Flow and chemical characteristics of the St. Johns River at Jacksonville, Florida ( FGS: Information circular 82 )

STATE OF FLORIDA
DEPARTMENT OF NATURAL RESOURCES
Randolph Hodges, Executive Director

DIVISION OF INTERIOR RESOURCES
R. O. Vernon, Director

BUREAU OF GEOLOGY
C. W. Hendry, Jr., Chief

Information Circular No. 82

FLOW AND
THE ST. JOHNS

CHEMICAL CHARACTERISTICS OF
RIVER AT JACKSONVILLE, FLORIDA

Warren Anderson and D. A. Goolsby

Prepared by the
UNITED STATES GEOLOGICAL SURVEY
in cooperation with the
BUREAU OF GEOLOGY
FLORIDA DEPARTMENT OF NATURAL RESOURCES
and the
CONSOLIDATED CITY OF JACKSONVILLE

TALLAHASSEE
1973

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FG36 Ir
ho0%'

DEPARTMENT
OF
NATURAL RESOURCES

REUBIN O'D. ASKEW
Governor

RICHARD (DICK) STONE
Secretary of State

THOMAS D. O'MALLEY
Treasurer

FLOYD T. CHRISTIAN
Commissioner of Education

ROBERT L. SHEVIN
Attorney General

JR.

lComptroller

DOYLE CONNER
Commissioner ofAgriculture

W. RANDOLPH HODGES
Executive Director

LETTER OF TRANSMITTAL

Bureau of Geology
Tallahassee
August 24, 1973

Honorable Reubin O'D. Askew, Chairman
Department of Natural Resources
Tallahassee, Florida

Dear Governor Askew:

The Bureau of Geology of the Division of Interior Resources is printing as
its Information Circular No. 82 a report prepared by Warren Anderson and D. A.
Goolsby of the U. S. Geological Survey entitled, "Flow and Chemical
Characteristics of the St. Johns River at Jacksonville, Florida".

This report will be of substantial value to water managers in developing the
St. Johns River as a multiple resource. Evaluation of the capacity of the river to
accept pollutants without adversely affecting other uses requires detailed data of
flow and chemical characteristics and an understanding of how they interact.

Respectfully yours,

Charles W. Hendry, Jr., Chief
Bureau of Geology

Completed manuscript received
June 27, 1973
Printed for the Florida Department of Natural Resources
Division of Interior Resources
Bureau of Geology
by Ambrose the Printer
Jacksonville, Florida

iv

CONTENTS

Abstract .. .. ....................................
Introduction ......................................
Purpose and Scope ............. .....................
Data collection and computation of flow records . . . . .
Acknowledgments .................................
Previous investigations ...............................
Description of the system ...............................
Factors affecting the river flow and quality . . . . . .
Tides . .. . . . . . . . .
The tidal cycle .............. ... .................
Relation of chloride concentration to the tidal cycle . . . .
Non-tidal factors ..................................
Wind ......................................
Fresh-water input ................................
Storage .. .. .. ... .. .. ... .. .. .. .. .... .. .. .
Flow statistics .....................................
Flow distribution and frequency . . . . ... . . ..
Maximum periods of flow deficienty . . . . . . .
Chemical characteristics ................................
Variations in chemical characteristics
at Main Street Bridge ..............................
Variations in chloride concentration
in the Lower St. Johns River ...........................
Seasonal variation in flow and chloride concentration . . . . .
Temperature ......................................
Relation of flow and quality characteristics to use of the river . . . .
Summary and conclusions ...............................
Continuing and future studies .......... ...................
References .......................................

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ILLUSTRATIONS

Figure Page
1. Map of northeastern Florida showing major elements of the St. Johns River
system ..................................... 4

2- Map of the lower St. Johns River in the vicinity of Jacksonville ....... .. 5

3. Relation of point velocity at Station 1300 to discharge of the St. Johns River
at Main Street Bridge ............................... 6

4. Relation of area between superimposed stage graphs to volume of tidal flow at
Main Street Bridge ............................... 7

5. Superimposed state graphs for the St. Johns River at Jacksonville . 7

6. Diagram of a tidal cycle in the St. Johns River at Jacksonville showing
variations of point velocity, discharge, gage heights, cumulative flow volume,
and chloride concentration with time and gage heights and times of mean tidal
levels ... ............. ...................... 12

7A. Relation of the observed times of occurrence of maximum velocities to the
predicted times of occurrence ......................... 14

7B. Relation of the observed maximum dishcarges at Jacksonville to the predicted
maximum current velocities at St. Johns River Entrance during 28 tidal cycles
observed in 1954, 1955, 1956, 1963 and 1964 . . . .... 14

8. Relation of adjusted yearly average downstream and upstream tidal flow per
cycle to yearly average net flow per tidal cycle . . . .... 16

9. Relation of average volume of tidal flow at Jacksonville to range of tide at
Mayport ................ .................. 17

10. Graph showing the monthly average change in storage in the St. Johns River
estuary, the monthly average difference in the estimated monthly rainfall on
and evapotranspiration from the estuary, and the average annual variation in
sealevel ..................... ... .... .... .. 19

11. Relation of yearly average discharge at Jacksonville to proportional yearly
average inflow to the estuary . . . . . 21

12. Hydrographs showing monthly mean flow volumes (graph A), monthly
averages of the monthly mean-flow volumes (graph B), and monthly mean net
flow volumes (graph D) at Jacksonville and monthly mean predicted tidal
range (graph C) at Mayport from March 1954 to September 1966 ....... 23

13. Flow distribution and cumulative flow-distribution curves for downstream
flow at Main Street Bridge ........................... 26

14. Flow distribution and cumulative flow-distribution curves for upstream flow
at Main Street Bridge ................... .......... 27

ILLUSTRATIONS continued

15. Cumulative flow-distribution curve of daily net flow of the St. Johns River at
Main Street Bridge ............................... 28

16. Frequency of monthly and annual maximum downstream flows in the St.
Johns River at Main Street Bridge . . . . . 29

17. Frequency of monthly and annual maximum upstream flows in the St. Johns
River at Main Street Bridge .......................... 30

18. Frequency of monthly and annual minimum downstream flows in the St.
Johns River at Main Street Bridge . . . ..... ..... 31

19. Frequency of monthly and annual minimum upstream flows in the St. Johns
River at Main Street Bridge .......................... 32

20. Frequency of monthly and annual maximum daily net flow in the St. Johns
River at Main Street Bridge .......................... 33

21. Frequency of monthly and annual minimum daily net flow in the St. Johns
River at Main Street Bridge .......................... 35

22. Maximum periods of deficient daily net flow in the St. Johns River at Jackson-
ville . . . . . . . . . .. 36

23. Relation of specific conductance to concentration of major chemical
constituents in the St. Johns River at Main Street Bridge . .... 38

24. Daily maximum specific conductance near the surface of the St. Johns River
at Main Street Bridge, October 1966 to April 1967 . . .... 38

25. Cumulative discharge and specific conductance at the end of each tidal flow
beginning December 12, 1966 and ending January 31, 1967 . ... 40

26. Duration curves of major chemical constituents in the St. Johns River at Jack -
sonville . .. . . . . . . . 42

27. Longitudinal and vertical variation in specific conductance of the water in the
lower St. Johns River from river mile 12 to river mile 31 at slack water on
selected days ....................... .......... 43

28. Variations with time in the specific conductance of the St. Johns River near
the surface and bottom at selected points in the Jacksonville area ...... .. 45

29. Relation of maximum chloride concentration at Main Street Bridge to
maximum chloride concentration at Orange Park and Drummond Point at
slack before the downstream flow of common tidal cycles. . ... 46

30. Approximate longitudinal variation in the daily maximum chloride
concentration which will be exceeded less than 7 percent of the days and 50
percent of the days in the lower St. Johns River . . . ... 47

vii

ILLUSTRATIONS continued

31. Graphs showing the highest, lowest, and average monthly mean net discharge
of the St. Johns River at Jacksonville . . . . . .

32. Graphs showing the average net flow and the average maximum and minimum
chloride concentrations in the St. Johns River at Jacksonville for alternate
months. Flow records and chloride records June 1959 to October 1966 .

33. Approximate average daily water temperatures of the St. Johns River at Main
Street Bridge and ground-water at specified depths . . . .

TABLES

Tables
1. Selected flow statistics for the St. Johns River at Jacksonville . ..

2. Chemical analyses of the St. Johns River at Jacksonville, Florida (samples
collected at Main Street Bridge) .......................

Page
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39

FLOW AND CHEMICAL CHARACTERISTICS OF
THE ST. JOHNS RIVER AT JACKSONVILLE, FLORIDA

by
Warren Anderson and D. A. Goolsby

ABSTRACT

The St. Johns River at Jacksonville, which is 21 miles upstream from the
ocean, is part of a tidal estuary that for practical purposes may be considered to
end at Lake George, 106 miles upstream from the ocean. Occasionally, tidal
effects are noted 161 miles upstream.

The channel of the estuary above Jacksonville is capable of storing huge
amounts of water, and rising ocean tides at the mouth of the river force large
amounts of water up the river past Jacksonville. Most of this water subsequently
flows back past Jacksonville as the ocean tide falls. These tidal flows average
87,000 cubic feet per second at Jacksonville, and peak flows exceeding 150,000
cubic feet per second are common. The average tidal flows are more than seven
times as large as the average net or fresh-water flow.

Fresh water draining from the estuary increases the volume and duration
of ebb tidal flows (downstream) and diminishes the volume and duration of
flood tidal flows (upstream). About a quarter of the fresh water that flows into
the estuary from April through September is released to the ocean from October
through March. When evapotranspiration from the estuary above Jacksonville
exceeds rainfall and fresh-water inflow into the estuary, the net loss of water
tends to cause the volume and duration of the upstream flows to exceed those of
the downstream flows.

The net flow of the St. Johns River at Main Street Bridge in Jacksonville
was downstream about 70 percent of the days of record and upstream about 30
percent of the days of record. Zero net flow occurred on 13 of the 4,597 days of
record, or 0.3 percent of the time. The greatest number of consecutive days that
the net flow was zero or upstream was 14 days.

Sea water moving upstream from the mouth of the St. Johns River mixes
with the fresher water already in the river channel to form a zone of transition.
The chloride concentration in this zone varies from that of sea water to that of
the fresh-water input. When the zone of transition extends upstream from
Jacksonville, the chloride concentration in the river at Jacksonville increases
with upstream flow and decreases with downstream flow. During a particular
tidal cycle, the magnitude and range in chloride concentration in the river at

2 BUREAU OF GEOLOGY

Jacksonville depends on the length and gradient of the zone of transition and on
the volumes of the tidal flows. About 80 percent of the time the chloride
concentration at Main Street Bridge exceeds 250 milligrams per liter.

Between Jacksonville and the ocean the river shows some stratification
between the sea water and overlying river water. However, stratification tends to
weaken or disappear in the vicinity of Jacksonville, probably because of
increased turbulence caused by channel constriction and bridge piers. The
temperature of the river averages less than 15 C (Celsius) (590 F) in January
and February and more than 28 C (82 F) in summer.

INTRODUCTION

The St. Johns River, which flows through the city of Jacksonville,
discharges about one tenth of the 40-billion-gallon average daily surface runoff
from the State of Florida -- a generous share of the 150-billion-gallon average
daily rainfall on the State. This prodigious and continually renewed resource can
be used for diverse and, in some instances, conflicting purposes such as water
supply, waste disposal, transportation, heat disposal, fisheries, and recreation. In
the Jacksonville area, the river (a tidal estuary) is used for all these purposes
except water supply.

There is continuing concern about the effect that the rapidly growing
population and economy in the St. Johns River basin will have on the potential
for pollution of the river by industrial and domestic waste. Evaluation of the
capacity of the river to accept pollutants without adversely affecting other uses
requires detailed data on flow and chemical characteristics and an understanding
of how they interact.

PURPOSE AND SCOPE

This report was prepared to present and interpret information on the flow
and chemical characteristics of the lower St. Johns River in the vicinity of
Jacksonville (figs. 1 and 2). It is intended that the report (1) describe the flow
and chemical characteristics with respect to variations with time, frequency of
occurrence, and magnitude of tidal flows; (2) indicate the factors that affect
flow and portray the manner in which they interact to product characteristic
flow patterns; and (3) relate the chemical quality of the river to the flow regime.

Flow records computed through September 30, 1966 for the lower St.
Johns River and chemical quality data obtained through May 1967 were

2 BUREAU OF GEOLOGY

Jacksonville depends on the length and gradient of the zone of transition and on
the volumes of the tidal flows. About 80 percent of the time the chloride
concentration at Main Street Bridge exceeds 250 milligrams per liter.

Between Jacksonville and the ocean the river shows some stratification
between the sea water and overlying river water. However, stratification tends to
weaken or disappear in the vicinity of Jacksonville, probably because of
increased turbulence caused by channel constriction and bridge piers. The
temperature of the river averages less than 15 C (Celsius) (590 F) in January
and February and more than 28 C (82 F) in summer.

INTRODUCTION

The St. Johns River, which flows through the city of Jacksonville,
discharges about one tenth of the 40-billion-gallon average daily surface runoff
from the State of Florida -- a generous share of the 150-billion-gallon average
daily rainfall on the State. This prodigious and continually renewed resource can
be used for diverse and, in some instances, conflicting purposes such as water
supply, waste disposal, transportation, heat disposal, fisheries, and recreation. In
the Jacksonville area, the river (a tidal estuary) is used for all these purposes
except water supply.

There is continuing concern about the effect that the rapidly growing
population and economy in the St. Johns River basin will have on the potential
for pollution of the river by industrial and domestic waste. Evaluation of the
capacity of the river to accept pollutants without adversely affecting other uses
requires detailed data on flow and chemical characteristics and an understanding
of how they interact.

PURPOSE AND SCOPE

This report was prepared to present and interpret information on the flow
and chemical characteristics of the lower St. Johns River in the vicinity of
Jacksonville (figs. 1 and 2). It is intended that the report (1) describe the flow
and chemical characteristics with respect to variations with time, frequency of
occurrence, and magnitude of tidal flows; (2) indicate the factors that affect
flow and portray the manner in which they interact to product characteristic
flow patterns; and (3) relate the chemical quality of the river to the flow regime.

Flow records computed through September 30, 1966 for the lower St.
Johns River and chemical quality data obtained through May 1967 were

INFORMATION CIRCULAR NO. 82

analyzed during preparation of this report. The procedures used in the
procurement and computation of the flow data are described in the following
section. Field reconnaissance trips and special observation of water quality and
flow characteristics were also necessary to this analysis.

This report is one of several to result from a comprehensive investigation
of the water resources of Duval County by the U. S. Geological Survey in
cooperation with the Consolidated City of Jacksonville and the Bureau of
Geology, Florida Department of Natural Resources.

The report was prepared under the direct supervision of L. J. Snell, former
Subdistrict Chief, Joel O. Kimrey, Subdistrict Chief, and B. F. Joyner, District
Laboratory Chief, Ocala, and under the general supervision of C. S. Conover,
District Chief, Tallahassee, all of the U. S. Geological Survey.

DATA COLLECTION AND COMPUTATION OF FLOW RECORDS

Stage data used in the computation of flow records for the St. Johns River
at Jacksonville are obtained at Main Street Bridge, at the Naval Air Station 8.2
miles upstream from Main Street Bridge and at the U. S. Corps of Engineers
Dredge Depot 4.8 miles downstream from Main Street Bridge. The upstream and
downstream gages are set at datums 10.00 feet below mean sea level and the base
gage is set at a datum 9.99 feet below mean sea level. The stage record collected
at Main Street Bridge is only used for flow computation if record is lost at one
of the other two gages.

Discharge measurements and point-velocity measurements are made from
the downstream (east) side of Main Street Bridge. Point-velocity measurements
are made at station 1,300, which is 1,005 feet from the south bank of the river.
The point velocity consists of the average of current-meter readings taken at 0.2
and 0.8 of the depth at station 1,300. Rapid discharge measurements, which
include velocity determinations at station 1,300 are occasionally made with four
current meters. The discharges and point velocities thus obtained are plotted
against each other for both upstream and downstream flow as shown in figure 3.
These relations, though they differ slightly, are linear. The discharge during a
tidal cycle is determined from frequent point-velocity readings (see fig. 6) by use
of these curves of relation. The volume of flow during the tidal cycle, both
upstream and downstream, is computed from the area under the discharge graph
thus obtained. As shown by figure 4, the volumes of flow are then plotted
against the area between the superimposed stage graphs (see fig. 5) obtained by
the gages at the Naval Air Station and the Dredge Depot. The volume of each
upstream and downstream flow is then determined from the stage record using
this latter curve of relation.

BUREAU OF GEOLOGY

82* 818
I10

MAYPORT
JACKSONVILLE,

ORANGE \
PARK -

oo^ \\ .
30 GREEN 300
COVE
SPRINGS a

PALATKA

CRESCENT \
LAKE
ORlANGE
LAKE
LAKE

O
OCALA "

29* ODE LAND 29.

82' 816

Figuqe 1. Map of northeastern Florida showing major elements of the St.
Johns River system.

INFORMATION CIRCULAR NO. 82

Figure 2. Map of the lower St. Johns River in the vicinity of Jacksonville.

Flow records computed for February 10, 1954, to September 30, 1966,
were used in this analysis. A year of record beginning on October 1 and ending
the following September 30 is called a water year. For example, the 1955 water
year began on October 1, 1954 and ended on September 30, 1955.

BUREAU OF GEOLOGY

-3Du,UUU U U,UUu
DISCHARGE, CUBIC FEET PER SECOND

Figure 3. Relation of point velocity at Station 1300 to discharge of the St.
Johns River at Main Street Bridge.

0>

W.-

aL .
U-8

-w
2. 0

um

INFORMATION CIRCULAR NO. 82

(,

0
1-3
0
o
0
IL

2

_1

_1

-4,00 -3,000 -2,000 -1,000 0 1,000
TIDAL FLOW, MILLIONS OF CUBIC FEET

2,000 3,000

Figure 4. Relation of area between superimposed stage graphs to volume
of tidal flow at Main Street Bridge.
TIME AT JACKSONVILLE NAVAL AIR STATION
2400 0600 1200 1800 2400 0600

2400 0600 1200 1800 2400
TIME AT CORPS OF ENGINEERS DREDGE DEPOT
Figure 5. Superimposed stage graphs for the St. Johns
Jacksonville.

UPSTREAM FLOW DOWNSTREAM FLOW

\ *. 6

: -
S.* .

NOTE FALL IS DIFFERENCE N GAGE TIME IS DURATION,IN HOURS, OF
6,. 0 **

NOTE: FALL IS DIFFERENCE IN GAGE TIME IS DURATION, IN HOURS, OF
HEIGHT AT THE CORPS OF PERIODS BETWEEN OCCURRENCES
ENGINEERS DREDGE DEPOT AND OF EQUAL GAGE HEIGHT AT THE
AT THE JACKSONVILLE NAVAL TWO GAGES
AIR STATION
i I I I I

4,000

River at

i

BUREAU OF GEOLOGY

ACKNOWLEDGMENTS

The authors express their appreciation to the following employees of the
city of Jacksonville: Tom Ard, Director, Air and Water Pollution Control,
Department of Health, Welfare and Bioenvironmental Services; E. T. Owens,
Engineer, and S. Hay, Assistant Engineer, City Engineering Department; who
provided valuable data and assisted in tests; and to Messrs. James English,
Director of Public Works and Robert B. Nord, Director, Water and Sewer
Department, whose valuable assistance enhanced the collection of basic data.
The contribution of E. T. Owens is especially appreciated, as it was he who
fostered the data-collection program from its inception.

PREVIOUS INVESTIGATIONS

The earliest investigation to yield data applicable to the present physical
conditions in the St. Johns River estuary was led by E. F. Hicks in the winter of
1933-34. The results of this investigation were reported by F. J. Haight in 1938.
Measurements of the stage, velocity, and discharge of the river at Jacksonville
were made by the U. S. Geological Survey on May 10, 1945. The U. S.
Geological Survey investigated the river August 16-24, 1945, to determine the
change in position from Main Street Bridge of a particle of river water during the
course of a tidal cycle. E. E. Pyatt investigated the distribution of pollutants in
the river in 1959.

DESCRIPTION OF THE SYSTEM

The source of the St. Johns River is a marsh near Fort Pierce, Florida, 312
miles from its mouth near Mayport. The river flows on a generally northward
course to Jacksonville and then eastward to the ocean. The topographic drainage
area of the St. Johns River is 9,430 square miles, nearly one-sixth of the land
area of Florida.

From the ocean to Jacksonville, the river ranges in width from about
1,250 feet at Main Street Bridge to more than 2 miles at Mill Cove, and in the
reach from Jacksonville to Palatka the width ranges from 1 to 3 miles. From just
south of Palatka to Lake George, the river narrows to generally less than half a
mile and in one place to only about 600 feet. Lake George, the largest expansion
in width (nearly 7 miles) along the entire river, is about 70 square miles in area
and normally shows no tidal fluctuation. South of Lake George, the river
channel is generally much narrower than to the north, although several large
lakes or widening of the river exist. The shore line of the river north of Palatka
is indented by many coves and enlarged mouths of tributaries.

INFORMATION CIRCULAR NO. 82

The Corps of Engineers, U. S. Army, maintains a navigation channel in the
river. The channel is 34 feet deep and 400 to 900 feet wide between the ocean
and Jacksonville, 13 feet deep and 200 feet wide between Jacksonville and
Palatka, 12 feet deep and 100 feet wide between Palatka and Sanford, and 5 feet
deep and 100 feet wide between Sanford and Lake Harney.

At low water, the flood plain of the St. Johns River contains openwater
areas totaling more than 300 square miles. Lake George, Crescent Lake, and the
river between Lake George and the ocean occupy about two-thirds of this area.

At the mouth of the St. Johns River the tidal range averages 4.9 feet. The
ocean tide generates a progressive tidal wave that moves up the river with
gradually diminishing amplitude until at Orange Park the range is only 0.7 foot.
From Orange Park southward; the amplitude of the wave increases until at
Palatka the range is 1.2 feet, the same as that at Main Street Bridge in
Jacksonville. From Palatka to Lake George, the amplitude again decreases and
becomes practically zero at the outlet of Lake George, 106 miles upstream from
the mouth of the river (Haight, 1938).

Occasionally, during severe droughts, high tide and northeasterly winds
combine to cause upstream flow at the outlet of Lake Monroe 161 miles
upstream from the mouth of the river. During the drought in 1945, a river stage
of 0.42 foot below mean sea level was recorded south of Lake Harney, 191 miles
upstream from the mouth of the river.

FACTORS AFFECTING THE RIVER FLOW AND QUALITY

The flow of the St. Johns River at Jacksonville is affected by the ocean
tide, wind, runoff from the land in the river basin, rainfall, and
evapotranspiration. The extent to which these factors can affect the flow is
controlled by the channel geometry and available storage capacity upstream
from Jacksonville. Therefore, the interaction of these factors cause wide
variations in the volume of flow at Jacksonville.

Normally, tides are the dominant flow-producing factor at Jacksonville,
but winds as strong as those associated with Hurricane Dora in September 1964
can completely offset or significantly accentuate the effect of tide. The factors
that affect the flow of the river also affect the chemical characteristics of the
water and cause it to range from relatively fresh water to a mixture of fresh and
marine water consisting of more than 60 percent sea water.

BUREAU OF GEOLOGY

ACKNOWLEDGMENTS

The authors express their appreciation to the following employees of the
city of Jacksonville: Tom Ard, Director, Air and Water Pollution Control,
Department of Health, Welfare and Bioenvironmental Services; E. T. Owens,
Engineer, and S. Hay, Assistant Engineer, City Engineering Department; who
provided valuable data and assisted in tests; and to Messrs. James English,
Director of Public Works and Robert B. Nord, Director, Water and Sewer
Department, whose valuable assistance enhanced the collection of basic data.
The contribution of E. T. Owens is especially appreciated, as it was he who
fostered the data-collection program from its inception.

PREVIOUS INVESTIGATIONS

The earliest investigation to yield data applicable to the present physical
conditions in the St. Johns River estuary was led by E. F. Hicks in the winter of
1933-34. The results of this investigation were reported by F. J. Haight in 1938.
Measurements of the stage, velocity, and discharge of the river at Jacksonville
were made by the U. S. Geological Survey on May 10, 1945. The U. S.
Geological Survey investigated the river August 16-24, 1945, to determine the
change in position from Main Street Bridge of a particle of river water during the
course of a tidal cycle. E. E. Pyatt investigated the distribution of pollutants in
the river in 1959.

DESCRIPTION OF THE SYSTEM

The source of the St. Johns River is a marsh near Fort Pierce, Florida, 312
miles from its mouth near Mayport. The river flows on a generally northward
course to Jacksonville and then eastward to the ocean. The topographic drainage
area of the St. Johns River is 9,430 square miles, nearly one-sixth of the land
area of Florida.

From the ocean to Jacksonville, the river ranges in width from about
1,250 feet at Main Street Bridge to more than 2 miles at Mill Cove, and in the
reach from Jacksonville to Palatka the width ranges from 1 to 3 miles. From just
south of Palatka to Lake George, the river narrows to generally less than half a
mile and in one place to only about 600 feet. Lake George, the largest expansion
in width (nearly 7 miles) along the entire river, is about 70 square miles in area
and normally shows no tidal fluctuation. South of Lake George, the river
channel is generally much narrower than to the north, although several large
lakes or widening of the river exist. The shore line of the river north of Palatka
is indented by many coves and enlarged mouths of tributaries.

INFORMATION CIRCULAR NO. 82

The Corps of Engineers, U. S. Army, maintains a navigation channel in the
river. The channel is 34 feet deep and 400 to 900 feet wide between the ocean
and Jacksonville, 13 feet deep and 200 feet wide between Jacksonville and
Palatka, 12 feet deep and 100 feet wide between Palatka and Sanford, and 5 feet
deep and 100 feet wide between Sanford and Lake Harney.

At low water, the flood plain of the St. Johns River contains openwater
areas totaling more than 300 square miles. Lake George, Crescent Lake, and the
river between Lake George and the ocean occupy about two-thirds of this area.

At the mouth of the St. Johns River the tidal range averages 4.9 feet. The
ocean tide generates a progressive tidal wave that moves up the river with
gradually diminishing amplitude until at Orange Park the range is only 0.7 foot.
From Orange Park southward; the amplitude of the wave increases until at
Palatka the range is 1.2 feet, the same as that at Main Street Bridge in
Jacksonville. From Palatka to Lake George, the amplitude again decreases and
becomes practically zero at the outlet of Lake George, 106 miles upstream from
the mouth of the river (Haight, 1938).

Occasionally, during severe droughts, high tide and northeasterly winds
combine to cause upstream flow at the outlet of Lake Monroe 161 miles
upstream from the mouth of the river. During the drought in 1945, a river stage
of 0.42 foot below mean sea level was recorded south of Lake Harney, 191 miles
upstream from the mouth of the river.

FACTORS AFFECTING THE RIVER FLOW AND QUALITY

The flow of the St. Johns River at Jacksonville is affected by the ocean
tide, wind, runoff from the land in the river basin, rainfall, and
evapotranspiration. The extent to which these factors can affect the flow is
controlled by the channel geometry and available storage capacity upstream
from Jacksonville. Therefore, the interaction of these factors cause wide
variations in the volume of flow at Jacksonville.

Normally, tides are the dominant flow-producing factor at Jacksonville,
but winds as strong as those associated with Hurricane Dora in September 1964
can completely offset or significantly accentuate the effect of tide. The factors
that affect the flow of the river also affect the chemical characteristics of the
water and cause it to range from relatively fresh water to a mixture of fresh and
marine water consisting of more than 60 percent sea water.

BUREAU OF GEOLOGY

TIDES

The gravitational interaction of the earth, moon, and sun cause a vertical
motion of the ocean surface, called tide, and a horizontal motion of the water,
called tidal current. The amount of vertical motion of the surface is called range
of tide, and the limits of the motion are called high water and low water..Tidal
heights are referenced by the NOS (National Ocean Survey) (formerly the U. S.
Coast and Geodetic Survey) to mean low water, which at Jacksonville is 0.6 foot
below mean sea level. In an estuary such as the lower St. Johns River, the
current flows both upstream and downstream. The current first increases in one
direction from zero velocity (called slack water) to a maximum velocity (called
strength of the current), then decreases to slack water. The process is then
repeated in the opposite direction.

In a progressive tidal wave the time of slack water comes, theoretically,
exactly midway between high and low tide. Also, maximum upstream current
velocity (flood strength) occurs, theoretically, at high water; and maximum
downstream current velocity (ebb strength) occurs, theoretically, at low water
(Haight, 1938). The range of tide and strength of current resulting solely from
gravitational tide-producing forces are closely but not precisely related. The
relation is not precise because forces involving the angular distances of the sun
and moon from the equator (declination) affect the range of tide about twice as
much as they affect the strength of current.

Yearly tables, which give the predicted times of occurrence and heights of
high and low tides, are published by the NOS. The NOS also publishes yearly
tidal current tables, which give the predicted times of occurrence of slack water,
flood strength, and ebb strength and the magnitudes of the flood and ebb
strengths. Tables from the tide at Mayport and the tidal current at St. Johns
Entrance are included in these publications. The tide tables and tidal current
tables published by the NOS for 1954-66 were used extensively in this analysis.

THE TIDAL CYCLE

A graphic representation of the rise and fall of the tide, in which time is
represented by the abscissas and the height of the tide by ordinates, is called a
tide curve. A graphic representation of a reversing type of current, in which time
is represented by the abscissas and the velocity by the ordinates, is called a
current curve. In general, these curves approximate a cosine curve (Schureman,
1963).

INFORMATION CIRCULAR NO. 82

The NOS designates flood velocity (upstream velocity) positive and ebb
velocity (downstream velocity) negative so that tide curves and current curves
will be in phase. However, designating the signs in this manner results in the
average net current -- and, therefore the average net discharge -- being negative.
In this report, upstream flow is considered negative, and downstream flow is
considered positive, and therefore, the current and discharge curves are
theoretically 1800 out of phase with the tide curve.

The current or velocity curve and the corresponding discharge curve for a
tidal cycle measured August 5, 1955, is shown by figure 6. The tide curve for
this tidal cycle is also shown on figure 6, with height of tide given as gage height
above a datum 9.99 feet below mean sea level rather than heights above MLW
(mean low water), which is the datum used for tide predictions by the NOS. The
datum of 9.99 feet below mean sea level is used to avoid negative water-level
readings. The tidal cycle measured August 5, 1955, was used to illustrate flow
and stage relations because the volumes of flow measured during this tidal cycle
more nearly approximate those of an average tidal cycle than any other cycle
measured from February 1954 to September 1966. Also, determinations of the
chloride concentration in the river at Main Street Bridge were made while this
tidal cycle was being measured.

The curves in figure 6 show that the actual time relationships of the tidal
cycle do not conform to the previously discussed theoretical time relationships
for a progressive tidal wave. Instead, the current curves, represented by the
point-velocity and discharge curves, lag the tide curve, represented by the
gage-height curve, by 20 to 60 minutes.during this particular cycle.

RELATION OF CHLORIDE CONCENTRATION TO THE TIDAL CYCLE

Curves of the cumulative volume of flow and the variation in the chloride
concentration near the bottom of the river at the Main Street Bridge during the
tidal cycle measured August 5, 1955, are also shown on figure 6. As shown, the
chloride concentration increased with increasing upstream flow volume and
reached a maximum when upstream flow stopped. The concentration
subsequently decreased as the water stored during upstream flow moved back
out during the downstream flow. When the volumes of downstream and
upstream flow were equal the chloride concentration was about the same as that
at the beginning of upstream flow. Subsequently, the concentration continued
to decline because the volume of the downstream flow exceeded that of the
upstream flow. Therefore, the curve of the chloride concentration for the
ensuing cycle began at a lower base concentration. Had the volume of the
downstream flow been less than that of the upstream flow, the ensuing cycle

BUREAU OF GEOLOGY

*r r m rt Ir^
I i

KI...
4rj t-d

] 7

..I I..........

1-."- 1 ".

I ^ / -

W i M -- ... ,x,

S i w -

Figure 6. Diagram of a tidal cycle in the St. Johns River at Jacksonville
showing variations of point velocity, discharge, gage height,
cumulative flow volume, and chloride concentration with time
and gage heights and times of mean tidal levels.
would have begun at a higher base chloride concentration. Changing of the base
chloride concentrations as a result of unequal volumes during consecutive tidal
flows is the cause of the wide variation in the chloride concentration in the river.

The chemical characteristics of the lower St. Johns River vary from that
of sea water near the ocean to that of the fresh-water input farther inland.
Fresh-water input consists of a mixture of rainfall directly into the river, direct
runoff from the land, and ground-water inflow. The reach of river in which sea
water and fresh water are mixed is called the zone of transition in this report.
This zone of transition shifts bodily toward the ocean and thus shortens with
each downstream flow. The opposite occurs with each upstream flow.

The length and gradient of the zone of transition varies with changes in
the general level of the ocean and fresh-water runoff as these factors affect the
individual tidal flows. The length of the zone of transition is reduced, and its
average gradient is increased by downstream movement of the terrestrial end of
the zone, which results from a series of cycles having predominantly excessive
downstream flow volumes. After a prolonged period of high fresh-water runoff,

l'-'' ).OW) t ~MKK CUWC tt,

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,

K_.H. .rO,_

4 44 -4i rah

L .....

INFORMATION CIRCULAR NO. 82

the zone of transition sometimes becomes so short that the entire zone remains
downstream from the Main Street Bridge. During such periods, the chloride
concentration at Main Street Bridge is nearly constant at the level of the
fresh-water runoff.

When the balance between the ocean level and runoff favors upstream
flow, the zone of transition lengthens in increments proportional to the excess in
volume of the upstream flows over the downstream flows. The terrestrial end of
the zone of transition does not migrate upstream as the result of a continuous
series of tidal cycles during which all the upstream flows are excessive. Instead, it
migrates upstream as the result of a series of cycles, some of which have
excessive downstream flows but most of which have excessive upstream flows.
Sometimes, especially during droughts, predominance of excessive upstream
flows causes the zone of transition to extend a considerable distance upstream
from Jacksonville.
After each incremental increase in the length of the zone of transition,
the river at Main Street Bridge is more saline, and the magnitude of the chloride
concentration depends on how far upstream the zone of transition extends.
Conceivably, the chloride concentration at Main Street Bridge could approach
that of sea water diluted only by local inflow if the entire zone of transition
moved upstream from the bridge, but this condition has not been observed.

NON-TIDAL FACTORS
Although tide exerts the greatest influence on the flow regime of the St.
Johns River at Jacksonville, the regime is continually affected by other factors,
which are non-tidal in origin. These factors, which include wind, runoff, channel
storage, rainfall, and evapotranspiration may interact in any number of
combinations to superimpose their combined effect on the tidal flow regime. It
is thus not possible to distinguish the proportionate effect of the individual
factors on a single tidal event. However, the net effect can be shown by
comparing characteristics of observed tidal events with those of the theoretical
event. Both the time of occurrence and the magnitude of flood and ebb
strengths caused by the gravitational tide-producing forces are theoretically fixed
and predictable. The predicted times and maximum velocities of the tidal
currents at St. Johns River Entrance and at Jacksonville near the Main Street
Bridge are published by the NOS. A constant relation exists between the times
that maximum velocity occurs at these two sites and also between the maximum
velocities attained.

The scatter of the points in figure 7A around the line of agreement
between predicted and observed data shows the net effect of non-tidal factors on
the time of occurrence of maximum velocity in the St. Johns River during 28
tidal cycles for which the actual times of ebb and flood strength were observed.
A small part of the departures from the line may be owing to difficulty in
determining the exact time of maximum velocity by observation.

fC
0

5U
L6

LL6
L6

0 5 10 15 20
PREDICTED TIME OF MAXIMUM VELOCITY, HOURS

2 I O
PREDICTED MAXIMUM VELOCITY, KNOTS

I 2 3
AT ST. JOHNS RIVER ENTRANCE

Figure 7A. Relation of the observed times of occurrence
of maximum velocities to the predicted
times of occurrence.

Figure 7B. Relation of the observed maximum dicharges at
Jacksonville to the predicted maximum current velo-
cities at St Johns River Entrance during 28 tidal
cycles observed in 1954, 1955, 1956, 1963 and
Cycles observed in 1954, 1955, 1956, 1963 and 1964.

INFORMATION CIRCULAR NO. 82

Comparisons of the maximum upstream and downstream discharges at
Main Street Bridge with the concurrent predicted maximum velocities at St.
Johns River Entrance during the 28 observed tidal cycles are shown on figure
7B. The peak discharges at Main Street Bridge may be compared directly with
the current strengths at St. Johns Entrance because the peak discharge is directly
proportional to the maximum velocity at Jacksonville (fig. 3), and the maximum
velocity at Jacksonville has a fixed relation to the maximum velocity at St.
Johns River Entrance. (See annual tidal current tables.) The linear curves,
representing unaltered tidal flow, pass through the average maximum upstream
and downstream discharges at Main Street Bridge and the average maximum
upstream and downstream velocities of St. Johns River Efitrance. The departures
from the curves represent the influence of non-tidal factors.

WIND
In general, winds from the northern quadrants increase the upstream flow
and decrease the downstream flow; whereas winds from the southern quadrants
have the opposite effect. The greatest effects from winds of comparable speed
are those caused by winds blowing from the northeast or southwest. Winds that
add energy to the system elsewhere can affect the flow at Jacksonville. As stated
earlier, occasionally wind effect is greater than the tidal effect.
FRESH-WATER INPUT
Fresh water enters the estuary as direct runoff, spring flow and
ground-water seepage, and direct rainfall; the total from these sources minus the
evapotranspiration from the estuary is the fresh-water input. When the input is
positive, that is when evapotranspiration is exceeded by the total of the other
elements of input, it tends to increase the duration and volume of downstream
flows and to decrease the duration and volume of upstream flows. However,
especially during droughts, evapotranspiration sometimes exceeds the total of
the other elements of input, and fresh-water input is negative. During such
periods, if insufficient water is stored in the estuary to keep its level higher than
the level of the ocean, ocean water will flow upstream. When this happens, the
duration and volume of the upstream flows tend to be greater than those of the
downstream flows and the zone of transition moves upstream relatively fast.

The effect of fresh-water inflow to the estuary on the volumes of both
the upstream and downstream flows is shown by figure 8. The average volume of
the downstream flows during the water years 1955 to 1966 was computed to be
2,076 mcf (million cubic feet) and that of upstream flows 1,806 mcf. Thus, the
computed average net (fresh-water) flow, was 270 mcf per tidal cycle in the
downstream direction. Had the net, or fresh-water flow, not been superimposed
on the tidal flow during this period, the average volume of a tidal flow would
have been the average of the computed upstream and downstream volumes or,
1,941 mcf. Thus, the average relation of the computed tidal flow volumes to the
computed net fresh-water volumes is as shown by the two linear curves in figure

BUREAU OF GEOLOGY

UPSTREAM I I
WATER YEARS 1955-66 ADJUSTED FOR e
0 ANNUAL AVERAGE TIDAL RANGE
O 100 200 300 400 500 600
YEARLY AVERAGE NET FLOW PER TIDAL CYCLE, MILLIONS OF CUBIC FEET
Figure & Relation of adjusted yearly average downstream and upstream
tidal flow.per cycle to yearly average net flow per tidal cycle.

The data for the individual water years would be expected to plot on
these curves if the average range of tide for the individual years were the same as
that for the 12-year period. However, the average ranges of tide determined from
the tide tables for Mayport were not the same for the individual years.
Therefore, the average tidal volumes for the individual years were adjusted to
allow for these differences. These adjustments were based on the linear curve of
relation shown on figure 9. This curve passes through the average range of tide
(4.57 feet) at Mayport and the average volume of tidal flow (1,941 mcf) at
Jacksonville. The curve is nearly parallel to the plot of average volume of flow
against range of tide shown by the solid circles on figure 9, especially in the

INFORMATION CIRCULAR NO. 82

3000

uI

u')
U.

0
z
0
.J

I-
0
w

0
w
!q
Qr.
LJ

0 I 2 3 4
PREDICTED RANGE OF TIDE, FEET

5 6 7

Figure 9. Relation of average volume of tidal flow at Jacksonville to range
of tide at Mayport.

range between the maximum and minimum yearly average predicted ranges of
tide from 1955 to 1966. Thus, the difference between values derived from the
linear curve of relation and those that would be derived from a curve based on
all the data for the 12-year period is considered negligible.

The plot of solid circles on figure 9 was obtained by matching each range
of tide on rising tide at Mayport with the volume of the ensuing upstream tidal
flow at Jacksonville and each range of tide on falling tide with the volume of the
ensuing downstream tidal flow at Jacksonville. Thus, each time the range of tide
was a specific value, the corresponding volume of tidal flow was listed under that
value. The volumes of tidal flow plotted on figure 9 are the averages of these lists
of volumes.

The linear relation through the average volume of tidal flow and the
average range of tide indicates a volume adjustment of 425 mcf per foot of
departure of the yearly average range of tide from the 12-year average range of
tide. Thus, if the average range of tide during a year were 0.1 foot less than the
12-year average, 42.5 mcf were added to the volumes of tidal flow for that year.

2,500

2,000

1,500

1,000

500

I I I I I I

* AVERAGE VOLUME OF THE TIDAL FLOWS THAT
OCCURRED IN 1960,1962 AND 1965 WHEN
PREDICTED RANGE OF TIDE WAS THAT INDICATED
*

MINIMUM YEARLY AVERAGE PREDICTED
RANGE OF TIDE (1955-66) *

-~
'
**0 MAXIMUM YEARLY
*9 AVERAGE PREDICTED
e / RANGE OF TIDE (1951
-**
0
0

LINEAR CURVE THROUGH AVERAGE VOLUME OF
TIDAL FLOW (1954-66) AND AVERAGE RANGE OF TIDE

I I I I I

W ....

5-66)

BUREAU OF GEOLOGY

The adjusted yearly average volumes of downstream tidal flow are plotted
against the corresponding average net flow per tidal cycle on the upper curve,
and those of the upstream tidal flows, on the lower curve, in figure 8. The
departures from the curves for the 12-year period are probably caused mostly by
errors in determining the volumes of tidal flow. The maximum departure is 5.7
percent and the average departure is 2.7 percent.

STORAGE
Water enters the reach of the St. Johns River estuary that lies between
Jacksonville and De Land as downstream flow at De Land, upstream flow at
Jacksonville, inflow from the intervening tributaries, ground-water inflow, and
rainfall directly onto the estuary. Water leaves this reach of the estuary as
upstream flow at De Land, downstream flow at Jacksonville, and
evapotranspiration from the estuary. These eight factors can interact in any
number of combinations to change the amount of water stored in the estuary. If
these factors interact to increase storage, the effect is to decrease the volumes
and durations of downstream flows and to increase the volumes and durations of
upstream flows at Jacksonville. If they interact to reduce storage, the effect is to
increase downstream flows and decrease upstream flows. Most of the time
storage in the estuary -- and, therefore, the flow at Jacksonville -- is affected
more by fresh-water inflow and outflow than by rainfall and evapotranspiration.
Figure 10 shows for the period of record, March 1, 1954 to September
30, 1966, the average monthly change in storage in the estuary and the
estimated average monthly difference in rainfall and evapotranspiration. The
average annual variation in sea level is also shown in figure 10 because it has a
pronounced effect on the flow at Jacksonville and, therefore the storage in the
estuary.
Storage changes in the reach of the estuary between De Land and
Jacksonville, which are shown by figure 10, were computed as follows:
1. The average discharge at Jacksonville was computed for the entire
period of record and for the individual months by subtracting the
computed upstream flow from the computed downstream flow.
2. Rainfall and evapotranspiration were assumed equal for the
12-year period, and change in storage over the period relative to
the total flow during the period was considered negligible, so that
total average inflow equals average discharge at Jacksonville.
3. The average gaged inflow to the estuary upstream from
Jacksonville during the 12-year period was computed for the
individual months, and the percentage of the total average gaged
inflow occurring in each month was determined.
4. The average discharge at Jacksonville was multiplied by the
percentage of gaged inflow determined for the individual months
to obtain the total average monthly inflow.
5. The average monthly discharges at Jacksonville were subtracted
algebraically from the total average monthly inflow to obtain the
average monthly change in storage.

INFORMATION CIRCULAR NO. 82

I-

-J
W

-J

(I,

CHANGE IN STORAGE IN ESTUARY
RAINFALL ON ESTUARY
EVAPTRANSPIRATION FROM ESTUARY

ID I I I I I
AVERAGE ANNUAL VARIATION
0.5--

I---z \MEAN SEA LEVEL
-0.5___( -I AFTER MARMER, 1951) I |
JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT OCT NOV DEC.

Figure 10. Graph showing the monthly average change in storage in the St.
Johns River estuary, the monthly average difference in the
estimated monthly rainfall on and evapotranspiration from the
estuary, and the average annual variation in sea level

Average monthly rainfall and evapotranspiration were estimated on the
basis of Weather Bureau record at various places in the St. Johns River basin.

The results of these procedures indicate that, on the average, storage
increases about 1,250 cfs in April and May, even though evapotranspiration
exceeds rainfall by about 700 cfs (fig. 10). This is because backwater from rising
sea level during these months holds back the outflow, so that the average inflow
exceeds the average outflow by about 1,950 cfs. Even in very dry years storage
increases during April and May, because, if fresh-water input is insufficient to
hold the estuary at a level at least as high as that of the ocean, sea water flows

.A

BUREAU OF GEOLOGY

upstream into the estuary, where it is stored until the level of the estuary
becomes higher than the level of the ocean.

The tendency for sea water to move upstream, when the amount of water
stored in the estuary is low in March and fresh-water inflow is small during the
subsequent period of rising sea level, is illustrated by the period March to
September 1956. Inflow to the estuary for this period was estimated to be 3,720
cfs. Fresh-water input accounted for 2,160 cfs of this inflow, and upstream flow
of sea water accounted for the other 1,560 cfs. Evaporation from the surface of
the estuary was estimated to have exceeded rainfall onto the surface during the
period by only 300 cfs. This indicates that the long periods of average net
upstream flow at Jacksonville result more from the coincidence of low storage in
the estuary at the start of the annual general rise in sea level than from an excess
in evaporation over rainfall. In fact, May 1962 was the only month during the
period March 1954 to September 1966 that the inflow of fresh water was
estimated to be less than the excess of evaporation over rainfall.

Figure 10 shows, further, that storage in the estuary on the average
continues to increase from June through September. Average input is greater
than average output during this period because of increasing backwater from
rising sea level during much of the period and because average rainfall exceeds
average evaporation throughout the period. On the average, fresh-water inflow in
July increases so rapidly that storage in the estuary increases despite a small
decline in sea level.

Figure 10 also shows that from October through March fresh-water input
shows a general decline in concert with the annual decline in sea level, which
results in the release of the water stored from April through September. On the
average, only about three quarters of the water that enters the estuary from
April through September is discharged at Jacksonville during that period. The
rest is stored and released from October through March.

Figure 11 compares average discharge at Jacksonville during each water
year with the proportional yearly average inflow to the estuary from 1954 to
1966. The departures of the individual years from the equal-flow line represent
the changes in storage in the estuary during the individual water years. The
average yearly discharge at Jacksonville was computed by subtracting the
upstream flow from the downstream flow for each year. The proportional yearly
average inflow was computed by totaling the yearly average discharges at the
gaging stations contributing to the estuary, computing the ratio of these totals to
the total of the 12-year average discharges at these stations, and multiplying the
12-year average discharge at Jacksonville by these ratios. This procedure
presupposes that rainfall on the estuary and evapotranspiration from the estuary

INFORMATION CIRCULAR NO. 82

12,000

z
0
L 10,000

W

8,000

6,000

4,000

2,000

0

6,000 8,000 10,000
TO ESTUARY, CUBIC FEET PER SECOND

Figure 11. Relation of yearly average discharge at Jacksonville to
proportional yearly average inflow to the estuary.

during the 12-year period were equal and that the change in storage over the
12-year period was insignificant.

The years that fall to the right of the equal flow line in figure 11 are those
during which storage in the estuary increased, and those that fall to the left are
those during which storage decreased. The amount of water in the estuary at the
onset of rising sea level in the years to the right was relatively small, and,
therefore, much capacity was available for added storage. In fact, the water level
in the estuary was so low in each of these years that the net flow at Jacksonville
was upstream for at least 1 month. In the years to the left, high water levels at

\ 1956
I 1962
I I
2,000 4,000
PROPORTIONAL AVERAGE INFLOW

12,000

BUREAU OF GEOLOGY

the onset of rising sea level coupled with exceptionally high rates of outflow
during the period of falling sea level resulted in decreases in storage comparable
to the increases during the years that fall to the right. Parts of the storage
changes resulted from the imbalance in the yearly rainfall and evapotranspiration
totals, but, as indicated earlier, these imbalances play a minor role in the storage
regime.

FLOW STATISTICS

Flow statistics for the St. Johns River at Jacksonville, based on the records
computed for the period March 1, 1954 to September 30, 1966 are given in
table 1. This period covers 4,597 days, during which 8,883 tidal cycles occurred.
Therefore, the average duration of a tidal cycle during the period was, 0.5175
day, or 12.42 hours.

Table 1. Selected flow statistics for the St. Johns River at Jacksonville.

Direction of Flow
Statistic Downstream Upstream

Average discharge, cfs 46,419 40,536

Average net discharge,cfs 5,883

Maximum daily net flow, cfs 87,000

Minimum daily net flow, cfs 51,500

Average volume per tidal 2,075.5 1,812.4
cycle, mcf

Average net volume per tidal 263.1
cycle, mcf

Maximum volume per tidal 5,280 4,410
cycle, mcf

Minimum volume per tidal 0 0
cycle, mcf

INFORMATION CIRCULAR NO. 82

2,000

Figure 12. Hydrographs showing monthly mean flow volumes (graph A),
monthly averages of the monthly mean flow volumes (graph B),
and monthly mean not flow volumes (graph D) at Jacksonville
and monthly mean predicted tidal range (graph C) at Mayport
from March 1954 to September 1966.
The monthly mean upstream and downstream volumes of flow per tidal
event for the period indicated are shown by graph A on figure 12. This graph is
the composite of the flow caused by both tidal and non-tidal factors. Graph B
on figure 12 shows the averages of the upstream and downstream volumes of
flow shown in graph A. These volumes represent the part of the composite flow
caused by the tide because non-tidal factors that tend to increase flow in one
direction also tend to decrease flow in the other direction, so that averaging the
flow in both directions cancels the non-tidal influences. As indicated previously,
the flow is approximately proportional to the range of tide, and over the period
of a month it is very nearly proportional, as the effects of lunar declination are
largely self cancelling. Therefore, the distribution of the values in graph B about
the mean value should be similar to the distribution of the monthly average
predicted ranges of tide about the mean of the predicted range of tide during the

BUREAU OF GEOLOGY

same period as shown by graph C on figure 12. However, a comparison of graphs
B and C shows that the distributions about the means are not similar. For
example, in October 1958, when the indicated flow caused by tide was the
smallest during the period of record, the mean predicted range of tide was 0.9
foot above the average value. Conversely, in January 1964, when the indicated
tidal flow was the greatest during the period of record, the mean predicted range
of tide was 0.6 foot below the average value. Some of this nonconformity may
be caused by errors in the computation of the flow values.

Graph D on figure 12 shows the monthly mean net flow per tidal cycle in
the St. Johns River at Jacksonville. The monthly mean net volume of flow per
tidal cycle for each month is the algebraic difference in the monthly mean
volume of downstream flows and the monthly mean volume of upstream flows,
shown by graph A, for the corresponding month. The mean net volume of flow
per tidal cycle for each month is equal to the average fresh-water inflow into the
estuary per tidal cycle, plus the average rainfall on the estuary per tidal cycle,
minus the average evapotranspiration from the estuary per tidal cycle, plus or
minus the average change in storage per tidal cycle during the month. If the sum
of fresh-water inflow and rainfall is greater than evapotranspiration plus or
minus the change in storage in a month, the average net flow per tidal cycle will
be downstream. If the sum of fresh-water inflow and rainfall is less than
evapotranspiration plus or minus the change in storage in a month, the average
net flow per tidal cycle will be upstream.

The 21 months during which the average net flow was upstream all
occurred during the dry season in exceptionally dry years except, possibly,
February 1966, which followed the very dry year 1965. During these months,
storage in the estuary was relatively small, and this condition coupled with high
losses by evapotranspiration permitted more water to flow upstream into the
estuary than flowed out. In 1962, the excess of upstream flow was so great that
enough sea water entered the estuary to cause the chloride concentration to
exceed 2,000 mg/1 (milligrams per liter) at Green Cover Springs, where the
chloride concentration is ordinarily less than 400 mg/l.

FLOW DISTRIBUTION AND FREQUENCY

The distribution of the volumes of tidal flows in the St. Johns River at
Main Street Bridge in Jacksonville is shown in figures 13 and 14. The
distribution of flow volumes during tidal flows in increments of 100 million
cubic feet is shown as percentages of the total number of tidal flows.

BUREAU OF GEOLOGY

the onset of rising sea level coupled with exceptionally high rates of outflow
during the period of falling sea level resulted in decreases in storage comparable
to the increases during the years that fall to the right. Parts of the storage
changes resulted from the imbalance in the yearly rainfall and evapotranspiration
totals, but, as indicated earlier, these imbalances play a minor role in the storage
regime.

FLOW STATISTICS

Flow statistics for the St. Johns River at Jacksonville, based on the records
computed for the period March 1, 1954 to September 30, 1966 are given in
table 1. This period covers 4,597 days, during which 8,883 tidal cycles occurred.
Therefore, the average duration of a tidal cycle during the period was, 0.5175
day, or 12.42 hours.

Table 1. Selected flow statistics for the St. Johns River at Jacksonville.

Direction of Flow
Statistic Downstream Upstream

Average discharge, cfs 46,419 40,536

Average net discharge,cfs 5,883

Maximum daily net flow, cfs 87,000

Minimum daily net flow, cfs 51,500

Average volume per tidal 2,075.5 1,812.4
cycle, mcf

Average net volume per tidal 263.1
cycle, mcf

Maximum volume per tidal 5,280 4,410
cycle, mcf

Minimum volume per tidal 0 0
cycle, mcf

INFORMATION CIRCULAR NO. 82

A cumulation of a flow-distribution curve of data for flow occurring
continuously in time is called a flow-duration curve. Tidal flow is not continuous
in one direction, and, therefore, the duration of flow in any one duration can be
described only in terms of percentage of the total number of tidal flows during
which the flow was in that direction. The volume of a tidal flow is a function of
both the duration of and the average discharge during the tidal flow. The
relation between these three parameters is not constant, and, therefore, the
volume of an individual tidal flow does not determine its duration. Therefore, in
this report, the cumulation of flow-distribution curves.

Cumulative flow-distribution curves that show the percentage of the total
number of tidal flows during which specific volumes were equaled or exceeded
during tidal flows are defined by the open circles on figures 13 and 14.
Cumulative flow-distribution curves that show the percentage of the total
number of days of record during which specific total daily volumes of
downstream or upstream flow were equaled or exceeded are defined by the solid
circles in figures 13 and 14. Values for equal percentages in figures 13 and 14
cannot be subtracted to obtain the net flow for that percentage because it is
necessary to take the algebraic sum of consecutive downstream and upstream
flows to obtain the net flow for a tidal cycle. Figure 15 is a cumulative
flow-distribution curve of the daily net flow in the St. Johns River at Main
Street Bridge. The curve was computed using the algebraic sum of the daily
downstream and upstream volumes of flow. The volumes of downstream and
upstream flows are increasingly large in comparison with the net flow volume as
the net flow volume approaches zero, and, therefore, the computed net flow
volume is subject to increasingly greater percentage error as the net flow volume
approaches zero. However, the smooth transition of the cumulative flow
distribution curve from positive to negative net flow indicates that, although
values for individual days may be grossly erroneous, the errors may be mutually
compensating, and the curve may be approximately correct.

The average recurrence intervals in months and years of specific monthly
and yearly extremes in volumes of tidal flow are shown by figures 16 through
21. The curves are based on data obtained between March 1954 and September
1966. The following discussions of the figures presuppose that conditions during
the period of record are representative of long-term conditions.

Figure 16 shows the average recurrence intervals in months and years of
downstream tidal flow volumes that occur as monthly and yearly maximums.
For example, the average recurrence interval of monthly maximum downstream
tidal flows of 4,000 mcf or more is 60 months. Likewise, the average recurrence
interval of yearly maximum downstream tidal flows of 4,000 mcf or more is 6.7
years.

BUREAU OF GEOLOGY

same period as shown by graph C on figure 12. However, a comparison of graphs
B and C shows that the distributions about the means are not similar. For
example, in October 1958, when the indicated flow caused by tide was the
smallest during the period of record, the mean predicted range of tide was 0.9
foot above the average value. Conversely, in January 1964, when the indicated
tidal flow was the greatest during the period of record, the mean predicted range
of tide was 0.6 foot below the average value. Some of this nonconformity may
be caused by errors in the computation of the flow values.

Graph D on figure 12 shows the monthly mean net flow per tidal cycle in
the St. Johns River at Jacksonville. The monthly mean net volume of flow per
tidal cycle for each month is the algebraic difference in the monthly mean
volume of downstream flows and the monthly mean volume of upstream flows,
shown by graph A, for the corresponding month. The mean net volume of flow
per tidal cycle for each month is equal to the average fresh-water inflow into the
estuary per tidal cycle, plus the average rainfall on the estuary per tidal cycle,
minus the average evapotranspiration from the estuary per tidal cycle, plus or
minus the average change in storage per tidal cycle during the month. If the sum
of fresh-water inflow and rainfall is greater than evapotranspiration plus or
minus the change in storage in a month, the average net flow per tidal cycle will
be downstream. If the sum of fresh-water inflow and rainfall is less than
evapotranspiration plus or minus the change in storage in a month, the average
net flow per tidal cycle will be upstream.

The 21 months during which the average net flow was upstream all
occurred during the dry season in exceptionally dry years except, possibly,
February 1966, which followed the very dry year 1965. During these months,
storage in the estuary was relatively small, and this condition coupled with high
losses by evapotranspiration permitted more water to flow upstream into the
estuary than flowed out. In 1962, the excess of upstream flow was so great that
enough sea water entered the estuary to cause the chloride concentration to
exceed 2,000 mg/1 (milligrams per liter) at Green Cover Springs, where the
chloride concentration is ordinarily less than 400 mg/l.

FLOW DISTRIBUTION AND FREQUENCY

The distribution of the volumes of tidal flows in the St. Johns River at
Main Street Bridge in Jacksonville is shown in figures 13 and 14. The
distribution of flow volumes during tidal flows in increments of 100 million
cubic feet is shown as percentages of the total number of tidal flows.

BUREAU OF GEOLOGY

0 I PERIOD OF RECORD: FEBRUARY 1954 TO SEPTEMBER 1966
COt 00501 02 OS 1 2 5 10 20 30 40 50 60 70 80 90 95 98 99 995 998999 9999
PERCENTAGE OF DAYS OR TIDAL CYCLES THAT INDICATED VOLUME OF DOWSTREAM FLOW WAS EQUALED OR EXCEEDED
AND PERCENTAGE OF TIDAL CYCLES THAT VOLUME OF DOWNSTREAM FLOW FELL WITHIN INCREMENT INDICATED
Figure 13. Flow distribution and cumulative flow-distribution curves for
downstream flow at Main Street Bridge.

Figure 17 shows the same information for upstream flows that figure 16
shows for downstream flows. For example, the average recurrence interval of
monthly maximum upstream tidal flows of 3,400 mcf or more is 60 months.
The average recurrence interval of yearly maximum upstream tidal flows of
3,400 mcf or more is 4.2 years.

Figure 18 shows the average recurrence intervals in months and years of
downstream tidal flow volumes that occur as monthly and yearly minimums.
For example, the average recurrence interval of monthly minimum downstream
tidal flows of 1,000 mcf or less is 5 months, and the average recurrence interval
of yearly minimum downstream tidal flows of 1,000 mcf or less is 1.18 years.

Figure 19 shows the same information for upstream flows that figure 18
shows for downstream flows. For example, the average recurrence interval of
monthly minimum upstream tidal flows of zero flow is about 86 months, and
the average recurrence interval of yearly minimum upstream tidal flows of zero
flow is 7.2 years.

INFORMATION CIRCULAR NO. 82

8,000

7,000

6,000

- MAXIMUM DAY

*1

UUU --

4,00- -

3,000

0
-1,000

2,000

-3,000

-4,000
,oooMINIMUM
-i,000 ---- ---- ---- --..-...- --- -- -----------

-35,000

PERIOD OF RECORD: FEBRUARY 1954 TO SEPTEMBER 1966

-6,000

-7000

" 0 10

30 40 50 60 70 80 90 100

PERCENTAGE OF DAYS NET DOWNSTREAM FLOW EQUALED OR EXCEEDED THAT SHOWN

Figure 14. Flow distribution and cumulative flow-distribution curves for
upstream flow at Main Street Bridge.

U VULUML ur UPIh SKAM FLOW PER DAY
50oo o O VOLUME OF UPSTREAM FLOW PER TIDAL CYCLE
I INCREMENT OF VOLUME OF UPSTREAM FLOW
m PER TIDAL CYCLE

0

z Ioo
0 0-- ___

1. 1 1
o IIO- f r 1 -' '; g -- -
> PERIOD OF RECORD: FEBRUARY 1954 TO SEPTEMBER 1966
0 I I I 1 1 1 1 1 1 1 I >N
0.01 0.050.1 Q2 0.5 2 5 10 20 30 40 50 60 70 80 90 95 98 99 995 991999 9199
PERCENTAGE OF DAYS OR TIDAL CYCLES THAT INDICATED VOLUME OF UPSTREAM FLOW WAS EQUALED OR EXCEEDED
AND PERCENTAGE OF TIDAL CYCLES THAT VOLUME OF UPSTEAM FLOW FELL WITHIN INCREMENT INDICATED

Figure 15. Cumulative flow-distribution curve of daily net flow of the St.
Johns River at Main Street Bridge.

I-
IJ
w
u
2 5,000

0 1
u. -
U
0

W
CO
0

S42,00 -

1.01
-J

3 4 5 7 10 20 2
RECURRENCE INTERVAL, IN YEARS AND MONTHS

50 40 50 70 100

Figure 16. Frequency of monthly and annual maximum downstream flows
in the St. Johns River at Main Street Bridge.

6,000

1.1 1.2 1.3 1.5 1.7 2

200

1.1 1.2 1.3 1.5 1.7 2 3 4 5 7 10 20 30 40 50 70 100
RECURRENCE INTERVAL, IN YEARS AND MONTHS

5,000

I-
w
=1
UJ.

,3
U
u.
0

0

z

0

3
o
U.
0

0J

4,000

3,000

2,000 -
1.01

I

I~ LI- ~P~YCIP~V.O aqprlLv npY4p~_ ~YSCI~H~ L~lrrplp, ~,,r ,

2,0 00 I I I I I I I I I 1 II I I

LJ.
,I PERIOD: 1954-66
2 0

o 1_000 MONTHS

o z

RECURRENCE INTERVAL I YEARS AND MONTHS
.J
0
o

-I-
I I I I I I I I I I I I
1.01 1.1 1.2 1.3 1.5 1.72 3. 4 5 7 10 20 30 40 50 70 100 200
RECURRENCE INTERVAL, IN YEARS AND MONTHS

Figure 18. Frequency of monthly and annual minimum downstream flows
in the St. Johns River at Main Street Bridge.

^ 2,000

U.
U

U.
u

-I
m 1,000

0
-J

O" YEARS

I1.

o
-J

1.01 I.I 1.2 1.3 1.5 1.7 2

3 4 5 7 10 20 30 40 50 70 100
RECURRENCE INTERVAL, IN YEARS AND MONTHS

Figure 19. Frequency of monthly and annual minimum upstream flows in
the St. Johns River at Main Street Bridge.

200

200

1.3 1.5 1.7 2 3 4 5 7 10 20 30 40 50 70 100
RECURRENCE INTERVAL, IN YEARS AND MONTHS

Figure 20. Frequency of monthly and annual maximum daily net flow in
the St. Johns River at Main Street Bridge.

9,000

8,000

7,000

6,o00

5,000

4,000

3,000

2,000

1,000

BUREAU OF GEOLOGY

Figure 20 shows the average recurrence intervals in months and years of
daily net flows that occur as monthly and yearly maximums. For example, the
average recurrence interval of monthly maximum net flows of 5,000 mcf or
more is 120 months, and the average recurrence interval of yearly maximum net
flows of 5,000 mcf or more is 10.3 years.

Figure 21 shows the average recurrence intervals in months and years of
daily net flows that occur as monthly and yearly minimums. For example, the
average recurrence interval of monthly minimum net flows of minus 3,000 mcf
or less is about 74 months, and the average recurrence interval of yearly
minimum net flows of minus 3,000 mcf or less is 6.3 years.

The extremes caused by Hurricane Dora do not fit these relations except,
possibly, the minimum upstream flow. This is probably because the conditions
that caused the extremes are unlikely to occur frequently. The minimum
upstream flow, however, is more likely to occur than the other extremes because
the conditions required to cause small upstream flows occur much more
frequently than the conditions required to cause the other extremes. In fact, the
volumes of four upstream flows during the period of record were less than 100
million cubic feet.

MAXIMUM PERIODS OF FLOW DEFICIENCY

Figure 22 shows the maximum number of consecutive days that the daily
net flow was less than specified amounts between October 1954 and September
1966. However, the figure does not indicate how much less than a specific
amount the daily net flow was for any specific number of days. The number of
consecutive days that the flow remains below a specific volume has no relation
to the total amount of net flow during those days. For example, even though the
net flow was upstream in excess of 518 million cubic feet per day for 7
consecutive days in both 1963 and 1966, during the 1963 period the average net
flow was only 8,660 cfs upstream, whereas during the 1966 period the average
net flow was 22,720 cfs upstream.

Between March 3 and October 15, 1956, the cumulative net upstream flow
was 34 billion cubic feet, an average of 150 million cubic feet per day. Between
January 26 and August 14, 1962, the cumulative net upstream flow was 39
billion cubic feet, an average of about 200 million cubic feet per day. Most of
this flow was sea water moving in to replace water lost by evaporation or to
provide the normal increase in channel storage that results from the annual rise
in sea level from March to October. In wet years this water is provided by
fresh-water inflow.

1,000 I I I I I I I I I I I I

PERIOD: 1954-66
LI-
w
w
u 0

" -2,000 *-<- "-' -MONTHS
3,000

-j0

I -2,000

-,000 I 1 II I [ I II I HURRICANE DORA '' I I I- .
1.01 .I 1.2 1.3 1,5 1.7 3 4 5 7 I0 20 30 40 50 70 100 200 9
RECURRENCE INTERVAL, IN YEARS AND MONTHS
SYEARS00
00

t')

Figure 21. Frequency of monthly and annual minimum daily net flow in
the St. Johns River at Main Street Bridge.

3,000

'z
0

-I,00 0 -

S2,000 I I I I I I I
I-20

I 2 3 5 7 10 20 30 50 70 100 200 300 500 1,000
MAXIMUM NUMBER OF CONSECUTIVE DAYS IN WHICH THE DAILY NET FLOW WAS LESS THAN THAT INDICATED

Figure 22. Maximum periods of deficient daily net flow in the St. Johns
River at Jacksonville.

BUREAU OF GEOLOGY

Figure 20 shows the average recurrence intervals in months and years of
daily net flows that occur as monthly and yearly maximums. For example, the
average recurrence interval of monthly maximum net flows of 5,000 mcf or
more is 120 months, and the average recurrence interval of yearly maximum net
flows of 5,000 mcf or more is 10.3 years.

Figure 21 shows the average recurrence intervals in months and years of
daily net flows that occur as monthly and yearly minimums. For example, the
average recurrence interval of monthly minimum net flows of minus 3,000 mcf
or less is about 74 months, and the average recurrence interval of yearly
minimum net flows of minus 3,000 mcf or less is 6.3 years.

The extremes caused by Hurricane Dora do not fit these relations except,
possibly, the minimum upstream flow. This is probably because the conditions
that caused the extremes are unlikely to occur frequently. The minimum
upstream flow, however, is more likely to occur than the other extremes because
the conditions required to cause small upstream flows occur much more
frequently than the conditions required to cause the other extremes. In fact, the
volumes of four upstream flows during the period of record were less than 100
million cubic feet.

MAXIMUM PERIODS OF FLOW DEFICIENCY

Figure 22 shows the maximum number of consecutive days that the daily
net flow was less than specified amounts between October 1954 and September
1966. However, the figure does not indicate how much less than a specific
amount the daily net flow was for any specific number of days. The number of
consecutive days that the flow remains below a specific volume has no relation
to the total amount of net flow during those days. For example, even though the
net flow was upstream in excess of 518 million cubic feet per day for 7
consecutive days in both 1963 and 1966, during the 1963 period the average net
flow was only 8,660 cfs upstream, whereas during the 1966 period the average
net flow was 22,720 cfs upstream.

Between March 3 and October 15, 1956, the cumulative net upstream flow
was 34 billion cubic feet, an average of 150 million cubic feet per day. Between
January 26 and August 14, 1962, the cumulative net upstream flow was 39
billion cubic feet, an average of about 200 million cubic feet per day. Most of
this flow was sea water moving in to replace water lost by evaporation or to
provide the normal increase in channel storage that results from the annual rise
in sea level from March to October. In wet years this water is provided by
fresh-water inflow.

INFORMATION CIRCULAR NO. 82

CHEMICAL CHARACTERISTICS

Variation in the flow of the St. Johns River at Jacksonville is accompanied
by variations in the chemical characteristics of the water in the river. Ocean
water advances up the lower St. Johns River during each upstream flow and
recedes from the river during each downstream flow. While it is in the river,
some of the ocean water mixes with fresh water within a zone in which a
transition from water having the chemical characteristics of ocean water at its
downstream end to water having the chemical characteristics of the fresh water
at its upstream end takes place. This zone of transition was discussed in the
section of this report on the relation of chloride concentration in the river to the
tidal cycle.

Reliable estimates of the concentration of dissolved chemical constituents
in the St. Johns River can be made quickly and conveniently by use of the
curves of relation shown in figure 23 between the concentration of the chemical
constituents and the specific conductance of the water in the river (specific
conductance is a measure of the ability of water to conduct electricity, and it is
reported in micromhos per centimeter at 25 C).

Chemical analyses of samples of water from the St. Johns River at Main
Street Bridge, obtained from April 1966 through May 1967, are given in table 2.
The curves shown in figure 23 are based primarily on the data given in table 2.

VARIATIONS IN CHEMICAL CHARACTERISTICS
AT MAIN STREET BRIDGE
The relation of specific conductance to the concentration of chemical
constituents was used in evaluating the variations in chemical characteristics of
the St. Johns River at Main Street Bridge.

In 1966, an instrument was installed at Main Street Bridge to obtain a
continuous record of the specific conductance of the river. The daily maximum
specific conductance near the surface of the river recorded by this instrument
from October 1, 1966, to April 21, 1967, is shown in figure 24. The extreme
variability in chemical quality is indicated by the changes in specific
conductance from November 19-28, 1966. The specific conductance increased
from about 8,000 micromhos on the 19th to more than 30,000 micromhos on
the 23rd and then decreased to about 8,000 micromhos by the 28th. Changes in
specific conductance of as much as 12,000 micromhos during a single tidal cycle
are common. (See fig. 15).

BUREAU OF GEOLOGY

10 100 1,000 10,000
CONCENTRATION OF CHEMICAL CONSTITUENT, MILLIGRAMS PER LITER
Figure 23. Relation of specific conductance to concentration of major
chemical constituents in the St. Johns River at Main Street
Bridge.

32I I I I I I I
.r- ----------

Ti-
r II

t: -
2 1

2 0 I I

t- "

Fige 24. Daily maximum specific conductance near the surface of the St.
Johns River at Main Street Bridge, October 1966 to April 1967.

Table 2. Chemical analyses of the St. Johns River at Jacksonville, Florida (samples collected at Main Street Bridge).

milligrams per liter

Dissolved Hardness
-" solids as CaCO3 0

Dateof S S 0 u

1966
bApr.26 0.7 0.01 41 26 201 7.3 66 88 359 0.3 0.1 0.00 765 820 210 156 1470 7.3 70
tOct. 5 4.7 .05 1.04 274 2320 84 80 571 4090 .5 2.1 .16 7490 7830 1390 1320 1300 7.0 100 1.8
b Oct. 5 2.4 .00 138 377 3240 119 84 750 5690 .6 3.3 .20 10400 10500 1900 1830 17500 7.1 80 2.4
tOct. 10 3.6 .05 29 14 95 3.6 64 42 176 .3 .1 .15 396 459 130 78 790 7.0 100 .54
bOct. 10 3.9 .05 28 14 96 3.6 60 43 174 .3 .2 .26 394 462 128 79 790 6.8 100 .54

tNov. 3 4.6 .04 27 10 71 2.6 40 34 136 .3 .2 .11 306 360 109 76 618 6.9 120 .55
bNov. 3 2.6 .13 27 10 72 2.6 78 28 128 .3 .3 .10 310 363 109 45 770 6.8 110 .52
tNov. 16 5.2 .08 211 608 5340 196 85 1240 9470 .9 1.5 .26 17100 18200 3030 2960 28000 7.0 40' .3.5
b Nov. 16 2.5 .05 225 633 5520 200 109 1320 9720 .9 11 .24 17700 18700 3170 3080 30000 7.1 60 3.7
t Nov. 21 4.6 .11 104 263 2310 82 84 563 4090 .6 1.2 .30 7460 7560 1340 1270 12500 7.1 120 1.8

bNov.21 3.4 .10 131 351 3110 122 112 756 5540 .6 6.3 .22 10100 10600 1770 1680 18000 7.0 100 2.4
tDec. 22 3.4 .12 72 141 1180 46 78 304 2100 .3 1.1 .18 3890 4150 760 696 6700 7.1 100 1.2

1967
t May 10 3.6 .05 215 448 3690 143 95 933 6800 .7 5.7 .32 12300 2380 2310 20800 6.9 45 4.8

(t) top sample
(b) bottom sample

BUREAU OF GEOLOGY

Figure 25. Cumulative discharge and specific conductance at the end of
each tidal flow beginning December 12,1966 and ending January
31, 1967.
The specific conductance at the end of each tidal flow and the cumulative
discharge at Main Street Bridge is shown by figure 25 for the period December
12, 1966, to January 31, 1967. The scale on the cumulative discharge graph is
inverted so that the graphs may be more easily compared. The graphs show that
as long as the zone of transition extends upstream from Main Street Bridge the
specific conductance of the river at Main Street Bridge decreases with increasing
discharge accumulation and increases with decreasing discharge accumulation.
Discharge accumulation increases with downstream flow and decreases with
upstream flow.

The amount of change in the specific conductance of the river is not
always the same for a specific change in cumulative discharge because the rate of
change in specific conductance is dependent on the gradient of the zone of

INFORMATION CIRCULAR NO. 82

transition. If the zone of transition is entirely downstream from the Main Street
Bridge when cumulative downstream flow begins, little or no change in specific
conductance occurs at Main Street Bridge as a result of tidal action. The specific
conductance would be that of the fresh-water input. Conversely, if enough
cumulative upstream flow were to occur, the specific conductance of the river at
Main Street Bridge could approximate that of sea water; however, this condition
has not been observed. The specific conductance near the surface of the river
also tends to increase during periods of non-accumulating flow because of
mixing in of water with higher conductance from greater depth. It follows that
the specific conductance at greater depth decreases during such periods.
However, this hypothesis has not been verified.

From October 1954 to September 1966, the Jacksonville Department of
Public Health obtained water-quality data at the Main Street Bridge at about
2-month intervals in each year except 1956. These data were collected
throughout a total of 63 complete tidal cycles. The chloride concentration was
determined by chemical analysis of samples collected hourly during each of the
tidal cycles. Concentrations of sulfate, sodium, hardness and dissolved solids
during these cycles were calculated from their relation to the chloride
concentration using figure 23. Duration curves of these chemical constituents in
the river during the 63 tidal cycles sampled are shown in figure 26. Although in a
strict sense the data apply only to the cycles sampled, they are considered fairly
representative of the long-term duration because the sampling was done at
uniform intervals. However, had continuous data been available for the period,
the durations, especially the extremes, probably would differ some from those
shown in figure 26. The curves show the percentage of time that the
concentration of any of the major constituents is equal to or more than any
specified amount. For example, the curve for duration of chloride concentration
shows that the chloride concentration equals or exceeds 250 mg/l 82 percent of
the time.

VARIATIONS IN CHLORIDE CONCENTRATION IN
THE LOWER ST. JOHNS RIVER

Chloride concentrations in the lower St. Johns River were investigated by
measuring the specific conductance of the water in mid-channel at selected
points on May 18, October 18, and December 12, 1966. Figure 27 shows the
results of these measurements for the reach of the river from 12 to 31 miles
upstream from its mouth. The measurements were made near both the bottom
and surface of the river at each of the points indicated. On May 18 and October
18, 1966, measurements were made at slack water before both downstream and
upstream flow, but. on December 12, 1966, measurements were made at slack
water before the downstream flow only. The average daily net flow was 3,120

BUREAU OF GEOLOGY

'CU4IUU --- -- -- -- --- -- ----- --- -- -1- --- --- ----- -- --i ----

Oissolaed
Solids

Oicco Chi ond. --

Sodium
I ,II ] _

Total
-- T- -^ -----

CI
t0

0 0.0901 02 0. I 2 5 to 20 30 40 50 60 70 80 90 95 98 99 995 998 999 9999
PERCENTAGE OF TIME INDICATED CONCENTRATION WAS EO'!ALED OR EXCEEDED

Figure 26. Duration curves of major chemical constituents in the St. Johns
River at Jacksonvile.
; .-. ..C^^^ ^^
x \ A
L --o,^' \

*" ---- \ \ \ ^ ^ -

~ ~ ~ ~ _\ \ ^

EiEEEEES^EE
g ,,, \

,0 ----- ----------- __ ---------------- __ ----\-- ___
OC 030 Q a Z 5 0 0 040506070 8 9 9 9 9 959999 9\
PECETAEOFTIE NICTE ONENRAIN ASE'- ,,,,REXEEE

INFORMATION CIRCULAR NO. 82

OCTOBER 18,1966 4 MAY 18, 1966
AVERAGE NET FLOW \". \ AVERAGE NET FLOW 3,120 CUBIC
4 9,370 CUBIC FEET PER FEET PER SECOND UPSTREAM
f .SECOND DOWNSTREAM "" _

o -- ~-e -- ... .I
12 14 16 18 20 22 24 26 28 30 32
DISTANCE UPSTREAM FROM MOUTH OF ST. JOHNS RIVER, STATUTE MILES
Figure 27. Longitudinal and vertical variation in specific conductance of the
water in the lower St. Johns River from river mile 12 to river
mile 31 at slack water on selected days.

cfs upstream on May 18, 9,370 cfs downstream on October 18, and 5,320 cfs
upstream on December 12. Although the general level of the specific
conductance and chloride concentration do not depend wholly on the net flow
of the river for any single day but rather on the cumulative flow over many days,
the specific conductance was higher on May 18 and December 12, when the net
flow was upstream, than it was on October 18, when the net flow was
downstream. Further, both the specific conductance and the rate of increase in
specific conductance with river mileage were higher on December 12, when the
average net flow was 5,320 cfs upstream, than on May 18, when the average net
flow was only 3,120 cfs upstream. Also, at slack water before downstream flow
on October 18, the specific conductance near the surface was lower at river miles
12.2 and 15 than at some points farther upstream. This was pro caused by
high fresh-water inflow to the St. Johns River from Trout River and other
nearby tributaries, as indicated by high discharges recorded on nearby Ortega
River. At slack water before upstream flow on October 18, virtually fresh water
was observed as far downstream as the mouth of Trout River.

BUREAU OF GEOLOGY

A vertical gradient in chloride concentration tends to exist in estuaries
such as the St. Johns River because the lighter fresh water tends to override the
denser sea water. In a straight and uniform river channel, sea water enters and
recedes from the channel as a wedge of salt water between the river bottom and
the overlying fresh water and mixing is caused primarily by turbulence at the
salt-water-fresh-water interface. However, the channel of the St. Johns River is
neither straight nor uniform. Instead, it bends and varies in both width and
depth, so that a well defined interface between salt water and fresh water does
not exist in the river in the Jacksonville area. Thus, the river either has no
vertical gradient in chloride concentration or has a uniform increase in chloride
concentration with depth.

The change with time in specific conductance, which is indicative of the
chloride concentrations near the surface and the bottom of the river, is shown in
figure 28 for four of the points measured May 18, 1966. The amount of vertical
variation in specific conductance is indicated by the shaded areas. The data show
that vertical variation in specific conductance increases with distance
downstream from the river constriction and bridge piers near Main Street Bridge
(river mile 21) but changes little with distance upstream from the constriction.
This indicates that the vertical variation in chloride concentration, which tends
to decrease gradually between the ocean and Main Street Bridge during upstream
flows, is almost eliminated by the turbulence and eddies created by the
constriction and bridge piers. At the beginning of the measurement period
(figure 28), flow was upstream, and the major change in the vertical variation in
chloride concentration took place between Commodore Point and Acosta
Bridge, showing the great effect of the constriction and piers on the vertical
variation in chloride concentration. Near the end of the measurement period,
however, the major change in the vertical variation in chloride concentration
took place between Commodore Point and Dredge Depot. By this time, the flow
had been downstream for more than 6 hours and then upstream for about 2
hours, and the shift in the reach of major change in variation represents the
displacement of the zone of transition by the downstream flow. The greater
vertical variation in chloride concentration at Dredge Depot at the end of the
measurement period than at the beginning is probably related to the tendency
for sea water to flow upstream beneath the fresh water late in the downstream
part of the tidal cycle. This results in greater vertical variation in chloride
concentration in the early stages than in later stages of the upstream part of the
cycle.

Data from the survey shown in figure 27 and from pollution surveys by
the Jacksonville Department of Public Health indicate that there is no fixed
relation between chloride concentrations at different sampling points along the
river. However, a fair relation was indicated between the maximum chloride

INFORMATION CIRCULAR NO. 82

cn 16 1 1 1 -1 I 1 1 I -- I
0 I. CORPS OF ENGINEERS DREDGE
DEPOT, MILE 170
S2. COMMODODORE POINT, MILE 2u.0
j _- BOTTOM--,--' 3. ACOSTA BRIDGE, MILE 22.4
u0o 1- POINT LA VISTA, MILE 26.5

Z W TOP
U) V
OHU
- i2.
Figure -- V with time in t -.-
w -
Jcsn

11 BOTTOM,
Z I
z 4- TOP 0
.0: 4. Ino IL

Ll _
w MAY 18, 1966
0a.
v) I I I i I I I I I I
0800 0900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900
HOURS
Figure 28. Variations with time in the specific conductance of the St. Johns
River near the surface and bottom at selected points in the
Jacksonville area.
concentrations at different sampling points at slack before the downstream flow
of common tidal cycles. Figure 29 shows the relation between the maximum
chloride concentration at the Main Street Bridge and those upstream at Orange
Park and downstream at Drummond Point for the same tidal cycle. The figure
shows that, with increasing chloride concentration at Main Street Bridge, the
chloride concentration at Orange Park at first increases less rapidly but later on
increases more rapidly than at Main Street Bridge. The opposite relation prevails
between the chloride concentrations at Drummond Point and Main Street
Bridge.

The maximum chloride concentration observed at the Main Street Bridge
from October 1954 to October 1966 was 12,700 mg/1 on February 12, 1962.
Extrapolation of the relation in figure 29 indicates that the maximum chloride
concentrations at Orange Park and Drummond Point on February 12, 1962, may
have been about 10,000 and 17,000 mg/1, respectively.

The longitudinal variation in the chloride concentration at slack water
before the downstream flows of common tidal cycles in the St. Johns River
'between its mouth and Palatka, which would be exceeded as the daily maximum
less than 7 percent of the days, is shown in figure 30. The longitudinal variation

BUREAU OF GEOLOGY

4 5 6 7 8 9 10 II 12 13 14
MAXIMUM CHLORIDE CONCENTRATION AT ORANGE PARK AND
DRUMMOND POINT, THOUSANDS OF MILLIGRAMS PER LITER

Figure 29. Relation of maximum chloride concentration at Main Street
Bridge to maximum chloride concentration at Orange Park and
Drummond Point at slack before the downstream flow of
common tidal cycles.
in chloride concentration which would be exceeded as the daily maximum 50
percent of the days is similarly shown for the reach between Drummond Point
and Orange Park. The chloride concentrations for all points shown in the figure
other than at Main Street Bridge were derived from relations like those shown in
Figure 29.

SEASONAL VARIATION IN FLOW AND CHLORIDE CONCENTRATION

The average monthly mean tidal flow at Jacksonville during the period of
record from March, 1954, to September, 1966, should be about the same for
every month. Thus, there should be no seasonal variation in the tide induced
flow. This is because the tidal flow is approximately proportional to the range of
tide (Haight, 1938) and the monthly mean ranges of tide as determined from the
tide tables for the period of record were almost the same for every month. The
difference between the highest and lowest monthly mean range of tide was
0.027 foot. The record shows a difference of 235 mcf between the highest and
lowest monthly mean tidal flow which ranged from 7.4 less than to 4.7 percent
more than the mean tidal flow.

1212- I ...

CONDITION A

20 -

CHLORIDE CONCENTRATION WHICH WOULD
BE EXCEEDED LESS THAN 7 PERCENT OF
THE DAYS AS THE DAILY MAXIMUM

z
0o
\ 0
u w
LL 0

0
0
w
\

0aX
S!5 16
I -S

-UZ
--d
P UJ

4i
z 2a

-J 12

So

g 4
2z

0j6
r-

4

2

CONDITION B CHLORIDE CONCENTRATION WHICH WOULD
BE EXCEEDED 50 PERCENT OF THE DAYS
AS THE DAILY MAXIMUM

0: Z0
-z
a.

z w
I. ,

w
BN-

DTINBCONDITION A .
EDITION B
;"Q-i

0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76
APPROXIMATE DISTANCE UPSTREAM FROM ST JOHNS RIVER ENTRANCE, STATUTE MILES

Figure 30. Approximate longitudinal variation in the daily maximum
chloride concentration which will be exceeded less than 7
percent of the days and 50 percent of the days in the lower St.
Johns River.

I I I I I I

,,

I I

I I I I

I I I I. I I I I I I I

BUREAU OF GEOLOGY

Because, as indicated by the foregoing discussion, all average monthly
mean tidal flows should be almost the same, any seasonal variation in the flow of
the river is manifested by the net flow. Determination of the net flow of the
river can be no more accurate than that of the tidal flow and on a percentage
basis, it must be considerably poorer. This is especially true for periods when the
net flow is small. The inaccuracy of the record is indicated by the computed
average net flow of only 5,883 cfs whereas the average net flow based on the
gaged inflow and estimated inflow from ungaged areas is about 8,100 cfs.
Nevertheless, the average and extreme monthly mean discharges based on the
records for the river at Jacksonville are shown by figure 31. The distribution
pattern, if not the values, is probably valid as is the departure from average
conditions indicated by the extremes.

Figure 31 shows the seasonal net flow regime of the St. Johns River at
Jacksonville to consist of four periods, which result from the interplay of the
rainy season from June through October, the dry season from November
through May, the period of increasing storage from April through September,
and the period of decreasing storage from October through March. The four
periods are that of low net discharge in May and June, that of increasing net
discharge from July through September, that of high net discharge from October
through January, and that of decreasing net discharge from February through
April.

Some insight into the seasonal variation in chloride concentration was
obtained from the bimonthly chloride data collected by the Jacksonville
Department of Public Health. A generalized comparison between the average of
extremes in chloride concentration and average net outflow at Jacksonville for
the same months is shown in figure 32. As would be expected, there is an inverse
relation between chloride concentration and net discharge. The range between
the average maximum and average minimum chloride concentration at
Jacksonville is greatest when net outflow is low because the gradient of the zone
of transition is steeper at Jacksonville under these conditions than when net
outflow is high. That is, low net outflow places Main Street Bridge closer to the
sea-water end of the zone of transition, where the gradient is steep; whereas,
high net outflow places Main Street Bridge near the fresh-water end of the zone,
where the gradient is gentle.

TEMPERATURE

In 1966, about 180 million gallons of water per day was withdrawn from
aquifers in the Jacksonville area (Leve, 1969). Perhaps 30 to 50 mgd (million
gallons per day) of this water was used for cooling in various processes. If

BUREAU OF GEOLOGY

4 5 6 7 8 9 10 II 12 13 14
MAXIMUM CHLORIDE CONCENTRATION AT ORANGE PARK AND
DRUMMOND POINT, THOUSANDS OF MILLIGRAMS PER LITER

Figure 29. Relation of maximum chloride concentration at Main Street
Bridge to maximum chloride concentration at Orange Park and
Drummond Point at slack before the downstream flow of
common tidal cycles.
in chloride concentration which would be exceeded as the daily maximum 50
percent of the days is similarly shown for the reach between Drummond Point
and Orange Park. The chloride concentrations for all points shown in the figure
other than at Main Street Bridge were derived from relations like those shown in
Figure 29.

SEASONAL VARIATION IN FLOW AND CHLORIDE CONCENTRATION

The average monthly mean tidal flow at Jacksonville during the period of
record from March, 1954, to September, 1966, should be about the same for
every month. Thus, there should be no seasonal variation in the tide induced
flow. This is because the tidal flow is approximately proportional to the range of
tide (Haight, 1938) and the monthly mean ranges of tide as determined from the
tide tables for the period of record were almost the same for every month. The
difference between the highest and lowest monthly mean range of tide was
0.027 foot. The record shows a difference of 235 mcf between the highest and
lowest monthly mean tidal flow which ranged from 7.4 less than to 4.7 percent
more than the mean tidal flow.

INFORMATION CIRCULAR NO. 82

HIGHEST

C 16
z
0
o
w
i, 14

w
Q 12
I-
w
-L 10

L)
0
( n
0
z
c, 4

I
S2

I-2

W
Z -4

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT NOV. DEC.
Figure 31. Graphs showing the highest, lowest, and average monthly mean
net discharge of the St. Johns River at Jacksonville.

LOWEST

BUREAU OF GEOLOGY

Because, as indicated by the foregoing discussion, all average monthly
mean tidal flows should be almost the same, any seasonal variation in the flow of
the river is manifested by the net flow. Determination of the net flow of the
river can be no more accurate than that of the tidal flow and on a percentage
basis, it must be considerably poorer. This is especially true for periods when the
net flow is small. The inaccuracy of the record is indicated by the computed
average net flow of only 5,883 cfs whereas the average net flow based on the
gaged inflow and estimated inflow from ungaged areas is about 8,100 cfs.
Nevertheless, the average and extreme monthly mean discharges based on the
records for the river at Jacksonville are shown by figure 31. The distribution
pattern, if not the values, is probably valid as is the departure from average
conditions indicated by the extremes.

Figure 31 shows the seasonal net flow regime of the St. Johns River at
Jacksonville to consist of four periods, which result from the interplay of the
rainy season from June through October, the dry season from November
through May, the period of increasing storage from April through September,
and the period of decreasing storage from October through March. The four
periods are that of low net discharge in May and June, that of increasing net
discharge from July through September, that of high net discharge from October
through January, and that of decreasing net discharge from February through
April.

Some insight into the seasonal variation in chloride concentration was
obtained from the bimonthly chloride data collected by the Jacksonville
Department of Public Health. A generalized comparison between the average of
extremes in chloride concentration and average net outflow at Jacksonville for
the same months is shown in figure 32. As would be expected, there is an inverse
relation between chloride concentration and net discharge. The range between
the average maximum and average minimum chloride concentration at
Jacksonville is greatest when net outflow is low because the gradient of the zone
of transition is steeper at Jacksonville under these conditions than when net
outflow is high. That is, low net outflow places Main Street Bridge closer to the
sea-water end of the zone of transition, where the gradient is steep; whereas,
high net outflow places Main Street Bridge near the fresh-water end of the zone,
where the gradient is gentle.

TEMPERATURE

In 1966, about 180 million gallons of water per day was withdrawn from
aquifers in the Jacksonville area (Leve, 1969). Perhaps 30 to 50 mgd (million
gallons per day) of this water was used for cooling in various processes. If

BUREAU OF GEOLOGY

X 10
s--

S9

U-

0
J 7

, 6

I 5
o

C-)
Z 4
0
r-

13

a

-,
0~ (

Figure 32. Graphs showing the average net flow and the average maximum
and minimum chloride concentrations in the St. Johns River at
Jacksonville for alternate months. Flow records and chloride
records June 1959 to October 1966.

surface-water sources such as the St. Johns River could be substituted for
ground-water sources to provide this cooling water, all the projected increase in
water demand from 1966 to 1980 could be met without increasing the rate of
withdrawal of water from the aquifers.

Water-temperature measurements of the St. Johns River taken at random
over a period of several years and temperature of ground water at different
depths in the area are protrayed by figure 33. Water tempatures in the artesian

INFORMATION CIRCULAR NO. 82 5
35 --1-| -1-- ---- -- -- 1 95

-9
30I I I I

- WELLS GREATER THAN 1,000 FEET DEEP -------
- WELLS 800 TO 1,000 FEET DEEP
- WELLS 500 TO 800 FEET DEEP-

I l l I i I I

S_ GROUND WATER
S GROUND WATER
GROUND WATER

65 2

W
60

55

JAN FEB. MAR APR. MAY JUNE JULY AUG. SEPT OCT. NOV. DEC.

Figure 33. Approximate average daily water temperatures of the St. Johns
River at Main Street Bridge and ground-water at specified
depths.

aquifer in the area are nearly constant but increase with depth. The temperature
of water from wells 500 to 800 feet deep averages about 24 C (75 OF) and that
of water from wells greater than 1,000 feet deep about 27 C (81 OF).

Figure 33 shows that the water in the St. Johns River has a lower
temperature, and, therefore, a greater cooling capacity than any water from the
artesian aquifer from November through April. In January and February, the
temperature of the river water averages less than 15 C (59 F). The temperature
of the river water is higher than that of all water now being withdrawn from the
artesian aquifer only from June through mid September when the temperature
of the river water averages more than 28 C (82 F). Thus, use of ground water in
the Jacksonville area could be reduced if installations now perennially using
ground water for cooling were to use river water from November through April,
with the realization of some gain in efficiency of the installations.

RELATION OF FLOW AND QUALITY CHARACTERISTICS
TO USE OF THE RIVER

Most uses of the St. Johns River at Jacksonville depend on the chemical
and biological quality of the river. The water quality of the river is controlled by
the flow of the river. The flow characteristics of the river are such that the river
at Jacksonville can become saline, as a result of upstream flow, or severely

i

BUREAU OF GEOLOGY

polluted with wastes as a result of low net flow. High chloride concentrations
restrict use of the river for public water supply and industrial processes. High
concentrations of wastes in the river, which can persist after the resumption of
net upstream or downstream flow, adversely affect the esthetic and recreational
value of the river.

SUMMARY AND CONCLUSIONS

The St. Johns River drains about one-sixth of the State of Florida and in
its lower reaches is a tidal estuary in which about 1 in every 10 gallons of water
that drains from Florida passes beneath the Main Street Bridge at Jacksonville.
Daily tidal effects are evident as far upstream as Lake George, and, during
droughts, the higher tides aided by northeasterly winds sometimes cause tidal
fluctuations as far upstream as Lake Monroe. River levels below mean sea level
have been observed near the southern end of Lake Harney.

The tide generates progressive tidal waves, which move up the river in
cycles accompanied by tidal currents. When the tide at Jacksonville is about
midrange, the current is slack. When the tide rises above about midrange, the
current sets inland as upstream flow and reaches a maximum velocity at near
high tide. When the tide falls below about midrange, the current sets seaward as
downstream flow and reaches a maximum velocity at about low tide. Slack
water does not occur at exactly midrange nor do the maximum velocities occur
at exactly high and low tides. Instead, the tidal currents slightly lag the tides
because of inertia and channel friction.

The main variable factors controlling the amounts of water flowing back
and forth at Jacksonville are the height of the tides, the tidal range, and wind.
The height of the tides varies annually and over even longer periods. The tidal
range varies more rapidly, reaching a maximum and a minimum once in each
lunar month. Both the tidal height and range are uniformly periodic in response
to gravitational forces. The effect of wind on the flow of the St. Johns River at
Jacksonville ranges from none at all to more than that of the tide.

Tidal and wind effects can work in concert or in opposition and thereby
increase the variation in their net effect on the flow. The long-term effect of
both tide and wind on the net downstream flow at Jacksonville is negligible,
although, when evapotranspiration exceeds fresh-water input, tidal effect causes
a small net upstream flow, which eventually is approximately offset by rainfall
on the estuary.

INFORMATION CIRCULAR NO. 82 5
35 --1-| -1-- ---- -- -- 1 95

-9
30I I I I

- WELLS GREATER THAN 1,000 FEET DEEP -------
- WELLS 800 TO 1,000 FEET DEEP
- WELLS 500 TO 800 FEET DEEP-

I l l I i I I

S_ GROUND WATER
S GROUND WATER
GROUND WATER

65 2

W
60

55

JAN FEB. MAR APR. MAY JUNE JULY AUG. SEPT OCT. NOV. DEC.

Figure 33. Approximate average daily water temperatures of the St. Johns
River at Main Street Bridge and ground-water at specified
depths.

aquifer in the area are nearly constant but increase with depth. The temperature
of water from wells 500 to 800 feet deep averages about 24 C (75 OF) and that
of water from wells greater than 1,000 feet deep about 27 C (81 OF).

Figure 33 shows that the water in the St. Johns River has a lower
temperature, and, therefore, a greater cooling capacity than any water from the
artesian aquifer from November through April. In January and February, the
temperature of the river water averages less than 15 C (59 F). The temperature
of the river water is higher than that of all water now being withdrawn from the
artesian aquifer only from June through mid September when the temperature
of the river water averages more than 28 C (82 F). Thus, use of ground water in
the Jacksonville area could be reduced if installations now perennially using
ground water for cooling were to use river water from November through April,
with the realization of some gain in efficiency of the installations.

RELATION OF FLOW AND QUALITY CHARACTERISTICS
TO USE OF THE RIVER

Most uses of the St. Johns River at Jacksonville depend on the chemical
and biological quality of the river. The water quality of the river is controlled by
the flow of the river. The flow characteristics of the river are such that the river
at Jacksonville can become saline, as a result of upstream flow, or severely

i

BUREAU OF GEOLOGY

polluted with wastes as a result of low net flow. High chloride concentrations
restrict use of the river for public water supply and industrial processes. High
concentrations of wastes in the river, which can persist after the resumption of
net upstream or downstream flow, adversely affect the esthetic and recreational
value of the river.

SUMMARY AND CONCLUSIONS

The St. Johns River drains about one-sixth of the State of Florida and in
its lower reaches is a tidal estuary in which about 1 in every 10 gallons of water
that drains from Florida passes beneath the Main Street Bridge at Jacksonville.
Daily tidal effects are evident as far upstream as Lake George, and, during
droughts, the higher tides aided by northeasterly winds sometimes cause tidal
fluctuations as far upstream as Lake Monroe. River levels below mean sea level
have been observed near the southern end of Lake Harney.

The tide generates progressive tidal waves, which move up the river in
cycles accompanied by tidal currents. When the tide at Jacksonville is about
midrange, the current is slack. When the tide rises above about midrange, the
current sets inland as upstream flow and reaches a maximum velocity at near
high tide. When the tide falls below about midrange, the current sets seaward as
downstream flow and reaches a maximum velocity at about low tide. Slack
water does not occur at exactly midrange nor do the maximum velocities occur
at exactly high and low tides. Instead, the tidal currents slightly lag the tides
because of inertia and channel friction.

The main variable factors controlling the amounts of water flowing back
and forth at Jacksonville are the height of the tides, the tidal range, and wind.
The height of the tides varies annually and over even longer periods. The tidal
range varies more rapidly, reaching a maximum and a minimum once in each
lunar month. Both the tidal height and range are uniformly periodic in response
to gravitational forces. The effect of wind on the flow of the St. Johns River at
Jacksonville ranges from none at all to more than that of the tide.

Tidal and wind effects can work in concert or in opposition and thereby
increase the variation in their net effect on the flow. The long-term effect of
both tide and wind on the net downstream flow at Jacksonville is negligible,
although, when evapotranspiration exceeds fresh-water input, tidal effect causes
a small net upstream flow, which eventually is approximately offset by rainfall
on the estuary.

INFORMATION CIRCULAR NO. 82

Fresh-water input affects the tidal flow appreciably during very wet
periods, but it is unlikely that its effect is ever sufficient to offset even the lesser
tidal effects. When fresh-water input is equal to or less than evapotranspiration
from the estuary, it cannot cause net downstream flow at Jacksonville. The
average net or fresh-water flow at Jacksonville is about 14 percent of the average
tide-induced flow.

Volumes of flow induced by tide average 1,944 mcf and range from about
1,250 mcf to about 2,750 mcf per tidal event. Average fresh-water flow
computed from the flow records is 264 mcf per tidal cycle. The maximum effect
of fresh-water flow and wind on tidal flow cannot be determined, but their
minimum effect is zero.

Evapotranspiration from the river surface exceeds the sum of the rainfall
on the river and the fresh-water inflow to the river during some droughts. When
these conditions prevail at a time when storage in the estuary is low, they may
work in concert with the annual rise in sea level to cause a cumulative net inflow
of as much as 40 billion cubic feet of sea water over a period of months. The
river becomes salty for many miles upstream from Jacksonville when this
happens.

Frequency analysis of the flow records indicate that extremes in flow
volume such as those caused by Hurricane Dora in September 1964 are rare,
except for the minimum upstream flow volume, which was zero. The analysis
indicates that the minimum upstream flow will be zero on an average of once in
7 years, whereas occurrences of the maximum and minimum downstream flow
volumes of record and the maximum upstream flow volume of record are much
less frequent.

The average seasonal flow regime of the St. Johns River can be divided
into four periods, that of low net outflow in May and June, that of increasing
net outflow from July through September, that of high net outflow from
October through January, and that of decreasing net outflow from February
through April. Wide departures from the average seasonal net flow regime can
and often do occur as a result of abnormal rainfall.

The seasonal variation in chemical quality on the St. Johns River, as
indicated by the chloride concentration in the water, is inversely related to the
seasonal net outflow. The chloride concentration is generally lowest and varies
the least as a result of tidal flow during the high net-flow period and is generally
highest and varies the most as a result of tidal flow during the low net-flow
'period. The chloride concentration in the river generally increases during the
period of decreasing flow and decreases during the period of increasing flow.

BUREAU OF GEOLOGY

The quality and chemical composition of water in the St. Johns River is
highly variable in the vicinity of Jacksonville. The chloride concentration may
increase or decrease more than fourfold in a matter of a few hours and more
than tenfold in several days. Variations in quality are controlled by the flow
characteristics of the river. Chloride concentration in the river sometimes shows
considerable vertical variation, which seems to be greatest at the time the river
begins to flow downstream. There is some correlation between maximum
chloride concentrations at Main Street Bridge and at other points on the river.

From November to April, water in the St. Johns River is cooler than
ground-water at any depth, and, from October to May, river water is cooler than
ground water at depths greater than 1,000 feet. Use of river water for industrial
cooling would reduce the demand for ground-water supplies.

The flow and chemical characteristics of the St. Johns River at
Jacksonville are dominated by tide, on a tide-to-tide, monthly, and annual basis.
Fresh-water drainage from the river basin is the only factor that has a significant
cumulative long-term effect on the flow of the river, all other factors, which
include wind, rainfall, and evapotranspiration along with tide, are virtually self
cancelling and have no cumulative effect on the flow of the river. The seasonal
and short-term interaction of the factors that affect the flow of river are greatly
modified by the availability of huge storage capacity in the tidal estuary
upstream from Jacksonville.

The chemical characteristics and esthetic condition of the river are
controlled by the flow characteristics of the river, which cause high
concentrations of chemical constituents to occur at Jacksonville as a result of
excessive upstream flow and, possibly, high concentrations of wastes in the river
as a result of periods of little or no net river movement.

CONTINUING AND FUTURE STUDIES

One of the concerns for the future of the St. Johns River is the potential
for pollution from industrial and domestic wastes. In addition to knowledge
about the flow and chemical and temperature variations in the river, knowledge
about the variations in dissolved oxygen, coliform populations, and eddy and
turbulence regimes is essential in attaching the problems of pollution evaluation
and control. Further, knowledge of the movements of the water and its
contents, both really and chronologically, is necessary to determine where
wastes enter the river at Jacksonville, where they subsequently go, and how long
they reside at a particular locale;

INFORMATION CIRCULAR NO. 82 55

To help meet the need for information, continuous records of the stage,
flow, conductivity, dissolved oxygen content, temperature, and pH of the river
are being collected.

Study of the tidal parts of tributaries to the St. Johns River in and near
Jacksonville by the U. S. Geological Survey show that very poor quality
conditions sometimes exist in the tributaries. However, more definitive studies
of the water quality in the tributaries are needed to determine the magnitude
and duration of this problem.

BUREAU OF GEOLOGY

The quality and chemical composition of water in the St. Johns River is
highly variable in the vicinity of Jacksonville. The chloride concentration may
increase or decrease more than fourfold in a matter of a few hours and more
than tenfold in several days. Variations in quality are controlled by the flow
characteristics of the river. Chloride concentration in the river sometimes shows
considerable vertical variation, which seems to be greatest at the time the river
begins to flow downstream. There is some correlation between maximum
chloride concentrations at Main Street Bridge and at other points on the river.

From November to April, water in the St. Johns River is cooler than
ground-water at any depth, and, from October to May, river water is cooler than
ground water at depths greater than 1,000 feet. Use of river water for industrial
cooling would reduce the demand for ground-water supplies.

The flow and chemical characteristics of the St. Johns River at
Jacksonville are dominated by tide, on a tide-to-tide, monthly, and annual basis.
Fresh-water drainage from the river basin is the only factor that has a significant
cumulative long-term effect on the flow of the river, all other factors, which
include wind, rainfall, and evapotranspiration along with tide, are virtually self
cancelling and have no cumulative effect on the flow of the river. The seasonal
and short-term interaction of the factors that affect the flow of river are greatly
modified by the availability of huge storage capacity in the tidal estuary
upstream from Jacksonville.

The chemical characteristics and esthetic condition of the river are
controlled by the flow characteristics of the river, which cause high
concentrations of chemical constituents to occur at Jacksonville as a result of
excessive upstream flow and, possibly, high concentrations of wastes in the river
as a result of periods of little or no net river movement.

CONTINUING AND FUTURE STUDIES

One of the concerns for the future of the St. Johns River is the potential
for pollution from industrial and domestic wastes. In addition to knowledge
about the flow and chemical and temperature variations in the river, knowledge
about the variations in dissolved oxygen, coliform populations, and eddy and
turbulence regimes is essential in attaching the problems of pollution evaluation
and control. Further, knowledge of the movements of the water and its
contents, both really and chronologically, is necessary to determine where
wastes enter the river at Jacksonville, where they subsequently go, and how long
they reside at a particular locale;

56 BUREAU OF GEOLOGY

INFORMATION CIRCULAR NO. 82

REFERENCES

Haight, F. J.
1938 Currents in the St. Johns River, Savannah River and intervening waterways: U.
S. Department of Commerce, Coast and Geodetic Survey Spec. Pub. No. 211.

Keighton, W. B.
1965 Fresh-water discharge salinity relations in the tidal Delaware River: U. S.
Geol. Survey Open-File report.

Leve, G. W.
1969 (and Goolsby, D.A.) Production and utilization of water in the metropolitan
area of Jacksonville, Florida: Florida Board of Conservation, Division of Geol.
Inf. Circ. 58.

Marmer, H. A.
1951 Tidal datum planes: U. S. Department of Commerce, Coast and Geodetic
Survey Spec. Pub. No. 135.

Pillsbury, G. B.
1939 Tidal hydraulics: War Department, Corps of Engineers, U. S. Army, Prof.
Paper of the Corps of Engineers No. 34.

Pyatt, E. E.
1964 On determining pollutant distribution in tidal estuaries: U. S. Geol. Survey
Water-Supply Paper 1586-F.

Schureman, Paul
1941 Manual of harmonic analysis and prediction of tides: U. S. Department of
Commerce, Coast and Geodetic Survey Spec. Pub. No. 98.

1963 Tide and current glossary: U. S. Department of Commerce, Coast and
Geodetic Survey Spec. Pub. No. 228.

Snell, L. J.
1970

(and Anderson, Warren) Water resources of northeast Flordia (St. Johns River
and adjacent coastal areas): Florida Department of Natural Resources, Bureau
of Geol. Rept. Inv. 54.

U. S. Department of Commerce, Coast and Geodetic Survey
1954-66 Tide tables, east coast of North and South America, including Greenland.

1954-66 Tidal current tables, Atlantic Coast of North America.

U. S. Geological Survey
1958-60 Surface water supply of the United States, Part 2-B: U. S. Geol Survey
Water-Supply Papers 1554, 1624, 1704.

1961-64 Surface water records of Florida: V. 1 streams.

1965-66 Water resources data for Florida, part 1, surface water records.

FLRD GEOLOSk ( IC SUfRiW

COPYRIGHT NOTICE
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The Florida Geological Survey holds all rights to the source text of
this electronic resource on behalf of the State of Florida. The
Florida Geological Survey shall be considered the copyright holder
for the text of this publication.

Under the Statutes of the State of Florida (FS 257.05; 257.105, and
377.075), the Florida Geologic Survey (Tallahassee, FL), publisher of
the Florida Geologic Survey, as a division of state government,
makes its documents public (i.e., published) and extends to the
state's official agencies and libraries, including the University of
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The Florida Geological Survey has made its publications available to
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The Florida Geological Survey reserves all rights to its publications.
All uses, excluding those made under "fair use" provisions of U.S.
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restricted. Contact the Florida Geological Survey for additional
information and permissions.

	Front Cover
	Department of Natural Resources...
	Letter of transmittal
	Contents
	Abstract
	Introduction, purpose and...
	Description of the system
	Factors affecting the river flow...
	Flow statistics
	Flow distribution and frequenc...
	Maximum periods of flow defici...
	Chemical characteristics
	Seasonal variation in flow and...
	Temperature
	Relation of flow and quality characteristics...
	Summary and conclusions
	Continuing and future studies
	References

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