, at Gap Creek and at Williams

Creeks was also used with similar results. Conservation Consultants, Inc. (CCI), a consulting company for

the city of Bradenton, developed regression equations

based on 48 sets of measurements and also concluded

that, because of scatter in the data at low flows, the

equations could not reliably predict the position of isohaline lines (CCI, 1997). Antecedent salinity conditions in the river probably have a greater effect on the

position of isohaline lines than low-to-moderate flow

rates at the outfall. Another factor influencing the

regression analysis is the assumption that the lowest

salinity is at the outfall and the highest salinity is at the

mouth of the river. Often, the lowest salinities were

measured at the confluence of Williams and Gap

Creeks, about 1-mi downstream of the outfall. Four

salinity profiles of the Braden River estuary representing several different freshwater-flow conditions are

shown in figure 10.

On October 4, 1994, following a long wet

season and a recent storm event, salinity was the

lowest measured during the study. Salinity was below

3.0 ppt from the outfall to near the mouth (fig. 10a).

Flow at the time of measurement was 432 ft3/s.

Continuous specific conductance data indicate salinity

was below 0.5 ppt for most of July, 1994 and from

August 9 through October 18, 1994. The low salinity

antecedent condition and a moderate-flow event

caused the 0.5-ppt isohaline line to be located about

3 mi downstream of the outfall.

Figure 10b shows the salinity distribution in the

estuary on March 29, 1996, the first day of a moderate

freshwater-flow event that occurred after a period of

no flow at the outfall. Flow at the time of measurement

was 186 ft3/s. The 0.5-ppt isohaline line was located

near the outfall and a stratified condition existed for

about 2 mi downstream. The extent of the lens of
Characteristics of the Braden River Estuary 25

fresher water was enhanced by flows from Williams

and Gap Creeks. The 6-, 9-, 12-, and 15-ppt isohaline

lines are closely spaced about 3 mi downstream of the

outfall. High salinity antecedent conditions existing in

the river prior to the moderate-flow event resulted in

stratification in the upper part of the river and confinement of the 0.5-ppt isohaline line to a small area near

the outfall.

 Salinity data collected on March 8, 1994, at the

end of a week-long moderate, freshwater-flow event,

showed stratification occurs for about 2 mi downstream of the outfall (fig. 10c). Flow at the time of

measurement was 1.7 ft3/s. High antecedent salinity

conditions existed prior to the flow event. The lowest

salinity was not measured near the outfall, but in the

vicinity of Williams and Gap Creeks. This profile

is common in about 35 percent of the profiles

constructed from USGS data and illustrates the

influence of Williams and Gap Creeks on the salinity

distribution in the upper estuary.

On April 25, 1997, after an extended dry period

with no flow at the outfall, the lowest salinity measurements were again in the vicinity of Williams and

Gap Creeks (fig. 10d). High antecedent salinity conditions existed in the estuary and there was no flow at

the outfall. However, mean daily outflow from the

creeks to the estuary for the week prior to the measurement was about 11 ft3/s.

The salinity profiles show the influence of freshwater flows from Williams and Gap Creeks on the distribution of salinity in the river. They also illustrate the

difficulty in fitting the measured data to linear regression models that assume that freshwater flow from the

outfall is the only input to the system.

0 10 20 30 40 50 60 70 80 90 100 100

50,000

200

300

400

500

700

1,000

2,000

3,000

4,000

5,000

7,000

10,000

20,000

30,000

40,000

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER

PERCENT OF TIME SPECIFIC CONDUCTANCE WAS EQUALED OR EXCEEDED

EXPLANATION

MINIMUM

MEAN

MAXIMUM

ELWOOD PARK

BRADENTON

Figure 9. Duration curves of specific conductance at the Braden River near Elwood Park and the Braden River

near Bradenton stations.
26 Water Budget and Water Quality of Ward Lake, Flow and Water-Quality Characteristics of the Braden River Estuary,

and the Effects of Ward Lake on the Hydrologic System, West-Central Florida

3

0.5

21

18

15

0.5

12

9

6

3

Sea

Level

 1

 2

 3

 4

 5

 6

 7

 8

 9

 10

Sea

Level

 1

 2

 3

 4

 5

 6

 7

 8

 9

 10

65432 1 0

October 4, 1994

Q Outfall = 432 cubic feet per second

a

b

Channel

bed

water surface

water surface

March 29, 1996

Q Outfall = 186 cubic feet per second

Bradenton Station

Glen Creek

Williams and Gap Creeks

Elwood Park Station

Ward Lake Outfdall

27

24

21

18

18

15

12

27

21

18

15

12

9

6 3

30

24

March 8, 1994

Q Outfall = 1.7 cubic feet per second

water surface

Sea water surface Level

 1

 2

 3

 4

 5

 6

 7

 8

 9

 10

Sea

Level

 1

 2

 3

 4

 5

 6

 7

 8

 9

 10

DISTANCE, IN MILES FROM THE OUTFALL

c

d

VERTICAL SCALE GREATLY EXAGGERATED

15 Isohaline line, showing equal salinity concentration in parts per thousand. Interval varied 

EXPLANATION

April 25, 1997

Q Outfall = 0 cubic feet per second

DEPTH, IN FEET BELOW MEAN SEA LEVEL

Figure 10. Salinity profiles of the Braden River estuary.
Characteristics of the Braden River Estuary 27

The effects of a large flow event at the outfall on

the entire estuary are shown in figure 11. A storm event

at the end of October 1995 caused a peak flow of

1,250 ft3/s at the outfall on November 1. Flow in

Williams and Gap Creeks also peaked on November 1,

with a combined peak flow of 317 ft3/s. Specific conductance at the Elwood Park station decreased immediately. Conductance at the Bradenton station decreased

over a 12-hr period to below 5,000 μS/cm, and

remained at that level for about 4 days. Conductance at

the Elwood Park station remained below 1,000 μS/cm

for about 18 days, even though flow at the outfall had

fallen to below 100 ft3/s after 5 days. Conductance

began to rise at the Elwood Park station after 18 days,

but after only 3 days at the Bradenton station. A large

freshwater-flow event affects the specific conductance

near the Bradenton station for a much shorter time

period because of its proximity to the Manatee River

and the Gulf of Mexico. Fluctuations in the conductance data shown in figure 10 are the result of tidal

pumping as the salinity wedge is moved further

upstream with each successive tide cycle.

0

1,400

200

400

600

800

1,000

1,200

DISCHARGE,

IN CUBIC FEET PER SECOND

0

10,000

2,000

4,000

6,000

8,000

SPECIFIC CONDUCTANCE,

IN MICROSIEMENS PER CENTIMETER

28 29 30 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

October November

1995

0

30,000

10,000

20,000

Braden River at Ward Lake Outfall

02300042

Braden River near Elwood Park

02300044

Braden River near Bradenton

02300064

Figure 11. Comparison of instantaneous discharge at the Ward Lake outfall with specific conductance at the

Braden River near Elwood Park and the Braden River near Bradenton stations, October 28 to November 20, 1995.
28 Water Budget and Water Quality of Ward Lake, Flow and Water-Quality Characteristics of the Braden River Estuary,

and the Effects of Ward Lake on the Hydrologic System, West-Central Florida

Water Quality in the Tributaries that Drain to

the Braden River Estuary

The Williams Creek subbasin was largely an

agricultural area with some residential areas for most

of the study; however, rapid residential and commercial development has occurred recently in the western

part of the subbasin. The Gap Creek subbasin is the

largest of the subbasins draining to the estuary and

contains heavily developed residential, commercial,

and industrial areas, as well as citrus groves and some

cattle grazing areas. The Glen Creek subbasin is the

smallest of the three subbasins and drains urban and

highly industrialized areas and a large orange grove.

Specific conductance values at the three tributaries ranged from 144 to 1,270 μS/cm (table 10). The

highest conductance value was measured at the Glen

Creek station. The lowest conductance value was

measured at the Williams Creek station. Mean specific

conductance values for the Williams, Gap, and Glen

Creek subbasins were 352, 733, and 1,010 μS/cm,

respectively (table 10). Significant trends in specific

conductance were not observed in the tributaries

during the study.

The major ions in samples from these tributaries

are dominated by calcium bicarbonate and calcium

sulfate, similar to samples from tributaries that drain

to Ward Lake. Ground water from the surficial aquifer

system is, at times, a major source of water in the

tributaries. The major ion concentrations, particularly

sulfate and strontium (table 10), in samples from these

creeks indicate that the shallow ground-water and the

surface-water systems have been influenced by water

Table 10. Statistical summary of selected water-quality data from the tributaries draining to the Braden River estuary, water

years 1995-97

[μS/cm, microsiemens per centimeter; mg/L, milligrams per liter; μg/L, micrograms per liter; No., number]

1Mean value is estimated using a log-probability regression to predict the values below the detection limit.

Property or constituent

No.

of

samples

Williams Creek

(02300050)

No.

of

samples

Gap Creek

(023000356)

No.

of

samples

Glen Creek

(02300062)

Max Mean Min Max Mean Min Max Mean Min

Specific conductance

(μS/cm)

17 748 352 144 18 1,060 733 586 18 1,270 1,010 342

Nitrogen, ammonia, total

(mg/L as N)

17 0.10 0.05 0.01 21 0.22 0.10 0.03 18 0.29 0.11 0.01

Nitrogen, ammonia plus organic, total

(mg/L as N)

17 1.5 .96 .48 21 2.1 .99 .68 18 1.4 .91 .57

Nitrogen, nitrite, total

(mg/L as N)

17 .03 1 .01 <.01 21 .07 .03 <.01 18 .26 1 .09 <.01

Nitrogen, NO2 + NO3, total

(mg/L as N)

17 .54 1 .06 <.02 21 .32 .20 .04 18 7.3 3.9 .19

Phosphorus, total

(mg/L as P)

17 .49 .21 .04 21 1.2 .54 .28 18 .44 .28 .08

Orthophosphorus, total

(mg/L as P)

17 .43 .18 .03 21 .93 .46 .26 18 .34 .22 .04

Organic carbon, total,

(mg/L as C)

 4 65 -- 27 6 70 50 16 4 74 -- 8.5

Dissolved solids

(mg/L)

17 524 253 134 21 782 492 292 17 936 726 210

Calcium, dissolved

(mg/L as Ca)

 4 63 -- 16 6 120 82 52 4 110 -- 41

Magnesium, dissolved

(mg/L as Mg)

 4 13 -- 4.8 6 43 22 11 4 60 -- 9.2

Sodium, dissolved

(mg/L as Na)

 4 14 -- 10 6 38 28 16 4 40 -- 14

Potassium, dissolved

(mg/L as K)

 4 5.1 -- 3.0 6 5.5 5.4 4.4 4 7.70 -- 3.6

Chloride, dissolved

(mg/L as Cl)

 4 26 -- 17 6 74 47 25 4 70 -- 15

Sulfate, dissolved

(mg/L as SO4)

 4 73 -- 12 6 280 139 65 4 290 -- 36

Strontium, dissolved

(μg/L as Sr)

 4 610 -- 320 6 8,800 3,420 1,300 4 1,200 -- 320

Fluoride, dissolved

(mg/L as F)

 4 .30 -- .10 6 .80 .55 .40 4 .80 -- .30
29

from the deeper aquifers, probably as a result of irrigation in the subbasins. The range in ion concentrations

in samples collected at the Williams, Gap, and Glen

Creek stations is similar to concentrations in samples

from the tributaries that drain to Ward Lake. Comparison of ion ratios for samples collected at Williams,

Gap, and Glen Creeks with samples collected from the

estuary at the Elwood Park station indicates the creeks

have not recently been affected by brackish water

from high tides. An insufficient number of samples

were available to determine if any trends existed for

the major ion concentrations. All constituent concentrations were below the limits specified by the FDEP

(1994) for Class I waters and are within the range

commonly found in Florida streams (Friedmann and

Hand, 1989).

Organic nitrogen was the dominant nitrogen

species in samples collected at the Williams and Gap

Creek stations. Nitrate nitrogen was the dominant

species in samples collected at the Glen Creek station

and is probably related to fertilizer used in the orange

groves and to stormwater runoff from the urban and

industrial areas in the western part of the subbasin.

Significant trends in the concentration of nitrogen

were not observed in these tributaries. Nitrogen concentrations in all samples from the tributaries are

below the limits specified by the FDEP (1994) for

Class I waters and the USEPA (1986) for drinking

water. However, nitrogen concentration in samples

from Glen Creek are greater than in all samples collected from the remaining watershed. Mean total

nitrogen concentration for the samples collected was

4.0 mg/L, and more than half of the samples collected

from this creek had a nitrate concentration greater than

4.0 mg/L. High nitrate concentrations can cause excessive aquatic growth in the creek or in downstream

receiving waters.

 Total phosphorus concentrations ranged from

0.04 to 1.2 mg/L. Orthophosphate was the dominant

species of phosphorus in most samples. Similar to the

tributaries above the outfall, most phosphorus concentrations were above the recommended upper concentration limit of 0.10 mg/L set by the USEPA (1986) for

eutrophication. The source is also from naturally

occurring phosphate deposits underlying the watershed. A significant trend was not observed in phosphorus concentrations during the study.

Total organic carbon concentrations in samples

from the three tributaries ranged from 8.5 to

74 mg/L, and also were similar to concentration

ranges observed in the tributaries above the outfall.

A significant trend was not observed in any of these

tributaries.

With the exception of samples collected at Glen

Creek, specific conductance and the concentration of

dissolved solids were slightly higher for samples

collected during the dry season. Nutrient concentrations were higher in samples collected during the wet

season. Seasonal variation could not be determined for

the Glen Creek subbasin.

EFFECTS OF THE RESERVOIR ON THE

HYDROLOGIC SYSTEM

 The dam, when originally built in 1936, created

a permanent backwater condition in the Braden River

for about 6 mi upstream. The immediate effects on the

hydrology of the watershed were to flood the middle

reach of the river and the lower reaches of the tributaries discharging to the river, raise water levels in the

surficial aquifer system adjacent to the river, change

water quality, and reduce freshwater flow to the estuary during periods of low flow.

The channel structure of the middle reach of the

river is similar to the river channel below the outfall

and appears to be a remnant of the estuarine environment that existed prior to construction of the dam. The

braided, meandering nature of the river channel can be

observed from the outfall upstream to a point about

0.5 mi below the confluence with Hickory Hammock

Creek (fig. 3, table 1). Upstream of this point, the river

exhibits a single channel structure with no evidence of

braiding or oxbows. The average channel slope of the

river changes from about 8 ft/mi to almost flat near

Hickory Hammock Creek. The nature of the river

channel and measurements of the elevation of the river

bottom indicate the extent of the tidal reach was near

Hickory Hammock Creek prior to construction of the

dam. Impoundment of the river raised water levels and

changed this reach from a brackish water estuarine

ecosystem to a freshwater lake ecosystem. Raised

water levels also drowned out the lower reaches of the

tributaries discharging to the river. The resulting backwater condition slows the conveyance of stormwater

from the subbasins and may have an effect on flooding.

Water levels in Ward Lake, which are usually 2

to 3 ft higher than tidal water levels, have raised head

levels in the surficial aquifer system adjacent to the

lake. There is a two-way exchange of water between
30 Water Budget and Water Quality of Ward Lake, Flow and Water-Quality Characteristics of the Braden River Estuary,

and the Effects of Ward Lake on the Hydrologic System, West-Central Florida

the lake and the surficial aquifer system. When lake

levels are higher than head levels in the surficial aquifer, the lake is a source of recharge water to the surficial aquifer system. When lake levels are lower than

head levels in the surficial aquifer system, flow

reverses and the lake receives water discharging from

the surficial aquifer system. Most flow is from the

surficial aquifer system to the lake because rainfall

usually maintains ground-water levels above lake

levels, except during storm events. The ground-water

component of the total flow at the outfall averaged

15.5 percent during the study. The shallow groundwater system is, at times, a major source of water to

the river and would still be a significant component of

the Braden River hydrologic system if the dam had not

been built. Ground water from the surficial aquifer

system discharges to the river throughout the entire

watershed and has often been an overlooked or underestimated component of this hydrologic system.

 The outfall forms a saltwater barrier between

the freshwater in Ward Lake and the brackish water in

the downstream estuary (except occasionally, when a

major storm causes a surge to overflow the dam).

This limits the upstream migration of the saline wedge

and effectively reduces the size of the brackish water

ecosystem available for spawning and for juvenile

saltwater fish populations. However, the outfall has

caused the evolution of a large freshwater ecosystem

with related plant, fish, and wildlife communities.

 Ward Lake appears to have some positive

effects on water quality, acting as a sink for total

organic carbon, dissolved solids, calcium, chloride,

and sulfate. During the study, loads of these constituents discharging to the estuary were less than loads

entering the lake. Only a small amount of the difference can be attributed to removal by pumpage from

the lake for water supply. Constituent loading would

not be expected to decrease if the river were not

dammed. While the lake may be reducing the loading

of some constituents to the estuary, expansion of the

reservoir in 1985, appears to have increased phosphorus loading to the estuary. Phosphatic-clay deposits

were exposed during excavation and increased dissolution of phosphorus from these deposits may be

occurring.

Evaporation losses from the lake are greater

than if the river was in a natural state because of

increased surface area. However, evaporation is a very

small part of the water budget and accounts for an

average of only 2.2 percent of all the outflow during

the study. Losses due to pumpage for public supply are

larger and account for an average of 11.4 percent.

Constituent enrichment caused by evaporation or constituent removal by pumpage have minimal effects on

the water quality of both the lake and the estuary.

Freshwater outflow to the estuary was reduced by an

average of 13.6 percent by evaporation and pumpage

during the study. Discharge to the estuary was less

than inflow to the lake during dry periods of the study

when flow rates were low. An average difference of

about 12 ft3/s (8 Mgal/d) was calculated for the dry

periods for water years 1993-97 and would have been

discharged to the estuary if the dam had not been built.

Reduction in the amount of freshwater flowing to the

estuary can affect the salinity concentration and distribution in the estuary.

SUMMARY AND CONCLUSIONS

The Braden River was dammed in 1936 to

provide the city of Bradenton a source of freshwater

supply. The resulting impoundment was called Ward

Lake and had a storage capacity of about 585 Mgal of

water. Reconstruction in 1985 increased the size of the

reservoir to about 1,400 Mgal, at an elevation of about

3.82 ft above sea level. The lake has been renamed the

Bill Evers Reservoir and drains about 59 mi2.

The Braden River watershed can be subdivided

into three hydrologic reaches which have been

referred to in a previous report as the upper, middle,

and lower reaches of the river. The upper reach consists of a naturally incised, free flowing channel. The

middle reach consists of a meandering channel where

the flow is affected by backwater as a result of the

dam. The lower reach is a tidal estuary, extending

from the outfall to the confluence with the Manatee

River. Six principal tributaries flow into Ward Lake

and three flow into the estuary.

Three major hydrogeologic units underlie the

watershed. They are the surficial, intermediate, and

Floridan aquifer systems. The surficial aquifer system

is primarily an unconfined sand aquifer that is contiguous with land surface and less than 40 ft thick.

The intermediate aquifer system is about 350 ft thick;

however, the aquifer system acts as a confining unit in

the study area. The Floridan aquifer system is a confined system, and only the upper part contains freshwater. The Floridan aquifer system has little effect on

the surficial aquifer or surface-water systems because

of the confining characteristics of the overlying intermediate aquifer system.
Summary and Conclusions 31

Ward Lake receives water from precipitation

falling directly on the lake, surface-water inflows,

direct runoff from adjacent land, and from groundwater seepage. Rainfall measured at two stations was

averaged and used as the rainfall input to the water

budget. Surface-water inflows to the lake were measured at seven streamflow stations and estimated for

the ungaged area by calculating runoff-per-squaremile from the gaged areas. Ground-water seepage,

which ranged between 0.82 and 1.0 in/d, was estimated using flow-net analysis.

Water leaves the lake by evaporation, surfacewater outflow, ground-water outflow, and as withdrawals for public water supply. Evaporation was estimated from pan evaporation measured at the Bradenton 5ESE weather station. Surface outflow was measured at the Ward Lake outfall. Outflow from the lake

to the surficial aquifer system appear to be of limited

extent and duration. Withdrawals for water supply

were obtained from the city of Bradenton.

Water budgets were calculated for the 1993

through 1997 water years. Mean surface-water inflow

to Ward Lake for the 5-year period was 1,645 in/yr, or

about 81.8 percent of the mean inflow. Ground-water

inflow to the lake is the second most significant part of

the inflow component of the budget. Mean groundwater inflow was 311 in/yr, which represents about

15.5 percent of the mean inflow. Rain falling directly

on the lake accounts for about 2.7 percent of the

inflow. Mean surface-water outflow was 1,736 in., or

about 86.4 percent of the mean total outflow. There

was no net ground-water outflow from the lake. Mean

surface-water withdrawals for water supply were

229 in., or about 11.4 percent of the mean total outflow. Evaporation accounted for only 2.2 percent of

the mean total outflow. Change in lake storage on the

water budget was negligible.

Surface water and ground water from the surficial aquifer system in the upper reach of the watershed

has been influenced by more mineralized water from

the intermediate aquifer system and the Upper Floridan aquifer. Ground-water pumpage for agricultural

activities has occurred in this reach of the watershed

for many years. Oganic nitrogen is the dominant species of nitrogen in the surface water at the Braden

River near Lorraine station. Agricultural activities are

the sources of nitrogen in this part of the watershed.

Phosphorus concentrations in most samples exceeded

the USEPA limit of 0.10 mg/L; however, the source of

the phosphorus is naturally occurring phosphate

deposits that underlie most of west-central Florida.

Significant trends in specific conductance or the concentrations of major ions and nutrients were not

observed in samples collected at the Braden River near

Lorraine station. The concentration of total organic

carbon in samples from this station showed an increasing trend of about 5.7 (mg/L)/yr during the study.

The six tributaries that drain to Ward Lake have

been influenced by water from the intermediate aquifer system and the Upper Floridan aquifer. Water is

pumped from these aquifers to irrigate golf courses,

lawns, and landscaping in these rapidly developing

subbasins. Increasing trends in the concentration of

chloride and dissolved solids were observed in samples from Hickory Hammock and Cedar Creeks.

A decreasing trend in the concentration of chloride

was observed in samples from Rattlesnake Slough.

Oganic nitrogen was the dominant species of nitrogen

in water from all six tributaries. Cattle grazing and fertilizer are the sources of nitrogen in these subbasins.

Phosphorus concentrations in most samples exceeded

the USEPA limit of 0.10 mg/L. Decreasing trends in

the concentration of phosphorus were observed in

samples from Hickory Hammock and Cedar Creeks,

and an increasing trend was observed in samples from

Cooper Creek. The concentration of total organic

carbon in samples from the six tributaries ranged

from 6.1 to 84 mg/L. An increasing trend of about

3.1 (mg/L)/yr was observed in samples from Hickory

Hammock Creek. Significant trends were not observed

in samples from the remaining tributaries.

Water in Ward Lake is a composite of all water

flowing from the upper reach of the Braden River, the

tributaries to the lake, and from the surficial aquifer

system near the lake. The surficial aquifer system near

the lake has not been influenced by more mineralized

water from the intermediate aquifer system and the

Upper Floridan aquifer. Oganic nitrogen is the dominant species of nitrogen in the lake water and nitrate

nitrogen was the dominant species in surficial aquifer

system samples. Phosphorus concentrations in most

samples exceeded the USEPA limit of 0.10 mg/L.

The concentration of total organic carbon in samples

from the lake ranged from below the detection limit to

41 mg/L and from 1.8 to 2.5 mg/L in samples from the

surficial aquifer system. Significant trends in any waterquality constituent were not observed during the study.

 Constituent loads for total nitrogen, phosphorus, organic carbon, dissolved solids, calcium, chloride, and sulfate were calculated for each water year.

The greatest loading of nitrogen, phosphorus, chloride, and dissolved solids occurred in 1995. Calcium

and sulfate loading to the lake was greater in 1993.

Loading of most constituents was the least during the
32 Water Budget and Water Quality of Ward Lake, Flow and Water-Quality Characteristics of the Braden River Estuary,

and the Effects of Ward Lake on the Hydrologic System, West-Central Florida

1994 and 1996 water years. Both years were dry, with

rainfall and subsequent inflow to the lake being less

than during the remaining water years of the study.

Total organic carbon loads were higher in the 1995,

1996, and 1997 water years. Loading of most constituents to Ward Lake generally increases as inflow

increases. However, during the 1995, 1996, and 1997

water years, total organic carbon increased unrelated

to flow. The greatest outflow from Ward Lake also

occurred during the 1995 water year. Volumes of total

organic carbon, dissolved solids, calcium, chloride,

and sulfate being discharged to the estuary were less

than those entering the lake. Only a small amount of

the difference can be attributed to pumpage from the

lake for water supply. The lake appears to be a sink for

these constituents. The difference in nitrogen loading

to the lake and to the estuary was variable and may be

attributed to growth cycles of aquatic vegetation in

and around the lake. Phosphorus loading to the estuary

exceeded loading to the lake during the entire study

and may be related to dissolution of phosphate from

clayey deposits underlying the lake.

The Braden River estuary receives freshwater

from four major sources: Ward Lake, Williams Creek,

Gap Creek, and Glen Creek. Ward lake is the main

source of freshwater to the estuary, with an annual

mean flow of 69.2 ft3/s and a median flow of 6.5 ft3/s.

Gap Creek is the second largest source of freshwater

to the estuary and has an annual mean flow of

11.2 ft3/s and a median flow rate of 3.5 ft3/s. Williams

and Glen Creeks have annual mean flows of 2.5 and

3.2 ft3/s and median flows of 0.5 and 1.2 ft3/s,

respectively.

There is about a 1-hour lag in tides between the

mouth of the river and at the Ward Lake outfall. Mean

tidal elevation is higher in the wet season than in the

dry season. Elevation of the high tide in the river is

normally several feet below the crest of the outfall;

however, storm events have caused tidal elevations to

overtop the outfall, impacting the city of Bradenton’s

water supply.

Antecedent salinity conditions in the river probably have a greater effect on salinity profiles than lowto-moderate flow rates at the outfall. Freshwater flows

from Williams and Gap creeks affect the salinity in the

upper part of the estuary, and often, the lowest salinities in the river were measured at the confluence with

Williams and Gap Creeks.

The water draining to the Braden River estuary

from Williams, Gap, and Glen Creeks appears to be

influenced by water from the intermediate aquifer

system and the Upper Floridan aquifer. Comparison of

ion ratios for samples from these tributaries with samples from the estuary at the Elwood Park station also

indicates that saltwater from high tides has not

recently affected the water quality in the creeks.

Organic nitrogen is the dominant species of nitrogen

in water from Williams and Gap Creeks. Nitrate nitrogen was the dominant species in water from Glen

Creek and is probably related to fertilizer use in the

orange groves and to stormwater runoff from the

urban and industrialized areas of the subbasin. Nitrogen concentration in samples from Glen Creek are

greater than in all samples collected from the remaining watersheds. Phosphorus concentrations in most

samples exceeded the USEPA limit of 0.10 mg/L.

Total organic carbon concentrations ranged from 8.5

to 74 mg/L and also were similar to concentration

ranges observed in the tributaries above the outfall.

Significant trends in any water-quality constituents

were not observed in samples from these tributaries.

Prior to the construction of the dam, the tidal

reach of the river probably extended to an area near

Hickory Hammock Creek. Impoundment of the river

raised water levels 2 to 3 feet above tidal water levels,

flooding the middle reach of the river and the lower

reaches of the tributaries that drain to the river. Head

levels also were raised in the surficial aquifer system

adjacent to the lake. Ground water from the surficial

aquifer system discharges to the river throughout the

watershed. During the study, ground water accounted

for an average of 15.5 percent of the total annual flow

at the outfall. Ground water has been an overlooked or

underestimated component of the Braden River

hydrologic system.

The dam forms a barrier between the freshwater

in the lake and the brackish water in the estuary, limiting the upstream migration of the saltwater wedge,

except occasionally when a storm surge causes brackish water to overflow the dam. The lake also acts as a

sink for total organic carbon, dissolved solids, calcium, chloride, and sulfate, decreasing the loads of

these constituents to the estuary.

Discharge to the estuary was decreased by an

average of 13.6 percent by evaporation from the lake

and by pumpage for water supply during the study

period. Reduction in the amount of freshwater flowing

to the estuary can affect the salinity concentration and

distribution in the estuary.
Selected References 33

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