U.S. Geological Survey

Open-File Report 96–634

Prepared in cooperation with

CITY OF BRADENTON PUBLIC WORKS DEPARTMENT

MANATEE COUNTY ENVIRONMENTAL MANAGEMENT DEPARTMENT

SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT

Tallahassee, Florida

1997

Hydrologic Description of the Braden River 

Watershed, West-Central Florida

By M.J. DelCharco and B.R. Lewelling
U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Gordon P. Eaton, 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 80225-0286

Tallahassee, FL 32301 Phone: 800-USA-MAPS
Contents III

CONTENTS

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

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

Purpose and Scope .......................................................................................................................................................... 2

Previous Investigations .................................................................................................................................................... 2

Acknowledgments ........................................................................................................................................................... 2

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

Physiography.................................................................................................................................................................... 4

Climate ............................................................................................................................................................................. 4

Soils.................................................................................................................................................................................. 4

Land Use .......................................................................................................................................................................... 7

Hydrogeology ........................................................................................................................................................................... 9

Surficial Aquifer ............................................................................................................................................................ 11

Intermediate Aquifer System ........................................................................................................................................ 12

Floridan Aquifer System ............................................................................................................................................... 12

Methods of Study..................................................................................................................................................................... 12

Surface Drainage and Gage Network ...................................................................................................................................... 17

Upper Reach................................................................................................................................................................... 18

Braden River near Verna...................................................................................................................................... 18

Tributary No. 1 to Braden River near Lorraine.................................................................................................... 18

Tributary No. 2 to Braden River near Lorraine.................................................................................................... 19

Wolf Slough near Lorraine .................................................................................................................................. 19

Braden River near Lorraine.................................................................................................................................. 19

Middle Reach ................................................................................................................................................................. 19

Hickory Hammock Creek near Lorraine.............................................................................................................. 19

Cooper Creek at University Parkway near Sarasota ............................................................................................ 20

Tributary No. 1 to Cooper Creek near Lorraine................................................................................................... 20

Cedar Creek near Sarasota .................................................................................................................................. 20

Rattlesnake Slough near Sarasota ........................................................................................................................ 20

Nonsense Creek near Bradenton .......................................................................................................................... 21

Ward Lake Outfall near Bradenton ...................................................................................................................... 21

Lower Reach .................................................................................................................................................................. 22

Braden River near Elwood Park........................................................................................................................... 22

Williams Creek near Bradenton ........................................................................................................................... 22

Gap Creek near Bradenton ................................................................................................................................... 22

Glen Creek near Bradenton ................................................................................................................................. 23

Braden River near Bradenton............................................................................................................................... 23

Streamflow at the Ward Lake Outfall ............................................................................................................................ 23

Direct Streamflow Measurements........................................................................................................................ 23

Streamflow Estimate Calculations ....................................................................................................................... 24

Seepage and Leakage Studies .............................................................................................................................. 27

Summary and Conclusions ...................................................................................................................................................... 29

References................................................................................................................................................................................ 29

Figures

1-3. Maps showing:

1. Location of the study area in west-central Florida, showing upper, middle, and lower reaches of the 

Braden River .......................................................................................................................................................... 3

2. Physiographic zones of the Braden River watershed ............................................................................................. 5

3. Braden River watershed drainage network and depressional features................................................................... 6

4. Graph showing average monthly rainfall percentage within the Braden River watershed, 1954-93 ........................... 7

5-10. Maps showing:

5. Dominant soil series in the Braden River watershed ............................................................................................. 8

6. Land use in the Braden River watershed, 1990.................................................................................................... 10
IV Contents

7. Hydrogeologic section A-A′ in southwestern Florida ..........................................................................................11

8. Areas of potential flow at land surface from wells open to the Upper Floridan aquifer ..................................... 13

9. Location of gaging stations and subbasins in the Braden River watershed ......................................................... 15

10. Aerial view of Ward Lake Outfall and piezometer network ................................................................................ 17

11. Graph showing river-bottom profile from mouth to headwaters ................................................................................ 18

12. Sketch showing Ward Lake weir survey..................................................................................................................... 21

13–16. Graphs showing:

13. Rating curve for Ward Lake Outfall near Bradenton ........................................................................................... 24

14. Flow duration curve for Ward Lake Outfall, water years 1993-94 ...................................................................... 25

15. Gage heights and weir coefficients ..................................................................................................................... 26

16. Mean, maximum, and minimum water levels in piezometers at Ward Lake Outfall .......................................... 27

Tables

1. Physical properties and lithology of dominant soils ............................................................................................................ 9

2. Land use in the Braden River watershed .............................................................................................................................11

3. Wells used in hydrogeologic section A-A′ ..........................................................................................................................11

4. Gaging network in the Braden River watershed................................................................................................................. 16

5. Piezometer water levels around Ward Lake weir ............................................................................................................... 28

Conversion Factors, Vertical Datum, and Additional Abbreviations 

Temperature can be converted between degrees Fahrenheit (oF) and degrees Celsius (oC) as follows: 

oF = 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.

Additional Abbreviations

Multiply inch-pound unit By To obtain

inch (in.) 25.40 millimeter

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

foot (ft) 0.3048 meter

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

foot per mile (ft/mi) 0.3048 meter per mile

mile (mi) 1.609 kilometer

foot squared (ft2

) 0.0929 square meter

cubic foot per second (ft3

/s) 0.02832 cubic meter per second

cubic foot per second per year [(ft3/s)/yr] 0.02832 cubic meter per second per year

gallon (gal) 3.785 liter

million gallons per day (Mgal/d) 0.4381 cubic meter per second

CSI = Crest-stage indicator

NOAA = National Oceanic and Atmospheric Administration

PVC = Polyvinylchloride

ROMP = Regional Observation Monitor Well Program

SWFWMD = Southwest Florida Water Management District

USGS = U.S. Geological Survey
Abstract 1

Hydrologic Description of the Braden River Watershed, 

West-Central Florida

By M.J. DelCharco and B.R. Lewelling

Abstract

The Braden River watershed drains an 

83-square mile area in west-central Florida and is 

the largest tributary to the Manatee River. The 

hydrology of the Braden River was altered in 1936 

when the city of Bradenton created Ward Lake, a 

reservoir with an 838-foot broad-crested weir 6 

miles upstream from the mouth. In 1985 the reservoir, which is the sole source of drinking water for 

the city of Bradenton, was expanded and supplies 

an annual average of 5.7 million gallons of water 

per day. The Braden River can be hydrologically 

divided into three distinct sections that include an 

8.6-mile reach of naturally incised, free-flowing 

channel; a 6.4-mile reach of impounded river created by the Ward Lake reservoir and weir; and a 

6-mile reach of tidal estuary. Ten first-order and 

two second-order tributaries that flow into the 

Braden River were examined in this report.

The Braden River watershed is dominated by 

low topographic relief. The two physiographic 

zones that contain the Braden River watershed, the 

Gulf Coast Lowlands and De Soto Plain, are both 

poorly drained and have numerous depressional 

features. The climate is subtropical with an annual 

average rainfall of 56 inches, annual average temperatures of 72 degrees Fahrenheit, and estimated 

annual lake evaporation of 52 inches. The soil 

series in the watershed are predominantly 

Myakka-Cassia and the EauGallie-Floridana; 

these series are characterized as nearly level and 

poorly drained soils. Land use within the watershed is the fastest changing characteristic that 

affects the hydrology of the system. The western 

half of the watershed is typically urban and 

includes parts of the city of Bradenton. Land use in 

the eastern half of the watershed is predominantly 

agricultural, but the explosive population growth 

of the area is driving the development of medium 

to high-density residential communities. 

The three major aquifers underlying the 

Braden River watershed are the surficial, intermediate, and Floridan aquifer systems. The surficial 

aquifer generally is underlain in places by a clay 

layer that enhances the ground-water flow of the 

surficial aquifer to surface-water bodies. The 

intermediate aquifer system has discontinuous 

water-bearing units, but retards ground-water 

movement between the surficial and Floridan 

aquifer system. The Floridan aquifer system consists of the Upper and Lower Floridan aquifers 

separated by a middle confining unit. The Upper 

Floridan aquifer is the primary source for groundwater withdrawals in the watershed and has, at 

times, heads 20 feet higher than land-surface elevation.

Discharge over the Ward Lake weir into the 

tidal estuary was measured using volumetric and 

standard discharge measurement techniques. 

Annual mean flow for water years 1993 and 1994 

were 59.7 and 57.3 cubic feet per second, respectively. Weir coefficients, calculated from discharge 

measurements, ranged from 0.023 to 2.99, depending on the head of water over the weir, and the 

method of determining length of flow on the weir. 
2 Hydrologic Description of the Braden River Watershed, West-Central Florida

Weir coefficients calculated from the theoretical rating ranged from 0.032 to 3.11. No significant seepage was found around the ends of the weir, and no 

leakage was detected through the weir.

INTRODUCTION

The Braden River is the source of water supply for 

Bradenton, a city with a population of 46,600 people 

in west-central Florida (University Press of Florida, 

1994). The population of west-central Florida has 

increased substantially, and the demand for land and 

water has increased accordingly. Population growth, 

and subsequent land development, is expected to continue. Changing land-use patterns, due to increased 

development, will affect the hydrology of the Braden 

River watershed by altering the runoff characteristics. 

While the population and water-supply needs have 

increased, so has the awareness of potential environmental stresses that result from modifying the volume 

of freshwater flow to estuarine systems. It is necessary 

to identify and evaluate the physical characteristics 

that influence the hydrology of the watershed for 

future water-resource development and planning.

Purpose and Scope

The purpose of this report is to: (a) provide a 

general hydrologic description of the watershed; 

(b) identify ground- and surface-water contributions of 

flow to the Braden River; (c) describe the data collection network established to monitor surface drainage 

in the Braden River watershed, and; (d) present results 

of a preliminary investigation to measure streamflow 

at the Ward Lake Outfall, including surface flow and 

subsurface seepage. This study was conducted in 

cooperation with the City of Bradenton Public Works 

Department, Manatee County Environmental Management Department, and the Southwest Florida Water 

Management District (SWFWMD).

Previous Investigations

Many of the previous investigations that have 

been conducted in the Braden River watershed have 

addressed local effects of specific developments or 

involved limited assessments of the hydrologic 

systems. Geraghty and Miller (1977) investigated the 

ground-water resources of the Palm Aire development 

in the central part of the watershed using existing 

hydrologic and geologic information. Brown (1983) 

investigated the geology, hydrology, and water quality 

of Manatee County and described water-resource 

development and water use for the county. Brown also 

described general land use within the county. Conservation Consultants, Inc. (1983) described the waterquality condition of Ward Lake prior to reconstruction 

of its weir, and provided estimates of flow over the 

weir using theoretical weir coefficients. During the 

expansion of Ward Lake, Camp, Dresser, and McKee 

(1985) studied the land use and land cover in the 

Braden River watershed upstream of the weir for a 

stormwater management plan. Recognizing the need 

for a comprehensive watershed study, the Tampa Bay 

Regional Planning Council (1986) used existing 

studies and data to characterize the watershed with an 

emphasis on water quality. Wanalista (1989) characterized the watershed upstream of the dam, provided a 

volume mass balance for the reservoir and developed 

stormwater management criteria. Wanalista also 

provided estimates for annual streamflow over the 

weir by using drainage area and discharge ratios for 

nearby watershed basins. 

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 Earl Crawley and William Taylor, Bradenton Public Works Department, for their many contributions to the study. Thanks to Bradenton personnel at 

the water treatment plant, Keith McGurn and Clyde 

Crews, who helped to keep the gages in good order. 

Thanks also to the Bradenton Public Works crews who 

helped construct a gage at the weir and who helped 

keep the weir clear of debris. Special thanks are given 

to Robert Brown and Greg Blanchard of the Manatee 

County Environmental Management Department who 

contributed to the study and maintained access paths 

to several of our gaging stations. Thanks are also 

extended to Roger Hill, with the Schroder-Manatee 

Ranch, for authorizing access to ranch property and 

permission to install several streamflow gaging stations and monitor wells. In addition, thanks to Wayne 

Rilko, of Quality Aggregates Inc., for providing information on hydraulic properties and drilling records of 

selected surficial aquifer wells.
Description of the Study Area 3

DESCRIPTION OF THE STUDY AREA

The Braden River is a tributary of the Manatee 

River, which empties into Tampa Bay on the gulf coast 

of Florida (fig. 1). Ward Lake is an impoundment on 

the Braden River that is the sole water supply for the 

city of Bradenton. The lake was formed in 1936 when 

the river was dammed with a weir structure, named the 

John Ward Dam. Ward Lake was enlarged by expanding the reservoir and reconstructing the weir in 1985 to 

assure an annual average supply of 5.7 Mgal/d for the 

city. Bradenton’s current withdrawal permit for the 

reservoir is for an annual average of 5.7 Mgal/d, a 

monthly peak of 6.5 Mgal/d, and a maximum daily 

withdrawal of 8.2 Mgal/d. The water treatment plant is 

designed to withdraw in excess of 6 Mgal/d. The 

Bradenton City Council renamed Ward Lake the Bill 

Evers Reservoir in 1985. This report will use the name 

Ward Lake for the reservoir and Ward Lake weir or 

Outfall for the John Ward Dam. The surface area of 

the lake was enlarged from 167 to 359 acres by 

dredging the channel and the surrounding riverbank 

upstream of the weir (Tampa Bay Regional Planning 

Council, 1986). 

Downstream from the 838-ft wide Ward Lake 

weir, the Braden River is a coastal plain estuary that is 

brackish and tidally influenced. Salinity in the tidal 

reach is affected by the amount of freshwater discharging over the weir, by tributaries that flow directly 

into the reach from nearby drainage basins downstream of the weir, and by upstream migration of 

brackish waters from the Manatee River and Tampa 

Bay. Water-supply withdrawals from the lake are regulated by the SWFWMD. The SWFWMD is concerned 

that withdrawals from the reservoir are decreasing 

freshwater discharges to the estuary.

The study area generally is urban near the western 

watershed boundary, but consists of agricultural land 

and rangelands in the east. Physical aspects, such as 

climate and soils, affect hydrology in the watershed 

though they remain relatively constant; however, other 

aspects that also affect hydrology, such as land use, 

can change rapidly.

Approximately 90 percent of the Braden River 

watershed is in Manatee County, with the remaining 

10 percent in northern Sarasota County. The 83-mi2

watershed extends south-southeast from the Manatee 

27°40′

82°50′ 40′ 30′ 82°20′

30′

27°20′

Braden River

Little Manatee River

Myakka River

Manatee River

Tampa Bay

PINELLAS

CO

HILLSBOROUGH CO

MANATEE CO

SARASOTA CO

Parrish

Lorraine

Sarasota

Bradenton

0 5 10 KILOMETERS

0 5 10 MILES

EXPLANATION

Locations of wells used

 for hydrogeologic section

 A - A′

A - A′ Line of hydrogeologic

 section shown in figure 7

Basin boundary

A

A′

Upper

Middle

Lower

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′

 275

75

75

64

62

675

301

301

301

41

41

Figure 1. Location of the study area in west-central Florida, showing upper, middle, and lower reaches of the 

Braden River.
4 Hydrologic Description of the Braden River Watershed, West-Central Florida

River. Braden River is the largest tributary to the 

Manatee River, encompassing 24 percent of its 

345-mi2

 drainage area. The confluence of the Braden 

and Manatee Rivers is about 7 mi upstream from the 

mouth of the Manatee River at Tampa Bay.

Physiography

The Braden River watershed generally is 

characterized by low topographic relief. Land-surface 

elevations range from about 100 ft above sea level at 

the headwaters, along the eastern boundary of the 

watershed, to sea level along the gulf coast to the west. 

Land-surface elevations within the western half of the 

watershed are approximately 25 ft or less above sea 

level. Near the Braden River mouth, land surface 

commonly is less than 15 ft above sea level.

The Braden River watershed lies within the 

midpeninsular physiographic zones described by 

White (1970) as the Gulf Coastal Lowlands and 

De Soto Plain (fig. 2). These subdivisions correspond 

approximately to several marine plains or terraces that 

were formed by invasions of the sea during the 

Pleistocene Epoch. The relatively flat, poorly drained 

Gulf Coastal Lowlands include the Pamlico Terrace, 

generally less than 25 ft above sea level, and the 

Talbot Terrace, about 25 to 40 ft above sea level. The 

Penholoway Terrace, about 40 to 70 ft above sea level, 

and the Wicomaco Terrace, about 70 to 90 ft above sea 

level, compose the De Soto Plain along the eastern 

boundary of the Braden River watershed (Brown, 

1983). The land surface in these two subdivisions is 

poorly drained and has numerous marshes, many in 

saucer-like depressions ( fig. 3). Areas of the watershed, mainly in the eastern half, have been channelized to accelerate natural drainage from areas that 

previously experienced temporary flooding during 

periods of average rainfall.

Climate

Climate in the study area is subtropical and is 

characterized by high average annual rainfall and 

temperatures. Monthly humidities average more than 

70 percent. Intense rainfall, generated by localized 

convective thunderstorm activity from June through 

September, accounts for about 62 percent of the annual 

rainfall. Periodic cold fronts account for most of the 

rainfall from December through March (fig. 4). From 

June to November, heavy rainfall associated with tropical storms and hurricanes can affect the study area. 

An intense tropical storm during June 24-30, 1992, 

produced 16.95 in. of rainfall within the watershed 

(National Oceanic and Atmospheric Administration 

(NOAA), 1992) and resulted in widespread flooding. 

In the Braden River watershed, this amount of rainfall 

produced over a 7-day period is categorized as a 

25-year storm (U.S. Department of Commerce, 

Weather Bureau, 1964).

A long-term NOAA reporting weather station is 

located at the Gulf Coast Research and Education 

Center for the Institute of Food and Agricultural Sciences of the University of Florida, and is located 

within the Braden River watershed about 0.5 mi north 

of Ward Lake. Meteorological data have been collected at this site since 1965 and, previously, at a location about 5 mi west of the present site from 1954-65. 

Meteorological data collected include: air temperature, 

rainfall, total accumulated solar radiation, wind speed 

and direction, humidity, and daily pan evaporation. 

Based on the 40-year period of record from 1954-93, 

the annual rainfall averages 56.0 in. and annual air 

temperature averages 72 oF (NOAA, 1993). A second 

long-term weather reporting station also is located 

nearby at the Sarasota-Bradenton Airport, about 2 mi 

west of the watershed. Evapotranspiration in Manatee 

County is estimated to be about 39 in/yr (Cherry and 

others, 1970). This estimate is computed from a 

water-balance difference between rainfall (56 in.) and 

surface runoff (18 in., calculated from six basins) plus 

ground-water recharge (about 1 in.). Average annual 

lake evaporation is estimated to be about 52 in. 

(Kohler and others, 1959, p. 2), and evapotranspiration 

from the numerous predominant wet-weather vegetation-filled ponds in the area could exceed 60 in. a year 

(Joyner and Sutcliffe, 1976).

Soils

Detailed soil survey information can indicate 

certain hydrologic conditions of an area, such as the 

runoff and drainage characteristics, and also can 

indicate the hydraulic conductivity of the surficial 

aquifer. The Natural Resources Conservation Service 

(formerly, Soil Conservation Service) of the U.S. 

Department of Agriculture (1983) has identified six 
Description of the Study Area 5
6 Hydrologic Description of the Braden River Watershed, West-Central Florida
Description of the Study Area 7

Figure 4. Average monthly rainfall percentage

within the Braden River watershed, 1954-93.

general soil series in the Braden River watershed 

(fig. 5). Each soil series is a group of two or three soil 

types that have profiles similar in composition, thickness, and arrangement yet have differences in relative 

proportions of sand, silt, and clay of the surface layer or 

underlying material. Soil series are classified by naming the most prevalent soil type first, followed by soil 

types having smaller percentages. The physical characteristics of each soil series, such as slope, drainage, permeability, depth to water table, saturation, and 

stratigraphy, determine the efficiency of the watershed 

to facilitate runoff, interflow, and recharge. 

The dominant two soil series in the Braden River 

watershed are the Myakka-Cassia and the EauGallieFloridana. The Myakka-Cassia series is prevalent in 

the eastern half of the watershed, whereas the 

EauGallie-Floridana series is prevalent in the western 

half of the watershed. Both series are characterized as 

nearly level, poorly drained soils of moderate to rapid 

permeability, formed in sandy marine deposits, and are 

found mainly in flatwoods. The permeability of these 

soils is similar but varies with depth and clay content 

(table 1). Depth to water table typically ranges from 10 

to 40 in. below land surface. The Myakka-Cassia 

series can be further characterized as underlain by 

shells and shell fragments in places. The Floridana 

soils make up a small part of both series and occur in 

the numerous depressions and low flat areas throughout the watershed. This soil is poorly drained and has 

low permeability on low gradient terrain. The Floridana soils create hard-pan features that function as 

depressional wetlands and probably are not connected 

to ground-water sources (Juan Vega, Natural 

Resources Conservation Service, oral commun., 

1995). Other major soil types in the watershed are: 

Wabasso-Bradenton-EauGallie; Delray-Floridana; 

Okeelanta; Felda-Wabasso. These soil types have 

similar characteristics to those previously discussed, 

being nearly level and poorly drained sandy soils. 

 The permeability of soils in the Braden River 

watershed is a major factor in determining the extent 

of surface and ground-water interaction. Although the 

overall permeability of the dominant soil types in the 

watershed is moderate to rapid, drainage remains poor 

because of underlying soil horizons with low permeability. For example, the Cassia soil type is moderate 

to highly permeable in the top 24 in. and below about 

33 in., but has a very low permeability between 25 and 

33 in. below land surface. It is this layer, or horizon, of 

low-permeable soil which helps to create a poorly 

drained soil. Other characteristics that encourage 

poorly drained soils are the low topographic relief of 

the area, and underlying clay layers (typically the top 

of the intermediate aquifer system) that restrict the 

downward migration of flow in the surficial aquifer. 

Water percolating through the soil is impeded by these 

clay layers and thus saturates the overlying soil, creating locally high water-table elevations. Where clay 

layers exist near the Braden River and its tributaries, 

rainfall infiltration saturates the soil and discharges 

into the surface-water systems.

Land Use

Rapid population growth in Manatee County is 

indicative of the explosive population growth experienced along the gulf coast of west-central Florida. 

The population in Manatee County has increased from 

148,400 in 1980 to 223,500 (estimated) in 1993 

(University Press of Florida, 1994). This accelerated 

population growth and subsequent development is 

rapidly changing land-use characteristics within large 

areas of the Braden River watershed. In the eastern 

half of the watershed, large tracts of agricultural land 

and rangelands are being developed into subdivisions 

of medium to high density single-family homes, golf 

courses, and commercial centers. Changes in land-use 

patterns in the watershed can have a significant effect 

on the hydrology of the watershed. For example, 

ground-water recharge to the surficial aquifer and 

surface-water systems can be affected by land-use 

changes. These changes and their effects on hydrologic systems are difficult to evaluate.

January

5.0%

February

5.0%

March

6.0%

April

3.0%

May

6.0%

June

13%

July

17%

August

17% September

15% October

5.0%

November

4.0%

December

4.0%
8 Hydrologic Description of the Braden River Watershed, West-Central Florida
Hydrogeology 9

Land use within the Braden River watershed 

ranges from the highly developed urban areas that 

include parts of Bradenton, to the undeveloped forested lands adjacent to the Braden River. Available 

information on land use and land cover in the watershed, upstream from Ward Lake, was prepared in a 

study by Camp, Dresser, and McKee (1985) for the 

Manatee County Planning and Development Department. In addition, during 1990, the SWFWMD generated land use and land cover maps using color infrared 

photography for the Braden River watershed (fig. 6). 

Land-use acreage and percentage of total area for 1985 

and 1990 as a result of these studies are presented in 

table 2. 

Although the watershed is becoming increasingly 

residential, much of the land remains agricultural, as 

shown in fig. 6. Agriculture can affect the hydrology 

of the Braden River watershed in several ways. 

Irrigation of crops can create artificial recharge resulting in increased base flow to creeks as the irrigation 

water seeps through the surficial aquifer to a surfacewater body. Pumping of ground water also can result 

in lowering the water-level elevation in overlying 

surface-water features, such as streams and lakes. 

In the eastern half of the watershed, agricultural land 

and rangeland typically are ditched and channelized 

to enhance surface-water drainage.

Surface mining accounts for a small percentage 

of overall land use and is confined to the southcentral part of the watershed. This mining is done to 

extract sand and shell from surficial deposits; no 

chemicals are used in the process (Wayne Rilko, 

Quality Aggregates, Inc., written commun., 1993). 

Mining activities have altered the natural flow patterns within the Braden River watershed by creating 

borrow pits and settling ponds. Dewatering of shell 

pits, which is done intermittently, also can affect both 

ground-water and surface-water flow.

HYDROGEOLOGY

The hydrogeologic system in the Braden River 

watershed area consists of thick sequences of 

carbonate rocks and clastic sediments which are 

intermittently hydraulically connected. Principal 

hydrogeologic units are the surficial, the intermediate, and the Upper Floridan aquifer systems. The 

surficial aquifer, in places, has discontinuous layers 

of clay stringers that can restrict vertical groundwater flow. The surficial aquifer also is underlain 

with a thick clay layer, the top of the intermediate 

aquifer system, that also can restrict vertical groundwater flow. The Upper Floridan aquifer system is 

separated from the surficial aquifer by the intermediate aquifer system.

The hydrogeologic section A-A′, shown in 

figure 7, intersects the Braden River watershed from 

west to east. The hydrogeologic section A-A′ incorporates the lithology from several wells in the Braden 

River watershed including TR 7-4, a Regional Observation and Monitor Well Program (ROMP) well at 

the west edge of Ward Lake. The surficial aquifer 

generally is about 30 ft thick and overlies an intermediate aquifer system confining unit that ranges in 

thickness from 60 to 140 ft. Well descriptions for the 

wells used to define the hydrogeologic section 

(Barr, 1996) are presented in table 3.

Table 1. Physical properties and lithology of dominant soils

[in., inches; %, percent; in/h, inches per hour. Modified from Soil 

Conservation Service, 1983]

Soil

type

Depth

(in.)

Clay

(%)

Permeability

(in/h)

Lithology

Myakka 0-23

23-37

37-80

<2

2-8

<2

6.0-20

0.6-6.0

6.0-20

fine sand

sand, fine sand, loamy fine 

sand

sand, fine sand

Cassia 0-24

24-33

33-80

1-4

2-10

1-5

6.0-20

0.6-6.0

6.0-20

fine sand

sand, fine sand, loamy sand

sand, fine sand

Eau 

Gallie

0-28

28-42

42-50

50-65

<5

1-8

13-31

1-13

6.0-20

0.6-6.0

0.6-6.0

2.0-6.0

fine sand

sand, fine sand

sandy loam, fine sandy 

loam, sandy clay loam

sand, loamy sand, loamy 

fine sand

Floridana 0-19

19-36

36-63

3-10

1-7

15-30

6.0-20

6.0-20

<0.2

fine sand

sand, fine sand

sandy loam, fine sandy 

loam, sandy
10 Hydrologic Description of the Braden River Watershed, West-Central Florida u

o

o

o

i75

64

67

683

301

u301

Low Density ResidentialMed. Density ResidentialHigh Density Residential

MiningPasture/Open LandAgriculture

WetlandsForestWater

TransportationRecreationCommercial/Industria

EXPLANATION

27°30′

82°30′ 25′ 82°20′

27°25′

0 1 2 

0 1 2 KILO

Figure 6. Land use in the Braden River watershed 1990. (From Southwest Florida Water Management District GIS data base.)
Hydrogeology 11

Surficial Aquifer

The surficial aquifer is the principal hydrologic 

unit that exchanges water with surface-water systems. 

The surficial aquifer is contiguous with land surface 

and consists primarily of unconsolidated sand, clay, 

shell, and phosphate gravel intermixed with stringers 

of limestone and marl of Quaternary to Upper Tertiary 

age (Brown,1983; Barr, 1996). The aquifer generally 

is unconfined; however, lenses of sand, marl, and 

limestone contain water under confined conditions in 

some areas (Hutchinson, 1984). Hydraulic properties 

of the surficial aquifer are highly variable considering 

the physical characteristics of the rock and sand 

matrix, such as grain size, sorting, and thickness. 

These characteristics influence porosity and permeability thereby affecting the ability of the unit to transmit water (Knochenmus and Thompson, 1991). The 

hydraulic properties of the surficial sediments can 

enhance or retard the exchange of water between 

surface-water bodies and the surficial aquifer. 

Sediment deposits of the surficial aquifer are 

mined along the southern boundary of the Braden 

River watershed, mainly within the Cooper Creek 

Table 2. Land use in the Braden River watershed

a

 Camp, Dresser, and McKee, Inc., 1985, Southeast area stormwater 

management study: Final Report, 111 p. b

 Southwest Florida Water Management District, 1990, GIS data base.

Land use

Braden River 

watershed 

upstream of Ward 

Lake weira 1985

Total

Braden River 

watershedb

1990

Acres

Percent

of total 

area

Acres

Percent

of total 

area

Forest 2,980 7.7 9,614 18.0

Pasture/Open land 29,108 75.4 6,094 11.4

Recreation 291 0.8 915 1.7

Agriculture 1,778 4.6 17,585 32.9

Wetlands 1,607 4.2 7,440 13.9

Low-density single 

family residences

382 1.0 2,321 4.3

Medium-density single

family residences

545 1.4 1,057 2.0

High-density residences 179 0.5 3,237 6.1

Commercial/Industrial 115 0.3 760 1.4

Mining 1,013 2.6 1,506 2.8

Transportation/Utilities 244 0.6 903 1.7

Water 354 0.9 2,056 3.8

Total 38,596 100.0 53,489 100.0

100 100

100 100

SEA

LEVEL SEALEVEL

200 200

300 300

400 400 PERICO WELL TR7-2NS-8 W-3612

SURFICIAL

ROMP-33

AQUIFER

SYSTEM

CONFINING

UNIT

CONFINING UNIT

PERMEABLE ZONE

UPPER

FLORIDAN

AQUIFER

PERMEABLE

ZONE

INTERMEDIATE

AQUIFER

SYSTEM

A A

FEET FEET

0

0

5 MILES

5 KILOMETERS

TR7-4

VERTICAL SCALE

GREATLY EXAGGERATED

Figure 7. Hydrogeologic section A-A’ in southwestern Florida.

(Modified from Barr, 1996. Line of section is shown in figure 1.)

Table 3. Wells used in hydrogeologic 

section A-A′

[Modified from Barr, 1996]

Well

name

(as shown

in fig. 7)

Site

identification 

number

Depth of 

well

(in feet 

below land

surface)

Perico Island 2729490824040 595

TR 7-2 2726120823301 1,075

TR 7-4 2725390822920 800

MS 8 2726510822625 800

W-3612 2727020822241 740

ROMP 33 2727280821530 675
12 Hydrologic Description of the Braden River Watershed, West-Central Florida

subbasin (fig. 9). Unconsolidated overburden and the 

underlying deposits of the clay-shell matrix that form 

the Caloosahatchee Formation occur at depths of 20 to 

30 ft and are mined for commercial and industrial 

applications, such as fill and roadbed material and 

cement aggregate (Wayne Rilko, Quality Aggregates, 

Inc., oral commun., 1995).

Intermediate Aquifer System

The intermediate aquifer system includes all 

water-bearing units and confining units between the 

overlying surficial aquifer and the underlying Upper 

Floridan aquifer (Southeastern Geological Society, 

1986). The water-bearing units of the intermediate 

aquifer system consist of discontinuous sand, gravel, 

shell, and limestone and dolomite beds in the Tamiami 

Formation of early Pliocene and late Miocene age 

and the Hawthorn Formation of late and middle 

Miocene age (Southeastern Geological Society, 1986). 

The confining units consist of sandy clay, clay, and 

low to very low permeability carbonate sediments 

(marl) retarding the vertical movement of ground 

water between the water-bearing units of the overlying 

surficial aquifer and the underlying Upper Floridan 

aquifer (Duerr and others, 1988). However, if the top 

of the intermediate aquifer system is not confined or 

if there is a breach in the confining unit, flow might 

occur from the intermediate water-bearing units to the 

surficial aquifer or surface-water systems. The altitude 

of the top of the intermediate aquifer system in the 

study area ranges from about 40 ft above sea level near 

the eastern watershed boundary to about sea level 

from midwatershed westward (fig. 7). The bottom 

of the intermediate aquifer system (top of the Upper 

Floridan aquifer) ranges from about 300 ft below sea 

level at the western watershed boundary to about 250 ft 

below sea level at the eastern watershed boundary 

(fig. 7).

Floridan Aquifer System

The Floridan aquifer system consists of a vertically continuous sequence of Tertiary age carbonate 

and clastic sediments that are generally hydraulically 

connected to each other. The permeability of these 

sediments is several orders of magnitude greater than 

that of the sediments that bound the system from 

above and below (Ryder, 1985). The Floridan aquifer 

system is subdivided into the Upper Floridan aquifer, 

the middle confining unit, and the Lower Floridan 

aquifer (Miller, 1986). The middle confining unit and 

Lower Floridan aquifer generally contain saltwater 

(Ryder, 1985). The Upper Floridan aquifer is the 

primary source for ground-water supply in the area; 

agriculture accounts for most of its use.

When the potentiometric surface of either the 

Upper Floridan or intermediate aquifer is at or above 

land surface, the upward movement of water into the 

surficial aquifer or surface-water bodies is possible. 

The potentiometric surface is an imaginary surface 

connecting points where water would rise in a tightly 

cased well from a given point in the aquifer (Lohman, 

1972). Areas within the Braden River watershed 

where the potentiometric surface of the Upper 

Floridan aquifer exceeds land surface elevation during 

typical seasonal periods of low (May) and high 

(September) water-level conditions are shown in 

figure 8. When the potentiometric surface is above 

land surface, water in wells cased in the Upper 

Floridan aquifer can flow at land surface. Although the 

intermediate aquifer system restricts vertical flow 

between the Upper Floridan and the surficial aquifer, 

higher potentiometric surface levels in the Upper 

Floridan aquifer indicate when ground-water has the 

potential to migrate to the surface-water systems. 

Water-level measurements by the USGS have ranged 

from 1.01 ft below to 22.72 ft above sea level at 

ROMP TR 7-4 Upper Floridan aquifer well, located 

near the western shore of Ward Lake.

METHODS OF STUDY

This section describes the data-collection methods 

used to: (a) characterize surface drainage in the 

Braden River watershed; (b) measure streamflow at 

the Ward Lake weir including direct measurement 

methods, weir coefficient equations, and dischargedrainage area calculations, and; (c) define subsurface 

flow (seepage) around the ends of the weir and check 

for leakage through the weir structure.

 To characterize the surface drainage of the Braden 

River watershed, an extensive network of continuous 

and partial-record streamflow gaging stations was 

established. A continuous streamflow gaging station 

records water levels (stage) of the tributary or river.
Methods of Study 13
14 Hydrologic Description of the Braden River Watershed, West-Central Florida

These water levels can be used to compute discharge 

using a stage/discharge relation developed from a 

series of discharge measurements. The gaging station 

network monitors 80 percent of the watershed drainage 

upstream of the Ward Lake weir and 51 percent of the 

watershed drainage downstream of the weir. Stations 

upstream of the Ward Lake weir include gages on eight 

first-order tributary, one second-order tributary, and 

two gages on the main-channel of the Braden River. 

Downstream of the Ward Lake weir, continuous gaging 

stations were established at two first-order and one 

second-order tributaries that flow into the tidal reach 

downstream of Ward Lake and at two tidal sites, one 

located at the mouth of the Braden River and the other 

just downstream of the Ward Lake weir. Descriptions 

of each of the subbasins monitored within the watershed are discussed in downstream order and locations 

are shown in figure 9. Table 4 summarizes data for each 

creek within the subbasins. Discharge computed at 

each of the main-channel gages is an accumulation of 

all the flow upstream of that point. The tidal stations 

record water levels and specific conductance, but are 

not used to calculate discharge.

All drainage basin boundaries were delineated 

using USGS topographic maps. Because of the 

physical limitation associated with accurate ground 

truthing of contour maps, delineation of the basin and 

subbasin boundaries are approximations, especially in 

areas of heavy urban development and places where 

the land surface has little topographic relief. Also, 

changes in land use or surface topography, such as 

agricultural ditching and mining practices, alter flow 

patterns and make watershed boundaries difficult to 

distinguish.

To measure streamflow at the Ward Lake weir, 

a direct measurement method needed to be established. Due to irregularities in the construction of the 

weir and associated inaccuracies related to theoretical 

weir flow calculations, a reconnaissance study was initiated to explore the possibility of establishing a direct 

discharge measurement method. Several different 

standard measurement methods proved to be successful, dependent upon the volume and velocity of flow 

over the weir. Direct discharge measurements can be 

made using volumetric and standard current-meter 

methods.

A volumetric method of measuring discharge is 

used during low-flow conditions when the depth of 

water over the weir is less than or equal to 0.3 ft (about 

200 ft3

/s). Discharge measurements using this method 

are made by timing the rate needed to fill a container 

of known volume (Rantz and others, 1982). However, 

the volumetric method presented here is not a standard 

volumetric method because it is not feasible to capture 

all of the flow discharging over the 838-ft-long broadcrested weir. A volumetric method is used to give a 

discharge per unit width of the weir. In this way, the 

discharge over the weir can be divided into 20 or more 

subsections of uniform flow and a volumetric measurement can be made within each subsection, similar 

to a vertical section in a standard current-meter measurement. To do this, the volumes of different containers are divided by their width to give a volume per 

foot. The time required to fill an individual container 

is recorded so that a volume per time (discharge) per 

foot of width can be calculated. Subsections are generally chosen so that no subsection flow exceeds 5 percent of the total flow. Discharge measurements are 

made using a combination of both the volumetric and 

current-meter (pygmy) methods for a range of flow 

from 200 to 300 ft3

/s. Discharge measurements during 

high-flow conditions (greater than 300 ft3

/s) are made 

by boat at a cross section about 250 ft upstream from 

the weir for improved accuracy and safety. Flow measurements made at the weir and those made by boat for 

similar flow conditions are well correlated.

Discharge measurements were made at various 

levels of stage for Ward Lake. These discharge measurements and the corresponding stage are related to 

define a rating curve. This relation can be used to estimate discharge from the recorded stage data. Stage for 

Ward Lake is recorded at the Ward Lake Outfall 

streamflow gaging station, located approximately 50 ft 

upstream of the west end of the weir.

Prior to the development and implementation of a 

direct-discharge measurement method by the USGS, 

two methods were used for estimating discharge at the 

Ward Lake Outfall. These methods included a flow 

equation using (broad-crested) weir coefficients and 

discharge-drainage area ratio calculations. Each 

method of estimating discharge has advantages and 

disadvantages.
Methods of Study 15 Figure 9. Location of gaging stations and subbasins in the Braden River watershed.

Site location and nu listed in table 4

Lorraine

MANATEE COUNTY

SARASOTA COUNTY

82°30′ 25′ 82°20′

27°30′

27°25′

9

1

2

2

3 4

5 6

7

8

10

11

12

13 14

15

16

17

EXPLANATION

Basin boundary. S are distinguished 

0 1 2 MILES

0 1 2 KILOMETERS

75

64

675

683

301

301
16 Hydrologic Description of the Braden River Watershed, West-Central Florida

A standard, simplified weir flow equation applied 

at the Ward Lake weir is:

Q = Cw L H3/2 (1)

in which Q is the flow rate in cubic feet per second; Cw

is the weir coefficient; L is the length of the weir, in 

feet, with end slope additions given by

L = 838 + 24.2(H) (2)

and H is the water-level elevation over the weir, in feet. 

The water-level elevation over the weir, or head on the 

weir, is calculated by subtracting the lowest flow elevation of the weir from the water-level elevation of the 

gage. Weir coefficients have been explored extensively, 

and various coefficient tables are available for common 

weir shapes (Horton, 1907; and King and others, 1948). 

The advantage of this method is that the only data 

needed to calculate flow are the head of water on the 

weir, if the weir coefficient can be calibrated or accurately estimated. The disadvantage of this method is 

that using standard weir coefficients without first calibrating each individual weir may not be accurate.

The second method used to estimate flow at the 

Ward Lake Outfall is discharge-drainage area ratio calculations. This method estimates the flow in a basin by 

calculating the ratios of flow per square mile in nearby 

basins for which flow data are available. The advantage of this method is that flow can be estimated using 

only drainage area data and discharge-drainage area 

ratios of nearby basins. The disadvantage of this 

method is that comparisons made with nearby basins 

may not be accurate due to differing soil types, land 

uses, rainfall amounts, and drainage patterns. This 

method typically is used to calculate a monthly mean 

or annual mean flow rate.

Two studies also were done to define subsurface 

flow (seepage) around the ends of the weir and to evaluate leakage through the weir structure. A network of 

piezometers was installed to define seepage around the 

ends of the weir by measuring water-table gradients. 

A dye study was performed to examine potential leakage through the weir.

Ten shallow piezometers were set into the bank 

around both ends of the Ward Lake weir to monitor 

water-table fluctuations and the rate of seepage 

(fig. 10). The water-table gradients indicate subsurface flow around the weir. Seven piezometers were 

installed around the west end of the weir, an area of 

low topographic relief, and three around the more 

elevated east end. Water-level data from the three piezometers at the east end of the weir did not indicate 

fluctuations in the water table around the weir because 

of the effect from the high percentage of clay in the fill 

material; therefore, these data were not used. The well 

screen and casing of each piezometer was constructed 

with 2 in. PVC. The bottom of each 4.8-ft long 

screened interval was set at a depth of 8 to 10 ft below 

Table 4. Gaging network in the Braden River watershed

Station

number

USGS

downstream

order

number

Station name Type of data collected

Period

of

record

Drainage

area

(square

miles)

1 02300024 Braden River near Verna Crest stage indicator 1993-96 6.8

2 02300025 Tributary No. 1 to Braden River near Lorraine Crest stage indicator 1993-96 5.2

3 02300027 Tributary No. 2 to Braden River near Lorraine Crest stage indicator 1993-96 3.8

4 02300031 Wolf Slough near Lorraine Crest stage indicator 1993-96 4.0

5 02300032 Braden River near Lorraine Continuous discharge 1988-96 25.6

6 02300034 Hickory Hammock Creek near Lorraine Continuous discharge 1988-96 2.4

7 023000355 Cooper Creek at University Parkway near Sarasota Continuous discharge 1988-96 9.0

8 02300036 Tributary No. 1 to Cooper Creek near Lorraine Continuous discharge 1994-96 4.4

9 02300037 Cedar Creek near Sarasota Continuous discharge 1988-96 1.7

10 02300038 Rattlesnake Slough near Sarasota Continuous discharge 1988-96 3.8

11 02300039 Nonsense Creek near Bradenton Continuous discharge 1988-96 1.4

12 02300042 Ward Lake Outfall near Bradenton Continuous discharge and elevation 1942-47;

1976-96

59.2

13 02300044 Braden River near Elwood Park Elevation and conductance 1989 60.0

14 02300050 Williams Creek near Bradenton Continuous discharge 1996 2.7

15 02300056 Gap Creek near Bradenton Continuous discharge 1996 7.2

16 02300062 Glen Creek near Bradenton Continuous discharge 1996 2.5

17 02300064 Braden River near Bradenton Elevation and conductance 1996 83.0
Surface Drainage and Gage Network 17

land surface so that the complete range of water-table 

fluctuations would be measured. In addition to the 

range of water-table fluctuations, the formation lithology at the west end of the weir also was considered in 

determining well configuration and depth. The lithology of the upper 5 to 6 ft of surficial material collected 

during drilling at the west end of the weir was fill 

material deposited during construction of the weir. 

Most importantly, the lithology indicated a thick clay 

layer at approximately 10 ft below land surface that 

would restrict vertical ground-water movement. 

The concrete sheet piles used to make the weir are 

imbedded into this clay layer.

To assure confidence and accuracy in established 

direct-discharge measurement methods, it was necessary to verify that leakage was not occurring through 

the sheet piles of the Ward Lake weir. To address this 

concern, rhodamine dye, used as a fluorescent tracer, 

was poured along the length of the upstream side of 

the weir. This was performed during a period when 

water from Ward Lake was not flowing over the weir, 

and the elevation of the lake was about 0.5 ft below the 

crest of the weir. Water-level gradients between the 

reservoir and the tidal reach typically are over 1.5 ft, 

even at normal high tide. Water samples were collected along the length of the downstream side of the 

weir throughout the day, and with 

an automatic sampler hourly 

throughout the night. A sampling 

duration of 36 hours was determined to be long enough to detect 

any significant leakage through or 

under the weir. 

SURFACE DRAINAGE AND 

GAGE NETWORK

The Braden River watershed 

drains an 83-mi2

 area of southcentral Manatee and northern 

Sarasota Counties which forms the 

southern part of the Manatee River 

Basin (fig. 1). The watershed is 

elongated in shape (approximately 

16 mi from east to west and ranging 

from about 3.5 to 9.0 mi in width 

from north to south). The Braden 

River is approximately 22-mi long, 

and has an average channel slope of 8 ft/mi for the 

upper 12 mi of the river’s reach (fig. 11). The lower 12 

mi of river is nearly flat in the area of the reservoir and 

tidal reaches. The elevation of the main channel of the 

Braden River ranges from approximately 85 ft above 

sea level at the east boundary of the watershed to sea 

level at the mouth of the river. The direction of flow in 

the Braden River generally is westward from the headwaters to approximately the midpoint of the watershed, then northwest to the mouth. The drainage 

pattern within the watershed generally is dendritic, 

formed from a series of first-order tributaries.

 Natural flow characteristics of the tidally dominated lower half of the Braden River were altered in 

1936 by the city of Bradenton, which constructed the 

Ward Lake weir to create a freshwater impoundment. 

The weir structure is located approximately 6 mi 

upstream of the confluence with the Manatee River. 

The Ward Lake weir creates a permanent backwater 

condition to the Braden River, extending upstream for 

approximately 6 mi. Lower reaches of adjacent tributaries to the lake also are affected by backwater.

The Braden River can be divided into three distinct river reaches of approximate equal length: the 

upper, middle, and lower reaches (fig.1). This division 

is based on differing streamflow characteristics. 

N

WARD LAKE WEIR

10

3 4

9

2

2

1

7

6

DYE PLUME

GAGING

STATION EXPLANATION

8 5

D

D

NOT TO SCALE

BRADEN RIVER

(TIDAL)

WARD LAKE

HIGH FLOW

MEASUREMENT SECTION FLOW

838 FEET

Location of piezometer

and number

Distance from west

edge of water

Figure 10. Areal view of Ward Lake Outfall and piezometer network.
18 Hydrologic Description of the Braden River Watershed, West-Central Florida

The upper reach of the Braden River is 8.6-mi long, 

drains a 26-mi2

 area of the headwaters and generally is 

a straight, naturally incised channel that is unaffected 

by backwater from Ward Lake because of the slope of 

the river. The middle reach of the Braden River drains 

a 33-mi2

 section of the Braden River watershed 

(59 mi2

 including the upper reach) and is 6.4-mi long. 

The meandering channel of the middle reach is characteristic of a low-gradient river and a remnant of the 

tidal conditions that existed prior to construction of the 

Ward Lake weir. Backwater conditions exist throughout the length of the middle Braden River reach and 

the lower reaches of all adjacent tributaries. The lower 

reach of the Braden River is a 6-mi long, tidally dominated channel that drains a 24-mi2

 area (83 mi2 including the upper reaches), extending from its mouth at the 

Manatee River, upstream to the weir at Ward Lake. 

The lower reach of the Braden River is a typical 

coastal-plain estuary containing tidal flats, oyster 

beds, seagrass flats, salt marsh plants, and mangroves. 

The lower reach of the river is also a productive juvenile fishery, seasonal manatee habitat, and home to 

many freshwater and saltwater birds.

Upper Reach

The upper reach of the Braden River and the tributaries that flow to it typically are free of the effects of 

backwater from Ward Lake. These creeks flow freely 

through areas of minor topographic relief.

Braden River near Verna

The gaging station on the main channel of the 

Braden River near Verna (station 1, fig. 9), is approximately 16.5 mi upstream of the mouth. The gage is a 

crest-stage indicator (CSI) partial-record station that 

records a peak water-level elevation during high flow 

events. The main channel of the river, within the gaged 

subbasin, is about 4.6 mi in length and flows west 

from the headwaters to the gage. The subbasin is 

bounded on the north by Tributary No. 2 and on the 

south by Tributary No. 1. The subbasin is elongated in 

shape (approximately 2.4-mi wide and 4.6-mi long) 

and drains a 6.8-mi2

 area of land developed primarily 

for agriculture and rangeland. Total topographical 

relief in the subbasin is about 60 ft, ranging from 

approximately 100 ft above sea level (the highest area 

of the Braden River watershed) at the eastern boundary, to about 40 ft above sea level at the gage. The 

average channel slope is about 9 ft/mi. 

Tributary No. 1 to Braden River near Lorraine

The Tributary No. 1 subbasin of the Braden River 

(station 2, fig. 9) drains approximately 5.2 mi2 of primarily agricultural land at the gage and is elongated in 

shape (1.9-mi wide and 4.2-mi long). The tributary 

generally flows west for approximately 5.4 mi from its 

headwaters to the station, a CSI located approximately 

0.3 mi upstream from its mouth. Total topographic 

-20

100

0

20

40

60

80

ELEVATION ABOVE SEA LEVEL, IN FEET

0 2 4 6 8 10 12 14 16 18 20 22 24

RIVER MILES FROM MOUTH

River Bottom

Ward Lake Outfall

Nonsense Creek

Rattlesnake Slough

Cedar Creek

Cooper Creek

Hickory Hammock Creek

Braden River 

Hwy I-75

near Lorraine

Glen Creek 

Gap/Williams Creek

Braden River near 

Elwood Park/Hwy 70

Wolf Slough

Tributary No. 2 to Braden River

Braden River 

 near Verna

Tributary No. 1 to

 Braden River

Hwy 64

Upper Reach

Ward Lake

Lower Reach Middle Reach

sea level

approximate water level of lake

weir

Figure 11. River-bottom profile from mouth to headwaters.
Surface Drainage and Gage Network 19

relief in the subbasin is about 50 ft, and the average 

channel slope is about 10 ft/mi. Extensive ditching and 

channelization were done within the subbasin to 

promote drainage of agricultural areas. 

Tributary No. 2 to Braden River near Lorraine

Tributary No. 2 to Braden River is about 5.6-mi 

long and meanders through many low marsh areas 

(station 3, fig. 9). The tributary flows west for most of 

its length, then travels about 1.0 mi southwest to the 

gage located 0.5 mi upstream from its mouth at the 

Braden River. The drainage area of the tributary 

upstream of the CSI gage is 3.8 mi2

. The subbasin is 

irregularly shaped (approximately 1.3-mi wide and 

4.7 mi long) with a total topographic relief of 43 ft 

(from 79 ft at the headwaters to 36 ft at the mouth). 

The average channel slope is 7.8 ft/mi. Channel 

modifications were made to enhance drainage of 

agricultural areas. Land use is mainly agriculture and 

rangeland.

Wolf Slough near Lorraine

Wolf Slough meanders southwest for about 2 mi 

from its headwaters to the gage, a CSI (station 4, 

fig. 9). The station was established about 0.5 mi 

upstream from the mouth of Wolf Slough where it 

drains an area of 4.0 mi2

. Wolf Slough flows through 

low marsh, agriculture (row crops and groves), rangeland, and residential areas, including the town of 

Lorraine. Several large borrow pits (now lakes) have 

altered parts of the drainage subbasin. The area is 

currently being developed for medium to high density 

single-family housing. The subbasin is rectangular 

(1.9-mi wide and 2.1-mi long) with a total relief of 

45 ft. The average channel slope is about 7.9 ft/mi.

Braden River near Lorraine

The upper one-third of the Braden River watershed drains to the Braden River near Lorraine streamflow-gaging station (station 5, fig. 9). The gage is 

instrumented by a continuous-stage recorder with 

water-level data transmitted by satellite. The gaging 

station was established upstream from the influence of 

backwater from Ward Lake, approximately 7 mi 

upstream of the weir. The channel near the gage is 

deeply incised and cuts into the Caloosahatchee 

Formation of the surficial aquifer. The drainage area of 

the river upstream of the gaging station is 25.6 mi2

. 

The Braden River flows west approximately 8 mi from 

its headwaters to the Lorraine station. Land use in the 

subbasin is predominantly agricultural with increasing 

residential development. Total relief in the subbasin is 

approximately 90 ft with the highest area being a knoll 

on the eastern drainage divide that is about 100 ft 

above sea level. The elevation of the channel at the gage 

is approximately 10 ft above sea level. The average 

channel slope is about 12 ft/mi.

Middle Reach

The middle reach of the Braden River and the 

tributaries that flow to it typically are affected by 

backwater caused by the Ward Lake reservoir and 

weir. Gaging stations on tributaries typically are 

located far enough upstream from the confluence with 

the Braden River so that they are not affected by backwater conditions.

Hickory Hammock Creek near Lorraine

The Hickory Hammock Creek subbasin is located 

in the north-central region of the Braden River watershed. The tributary is 2.8-mi long and drains residential and agricultural areas. Drainage of the Hickory 

Hammock Creek subbasin has been altered by agricultural drainage ditches and retention ponds built to contain runoff from medium to high-density residential 

areas. Currently, large areas of this subbasin are being 

developed. The streamflow gaging station (station 6, 

fig. 9) is instrumented with a continuous-stage 

recorder at the upstream side of two 10-ft box culverts, 

approximately 1,500 ft upstream from the mouth of 

the creek at the Braden River. The mouth of Hickory 

Hammock Creek is about 5.7 mi upstream of the Ward 

Lake weir. The drainage area of Hickory Hammock 

Creek at the gaging station is about 2.4 mi2

. Permanent 

backwater conditions from Ward Lake affect the water 

levels in the mouth and lower reach of Hickory Hammock Creek. During periods of extreme high water, 

streamflow at the gaging station also can be affected 

by backwater. The subbasin is trapezoidal (approximately 2-mi wide and 2-mi long) and has a total relief 

of about 40 ft. The highest area in the subbasin is a 

grove along the northeastern drainage divide that is 

approximately 47 ft above sea level. The elevation of 

the channel at the gaging station is about 7 ft above sea 

level, and the average channel slope is about 14.3 ft/mi.
20 Hydrologic Description of the Braden River Watershed, West-Central Florida

Cooper Creek at University Parkway near Sarasota

The Cooper Creek subbasin is located in southwest Manatee and northeast Sarasota Counties. This 

subbasin drains parts of Sarasota County, along the 

south-central part of the Braden River watershed. The 

creek drains improved pasture, a mine-spoil tailings 

area, and a residential development. The streamflow 

gaging station, which is instrumented with a continuous-stage recorder, was established at the ManateeSarasota County line, approximately 2 mi upstream 

from the mouth of Cooper Creek, which is about 4.6 

mi upstream of the Ward Lake weir (station 7, fig. 9). 

Part of the lower reach of Cooper Creek, beginning at 

the mouth, is affected by backwater from Ward Lake. 

The drainage area of Cooper Creek at the gaging 

station is 9.0 mi2

.

The Cooper Creek subbasin is rectangular 

(approximately 2-mi wide and 5-mi long). The channel is approximately 5 mi in length and has undergone 

extensive mining and agricultural modifications. 

Surface mining for topsoil, sand, and aggregates has 

altered the main channel and the natural drainage pattern along a 2-mi2

 strip near the south-central subbasin 

boundary. Agricultural practices in the eastern section 

of the subbasin have ditched pastureland to improve 

surface drainage. The subbasin is poorly drained and 

characterized by numerous depressional ponds. Total 

relief in the subbasin is 37 ft, and the highest area is a 

roadway along the northeastern drainage divide that is 

51 ft above sea level. The elevation of the channel bed 

at the gaging station is about 14 ft above sea level. 

Cooper Creek’s channel has an average slope of 

7.4 ft/mi.

Tributary No. 1 to Cooper Creek near Lorraine

The Tributary No. 1 to Cooper Creek (station 8, 

fig. 9) streamflow gaging station was initially established as a partial-record station, but was replaced by 

a continuous-record gage to monitor instantaneous 

streamflow data. The continuous record will provide 

baseline data of the stream characteristics prior to, during, and after development as the subbasin land use 

changes from undeveloped land to a residential community. The drainage area for Tributary No. 1, a 

second-order tributary, is approximately 4.4 mi2

, and 

flow is to the west into Cooper Creek, about 0.5 mi 

upstream of the mouth of Cooper Creek. The subbasin 

is irregular in shape (1.9-mi wide and 4.1-mi long), 

and Tributary No. 1 is about 1.5-mi long. Total relief 

of the gaged subbasin is approximately 43.5 ft, with 

the highest elevation along the east end of the subbasin, approximately 51 ft above sea level. The lowest 

elevation, approximately 7.5 ft above sea level, is the 

streambed at the gaging station. Land use within the 

subbasin includes areas that have been mined, a golf 

course, and residential developments. The average 

channel slope is 11.6 ft/mi.

Cedar Creek near Sarasota

Cedar Creek is located approximately 2 mi 

upstream of the Ward Lake weir, draining part of the 

south-central region of the Braden River watershed. 

The continuous-record gaging station was established 

0.4 mi upstream of the mouth (station 9, fig. 9), which 

is permanently affected by backwater from Ward 

Lake. Cedar Creek drains a highly developed subbasin 

that has predominantly single and multifamily homes 

and a golf course. The drainage area of Cedar Creek at 

the gaging station is about 1.7 mi2

. The subbasin is 

irregular (0.95-mi wide and 1.8-mi long). The main 

channel is 1.6-mi long and has been modified to 

increase drainage. Sections of the creek have been 

routed through various retention ponds for flood control. The subbasin is relatively flat and has a total relief 

of about 25 ft. The highest elevation is approximately 

30 ft above sea level along the eastern drainage divide. 

The average channel slope is 15.6 ft/mi.

Rattlesnake Slough near Sarasota

The gaging station on Rattlesnake Slough is 

located approximately 1.2 mi upstream of the Ward 

Lake weir, and drains a part of the southwestern 

Braden River watershed (station 10, fig. 9). The continuous-record station was established in a reach that 

has a natural control, approximately 0.5 mi upstream 

from the mouth of the slough to avoid the effects of 

backwater from Ward Lake. The main channel of 

Rattlesnake Slough is approximately 2.5-mi long 

upstream of the gage, and drains an area of 3.8 mi2

. 

The shape of the subbasin is irregular, and the drainage 

pattern is dendritic. Land use within the subbasin is 

dominated by improved pasture, a residential area, and 

a golf course. Total relief in the subbasin is approximately 29 ft. The highest elevation is a highway along 

the southwestern drainage divide that is about 35 ft 

above sea level. The elevation of the channel at the 

gage is approximately 6 ft above sea level. Average 

channel slope is approximately 5.6 ft/mi.
Surface Drainage and Gage Network 21

Nonsense Creek near Bradenton

The mouth of Nonsense Creek is located 1.1 mi 

upstream of the Ward Lake weir. The creek at the gage 

drains a 1.4-mi2

 area in the north-central area of the 

Braden River watershed. Until recently, the subbasin 

was largely undeveloped, except for a segment at the 

intersection of Interstate Highway 75 and State Highway 70. Currently, the subbasin is being developed 

with commercial centers and medium- to high-density 

housing. A continuous-record streamflow-gaging 

station was established on Nonsense Creek approximately 0.8 mi upstream of its mouth (station 11, fig. 9). 

Backwater from Ward Lake does not affect flow at 

the gage because of the control and elevation of the 

gage. The subbasin is rectangular (approximately 

0.9-mi wide and 1.6-mi long). The main channel is 

about 0.9-mi long and flows from a small lake surrounded by marsh at the headwaters. The subbasin 

generally is flat and has a total relief of approximately 

20 ft. The highest elevation in the subbasin is about 

43 ft above sea level along the northeastern drainage 

divide. The lowest elevation is the stream channel at 

the gaging station, 13 ft above sea level. The average 

channel slope is 33 ft/mi.

Ward Lake Outfall near Bradenton

The Ward Lake Outfall (originally the John Ward 

Dam) is an 838-ft-long sheet-pile weir that impounds 

the Braden River to form Ward Lake (also known 

locally as the Bill Evers Reservoir), approximately 6 mi 

upstream from the mouth. The weir separates the 

upper freshwater part of the Braden River from the tidally influenced, brackish-water estuary downstream. 

 Originally built in 1936, the 838-ft-wide weir was 

reconstructed in 1985 with 20-ft sections of 12-in. 

thick concrete sheet pile, driven to a depth of about 

20 ft below sea level, except at the edges where 40 ft 

of 8-in. thick sheet pile was driven 12 ft below sea 

level (written commun., Smith and Gillespie Engineering, 1982). The sheet pile was finished with a 

2.3-ft-wide cap. In addition, continuous synthetic 

membrane liners were bolted at the top of the sheet 

pile at both the upstream and the downstream faces of 

the weir and covered with rip-rap. The upstream crest 

of the weir averages 3.93 feet above sea level, but varies between 3.82 and 4.10 ft above sea level (fig. 12, 

Smith and Gillespie Engineering, 1990). Due to the 

effects of changing influences such as wind generated 

waves, seiche, algae growth, and hydrilla on the water 

838 FEET

3.24 FEET 3.12 FEET

ELEVATION ELEVATION 7.0 FEET 7.03 FEET

37 FEET

40 FEET

WEST EAST

LINER

FLOW

HIGH 4.10 FEET

AVERAGE 3.93 FEET

LOW 3.82 FEET

HIGH 4.11 FEET

AVERAGE 3.91 FEET

LOW 3.80 FEET

CROSS SECTION

NOT TO SCALE

Liner Elevation Liner Elevation

(Upstream)

(Downstream)

ELEVATION VIEW

(Looking downstream)

Figure 12. Ward Lake weir 

survey. (Modified from Smith 

and Gillespie, 1990.)
22 Hydrologic Description of the Braden River Watershed, West-Central Florida

levels and flow at the weir, it is very difficult to determine the exact water elevation of zero flow. Although 

the survey (fig. 12) indicted the lowest elevation of the 

upstream crest of the weir to be 3.82 ft, field reconnaissance has shown the elevation of zero flow to be, 

at times, 3.80 ft. The water surface of the downstream 

reach, even at high tide, is usually more than 1.5 ft 

below the top of the weir. Water-level fluctuations for 

the tidal reach of the Braden River can be affected by 

storm surge and seiche created by tropical storms and 

hurricanes. On March 13, 1993, the gage at the 

Elwood Park station (station 13, fig. 9) recorded a 

water-level elevation of 4.91 ft above sea level due to 

an unnamed tropical storm. During this elevated tide, 

brackish water from the estuary contaminated the 

drinking-water supply for the city of Bradenton, causing the water-treatment plant to shut down for several 

hours. Fluctuations of stage in Ward Lake have ranged 

from 2.60 ft below sea level to 6.15 ft above sea level.

The drainage area of the Braden River watershed 

at the Ward Lake Outfall gaging station is 59.2 mi2

(station 12, fig. 9). Effects of backwater from the lake 

extend upstream approximately 6 mi to just downstream of the gaging station at Braden River near 

Lorraine. Total relief in the subbasin is about 43 ft 

with the highest elevation in the subbasin about 47 ft 

above sea level at the northeastern drainage divide. 

The average channel slope is approximately 6.1 ft/mi. 

Lower Reach

The lower 6-mi reach of the Braden River and the 

tributaries that flow to it typically are affected by the 

tidal fluctuations in the estuary. The gaging stations on 

the tributaries to this lower reach are located upstream 

from their mouth far enough so that tidal effects are 

not present.

Braden River near Elwood Park

The Braden River gaging station near Elwood 

Park (station 13, fig. 9) was established about 2,100 ft 

downstream of the Ward Lake weir in the tidal estuary 

part of the Braden River. Tidal elevations and conductance are recorded. Conductance (which is related to 

salinity) is recorded at this station to monitor freshwater flows from Ward Lake into the receiving tidal 

estuary and also to measure the movement of brackish 

water (the saline wedge) from the estuary toward the 

weir. Two conductivity probes were attached to a pile 

on the Highway 70 bridge, one probe near the top of 

the water column and the other near the streambed, so 

that salinity stratifications could be measured. These 

stratifications are somewhat artificial in that the depth 

at the bridge (about 12 ft) is greater than the average 

stream depth (about 3-6 ft). The consequence of this 

deeper than average stream depth is that the brackish 

water pools around the bridge.

Williams Creek near Bradenton

Williams Creek is located about 4.8 mi upstream 

of the mouth of the Braden River, and drains a 2.7-mi2

area at the streamflow-gaging station (station 14, 

fig. 9). Williams Creek flows west from its headwaters, formed from several interconnected depressions, for approximately 4.1 mi where it empties into 

the lower reach of the Braden River. The gage record 

is not affected by the tidal waters of the Braden River. 

The subbasin, roughly 4-mi long and 1-mi wide, is 

bisected by Interstate Highway 75. Topography in the 

eastern two-thirds of the subbasin is flat and poorly 

drained, with an elevation ranging from about 25 to 

45 ft above sea level. The slope of the gaged Williams 

Creek channel is about 8.8 ft/mi. Parts of the upper 

subbasin have been ditched to improve drainage for 

agriculture and residential development. Topographic 

relief in the western one-third of the subbasin is more 

pronounced and the channel slope is about 14.7 ft/mi.

Gap Creek near Bradenton

Gap Creek empties into the lower reach of the 

Braden River about 4.8 mi upstream of the mouth of 

the Braden River, on the opposite bank and just 

upstream of Williams Creek. Gap Creek drains 7.2 mi2

at the streamflow-gaging station (station 15, fig. 9), 

located approximately 1.8 mi upstream of the creek’s 

mouth. Gap Creek is formed at the confluence of two 

tributaries and the Pearce Canal. Flowing from south 

to north, the 3.5-mi-long Pearce Canal drains the largest part of the subbasin. The drainage divide for the 

Pearce Canal is difficult to determine because the 

canal also drains south into another drainage subbasin 

outside of the Braden River watershed. An earlier 

study indicates that the canal starts to flow north about 

1 mi north of the county line (Tampa Bay Regional 

Planning Council, 1986). Land use within the subbasin 

is largely dominated by residential, commercial, and 

industrial developments, interspersed among numerous citrus groves. Runoff from Highway 301, which 
Surface Drainage and Gage Network 23

forms part of the western watershed boundary, flows 

into Gap Creek. Because of the Pearce Canal and the 

heavily developed areas, the subbasin boundaries are 

difficult to delineate. The subbasin is irregular, 

roughly 4.8-mi long, and almost 3-mi wide. Land-surface elevations range from about 35 ft above sea level 

near the northern and southern extremes of the subbasin to sea level at the mouth of the creek.

The channel slope of Gap Creek is indeterminate 

from topographic maps because the creek has been 

deeply channelized for most of its length. Channelization allows tidal influences, including backwater, to 

extend upstream from the mouth of Gap Creek at the 

Braden River, to an undetermined distance upstream.

Glen Creek near Bradenton

Glen Creek (station 16, fig. 9), the largest tributary 

to the tidally affected Sugarhouse Creek, is the farthest 

downstream station monitored for discharge in the 

Braden River watershed. The drainage area contribution from Glen Creek accounts for about one-half of 

the total drainage area within the Sugarhouse Creek 

subbasin. The drainage area of Glen Creek is 2.5 mi2

 at 

the streamflow gaging station, which is approximately 

0.75 mi upstream from the mouth of the creek. The 

Glen Creek subbasin is oblong (about 2.0-mi long and 

1.0-mi wide) and drains an urban area, a large orange 

grove, and a citrus processing plant. The whole length 

of Glen Creek has been channelized to contain runoff 

from large storm events. Dredging of the lower reach 

of Glen Creek has resulted in the exposure of a limestone channel, which at one location creates an abrupt 

drop (waterfall) of approximately 2 ft. The drop helps 

isolate the gaging station from potential effects of tide 

and backwater from the Braden River. The headwaters 

to Glen Creek originate in an urban environment at a 

heavily industrialized area which is comprised of 

impervious surfaces. Discharge pipes route drainage 

from U.S. Highway 301 to Glen Creek. The elevation 

in the Glen Creek subbasin ranges from approximately 

30 ft above sea level along the southwestern boundary 

divide to sea level at the mouth. The slope of the 2-milong main channel, from the headwaters to the mouth, 

is about 15 ft/mi. 

Braden River near Bradenton

The Braden River near Bradenton gage is at the 

mouth of the Braden River just upstream of the confluence with the Manatee River (station 17, fig. 9). As the 

Braden River approaches the Manatee River, it begins 

to widen and flatten into a coastal plain estuary. The 

gage is located on a public boat dock on the left bank, 

about 50 ft upstream of the State Road 64 bridge. 

Because of the shallow depths (less than 2 ft), only one 

conductance probe was needed. Tidal elevation and 

conductance are measured at 15 minute intervals.

Streamflow at the Ward Lake Outfall

The Ward Lake weir has been in place for almost 

60 years, separating the tidal Braden River estuary 

from the freshwater reservoir. A preliminary study was 

undertaken in 1992 to directly measure streamflow at 

the Ward Lake weir. Previously, streamflow at the 

Ward Lake weir had been estimated using weir coefficient equations and discharge-drainage area ratio calculations. Results of these two methods of estimating 

streamflow are compared to results of the direct discharge measurement methods. A study was done to 

determine the extent of seepage around the ends of the 

weir and another study investigated potential leakage 

through the weir. 

Direct Streamflow Measurements

Measurements of discharge at the Ward Lake weir 

were made at various water-level stages. These discharge measurements and corresponding stages were 

used to define a relation between stage and discharge 

(a rating curve) for the Ward Lake weir (fig. 13). The 

rating was developed from a series of discharge measurement methods that included volumetric, pygmy 

and AA-standard current-meter, by wading rod and 

boat. For a complete description of USGS discharge 

measurement techniques see Rantz and others, 1982. 

The rating curve shown in figure 13 was put into use 

on October 1, 1993, and used for the 1994 and 1995 

water years. Ratings are updated and modified as more 

data are collected. Discharge for the Ward Lake Outflow ranges from 0 to 7,350 ft3

/s. 

Annual mean discharge at the Ward Lake Outfall 

for water years 1993 and 1994 was 59.7 and 57.3 ft3

/s, 

respectively (Coffin and Fletcher, 1993; 1994). 

Because of long periods of no flow and short periods 

of very high flow at the Ward Lake weir, daily mean 

flows are not reflected in annual mean discharge data. 

In the study area, as in many parts of west-central 

Florida, annual mean flows are strongly affected by 

the high flow events of the wet season (Hammett, 

1992). To better understand the flow conditions at the 
24 Hydrologic Description of the Braden River Watershed, West-Central Florida

Ward Lake weir, the flow duration curve, or 

exceedence curve, for water years 1993 and 1994 is 

shown in figure 14. Figure 14 shows the duration, as a 

percentage of time, for which a daily mean discharge 

was equaled or exceeded. Note that the daily mean discharge exceeded 0.01 ft3

/s about 70 percent of the 

time, 4.1 ft3

/s 50 percent of the time, 200 ft3/s 10 

percent of the time, and 330 ft3

/s 5 percent of the time. 

The annual mean discharge of about 60 ft3

/s is equaled 

or exceeded less than 25 percent of the time. Thus, 

there is a large skew in the annual mean and daily 

mean discharge data.

Streamflow Estimate Calculations

 A standard engineering practice for determining 

discharge over a weir includes using weir coefficient 

equations. These equations use the stage data for depth 

of water over the weir (head) and the physical characteristics of the weir, including type and length, to 

calculate discharge. The Ward Lake weir is classified 

as a broad-crested weir. For a discharge of 59 ft3

/s, the 

corresponding gage height from rating No. 3 is 3.99 ft. 

For this stage, 3.99 ft minus the 3.80 ft zero flow gage 

height gives a head of 0.19 ft. For a head of 0.19 ft, 

King and others (1948) suggest a weir coefficient for a 

broad crested weir of 2.70. The length of the weir, 

including end slopes, is calculated using equation 2 as:

L = 838 ft + 24.2(0.19 ft) = 843 ft (3)

and calculating discharge with equation 1:

Q = CwLH3/2 = (2.70) (843) (0.19)3/2 = 188 ft3

/s. (4)

This example shows the limitation of using the 

standard flow equation, for one gage height and corresponding discharge, without having calibrated the weir. 

In this example, a stage of 3.80 ft was used for the zero 

flow elevation. However, if no field reconnaissance 

had been done, it would be reasonable to assume that 

the lowest elevation (3.82 ft) of the upstream crest is 

the elevation at which flow would begin. Following the 

same example as above with a stage of 3.99 ft but an 

elevation of zero flow of 3.82 ft, the calculated discharge would be 159 ft3

/s. Had a mean elevation for the 

upstream crest been used (3.93 ft) for the elevation of 

zero flow, the above example for a stage of 3.99 ft 

4.00

4.20

4.40

4.60

DISCHARGE, IN CUBIC FEET PER SECOND

4.80

GAGE HEIGHT, IN FEET

4.00

4.10

4.20

4.30

4.40

4.50

4.60

4.70

100 1,000 10,000

3.90

0 10

250 750 1,250 1,750 2,250 2,750 3,250

RATING NUMBER 3.0

STARTING AT 10/1/93 (0001)

MEASUREMENT

Figure 13. Rating curve for Ward Lake Outfall near Bradenton.
Surface Drainage and Gage Network 25

would result in a discharge of 33.3 ft3/s. The stagedischarge rating developed for the weir shows that at 

the mean elevation of the upstream weir crest, 3.93 ft, 

about 10 ft3

/s of flow is discharging over the weir. It is 

significant that this amount of discharge was exceeded 

less than 45 percent of the time for water years 1993 

and 1994. These calculations show how sensitive the 

theoretical calculations of discharge using a weir coefficient equation are to the value used for the elevation 

of zero flow, especially for a weir 838-ft long. The discharge equations used for this analysis (eq. 1) are best 

used at high flows when the weir is fully submerged, a 

water-level elevation of at least 4.10 ft (fig. 13) on the 

Ward Lake weir. At this water level, rating 3 shows that 

about 212 ft3

/s is discharging over the weir, an amount 

exceeded less than 10 percent of the time.

To increase the accuracy of weir coefficient formulas for calculating discharge at the Ward Lake weir, 

the weir should be calibrated for each head of flow. 

It is possible to examine more closely the relation 

between the weir coefficients and measured discharge 

by rearranging equation 1 as

Cw = Q/(LH3/2). (5)

Weir coefficients, calculated from equation 5 and 

plotted with the corresponding gage heights, are 

shown in figure 15 as well as coefficients calculated 

by using measured and rating discharges. Also shown 

are coefficients calculated for individual discharge 

measurements using the length of weir L as computed 

by equation 2 and by the length of weir that was measured discharging over the weir. At low flows (less 

than 200 ft3

/s), because of the undulating shape of the 

weir crest, the length of flow over the weir can be 

much less than the 838 ft minimum in equation 2. For 

example, a measurement made at a gage height of 3.90 

measured a length of flow on the weir of 140 ft, but 

using equation 2 the calculated length would be 840 ft. 

0 10 20 30 40 50 60 70 80 90 100

100

10

1.0

0.1

PERCENT OF TIME FLOW IS EQUALED OR EXCEEDED

DISCHARGE, IN CUBIC FEET PER SECOND

1,000

Figure 14. Flow duration curve for Ward Lake Outfall, water years 1993-94.
26 Hydrologic Description of the Braden River Watershed, West-Central Florida

The difference in using a calculated or measured 

length is most apparent at gage heights of less than 

4.10 ft when the weir is not fully inundated. 

The weir formula (eq. 1) uses a weir coefficient 

that typically is calibrated for each individual weir and 

changes for different ranges of water levels (head) on 

the weir. Calibrated Ward Lake weir coefficients for a 

range of head from 0 to 2.0 ft, covering the period of 

record range of flow, are shown in figure 15. The coefficients change rapidly at the low gage heights, but 

begin to stabilize above about 4.6 ft. When weir 

coefficient formulas are used in the future to calculate 

discharge at the Ward Lake weir, figure 15 can be used 

to accurately choose an appropriate weir coefficient 

for each range of head on the weir.

The smallest weir coefficient calculated was 0.023 

using the calculated length method and 0.244 using the 

measured length method. The largest coefficient calculated was 2.99 using the calculated length method and 

2.97 using the measured length method. The smallest 

weir coefficient calculated from the theoretical rating 

developed from the measurements and gage readings 

was 0.032 and the largest weir coefficient calculated 

was 3.11. Weir coefficients calculated using rating 

curve number 3 used the calculated length for L (eq. 

2). 

Wanalista (1989) used a discharge/drainage area 

ratio calculation to estimate the annual streamflow at 

the Ward Lake weir. Wanalista estimated a ratio of 

1 ft3

/s of annual mean flow for every 1 mi2 of drainage 

basin using five watersheds of known area and annual 

mean flow, as recorded by the USGS. This 1:1 ratio of 

annual mean discharge to drainage area is not an exact 

fit for the data he presented but is what he used as an 

estimate. Using this 1:1 ratio and a drainage area of the 

Braden River above the Ward Lake weir of 60.3 mi2

(Camp, Dresser, and Mckee Inc., 1985), Wanalista 

estimated an annual mean flow of 60.3 ft3

/s for the 

Ward Lake weir. This estimate is within 1 to 5 percent 

of the annual mean discharges reported by the USGS 

for water years 1993 and 1994, respectively. The 1:1 

ratio seems to work well to estimate annual mean flow 

for the 1993 and 1994 water years, but may need to be 

adjusted to account for particularly wet or dry years.

-0.5

3.5

0

0.5

1.0

1.5

2.0

2.5

3.0

WEIR COEFFICIENT

3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6 5.8 6.0

GAGE HEIGHT IN FEET ABOVE SEA LEVEL

Cw - Calculated from theoretical rating --

 length calculated 

Cw-Length calculated

Cw-Length measured

Figure 15. Gage heights and weir coefficients.
Surface Drainage and Gage Network 27

Seepage and Leakage Studies

Two investigations were undertaken to determine 

whether a significant volume of water was seeping 

around or through the Ward Lake weir. In the first 

investigation, a series of water-level monitors were 

installed and the water levels were measured at both 

ends of the weir. In the second investigation, two leakage tests were conducted using rhodamine dye as a 

tracer.

Shallow water-table wells (piezometers) were 

installed to monitor water-table fluctuations at the 

ends of the Ward Lake weir (fig. 10), and were measured 11 times during the period from December 1992 

to September 1994 (fig. 16). The data are shown in 

table 5. The data show the water-table gradients 

declining in a clockwise direction, indicating a similar 

flow path for each measurement. Fluctuations in the 

periodically measured water-table levels at piezometer 

No. 1, at the upstream side of the west-end of the weir, 

ranged from a maximum altitude of 3.54 ft above sea 

level to a minimum of 2.69 ft above sea level. Watertable fluctuations at piezometer No. 4, at the downstream side of the weir, were lower, ranging from a 

maximum altitude of 2.71 ft above sea level to a 

minimum of 1.12 ft above sea level. 

To determine the rate of ground-water seepage 

through the riverbank around the west end of the weir, 

rhodamine dye was used as a fluorescent tracer in a 

time-of-travel study. The concrete sheet piles that form 

the west end of the weir extend horizontally approximately 40 ft into the river bank. A measured volume of 

rhodamine dye was placed in piezometer No. 1, having the highest water-level altitude and closest proximity to Ward Lake (fig. 10). Water samples were 

collected daily from piezometers 2, 3, 4, 9, and 10, and 

analyzed with a fluorometer for traces of rhodamine 

dye. After 17 consecutive days of sampling, the dye 

tracer remained undetected in all of the five monitored 

piezometers. Because water samples from the nearest 

downgradient piezometer, No. 2, did not record the 

dye tracer, a drive-point ground-water sampler was 

used to locate the extent of the dye-tracer seepage 

plume by drilling and sampling numerous locations 

downgradient from the dye injected piezometer. 

The farthest point sampled with the drive-point 

sampler that indicated dye tracer downgradient of the 

injected piezometer was about 13 ft from the injected 

piezometer. The flow path of the dye, determined from 

numerous drive-point water samples, migrated from 

piezometer No. 1 to the northwest, about 20 ft from the 

0

4.5

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

WATER LEVEL IN FEET ABOVE SEA LEVEL 

WARD PIEZOMETER 1 PIEZOMETER 2 PIEZOMETER 9 PIEZOMETER 3 PIEZOMETER 8

mean

maximum

minimum

ELEVATION OF ZERO FLOW FOR WARD LAKE OUTFALL

LAKE

Figure 16. Mean, maximum, and minimum water levels in piezometers at Ward Lake Outfall.
28 Hydrologic Description of the Braden River Watershed, West-Central Florida

end of the west end of the weir (fig. 10). The seepage 

velocity around the weir was calculated as:

V = 13 ft/17 days = 0.76 ft/day = 8.8 x 10-6 ft/s (6)

where V is the velocity of seepage around the weir. 

To calculate an area of seepage, the extent of flow was 

determined to be confined to the top of the water-table 

range, as measured in piezometer No. 1, to the top of 

the clay layer which restricts vertical flow. Since the 

top of the water table recorded in piezometer No. 1 was 

3.54 ft above sea level on February 8, 1993 (table 5), 

and the top of the clay layer was 2.5 ft below sea level, 

determined from cuttings collected during drilling, the 

area was calculated as:

A = (3.54 ft + 2.5 ft)* (D) = (6.04 ft)*D (7)

where A is the area of seepage, and D is the distance 

from the edge of the weir in feet (fig. 10). Using V and 

A in the equation for flow:

Q = V*A = 8.8 x 10-6 ft/s * (6.04 ft) * D (8)

= 5.3 x 10-5 ft2

/s* D 

where Q is the flow rate of seepage around the west end 

of the Ward Lake weir. This equation assumes a constant seepage velocity when, in fact, because the watertable gradients measured decrease with distance away 

from the reservoir, the velocity would drop off considerably. The amount of seepage around the west end of 

the weir is dependant, then, on the extent to which 

seepage occurs beyond the edge of the weir, D. If it is 

assumed that all significant seepage is contained to the 

first 20 ft west of the weir, then the flow rate of seepage 

would be:

Q = 5.3 x 10-5 ft2

/s * 20 ft = 0.0011 ft3/s (9)

This estimate of seepage is useful in evaluating the 

extent of seepage around the west end of the weir and 

indicates that seepage around both ends of the weir is 

relatively small in comparison to the surface flow.

A study was undertaken to determine if the 

concrete sheet-pile weir structure had any significant 

leaks or cracks. On June 3, 1992, 1 gal of rhodamine 

dye was poured into the Ward Lake reservoir, about 

5 ft upstream of the weir. The dye was poured onto the 

surface and also at a depth of several feet to ensure 

mixing. Water samples were collected downstream of 

the weir at five sites, four times a day, including one 

site at the Braden River near Elwood Park gage. 

An automatic sampler placed near the middle of the 

weir was used to sample hourly through the night. 

No measurable level of dye was detected above the 

detection limit of 0.01 ppb. The water samples were 

analyzed with a portable fluorometer. The dye study 

was repeated on May 24-25, 1993, to confirm the 

Table 5. Piezometer water levels around Ward Lake weir

[All values are in feet above sea level]

a

 Missing data. c Missing data, piezometer not established. b

 Missing data, piezometer destroyed. d Tidal elevation at Braden River near Elwood Park.

Piezometer

number

Dec 1, 1992

Dec 29, 1992

Feb 8, 1993

Mar 18, 1993

Apr 28, 1993

July 13, 1993

Nov 3, 1993

Dec 9, 1993

Mar 7, 1994

May 9, 1994

Sept. 6, 1994

1 3.23 3.29 3.54 3.47 3.39 --a 3.12 2.69 3.08 2.89 3.15

2 2.39 2.38 1.07 2.44 --a --a 2.62 2.02 2.46 2.28 2.58

3 1.48 1.35 1.73 0.35 1.62 1.70 1.68 1.55 --b --b --b

4 1.19 1.12 1.54 2.71 1.31 1.39 1.45 1.35 1.38 1.51 1.48

5 0.79 0.57 1.42 0.91 1.27 1.32 --a 1.23 1.19 1.53 1.62

6 3.43 3.56 3.82 3.80 3.67 3.70 --a 3.34 3.70 3.45 3.81

7 3.00 2.99 3.46 3.26 3.16 3.23 --a 2.90 3.21 2.95 3.45

8 --c --c --c --c --c --c 1.32 1.26 1.24 1.37 1.37

9 --c --c --c --c --c --c 2.31 1.92 2.16 1.95 2.27

10 --c --c --c --c --c --c 1.22 1.19 1.15 1.28 1.22

Ward Lake 3.77 3.85 3.98 4.04 3.99 4.03 4.03 3.62 3.98 3.75 3.94

tidal

elevationd 10.7 10.4 10.2 9.8 10.4 10.4 10.4 10.8 10.3 10.7 10.3
SUMMARY AND CONCLUSIONS 29

earlier findings. Results of the study indicate that there 

is no significant leakage through the weir structure 

because no rhodamine dye was detected downstream 

of the weir for a 36-hour period after the dye was 

poured.

SUMMARY AND CONCLUSIONS

The Braden River watershed lies along the gulf 

coast of Florida, below Tampa Bay. Ninety percent of 

the watershed is located in southern Manatee County 

with the remaining ten percent in northern Sarasota 

County. The Braden River is the largest tributary to the 

Manatee River, which flows into Tampa Bay. The 

watershed lies in the coastal terraces know as the 

Pamlico, Talbot, Penholoway and Wicomaco Terraces 

of the Gulf Coast Lowlands and De Soto Plain physiographic zones. The climate is subtropical with annual 

average temperatures about 72 o

F, annual average rainfall about 56 in, and estimated annual lake evaporation 

52 in. There are two dominant soil series in the watershed, the Myakka-Cassia and the EauGallie-Floridana. 

Both soils are found in flatwoods and are poorly 

drained.

Land use in the watershed is primarily urban in 

the western half and agricultural in the eastern half. 

However, the watershed is being developed for 

medium- to high-density housing at a rapid rate. 

Use of ground water is primarily for agriculture, 

whereas surface-water use is primarily for the city 

of Bradenton.

The three major aquifers underlying the watershed 

are the surficial, intermediate and Floridan aquifer systems. The surficial aquifer is underlaid by a clay layer 

that enhances the ground-water flow of the surficial 

aquifer to surface-water bodies. The intermediate 

aquifer system is confined, and has permeable zones 

that, at times, have high heads which indicate possible 

interaction with the surficial aquifer. The Floridan 

aquifer system also has a high head, but is confined 

from the surficial aquifer by the thick intermediate 

aquifer system.

Hydrologically, the Braden River can be divided 

into three distinct reaches: the lower reach, which is 

dominated by tides; the middle reach, which is 

affected by backwater from Ward Lake, and; the upper 

reach which is free-flowing, unaffected by backwater. 

There are 12 main tributaries to the Braden River 

examined in this study, 10 first-order and 2 secondorder. Three tributaries flow into the estuary and the 

other nine flow into the Braden River at or above the 

reservoir.

A volumetric discharge method was developed so 

that low flow over the weir could be measured. With 

gage-height records of lake elevations, volumetric discharge measurements, and measurements made at high 

flows with standard USGS techniques, a correlation 

between head of water and flow was developed. 

A continuous gage-height record of water level used in 

conjunction with the discharge rating table developed 

by the USGS can be used to determine the flow for the 

Ward Lake Outfall. From this relationship the weir 

coefficients for different heads of water were calculated and compared to actual field measurements. 

Annual mean flows for 1993 and 1994 water years 

were 59.7 and 57.3 ft3

/s, respectively. Annual mean 

discharges are not indicative of the daily mean discharges and are heavily influenced by high-flow 

events. 

Discharge from the Ward Lake Outfall into the 

estuary cannot easily be calculated using theoretical 

weir coefficients because of the undulating shape of 

the weir’s crest. However, weir coefficients can be 

determined for the weir using direct measurements. 

Calculating annual mean discharge using a 1:1 ratio of 

annual mean discharge to drainage area, as calculated 

from nearby watersheds, is a reasonable way to estimate the annual mean discharge of a drainage basin.

 By examining the horizontal flow around the west 

end of the weir, and by recording water-table elevations in piezometers, it was determined that no significant flows are seeping around the ends of the weir. 

A dye study investigated the possibility of leakage 

through the weir. No significant leakage was found.

REFERENCES

Barr, G.L., 1996, Hydrogeology of the surficial and intermediate aquifer systems in Sarasota and adjacent counties, Florida: U.S. Geological Survey Water-Resources 

Investigations Report 96-4063, 81 p.

Brown, D.P., 1983, Water resources of Manatee County, 

Florida: U.S. Geological Survey Water Resources 

Investigations Report 81-74, 112 p.

Camp, Dresser, and McKee, Inc., 1985, Southeast area 

stormwater management study: Final report: Consultant’s report to the Manatee County Planning and 

Development Department, 111 p.
30 Hydrologic Description of the Braden River Watershed, West-Central Florida

Cherry, R.N., Stewart, J.W., and Mann, J.A., 1970, General 

hydrology of the Middle Gulf area: Tallahassee, Florida Bureau of Geology, Report of Investigations 

no. 56, 96 p.

Coffin, J.E., and Fletcher, W.L., 1993, Water resources data 

for Florida: U.S. Geological Survey, v. 3A, Southwest 

Florida, 245 p.

-------- 1994, Water resources data for Florida: U.S. 

Geological Survey, v. 3A, Southwest Florida, 245 p.

Conservation Consultants, Inc., 1983, Bradenton reservoir 

improvements, preconstruction water quality monitoring and water quality impact assessment report; 

Consultant’s report to the city of Bradenton, 286 p.

Duerr, A.D., Hunn, J.D., Lewelling, B.R., and Trommer, 

J.T., 1988, Geohydrology and 1985 water withdrawals 

of the aquifer systems in southwest Florida, with 

emphasis on the intermediate aquifer system: U.S. 

Geological Survey Water-Resources Investigations 

Report 87-4259, 115 p. 

Freeze and Cherry, 1979, Groundwater, Englewood Cliffs, 

N.J., Prentice-Hall, Inc., 604 p.

Geraghty and Miller, 1977, Groundwater resources preliminary study of the Palm Aire area, southwestern Manatee County, Florida: Consultant’s report to 

Conservation Consultants, Inc., 30 p.

Hammett, K.M., 1992, Physical processes, salinity characteristics, and potential salinity changes due to freshwater withdrawals in the tidal Myakka River, Florida: 

U.S. Geological Survey Water-Resources Investigations Report 90-4054, 20 p.

Horton, R.E., 1907, Weir experiments, coefficients, and 

formulas: U.S. Geological Survey Water-Supply and 

Irrigation Paper 200, 159 p.

Hutchinson, C.B., 1984, Hydrogeology of the Verna wellfield area and management alternatives for improving 

yield and quality of water, Sarasota County, Florida: 

U.S. Geological Survey Water-Resources Investigations Report 84-4006, 53 p.

Joyner, B.F., and Sutcliffe, Horace, Jr., 1976, Water 

resources of the Myakka River basin area, southwest 

Florida: U.S. Geological Survey Water-Resources 

Investigations 76-58, 87 p.

King, Wisler, and Woodburn, 1948, Hydraulics (5th ed.), 

169 p.

Knochenmus, L.A., and Thompson, T. H., 1991, Hydrogeology and simulated development of the brackish 

ground-water resources in Pinellas County, Florida: 

U.S. Geological Survey Water-Resources Investigations Report 91-4026, 20 p.

Kohler, M.A., Nordenson, and Baker, 1959, Evaporation 

maps for the United States, U.S. Weather Bureau 

Technical Paper 37, 13 p.

Lohman, S.W., 1972, Groundwater hydraulics: U.S. 

Geological Survey Professional Paper 708, 70 p.

Miller, J.A., 1986, Hydrogeologic framework of the Floridan 

aquifer system in Florida and in parts of Georgia, 

Alabama, and South Carolina: U.S. Geological Survey 

Professional Paper 1403-B, 91 p., 33 pls.

Mularoni, R.A., 1994a, Potentiometric surface of the Upper 

Floridan aquifer system, west-central Florida, May 

1993: U.S. Geological Survey Open-File Report 94-32, 

1 sheet.

-------- 1994b, Potentiometric surface of the Upper Floridan 

aquifer system, west-central Florida, September 1993: 

U.S. Geological Survey Open-File Report 94-81, 

1 sheet.

National Oceanographic and Atmospheric Administration, 

1992a, Climatological Data, Florida, June 1992, 

Asheville, N.C., v. 96, no. 6.

-------- 1992b, Climatological Data - Annual Summary, 

Florida, 1992, v. 96, no. 13.

-------- 1993, Climatological Data - Annual Summary, 

Florida, 1993, v. 97, no. 13.

Rantz, S.E., and others, 1982, Measurement and computation 

of streamflow: Volume 1- Measurement of stage and 

discharge, U.S. Geological Survey Water-Supply Paper 

2175, 284 p.

Ryder, P.D., 1985, Hydrology of the Floridan aquifer system 

in west-central Florida: U.S. Geological Survey Professional Paper 1403-F, 63 p.

Southeastern Geological Society, Ad hoc committee, compilers, 1986, Hydrogeologic units of Florida: Tallahassee, 

Florida Geological Survey Special Publication no. 28, 

9 p.

Southwest Florida Water Management District, 1990 GIS 

data base.

Tampa Bay Regional Planning Council, 1986, Water quality 

studies of the Anclote and Braden Rivers: Tampa, Fla., 

133 p.

University Press of Florida, 1994, Florida Statistical Abstract 

(28th ed.): 794 p.

U.S. Department of Agriculture, 1983, Soil survey of Manatee County, Florida: Soil Conservation Service, 159 p.

-------- 1987, Soil survey of Sarasota County, Florida: Soil 

Conservation Service: 147 p.

U.S. Department of Commerce, 1964, Weather Bureau Technical Paper 49, 29 p.

Wanalista, M. P., 1989, Evers Reservoir hydrologic study: 

Orlando, University of Central Florida, 139 p.

White, W.A., 1970, The geomorphology of the Florida 

Peninsula: Tallahassee, Florida Bureau of Geology 

Bulletin 51, 164 p.