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 Title Page
 Table of Contents
 Abstract
 Introduction
 Purpose and methods of investi...
 Previous investigations
 Description of the surrounding...
 Hydrology
 Chemical characteristics of surface...
 Ground water
 Summary and conclusions
 References


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Hydrologic aspects of freshening upper Old Tampa Bay, Florida ( FGS: Information circular 76 )
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 Material Information
Title: Hydrologic aspects of freshening upper Old Tampa Bay, Florida ( FGS: Information circular 76 )
Series Title: ( FGS: Information circular 76 )
Physical Description: iv, 39 p. : ill. ; 23 cm.
Language: English
Creator: Mann, J. A
Geological Survey (U.S.)
Publisher: Bureau of Geology
Place of Publication: Tallahassee Fla
Publication Date: 1972
 Subjects
Subjects / Keywords: Hydrology -- Florida -- Tampa Bay   ( lcsh )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by J. A. Mann.
Bibliography: Bibliography: p.38-39.
General Note: Prepared by the U. S. Geological Survey in cooperation with Southwest Florida Water Management District and the Bureau of Geology.
Funding: Digitized as a collaborative project with the Florida Geological Survey, Florida Department of Environmental Protection.
 Record Information
Source Institution: University of Florida
Rights Management:
The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.
Resource Identifier: aleph - 001048699
oclc - 02022288
notis - AFD1777
System ID: UF00001136:00001

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Table of Contents
    Title Page
        Page i
        Page ii
    Table of Contents
        Page iii
        Page iv
    Abstract
        Page 1
        Page 2
    Introduction
        Page 2
        Page 3
    Purpose and methods of investigation
        Page 4
        Page 5
        Page 6
    Previous investigations
        Page 7
        Page 6
    Description of the surrounding area
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
    Hydrology
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
    Chemical characteristics of surface water
        Page 20
        Page 21
        Page 22
        Page 19
        Page 23
        Page 24
    Ground water
        Page 25
        Page 26
        Page 27
        Page 28
        Page 24
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
    Summary and conclusions
        Page 35
        Page 36
        Page 37
    References
        Page 38
        Page 39
        Copyright
            Copyright
Full Text







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




DIVISION OF INTERIOR RESOURCES
Robert O. Vernon, Director




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




Information Circular No. 76



HYDROLOGIC ASPECTS OF FRESHENING
UPPER OLD TAMPA BAY, FLORIDA



By
J. A. Mann


Prepared by the
UNITED STATES GEOLOGICAL SURVEY
in cooperation with
SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT
and the
BUREAU OF GEOLOGY
FLORIDA DEPARTMENT OF NATURAL RESOURCES


TALLAHASSEE
1972

















































Completed manuscript received
February 1, 1972
Printed for the Florida Department of Natural Resources
Division of Interior Resources
Bureau of Geology
by Rose Printing Company
Tallahassee, Florida


Tallahassee
1972


ii







CONTENTS


Page
Abstract ...................................... ... 1


Introduction ...................
Purpose and scope .............
Methods of investigation ..........
Acknowledgments .............
Previous investigations ...........
Description of the surrounding area .......
Topography and drainage .........
Culture and development .........
Climate ..................
Geology ..................
Hydrology ....................
Runoff to the proposed lake ........


. . . . ..... 4

. . . . . .. 6
. . . .. . 6
. . . . . 7

. . . . . 9

. . . . . 11
. . . . . 11
. . . . . 15
. . . . . 15


Inflow during average and above average conditions . . ... 16
Inflow during a critically dry year ...................... 18
Chemical characteristics of surface water . . . .. ... 19
Rate of freshening ................... .............. 22
Ground water .... ............... ..............24
Shallow aquifer ........ ......... ...........24
Floridan aquifer ...............................26
Fluctuations of the potentiometric surface . . ... 28
Chemical character of the water . . . .. .. 29
Recharge and discharge . . . . . ... 29
Hydraulic interconnection .............................30
Effects of freshening on the aquifer system . . . .. .. 33
Summary and conclusions ................................35
References ................... .......... ... ........ 38


ILLUSTRATIONS


Figure
1 Map showing location of the upper Old Tampa Bay area, Florida. . .
2 Map showing location of selected observation wells, municipal well fields, rainfall
stations, stream-flow gaging stations, and tidal recording stations in the upper Old
Tampa Bay area, Florida .............................
3 Map showing topography of the upper Old Tampa Bay area, Florida. . .
4 Map showing Lake Tarpon Water Control Project, Upper Tampa Bay Watershed
Project, and Brooker Creek Watershed Project . . . . .
5 Mean monthly rainfall, evaporation, and runoff, 1953-66 . . .
6 Map of the upper Old Tampa Bay area showing generalized contours on the top of
the first continuous limestone (Tampa Formation) of the Floridan aquifer. .
7 Cumulative total rainfall on, evaporation from, and inflow to proposed
fresh-water lake including Lake Tarpon-Brooker Creek watershed . .
8 Relation between specific conductance and discharge of Sweetwater Creek near
Sulphur Springs ................................


Page






ILLUSTRATIONS

Figure Page
9 Chloride concentrations at sites sampled in upper Old Tampa Bay and location of
auger holes. ................... ............... 21
10 Calculated rate of freshening of proposed lake by dilution. (Includes inflow from
Lake Tarpon-Brooker Creek watershed). . . . .. ... 23
11 Maximum and minimum monthly water levels in a shallow and a deep well near
the northeast edge of the study area. . . . .... ...... 25
12 Map of the upper Old Tampa Bay area showing generalized configuration of the
potentiometric surface of the Floridan aquifer and the area of artesian flow,
August-November, 1967 ................... .......... 27
13 Water-level fluctuations in a deep observation well on Booth Point that taps the
upper part of the Floridan aquifer. ........................ 28
14 Generalized section showing geohydrology of upper Old Tampa Bay area ... 32
15 Estimated long-term rise in fresh-water level in upper part of Floridan aquifer as
result of conversion of upper Old Tampa Bay into a fresh-water lake. . 36




TABLES

Table Page
1 Geologic formations in the upper Old Tampa Bay area, Florida . . ... 12
2 Results of sieve analyses of split-spoon samples collected from test wells
augered in Bay bottom and along Courtney Campbell Causeway. . . ... 31





HYDROLOGIC ASPECTS OF FRESHENING
UPPER OLD TAMPA BAY, FLORIDA


By J. A. Mann

ABSTRACT

Upper Old Tampa Bay, a 17-square mile area of Old Tampa Bay, Florida,
has been proposed for conversion to a fresh-water lake. The amount of runoff to
the proposed lake and its chemical quality are both adequate to freshen and
sustain a fresh-water lake in this part of the bay. During 1950-66 runoff to the
proposed lake, including discharge from Lake Tarpon, would have averaged 134
mgd (million gallons per day) and would have displaced the volume of the
proposed lake at normal pool stage (2.5 feet above mean sea level) about 1.7
times per year. Without discharge from Lake Tarpon, the volume of the
proposed lake would have been displaced 1.2 times. If the lake level was initially
at a normal pool stage during a critically dry year, such as 1956, the proposed
lake would have declined 0.25 to 0.5 foot below the minimum design level, (1.5
feet above mean sea level).
At points above tidewater, average mineral content of streamflow
contributing to the lake is less than 100 mg/1 (milligrams per liter), and average
chloride content is less than 20 mg/1. The average chloride concentration of the
bay proper, based on water samples collected in June, October, and November
of 1967, ranged from 14,000 to 16,000 mg/1.
Lake freshening would take place through a combined process of
displacement and dilution of the saline water in the lake at time of closure.
Freshening of the proposed lake to a chloride concentration of 250 mg/1 would
require about 4 years. Annual fresh-water losses through operation of locks
would amount to the volume of water lost by a 0.1-foot decline in lake level, a
relatively insignificant amount.
The study area is underlain by a shallow water-table aquifer. The
fine-grained beds at the base of this aquifer act as a confining layer for the
underlying artesian aquifer (the Floridan aquifer), which consists of limestone
beds of the Tampa Formation and older formations. At places the confining
layer has been breached, allowing an imperfect hydraulic interconnection
between the two aquifers.
Saline water occurs in both the shallow aquifer and the upper part of the
Floridan aquifer near the bay. Except for the Oldsmar area, present hydrologic
conditions preclude major fresh-water spring discharge from the Floridan aquifer
through the bottom of the bay.
Damming Upper Old Tampa Bay and maintaining the proposed lake at a
normal pool stage of 2.5 feet above mean sea level would cause a rise in





2 BUREAU OF GEOLOGY


fresh-water levels in both the water-table aquifer and the upper part of the
Floridan aquifer (Tampa and Suwannee Limestones), thereby eventually flushing
saline water from both aquifers. Because of the imperfect connection between
the proposed lake and the Floridan aquifer, leakage from the lake to the aquifer
would initially average less than 1 mgd upon closure of the dam and would
gradually decrease as the head difference diminishes.
Displacement of saline water from the Floridan aquifer and depression of
the fresh-water salt-water interface to a stable hydrostatic position might take 10
to 20 yeais. The long-term rise in water levels in the upper part of the Floridan
aquifer would be 2 to 3 feet within 1 mile of the lake and less than 1 foot 3 to 4
miles inland. This rise in water levels would not be sufficient to depress the
fresh-water salt-water interface to the base of the permeable zone in the upper
part of the Floridan aquifer near the bay.








INTRODUCTION

The proposed conversion of part of Old Tampa Bay (fig. 1) to a
fresh-water lake has been considered for many years. The water-control works
proposed in the engineering studies consisted of (1) a continuous landfill
adjacent to the north side of Courtney Campbell Causeway; (2) gated spillways
to permit discharge and regulation; and (3) two locks for boat navigation. The
larger of the two locks was for tugs and barges; the smaller for pleasure boats.
Small-boat passage was also provided for by proposed use of either mechanical
boat hoists, marine railways, or davits. The lake level was to be regulated
between 1.5 and 2.5 feet above msl (mean sea level) with a maximum
permissible level of 3.0 feet above msl.
The Lake Tarpon Water Control Project, utilizing an outfall canal from
Lake Tarpon to Old Tampa Bay and a cofferdam around a sinkhole in Lake
Tarpon, was not originally considered as part of the conversion project. Because
the Lake Tarpon project is a reality, the combined effects of the two projects are
considered in this report in evaluating the hydrologic aspects of freshening.
At the present time the project is inactive. This report summarizes for the
record the hydrologic effects of the proposed project and was prepared by the
U.S. Geological Survey in cooperation with the Southwest Florida Water
Management District and the Bureau of Geology, Florida Department of Natural
Resources.





2 BUREAU OF GEOLOGY


fresh-water levels in both the water-table aquifer and the upper part of the
Floridan aquifer (Tampa and Suwannee Limestones), thereby eventually flushing
saline water from both aquifers. Because of the imperfect connection between
the proposed lake and the Floridan aquifer, leakage from the lake to the aquifer
would initially average less than 1 mgd upon closure of the dam and would
gradually decrease as the head difference diminishes.
Displacement of saline water from the Floridan aquifer and depression of
the fresh-water salt-water interface to a stable hydrostatic position might take 10
to 20 yeais. The long-term rise in water levels in the upper part of the Floridan
aquifer would be 2 to 3 feet within 1 mile of the lake and less than 1 foot 3 to 4
miles inland. This rise in water levels would not be sufficient to depress the
fresh-water salt-water interface to the base of the permeable zone in the upper
part of the Floridan aquifer near the bay.








INTRODUCTION

The proposed conversion of part of Old Tampa Bay (fig. 1) to a
fresh-water lake has been considered for many years. The water-control works
proposed in the engineering studies consisted of (1) a continuous landfill
adjacent to the north side of Courtney Campbell Causeway; (2) gated spillways
to permit discharge and regulation; and (3) two locks for boat navigation. The
larger of the two locks was for tugs and barges; the smaller for pleasure boats.
Small-boat passage was also provided for by proposed use of either mechanical
boat hoists, marine railways, or davits. The lake level was to be regulated
between 1.5 and 2.5 feet above msl (mean sea level) with a maximum
permissible level of 3.0 feet above msl.
The Lake Tarpon Water Control Project, utilizing an outfall canal from
Lake Tarpon to Old Tampa Bay and a cofferdam around a sinkhole in Lake
Tarpon, was not originally considered as part of the conversion project. Because
the Lake Tarpon project is a reality, the combined effects of the two projects are
considered in this report in evaluating the hydrologic aspects of freshening.
At the present time the project is inactive. This report summarizes for the
record the hydrologic effects of the proposed project and was prepared by the
U.S. Geological Survey in cooperation with the Southwest Florida Water
Management District and the Bureau of Geology, Florida Department of Natural
Resources.






INFORMATION CIRCULAR NO. 76


GULF
OF
MEXICO


LLSBOROUGH AND
PINELLAS COUNTIES


Figure 1.-Map showing location of the upper Old Tampa Bay area, Florida.


1o (0
"1
KIo
lJ .CD
~-"O-






BUREAU OF GEOLOGY


PURPOSE AND SCOPE

The purpose of the study was to evaluate (1) the hydrology of upper Old
Tampa Bay under the conditions existing in 1966-69; (2) the hydrologic
feasibility of freshening the bay; and (3) the possible hydrologic effects that
freshening of the bay might have on the aquifer system, particularly with respect
to changes in both the level and chemical quality of water in the aquifers. This
report summarizes the findings of the study. Its aim is to provide an evaluation
of the surface- and ground-water resources of the area as related to the proposed
freshening; to describe the aspects of hydrology and geology that relate to
freshening of upper Old Tampa Bay; to evaluate possible hydrologic changes in
the bay and contiguous area caused by the freshening; and to define the effect of
freshening on the aquifer system.


METHODS OF INVESTIGATION

Streamflow data were available from four long-term gaging stations (fig. 2)
and two partial-record stations at inflow points to the bay. These data and the
derived estimates of flow for ungaged areas were used to establish the amount
and seasonal distribution of surface inflow.
Tidal fluctuations in the bay were recorded continuously at two locations.
These data were used in conjunction with fluctuations of water levels in
observation wells to qualify judgments concerning the degree of interconnection
between the aquifer systems and the bay.
Observation wells tapping both the shallow and deep aquifers were used to
monitor the water-level fluctuations and to provide information on the hydraulic
properties of the aquifers. Physical characteristics of the aquifers were
determined from a study of well cuttings, geophysical logs, and other
information obtained during well construction. Test wells were drilled in some
locations where additional data were needed. Paired shallow and deep test wells
were completed at sites adjacent to the bay to monitor the effects of tides on
water levels in the aquifers and to aid in evaluating the degree of interconnection
between the bay and the aquifers and causes of changes in water quality in the
aquifers.
A hollow-stem auger was used to drill test holes in the bay bottom and the
contiguous area. The results of this test drilling were used in conjunction with
other data to determine the areal extent of clay beds, the physical characteristics
of the sediments overlying the Floridan aquifer, and the degree of inter-
connection between the bay and the Floridan aquifer.
Aquifer tests and laboratory analyses of samples of nonindurated
sediments in adjacent areas, collected as part of other investigations, provided





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PINELLAS COUNTY CITY OF ST. PETERSBURG
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27 57' 30"
B250 40' 30' 82025,

Figure 2.- Map showing location of selectedobservation wells, municipal well fields, rainfall stations, streamflow gaging
stations, and tidal recording stations in the upper Old Tampa Bay area, Florida.






BUREAU OF GEOLOGY


useful data in evaluating the hydraulic characteristics of the aquifer and related
confining beds in the bay area.
Samples were collected from streams, wells, and the bay for chemical
analysis. Traverses were made periodically in the bay under differing hydrologic
conditions. During these traverses, water samples were collected in order to
detect possible variations in salinity and areas of possible inflow from submarine
springs.



ACKNOWLEDGMENTS

Excellent cooperation was received from city and county officials,
industry, and local residents during this investigation. Special acknowledgments
are given the Florida Department of Transportation, and Hillsborough and
Pinellas Counties, for permission to drill and maintain test wells on public lands,
and to the Florida Bureau of Geology and the Southwest Florida Water
Management District for information provided the author. Appreciation is also
expressed to J. S. Rosenshein and Gilbert H. Hughes of the Geological Survey
for their extensive revision, and technical and editorial review of the manuscript.
Work on the investigation was performed under the direction of C. S. Conover,
district chief for Florida, and under the immediate supervision of J. W. Stewart
and J. S. Rosenshein.



PREVIOUS INVESTIGATIONS

A report by Matson and Sanford (1913) contains the earliest known
published information on the hydrology and geology of this part of Old Tampa
Bay. Sellards and Gunter (1913) discussed artesian flow.
Reports by Collins and Howard (1928) and Black and Brown (1951)
included some information on the quality of water. Stringfield (1933, p. 13-17)
presented a generalized description of the hydrology and geology of Pinellas and
northwestern Hillsborough Counties.
The geologic features of the Tampa Bay area are described by Cooke
(1945). A report by Ferguson and others (1947, p. 137) describes one of the
larger springs in upper Old Tampa Bay. Heath and Smith (1954) described the
hydrology and geology of the study area in Pinellas County. Reynolds, Smith,
and Hills, Architects and Engineers, prepared a feasibility report in 1959 for the
Hillsborough-Pinellas County committee studying the proposed freshening
project. A report by Menke, Meredith, and Wetterhall (1961) describes the






INFORMATION CIRCULAR NO. 76


hydrology of the Tampa Bay area in Hillsborough County. A report to the
Hillsborough-Pinellas County committee by Reynolds, Smith, and Hills, in 1963,
considered the engineering feasibility of the freshening project. A 1965 report
by Black, Crow, and Eidsness, Consulting Engineers to the Board of County
Commissioners, Pinellas County, reviewed the proposed freshening project.




DESCRIPTION OF THE SURROUNDING AREA

Tampa Bay is in about the middle of the west side of the Florida peninsula
(fig. 1) and is open to the Gulf. It is surrounded on three sides by the Tampa-St.
Petersburg metropolitan area. The bay is one of the largest along Florida's many
miles of coastline. Tampa Bay is divided into an eastern and western embayment
by the interbay peninsula on which part of the city of Tampa is located. The
eastern part is known as Hillsborough Bay and the western part as Old Tampa
Bay. The northern part of Old Tampa Bay, north of Courtney Campbell
Causeway, is known locally as upper Old Tampa Bay. This northern part has
been proposed for conversion to a fresh-water lake.



TOPOGRAPHY AND DRAINAGE

The Tampa Bay area is in the Coastal Lowlands topographic region of
Florida as defined by Cooke (1945, p. 8). Altitudes range from sea level to about
100 feet along the western drainage divide just northwest of Safety Harbor (fig.
3). A hilly area extends northward from Safety Harbor to Lake Tarpon.
Interspersed among these hills are numerous sinkholes, the most well known of
which is on the northwest shore of Lake Tarpon and has a subterranean
connection with Spring Bayou at Tarpon Springs (Heath and Smith, 1954). The
high mineral content of Lake Tarpon (fig. 21, p. 44, Cherry, Stewart, and Mann,
1970) is caused chiefly by movement of saline water into the lake from Spring
Bayou through this subterranean connection.
The area is dotted with lakes and ponds of various sizes. Lake Tarpon is
the largest with a water surface of about 4 sq mi (square miles). The larger lakes
are clustered in three distinct groups: (1) those trending northward along the
hills west and northwest of Safety Harbor including Lake Tarpon; (2) those in
the central part including Keystone Lake and Lake Rogers; (3) and those
trending northward along the low sandy ridge of the eastern drainage divide,
including Lakes Magdalene and Carroll.






BUREAU OF GEOLOGY


useful data in evaluating the hydraulic characteristics of the aquifer and related
confining beds in the bay area.
Samples were collected from streams, wells, and the bay for chemical
analysis. Traverses were made periodically in the bay under differing hydrologic
conditions. During these traverses, water samples were collected in order to
detect possible variations in salinity and areas of possible inflow from submarine
springs.



ACKNOWLEDGMENTS

Excellent cooperation was received from city and county officials,
industry, and local residents during this investigation. Special acknowledgments
are given the Florida Department of Transportation, and Hillsborough and
Pinellas Counties, for permission to drill and maintain test wells on public lands,
and to the Florida Bureau of Geology and the Southwest Florida Water
Management District for information provided the author. Appreciation is also
expressed to J. S. Rosenshein and Gilbert H. Hughes of the Geological Survey
for their extensive revision, and technical and editorial review of the manuscript.
Work on the investigation was performed under the direction of C. S. Conover,
district chief for Florida, and under the immediate supervision of J. W. Stewart
and J. S. Rosenshein.



PREVIOUS INVESTIGATIONS

A report by Matson and Sanford (1913) contains the earliest known
published information on the hydrology and geology of this part of Old Tampa
Bay. Sellards and Gunter (1913) discussed artesian flow.
Reports by Collins and Howard (1928) and Black and Brown (1951)
included some information on the quality of water. Stringfield (1933, p. 13-17)
presented a generalized description of the hydrology and geology of Pinellas and
northwestern Hillsborough Counties.
The geologic features of the Tampa Bay area are described by Cooke
(1945). A report by Ferguson and others (1947, p. 137) describes one of the
larger springs in upper Old Tampa Bay. Heath and Smith (1954) described the
hydrology and geology of the study area in Pinellas County. Reynolds, Smith,
and Hills, Architects and Engineers, prepared a feasibility report in 1959 for the
Hillsborough-Pinellas County committee studying the proposed freshening
project. A report by Menke, Meredith, and Wetterhall (1961) describes the






INFORMATION CIRCULAR NO. 76


hydrology of the Tampa Bay area in Hillsborough County. A report to the
Hillsborough-Pinellas County committee by Reynolds, Smith, and Hills, in 1963,
considered the engineering feasibility of the freshening project. A 1965 report
by Black, Crow, and Eidsness, Consulting Engineers to the Board of County
Commissioners, Pinellas County, reviewed the proposed freshening project.




DESCRIPTION OF THE SURROUNDING AREA

Tampa Bay is in about the middle of the west side of the Florida peninsula
(fig. 1) and is open to the Gulf. It is surrounded on three sides by the Tampa-St.
Petersburg metropolitan area. The bay is one of the largest along Florida's many
miles of coastline. Tampa Bay is divided into an eastern and western embayment
by the interbay peninsula on which part of the city of Tampa is located. The
eastern part is known as Hillsborough Bay and the western part as Old Tampa
Bay. The northern part of Old Tampa Bay, north of Courtney Campbell
Causeway, is known locally as upper Old Tampa Bay. This northern part has
been proposed for conversion to a fresh-water lake.



TOPOGRAPHY AND DRAINAGE

The Tampa Bay area is in the Coastal Lowlands topographic region of
Florida as defined by Cooke (1945, p. 8). Altitudes range from sea level to about
100 feet along the western drainage divide just northwest of Safety Harbor (fig.
3). A hilly area extends northward from Safety Harbor to Lake Tarpon.
Interspersed among these hills are numerous sinkholes, the most well known of
which is on the northwest shore of Lake Tarpon and has a subterranean
connection with Spring Bayou at Tarpon Springs (Heath and Smith, 1954). The
high mineral content of Lake Tarpon (fig. 21, p. 44, Cherry, Stewart, and Mann,
1970) is caused chiefly by movement of saline water into the lake from Spring
Bayou through this subterranean connection.
The area is dotted with lakes and ponds of various sizes. Lake Tarpon is
the largest with a water surface of about 4 sq mi (square miles). The larger lakes
are clustered in three distinct groups: (1) those trending northward along the
hills west and northwest of Safety Harbor including Lake Tarpon; (2) those in
the central part including Keystone Lake and Lake Rogers; (3) and those
trending northward along the low sandy ridge of the eastern drainage divide,
including Lakes Magdalene and Carroll.











































Figure 3.-Map showing topography of the upper Old Tampa Bay area, Florida.


2 6018 0"


82025






INFORMATION CIRCULAR NO. 76


Drainage areas of streams range from 10 to 45 sq mi. Most of the land is
relatively flat-lying, and channel slopes are mild. Channels are poorly developed,
and stream courses are well defined only for short reaches. The larger streams,
except Alligator and Brooker Creeks, are open to the bay, and their flow is
affected by tidal fluctuation near their mouths.




CULTURE AND DEVELOPMENT

The study area is sparsely populated except adjacent to the bay and
around the larger lakes, where property is in demand for residential develop-
ment. The many lakes and the bay provide fishing, boating, skiing, and
swimming. Most of the land outside the residential areas is used for cattle
ranching, dairying and citrus farming.
Many current (1970) developments involving water resources in the bay
area will cause some alteration in the runoff pattern and possibly affect the
hydrologic regimen of the bay. The Soil Conservation Service, in conjunction
with local conservation districts, has two watershed projects (fig. 4) in planning
stages or under construction: the Upper Tampa Bay Watershed Project and the
Brooker Creek Watershed Project. Together, the project areas include most of
the 190-sq-mi drainage area of the bay. The Rocky Creek bypass channel
(channel G), which will carry floodwater around the community of Rocky
Creek, has been completed.
The outfall canal for Lake Tarpon has also been completed as a part of the
Four River Basins Project of the Corps of Engineers. This canal and structures,
along with a gated cofferdam around a sinkhole in Lake Tarpon, is designed to
control the level of the lake. If the gated cofferdam is effective over a long
period of time, the movement of salt water from Spring Bayou through the
subterranean connection into Lake Tarpon will be stopped as well as the
unregulated discharge of Lake Tarpon into the sinkhole. Under these conditions,
Lake Tarpon will gradually freshen, thus augmenting the available supply of
water for freshening the proposed bay lake by diversion of Lake Tarpon by way
of the outfall canal into upper Old Tampa Bay.
Land development is also changing the runoff pattern. New residential
subdivisions, with homes fronting on canals, are continually being built around
the bay. The extensive dredging and filling associated with the building is not
only changing the runoff pattern but in some places is increasing the natural
discharge from the shallow water table and the deeper limestone aquifers where
both are breached by canals. This increased discharge also results in lower water
levels in the aquifers adjacent to the canals.





20012' 30"
0 1 MILES


PAS O C



PRIG
Lk ITRU PEUTZ

'cou Tlp EXPLANATION
Sinkhole 6els Lake
10 LO k0 Lake Tarpon Water




I:Brooker Creok Water-
U) ITRUS PAR LoeA Movdeld shed Project

L .o kn hundary of study ar t.

OS/ t Gor Lake ,,..



S DUNEDIN I OLS



2800'- SAFETY Pot






200 0'' 30S 822T,

Figure 4.- Map showing Lake Tarpon Water Control Project, Upper Tampa Bay Watershed Project, and Brooker Creek
Watershed Project.
Vkdr
2 7 57' 30 82050' So 30' 82025
Fiur 4- apshwig ak aronWaerCotrl roetUperTapaBa WteshdPrjetan BooerCre
Watershed Project.-"'~' AC;C/~////N,~MA





INFORMATION CIRCULAR NO. 76


CLIMATE

The climate of this part of Florida is subtropical, and the prevailing
westerly winds moving across the Gulf have a cooling effect on the land areas in
the summer and a warming effect in winter.
The average annual rainfall is about 52 inches with 60 percent occurring
from June through September (fig. 5). Usually the driest month is November
and the wettest is July. Thundershowers during the spring and summer months
cause intense rainfall on small areas for short periods. Really extensive heavy
rainfalls are associated with (1) low-pressure cells that either move slowly or that
stall over the area and (2) tropical storms that generally occur in the early fall.
The average annual evaporation from open-water bodies is nearly equal to
the average annual rainfall. Based on pan evaporation data at Bay Lake near
Sulphur Springs and a pan coefficient of 0.8, the average annual evaporation
from open-water bodies in the Tampa Bay area is estimated to be 50 inches. This
evaporation varies seasonally from about 2 inches in January to about 6 inches
in May (fig. 5). In a given year, the evaporation may be greater or less than the
annual precipitation.
The average daily maximum temperature ranges from 70F to 90F and the
minimum temperature from 50F to 72F.



GEOLOGY

The report area is covered by surficial deposits of sand, silt, and clay.
Underlying these deposits is a thick sequence of marine limestones. In much of
the upper Old Tampa Bay area, clay of the Hawthorn Formation, which contains
thin discontinuous beds of sandy limestone, underlies the surficial deposits and
overlies the limestone of the Tampa and older formations. The lithologic
characteristics of the rock units in the upper 1,000 feet are summarized in table
1. The aquifer unit to which each formation is referred is also indicated in this
table.
The Tampa Formation is the first continuous limestone unit of the
Floridan aquifer underlying the area. Its contact with both the Hawthorn
Formation and the undifferentiated sand, silt, and clay is unconformable.
In adjacent wells, the top of the Tampa Formation can differ as much as
30 feet, and, therefore, is not easily mapped. However, a generalized
configuration of this surface is shown in figure 6 and is taken in part from
unpublished interpretive maps furnished by R. N. Cherry and J. W. Stewart of
the Geological Survey.
The Tampa Formation lies unconformably on the Suwannee Limestone




'TLle It Geolo lic formations in the Upper Old 'Tamp lay area, Ilorlda
System Series Iormnulion1 Approx- Lllh logy Aqulifer
inuto
thick-
ness (ft)


0-90


100-150


Sand and shell; alternating with clay,
blue-gray, and clay, gray-green, sandy,
caldreous, phosphatic; interbedded
with layers of limestone, gray, white,
and tan, sandy, phosphatic.


Limestone, white to gray, sandy;
locally crystalline; contains dolo-
mitic and silicified layers.


Suwannee Limestone, cream to tan, thin-bedded
Oligocene Limestone 250-300 fine-grained, dense, hard.


0-300


Coquina, white to cream, soft,
massive, with pasty calcite
matrix.


Coquina, cream-colored, or limestone,
Williston cream to tan, detrital;-loosely
Formation 30-50 cemented calcareous matrix; locally
silicified.


50-150


300-500



200-600


Limestone, cream to tan, granular,
porous, medium-hard, massive; dolomite,
locally tan to brown, near base.


Limestone, white to tan, soft, chalky,
granular; dolomite, tan to brown, hard,
crystalline

Limestone, tan to cream, soft, granular,
pasty; locally interbedded with layers
of dolomite and bentonitic clay; some
eYvSUm.


1Nomenclature conforms to that of the Bureau of Geology,
2Designated surficial deposits in this report


Shallow


Floridan


Florida Department of Natural Resources


Holocene
Pleistocene

Pliocene


Miocene


Quarter-
nary


Tertiary


Undifer-
entiated 2

Hawthorn
Formation


Tampa
Formation


Crystal
River
Formation


Inglis
Formation


Avon Park
Limestone



Lake City
Limestone


-


-







INFORMATION CIRCULAR NO.76 13


Figure 5.-Mean monthly rainfall evaporation, and runoff, 1953-66.


EVAPORATION, BAY LAKE
NEAR SULPHUR SPRINGS-
-
Adjusted to represent evoporotion
from an open body of water
( pan coefficient 0.8)




'I',hle I.- (Geaatnibgd rrrni'iallmia i otOtt I hinior Old TIallnn a I~v urira. IPhiride.


UI*l2' 30"
0 I 2 MILES


S CO CO

10

TARPON LUTZ

cs. so\ EXPLANATION
omwrn -40 f
tLak STRUCTURE CONTOUR
Z shoewm aIlsltude of teop of first ee-
0 at Lo 0fet. Matum Is mean s,,


4 oLA IonAderl of study area

I US IT US PA 0 MO


SC)


as rel@ .40







L *a ROR UPPER





S 82550' 40' 30' 82025'

Figure 6.-Map of the upper Old Tampa Bay area showing generalized contours on the top of the first
continuous limstone (Tampa Formation) of the Floridan aquifer.






INFORMATION CIRCULAR NO. 76


(Cooke, 1945, p. 145). The Suwannee Limestone is a hard generally fossiliferous
limestone, whereas the Tampa Formation is a hard sandy limestone. The
Suwannee Limestone is highly permeable and a good source of water. Most wells
of large yield in the area tap both the Tampa Formation and Suwannee
Limestone. Although the rock units below these formations generally contain
highly permeable zones-the Avon Park Limestone in particular-the water in
these deeper zones is highly mineralized. Therefore, these zones are not tapped
for potable water supplies.



HYDROLOGY

The hydrologic phase of the study of upper Old Tampa Bay is concerned
chiefly with two principal aspects: (1) the rate and degree of freshening, which is
a function of rainfall on the bay, evaporation from the bay, inflow to the bay,
and discharge from the bay; and (2) the effects of freshening upon the
fresh-water aquifer system, which are dependent on the degree of hydraulic
interconnection between the bay and the aquifers.



RUNOFF TO THE PROPOSED LAKE

The most important factor relative to the rate of freshening is adequacy of
inflow. Inflow to the proposed lake is derived chiefly from runoff from a
drainage area of 190 sq mi. The major streams contributing inflow are
Sweetwater Creek, Rocky Creek, Double Branch, Alligator Creek, and Brooker
Creek by way of the outfall canal from Lake Tarpon (fig. 4). Rocky Creek is the
only perennial stream within the drainage area of the proposed lake. Sweetwater,
Brooker, and Alligator creeks ceased to flow for 3 to 4 months each year during
the extreme drought of 1955-56.
Analyses of inflow to the upper bay were made, both including and
excluding runoff from the Lake Tarpon-Brooker Creek watershed. If the
cofferdam does not effectively close Lake Tarpon's underground connection
with Spring Bayou, a salt-water body, a control structure could be placed in the
Lake Tarpon outfall canal. This structure should prevent saline water in Lake
Tarpon from discharging into the proposed fresh-water lake. Therefore, runoff
from the Lake Tarpon-Brooker Creek watershed would not be available to the
proposed lake. However, if closure is effective and Lake Tarpon becomes
permanently fresh, this watershed would be a source of runoff for the proposed
lake.






BUREAU OF GEOLOGY


A 17-year period, calendar years 1950-66, inclusive, was chosen for
computing average runoff to the lake. This period included the most severe
drought of record, 1955-56, and the wettest 2 years of record, 1959-60. Average
annual rainfall during the 17-year period was 53 inches, 1 inch more than the
long-term average annual rainfall in the area. Thus runoff during the chosen
period was probably not greatly different from average runoff for a longer
period.
Runoff from the entire contributing area of 190 sq mi for the 17-year
period was estimated by averaging runoff at gages on Sweetwater, Rocky,
Alligator, and Brooker creeks and applying the average runoff per square mile to
the entire area. The average runoff from the gaged area of 80.4 sq mi for the
17-year period was 56 mgd (million gallons per day) and the average runoff from
the 190 sq mi, 130 mgd. During this same period, the average annual rainfall (R)
on the proposed lake and Lake Tarpon exceeded the estimated average rate of
evaporation (E) from both lake surfaces by 4 mgd (R E= 4 mgd), thereby
making a total of 134 mgd available on the average for freshening the proposed
lake.
Figure 7 provides a graphical comparison of the cumulative total rainfall
and evaporation for an open body of water in the bay area and the cumulative
total inflow into the proposed lake for the 17-year period 1950-66. The inflow
shown includes runoff from Lake Tarpon and Brooker Creek.



INFLOW DURING AVERAGE AND ABOVE-AVERAGE CONDITIONS
Inflow, including runoff from Lake Tarpon and Brooker Creek:-At the
normal operating level of 2.5 feet above msl, the volume of the proposed lake
would be about 87,000 acre-feet and the average depth 8.5 feet. Therefore, an
average inflow of 134 mgd (150,000 acre-feet per year) would be sufficient to
displace the volume of water in the lake 1.7 times each year.
The maximum annual runoff for the 17-year period was in 1959. The
runoff was estimated to average 476 mgd. With the gain from the rainfall minus
evaporation (R E) for 1959, average inflow would be 513 mgd (570,000
acre-feet per year). This rate of inflow would be sufficient to displace the
volume of water in the proposed lake 6.5 times.
Inflow excluding runoff from Lake Tarpon and Brooker Creek:-Inflow
from the Lake Tarpon-Brooker Creek watershed averaged 40 mgd during the
17-year period and 114 mgd during the maximum year (1959). With this runoff
excluded, inflow (runoff plus rainfall minus evaporation) would be as follows:
Maximum year (1959) 362 mgd
Average year 94 mgd
An average annual inflow of 94 mgd (105,000 acre-feet per year) would be















3200


I I I I I I TI I I I I T


2800)-


I-
LiJ
LL 2400


S0W
S 2000
I-





h-
S0 1600



2 1200


0
$ 800



400



0


I
'f



<*



-


INFLOW







/
/ ,


9-0


wo
-9 -


/ RAINFALL
- \ _





,I .." EVAPORATION

I f I I I I I I I I I


0 N
0 1t) t)


M, It to t- (D
ID in M0 U) W)


M0 N0 in
UM (0 W0 10 to


SFigure 7.-Cumulative total rainfall on, evaporation from, and inflow to proposed fresh-water lake including
Lake Tarpon-Brooker Creek watershed.


~1 -I 1 I


-


>.
m





BUREAU OF GEOLOGY


sufficient to displace the volume of water in the lake 1.2 times per year-4.5
times during a maximum year.



INFLOW DURING A CRITICALLY DRY YEAR
The most critical year for inflow in the 17-year period was 1956, when
runoff averaged only 14 mgd. In order to determine the minimum lake level
likely to be reached during such a critical year, monthly inflow (runoff + rainfall
- evaporation) for 1956 was mathematically routed through the proposed lake.
The lake was assumed to be initially at the normal operating level (2.5 feet above
msl). All inflow in excess of that required to hold the pool at this level was
assumed to be discharged.
With the inflow from Lake Tarpon-Brooker Creek watershed included in
the total inflow, the minimum level reached during the critical drought year was
0.5 foot below the minimum design level (1.5 feet above msl). With inflow from
this watershed excluded from the total inflow, the minimum lake level reached
was 0.25 foot below the minimum design level. This difference in minimum lake
levels is caused by several factors. Inflow to Lake Tarpon from Brooker Creek
ceased during March through July 1956, while the proposed lake received
appreciable inflow from Rocky Creek, which did not go dry. During these
months, Lake Tarpon and the proposed lake would have tended to stabilize at
about the same level. As a result, water supplied by Rocky Creek would be
distributed over the area of both lakes rather than the area of the proposed lake
alone causing a lower minimum level to be reached when the total inflow
included that from the Lake Tarpon-Brooker Creek watershed.
If a control structure were to be installed in the outfall canal that connects
the proposed lake to Lake Tarpon, water from Rocky Creek could be
constricted during droughts to the area of the proposed lake. With such a
provision, inflow from Lake Tarpon-Brooker Creek watershed could be used
beneficially to freshen the proposed lake without adverse effects during unusual
droughts.
The preceding analysis of minimum water-level elevations in the proposed
lake does not take into account losses by operation of the locks. Some
fresh-water losses occur as a result of lock operations. However, when these
losses are placed in hydrologic perspective, they are minor. Plans for existing and
anticipated navigation requirements call for two locks (Reynolds, Smith, and
Hills, December 1963). The larger lock, 350 feet long, 56 feet wide, and 15 feet
deep, would pass tugs and oil barges supplying the power plant at Booth Point.
To conserve fresh water, a smaller lock would be provided for pleasure craft.
This lock would have a chamber 65 feet long, 15 feet wide, and 8 feet deep.
The capacity of the larger lock is 294,000 cu ft (cubic feet). One-tenth of





INFORMATION CIRCULAR NO. 76


a foot of water from the lake surface (47,500,000 cu ft) would supply water for
160 lockages. Oil barges make about 25 trips per year. Assuming that fresh water
would be discharged on downstream lockages only, 135 lockages through the
large lock could be utilized for pleasure craft. The smaller lock has a capacity of
7,800 cu ft; and 135 lockages through the large lock would be equivalent to
5,100 lockages through the small lock. The small lock could accommodate
several pleasure craft at each lockage. With the boat lifts and marine railway to
permit passage of small pleasure craft without loss of fresh water, this number of
lockages should more than satisfy navigation needs for the bay area. If Lake
Tarpon is connected to the upper bay, additional surface area would be
available, and 200 lockages through the large locks would use only 0.1 foot of
water.




CHEMICAL CHARACTERISTICS OF SURFACE WATER

The chemical quality of streamflow discharging into the proposed lake is
generally good excluding consideration of the nutrient and biochemical content
which were not determined during this investigation. The mineral content of
samples collected above tidewater average less than 100 mg/1 (milligrams per
liter) and the chloride content about 20 mg/1. Both the mineral and chloride
contents vary seasonally according to flow conditions because the streamflow is
more highly mineralized during periods of low flow, when discharge is derived
chiefly from the ground-water reservoir, than during periods of high flow, when
the discharge is derived chiefly from runoff. These seasonal relations between
discharge and water quality are illustrated on figure 8. The data shown on figure
8 are for samples collected at a site above tidal influence, and the chemical
quality is representative of runoff from the entire area contributing to the
proposed lake.
The variation in specific conductance in figure 8 reflects the variation in
mineral content, and the actual mineral content (in milligrams per liter) is
equivalent numerically to about 55 percent of the specific conductance (in
micromhos).
The results of the salinity traverses across upper Old Tampa Bay (fig. 9)
indicate that in a large part of the bay the chloride concentration did not differ
from the average chloride concentration of the bay (average of all samples) by
more than 10 percent. Neither did the maximum and minimum chloride
concentrations at any specified sampling point differ from each other by more
than 10 percent. The differences in the concentration of chloride at each
sampling point for those samples collected from both the top and the bottom of
the bay were generally in the range of normal error in laboratory work,







g480
ovft

400 -40
W
f 0\
02 z

0 U
Wd W
Z 300 -30
0 SPECIFIC
CONDUCTANCE w
oo U
L) #I-





w
S- I DISCHARGE
\ / \5












1966 967 1968
Figure 8.-Relations between specific conductance and discharge of Sweetwater Creek near Sulphur Springs.
(n 0




i O N D J F M A M J 'J A S O N D J F M A M J J A S O

1966 1967 1968
Figure 8.-Relations between specific conductance and discharge of Sweetwater Creek near Sulphur Springs.




















EXPLANATION
-Avrogi, top and bottom samples C(0ol 0, 1967)


AagoaeifIop and bottom eamplas CaNov 30s, 19)
h'SampIlng point, illlnlly travert
-Avmrog, top and bottom samples (June 8, 1907)
i~~ .nt a lop ad ample (No 7, 1967) )
1 Smpllng point, lallnlly traverse
'* Aeroageltop and bottom ismples (June 0, 1967)
Inlagraled sample (Nov 7, 1967)
lgSampling point, isllnlt Iraverse
'vLireor, lop and bottom iomple (Juno a, li67)
,, ,-InlOircld lmplo (Nov 7i, I71)
i,'f,,, Sampllng polnl, Hllnlly trovler
'-Inlteroatd simple (June 8, 1917)
-i0 # Tilt wall. Number 'Is depthin fell,from which
eIdlmnl sample (Tablet ) was eollolted
for analysis
CS& Chloilde conlentrallon,
1,000 mtllllgiam per ller n? -


0 I MILE
I I


Figure 9.-Chloride concentrations at sites sampled in upper Old Tampa Bay and location of auger holes.






BUREAU OF GEOLOGY


regardless of whether the samples were collected from either the shallow part
(less than 6 feet deep) or the deep part (6 to 12 feet) of the bay. This lack of
significant vertical differences in chloride concentration indicates that current
movement and wind action is generally sufficient to keep the water in the bay
well mixed except in the vicinity of the mouths of the larger creeks during short
periods of high streamflow.
Samples of water were collected on July 12, 1965, from Mullet Creek near
Safety Harbor at both high and low tide. At that place the stream is affected by
tidal fluctuation. The range in concentration of chloride in milligrams per liter is
as follows:
7,000 (high-tide top).
13,000 (high-tide bottom).
5,800 (low-tide top).
9,200 (low-tide bottom).
The fresh-water discharge of Mullet Creek at the time of sampling in the stream
was about 10 cfs (cubic feet per second), estimated by comparison with
discharge of Alligator Creek near Safety Harbor. The difference in chloride
concentrations in top and bottom samples indicated that near points of
relatively large fresh-water inflow density separation does occur during the wet
season.
Chloride concentrations in the bay at Safety Harbor, where monitoring
was continuously carried out, ranged from 9,500 to 16,500 mg/1 during October
1966-September 1968. The maximum concentration occurred at the time of
minimum fresh-water inflow, and the minimum concentration occurred at the
time of maximum fresh-water inflow.


RATE OF FRESHENING

Factors that determine the rate of freshening in the proposed lake are: (1)
the rate and mineral concentration of inflow to the lake; (2) the degree of
mixing; (3) the original volume and mineral concentration of the water in the
proposed lake at the time of its separation from -Tampa Bay; and (4) the rate and
mineral concentration of discharge from the lake. To simplify the analyses
presented below the following assumptions were made: (1) lake level would be
at normal operating level (2.5 feet above msl) when closed; (2) at the time of
closure the average chloride concentration of water in the lake would be 14,000
mg/I; (3) the chloride concentration of the inflow water would be zero; (4) the
lake would be completely mixed at all times; and (5) inflow of saline water from
boat locks would not significantly affect the rate of freshening. The average
inflow has been established as sufficient to flush the proposed lake 1.7 times per
year with inflow, including that from Lake Tarpon-Brooker Creek watershed.





INFORMATION CIRCULAR NO. 76


a foot of water from the lake surface (47,500,000 cu ft) would supply water for
160 lockages. Oil barges make about 25 trips per year. Assuming that fresh water
would be discharged on downstream lockages only, 135 lockages through the
large lock could be utilized for pleasure craft. The smaller lock has a capacity of
7,800 cu ft; and 135 lockages through the large lock would be equivalent to
5,100 lockages through the small lock. The small lock could accommodate
several pleasure craft at each lockage. With the boat lifts and marine railway to
permit passage of small pleasure craft without loss of fresh water, this number of
lockages should more than satisfy navigation needs for the bay area. If Lake
Tarpon is connected to the upper bay, additional surface area would be
available, and 200 lockages through the large locks would use only 0.1 foot of
water.




CHEMICAL CHARACTERISTICS OF SURFACE WATER

The chemical quality of streamflow discharging into the proposed lake is
generally good excluding consideration of the nutrient and biochemical content
which were not determined during this investigation. The mineral content of
samples collected above tidewater average less than 100 mg/1 (milligrams per
liter) and the chloride content about 20 mg/1. Both the mineral and chloride
contents vary seasonally according to flow conditions because the streamflow is
more highly mineralized during periods of low flow, when discharge is derived
chiefly from the ground-water reservoir, than during periods of high flow, when
the discharge is derived chiefly from runoff. These seasonal relations between
discharge and water quality are illustrated on figure 8. The data shown on figure
8 are for samples collected at a site above tidal influence, and the chemical
quality is representative of runoff from the entire area contributing to the
proposed lake.
The variation in specific conductance in figure 8 reflects the variation in
mineral content, and the actual mineral content (in milligrams per liter) is
equivalent numerically to about 55 percent of the specific conductance (in
micromhos).
The results of the salinity traverses across upper Old Tampa Bay (fig. 9)
indicate that in a large part of the bay the chloride concentration did not differ
from the average chloride concentration of the bay (average of all samples) by
more than 10 percent. Neither did the maximum and minimum chloride
concentrations at any specified sampling point differ from each other by more
than 10 percent. The differences in the concentration of chloride at each
sampling point for those samples collected from both the top and the bottom of
the bay were generally in the range of normal error in laboratory work,







INFORMATION CIRCULAR NO. 76


1 )


14


.n .0
SX io-


z
WO \




0
z W
x 10 -CL



4-
J \

0 2250 mg/I
0
0 I 2 3 4 5
TIME YEARS
Figure 10.-Calculated rate of freshening of proposed lake by dilution.
(Includes inflow from Lake Tarpon-Brooker Creek watershed.)

Chloride concentration in the lake at the end of 1 year would be about 5,000
mg/1, and the dilution (freshening) would follow the relation shown in figure
10. Chloride concentrations would be less than 250 mg/1 in 3.5 to 4 years. If
mixing is not complete the denser salt or brackish water will tend to collect near
the bottom of the lake. To facilitate passing this water, spillways in the
engineering works have been designed for undergate discharge. Displacement of
saline water in this way would decrease the time required for freshening.
Documented information on rate of freshening of existing man-made
saline lakes in Florida has been published in two reports. Musgrove, Foster, and
Toler (1965, p. 45 and fig. 27, p. 46) showed that the chloride concentration of
Deer Point Lake in northwestern Florida decreased from 3,700 mg/1 to less than
250 mg/1 in about 4 months after flow over the spillway began. This reduction
occurred after the initial volume of the lake had been replaced about four times
by fresh-water inflow. Cherry, Stewart, and Mann (1970, p. 38) showed that the
chloride concentration in Seminole Lake in Pinellas County decreased from
2,300 mg/1 in 1950 to less than 250 mg/1 in 1957. Within 2 years after
completion of the dam that created the lake, the chloride concentration was
lowered to less than 250 mg/1 for extended periods. This concentration has
remained continuously less than 250 mg/1 since 1957. Although the hydrologic
setting, volumes of inflow, and initial chloride concentrations of these lakes
differ from those of the proposed lake, the foregoing information indicates that






BUREAU OF GEOLOGY


the calculated rate of freshening of the proposed lake is reasonable. The
information, particularly with respect to Deer Point Lake, indicates that
freshening of the proposed lake would occur chiefly by dilution after initial
displacement of some saline water by undergate flow.
The time required for freshening would be considerably shorter if the
suggested level of salinity for maintaining feeding areas for key water fowl were
generally acceptable. The Florida Game and Fresh Water Fish Commission has
suggested that a chloride concentration of 1,000 mg/1 be maintained in a large
part of the proposed lake to sustain growth of widgeon grass. The Commission
indicates that this level of salinity could be tolerated by fresh-water fish.
Adoption of this suggestion would necessitate the mixing of saline water from
the bay with the fresh-water inflow.





GROUND WATER

SHALLOW AQUIFER
A water-table aquifer overlies the Floridan aquifer in most of the area and
includes the surficial sands and the upper part of the Hawthorn Formation
except where it has been removed by erosion. The thickness of the material
forming the shallow aquifer in the bay area can be estimated by comparing
elevations on the map (fig. 6) showing the top of the first consistent limestone
and the topographic map (fig. 3). This thickness ranges from 20 to 40 feet
southwest of Oldsmar to as much as 100 feet northwest of Oldsmar.
The depth to the water table averages less than 5 feet below land surface
throughout most of the area. This depth increases in several areas (fig. 2) where
large quantities of ground water are withdrawn from the underlying Floridan
aquifer for municipal supply. Near these well fields the water table lies as much
as 15 feet below the land surface.
The water table in the shallow aquifer slopes generally toward the bay, and
its elevation is highest along the ridge area west of Safety Harbor and in the
northeastern part of the study area. The natural seasonal fluctuation of the
water table generally ranges from 1 to 2 feet except during extremely wet or dry
years. Figure 11 shows the monthly range in water levels during 1965-68 in two
wells, one tapping the shallow aquifer and the other the Floridan aquifer; both
of which are at the same site near the northeastern edge of the study area.
Although water levels in wells in the immediate vicinity of the bay are affected
by tidal fluctuations, seasonal water-level fluctuations in these wells follow the
same general pattern as observed in those inland.






INFORMATION CIRCULAR NO. 76



WELL, 807-229-141A
DEPTH, 22 FEET
SCREENED, 18-21 FEET


AQUIFER, WATER


TABLE


1965 1966 1967 1968


WELL, 806-229-121A
DEPTH, 134 FEET
CASED, 44 FEET


AQUIFER,
50



40 -


FLORIDAN


1965 1966 1967 1968


Figure 11.-Maximum and minimum monthly water levels in a shallow and a
deep well near the northeast edge of the study area.






BUREAU OF GEOLOGY


Chemical character of water in the shallow aquifer.-In most of the area
water from the shallow aquifer is of suitable quality for domestic and municipal
supplies although high iron content is a local problem. Because of its low
permeability, no public water suppliers derive their water from this aquifer. In
the area immediately adjacent to the bay, water from the shallow aquifer is
generally high in chloride, about 7,000 mg/1, and in dissolved solids. The water
in the aquifer is generally saline where (1) the land surface is subject to some
tidal flooding and (2) the fresh-water head in the aquifer is generally less than 1
foot above mean sea level.



FLORIDAN AQUIFER
The Floridan aquifer, the major aquifer underlying the bay and adjacent
area, is not everywhere under artesian or confined conditions. The overlying clay
of the Hawthorn Formation together with clay beds in the surficial deposits
form a relatively impermeable but leaky confining layer. In much of the area
adjacent to the bay, this clay is absent either as result of nondeposition or
removal by erosion or having been breached by sinkholes. In these areas the
Floridan aquifer is under water-table conditions. These conditions may change
from chiefly water table to chiefly artesian in areas a few miles apart, depending
on the presence or absence of the confining layer.
The potentiometric surface of the Floridan aquifer slopes generally toward
the bay in Hillsborough and Pinellas Counties, as shown in figure 12. The
altitude of this surface is less than the altitude of the water table in the shallow
aquifer in the northeastern part of the drainage area. In some areas adjacent to
the bay, the potentiometric surface is above land surface, and wells that tap the
Floridan aquifer flow.
The trough in the potentiometric surface in the vicinity of Oldsmar is
caused by natural discharge of water by seepage from the Floridan aquifer to the
bay. The location of the zero-potential contour is inferred. This contour
delineates the boundary of the area of natural fresh-water discharge from the
aquifer. Bayward from the zero-potential contour, the aquifer contains saline
water.
The position of the zero contour on the potentiometric surface is not a
fixed one. The contour moves bayward during wet periods and landward during
dry periods. Fluctuation of the position of zero contour is indicated by
fluctuation of water levels (fig. 13) in a deep observation well (800-239-334) on
Booth Point that taps the Floridan aquifer. In September 1967, the average
water level in the deep well was 1.5 feet above msl. In September 1968, its
average water level was about mean sea level. Thus, at this well the head in the
Floridan aquifer fluctuated from 0.5 foot below msl to 2.5 feet above msl during




28012'


o LP keR L' oe Ii Arena of artleson flow
O f 0 ...
SSt.Petersburg. POTENTIOMETRIC CONTOUR
S St. Petrsburg l D Section 21 Sow ollitud of potenlometric
x V t i\ Cosine bb- ( well field surfaoce;doahed where inferred.. >
i \* i / /(95 w ell n 7 "1 . C ontour interval IO f e t wt h upp-
4.1 lk \ i am$ I,, -.- m contour at 5 fet. ct
o 0 Ro9, i. mean sea level O

SC sTRUS at oPAR 10*0
,4 U) sa Lake














2800' RBOR UPPER OLD30 8225
J A-/-C-o TAMP


George Lake Carll t_4







27a 2o7' W30 t50 >








Figure 12.- Map of the upper Old Tampa Bay area showing generalized configuration of the potentiometric surface of the
Floridan aquifer and the area of artesian flow, August-November, 1967.
Floridan aquifer and the area of artesian flow, August-November, 1967.







28 BUREAU OF GEOLOGY



the investigation, indicating that the position of the zero-potential contour was
at times inland from the well.


FLUCTUATIONS OF THE POTENTIOMETRIC SURFACE
Water levels in the Floridan aquifer fluctuate seasonally less than 5 feet in
coastal areas and 10 feet in inland areas. This general range in fluctuation may be


1.0




05



SEA
LEVEL



05




1.0




2.5




2.0




1.5




1.0


September 26, 1968 27


Figure 13.-Water-level fluctuations in a deep observation well on Booth
Point that taps the upper part of the Floridan aquifer.






BUREAU OF GEOLOGY


the calculated rate of freshening of the proposed lake is reasonable. The
information, particularly with respect to Deer Point Lake, indicates that
freshening of the proposed lake would occur chiefly by dilution after initial
displacement of some saline water by undergate flow.
The time required for freshening would be considerably shorter if the
suggested level of salinity for maintaining feeding areas for key water fowl were
generally acceptable. The Florida Game and Fresh Water Fish Commission has
suggested that a chloride concentration of 1,000 mg/1 be maintained in a large
part of the proposed lake to sustain growth of widgeon grass. The Commission
indicates that this level of salinity could be tolerated by fresh-water fish.
Adoption of this suggestion would necessitate the mixing of saline water from
the bay with the fresh-water inflow.





GROUND WATER

SHALLOW AQUIFER
A water-table aquifer overlies the Floridan aquifer in most of the area and
includes the surficial sands and the upper part of the Hawthorn Formation
except where it has been removed by erosion. The thickness of the material
forming the shallow aquifer in the bay area can be estimated by comparing
elevations on the map (fig. 6) showing the top of the first consistent limestone
and the topographic map (fig. 3). This thickness ranges from 20 to 40 feet
southwest of Oldsmar to as much as 100 feet northwest of Oldsmar.
The depth to the water table averages less than 5 feet below land surface
throughout most of the area. This depth increases in several areas (fig. 2) where
large quantities of ground water are withdrawn from the underlying Floridan
aquifer for municipal supply. Near these well fields the water table lies as much
as 15 feet below the land surface.
The water table in the shallow aquifer slopes generally toward the bay, and
its elevation is highest along the ridge area west of Safety Harbor and in the
northeastern part of the study area. The natural seasonal fluctuation of the
water table generally ranges from 1 to 2 feet except during extremely wet or dry
years. Figure 11 shows the monthly range in water levels during 1965-68 in two
wells, one tapping the shallow aquifer and the other the Floridan aquifer; both
of which are at the same site near the northeastern edge of the study area.
Although water levels in wells in the immediate vicinity of the bay are affected
by tidal fluctuations, seasonal water-level fluctuations in these wells follow the
same general pattern as observed in those inland.






INFORMATION CIRCULAR NO. 76


exceeded during extreme wet or dry years or in areas of large ground-water
withdrawal. The fluctuation of water levels in 1965-68 in an observation well
that taps the Floridan aquifer is shown in figure 11. This well is south of Lutz
and lies just outside the northeast edge of the area (fig. 2).

CHEMICAL CHARACTER OF THE WATER
Water of good quality is obtained from the upper part of the Floridan
aquifer (Tampa and Suwannee Limestones) by municipal well fields in northwest
Hillsborough and northeast Pinellas Counties. Downgradient from the well fields,
water containing a high chloride concentration occurs at relatively shallow
depths in the upper part of the aquifer (Cherry, 1966 and Shattles, 1965). Both
the altitude of the potentiometric surface and the thickness of the fresh-water
section in the aquifer decrease bayward. This saline water at shallow depths in
the upper part of the aquifer has resulted in wells being abandoned in the
Oldsmar area and in the west-central part of Tampa owing to lowering of
fresh-water levels by pumping, thereby permitting upward movement of saline
water in the aquifer into the wells. The chloride concentration in the upper part
of the aquifer (Tampa and Suwanee Limestones) exceeds 1,000 mg/1 adjacent to
the bay, and the concentration probably increases markedly bayward of the
zero-contour on the potentiometric surface, as indicated by data collected from
the observation well (800-239-332) at Booth Point. Water samples collected
from the well contained chloride concentrations of 18,000 mg/1 when the zero
contour was inland from the well and 7,000 mg/1 when the contour was
bayward from the well.

RECHARGE AND DISCHARGE
The Floridan aquifer is recharged by percolation of rainfall through the
overlying sediments and from ground-water inflow from adjacent areas (Stewart,
1968, p. 206-209). The aquifer is discharged along stream channels where the
channel bottom intersects the aquifer, in the area of artesian flow around the
northern and northeastern parts of the bay (fig. 12), and in areas where canals
have cut into the aquifer.
Pumping tests in the area just west of Safety Harbor and in the well fields
in northwestern Hillsborough County indicate that the Floridan aquifer
underlying the study area has a transmissivity of about 400,000 gpd per ft
(gallons per day per foot). The gradient of the potentiometric surface averages
about 4 feet per mile immediately inland from the bay. Based on these figures,
about 32 mgd moves through the Floridan aquifer toward the bay. Much of this
32 mgd is discharged to streams that flow into the bay. Part of the ground-water
inflow to the bay occurs as seeps along the northwestern and western parts of
the bay. This amount will probably remain about the same even if the proposed
lake becomes a reality.





BUREAU OF GEOLOGY


HYDRAULIC INTERCONNECTION

Important aspects of the investigation involved the evaluation of the
effects of bay freshening upon: (1) the aquifer system beneath and adjacent to
the bay; (2) the part of the aquifer that contains salty water; and (3) the part of
the aquifer that contains fresh water.
Water levels in wells near tidal waters respond to changes in tide in
different ways, depending on whether the wells tap unconfined or confined
aquifers. In confined aquifers having an outcrop exposed to tidal bodies of
water, tidal waters may move into and out of the aquifers, depending on the
onshore head in the aquifers. Tidal fluctuations can also be transmitted to a
confined aquifer through its confining layer, as a pressure-loading response to
incoming or outgoing tides. As the tidal fluctuations increase, water-level
fluctuations in wells increase, whether the fluctuations are caused by tidal
loading or horizontal movement of water in an aquifer in response to the
introduction of tidal water. Therefore, the observed water-level response in wells
in itself is not evidence of either direct or a high degree of interconnection
between the Floridan aquifer and upper Old Tampa Bay.
The occurrence and wide distribution of natural fresh-water springs in the
bay would indicate a high degree of connection between the bay and the
Floridan aquifer. Prior to lowering of the head in the Floridan aquifer, springs
reportedly flowed around the bay, at places such as Phillippi Springs, at Safety
Harbor. However, this spring ceased to flow before 1959 (Wetterhall, 1965, p.
13). The famous Espiritu Santo mineral springs in Safety Harbor are reported to
have been points of natural discharge from the aquifer.
The springs did not flow in 1946 (Ferguson and others, 1947, p. 137).
Reportedly, spring zones were breached during the construction of several of the
subdivision canals in the area. However, salinity traverses did not indicate
fresh-water inflow to these canals. Spring zones were reportedly breached also in
the construction of the Lake Tarpon outfall canal. The bottom of the canal is
about at the elevation (15 feet below msl) of the top of the limestone of the
Floridan aquifer, and, during construction, the top of the limestone was
breached in places. Water is retained in this canal between earthen plugs that
prevent salt-water movement from Upper Tampa Bay to Lake Tarpon and the
reverse. In 1968 the water between the plugs was considerably fresher (chloride
content, 160 mg/1) than water in Lake Tarpon (chloride content, 6,000 mg/1)
or water in the Bay (chloride content, 15,000 mg/1). The large fresh-water
overflow from a culvert placed in the top of the plug on the bayward side
indicates that the upper part of the Floridan aquifer immediately below the
confining layer is highly permeable.
Clay beds in the Hawthorn Formation and in the surficial deposits act as a
confining layer for the Floridan aquifer. These clay beds extend beneath the bay













Table 2,-Results of sieve analysis of split-spoon samples collected from test wells augured in bay bottom
and along Courtney-Campbell Causeway
Well: See figure 10 for location. Interval sampled: Either in feet below water surface or land surface.


l Interval
el sampled


36-37.5
26-27.5
41-42.5
25-26.5
36-37.5
46-47.5
21-22.5
16-17.5

30-31.5


M 18-19.5
23-24.5
N 23-24.5
Q 38-39.5


Grain size (millimeters)
10 percentile 25 percentile Median 75 percentile


0.102
.072


0.125
.112


.004
.092

.122


0.010
.205
.155
.049


.010
.003


.082

.122
.155
.078
.195


0.175
.235
.215
.165
.011
.122
.155
.040

.135

.205
.205
.102
.235


Percent
Sand Silt and clay


43.8
94.0
91.4
45.8
15.8
32.6
34.6
16.6

55.3

65.4
76.4
57.4
84.0


56.2
5.8
8.6
54.2
81.9
67.4
64.2
76.5

44.5

34.6
21.6
42.6
16.0


Remarks

Well in bay.
Do.
Do.
Do.
Do.
Do.
Do.
Do.
Well on
causeway.
Well on
shore.
Do.
Do.
Do.






BUREAU OF GEOLOGY


VERTICAL EXAGGERATION ABOUT X200
For location of lines of section A-B-C-D
see figure 12

0 I 2 3 4 MILES
I I I I


Figure 14.-Generalized section showing geohydrology
Bay area.


of upper Old Tampa


and generally overlie the Floridan aquifer and underlie the silty or clayey fine to
medium sand that forms the bay bottom in many areas. Breaches in this
confining layer must occur offshore (fig. 14) in a manner similar to that in which
they occur onshore in the area adjacent to upper Old Tampa Bay, as indicated
by samples obtained from two test wells (B and C) drilled in the bay (table 2 and
fig. 9). In these two test wells, no clay beds were penetrated, and sand extended
from the bay bottom either to the top of the Tampa limestone (well B) or to the
bottom of the well (well C). Onshore breaches in the confining layer have been
reported by Heath and Smith (1954, p. 29) and Stewart (1968, p. 43). These
breaches allow direct interconnection between the shallow and deep aquifers and
probably represent areas underlain by relict sinkholes that have been filled with
permeable material. Aerial photographs of the upper Old Tampa Bay area show
that filled-in sinkholes do occur immediately adjacent to the bay; particularly in
the marshy area between Rocky and Double Branch Creeks. Some of these
sinkholes would probably be submerged by the proposed lake during high water
periods.


A
100' -


SEA
LEVEL





INFORMATION CIRCULAR NO. 76


The high degree of interconnection between the shallow aquifer and the
Floridan aquifer in the well field 6 to 8 miles northeast of the bay further
indicates that, at least locally, a good interconnection between the bay and the
Floridan aquifer can occur. The effectiveness of the confining layer in retarding
downward movement of water in the well fields is probably not greatly different
from that beneath the bay. However, the permeability of the bay sediments
themselves may markedly reduce the degree of interconnection; particularly
where the bay sediments are relatively impermeable and overlie areas where
breaches in the confining layer are filled with permeable sand. Laboratory
determinations of coefficient of permeabilities made on repacked core samples
of sediments underlying the bay indicate that the permeabilities range from less
than 0.001 gpd per square foot to more than 2 gpd per square foot. Although all
the samples were collected at depths greater than 10 feet below the bottom of
the bay, the range in permeabilities are representative of similar materials in the
upper part of the test wells. Based on these permeabilities, the initial rate of
recharge through the bay bottom to the Floridan aquifer at normal pool stage
(2.5 feet msl) of the proposed lake would range from 0.002 mgd to 4 mgd per
square mile of lake bottom and average less than 1.0 mgd. Based on the initial
average rate of leakage alone (1.0 mgd), at least 10 years would be required to
depress the fresh-water salt-water interface in the upper part of the Floridan
aquifer beneath the proposed lake to the hydrostatic position at which it should
stabilize, according to the Ghyben-Herzberg principle (100-120 feet below mean
sea level). However, these rates of leakage will decrease as the difference in head
between the Floridan aquifer and the proposed lake decreases. As a result,
depression of the interface to a stable hydrostatic position may take more than
20 years.
Historical information on springs associated with suboutcroppings of
limestone along the shoreline of part of the bay indicates that the bay and the
upper part of the Floridan aquifer are locally interconnected. These points of
local interconnection will have an undetermined effect on the rate of inflow of
water during freshening into the part of the aquifer beneath the bay as well as
that in the area immediately adjacent to the bay and may reduce somewhat the
time required for the hydrostatic position of the fresh-water salt-water interface
to stabilize in the aquifer.


EFFECTS OF FRESHENING ON THE AQUIFER SYSTEM

The water-table aquifer.-Construction of the dam across the south end of
the embayment would have relatively rapid effects on the water levels in
water-table wells in the surrounding area provided closure occurs during the
rainy season. Prior to closure of the dam, the gradient of the water table will be





BUREAU OF GEOLOGY


toward the lake. Upon closure, the lake and the water-table aquifer will respond
in a manner similar to that reported by Musgrove, Foster, and Toler (1965, p.
45) for Deer Point Lake in northwestern Florida. The level of the proposed lake
will rise in response to fresh-water inflow; the gradient from the aquifer to the
lake will be temporarily reversed; and water will move for an undetermined time
from the lake to the water-table aquifer. Saline water from the lake will invade
the aquifer, and chloride concentrations in the aquifer will increase for at least
several hundred feet inland. Saline water will remain in the aquifer until such
time that fresh-water levels in the water-table aquifer rise above the normal pool
stage of the lake. At this time, the water table will again slope toward the lake,
and water in the shallow aquifer will again discharge to the lake. In time, the
saline water will be flushed from the aquifer. The net result on the water table in
the immediate vicinity of the lake will be a rise equal to the rise in lake level.
The Floridan aquifer.-Upon closure of the dam, the level of the proposed
lake will rise in response to fresh-water inflow, and water will gradually move
from the lake into the Floridan aquifer. Initially this water will be highly saline.
After 2 to 3 years of fresh-water inflow, the water in the proposed lake will
become progressively fresher (fig. 10) than that in the Floridan aquifer beneath
the bay.
Because of the imperfect interconnection between the lake and the
aquifer, leakage to the aquifer will be greatest in those local areas where the lake
is underlain by breaches in the confining layer that are not covered by finer
grained bay sediments and where bedrock crops out in the proposed lake. The
effect of this leakage should first result in a gradual freshening of the water in
the upper part of the aquifer beneath the bay and immediately adjacent to the
bay. The gradual adjustment of the fresh-water salt-water interface in the aquifer
to the hydrostatic position at which it should stabilize (100-120 feet below msl)
may require more than 20 years.
Fresh water will move inland as the fresh-water head in the aquifer at the
shoreline gradually stabilizes at about 2.5 feet above mean sea level. The effects
of this movement will not greatly alter the existing balance between recharge
and discharge in the aquifer or the current gradient toward the bay until a
fresh-water head above msl is established along the bayward edge of the zero-
potential contour. At the time this occurs, the head in the aquifer will slowly
rise, resulting in a temporary imbalance in rates of discharge from and recharge
to the aquifer as water goes into storage. The fresh-water head in the aquifer will
continue to increase until the water level in the aquifer stabilizes at a new
gradient to the proposed lake, and a new local balance is established between
recharge and discharge. These readjustments will probably not markedly alter
the amount of discharge (p. 29) from the aquifer in the vicinity of the proposed
lake.
The greatest long-term change in water level in the aquifer will be within 1





INFORMATION CIRCULAR NO. 76


mile of the proposed lake (fig. 15). Where the zero potentiometric contour
presently occurs, the water level in the Floridan aquifer will rise 2 to 3 feet
above mean sea level, depending upon the inland position of the zero contour.
Inland from the edge of the bay, most of the water-level rise will occur within 3
to 4 miles of the shoreline. Farther inland the rise in water level in the aquifer
will be less than 1 foot.
The increase in the fresh-water head above mean sea level will cause the
fresh-water salt-water interface in the areas where the potentiometric surface is
currently at mean sea level to be depressed 100 to 120 feet below sea level. One
to two miles inland, the current position of the fresh-water salt-water interface
will generally be depressed less than 70 feet. Three to four miles inland the
change in the position of fresh-water salt-water interface will be less than 50
feet.
The displacement of the fresh-water salt-water interface will increase the
fresh-water supply that is available for development only in the immediate
vicinity of the bay, where wells requiring relatively small quantities of water
containing a low chloride concentration can tap the upper 60 to 80 feet of the
Floridan aquifer. However, careful control of pumping levels will be required in
these areas to prevent upward movement upcomingg) of saline water into the
wells as a result of decline in fresh-water head owing to local pumping.
Displacement of the interface will have minor effects with respect to controlling
upcoming of saline water as a result of pumping further inland because the
interface will not be depressed to the base of the permeable zone in the upper
part of the Floridan aquifer near the bay.



SUMMARY AND CONCLUSIONS

Adequate inflow of water of good quality is available to freshen the
proposed lake in a reasonable period (about 4 years). During an average year, the
inflow would be sufficient to displace the volume of the proposed lake 1.2 to 1.7
times, depending upon whether discharge from Lake Tarpon contributes to lake
inflow. During a critically dry year, such as 1956, inflow would not be adequate
to maintain lake levels at minimum design level, and the level of the proposed
lake would decline 0.25 to 0.50 feet below this desired low level. Loss of water
through boat lockages would not be sufficient to affect these lake levels
significantly during either average or critically dry periods.
An imperfect interconnection exists between upper Old Tampa Bay
(proposed lake) and the upper part of the Floridan aquifer. Leakage of fresh
water from the proposed lake to the Floridan aquifer will occur chiefly where
the confining layer is breached and where bedrock crops out in the proposed








88246' 40 8e33'
0 I I
seo0'



EXPLANATION
Upper part of Floridan Aquifer

Water. level rise estImated 2 to 3
feet. Estimated Increase in depth
below mean sea level to fresh-water-
salt-water Interface 80.120 feet

Water- level rise estimated I to 2 feet.
Estimated increase in depth below
mean sea level to fresh-water-salt.
water Interface 40 to 60 feet

Water- level rise estimated less than I
foot. Estimated Increase In depth below
mean sea level to fresh-water-salt-
water interface less than 40 feet
28000' ....
2...x:::::::::::::.


0 I 2 MILES
I I I

27057' 30"1





Figure 15.-Estimated long-term rise in fresh-water levels in the upper part of the Floridan aquifer as a
result of conversion of upper Old Tampa Bay into a fresh-water lake.






INFORMATION CIRCULAR NO. 76 37


lake. Upon closure of the dam this leakage should average initially less than 1
mgd per square mile of lake bottom and gradually decrease as the head
difference decreases with time. As a result, the gradual adjustment of the
fresh-water salt-water interface in the upper part of the Floridan aquifer to the
hydrostatic position at which it should stabilize beneath the lake (100-120 feet
below msl) may require more than 20 years.
The proposed lake will result in a rise in water levels in the shallow aquifer
in the immediate vicinity of the lake. The rise will be equal to the rise in lake
level. A comparable long-term rise will also occur in water levels in the upper
part of the Floridan aquifer. Within 1 mile of the proposed lake, water levels in
the Floridan aquifer should rise 2 to 3 feet above mean sea level. Three to four
miles inland the rise in the water level in the aquifer should be less than 1 foot.
The long-term rise in water levels in the Floridan aquifer will not be sufficient to
depress the fresh-water salt-water interface to the base of the permeable zone in
the upper part of the Floridan aquifer near the bay. Therefore, the displacement
of the interface will have minor effects with respect to controlling upward
movement of saline water as a result of pumping farther inland.







BUREAU OF GEOLOGY


REFERENCES


Black, A. P.
1951

1953

Black, Crow, and
1965
Brown, Eugene
Brown, R. H.
Cherry, R. N.
1966

1970

Collins, W. D.
1928

Cooke, C. W.
1945
Ferguson, G. E.
1947


Ferris, J. G.
1962

Foster, J. B.
Gunter, Herman
Heath, Ralph C.
1954

Howard, C. S.
Knowles, D. B.
Love, S. K-
Mann, J. A.
Matson, G. C.
1913

Menke, C. G.
1961


(and Brown, Eugene) Chemical character of Florida's waters-1951:
Florida Board of Conserv., Water Survey and Research Paper 6.
(and Brown, Eugene, Pearce, J. M.) Salt-water intrusion in Florida-
1953: Florida Board of Conserv., Water Survey and Research Paper 9.
Eidsness
Review of water resources, Pinellas County, Florida, 1965.
(see Black, A. P.)
(see Ferris, J. G.)

Chloride content of ground water in Pinellas County, Florida, in 1950
and 1963: Florida Geol. Survey Map Ser. 20.
(Stewart, J. W., and Mann, J. A.) General hydrology of the middle Gulf
area, Florida: Florida Bur. Geology Rept Inv. 56.

(and Howard, C. S.) Chemical character of waters of Florida: U.S. Geol.
Survey, Water-Supply Paper 596-G.


Geology of Florida: Florida Geol. Survey Bull. 29.

(Lingham, C. W., Love, S. KI, and Vernon, R. O.) Springs of Florida:
Florida Geol. Survey Bull. 31.


(and Knowles, D. B., Brown, R. H., Stallman, R. W.) Theory of aquifer
tests: U.S. Geol. Survey Water-Supply Paper 1536-E.
(see Musgrove, R. H.)
(see Sellards, E. H.)

(and Smith, Peter C.) Ground-water resources of Pinellas County,
Florida: Florida Geol. Survey Rept. Inv. 12.
(see Collins, W. D.)
(see Ferris, J. G.)
(see Ferguson, G. E.)
(see Cherry, R. N.)

(and Sanford, Samuel) Geology and ground waters of Florida: U.S.
Geol. Survey Water-Supply Paper 319.

(and Meredith, E. W., Wetterhall, W. S.) Water resources of Hills-
borough County, Florida: Florida Geol. Survey Rept. Inv. 25.







INFORMATION CIRCULAR NO. 76


Meredith, E. W. (see Menke, C. G.)
Musgrove, R. H.
1965 (Foster, J. B. and Toler, L. G.) Water resources of the Econfina Creek
basin area in northwestern Florida: Florida Geol. Survey Rept. Inv. 41.
Parker, Gerald G.


Pearce, J.
Reynolds,


Sanford, S


1945 Salt-water encroachment in southern Florida: Am. Water Works Assoc.
Jour., vol. 37, no. 6.
1950 (and Stringfield, V. T.) Effects of earthquakes, trains, tides, winds, and
atmospheric pressure changes on water in the geologic formations of
southern Florida: Econ. Geology, voL 45, no. 5.
M. (see Black, A. P.)
Smith, and Hills
1959 Tampa Bay fresh-water lake study for Hillsborough-Pinellas County.
Jacksonville, 1959.
1963 Tampa Bay fresh-water lake study for Hillsborough-Pinellas County.
Jacksonville, 1963.
,amuel (see Matson, G. C.)


Sellards, E. H.
1913

Shattles, D. E.
1965

Smith, Peter C.
Stallman, R. W.
Stewart, J. W.
1968


Toler, L. G.
Stringfield, V. T.
1933
Vernon, R. O.
Wetterhall, W. S.


(and Gunter, Herman) The artesian water supply of eastern and
southern Florida: Florida Geol. Survey 5th Ann. Rept.

Quality of water from the Floridan aquifer in Hillsborough County,
Florida, 1963: Florida Geol. Survey Map Ser. 9.
(see Heath, Ralph C.)
(see Ferris, J. G.)
(see Cherry, R. N.)
Hydrologic effects of pumping from the Floridan aquifer in northwest
Hillsborough, northeast Pinellas, and southwest Pasco counties, Florida:
U.S. Geol. Survey open-file report.
(see Musgrove, R. H.)
(Also see Parker, Gerald G.)
Ground-water investigations in Florida: Florida Geol. Survey BulL 11.
(see Ferguson, G. E.)
(Also see Menke, C. G.)
Reconnaissance of springs and sinks in west-central Florida: Florida
Geol. Survey Rept Inv. 39.










FLRD GEOLOSk ( IC SUfRiW


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