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 Title Page
 Front Matter
 Transmittal letter
 Contents
 Abstract
 Introduction, purpose and...
 Methods of investigation
 Geography
 Hydrology
 Water balance
 Hydrologic relations
 Water-resources development in...
 Summary
 Selected references
 Copyright


FGS



General hydrology of the Middle Gulf area, Florida ( FGS: Report of investigations 56 )
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Permanent Link: http://ufdc.ufl.edu/UF00001243/00001
 Material Information
Title: General hydrology of the Middle Gulf area, Florida ( FGS: Report of investigations 56 )
Series Title: ( FGS: Report of investigations 56 )
Physical Description: x, 96 p. : ill., maps ; 23 cm.
Language: English
Creator: Cherry, R. N ( Rodney N. ), 1928-
Stewart, J. W ( Joe W. ), 1918-
Mann, J. A
Geological Survey (U.S.)
Florida -- Bureau of Geology
Southwest Florida Water Management District (Fla.)
Publisher: State of Florida, Bureau of Geology
Place of Publication: Tallahassee
Publication Date: 1970
 Subjects
Subjects / Keywords: Hydrology -- Florida   ( lcsh )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by R. N. Cherry, J. W. Stewart, and J. A. Mann.
Bibliography: Bibliography: p. 93-96.
General Note: Prepared by U.S. Geological Survey in cooperation with Florida Bureau of Geology and the Southwest Florida Water Management District.
 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 - 000861434
notis - AEF8096
lccn - 79634454 //r84
System ID: UF00001243:00001

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Table of Contents
    Title Page
        Page i
    Front Matter
        Page ii
        Page iii
        Page iv
    Transmittal letter
        Page v
        Page vi
    Contents
        Page vii
        Page viii
        Page ix
        Page x
    Abstract
        Page 1
        Page 2
    Introduction, purpose and scope
        Page 2
        Page 3
        Page 4
    Methods of investigation
        Page 5
        Page 4
        Page 6
        Page 7
    Geography
        Page 8
        Page 9
        Page 7
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
    Hydrology
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 14
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
        Page 42
        Page 43
        Page 44
        Page 45
        Page 46
        Page 47
        Page 48
        Page 49
        Page 50
        Page 51
        Page 52
        Page 53
        Page 54
        Page 55
        Page 56
        Page 57
        Page 58
        Page 59
        Page 60
        Page 61
        Page 62
    Water balance
        Page 63
        Page 64
        Page 65
        Page 66
        Page 67
        Page 68
        Page 69
        Page 70
        Page 71
        Page 72
        Page 73
        Page 74
        Page 75
        Page 76
        Page 77
        Page 62
    Hydrologic relations
        Page 78
        Page 79
        Page 80
        Page 81
        Page 82
        Page 83
        Page 84
        Page 85
        Page 86
    Water-resources development in the middle Gulf area
        Page 87
        Page 88
        Page 89
        Page 86
    Summary
        Page 90
        Page 91
        Page 89
        Page 92
    Selected references
        Page 93
        Page 94
        Page 95
        Page 96
        Page 97
    Copyright
        Copyright
Full Text






STATE OF FLORIDA
DEPARTMENT OF NATURAL RESOURCES


BUREAU OF GEOLOGY
Robert 0. Vernon, Chief




REPORT OF INVESTIGATION NO. 56



GENERAL HYDROLOGY
OF THE
MIDDLE GULF AREA, FLORIDA


By
R.N. Cherry, J. W. Stewart, andJ. A. Mann
U. S. Geological Survey



Prepared by the
U. S. GEOLOGICAL SURVEY
in cooperation with the
BUREAU OF GEOLOGY
DIVISION OF INTERIOR RESOURCES
FLORIDA DEPARTMENT OF NATURAL RESOURCES
and the
SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT




Tallahassee, Florida
1970




55T7.57



Y)6, 5>(

C.Z^













DEPARTMENT
OF
NATURAL RESOURCES





CLAUDE R. KIRK, JR.
Governor
.


TOM ADAMS
Secretary of State




BROWARD WILLIAMS
Treasurer




FLOYD T. CHRISTIAN
Commissioner of Education


EARL FAIRCLOTH
Attorney General




FRED 0. DICKINSON, JR.
Comptroller




DOYLE CONNER
Commissioner of Agriculture


W. RANDOLPH HODGES
Executive Director











LETTER OF TRANSMITTAL


Bureau of Geology
Tallahassee
April 14, 1970
Honorable Claude R. Kirk, Jr., Chairman
Florida Department of Natural Resources
Tallahassee, Florida

Dear Governor Kirk:

The Bureau of Geology, Department of Natural Resources, is
publishing as Report of Investigation No. 56, a report on the "General
Hydrology of the Middle Gulf Area, Florida" prepared by the U.S.
Geological Survey in cooperation with the Bureau of Geology and
the Southwest Florida Water Management District.
The area covered in this report is one of the metropolitan centers
in the State. Its growth is intimately tied in to the occurrence and
availability of adequate potable water. The 2V2 year study has pro-
vided many hydrologic aspects of the area that will aid in the formu-
lation of water-control designs and water-management practices.
The findings of the investigation are contained in two separate
reports. This report contains an evaluation of the general hydrology
of the entire Middle Gulf area, and includes both a water balance
analysis, and a description of the movement and chemical character
of the water. An earlier report by J. W. Stewart, U. S. Geological
Survey, evaluated the effects of pumpage in northwest Hillsborough
and northeast Pinellas r-unties.
Respectfully yours,


Robert 0. Vernon, Chief























































Completed manuscript received
April 14, 1970
Printed for the Bureau of Geology
Division of Interior Resources
Florida Department of Natural Resources
By Designers Press
Orlando, Florida

vi









TABLE OF CONTENTS


Abstract .. . . ........ ....
Introduction . . . . . .
Purpose and scope .. .. .. .. .. .
Previous investigation . . . .
Methods of investigation . . . .
Acknowledgments . . . . .
Geography .....................
Location and extent of area .. . . .
Climate ...................... .
Topography and drainage . . . .
Geology .. .. .. .. .. .. .. .. . .
Hydrology . ........ . .
Streams ............... ........
Crystal River .. .......... ..
Homosassa River .. .. .. .. .. .
Chassahowitzka River . . . .
Weekiwachee River . . . .
Pithlachascotee River . . . .
Anclote River ................
Brooker Creek .................
Curlew Creek . . . . .
Stevenson Creek . . . .
SMcKay Creek . ......... .
Seminole Lake Outlet . . .
Allen Creek ..................
Alligator Creek . . . .
Rocky Creek ................ .
Sweetwater Creek ..............
Cypress Creek ............... .
Trout Creek . . . . .
Busy Branch ................ .
New River ................. .
Long-term trends in streamflow ........ ..
4Lakes .... ....................
General characteristics ..........
Lake Tarpon .................
Aquifers .......................
Shallow aquifer . . .
Floridan aquifer ...............
Water balance .....................
Precipitation ....................
Evapotranspiration ...............
Runoff .......................
Ground-water outflow . . . .
Ground-waterinflow ..............
Change in storage ................
Analysis of the water balance ..........
Hydrologic relations . . . . .
Water-resources development in the Middle Gulf area
Summary...... ..................
Selected references . . . . .


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S. 69
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ILLUSTRATIONS


Figure Page
1. Map showing location and data-collection sites in and
near the Middle Gulf area ................................... .5
2. Diagram illustrating the well-numbering system . . . . . .7
3. Map showing Middle Gulf hydrologic system boundary
and Middle Gulf area . . ... . . . . . .9
4. Map showing normal annual rainfall in Middle
Gulf area 1931-1960 . . . . . . . . 10
5. Map showing topography of the Middle Gulf area . . . . . 12
6. Map showing location of selected sinks in and
near Middle Gulf area .................................... 18
7. Generalized geology of the Middle Gulf area ................. ..... 15
8. Map showing mineral content and chloride
concentration of water at selected sites on Crystal
River and adjacent areas, March 25,1964 . . ................ 20
9. Map showing mineral content and chloride concentration
of water at selected sites on Homosassa River and
adjacent areas, March 26-27,1964 ..... ........................ 21
10. Graphs showing relation between stage and
streamflow, Hidden River near Homosassa . . . . . . 22
11. Map showing mineral content and chloride concentration
of water at selected sites on Chassahowitzka River
and adjacent areas, April 8-10, 1964 . . . . . . 24
12. Map showing mineral content and chloride concentration
of water at selected sites on Weekiwachee River,
April29,1964 ........................ . . ........ 26,
13. Graph showing comparison of the average daily of the
Pithlachascotee River near New Port Richey and Floridan
aquifer seepage (calculated) to the river . . . . . . 30
14. Graph showing comparison of average daily flow of the
Anclote River near Elfers and Floridan aquifer
seepage (calculated) to the river ............................. 32
15. Graph showing comparison of average daily flow of
Cypress Creek near San Antonio and Floridan aquifer
seepage (calculated) to the creek ............................. 35
16. Hydrographs of long-term streamflow for selected
streamsin the Middle Gulf area ......... .......... .. .. .. ......38
17. Map showing ranges of fluctuation of selected lakes
in Middle Gulf area during the study period . . . . . . 39
18. Hydrographs showing comparison of stage fluctuations
of Neff Lake (in upgradient area), Hunters Lake (in
downgradient area), Round Lake (affected by
ground-water withdrawals), and Alligator and
Seminole Lakes (stage controlled) ............................ 40
19. Map showing mineral content of water in selected
lakes in and near the Middle Gulf area, May 1965 . . . . . 41
20. Graph showing changes in chloride concentration
and water levels of Seminole Lake, 1950-1966 . .. . . . 42
21. Graph showing water levels in Lake Tarpon and Slring
Bayou and the mineral content of water in Lake
Tarpon during the period of study .... . . ...... . . 44

viii









22. Map of Middle Gulf area showing contours of water
levels in the shallow aquifer during a period of high
water levels, August-November 1965 . . .
23. Map of Middle Gulf area showing contours of
water levels in the shallow aquifer during a
period of low water levels, May 1966 ... .... .. .
24. Graph showingrainfall at Starvation Lake weather
station, and water-level fluctuation in thj shallow
aquifer in the southern part of the Middle Gulf
area,January 1965-June 1966 .............
25. Map showing location of sediment sampling sites
and permeabilities of selected samples in the
Middle Gulf area . . ...........
26. Map of Middle Gulf area showing contours on top
of the Floridan aquifer . . .... .
27. Map of Middle Gulf area showing contours of
water levels in the Floridan aquifer during a
period of high water levels, August-September 1965 .
28. Map of Middle Gulf area showing contours of water
levels in the Floridan aquifer during a period of
low water levels, May 1966 ...............
29. Hydrographs showing seasonal changes in water
levels in the Floridan aquifer ..............
30. Map of Middle Gulf area showing range in water-level
fluctuations in the Floridan aquifer, January
1964-June1966 . .. . . .
31. Hydrographs showinglong-term water-level
records for wells in Middle Gulf area ...........
32. Hydrographs showing water-level fluctuations in
paired shallow and deep wells, Pasco County . .
33. Time-drawdown curves, Eldridge-Wilde well field .
34. Time-drawdown curves, Section 21 well field .. .
35. Map of Middle Gulf area showing mineral content and
chloride concentration in the Floridan aquifer . .
36. Map showing water levels in wells penetrating
the Floridan aquifer, topographic divides, and
boundary of the hydrologic system ..........
37. Map showing accumulated precipitation for period
June 1964 May 1966, Middle Gulf hydrologic system
38. Map showing average stream discharge and runoff
for the total Middle Gulf hydrologic system .. .. .
39. Map of southern part of Middle Gulf area showing flow
net for computation of ground-water outflow . .
40. Graph showing monthly variations of precipitation
and evapotranspiration in the Middle Gulf area,
June 1964 May 1966 .................
41. Graph showing monthly accumulated change in storage
calculated from water balance and compared with
coincident fluctuations of stages of lakes and streams,
and water level in aquifers . . . .
42. Graph showing relation of streamflow, stage and time
in a tidal stream .....................
43. Graph showing relation of water level in aquifers
(shallow and Floridan) to flow of streams . .


S. . . . .. 46


S. . . . .. 47




. . . . 49


................. 50

. .. .. .. ......... 53


. . . . .. 54


. .. . .. . ..55

. .. .... .. ...... .. 57


... .. .... .... .... 58

. .. .... .... .. .... 60

. . . . . 61
. . . . . 63
. . . . .. 64

. . . . .. 65


. . . . 69

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. . . . 74

. . . . . 75


. .. .. ........ .. .. 77




... ............. 78

........... .. .... 82

. . . . . 83








44. Graph showing correlations of monthly mean flows
of Crystal River and Weekiwachee, Rainbow and
Silver springs ......................................... 84
45. Graph showing similarities in seasonal changes in
mineral content of water of selected streams in the
middle Gulf area,January 1964 -June 1966 . . . . . 85


TABLES
Table
1. Laboratory analysis of unconsolidated
sediment samples ................
2. Analyses of water from selected wells
in Middle Gulf area . . . .
3. Summary of stream discharge and runoff
for total system and Middle Gulf area ... .. .
4. Summary of the water balance for the
Middle Gulf area,June 1964 May 1966 ....


Page

. .. .. . .. . .. 51

. .. .. ...... ..... ... ..66

. . . . . .. 73

. .. . . .. . 79










GENERAL HYDROLOGY
OF THE
MIDDLE GULF AREA, FLORIDA
By
R. N. Cherry, J. W. Stewart, andJ. A. Mann



ABSTRACT

The Middle Gulf area is in the west-central coast of peninsular
Florida and encompasses about 1,700 square miles. It contains the
cities of Tampa, St. Petersburg, Clearwater, Brooksville, and Crystal
River. The area is drained principally by seven streams, Crystal, Homo-
sassa, Chassahowitzka, Weekiwachee, Pithlachascotee and Anclote
Rivers and Cypress Creek. The average daily discharge from the area
not including peninsular Pinellas County and some coastal areas, for
the period January 1964 -June 1966, was 2,300 cfs (cubic feet per
second), or about 1.5 bgd (billion gallons a day). The average daily
discharge of Crystal River alone was 930 cfs (0.60 bgd), or nearly 40
percent of the total.
No permanent regional declines in surface or ground-water levels
have occurred in the area. The greatest local declines, ranging from 6 to
14 feet, occurred in the area of the well fields in northwest Hills-
borough and northeast Pinellas counties.
The Middle Gulf area is part of a large hydrologic system. The
total system encompasses an area of about 3,500 square miles and
extends to the eastern topographic divide of the Withlacoochee River.
The source of water for the system is rainfall which averages about 55
inches annually. Principal outflow from the system is evapotranspira-
tion which amounts to about 67 percent of the total outflow. Runoff
amounts to about 32 percent and ground-water outflow about 1
percent.
The Middle Gulf area is in the downgradient part of the larger
Middle Gulf hydrologic system and most of the streamflow and
ground-water outflow from the hydrologic system discharges from the
Middle Gulf area. During a near average period, June 1964 May
1966, precipitation on the Middle Gulf area was 114 inches; ground-
water inflow, 24 inches; evapotranspiration, 77 inches; runoff, 59
inches; and ground-water outflow, 2 inches.






BUREAU OF GEOLOGY


Most of the runoff from the area is discharged either as springflow
or seepage to streams from the Floridan aquifer. Eighty percent of the
annual streamflow from the area is water derived from the Floridan
aquifer.
The water-level gradients in the system are about the same as the
topographic gradients (2-3 feet per mile). Water levels in all lakes,
streams, and aquifers within any one area fluctuate through about the
same range, but the fluctuations are greatest in the upgradient areas.
Water levels are highest in the late summer or early fall following
the rainy season and are lowest in late May or early June. Inflow to the
system occurs primarily from June to September.
The change in storage from periods of high water level in late
summer to low water level in late May is equivalent to about 8 inches of
water over the Middle Gulf area.
Tide has a pronounced effect on the outflow from the areas.
During periods of high tides, outflow is diminished and during periods
of low tides outflow is increased.
The chemical quality of ground and surface water is good. The
mineral content is generally less than 500 mg/1 (milligrams per liter) in
the ground water and 20 mg/1 in the surface water except near the
coast, where the mineral content of both surface and ground water may
approach or be the same as that of sea water.
Ample supplies of good quality water are available for existing
and foreseeable uses. The present (1969) problem is one of water
management and optimum development rather than the availability of
water. By properly spacing wells, avoiding excessive pumping rates in
localized areas and distributing well fields over wide areas, drawdowns
between wells and between respective well fields would be minimized.
Overdevelopment and subsequent declines in water levels, now re-
flected to some degree in lowered lake levels and in reduction in
streamflow, would be decreased. Implementation of measures noted
would tend to minimize conflicts of interest between various water
users throughout the area.
INTRODUCTION
PURPOSE AND SCOPE
The growth and economy of the Middle Gulf area, figure 1, and its
predicted expansion require ever-increasing quantities of water for a
variety of uses which include domestic and public supplies, for agricul-
ture and industry, for protection during droughts, for abatement of
pollution and saltwater intrusion, for preservation of fish and wildlife,






BUREAU OF GEOLOGY


Most of the runoff from the area is discharged either as springflow
or seepage to streams from the Floridan aquifer. Eighty percent of the
annual streamflow from the area is water derived from the Floridan
aquifer.
The water-level gradients in the system are about the same as the
topographic gradients (2-3 feet per mile). Water levels in all lakes,
streams, and aquifers within any one area fluctuate through about the
same range, but the fluctuations are greatest in the upgradient areas.
Water levels are highest in the late summer or early fall following
the rainy season and are lowest in late May or early June. Inflow to the
system occurs primarily from June to September.
The change in storage from periods of high water level in late
summer to low water level in late May is equivalent to about 8 inches of
water over the Middle Gulf area.
Tide has a pronounced effect on the outflow from the areas.
During periods of high tides, outflow is diminished and during periods
of low tides outflow is increased.
The chemical quality of ground and surface water is good. The
mineral content is generally less than 500 mg/1 (milligrams per liter) in
the ground water and 20 mg/1 in the surface water except near the
coast, where the mineral content of both surface and ground water may
approach or be the same as that of sea water.
Ample supplies of good quality water are available for existing
and foreseeable uses. The present (1969) problem is one of water
management and optimum development rather than the availability of
water. By properly spacing wells, avoiding excessive pumping rates in
localized areas and distributing well fields over wide areas, drawdowns
between wells and between respective well fields would be minimized.
Overdevelopment and subsequent declines in water levels, now re-
flected to some degree in lowered lake levels and in reduction in
streamflow, would be decreased. Implementation of measures noted
would tend to minimize conflicts of interest between various water
users throughout the area.
INTRODUCTION
PURPOSE AND SCOPE
The growth and economy of the Middle Gulf area, figure 1, and its
predicted expansion require ever-increasing quantities of water for a
variety of uses which include domestic and public supplies, for agricul-
ture and industry, for protection during droughts, for abatement of
pollution and saltwater intrusion, for preservation of fish and wildlife,







REPORT OF INVESTIGATION NO. 56


or recreational and navigational needs, and for maintaining minimum
low in the streams and desired levels in the many lakes in the area.
Expansion has been from the Tampa St. Petersburg area northward
primarily along the coast into relatively undeveloped areas and is only a
ocal phase of active expansion of the population and the economy of
he state.
The water supplies to accommodate the anticipated increase in
lemand will be obtained mostly from the Floridan aquifer. Fresh water
s available in some parts of the coastal areas at shallow depths, but in
theirr coastal areas salt-water encroachment in the Floridan aquifer has
limited the utility of the water.
In parts of the area pumpage from the Floridan aquifer has
owered some lake levels and reduced the flow of affected streams.
Vater that has previously been utilized for recreation is now being
diverted to municipal or industrial use. The competition for water
vithin the area has intensified in recent years and conflicts of interest
iave arisen.
Recognizing that an understanding of the water resource is pre-
equisite to efficient.water management, the Southwest Florida Water
management District and the Bureau of Geology, Florida Division of
interior Resources, Department of Natural Resources, requested that
;he U. S. Geological Survey evaluate the potential water supply of the
Vfiddle Gulf area. In the course of evaluating the potential water
;upply, many hydrological aspects were investigated during the 21/2
gears of study which began January 1,1964. These evaluations should
lid in the formulation of water-control designs and water-management
practices. Special emphasis was placed in the study on northwest
Hillsborough and northeast Pinellas counties, where heavy demands
have been placed on the water supply and where increasingly greater
demands are expected to occur because this area is rapidly becoming
urbanized.
The findings of the investigation are contained in two separate
reports. This report contains an evaluation of the general hydrology of
the entire Middle Gulf area, and includes both a water balance analysis,
and a description of the movement and chemical character of the
water. An earlier report by Stewart (1968) evaluated the effects of
pumpage in northwest Hillsborough and northeast Pinellas counties.

PREVIOUS INVESTIGATIONS
References to the hydrology and geology of the Middle Gulf area
have been made in several reports published by the Florida Geological







BUREAU OF GEOLOGY


Survey and the U. S. Geological Survey. Ferguson and others (1947), as
part of a state-wide inventory of the larger springs in Florida, described
several of the large springs in the area. Heath and Smith (1954, p.
38-42) discussed the hydrology of Pinellas County and Taylor (1953)
described the drainage of Lake Tarpon in detail and some of the springs
and sinks in the vicinity of Lake Tarpon. Wetterhall made a geohydro-
logic reconnaissance of Pasco and southern Hernando counties (1964)
and a reconnaissance of springs and sinks in the general area (1965).
Parker and others (1955) named and described the Floridan aquifer.
Cooke (1945) and Vernon (1951) described the geology of Florida,
and Vernon (1964) described the geology of Citrus and Levy counties.
Matson and Sanford's report (1913) on the geology and groundwater
of Florida has been particularly useful in this study. Their report has
pertinent information on the area. Menke, Meredith and Wetterhall
(1961) described the water resources of Hillsborough County.
The Florida Department of Water Resources made a reconnais-
sance of the hydrology of the Gulf Coast Basins in 1961, and in 1966
published a report entitled "Florida Land and Water Resources, South-
west Florida." The Florida Division of Water Resources and Conserva-
tion's Gazetteer of Florida Streams (1966) gives statistics pertaining to
several streams in the area.

METHODS OF INVESTIGATION
To evaluate and understand the water resources of the area, the
entire hydrologic environment were studied. Rainfall, streamflow, and
lake and ground-water level data was collected during the study at sites
shown in figure 1. Additional data on rainfall and temperatures were
obtained from the U. S. Weather Bureau for six stations in the Middle
Gulf hydrologic system outside of the Middle Gulf area.
Drainage characteristics of the area were determined by collecting
daily streamflow and water-quality data, by making field and aerial
reconnaissances, and by studying maps and aerial photographs.
A detailed field reconnaissance was made during May and June,
1964, of all known or probable sites of stream discharge from the
hydrologic system. Specific conductance of the water was measured at
these sites to determine if the water was fresh or salty. If the water was
fresh less than about 5,000 micromhos and the flow was greater
than about 5 cfs (cubic feet per second) or 3.2 mgd (million gallons per
day), a streamflow measurement was made. Most streamflow measure-
ments were not affected by Gulf tides. Continuous recorders were
operated at sites on major streams, and periodic measurements were
made at minor flow sites. The flow of streams for which only periodic








REPORT OF INVESTIGATION NO. 56


Figure 1. Map showing location and data-collection sites in and near
the Middle Gulf area







BUREAU OF GEOLOGY


Survey and the U. S. Geological Survey. Ferguson and others (1947), as
part of a state-wide inventory of the larger springs in Florida, described
several of the large springs in the area. Heath and Smith (1954, p.
38-42) discussed the hydrology of Pinellas County and Taylor (1953)
described the drainage of Lake Tarpon in detail and some of the springs
and sinks in the vicinity of Lake Tarpon. Wetterhall made a geohydro-
logic reconnaissance of Pasco and southern Hernando counties (1964)
and a reconnaissance of springs and sinks in the general area (1965).
Parker and others (1955) named and described the Floridan aquifer.
Cooke (1945) and Vernon (1951) described the geology of Florida,
and Vernon (1964) described the geology of Citrus and Levy counties.
Matson and Sanford's report (1913) on the geology and groundwater
of Florida has been particularly useful in this study. Their report has
pertinent information on the area. Menke, Meredith and Wetterhall
(1961) described the water resources of Hillsborough County.
The Florida Department of Water Resources made a reconnais-
sance of the hydrology of the Gulf Coast Basins in 1961, and in 1966
published a report entitled "Florida Land and Water Resources, South-
west Florida." The Florida Division of Water Resources and Conserva-
tion's Gazetteer of Florida Streams (1966) gives statistics pertaining to
several streams in the area.

METHODS OF INVESTIGATION
To evaluate and understand the water resources of the area, the
entire hydrologic environment were studied. Rainfall, streamflow, and
lake and ground-water level data was collected during the study at sites
shown in figure 1. Additional data on rainfall and temperatures were
obtained from the U. S. Weather Bureau for six stations in the Middle
Gulf hydrologic system outside of the Middle Gulf area.
Drainage characteristics of the area were determined by collecting
daily streamflow and water-quality data, by making field and aerial
reconnaissances, and by studying maps and aerial photographs.
A detailed field reconnaissance was made during May and June,
1964, of all known or probable sites of stream discharge from the
hydrologic system. Specific conductance of the water was measured at
these sites to determine if the water was fresh or salty. If the water was
fresh less than about 5,000 micromhos and the flow was greater
than about 5 cfs (cubic feet per second) or 3.2 mgd (million gallons per
day), a streamflow measurement was made. Most streamflow measure-
ments were not affected by Gulf tides. Continuous recorders were
operated at sites on major streams, and periodic measurements were
made at minor flow sites. The flow of streams for which only periodic







BUREAU OF GEOLOGY


measurements were available was computed by correlation with nearby
continuous record stations.
Spring flow does not vary greatly within short periods, and
monthly flow values were sufficient to compute the average flow. For |
example, monthly average flows determined from the monthly flow
values of Rainbow Springs in Marion County are in close agreement
with those determined from the daily flows. The flow for the period of
study from large springs such as Weekiwachee, Chassahowitzka, and
Homosassa were determined from hydrographs of monthly flow
measurements. The flows of smaller springs, such as Bobhill and Salt in
Hernando County, were measured about two to three times per year.
The measurements were made at times of both high and low flow and
were averaged to obtain the average flow for the period of study.
Occurrence and quality of ground water were determined by
collecting data on water levels, surface and subsurface geology, and
water samples for chemical analysis from springs and wells, most of
which are supplied by the Floridan aquifer. Continuous records of
water-level fluctuations in the aquifer were supplemented by periodic
measurements of water levels in wells. The level of water in each well
relative to mean sea level datum was determined from topographic
maps or by a spirit level.
To obtain specific information on the occurrence of ground water
in the Middle Gulf area, test wells were drilled. Additional subsurface
information was obtained by interpretation of electric, gamma-ray,
and drillers' logs of wells in the area. All well sites were numbered,
based on coordinates of a state-wide grid of 1-minute parallels of
latitude and 1-minute meridians of longitude as shown in figure 2.

ACKNOWLEDGMENTS

The writers wish to express their appreciation to the many citi-
zens of the area who permitted the sampling of water and measuring of
water levels in their wells and to the well drillers for furnishing drill
cuttings, water-level data, and other helpful information. Special
acknowledgments are due to the Florida State Road Department and
the counties of Citrus, Hernando, Pasco, Hillsborough, and Pinellas for
granting permission to drill test wells on public lands.
Special thanks are due to Drs. Luther C. Hammond, R. E. Cald-
well and V. W. Carlisle of the University of Florida and their aid and
suggestions in the determination of evapotranspiration by the Thorn-
thwaite method.







REPORT OF INVESTIGATION NO. 56


Figure 2. Diagram illustrating the well-numbering system


Special thanks are also due to Dale Twachtmann, Executive
Director, Southwest Florida Water Management District, for his
patient encouragement throughout the investigation, and to Garald G.
Parker, Chief Hydrologist, of the same agency for his review of the
manuscript.
Appreciation is expressed for the extensive technical and editorial
review of the manuscript by J. S. Rosenshein, Eugene R. Hampton,
Gilbert H. Hughes and C. A. Pascale, all of the U. S. Geological Survey.
The work on this project was done under the general direction of
C. S. Conover, District Chief, Water Resources Division, U. S. Geologi-
cal Survey.
GEOGRAPHY
LOCATION AND EXTENT OF AREA
The Middle Gulf area, about 1,700 square miles, is in the central
west coast of peninsular Florida and includes parts of Citrus, Her-







BUREAU OF GEOLOGY


nando, Pasco, and Hillsborough counties and all of Pinellas County (fig.
1). The area is bounded on the east and north by the western edge of
the Withlacoochee drainage basin, on the south by the Hillsborough
River and Tampa Bay, and on the west by the Gulf of Mexico. This area
contains a number of major cities and towns which had the following
population according to the 1960 census: Tampa, 288,000; St. Peters-
burg, 193,000; Clearwater, 37,000; Dunedin, 8,444; Tarpon Springs,
6,768; New Port Richey, 3,520; Brooksville, 3,301; and Crystal River,
1,423. Both the population and industry of the area are rapidly
increasing and the demands for water accelerating. The Middle Gulf
area is a part of the Middle Gulf hydrologic system, (figure 3). The
system encompasses an area about 3,500 square miles and extends to
the eastern topographic divide of the Withlacoochee River. The Middle
Gulf area forms the downgradient part of the total water system.

CLIMATE

The climate is characterized by warm and relatively humid sum-
mers and mild relatively dry winters. The normal annual rainfall varies
from about 51 to 58 inches, figure 4, and is unevenly distributed with
more than half falling from June to September. Tropical storms in the
summer and fall and occasionally in the winter bring intense rains to
the area. The distribution of the normal annual rainfall in the Middle
Gulf area is shown in figure 4.
Evaporation is greatest during May and June and in some years the
evaporation in these two months accounts for nearly 25 percent of the
annual total (Florida Board of Conservation 1966, p. 18).
Variations in day to day maximum temperatures during the
summer range from about 720F to 90*F and during the winter from
about 550F to 750F. During the winter, occasional cold fronts move
through the area that drop temperatures into the low and middle 20's.

TOPOGRAPHY AND DRAINAGE
Land elevations range from sea level at the shoreline or coastline
to about 280 feet above msl (mean sea level) near Dade City. The areas
of highest elevations are a series of eroded ridges that trend to the
northwest and a ridge of poorly defined sand hills that parallels the
gulf. These hilly areas occupy much of Citrus and Hernando counties
and eastern Pasco and southern Pinellas counties. The western part of
the Middle Gulf area between the Gulf and the sand hills, and the
southern part of the area adjacent to Old Tampa Bay are characterized








REPORT OF INVESTIGATION NO. 56


Figure 3. Map showing Middle Gulf hydrologic system boundary
and Middle Gulf area







REPORT OF INVESTIGATION NO. 56


Figure 2. Diagram illustrating the well-numbering system


Special thanks are also due to Dale Twachtmann, Executive
Director, Southwest Florida Water Management District, for his
patient encouragement throughout the investigation, and to Garald G.
Parker, Chief Hydrologist, of the same agency for his review of the
manuscript.
Appreciation is expressed for the extensive technical and editorial
review of the manuscript by J. S. Rosenshein, Eugene R. Hampton,
Gilbert H. Hughes and C. A. Pascale, all of the U. S. Geological Survey.
The work on this project was done under the general direction of
C. S. Conover, District Chief, Water Resources Division, U. S. Geologi-
cal Survey.
GEOGRAPHY
LOCATION AND EXTENT OF AREA
The Middle Gulf area, about 1,700 square miles, is in the central
west coast of peninsular Florida and includes parts of Citrus, Her-







BUREAU OF GEOLOGY


Figure 4. Map showing normal annual rainfall in Middle Gulf area
1931-1960






REPORT OF INVESTIGATION NO. 56


)y relatively flat swampy lowlands, figure 5. These lowlands form a
)road plain with gentle relief in the western parts of southern Pasco,
Flillsborough, and northern Pinellas counties. In eastern Pasco and
northeastern Hillsborough counties the land surface becomes gently
rollingg with smoothly rounded hills and shallow depressions.
The principal streams in the Middle Gulf area are Crystal, Homo-
sassa, Chassahowitzka, Weekiwachee, Pithlachascotee, and Anclote
rivers; and Rocky, Sweetwater, and Cypress creeks. Streams in the
northern part generally originate at springs and carry little overland
flow whereas streams in the southern part carry substantial overland
flow.
The area contributing water to a stream is usually delineated by
topographic divides. However, in the Middle Gulf area, the area con-
itributing water to a stream may better be delineated by ground-water
divides than by surface-water divides, because most of the larger
streams are fed by ground water issuing from springs and seeps.
In Citrus and Hernando counties and northern Pasco county
surface drainage is almost nonexistent. Sand hills and highly permeable
land surfaces capture most of the precipitation that falls on them, and
sinkholes capture a large part of the surface drainage.
Some of the sinks in the area that are known to be hydraulically
connected to the Floridan aquifer and to transmit large quantities of
water vertically are shown in figure 6. In the Brooksville area large
volumes of water recharge the aquifer through sinks. Blue Sink, north-
east of Brooksville, is capable of leaking large quantities of water
underground. This sink has a drainage area of about 30 square miles.
Numerous other sinks also occur in this area, including a large group of
sinkholes in the prairie southwest of Brooksville. Some sinks, such as a
sink in the southeast part of Neff Lake, have made prairies of former
lake bottoms.
Pecks Sink near Brooksville accepts drainage from an area of more
than 15 square miles and is one of a group of four or five sink
complexes in the area. No flow into the sink was observed during the
period of study. However, flow was observed during other periods.
During extremely wet periods the overflow from Horse Lake drains
into Pecks Sink.
The sinks in the Squirrel Prairie area southeast of Brooksville
accept drainage from about 20 square miles in the upper reaches of the
Pithlachascotee River. Crews Lake, which is southwest of Squirrel
Prairie, is in the headwaters of the Pithlachascotee River. The lake has
an active sink which drains about half the inflow to the lake (about 10
cfs, or 6.4 mgd).







BUREAU OF GEOLOGY


EXPLANATION


Middle Gulf Area Boundary
50-----
Contour shows the elevation of land
surface. Contour Interval 25
feet. Datum is mean sea level.


/


.~troo{


o < MILES


Figure 5. Map showing topography of the Middle Gulf area








REPORT OF INVESTIGATION NO. 56 1


arod -Vmp oo


LOCATION MAP RY&TAL R



4,, EXPLANATION W


Middle Gulf Area Boundary '- "
o BLUE INK


SQUIRREL ELl .-
s ,, SINK A A

/ F :RNASCO 8l DW o,
ONNAMI D SINCE


Figure 6. Map showing location of selected sinks in and near Middle
Gulf area







BUREAU OF GEOLOGY


The "Blue Sink" area of Sulphur Springs at the northern limits of
Tampa and lying immediately west of U. S. Highway 41 receives much
of the drainage from about 15 square miles. At least some of the flow
into this sink complex emerges in Sulphur Springs, about 2 miles south
of the Blue Sink area. The average flow into this sink complex during
the study was less than a cubic foot per second (0.5 mgd). Maximum
flow to the sinks for the period of record August 1945 September
1950, August 1964 June 1966, was about 100 cfs (65 mgd). Studies
in this area in September 1945 indicated that this sink complex had a
vertical drainage capacity of about 40 cfs (26 mgd). During periods of
excessive rainfall when the intake capacity is exceeded, adjacent resi-
dential sections are flooded. The flow to the Bear Sink complex, about
7 miles northeast of New Port Richey, was measured as part of the
study. The average inflow of Bear Creek was about 30 cfs (19 mgd) and
the maximum inflow (March 1965 -June 1966) was 350 cfs (220
mgd) in August 1965. Maximum inflow during the period of study was
probably about 600 cfs (388 mgd) in September 1964. This sink
complex is in a sandhill area that has no surface drainage except the
inflow channel.
GEOLOGY
The Middle Gulf area is underlain at depth by several hundred feet
of solution-riddled limestone and dolomite that compose the following
formations in ascending order: Lake City Limestone, Avon Park Lime-
stone, the Ocala Group, Suwannee Limestone, Tampa Formation, and
the Alachua and Hawthorn Formations. These formations1 range in
age from Eocene to Miocene.
The solution-riddled and faulted limestone formations comprise
the Floridan aquifer. This aquifer is the principal storage and water-
conveying component of the hydrologic system in the Middle Gulf
area. It is the source of nearly all ground-water supplies in the area.
The aquifer is overlain by sand, silt, and clay of varying thickness.
The more permeable beds within the sand, silt, and clay unit form a
subsurface reservoir called the shallow aquifer. Where clay is present,
the downward water movement is retarded. The physical characteris-
tics of the rock units underlying the area are summarized in figure
7 the areal distribution of the Hawthorn Formation and older units
beneath surficial deposits is shown.
HYDROLOGY
The quantity and quality of water at a particular place may vary
greatly from time to time. The changes may be rapid or very slow and
IThe nomenclature used in this report conforms to that of the Bureau of Geology, Florida
Division of Interior Resources, Department of Natural Resources, and not necessarily to that
of the U.S. Geological Survey.




























Manp "lW4 09~14M mkle -n f NofHow &" o O esidw
(eg n fmei a, *md Ver n, 19s4)


seeo w ({ (4 te (s (7) (fl M W






1400'

EXPLANATION


UM-MNieene ,m and rodunr
hM Miocee o
0 Ni190u8 Nf

I Twoe" roftoelon
c' Cr.,,l Rie fwm.uln
WillulUe9 Foermeole
I 1tii rrimulUm
Si AMi PNrk Umnim
I@ Ldk@ Cilt LImeeIone
S-- MIddle Qulf Aee loundery


System


Quater-
nary


Tertiary


40e' I m 02)
woo'-, wauIi -

I a- top "
frm Wttllrholl (1M4)


I-, Y-Y


Series


focene
Ple ocene




Miocene
(M)


Formation/


.Hawthorng/


Tampa
Formation/
frt(


kpprox-
ia=te
thick-
ase.(ft.t


0-90


100-150


Lithology


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


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


Sw ee Limestone, cream to tan, thin-bedded,
SOlio ne stene( 0-300 fine-grained, dense, hard.


Crystal
River
Formation


0-300


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


Coquina, cream-colored, or limestone,
Williston cream to tan, detrital;j-loosely cemen
Formation 30-50 ted calcareous matrix; locally
S (w) silicified.
S Inglis Limestone, cream to tan, granular,
g Formation 50-150 porous, medium-hard, massive; dolo-
S () mite, locally tan to brown, near base.

Avon Park Limestone, white to tan, soft, chalky,
Limestone 50-500 granular; dolomite, tan to brown, hard
(ap) crystalline.


Lake City
Limestone
(lc)


500-1000


Limestone, tan to cream, soft, granu-
lar, pasty; locally interbedded with
layers of dolomite and bentonitic
clay; some gypsum.


Aquifer


Shallow


Floridan


1/ Nomenclature conforms to that of the Bureau of Geology, Florida Department of
Natural Resources
2/ Designntf:d surficial deposits in this report
3/ St. Marks Formation of Puri and Vernon (1964)
Figure 7. Generalized geology of the Middle Gulf area.


Figure 7. Generalized geology of the Middle Gulf area


____ --- 111111=


aessIt.


i i 1 .. ...


r~rmstiI


. ......







BUREAU OF GEOLOGY


may occur on the surface, underground, or in the atmosphere. Opti-
mum development and management of the water resource depends to a
large extent on an adequate understanding of these changes and the
complex patterns of water circulation from ocean to atmosphere to
land, and its return by various routes to the ocean or atmosphere. This
complex water circulation system is known as "the hydrologic cycle".
The hydrologic system conveys all water from where it falls as rain
either to the ocean or to the atmosphere. All streams, lakes, springs,
sinks, and aquifers in the Middle Gulf area are part of a much larger
complex hydrologic system. The amount of water in this system and
the boundaries of the area contributing water to the system are
constantly fluctuating in response to recharge and discharge.

Water moves from where it falls as rain, down-gradient through
the various interconnected water-conveying components of the sys-
tem. The principal conveying units may be streams in one area and
aquifers permeable rock units capable of storing and yielding usable
quantities of water to wells or springs in another area or a combina-
tion of both. The water may consecutively pass either from stream into
aquifer, aquifer into stream, or may be evapotranspired to the atmo-
sphere while enroute to the sea.
Lakes in one area may be directly connected to the aquifer and in
another area only indirectly connected or they may be perched above
the aquifer on an impermeable floor such that the lake is insulated from
the effects of storage changes going on in the aquifer. For example,
water may move from a lake by seepage through its bottom (direct) or
water that is moving to the lake may be diverted through some
upgradient connection (indirect) to the aquifer. Lakes may be drained
by streams in one area and be landlocked in another. Generally, factors
that affect water levels in one of the components of the system will
affect water levels in another component to some degree; sometimes
these effects are so small as not to be measureable. Pumpage from an
aquifer may either directly or indirectly cause a decrease in a lake level
or a decrease in the flow of a stream or where the lake is insulated from
the aquifer it is not affected by aquifer responses at all. This appears to
be the situation with some of the lakes in the heavily pumped areas of
northwest Hillsborough County.
Water enters the Middle Gulf area as rainfall and ground-water
inflow and is temporarily stored in streams, lakes or aquifers while
enroute to points of discharge from the area. During periods of heavy
rainfall, the rate of recharge to the area usually exceeds the rate of
discharge; therefore storage increases and water levels rise accordingly.







REPORT OF INVESTIGATION NO. 56 17

The principal recharge to the acuifers occur during the summer months
because precipitation during these months exceeds evapotranspiration.
When the discharge rate exceeds the recharge rate, the volume of
water stored declines; this lease of water stored at higher levels
sustains movement down-gradient, and water levels fall accordingly.
Aquifers hold water in /storage for longer periods than do lakes
and streams, and in effect meter out water at more constant rates to the
various points of discharge. Thus, discharge from the aquifers distrib-
utes the flow more evenly in time and maintains streamflow during dry
periods. This is of great importance in the Middle Gulf area because
about 80 percent of the runoff from the area is from ground-water
storage. The percentage of runoff derived from ground water ranges
from almost 100 percent in the northern part of the area to about 10
percent in the southern part. The runoff from the northern part is
about five times greater than that from the southern part. The principal
factors that determine the quantity of water stored in the aquifer are
the volume of the aquifer, the percentage of drainable interconnected
pore spaces in the aquifer and the elevation of the discharge outlet.
The estimated amount of recoverable water in the aquifer in the
Middle Gulf based on an area of 1,700 square miles, an average of 1,000
feet of aquifer thickness, and a specific yield of 15 per cent, is 53
trillion gallons, or 160 million acre-ft. This volume in storage greatly
exceeds some of the largest surface water reservoirs in the eastern
United States. For a comparison, the storage capacity of some of the
reservoirs are as follows (Thomas, 1956): Clark Hill, Savannah River,
Georgia, 2.9 million acre-ft; Gunthersville, Tennessee River, Alabama,
1.0 million acre-ft; Wheeler, Tennessee River, Alabama, 1.1 million
acre-ft; Kentucky Lake, Tennessee River, Kentucky, 6.0 million
acre-ft; and Lake Martin, Tallapoosa River, Alabama, 1.6 million
acre-ft.
The Middle Gulf area is underlain by a great and generally little
appreciated natural reservoir of almost staggering proportions -
almost 12 times the combined storage of all the above mentioned
reservoirs. However to use this stored water effectively and protect it
from waste, pollution and salt water encroachment, the aquifer must
have careful management.


STREAMS
The general direction of flow of the few streams in the Middle
Gulf area is southwestward or westward to the Gulf of Mexico. Streams
in the northern part of the area generally originate as springs and







BUREAU OF GEOLOGY


receive little direct runoff. Based on the short period of record (about 2
years) obtained during this study, it would appear that the flows of
these spring-fed streams are among the largest in the state.
Streams in the southern part of the area receive substantial
quantities of water from direct runoff. Generally the channels are
poorly defined in the upper reaches but the channels in the lower
reaches are better defined and are meandering.
The area contributing water to a stream is usually bordered by a
topographic divide but because of the interconnection between ground
and surface water in the Middle Gulf area, the ground-water divide may
better define the area which contributes water to the stream than the
topographic divide.
The principal streams draining the Middle Gulf area are Crystal,
Homosassa, Chassahowitzka, Weekiwachee, Pithlachascotee and
Anclote Rivers and Rocky, Sweetwater and Cypress creeks.
CRYSTAL RIVER
Crystal River heads at a group of springs in and around Kings Bay
at Crystal River community, and flows about 7 miles to the Gulf of
Mexico. Its channel, which ranges in depth from 2 to more than 20 feet,
is relatively wide and in many places is weed-choked. The area contrib-
uting water to the river is estimated at 80 square miles. Little overland
flow to the stream channel occurs and water gained is largely a
ground-water increment.
The flow of the river is measured just above its confluence with
Salt River and the average discharge to the gulf at this site during the
study was about 930 cfs, or 600 mgd (average discharge for 24-hour
period). The average range in stage at the measuring sites was about 1.5
feet. The stage is nearly identical to that of the Gulf of Mexico near
Bayport, about 25 miles to the south.
The maximum flow carried by the channel during normal tidal
cycles is about 4,000 cfs (2,600 mgd). During Hurricane Donna in
September 1964 the maximum flow was estimated to be more than
10,000 cfs (6,500 mgd) largely caused by wind tides and stage
exceeded 5 feet above msl. As a result of the high tides during the
hurricane, as well as at several other occasions during the study, the
net daily flow was negative, i.e., flow was inland.
Springs in Kings Bay, numerous springs east of the bay, seeps in
the many canals excavated into the limestone bedrock, and springs in
the tributaries contribute to the flow of Crystal River. The largest
group of springs near the head of the river, locally known as Tarpon







REPORT OF INVESTIGATION NO. 56


Springs, appears to contribute much of the river's flow. A reconnais-
sance of tributaries below Salt River indicated no significant fresh-
water flow.
The fresh and salt water in the river appears to be well mixed and
little, if any, stratification occurs. During tidal cycles, the change in
direction of flow near the surface of the stream and near the bottom
occur at about the same time.
The mineral content of the river water, which is due mostly to
sodium chloride from sea water, is high near the mouth and decreases
upstream as shown in figure 8. Near the head of the eastern-most
tributaries, the water contains little or no salt (sodium chloride). The
mineral content of water of the river at the gaging station just upstream
from Salt River ranges from about 300 to 15,000 mg/1 (milligrams per
liter). By comparison, normal sea water contains about 20,000 mg/1
chloride.
HOMOSASSA RIVER
Homosassa River and its spring complex lies about an equal
distance (8 miles) from Crystal River on the north and Chassahowitzka
River on the south. The river meanders through about 6 miles of
swampy tropical lowlands to the Gulf of Mexico. Its average flow near
the town of Homosassa, about halfway between the main springs and
the Gulf, is about 390 cfs (252 mgd). Of this flow, springs in the
headwaters contribute about 140 cfs (90 mgd); the Southeast Fork of
Homosassa Springs about 80 cfs (52 mgd); and Halls River about 170
cfs (110 mgd).
The overland flow from the area surrounding Homosassa River is
negligible. No stream channels have formed except for Hidden River,
but numerous drainage canals and boat channels have been constructed
in and near the town of Homosassa Springs.
Sea water migrates upstream during high tides as far as the main
springs and the headwaters of Hall River. Springs in the headwaters of
the Southeast Fork are relatively fresh, figure 9, whereas the main
spring (Homosassa Springs) and small springs in the headwaters of Halls
River, are salty (sodium chloride).
Hidden River, about 2 miles southeast of Homosassa, flows about
2 miles overland and disappears underground and apparently enters
Homosassa River downstream from Homosassa. The average of five
streamflow measurements of Hidden River during the study was about
30 cfs (19 mgd). The minimum stage of the river during this time was
about 2 feet above msl. The flow of the river appears to be little
affected by tides, although the mineral content of the water varies from
about 400 to 3,400 mg/1 as show in figure 10.








S42' 40' 38' 82036'
5 6 ,Jb-....,----,-,.-.---------- --,---........-! 56 '
rI ,







56'


28054' EXPLANATION Crystalol River 2854'
830
Streamflow Measuring Site 40 698


Upper number Is mineral content, lower number Is chlo-
ride concentration both In milligrams per liter. Bracketed / '
53' numbers are values for top and bottom samples; 53'
uobracketed numbers are values for single samples. 1 a n springs
All samples on main stem collected during high tide, sr
within a 2 hour period, March 25, 1964.

421 40' 38 820 36'


Figure 8. Map showing mineral content and chloride concentration of water at selected sites on Crystal
River and adjacent areas, March 25, 1964







BUREAU OF GEOLOGY


The "Blue Sink" area of Sulphur Springs at the northern limits of
Tampa and lying immediately west of U. S. Highway 41 receives much
of the drainage from about 15 square miles. At least some of the flow
into this sink complex emerges in Sulphur Springs, about 2 miles south
of the Blue Sink area. The average flow into this sink complex during
the study was less than a cubic foot per second (0.5 mgd). Maximum
flow to the sinks for the period of record August 1945 September
1950, August 1964 June 1966, was about 100 cfs (65 mgd). Studies
in this area in September 1945 indicated that this sink complex had a
vertical drainage capacity of about 40 cfs (26 mgd). During periods of
excessive rainfall when the intake capacity is exceeded, adjacent resi-
dential sections are flooded. The flow to the Bear Sink complex, about
7 miles northeast of New Port Richey, was measured as part of the
study. The average inflow of Bear Creek was about 30 cfs (19 mgd) and
the maximum inflow (March 1965 -June 1966) was 350 cfs (220
mgd) in August 1965. Maximum inflow during the period of study was
probably about 600 cfs (388 mgd) in September 1964. This sink
complex is in a sandhill area that has no surface drainage except the
inflow channel.
GEOLOGY
The Middle Gulf area is underlain at depth by several hundred feet
of solution-riddled limestone and dolomite that compose the following
formations in ascending order: Lake City Limestone, Avon Park Lime-
stone, the Ocala Group, Suwannee Limestone, Tampa Formation, and
the Alachua and Hawthorn Formations. These formations1 range in
age from Eocene to Miocene.
The solution-riddled and faulted limestone formations comprise
the Floridan aquifer. This aquifer is the principal storage and water-
conveying component of the hydrologic system in the Middle Gulf
area. It is the source of nearly all ground-water supplies in the area.
The aquifer is overlain by sand, silt, and clay of varying thickness.
The more permeable beds within the sand, silt, and clay unit form a
subsurface reservoir called the shallow aquifer. Where clay is present,
the downward water movement is retarded. The physical characteris-
tics of the rock units underlying the area are summarized in figure
7 the areal distribution of the Hawthorn Formation and older units
beneath surficial deposits is shown.
HYDROLOGY
The quantity and quality of water at a particular place may vary
greatly from time to time. The changes may be rapid or very slow and
IThe nomenclature used in this report conforms to that of the Bureau of Geology, Florida
Division of Interior Resources, Department of Natural Resources, and not necessarily to that
of the U.S. Geological Survey.



































Figure 9. Map showing mineral content and chloride concentration of water at selected sites on
Homosassa River and adjacent areas, March 26-27, 1964







BUREAU OF GEOLOGY


4
(n
z
UJ

4
CO
IUl


Lii
4>


Ll
i,
8._


0

Lii
il


2 400 1 3 I I I I i
0 10 20 30 40 50 60 70
STREAMFLOW, CUBIC FEET PER SECOND
Figure 10. Graphs showing relation between stage and streamflow
and mineral content and streamflow, Hidden River near
Homosassa
CHASSAHOWITZKA RIVER
The Chassahowitzka River is a shallow stream that meanders
through about 6 miles of tidal marshes and lowlands to the Gulf of
Mexico. Its flow is derived chiefly, from springs most of which are at the
heads of tributaries in densely-wooded areas that are. practically in-.
accessible except by boat. Chassahowitzka and Crab Creek springs
apparently contribute most of the flow (fig. 11). The average flow of
Chassahowitzka River downstream from the springs at the gaging
station below Crab Creek was about 140 cfs (90 mgd) for the period






REPORT OF INVESTIGATION NO. 56


January 1, 1964 -June 30, 1966. The average flow of the river,
including all its tributaries, was estimated to be about 210 cfs (136
mgd) for the same period.
Springs just above the main boil of Chassahowitzka Springs are
the freshest of any discharging to the river. Their mineral content when
sampled was less than 300 mg/l, figure 11. In comparison, the mineral
content of Chassahowitzka Springs ranged from about 300 to 2,100
mg/1. This wide range in mineral content is due in part to changes in
salinity during tidal cycles. Because only daily samples were collected,
the actual range of mineralization during tidal cycles has not been
determined.
Crab Creek is about half a mile long, and enters the river from the
north bank. Its average flow is about 50 cfs (32 mgd), derived from
several boils at its head. The mineral content ranges from about 1,200
to 4,800 mg/1.
Lettuce Creek enters the river at the north bank about a quarter of
a mile downstream from Crab Creek. The creek is about a quarter of a
mile long and several small spring boils occur in the headwater area.
Less than 5 cfs (3.2 mgd) issues from Lettuce Creek springs but the
water is fresh (mineral content is less than 200 mg/1). The elevation of
these springs is about 5 feet above-msl about the same elevation as
the small springs upstream of the main spring boils of Chassahowitzka
Springs (mineral content 300 mg/1).
Baird Creek enters the river about half a mile downstream from
Lettuce Creek. Baird Creek appears to flow during all normal tides (the
average of 5 streamflow measurements near low tide was about 30 cfs,
19 mgd) but may cease to flow during higher storm tides. The mineral
content of the water at its mouth varied from 1,700 to about 6,000
mg/1.
Salt Creek enters the river about three-fourths mile downstream
from Baird Creek. Salt Creek springs do not appear to flow during
incoming or high tides. The mineral content of water at the head of Salt
Creek was about 4,000 mg/1.
Potter Creek enters the river about half a mile downstream from
Salt Creek. The flow of this stream averaged about 10 cfs, 6.4 mgd,
(average of 5 discharge measurements near low tide). The springs at the
head of the stream cease flowing during incoming or high tides. The
mineral content of the water was about 1,000 mg/1.
Crawford Creek enters the river at the south bank about 2 miles
downstream from Salt Creek. The flow from the creek averaged about
30 cfs (19 mgd), most of which appeared to come from a spring at the
head of the creek. About a quarter of a mile downstream from the main

















bes are values for top and bottom 740
samples; unbracketed numbers are :6740
values for single samples. All samples '< ,
on main stem collected during high
tide, within a 2-hour period, April
8, 1964,
28042' 28042'

2700







40' 38' 36' 82034'



Figure 11. Map showing mineral content and chloride concentration of water at selected sites on Chas-
sahowitzka River and adjacent areas, April 8-10, 1964







REPORT OF INVESTIGATION NO. 56


springs, several spring boils flow during low tides but not during
incoming or high tides. The water issuing from these boils contains an
iron bearing floc-like material, the exact nature of which has not been
determined. The mineral content of water from the boils was about
2,700 mg/1.
The flow from Blue Run, a tributary of Crawford Creek, about a
quarter of a mile downstream from the head springs, was small. The
mineral content of its water was 3,400 mg/1 in April 1964. However, a
flow of 9.1 cfs (5.9 mgd) was measured on November 19, 1961
(Wetterhall, 1965).
Ryle Creek enters the Chassahowitzka River from the south bank
about a quarter of a mile downstream from Crawford Creek. The flow
appears to be negligible. However, some flow from small boils at the
head of the creek was observed during low tides. Water from these boils
contained a suspended red to yellowish-red, iron bearing floc-like
material. This material is similar to that which comes from boils in
Crawford and Baird creeks. The mineral content of the water from
Ryle Creek boil was about 6,000 mg/1.
Blind Creek (not shown on map) enters Chassahowitzka Bay
about 31/2miles downstream from Ryle Creek. The source of the creek's
water is from several boils in the headwater area. The mineral content
of the water from these boils ranged from about 5,000 to 14,000 mg/1.

WEEKIWACHEE RIVER
Weekiwachee River heads at Weekiwachee Springs, about 5 miles
southeast of Bayport. The river meanders through about 7 miles of
swampy lowlands to the Gulf at Bayport. Its channel is well-defined
and is cut into the underlying bedrock. Many springs flow into the
stream through openings in the streambed.
The flow of the river is derived chiefly from Weekiwachee Springs.
During January 1964 to June 1966, these springs had an average flow
of about 220 cfs (142 mgd). In this same period, the average flow of the
river at a gaging site about 5 miles downstream from the springs was
about 260 cfs (168 mgd). The large quantities of water flowing in these
streams can be judged by comparison with the water currently (1966)
supplied by the Eldridge-Wilde, Cosme, and Section 21 well fields, 45
mgd, or 70 cfs.
-The water of Weekiwachee River is low in mineral content from
the headwater (at Weekiwachee Springs) to near its mouth, figure 12.
The mineral content of Weekiwachee Springs is nearly constant at 145
mg/1.























EXPLANATION

Streamflow Measuring Site

3,' v 3 1^ ^'
Upper number Is mineral content, lower 1
number Is chloride concentration,
both in milligrams per liter. All
samples collected within a 2-hour
period, near low tide.
o 2a MILES



28030' .. .1'"' *. .28.30d
30630 482 34'


Figure 12. Map showing mineral content and chloride concentration of water at selected sites on
.Weekiwachee River, April 29, 1964






REPORT OF INVESTIGATION NO. 56


PITHLACHASCOTEE RIVER

The Pithlachascotee River rises in south-central Hernando County
and flows southwestward through Pasco County to enter the Gulf of
Mexico at New Port Richey. The major tributaries are Jumping Gully
and Five Mile Creek. The upper reaches contains many lakes, sinks, and
depressions. The middle and lower reaches are swampy, and ill-defined
flow is affected by tide near the mouth. The estimated average flow at
the mouth was 55 cfs (36 mgd). Jumping Gully contributes about 25
cfs (16 mgd) to this flow and Five Mile Creek less than 5 cfs, or 3.2 mgd,
(estimated). The remainder, 25 cfs (16 mgd) is ground-water seepage
through the channel bottom downstream from these tributaries.
Land elevations range from 150 feet above msl in the headwaters
to mean sea level at the mouth. The slope of the river channel is about 9
feet per mile in its upper reaches, about 1.5 feet per mile in the middle
reaches, and about 5 feet per mile in the lower reaches.
In the headwater area, small channels connect lakes such as
Hancock, Moody, Middle, and Iola. These lakes have no visible outflow
channel to the Pithlachascotee River. Neff and Mountain lakes are
interconnected with a surface channel and likewise have no visible
outflow channel. Lakes Hancock and Neff, the down-gradient lakes in
each of the chains, have sinkholes open to the Floridan aquifer through
which drainage occurs and both lakes, in the past few years, have been
greatly reduced in size and depth. Neff Lake has become essentially a
wet prairie.
Crews Lake is divided north and south by an earthen dike that
contains a culvert connecting the two parts. Most of the inflow is from
Jumping Gully which flows into the southern part and then through a
culvert in the dike to the northern part. The northern part contains a
sinkhole through which lake water can freely drain to underlying
aquifers. This sequence is indicated by the following factors: (1) when
lake stages decline below the culvert, lake levels in the northern part
decline at a faster rate; (2) lake levels have declined sufficiently to
permit observation of inflow to the sinkhole; and (3) local reports
indicate that the lake has completely drained through the sinkhole
during exceptionally dry years. The peak inflow to Crews Lake from
Jumping Gully was about 920 cfs (595 mgd) on September 18, 1964.
At the outlet, the peak flow was about 270 cfs or 175 mgd (as
determined from a rating curve extended above 222 cfs, or 143 mgd).
The peak flow of the Pithlachascotee River at New Port Richey,
1,410 cfs (911 mgd) on September 11, 1964, preceded the peak flow at
Jumping Gully by 7 days. No secondary peak was observed at New Port







BUREAU OF GEOLOGY


Richey. The rain that caused this peak occurred September 10 13.
Because the peak occurred downstream prior to the peak upstream and
because of the presence of many sinkholes in upgradient areas, much of
the flow at New Port Richey was derived from the underground
reservoir.
Water in the upper reaches of the river is low in mineral content
(generally less than 100 mg/1). The mineralization increases down-
stream and is highest in the lower reaches owing to tidal mixing with sea
water. Springs near the coast are generally high in mineral content
(14,000 mg/1) of which about 8,000 mg/1 is chloride.
The mineral content of the water of the river varies seasonally at
the measuring site above the tidal influence. The highest concentra-
tions occur in late May or early June and the lowest generally in August
or September. The variation in mineral content is related to the source
of the river's flow. During low-flow periods most of the water is seepage
from the Floridan aquifer, and the mineral content is relatively high,
chiefly calcium bicarbonate. During high flow periods most of the
water is overland flow and the mineral content of the water is relatively
low.
The following relations were used to estimate a separation of the
hydrograph for the Pithlachascotee River into components of water
from the Floridan aquifer and water from overland flow and the
shallow aquifer, figure 13. The equation used to determine this separa-
tion is given below:
Qi + Q2 = Q3
ClQ1 + C2Q2 = C3Q3
where Q1 is the component of seepage in cfs, from the
shallow aquifer and from overland flow;
Q2 is the component of seepage in cfs, from the Floridan
aquifer;
Q3 is the streamflow in cfs, of Pithlachascotee River near
New Port Richey;
C1 is 30, the average mineral content in mg/1 of typical
water from overland flow and the shallow aquifer;
C2 is 275, the average mineral content in mg/1 of typical
water from the Floridan aquifer in the Pithlachascotee River
area;
C3 is the daily mineral content in mg/1 of water from
Pithlachacotee River near New Port Richey.

Computations using this equation indicate that water contributed






REPORT OF INVESTIGATION NO. 56


by the Floridan aquifer to the stream averaged about 8 cfs (5.2 mgd)
for the 2.5 years of study. Therefore, during this period the aquifer
contributed about 15 percent of the average flow of the river. The
computations show that at high streamflow the contribution from the
Floridan aquifer to the river is greatest although this contribution is
only a small percentage of total high streamflow. Conversely, during
periods of low streamflow, the contribution from the Floridan aquifer
to the river is lowest but comprises a large percentage of total low flow;
the remainder is derived mostly from the shallow aquifer.

ANCLOTE RIVER

The Anclote River rises in south-central Pasco County and flows
westward to the Gulf of Mexico. The area adjacent to the river is
sparsely populated, and the major land uses are tree farming, cattle
ranching and citrus farming. Land surface elevations is 80 feet above
msl in the headwaters. The slope of the river ranges from about 2 feet
per mile in the reach of channel near Elfers to 5 feet per mile in the
headwaters. The average flow of the river near Elfers for the period of
study was 95 cfs (61 mgd).
The mineral content of the river is greater near the Gulf (about
22,000 mg/1) than upstream (about 220 mg/1). Above the reach of the
river affected by tidal inflow, the mineral content at low flow is due
chiefly to calcium bicarbonate. The surficial deposits underlying the
Anclote River consists mostly of sand and clay which are essentially
insoluble in water. Therefore, the calcium bicarbonate in the river
water is due principally to seepage from the Flpridan aquifer.
Flow relations and chemical quality of water of the Anclote River
and aquifers were used again to estimate the contribution of the
Floridan aquifer to the stream and to separate the streamflow hydro-
graph of the river into components of water from the Floridan aquifer
and water from overland flow and the shallow aquifer, figure 14.
Computations indicate that seepage from the Floridan aquifer averaged
about 10 cfs (6.4 mgd) for the period of study. Therefore, during this
period the aquifer contributed about 10 percent of the average flow of
the river.
BROKER CREEK
Brooker Creek rises in northwestern Hillsborough County near
Keystone Lake and flows generally westward through swampy areas, in
places with no defined channel, to Lake Tarpon in northeastern
Pinellas County. Land-surface elevation ranges from about sea level at
Lake Tarpon to 60 feet above msl in the headwaters. The slope of the





1,000


1964 1965


1966


Figure 13. Graph showing comparison of the average daily flow of the Pithlachascotee River near New
Port Richey and Floridan aquifer seepage (calculated) to the river






REPORT OF INVESTIGATION NO. 56


river varies from about 5 feet per mile in the headwaters to about 2.5
feet per mile near Lake Tarpon. For the period of study its average flow
near Lake Tarpon was 25 cfs (16 mgd).
A canal recently (1968) constructed by the Southwest Florida
Water Management District connecting Lake Tarpon with Old Tampa
Bay carries the runoff from the Brooker Creek area into the bay.
CURLEW CREEK
Curlew Creek, a small stream north of Dunedin, drains west into
the Gulf of Mexico. The channel slope ranges from about 60 feet per
mile for a short distance in the headwaters to 5 feet per mile near the
mouth. The creek heads in -the hilly area northwest of Safety Harbor.
The average flow at the mouth of the creek was estimated to be about
20 cfs (13 mgd) during the period of study.
STEVENSON CREEK
Stevenson Creek heads in -the hilly area near the central part of
Pinellas County and drains northwestward to the Gulf of Mexico. The
lower reach of the- creek"is tidal. The average flow at its mouth was
estimated to be 20 cfs (13 mgd) during the period of study.
McKAY CREEK
McKay Creek in the southwestern part of Pinellas County, rises in
the hilly area south of Clearwater and flows to the Gulf of Mexico. The
flow at the mouth of the creek was estimated to be 5 cfs (3.2 mgd)
during the period of study.
SEMINOLE LAKE OUTLET
Seminole Lake lies south of Clearwater. This lake was created in
1950 by damming the upper reach of Long Bayou, a salt-water inlet.
The freshening of Seminole Lake is discussed in this report in the
section entitled "Lakes". The average flow at the lake outlet was 13 cfs
(8.4 mgd) during the period of study.
ALLEN CREEK
Allen Creek is northeast of St. Petersburg and flows eastward to
Old Tampa Bay. Its flow was measured in 1948 50 but was not
measured during this study. However, by correlating the 1948 50
flows with those of other streams in the area during the same period,
the flow at the mouth during this study period was estimated to be 15
cfs (9.7 mgd).
ALLIGATOR CREEK
Alligator Lake is near the town of Safety Harbor and was formed
by damming off a salt-water inlet. Alligator Creek flows into Alligator





oo00


I


U
U
B



I


1964 1965


Figure 14. Graph showing comparison of average daily flow of the Anclote River near Elfers and Floridan
aQuifer seepage (calculated) to the river


1966






REPORT OF INVESTIGATION NO. 56


Lake and drains the hilly area west of Safety Harbor. The average flow
of Alligator Creek for the period of study was 8 cfs (5.2 mgd).
ROCKY CREEK
Rocky Creek rises in north-central Hillsborough County and
flows southward to upper Old Tampa Bay.
It drains about 35 square miles and the average flow at the gaging
station near the mouth for the period of study was 40 cfs, or nearly 26
mgd. The Rocky Creek drainage area is sparsely populated except near
lakes in the upper reaches and near upper Old Tampa Bay in the lower
reaches. Some of the lakes in the upper reaches are Hobbs, Cooper,
Thomas, Starvation, and Round, the levels of some of which have been
lowered by pumpage from the underlying Floridan aquifer. Tributaries
of Rocky Creek drain the land surface that includes Cosme and Section
21 well fields.
A flood relief channel in the lower reaches, constructed in 1966 as
part of the Upper Tampa Bay watershed project of the U. S. Soil
Conservation Service, carries flood flow southwest into upper Old
Tampa Bay.
The mineral content ranges from about 35 to 60 mg/1 in the
middle and upper reaches of the creek. The lower reach is tidal and
contains concentrations of chloride approaching those of sea water.
SWEETWATER CREEK
Sweetwater Creek rises in western Hillsborough County and flows
southward into upper Old Tampa Bay. Its channel slopes about 10 feet
per mile in the middle reaches and about 1 foot per mile in the lower
reaches. The drainage area is more than 50 feet above msl in the
headwaters. In the headwaters, the land surface is poorly drained and is
occupied by many relatively shallow large lakes such as Magdalene,
Bay, Ellen, Carroll, and White Trout, all of which are interconnected by
canals and culverts. The upper reach of the stream also contains many
small lakes, ponds, and sinks along the eastern topographic divide
which is adjacent to the sinkhole complex known as Blue Sink. During
periods of extremely high water, such as occurred during the floods of
1960, some of the drainage from nearby lakes flows into Blue Sink.
During the period of study the average flow at the mouth was an
estimated 25 cfs, or more than 16 mgd. The flow of this stream is
regulated and in periods of high water, Sweetwater Creek receives some
overflow from Cypress Creek through a low, swampy area separating
the two streams.
The water of Sweetwater creek is a calcium bicarbonate type in
the headwaters and sodium chloride at the mouth. The mineral content







BUREAU OF GEOLOGY


ranges from about 50 mg/1 in the headwaters to about sea-water
concentration at the mouth.
CYPRESS CREEK
Cypress Creek rises in northern Pasco County and flows south-
ward to the Hillsborough River. The channel is not well-defined except
in the middle reaches near Worthington Gardens, where the banks are
relatively steep. In the upper reaches the creek emerges from'low sand
hills and sinkholes and in the lower reaches south of Worthingt6n
Gardens it flows through swampy lowlands to the Hillsborough River.
Streamflow was measured periodically at several sites and con-
tinously near San Antonio during the study period. Near San Antonio
in the upper reaches, the average flow was 41 cfs (26 mgd), and near the
mouth of the river the estimated flow was 190 cfs (122 mgd).
The water of Cypress Creek is a calcium bicarbonate type and its
mineral content ranges from about 25 to 150 mg/1. The mineralization
is lowest during periods of high flow and highest during periods of low
flow. The calcium bicarbonate water represents seepage from the
Floridan aquifer.
The following relations were used to estimate the contribution of
the Floridan aquifer to the stream and to separate the streamflow
hydrograph of the creek into components of water from the Floridan
aquifer and from overland flow and the shallow aquifer, figure 15. The
equation is the same as that used in the discussion of the Pithlacha-
scotee River except that C1 is 28 and C2 is 165. Computations show
that seepage from the Floridan aquifer averaged about 7 cfs for the
2.5-year study. Therefore, during this period the aquifer contributed
about 20 percent of the average flow of the creek (near San Antonio).
Computations also show that at high streamflows discharge from the
Floridan aquifer is a negligible part of the total streamflow but at low
flow the creek consists chiefly of water derived from the Floridan
aquifer.
TROUT CREEK
Trout Creek heads just east of U.S. Highway 1-75 and south of
State Highway 52 and flows southward to the Hillsborough River. The
area is sparsely populated, low and swampy, and is used mostly for
cattle ranching. The channel slope ranges from about 10 feet per mile in
the headwaters to less than 5 feet per mile at the mouth. The stream-
flow averaged about 70 cfs (45 mgd) for the period of study as
determined by correlating the streamflow of Trout Creek with that of
Cypress Creek and New River.




-----I


W(every 5th day)

Calculated seepage, Floridan
aquifer (every 5th day)
A, A


,l0 / /







I I II I I II I I I I JIII I I I I .. .
J F M A M 'd J A S O N D J F M A M J A S O N D J F M A M J
1964 1965 1966

Figure 15. Graph showing comparison of average daily flow of Cypress Creek near San Antonio and
Floridan aquifer seepage (calculated) to the creek







BUREAU OF GEOLOGY


BUSY BRANCH

Busy Branch, east of Trout Creek and south of State Highway 52,
flows generally southward to the Hillsborough River. The area adjacent
to this stream is sparsely populated, and is flat and swampy and is
dotted with small lakes and ponds. The channel slope is about 10 feet
per mile for its entire length. Periodic streamflow measurements were
made at a site near the mouth, and an average streamflow of about 5 cfs
(3.2 mgd) for the period of study was determined by correlation with
New River.

NEW RIVER

New River begins south of San Antonio and flows southward into
the Hillsborough River. The flow of the river averaged about 15 cfs (9.7
mgd) for the period of study.


LONG-TERM TRENDS IN STREAMFLOW

Long-term hydrographs for three streams are shown in figure 16.
The Hillsborough River near Zephyrhills is near the southeastern
boundary of the Middle Gulf area; the Anclote River near Elfers is in
the western part; and the Withlacoochee River near Holder is near the
northeastern boundary of the area. These hydrographs show that
stream-flow during the study period approximated the average for the
long-term period.
The flow of Weekiwachee Springs west of Brooksville has been
measured periodically since 1917. From 1917 through 1966,300 flow
measurements were made, and the average of these measurements was
174 cfs (112 mgd). The maximum and minimum flows measured
during this period were 275 (178 mgd) and 101 cfs (65 mgd), respec-
tively. For the study period, the average of 18 flow measurements was
223 cfs (144 mgd). The maximum and minimum measured flow during
the study period was 275 cfs (178 mid) and 170 cfs (110 mgd),
respectively.
The flow of Homosassa Springs at Homosassa Springs has been
measured periodically since 1932. From 1932 through 1966, 25 flow
measurements were made. The average of these measurements was 199
cfs (129 mgd), and the maximum and minimum flows measured were
257 cfs (166 mgd) and 125 cfs (81 mgd), respectively. The average of
12 measurements of the flow made during the study period was 224 cfs







REPORT OF INVESTIGATION NO. 56


(145 mgd). The maximum and minimum measured flow during the
study period was 257 cfs (166 mgd) and 170 cfs (110 mgd), respec-
tively.

LAKES

GENERAL CHARACTERISTICS

Lakes occur in most of the Middle Gulf area but are more
numerous in the eastern and southern part. The origin of Florida lakes
has been discussed by White (1958) and by Matson and Sanford
(1913).

Matson and Sanford (1913, p. 25) state that "In the central part
of the peninsula are lakes and swamps which appear to be the result
either of unequal depression of the surface sands or of solution of the
subjacent limestone and consequent lowering of the surface. ***Some
of the lakes are shallow and resemble those of the coastal belt, but
others are deep basins partly or wholly enclosed by a rim of rock. Many
of the smaller swamps contain peat or muck, but few of the deposits
attain any great thickness and many of them form only a thin coating
of partly decomposed vegetable matter mingled with more or less
sand."
Figure 17 shows areas of comparable range of stage fluctuations
of selected lakes within the area during the period of study. The
fluctuations show a range of less than two feet to more than four feet.
Lakes in the east-central and southern parts of the area have the
greatest range in fluctuation. Many of these lakes are hydraulically
connected to the Floridan aquifer through sinkholes.
Stage fluctuations of a lake in an upgradient area, stage fluctua-
tions of a lake in a downgradient area; stage fluctuations of a lake
affected by ground-water withdrawals, and stage fluctuations of lakes
formed by damming tidal inlets are compared on figure 18. Lake stages
tend to be highest in the summer or early fall during the rainy season
and lowest in late spring during the dry season. Lake levels in the
upgradient areas of the Middle Gulf tend to fluctuate through a greater
range than in lakes in downgradient areas. Where lakes are affected by
ground-water withdrawals, levels tend to decline at greater rates than in
lakes not so affected.
The range of fluctuations is minimal in controlled lakes, such as
Alligator and Seminole lakes, which were formed by damming tidal







BUREAU OF GEOLOGY


Figure 16. Hydrographs of long-term streamflow for selected streams
in the Middle Gulf area


inlets. Continuous gaging station records on these lakes show no
evidence of tidal fluctuation, and seasonal fluctuations are minimal.
Water from lakes in the northern and eastern parts of the area
contain a lower mineral content than water from lakes in the western
part of the area, figure 19. Waters of some lakes near the coast that
contain high mineral content have soidum chloride as the principal
constituent. In other coastal lakes and lakes in the southwestern part of
the area, calcium bicarbonate is the principal constituent.
The chloride concentration of Seminole Lake decreased from
about 2,300 mg/i in May 1950, when the dam was completed, to 25
mg/1 in November 1957, figure 20. The water in this lake has contained
less than 250 mg/1 chloride since October 1951, about 2 years after
completion of the dam. The -chloride concentration has ranged from








REPORT OF INVESTIGATION NO. 56


EXPLANATION



Area in which lake
stage fluctuated
less than 2 feet



Area in which lake
stage fluctuated
from 2 to 4 feet



Area in which lake
stage fluctuated
more than 4 feet

Middle Gulf Area
Boundary


Figure 17. Map showing ranges of fluctuation of selected lakes in
Middle Gulf area during the study period








BUREAU OF GEOLOGY


NEFF LAKE
100






96'
_4










AL.LIGTOR E -
ROLMN LAKE




49
-i


96 A4 19GATR LAKE1966









Figure 18. Hydrographs showing comparison of stage fluctuations of












equal to the average annual rainfall (Pride 1965). The mineral content
SEMINOLE LAKE


J F M A M J J A S 0 N D J F M A M J J A S O N D J F M A M J
1964 1965 1966

Figure 18. Hydrographs showing comparison of stage fluctuations of
Neff Lake (in upgradient area). Hunters Lake (in down-
gradient area), Round Lake (affected by ground-water
withdrawals), and Alligator and Seminole Lakes (stage
controlled)




about 30 to 180 mg/i since 1957. The average outflow from the lake
during the study period was about 10 cfs (6.4 mgd).

The evaporation from lakes in central Florida appears to be about
equal to the average annual rainfall (Pride 1965). The mineral content
of most of the lakes is relatively low and periodic sampling of several
lakes indicated little seasonal variation. The low mineral content is
controlled not only by rainfall and evaporation but by constant move-
ment of ground water through the lakes. Some of the lakes that have a
relatively high concentration of calcium bicarbonate may receive water
by upward leakage from the Floridan aquifer.







REPORT OF INVESTIGATION NO. 56


EXPLANATION


A 800
Sampling site, showing min-
eral content, in milligrams
per liter.


Middle Gulf Area Boundary


Figure 19. Map showing mineral content of water in selected lakes in
and near the Middle Gulf area, May 1965





































Figure 20. Graph showing changes in chloride concentrations and water levels of Seminole Lake,
1950-1966






REPORT OF INVESTIGATION NO. 56


LAKE TARPON

Lake Tarpon and its underground connection with Spring Bayou
has been studied in considerable detail by Taylor (1953) and Heath
(1954). Wetterhall (1965) made additional measurements of salinity in
the sink area. No extensive study of the lake was conducted as a part of
this investigation, although continuous stage was recorded for Lake
Tarpon and Spring Bayou and daily water samples were collected at
Lake Tarpon.
Figure 21 shows the water levels in Lake Tarpon and Spring
Bayou, and the mineral content of water in Lake Tarpon during the
period of study. The changes in mineral content are due mostly to
changes in salinity, and appears to be lowest during the early fall
months at the end of the rainy season and highest during the early
summer months, the dry season. During this study the lowest mineral
content, 630 mg/1, was observed in late September 1964. This low
occurred about 10 days after the lake stage reached the highest level for
the study period. From this low, the mineral content increased to its
highest value (3,600 mg/1) in late July 1965. During this period of
higher mineral content, the lake stage varied from about 1 to 3 feet and
generally was about 2 feet above msl. A sharp decrease in mineral
content occurred immediately following the high concentration
recorded in late July. At the same time, lake stage showed a sharp rise,
followed 10 days later by a decline. Thus, the most significant de-
creases in mineral content occurred following periods of highest lake
stages. The sharp decrease in mineral content in the period July -
August 1965 is due to displacement of salty water in Lake Tarpon by
fresh water inflow from Brooker Creek and rainfall. Dilution of the
mid-July 1965 Lake Tarpon water by fresh-water inflow could not
account for the sharp decrease in mineral content coincident with a
decrease in stage. The stage decrease was caused by drainage of the lake
through the sinkhole which resulted by early September in low stages
in the lake and low mineral content of water at the sampling site.
A comparison of the water stages in Spring Bayou with the water
stages of Lake Tarpon shows that water stages of Lake Tarpon are
generally higher than those in Spring Bayou. Discharge from the lake
through Spring Bayou occurred when the lake stages were above the
high-tide stage in Spring Bayou. However, the same head difference
between Lake Tarpon and Spring Bayou does not always cause flow
through the underground channel. Therefore, discharge from the lake
is probably due to a combination of head difference and the salinity









4000 I I l-l I II Il il l i l l l I 1


f 3000 --------. ----- --- ------------------
3j 000

S2000------ --_-- --------------- -----.....---
W, -LAKE TARPON
3 10006oo


0 ,





SPRING BAYOU




4.0 I lI I I I '

J F M A M J A SO N D J F M A M J J A S O N D J F M A M J
1964 1965 1966

Figure 21. Water levels in Lake Tarpon and Spring Bayou and the mineral content of water in Lake Tarpon
during the period of study .
I-






during the period of study.






REPORT OF INVESTIGATION NO. 56


conditions in the underground channel connecting Lake Tarpon with
Spring Bayou, as explained by Cooper in a personal written communi-
cation with Heath (1954).

AQUIFERS
The aquifers in the Middle Gulf area are the shallow aquifer and
the Floridan aquifer.

SHALLOW AQUIFER

The saturated coarser grained surficial deposits overlying the
limestone constitute an aquifer that receives water almost entirely
from local precipitation. The exception is recharge from artesian
seepage and springs and from man's activities and works, including
irrigation and effluent from septic tanks and cesspools. The depth to
water in the shallow aquifer averages less than 8 feet, and in much of
the area is less than 3 feet below land surface.
The slope of the water surface is controlled by the permeability of
the water-bearing materials, saturated thickness of the deposits, and
local variations in recharge and discharge. Rises in water level are
caused by recharge by rainfall, and declines in water level are caused by
seepage into streams, lakes, and canals, by evapotranspiration, by
leakage induced by pumpage from wells, and by natural leakage into
the Floridan aquifer.
The general shape of the water surface in the shallow aquifer for a
high-water period August November 1965, and a low-water period
May 1966, are shown in figures 22 and 23. The August-November map
represents a period when water levels are at seasonal highs, and the May
map represents a period when water levels are at or near seasonal lows.
The direction of movement of the water is down-gradient and
normal to the contour lines. The water moves generally westward in the
northern part of the area and south to southwestward and southeast-
ward in the southern part. The slope of the shallow water table is about
the same as the slope of the stream channels in the area, and the
configuration of the water table is similar to that of the land surface
and that of the potentiometric surface of the Floridan aquifer.
The water level in the shallow aquifer ranges from slightly below
to as much as 17 feet above the water level in the Floridan aquifer.
Throughout much of the area, water moves downward from the
shallow aquifer and recharges the Floridan aquifer. However, locally
around upper Old Tampa Bay and southeast of New Port Richey, the








BUREAU OF GEOLOGY


EXPLANATION
20---
Contour line shows elevation of
the water table in feet. Datumn
is mean sea level. Contour
interval 10 feet.



Middle Gulf Area Boundary
Q *


Figure 22. Map of Middle Gulf area showing contours of water levels
in the shallow aquifer during a period of high water levels,
August-November 1965








REPORT OF INVESTIGATION NO. 56


EXPLANATION
20--20--
Contour line shows elevation of c
the water table in feet. Datum-
is mean sea level. Contour
interval 10 feet.


Middle Gulf Area Boundary


0,
*


Figure 23. Map of Middle Gulf area showing contours of water levels
in the shallow aquifer during a period of low water levels,
May 1966







BUREAU OF GEOLOGY


water level in the shallow aquifer is lower than the level in the Floridan
aquifer and water flows upward to the shallow aquifer. In the northern
part of the area no apparent head difference exists between the shallow
and Floridan aquifers. The greatest difference occurs in the well fields
in the southern part, and in the topographically higher Brooksville area.
The shallow aquifer is not at present extensively used as a source
of domestic or public supply in the Middle Gulf area. Currently its most
extensive use is for lawn irrigation.
The hydrographs of the water levels in the shallow aquifer in the
southern part of the area and rainfall records at a nearby station are
shown in figure 24. The highest water levels generally occur in July and
August, the wettest months, and the lowest in late May or early June
just prior to the rainy season.
Undisturbed samples of sediments comprising the shallow aquifer
were collected at twelve sites at depths ranging from 1 foot to 9 feet
and at two sites from depths of 10 to 42 feet in the Middle Gulf area
figure 25. Selected samples of shallow aquifer materials were analyzed
for permeability, porosity, specific yield, and particle-size distribution.
The analyses were made by the Hydrologic Laboratory, U. S. Geologi-
cal Survey, Water Resources Division, Denver, Colorado. Table 1 shows
the results of the tests.
The coefficient of permeability ranged from 0.001 gpd per ft2
(gallons per day per square foot) at sampling sites 5 to 13 miles
northwest of Brooksville to 210 gpd per ft2 10 miles west of Brooks-
vflle. The porosity ranged from 32 to 45 percent and averaged 39
percent. The specific yield averaged about 29 percent. These values
indicate that although the shallow material has a relatively low perme-
ability, the storage capacity is large and the volume of water that will
drain from the material, given enough time, is large.
Table 1 shows the specific retention, porosity, specific yield and
the permeability for samples collected at 13 sites in the area. This table
indicates that permeability in the area is highly variable. The perme-
abilities are greatest near the surface of the ground and generally
decrease with depth. For example, the permeability of samples 13 to
13C decreased from 77 to 5 gpd per ft2 in the depth interval 1 foot to
8V2 feet; samples 10 to 10C decreased from 110 to 6 gpd per ft2 in the
depth interval 1 foot to 6 feet; and samples 4A to 4C decreased from 49
to 0.002 gpd per ft2 in the depth interval 3 to 6 feet. Samples 6 to 6A
collected east of Weekiwachee Springs and samples 7 to 7C collected
near the Hernando-Pasco County line did not show any significant
changes in permeabilities at depths of 1 foot to 9 feet.


















J


I I I I I I I I I I I I I
STARVATION LAKE WEATHER STATION 1



.1 ,, [ ,, I. ,I iI, L j .iL lJ .,d,..i . i ,. i iLii 4 I,,, .


J F M A M J


I ') A I S
1965


I N


J F M A
1966


z
C


Figure 24. Graph showing rainfall at Starvation Lake weather station, and water-level fluctuation in the
shallow aquifer in the southern part of the Middle Gulf area, January 1965 -- June 1966


____ 0

0


I J







BUREAU OF GEOLOGY


Figure 25. Map showing location of sediment sampling sites and
permeabilities of selected samples in the Middle Gulf area








REPORT OF INVESTIGATION NO. 56


Table 1. Laboratory analysis of unconsolidated sediment samples
(Analysis by U. S. Geological Survey Hydrologic Laboratory, Denver, Colorado)




Specific Total Specific Coefficient of
Sampling site Depth retention porosity yield permeability
(feet) (percent) (percent) (percent) (gpd per ft2)


1
2
3
4
4a
4b
4c
5
6
6a
7
7a
7b
7c
8
9
9a
10
10a
10b
10c
11
12
12a
12b
12c
12d
13
13a
13b
13c
13d
13e
13f


1.0-1.2
3.0-3.2
2.0-2.2
1.0-1.2
2.8-3.0
3.8-4.0
6.0-6.2
3.0-3.2
4.0-4.2
9.0-9.2
0.9-1.1
3.1-3.3
6.0-6.2
8.0-8.2
2.5-2.7
1.0-1.2
6.0-6.2
0.8-1.0
3.0-3.2
4.5-4.7
6.0-6.2
3.0-3.2
4.0-4.2
10-12
20-22
30-32
40-42
1.0-1.2
3.0-3.2
5.2-5.4
8.5-8.7
10-12
20-22
30-32


6.8

8.6
-



28.6
38.4

2.0



3.7
3.4

2.8



7.7
2.5
4.9
4.9
4.0
9.0
8.5



11.1
8.2
5.6
10.1


38.4

45.5



32.5
45.5

35.7



36.0
40.2

34.7



35.6
32.2
34.9
36.1
37.2
43.2
44.4



38.4
45.5
37.1
42.2


31.6

36.9
-



3.9
7.1

33.7



32.3
36.8

31.9


. -
27.9
29.7
30.0
31.2
33.2
34.2
35.9



27.3
37.3
31.5
32.1


78
91
42
.001
49
.1
.002
.001
200
210
39
56
43
44
56
92
66
110
150
74
6
46
12
180R/
180R/
67R/
17R/
77
62
6
5
40R/
190R/
67R/


R/Repacked samples







BUREAU OF GEOLOGY


FLORIDAN AQUIFER

The Fioridan aquifer, one of the most productive in the world,
underlies the Middle Gulf area. This aquifer supplies virtually all
ground water used in the area, feeds some of the largest fresh-water
springs in the world, and is the conveying unit by which most of the
water moves through the area. The aquifer is composed of a number of
thick permeable zones which more or less function as a single water
conveying and water storage unit within several geologic units. These
units consist of more than 1,000 feet of limestone and dolomite and in
descending order from younger to older include the lower part of the
Hawthorn Formation, the Tampa Formation, the Suwannee Lime-
stone, the Ocala Group (Crystal River Formation, Williston Formation,
and Inglis Formation), the Avon Park Limestone, and the upper part of
the Lake City Limestone. In most areas the upper predominantly sandy
and clayey part of the Hawthorn Formation is included in the shallow
aquifer.
Zones of different permeability occur within the aquifer. Some
zones yield large volumes of water whereas others yield little water.
The most productive zones are: (1) the uppermost limestone (Haw-
thorn Formation or Tampa Formation) that directly underlies the
surficial sand and clay deposits; (2) the lower part of the Suwannee
Limestone; (3) the Avon Park Limestone below the top 100 feet; (4)
and the upper part of the Lake City Limestone.
The depth to the top of the Floridan aquifer differs throughout
the area. In this report, the top of the aquifer is taken to be the top of
the first consistent limestone, figure 26. The highest elevation of the
aquifer top is in the eastern part of the area and the lowest elevation is
in the southern part near the coast. In the western third of the area, the
top of the aquifer is below mean sea level.
Figures 27 and 28 show the elevation of water levels in the
Floridan aquifer during August September 1965 and May 1966. The
configuration of the contours was about the same in September as in
May although the September water levels were about 2 feet higher.
These illustrations also show the mean sea level contour (zero
contour on maps) near the coast. The exact position of the mean sea
level contour is not well defined and its location was extrapolated from
the spacing of the next two up-gradient contours. The position of this
contour inland will markedly affect the hydrology of the inland area
and the hydrochemistry of the aquifer. Where this zero water level lies
inland, offshore outflow from the aquifer is negligible and discharge
from the aquifer takes place inland from the zero contour.








REPORT OF INVESTIGATION NO. 56


EXPLANATION
-20-
Contour shows elevation of the
top of the Floridan aquifer
in feet. Datum is mean sea
level. Contour interval 20 feet.


Middle Gulf Area Boundary


Figure 26. Map of Middle Gulf area showing contours on top of the
Floridan aquifer









BUREAU OF GEOLOGY


EXPLANATION
----20-
Contour line represents the elev-
ation of the potentlometric sur-
face, feet above mean sea
leveL Contour interval 10 feet.



Middle Gulf Area Boundary

4.Q


Figure 27. Map of Middle Gulf area showing contours of water levels
in the Floridan aquifer during a period of high water levels,
August-September 1965








REPORT OF INVESTIGATION NO. 56


EXPLANATION
---20
Contour line represents the elev-
ation of the potentiometric sur-
face, feet above mean sea
level. Contour interval 10 feet.


Middle Gulf Area Boundary


Figure 28. Map of Middle Gulf area showing contours of water levels
in the Floridan aquifer during a period of low water levels,
May 1966







BUREAU OF GEOLOGY


Recharge to the Floridan aquifer occurs wherever geologic and
hydrologic conditions are favorable for water to move into the aquifer.
Recharge is not restricted to areas of high water levels (as for example,
the Pasco high). A substantial part of the recharge occurs over the
entire area through permeable material overlying the aquifer, through
sinkholes, and from streams and lakes.
Water tends to move perpendicular to and toward contours of
progressively lower elevation. The general direction of water move-
ment in the Floridan aquifer in the Middle Gulf area is from east to
west, but in the southern part of the area movement is south to
southwest.
Discharge from the Floridan aquifer occurs as (a) seepage or
spring flow into streams; (b) pumpage from wells; (c) ground-water
outflow; and (d) evapotranspiration in areas where the aquifer is at or
near land surface.
A water balance was determined for the Floridan aquifer in the
southern part of the area and is discussed in detail in a later section.
Water-level fluctuations. The volume of water in the aquifer
varies with changes in the amount of recharge and discharge. When
recharge exceeds discharge, the water in storage increases and the water
levels rise; conversely, when discharge exceeds recharge, the water in
storage decreases and water levels decline. Thus, water-level fluctua-
tions are an index to seasonal and long-term changes in storage.
The hydrographs of wells penetrating the Floridan aquifer in the
Middle Gulf area shown in figure 29 illustrate seasonal and long-term
changes in water levels. The highest water levels generally occur in
September and October following the rainy season and the lowest
water levels occur in May, just preceding the rainy season. The patterns
of seasonal water-level fluctuations generally are similar throughout
the Middle Gulf area except for those wells in or near heavily pumped
areas. The greatest range in water-level fluctuations occurs in the
eastern part of the Middle Gulf area and in.an area of heavy pumping
north of Tampa; the smallest fluctuations occur in the western part of
the area, figure 30.
Long-term water-level records of two wells (808-245-424 and
815-226-112) within 5 to 11 miles of three large well fields in
northwest Hillsborough and northeast Pinellas counties do not show
any noticeable declines in water levels as a result of large ground-water
withdrawals from the fields, figure 31. This indicates that noticeable
regional declines have not occurred. However, long-term records for a
well (807-230-433) in the cone of depression caused by pumping in St.



















56
Well, 819-233-214A
Depth, 73 feet
. Casino. 60 feet


De. -- I-- ------- I-

48 -
68


Well, 819-231-211
Depth, 444 feet
60 Casingo 47 feet _


19635


1964


1965


1966


Well, 8191221-411 I I
Depth, 113 feet
Casingo 83 feet 80


I i I 76
| --- --- i -- -- i -- i -- i --- --- 28
Well, 812-239-322 ~
Depth, 301 feet
Casing, 76 feet 24


-I I I I 20

Well, 811-235-322
Depth, 316 feet
Casino. 65 feet 44





,----- I36

Well 811--30-132A 60
Depth, 345 feet
Casing, 178 feet 56


I I I I 5


1963


1964


1965 1966


Figure 29. Hydrographs showing seasonal changes in water levels in the Floridan aquifer


Well, 820-237-342 .
Depth, 73 feet
Casing, 58 feet /


-J
W
-J


z
w


go N








BUREAU OF GEOLOGY


EXPLANATION


Area in which ter levels
fluctuated less than 4 feet.



Area in which water levels tu
fluctuated from 4 to 8
feet. .
0-


Area in which water
levels fluctuated
more than 8 feet


die Gulf Area Boundary


Figure 30. Map of Middle Gulf area showing range in water-level
fluctuations in the Floridan aquifer, January 1964 June
1966






REPORT OF INVESTIGATION NO. 56


Petersburg's Section 21 well field indicate that water levels have
declined progressively almost 11 feet since pumping began at the
well field in February 1963. This continuous decline indicates that the
cone of depression is still expanding and that vertical leakage from the
shallow aquifer is not yet sufficient to support the withdrawal. There-
fore, the lateral extent of the cone of depression will continue to
expand with increases in pumping rates.
Ground-water withdrawals in the well-field areas increased from
about 3 mgdin 1930 to about 45 mgd in 1966.
Hydrographs of paired shallow and deep wells in Pasco County are
shown in figure 32. Water levels in the deep well (depth 150 ft.) are
representative of water levels in the Floridan aquifer and water levels in
the shallow well (depth 9 ft.) are representative of water levels in the
shallow aquifer. Both wells respond rapidly to rainfall, and the patterns
of water-level fluctuation are similar, thus indicating good hydraulic
connection between the aquifers.
Hydraulics of the aquifer The transmissivity of the Floridan
aquifer in the coastal area north of the Pasco-Hernando County line
was determined from the equation Q = TIL. The average hydraulic
gradient in the Floridan aquifer for a 37-mile section extending from a
point north of the town of Crystal River nearly to the Citrus-Hemando
county line was about 1V2 feet per mile. The total discharge of water in
this area was about 1,300 cfs (840 mgd), which included the flow of
Crystal River, Homosassa Springs, and Chassahowitzka River. Trans-
missivity of the aquifer was 15 mgd per foot. Using the same method,
the transmissivity was also computed for an 18-mile section extending
south of the Hemando-Citrus county line to south of the Hernando-
Pasco county line. This section included the Weekiwachee Springs area.
The hydraulic gradient in the section averaged about 2 feet per mile,
and the flow of the Weekiwachee averaged 300 cfs (194 mgd). The
computed transmissivity was about 5 mgd per foot. These large trans-
missivities of the aquifer were reflected by the large spring discharges
along the northern part of the Middle Gulf area.
A number of aquifer tests were made in the Southern part of the
Middle Gulf in Pinellas and Hillsborough counties to determine the
hydrologic properties of the Floridan aquifer. Analyses of these tests
indicated that the coefficient of transmissivity of the aquifer in the
southern part of the area ranged from 165,000 to 550,000 gpd per ft.
and the coefficient of storage from 0.002 to 0,007.
Analyses of data in engineering reports by Black and Associates,
and Briley, Wild and Associates (1952, 1954) for aquifer tests at the






BUREAU OF GEOLOGY


Figure 31. Hydrographs showing long-term water-level records for
wells in Middle Gulf area
Eldridge-Wilde field indicated that the vertical movement of water
through the overlying sediments was detectable within less than a day.
A leakage factor P'/m' (where P' is the coefficient of vertical perme-
ability of the confining bed and m' is the thickness of the bed) was
determined to be about 2 x 10-3 gpd per ft3 .The quantity of water
recharging the Floridan aquifer based on a head differential of 10 feet
was computed to be 560,000 gpd per square mile, and based on a head
differential of 15 feet on May 19, 1966, was about 840,000 gpd per
square mile.






108


"0 I06 Screen, 6-9 feet / ________



S 104 ,



0 98 1 1 1 1 I l lI 11 1 1 1
Well, 817-216-314 ,._
Depth, 150 feet
9 Casing, 57 feet _


49 ,-


^ 92 -
I / v^ /^V^-


1965 1966
Figure 32. Hydrographs showing water-level fluctuations in paired shallow and deep wells, Pasco County





BUREAU OF GEOLOGY


A 3-day test at the Section 21 well field indicated that the
permeability of the materials overlying the Floridan aquifer was small.
Data collected by Leggette, Brashears, and Graham (1966) during a
long-term test at the well field indicated that leakage occurred within
about 11 days. The leakage factor (P'/m') computed from the test was
about 1.5 x 10-3 gpd per ft3. Based on this value of P'/m', recharge to
the Floridan aquifer by leakage from the shallow aquifer ranged from
about 590,000 to about 670,000 per square mile.
Figures 33 and 34 show time-drawdown graphs based on values of
transmissivity, storage, and leakage obtained at the Eldridge-Wilde and
the section 21 fields. For example, at the Elridge-Wilde field the
drawdown in a well 100 feet from a well being pumped at 1,000 gpm
for 100 days is about 6.6 feet, and at a distance of 1,000 feet the
drawdown would be about 3 feet. Estimated water-level declines for
any pumping rate can be determined from the curves because the
drawdowns are directly related to the rate of pumping. Thus, if the
pumping rate is doubled, water-level declines will be double that shown
on the curves.
Water quality. The quality of water in the upper 300 feet of the
Floridan aquifer is generally good. The mineral content of the water is
less than 500 mg/1 except near the coast where the concentration
approaches that of sea water. Water that has a mineral content of less
than 500 mg/1 is usable for most purposes. The mineral content in the
inland area is mostly calcium bicarbonate, which causes the water to be
alkaline and moderately hard to hard. Other mineral constituents,
including silica, potassium, sulfate, sodium, and chloride occur in
concentrations generally less than 10 mg/1. Fluoride and nitrate are
usually present in concentrations of less than 1.0 mg/1. Analysis of
water from selected wells in the Middle Gulf area are presented in Table
2.
Figure 35 shows the mineral content and chloride concentration
of water in the Floridan aquifer in the Middle Gulf area. The high
mineral content of water in the aquifer near the coast is caused by sea
water. Generally water in the area bordering the coast contains chloride
in excess of 250 mg/1, especially in wells deeper than 100 feet.
Mineralized water occurs at depths greater than 700 feet in the well
fields in northwest Hillsborough and northeast Pinellas counties.

WATER BALANCE

The water balance is a method of accounting for the inflow and
outflow of a hydrologic system. The balance involves estimating the








r= 10,000 feet





r= 1,000 feet







7-" ra 100 feet
EXPLANATION r 100 feet
Transmlsslvity- 165,000 gpd per ft.
Storage x 0.0015
Discharge = 1000 gpm.
P'/m'' 0.002 gpd per ft.
0= 1,000 gpm
Distance= 100, 1,000, and 10,000 ft.
I_


10 100
TIME SINCE PUMPING BEGAN, DAYS


1000


10,000


Figure 33. Time-drawdown curves, Eldridge-Wilde well field


A






















0



0

*0


TIME SINCE PUMPING BEGAN, DAYS


Figure 34. Time-drawdown curves, Section 21 well field







REPORT OF INVESTIGATION NO. 56 65





oO c 2 0 o-
29 \MARION CO.


LOCATION MAP'R SA 12



EXPLANATION 175- m
"^ 203-14 76 79
45 096480-5 0 4 -
Upper number, preceding dosh, s minn- I
oral content, upper number, following .- -C1
doash, is chloride concentration, both RNANDO
In milligrams per liter. Lower numbers
snicate sampling interval in feet below
land surface.

Area where water In wells more than 100
feet deep Is likely to contain chloride
in excess of 250 milligrams per liter. 4
30 0 O 118-305 f S

Middle Gulf Area Boundary HERNANDC CO.
PASO PASCOCO.

0103-120

-0











28! 00 2 -8' 00'


Figure 35. Map of Middle Gulf area showing mineral content and
chloride concentration in the Floridan aquifer






BUREAU OF GEOLOGY


TABLE 2. ANALYSES OF WATER FROM SELECTED WELLS IN MIDDLE
GULF AREA (Chemical constituents are expressed in milligrams per
liter)


o u-2 ho 3





748-22-122 2-10-65 177 144 F 144-177 23.4 74 0.17 91 5








814-21-334 2-24-65 560 90 F 90-560 24.4 76 .07 46
820-216423 2-16-65 350 225 F 225-350 23.4 74 .82 46
821-211-213A 2-24-65 200 150 F 150-200 23.4 74 .03 43








74822-242-41122 2-17-65 17720 14403 F 14403-17720 23.8 74 0.17 91 15
75832-246-23212 2-14-65 21757 300 F 300-757 22.8 73 .7812 694 12
8405-233-42114 8-2-9-65 35176 10566 F 10566-176354 26.3 79 .0013 68 3.5
845-210-334 2-4-65 212 190 F 90-212 23.2 74 .25 46 1.2





84721-234-313 2-324-65 79 76150 F 15076-79 23.6 74 .03 43 4.5
85322-24035-211 2-317-65 152 100 F 100-152 23.2 74 .2408 55 4.6
85543-23327-243A 2-2-65 295176 166 F 166-176295 23.4 7 .1200 44 8.7



853-235-211 2-3-65 152 100 F 100-152 23.2 74 .24 28 5.4
855-227-243A 2-2-65 295 F -295 23.4 74 .12 33 2.5






REPORT OF INVESTIGATION NO. 56


Hardness
asCaCO3
m u 0 I
00C
? Z "- ^ 4 CO 4.- J '
v La 0 Zo
c3 0 .
S 0 >a W -e U *
Cd w ~ ~ Cd 010
Q Cd 11. 0 0 $.a rA ~b1 C. j
0 0 Cd 0 ~ .-4 U~ 0
En U m U Xd Z .^UE Z r,,.0. U


31
88
5.9
6.5
5.3
4.9
4.5
15
5.6
3.7
5.6
16

2.8
2.2


2.5
1.7
0.9
1.2
.3
.9
.2
.9
.5
.4
.6
1.1
.4
.3


236
209
222
244
136
143
134
167
221
168
129
142
94
111


13
14
2.4
5.8
3.6
6.2
11
3.0
11
7.2
2.4
9.2
15
.4


106
208
8.0
7.0
8.0
8.0
8.0
26
8.0
5.0
7.0
26
4.0
3.0


0.3
.4
.2
.2
.2
.1
.2
.1
.2
.3
.1
.2
.2
.1


0.1
.0
.1
.1
4.9
2.5
1.6
.0
.0
.0
.2
.0
.0
.0


406
532
211
229
145
151
148
193
216
161
127
175
110
104


288
284
184
198
120
128
126
156
196
146
110
124
92
92


94
112
2
0
8
11
16
19
15
8
4
8
15
1


689
975
349
370
249
258
250
331
360
290
225
309
182
178


7.7
7.7
7.8
7.9
7.5
7.7
7.7
7.8
7.7
7.3
7.7
7.9
7.9
7.9






BUREAU OF GEOLOGY


quantities of water involved in each component of inflow and outflow
parameters for a given period. Each component taken into considera-
tion in the balance is given in the equation below:
P+SI+GI- R- ET GO=A S (1).
where P = Precipitation, inches
SI = Surface-water inflow, inches
GI= Ground-water inflow, inches
R= Runoff, inches
ET = Evapotranspiration, inches
GO = Ground-water outflow, inches
AS = Change in storage, inches
The Middle Gulf area is delineated by a topographic divide.
Therefore, surface-water inflow to the area is zero. Precipitation,
runoff, and ground-water outflow can be measured or estimated with
reasonable accuracy. The period of time covered by the calculation can
be selected so that the change in storage is practically negligible. This
water balance was determined for a 2-year period, June 1964 May
1966.
A water balance for the Middle Gulf hydrologic system (2,830 sq.
mi.) which includes most of the Middle Gulf area and an area to the east
of the Middle Gulf area was determined. In determining a water balance
the boundaries of the Middle Gulf hydrologic system, figure 36, were
selected so that (1) ground-and surface-water inflow from adjacent
areas was zero or negligible, (2) the only significant source of inflow
was precipitation; and (3) all significant surface-and ground-water
outflow was either measured or computed from hydraulic properties of
the ground-water reservoir and water levels in the aquifer. The period
for the balance was selected so that the net change in storage was
negligible. Evapotranspiration was determined as a residual by the
balance equation:
ET=P-R-GO. (2)
ET, thus determined, is an average value for the larger system which can
be applied to the Middle Gulf area.
The water-balance equation for the Middle Gulf area, excluding
peninsular Pinellas County, is:
GI=P ET R GO +AS. (3)
A water balance for peninsular Pinellas County was estimated using
precipitation, adjusted ET, and by assuming no surface-and ground-
water inflow. Most of the streams in the peninsular area have not been







REPORT OF INVESTIGATION NO. 56


Figure 36. Map showing water levels in wells penetrating the Floridan
aquifer, topographic divides, and boundary of the
hydrologic system
gaged and data are not sufficient to estimate the ground-water outflow.
Therefore, the precipitation minus evapotranspiration was assumed to
equal the runoff plus ground-water outflow:
P- ET= R +GO. (4)

PRECIPITATION
The precipitation used for computations in the water balance was






BUREAU OF GEOLOGY


Figure 37. Map showing accumulated precipitation for period June
1964 May 1966, Middle Gulf hydrologic system

obtained from 14 U. S. Weather Bureau stations. Within the two-year
period of the balance, the distribution of the accumulated precipita-
tion varied from 80 to more than 125 inches over the area as shown by
the controus on figure 37.
Areal average precipitation was computed using the Thiessen
method. The monthly weighted-average precipitation for the Middle
Gulf area is tabulated in table 3 and shown on figure 37. The weighted-
average accumulation for the Middle Gulf hydrologic system was 114






REPORT OF INVESTIGATION NO. 56


inches and for that part of the Middle Gulf area included in the total
hydrologic system the accumulated precipitation was also 114 inches.
The weighted-average accumulation for peninsular Pinellas County was
90 inches.
EVAPOTRANSPIRATION

Evapotranspiration (ET), the discharge of water vapor to the
atmosphere, continues as long as open-water or other moist surfaces are
exposed to the atmosphere and as long as moisture is available for
transpiration by living plants. ET cannot be measured directly for large
areas and must be estimated. Therefore, evapotranspiration was ob-
tained as a residual in equation (2). This value is an average for the
total system. Local values of ET vary with local climate, soil condi-
tions, and vegetation. Evapotranspiration varies seasonally depending
on changes in temperature, vegetative cover, precipitation, and other
antecedent conditions which affect soil moisture.
The Thornthwaite method (1955) was used to adjust the average
ET for seasonal and areal variations. This method takes into account
(1) air temperature, (2) precipitation, (3) hours of sunlight, and (4) the
water-holding capacity of the soil and type of vegetation. If water is
available to supply the needs of plants and to maintain soil moisture,
the combined evaporation from the soil and transpiration through the
plants proceeds at a maximum rate referred to as the potential
evapotranspiration.
The monthly amounts of actual evapotranspiration for each
climatological station were computed by the method outlined by
Thornthwaite and Mather (1957). The accumulated monthly value of
ET for each climatological station was really weighted to obtain an
average value of ET for the Middle Gulf hydrologic system. The value
of ET as determined by the Thornthwaite method for the 2-year
balance period was 85 inches as compared with 78 inches as a residual
in equation (2). The really weighted monthly ET values obtained by
the Thorthwaite method for each climatological station were adjusted
to agree with the average value obtained as a residual in equation (2).
The adjusted monthly values are shown in table 5.
RUNOFF

Runoff (R) is defined as that part of the precipitation that occurs
in streams (Langbein and Iseri, 1960). It includes water that flows over
the ground surface to the streams as well as that which moves through
the aquifers and discharges to the streams. For example; the flow of






BUREAU OF GEOLOGY


Crystal River is almost entirely from the Floridan aquifer, and is
measured as runoff. About 85 percent of the total runoff from the
entire hydrologic system is from this aquifer.
The runoff was computed by distributing the total streamflow
over the area of the system and is the most accurately measured item in
the water balance. The runoff in terms of water over the Middle Gulf
hydrologic system (2,830 sq. mi.) was 36 inches for the 2-year balance
period. However, the runoff for that part of the Middle Gulf area
(1,110 sq. mi.) in the total hydrologic system, which includes all
streams except the Withlacoochee River, was 59 inches for the 2-year
balance period, or about 30 inches per year.
A summary of the runoff and streamflow values for each stream,
for both the total system and that part of the Middle Gulf area in the
total system, is presented in table 3. The location of the streams and the
average discharges are shown in figure 38.

GROUND-WATER OUTFLOW
Ground-water outflow is defined as that part of the discharge
from the system that occurs through the ground and is estimated to be
equal to about 1 inch of water over the system. Nearly all ground-water
outflow occurs in the southern part of the area. This estimate was
computed using a variation of Darcy's Law, Q= TIL, where
Q is the quantity of water that moves through the aquifer,
gallons per day (gpd);
T is the coefficient of transmissivity, gpd per ft;
I is the hydraulic gradient, ft. per mile;
L is the length of the flow section of the aquifer, in feet.
The transmissivities used in the computation ranged from 165,000 to
400,000 gpd per ft. and hydraulic gradients ranged from 3 to 6 feet per
mile. Using the above values the outflow along flow sections A, B, C,
and D, shown on figure 39, was computed to be 66 mgd or about 2
inches. Of this amount 37 mgd moves westward and southwestward
toward the gulf and Old Tampa Bay, 23 mgd moves southwest toward
Tampa Bay and Hillsborough River, and 6 mgd moves eastward toward
the Hillsborough River.
Because the ground water moves westward through the total
system and the middle Gulf area is on the west side of the system, the
ground-water outflow (GO) for the total system is discharged from the
Middle Gulf area. The outflow for the total system is estimated to be 1
inch, and for the Middle Gulf area 2 inches.








REPORT OF INVESTIGATION NO. 56


Table 3. Summary of stream discharge and runoff for total system and
Middle Gulf area.


MIDDLE GULF HYDROLOGIC SYSTEM
Area-2830 square milesa


Average
Runoff
For Period
June 1964-May 1966


Stream Name




Crystal River
Homosassa River
Chassahowitzka River
Weekiwachee River
Pithlachascotee River
Anclote River
,Brooker Creek
Rocky Creek
Sweetwater Creek
Cypress Creek
Sulphur Springs
Bear Creek
New River
Busy Branch
Trout Creek
Withlacoochee River
Withlacoochee-Hills-
borough overflow
Miscellaneous Springs
Total "


Cubic feet Million
per second gallons
per day


900
230
150
260
51
92
25
40
5
180
45
32
14
7
73
1,370

39
310
3,823


582
149
97
168
33
59
16
26
3
116
29
21
9
5
47
885

25
200
2,470


Inches
on area



8.65
2.21
1.45
2.48
.48
.88
.24
.38
.05
1.77
.43
.30
.13
.06
.70
13.09

.40
2.97
36.67


MIDDLE GULF AREA
Area-1110 square miles


Average
Runoff
For Period
June 1964-May 1966


Cubic feet
per second



900
230
150
260
51
92
25
40
5
180
45
32
14
7
73


Inches Million
on area gallons
per day


582
149
97
168
33
59
16
26
3
116
29
21
9
5
47


22.11
5.66
3.72
6.33
1.24
2.24
.61
.97
.13
4.52
1.11
.77
.34
.17
1.78


310 200 7.60
2,414 1,560 59.30


aDoes not include peninsular Pinellas County and some coastal areas.
See fig. 1 for boundary line.


GROUND-WATER INFLOW

Although the ground-water inflow to the Middle Gulf hydrologic
system is zero, the inflow (24 inches) to the Middle Gulf area for the
2-year period was computed as a residual from the water balance
equation (3). Most of the ground-water inflow occurs in the northern






BUREAU OF GEOLOGY


Figure 38. Map showing average stream discharge and runoff for the
total Middle Gulf hydrologic system




part of the area as determined from an examination of the map of the
potentiometric surface and an analysis of the flow of streams in the
Middle Gulf area. A comparison of figures 27 and 28 indicates that




































8200'


Figure 39. Map of southern part of Middle Gulf area showing flow net for computation of ground-water
outflow





BUREAU OF GEOLOGY


ground-water inflow could occur under certain stage conditions in the
southern part of the area, because the ground-water divide shifts
eastward across the boundary of the Middle Gulf area.

CHANGE IN STORAGE
Water in storage (S) includes that water on the surface (lakes and
streams) and in the ground (in the aquifer and soil zone). The change in
storage in the Middle Gulf area for the 2-year balance period was
insignificant.
The change in storage for the 3-month period June 1965 -
August 1965 was equal to an increase of 8.8 inches of water over the
area an increase of 6 billion gallons of water in the Middle Gulf area.
During the same period the rainfall and ground-water inflow was 1.03
trillion gallons. The total outflow as evapotranspiration, ground water
outflow, and runoff was 773 billion gallons.

ANALYSIS OF THE WATER BALANCE
The monthly variations of precipitation and evapotranspiration
for the Middle Gulf area are shown in figure 40. This figure shows that
the precipitation and evapotranspiration are highest in summer and
lowest in winter. The least precipitation occurs in November and May.
Because precipitation greatly exceeds evapotranspiration in the sum-
mer, the greatest increase in storage occurs at this time.
The accumulated change in storage (A S), which equals P + GI ET
R GO, for the 2 year balance period, is shown in figure 41. This figure
indicates reasonable agreement between the calculated monthly
change in storage and the observed storage reflected by end-of-month
stages in the various water-conveying components in the Middle Gulf
area. A summary of the Values used in the water-balance calculations is
presented in table 4.
In summary, the water balance for the total system is:
P=ET+ R+ GO+A S(2)
114=77+36+1+ 0,
and for that part of the Middle Gulf area in the total system,
GI = ET + R + GO P tAS (3)
24= 77 + 59 + 2 114 t0,
and for peninsular Pinellas County,
P-ET= R+GO AS (4)
90-69= 21 + 0








w 12-





8 0

Precipitation _

S/ -Evapotransplratlon







0 J A S N D J F M A 'M J J A S N D J F M A M
1964 1965 1966
Figure 40. Graph showing monthly variations of precipitation and evapotranspiration in the Middle Gulf
area,,June 1964-May 1966 '





BUREAU OF GEOLOGY


A 3-day test at the Section 21 well field indicated that the
permeability of the materials overlying the Floridan aquifer was small.
Data collected by Leggette, Brashears, and Graham (1966) during a
long-term test at the well field indicated that leakage occurred within
about 11 days. The leakage factor (P'/m') computed from the test was
about 1.5 x 10-3 gpd per ft3. Based on this value of P'/m', recharge to
the Floridan aquifer by leakage from the shallow aquifer ranged from
about 590,000 to about 670,000 per square mile.
Figures 33 and 34 show time-drawdown graphs based on values of
transmissivity, storage, and leakage obtained at the Eldridge-Wilde and
the section 21 fields. For example, at the Elridge-Wilde field the
drawdown in a well 100 feet from a well being pumped at 1,000 gpm
for 100 days is about 6.6 feet, and at a distance of 1,000 feet the
drawdown would be about 3 feet. Estimated water-level declines for
any pumping rate can be determined from the curves because the
drawdowns are directly related to the rate of pumping. Thus, if the
pumping rate is doubled, water-level declines will be double that shown
on the curves.
Water quality. The quality of water in the upper 300 feet of the
Floridan aquifer is generally good. The mineral content of the water is
less than 500 mg/1 except near the coast where the concentration
approaches that of sea water. Water that has a mineral content of less
than 500 mg/1 is usable for most purposes. The mineral content in the
inland area is mostly calcium bicarbonate, which causes the water to be
alkaline and moderately hard to hard. Other mineral constituents,
including silica, potassium, sulfate, sodium, and chloride occur in
concentrations generally less than 10 mg/1. Fluoride and nitrate are
usually present in concentrations of less than 1.0 mg/1. Analysis of
water from selected wells in the Middle Gulf area are presented in Table
2.
Figure 35 shows the mineral content and chloride concentration
of water in the Floridan aquifer in the Middle Gulf area. The high
mineral content of water in the aquifer near the coast is caused by sea
water. Generally water in the area bordering the coast contains chloride
in excess of 250 mg/1, especially in wells deeper than 100 feet.
Mineralized water occurs at depths greater than 700 feet in the well
fields in northwest Hillsborough and northeast Pinellas counties.

WATER BALANCE

The water balance is a method of accounting for the inflow and
outflow of a hydrologic system. The balance involves estimating the







78 BUREAU OF GEOLOGY


4O- NEFF LAKE neaw BROOKSVILLE


I-L



taPTLCACTEE RrIYER near- NE POR RIHE


8II SHALLOW AQIJFER WELL ~;I
TS l ii


- -2
ACCUMULATED CHANGE IN STORAGE
4- (CALCULATED) AS-P-ET-R-GO+GI
--6 J J A I S 1 0 1 N M D J I J A S 0 N D J0 F M A M
1964 1965 1966



Figure 41. Graph showing monthly accumulated change in storage
calculated from water balance and compared with coinci-
dent fluctuations of stages of lakes and streams, and water
level in aquifers



HYDROLOGIC RELATIONS

The water balance made in this study for the Middle Gulf area has
accounted for ah inflow and outflow for a 2-year period. The calcula-
tions of water in storage at a given time have been compared with actual
stages in streams, lakes, and aquifers.
Inflow to any part of the system causes an increase in stage in the
system, and outflow causes a decrease in stage. Water levels of streams,









REPORT OF INVESTIGATION NO. 56


Table 4. Summary of the water balance for the Middle Gulf area, June 1964-May 1966.



Monthly values in inches; positive except where noted


Precipitation (P): Areally weighted using Thiessen method.

Ground-water inflow (GI): Computed as residual in the water balance for
the Middle Gulf area. Prorated on a monthly
basis.


Evaportranspiration (ET):


Really weighted using Thiessen method. Com-
puted as a residual in the water balance for the
total system, Adjusted really and seasonally
based on the Thornthwaite method.


Runoff (R): Values are monthly summations of runoff.
Ground-water outflow (GO): Computed from flow-net analysis using a varia-
tion of Darcy's Law. Prorated on a monthly
basis.


INFLOW OUTFLOW STORAGE


Ground Evapo- Ground Change Accumu-
Precipi- water Accumu- trans- Run- water Accumu- in lated
station inflow lated piration off outflow lated storage change in
Month, Year (P) (GI) inflow (ET) (R) (GO) outflow (AS) storage


5.4 1 6.4
11.8 1 19.2
7.7 1 27.9
9.5 1 38.4
1.4 1 40.8
0.5 1 42.3
3.8 1 47.1
2.2 1 50.3-
3.6 1 54.9
3.2 1 59.1
2.9 1 63.0
.8 1 64.8
9.3 1 75.1
10.4 1 86.5
12.3 1 99.8
5.1 1 105.9
2.3 1 109.2
.9 1 111.1
2.6 1 114.7.
4.2 1 119.9
4.7 1 125.6
1.3 1 127.9
3.3 1 132.2
4.6 1 137.8

113.8 24 137.8
114 24 138.


5.2
5.8
5.8
4.7
2.7
1.6
1.6

1.4
2.1
3.4
3.1
5.3
5.7
5.7
5.0
3.0
1.6
1.2
.8
1.1
1.7
2.8
4.5

77.1


2.1
2.3
2.6
2.0
1.9

59.0


0.1 6.6
.1 15.0
.1 24.5
.1 34.1
.1 39.7
.1 43.2
.1 47.3
.1--- 50.9
.1 54.6
.1 59.3
.1 65.0
.1 70.3
.1 77.5
.1 85.9
.1 96.5
.1 104.0
.1 109.1
.1 112.6
.1 116.0
.1 119.0
.1 122.5
.1 126.9
.1 131.8
.1 138.3

2.4 138.3


77 59 2 138


-0.2 -0.2
4.4 4.2
-0.8 3.4
.9 4.3
-3.2 1.1
-2.0 -0.9
.7 -0.2
-0.4 -0.6
.9 .3
-0.5 -0.2
-1.8 -2.0
-3.5 -5.5
3.1 -2.4
3.0 .6
2.7 3.3
-1.4 1.9
-1.8 .1
-1.6 -1.5
.2 -1.3
2.2 .9
2.2 3.1
-2.1 1.0
-0.6 .4
-0.9 -0.5

-0.5 -0.5
0 0


1--


June, 1964
July
Aug.
Sept.
Oct. *
Nov.
Dec.
Jan., 1965
Feb.
Mar.
Apr.
May
June
July
Aug.
Sept.
Oct.
Nov.
Dec.
Jan., 1966
Feb.
Mar.
Apr.
May

Total






BUREAU OF GEOLOGY


lakes, and aquifers tend to respond similarly to inflow to and outflow
from the system. High and low stages occur in all at about the same
time. The movement of water within the hydrologic system is reflected
by changes in stage. The stages in all components in a given area
fluctuate through about the same range but water stages in the eastern
or upgradient areas generally fluctuate through a greater range than
stages in the down-gradient, or western part.
Water levels in the western part of the area are sustained by
downgradient movement of water from the east. Water levels in all
streams, lakes, and aquifers do not react identically because all convey-
ing bodies cannot transmit water equally, do not receive the same
amount of recharge within a given period, nor have the same storage
capabilities.
The Middle Gulf area is on the western side of the Middle Gulf
hydrologic system and outflow is largely by stream discharge and
evapotranspiration from the Middle Gulf area in the downgradient
coastal part. Stream discharge is the residual of the inflow to the system
after all the demands of nature and man's activities have been satisfied.
Therefore, an increase in stream discharge from the system without an
increase in inflow would result in a decrease in storage. This storage
decrease would be reflected by lower stages in all components within
the system. An increase in stream discharge could be brought about by
lowering the discharge outlet by dredging of canals or deepening
existing stream channels. The increase in stream discharge would
continue until the stages in all components of the system rebalance at a
lower level.
The flow of a stream is generally related to the water level in the
stream; flow in a nontidal stream generally increases with an increase in
water stage. The flow in tidal streams is generally greatest at low stages.
Figure 42 shows that the flow of Crystal River, which is affected by
tides, is less at high stage than at intermediate or low stage.
The flow of the spring-fed streams is related to the water stage in
the Floridan aquifer. Figure 43 shows the relation of water stage in a
well penetrating the Floridan aquifer to the flow of Weekiwachee
Springs, and the relation of a shallow-aquifer and a Floridan-aquifer
well to the flow of the Pithlachascotee River. The flow of Weekiwachee
Springs and the water stage in the aquifer are closely related. As
indicated by the scatter of points, the flow of the Pithlachascotee River
is less closely related to the water stage in the aquifer than is the flow of
Weekiwachee Springs.
Really, the flow patterns of spring-fed streams throughout the
Middle Gulf area are similar. The monthly mean flows of Crystal River







REPORT OF INVESTIGATION NO. 56


and Weekiwachee, Rainbow, and Silver Springs were compared to
determine the relation of flow of one stream to another, figure 44. The
plot of Weekiwachee-Rainbow Springs and Weekiwachee-Silver Springs
indicates a constant relationship between the flows of both springs.
Changes in slope of the plots of the flow of the Crystal River-
Weekiwachee Springs and the Crystal River-Rainbow Springs occur
about every six months. The change in slope is caused by a flow pattern
peculiar to Crystal River, because no pronounced change in slope
occurred in the Weekiwachee-Silver or Weekiwachee-Rainbow plots.
The change in slope of the Crystal River plots occurs at a time midway
between maximum and minimum tide levels during the year.
An analysis of flow records from these streams shows that, with
the exception of Crystal River, all of the spring discharges were highest
in the high rainfall periods, and the lowest in low rainfall periods. The
stages of the pools of Silver, Rainbow, and Weekiwachee are all 10 feet
or more above sea level. The stages of the spring pools of Crystal River
are near or below sea level and the discharge is influenced by tides. The
discharge of Crystal River is greatest during periods of low rainfall and
least during periods of high rainfall; a condition opposite to that
observed in the other springfed streams and caused by the annual
variation in mean tide level. These comparisons show that, with the
exception of Crystal River, the pattern of flow of spring-fed streams
many miles apart generally is similar and correlatable.
The mineral content of Cypress Creek, Anclote River, and Pith-
lachascotee River is shown in figure 45. The mineral content of the
streams varies seasonally, and the range in the fluctuations of mineral
content of each is similar. Both the flow and chemical composition of
many streams in the Middle Gulf area show similar patters of variation.
The stream discharge at the system boundary is essentially the
residual of the inflow to the system. A change in inflow or a change in
outflow upgradient from the boundary should be reflected by a change
in stream discharge at the boundary.
The flow records of four streams in the southern part of the area
were analysed to determine the effects on stream discharge of with-
drawal of water from the Floridan aquifer. The cones of depression of
well fields in northeast Pinellas and northwest Hillsborough counties
extend into areas drained by several streams. The cone of the Eldridge-
Wilde well field extends into an area drained by the Anclote River and
Brooker Creek. The cones of the St. Petersburg Cosinsme, and Section 21
well fields extend into areas drained by the Anclote River and Brooker,
Rocky, and Sweetwater creeks.






BUREAU OF GEOLOGY


/> N% Stage -
+ + +4

z \ -4


I0I I


m I \ / \ Om
SI -


I I I I --
0 \0
St I
SnI -2
\a -37





i-tl stream
Io -I f e flow of
-7








The low flow characteristic of the Anclote River and Brooker
Greek were analyzed to determine if they had changed as a result of
pumpage of water from the Floridan aquifer. Because the low flow of
Rocky Creek is affected by tides and the low flw of Sweetwater Creek
is affected by h regulations, the records of these two streams were not

The effect on streamflow of large withdrawals of water from the
aeifer should be most evident during periods of low rainfall, because
ground-water withdrawal is at a maximum, surface trunoffis at a
Rocky Creand discharge from the ground-watertreservoir comprises a
large part of the streamflow. s w no









REPORT OF INVESTIGATION NO. 56 83





. 15 3










16 --
z



0 6

M 15
















5 -.
Mr



z 17-
ic




-i








50 160 40 10 80 100 210 140 2f0
u-





















rand Floridan)to flow of streams
-j







STSHALLOW AQUIFER WELL, 816-237-234b

U-

W-j







Xn PITHLACHASCOTEE RIVER near NEW PORT RICHEY








and Floridan)- to flow of streams







BUREAU OF GEOLOGY


CUMULATIVE MONTHLY STREAMFLOW, CUBIC FEET PER SECOND


of RAINBOW SPRINGS
0 4000 8,000 12,000 16,000 20000
CUMULATIVE MONTHLY STREAMFLOW, CUBIC FEET PER SECOND

Figure 44. Graph showing Correlations of monthly mean flows of
Crystal River and Weekiwachee, Rainbow and Silver
springs





















F-

z

0,
0


SAN ANTONIO XA




250 l l -, i | l i i --i--,-,l,- i -l,- l -- l | -- l --I- l -- l -- -' -- -' -- l -- l -'
ANCLOTE RIVER .l
200 near ELFERS


100- y


0 I I I I I I I I I I

PITHLACHASCOTEE
RIVER near NEW\
200 PORT RICHEYI lL





1i00 I I I I I I il l I I I II INl I
J F M A M J J A S O N D J F M A M J J A S 0 N D J F M A M J
1964 1965 1966

Figure 45. Graph showing similarities in seasonal changes in mineral content of water of selected streams
in the Middle Gulf area,January 1964 June 1966


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