FLRD GEOLOSk ( IC SUfRiW


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FLORIDA STATE BOARD

OF

CONSERVATION


FARRIS BRYANT
Governor


TOM ADAMS
Secretary of State


J. EDWIN LARSON
Treasurer


THOMAS D. BAILEY
Superintendent of Public Instruction


RICHARD ERVIN
Attorney General


RAY E. GREEN
Comptroller


DOYLE CONNER
Commissioner of Agriculture


W. RANDOLPH HODGES
Director





LETTER OF TRANSMITTAL


5lorida geological Survey

Callakassee
December 15, 1961


Honorable Farris Bryant, Chairman
Florida State Board of Conservation
Tallahassee, Florida


Dear Governor Bryant:
I am pleased to forward the second of three papers to be pub-
lished as Report of Investigations No. 24, Part II, entitled "Hydro-
logic Studies in the Snapper Creek Canal Area, Dade County,
Florida."
These studies are contributing greatly to the basic data which
leads to a more complete understanding of the hydrology of the
area.
Respectfully yours,
Robert O. Vernon,Director






















































Completed manuscript received
September 15, 1961
Published by the Florida Geological Survey
E. O. Painter Printing Company
DeLand, Florida

iv







CONTENTS

Abstract _...----........---....--- __.... ... __..___ 1
Introduction 1
Purpose and scope --.._-.--- ____ -__--- 3
Acknowledgment 3__---------------_ 3
Previous investigations ------- ---__ ---..... -------__ --------- 4
Area of investigation ...--__------- --.---------.---------... 4
Climate -..-... _-_--.... _-_________ --..-----__...--.------_ 4
Topography and drainage -_--____- ___..............----_---__ -----__ 4
Geology _._-- -------_______------ -----_____--------- 7
Method of investigation _-------- ------_ ...---__.__-___-...__ 10
Collection of data 10
Analysis of data ________--___ 14
Changes in storage and flow ____ -___ 14
Aquifer coefficients _____ 23
Ground-water movement and canal flow ...................---- --.._ 27
Summary ..---...-........_.... --_----- ---.--_ 30
References .--..... .-.____... ______________-__-_ 31


ILLUSTRATIONS

Figure Page
1 The Greater Miami area showing selected hydrologic features,
drainage-area boundaries, and the area investigated ___..-- -.------_ 2
2 The Greater Miami area showing the configuration of the natural
drainageways and the coastal ridge ... ...___, .---___-...... 5
3 The Snapper Creek Canal area showing the location of wells and
geologic sections ____ 6
4 Geologic section along line A-A' _--..--...--- -- ---------_ ------- 8
5 Geologic section along line B-B' _-_.----- ___--- ------.- 9
6 Geologic section along line C-C' .....--.... .. 10
7 Hydrographs of selected wells and canal stations, discharge at the
control structure, and rainfall in the Snapper Creek area during
part of 1959 ______ 12
8 Hydrographs of ground-water levels and canal stage at selected
stations and discharge at the control structure, June 24-July 2, 1959 13
9 Hydrographs of ground-water levels and canal stages and discharge
at selected stations July 17-26, 1959 _____ 15
10 Hydrographs of canal stage and discharge at selected stations July
21 and 24, 1959 ____ ___ 16
11 Idealized sketch showing progressive changes of slope, directions of
flow, and storage in a tidal canal ----- 18







ILLUSTRATIONS (Continued)

Figure Page
12 The flow regime and water-level profiles in Snapper Creek Canal at
selected times on July 21 and 24, 1959 ____ --- _---_--- 20
13 Contour map showing water levels in the Snapper Creek area July
21, 1959 -__. ..-----_ 21
14 Contour map showing water levels in the Snapper Creek area July
24, 1959 23
15 Contour map showing water levels in the Southwest and Alexander
Orr well fields on April 22, 1958, and May 12, 1960, respectively -_. 25
16 Diagram showing water-level profiles along Palmetto Road and Gallo-
way Road on July 21, 1959 __._____---_-- ____- -.-___ 26
17 Contour map showing water levels in the Snapper Creek area and
flow at selected points in the canal on March 21, 1951 .- ..----------. 28
18 Contour map showing water levels in the Snapper Creek area on
June 12, 1951 .- ------------ ..-------------.-.._ ................ 29








HYDROLOGIC STUDIES IN THE SNAPPER
CREEK CANAL AREA,
DADE COUNTY, FLORIDA

By
C. B. SHERWOOD and S. D. LEACH

ABSTRACT

The Snapper Creek Canal drains the southernmost part of the
Greater Miami area and a part of the lower Everglades in Dade
County, Florida. The canal and a control structure near Biscayne
Bay are part of a water-control system designed to provide maxi-
mum drainage during flood periods and to maintain water levels
high enough to retard salt-water encroachment during dry periods.
The area is underlain by highly permeable limestone and sand
of the Biscayne aquifer. Because of the high permeability, there
is excellent hydraulic interconnection between the canal and the
aquifer, and inflow to or losses from the canal occur rapidly in
response to changes in canal levels. When the control structure
is closed, canal levels along the lower reach are generally higher
than ground-water levels and appreciable losses from the canal
occur by underflow toward the bay. Except under very low water
conditions, these losses are balanced by ground-water inflow from
the western part of the coastal ridge. When extreme drought con-
ditions prevail, it is estimated that about 50 cfs (cubic feet per
second) will be needed in the canal to balance the losses that will
occur if a water level of 2.75 feet above msl (mean sea level) is
maintained in the canal at the control structure. During pro-
longed droughts a large part of the water withdrawn by the near-
by city of Miami well fields will be derived from infiltration from
the canal. This loss could amount to more than twice as much as
the natural losses from the system.

INTRODUCTION

The development of the Greater Miami area has required the
construction of an extensive system of water-control facilities to
reduce flooding and to prevent further sea-water encroachment in-
to the aquifer. The continued rapid growth of the population in
the area has indicated an urgent need for a comprehensive plan





FLORIDA GEOLOGICAL SURVEY


to extend the existing water-control system to include a large low-
land area of anticipated urbanization west of the city, hereafter
referred to as Area B. Figure 1 shows Area B and the existing
major water-control facilities in the Miami area. Major develop-
ment in Area B is not now practicable because of perennially high
ground-water levels and frequent flooding. However, any major
water-control plan for the area must be designed not only to prevent
flooding within the area but also to maintain the existing carefully


Figure 1. The Greater Miami area showing selected hydrologic features,
drainage area boundaries, and the area investigated.






REPORT OF INVESTIGATIONS NO. 24


controlled ground-water conditions in the Miami area and to provide
for maximum future water use.
The hydrologic study of the Snapper Creek Canal area is one
of a series of canal area studies undertaken by the U. S. Geological
Survey, in cooperation with the Central and Southern Florida Flood
Control District, for the purpose of furnishing hydrologic data
that will be useful in formulating an overall water-control plan.
The investigation was made in 1959-60 under the general super-
vision of P. E. LaMoreaux, chief, Ground Water Branch, and E. L.
Hendricks, chief, Surface Water Branch, U. S. Geological Survey.
It was under the immediate supervision of Howard Klein, geologist
in charge, Ground Water Branch, and J. H. Hartwell, engineer in
charge, Surface Water Branch, Miami, Florida.

PURPOSE AND SCOPE

The main purpose of the series of investigations of the hydrology
of the canal systems in eastern Dade County is to determine the
following:
(1) The discharge rates at selected points in the drainage
canals.
(2) The discharge from ground-water storage to the canal
systems.
(3) The effect of water control in Area B on salt-water
encroachment in coastal areas.
The specific purpose of this study was to obtain a detailed
description of the hydrologic environment in the Snapper Creek
Canal area and to provide quantitative definition for the following
hydrologic factors:
1. Coefficients of transmissibility and storage of the aquifer.
2. Relation between ground-water movement and canal flow
in different reaches of the canal.
3. The quantity of water needed to maintain a given head
in the canal for the control of salt-water encroachment.
The feasibility of this type methodology for studies of other
canal areas in Dade County may be determined by a review of the
problems experienced in this study.

ACKNOWLEDGMENT

Appreciation is expressed for the wholehearted cooperation of
the personnel of the Dade County Public Works Department during
this study.






FLORIDA GEOLOGICAL SURVEY


PREVIOUS INVESTIGATIONS

A brief paper by Parker (1951) discusses the geologic and
hydrologic factors in the perennial yield of the Biscayne aquifer in
southeastern Florida and a later report by Parker and others
(1955) presents a comprehensive account of the geology and water
resources of southeastern Florida. Schroeder and others (1958)
summarize the hydrology and geology of the Biscayne aquifer and
evaluate the perennial yield of the aquifer from data obtained since
1950. Stallman (1956) gives the results of electrical analog studies
of the hydrology of intercanal areas of Dade County.

AREA OF INVESTIGATION

The investigation was made in an area about 4 miles wide along
the reach of the Snapper Creek Canal, which extends about 10
miles inland from Biscayne Bay to the approximate boundary be-
tween the coastal ridge and the lower Everglades (fig. 1). This
40 square mile area is the southernmost part of the highly urbanized
Greater Miami area.

CLIMATE

The climate in the Miami area is subtropical. Rainfall averages
approximately 60 inches per year, about 75 percent of which occurs
during June through October; this 5-month period includes both
the normal rainy season and the hurricane season. The average
annual temperature is approximately 750F.

TOPOGRAPHY AND DRAINAGE

The generally flat topography of the Snapper Creek area is
broken by several natural drainageways or transverse glades that
cut through the coastal ridge and by isolated limestone ridges upon
the coastal ridge. The configuration of the coastal ridge and the
natural drainageways is shown in figure 2. Throughout most of its
extent the Snapper Creek Canal follows a natural drainageway,
and in recent years its channel was widened and deepened.
The altitude of the land surface ranges from 5 to 7 feet above
msl in the eastern edge of the Everglades and along the transverse
glades, and from 9 to 21 feet above msl on the coastal ridge.
Drainage from the area is through the Snapper Creek Canal,
which flows generally eastward to Biscayne Bay. Canal flow is
maintained chiefly by ground-water inflow, but during periods of






REPORT OF INVESTIGATIONS NO. 24


r( SCALE IN MILES
.^i A .


Figure 2. The Greater Miami area showing the configuration of the natural
drainageways and the coastal ridge.

heavy rainfall the canal receives considerable runoff directly from
the natural drainage channels and from the eastern part of the
Everglades.
As shown in figure 1, the Snapper Creek Canal connects with
the Tamiami Canal and several secondary drainage canals in Area
B; thus, it not only acts as the primary drainage channel for the
southernmost part of Greater Miami, but also carries a large part
of the drainage from Area B. The Snapper Creek Canal intercepts
a secondary drainage canal, Ludlum Drain, at a point about 2 miles
inland from Biscayne Bay (fig. 3). Ludlum Drain follows the
southern part of a natural drainageway that extends northward
toward the Coral Gables Canal.
The flow in the Snapper Creek Canal is regulated by the opera-
tion of a control structure (submerged sluice gate) about 11/4 miles
upstream from Biscayne Bay. This control is regulated so that
water can be discharged to Biscayne Bay to reduce flooding in low



















































EXPLANATION
OSIIRVATION WILL ANO NUMBER
MUNICIPAL SUPPLY WILL
STAFF OA4S
WATIRALVEI L RigOGOING GAG
8- --B
LOAATIO OF GIOLOgIC 10OTION
/


Figure 3. The Snapper Creek Canal area showing the location of wells and

geologic sections.





REPORT OF INVESTIGATIONS No. 24


areas during periods of heavy rainfall. Before the rainy season
ground-water levels in the aquifer are lowered in order to provide
additional ground-water storage and thus lower flood peaks. The
maximum discharge recorded, since the canal was recently
improved, was 2,010 cfs at the control after the hurricane of
September 9-10, 1960. During dry periods the control is closed
to maintain water levels high enough to retard salt-water encroach-
ment into the aquifer and to prevent direct movement of salt water
up the canal channel.

GEOLOGY

The Snapper Creek Canal area is underlain by the Biscayne
aquifer, composed of highly permeable limestone, sandstone, and
sand. Within the area the aquifer ranges in thickness from about
85 feet in the western part, to about 120 feet at the coast. Farther
west, along the western edge of Area B, the aquifer is about 50 feet
thick. The surface materials of the area are permeable limestone
and sand, but the natural drainageways are bottomed by several
feet of marl or silt of relatively low permeability. Figures 4 and
5 show geologic sections of the area from west to east. The locations
of the sections and test wells are shown in figure 3.
A section of the materials penetrated by a line of test borings
along the canal from Galloway Road to a point 3,000 feet west is
shown in figure 6. The section indicates that a large percentage
of the shallow materials is composed of sand and marl, which is
of considerably lower permeability than the limestone. The section
also indicates some nonuniformity in the shallow materials. The
unconsolidated shallow materials persist chiefly within the natural
canal drainageway.
The Biscayne aquifer is the source of water for the Southwest
and Alexander Orr well fields of the city of Miami (fig. 3).
Supply wells in these fields tap highly permeable limestones in the
lower part of the aquifer. Pumping facilities in the Southwest
well field presently can withdraw 40 mgd (million gallons per day),
but additions now being made will increase the total capacity to
about 80 mgd. The Alexander Orr well field is designed to with-
draw about 50 mgd. Both well fields probably receive recharge
from the Snapper Creek Canal during periods of low ground-
water levels.








































Figure 4. Geologic section along line A-A'.


































Figure 5. Geologic section along line B-B'.






FLORIDA GEOLOGICAL SURVEY


Figure 6. Geologic section along line C-C'.


METHOD OF INVESTIGATION

Hydrologic tests in the Snapper Creek Canal area were made by
observing the effects of varying the amount of canal discharge
through the control structure. The control was opened and closed
at different times during June and July 1959 to cause abrupt
changes in area-wide surface-water and ground-water conditions.
Observations were made of the changes in water levels and flow
that resulted from changes in canal discharge at the control
structure. Data collected during previous investigations and the
continuing observational program were integrated with the test
data.

COLLECTION OF DATA

The continuous observation program in the area includes 37
observation wells, 7 wells equipped with recording gages, and
recording stations in the canal at Miller Drive and at the control
structure (fig. 3). The installation at the control structure includes
a recording deflection meter from which a continuous record of the
canal flow can be obtained. Records from these installations provide
data throughout the drainage area. In addition, 23 shallow


c c'



10






EXPLANATION

FILL
S- -20


MUCK
LIMESTONE
SAND
1 =1n
MARL
SHELLS


c a 'a. ETm00






REPORT OF INVESTIGATIONS NO. 24


observation wells were drilled for the purpose of obtaining water-
level measurements, and water-level recording gages were installed
on six privately owned wells and in the canal at Ludlum Drain and
half a mile east of Galloway Road. All observation points were
referred to mean sea level datum by spirit level. The locations of
all measurement sites are shown in figure 3. Figure 7 shows
hydrographs of water levels at selected wells and canal stations,
discharge at the control structure, and rainfall at the U. S. Plant
Introduction Station during part of 1959. The Plant Introduction
Station is about 11/2 miles south of the control structure (fig. 3).
The amount that the control gates could be manipulated during
the period of the tests was greatly influenced by the high-water
stages during May through July 1959 that resulted from extremely
heavy rainfall (fig. 7). The control structure remained partly or
wholly open throughout most of the spring and early summer to
reduce flooding in low areas. It was necessary, therefore, that any
closing of the control gates be for only short periods during the
tests. Under existing conditions the control normally would remain
open, in order to lower ground-water levels in preparation for the
rains of September and October.
During the period June 24-30 the methods and facilities were
tested to determine the magnitude of the fluctuations of stage and
discharge to be expected, and the general adequacy of the observa-
tional network. Figure 8 shows the fluctuation of the water surface
at different points along the canal and in selected wells near the
canal during the period June 24-July 2. Also shown is discharge
at the control structure during the period. The changes in discharge
at two additional stations on the canal during the tide cycle and
at the time of closing and opening the control are given in the
following tabulation:
Red Road Palmetto Road
Time Discharge (cfs) Time Discharge (cfs)
June 25
8:20 a.m. 1,000 8:35 a.m. 891
10:30 a.m. 806 10:30 a.m. 803
1:00 p.m. 666 1:00 p.m. 771
June 29
11:50 a.m. 828 11:45 a.m. 734
2:10 p.m. 587 2:10 p.m. 666
4:50 p.m. 508 4:50 p.m. 560
June 30


5:20 p.m.


,328






FLORIDA GEOLOGICAL SURVEY


4AM FEB% &MAR. A J
H) 0 10 20


JULY: AUG. SEPT.
10 20 In 2


DAILY HIGH


LL G 553

5 -



G LELLG F39







SNAPPER CREEK CANAL
SAT MILLER DR.

AVERAGE DAILY



3I AA__


SSNAPPER CREEK CAL
SAT CONTROL STRUCTUR


Figure 7. Hydrographs of selected wells and canal stations, discharge at the
control structure, and rainfall in the Snapper Creek area during part of 1959.





REPORT OF INVESTIGATIONS No. 24


Figure 8. Hydrographs of ground-water levels, and canal stage at selected
stations and discharge at the control structure June 24-July 2, 1959.


4.- -I ___I-____ I -
4.5
SNAPPER CREEK CANAL
4.0 ATMILLER DR/VE



WE\ LS1271





i ^1
_WELL F4.' 0 i
SNAPPER CREEK CANAL
A T CONTROL
\ STRUCTURE


I 9 9 R 'I I 1


oi


1959


JULY


JUNE


nn





FLORIDA GEOLOGICAL SURVEY


About 10 hours after closing the gates a partial opening was made
to prevent flooding in low areas along the canal. At 7:15 a.m.,
July 1, the gates were fully opened.
A more intensive test was conducted during the latter part of
July. Fluctuations of water levels and canal discharge at selected
points during the test period are shown in figure 9, and canal stage
and discharge data collected at the times of opening and closing
the control are shown on an expanded scale in figure 10.
For several days prior to July 21 the control gates were open
and ground water was discharging from storage. The hydrographs
in figure 9 indicate that during the period July 17-20 the rate
of recession of the water table in areas near the canal was very
slow. On July 21 the canal discharge was measured at Red Road,
Palmetto Road, and Galloway Road, along with the discharge
recorded at the control structure, and water-level measurements
were made in the network of observation wells. These measure-
ments furnish a picture of the canal system when flow and stage
are relatively steady.
At 10:30 a.m. on July 21 the control gates were closed, and
discharge and stage measurements were continued until 6:30 p.m.
The effect on the system is shown in the hydrographs (fig. 9, 10)
by the rise of water levels in the area and the sharp reduction of
discharge at different points in the canal. After 71/. hours (6:00
p.m.) the gates were adjusted in an effort to hold a high constant
head at the dam for as long a period as possible and at the same
time to prevent flooding along the banks of the lower reaches of
the canal.
On the morning of July 24, stage and discharge measurements
were made immediately before the control gates were opened and
were continued for 5 hours after the gates were opened.


ANALYSIS OF DATA

CHANGES IN STORAGE AND FLOW

An important part of the investigation of the Snapper Creek
Canal area flow system is the relation between the stage and
discharge of the canal and the change in ground-water storage in
the aquifer. Fluctuations of stage and discharge within the flow
system depend chiefly upon (1) the quantity of rainfall recharging
the system, (2) the quantity of inflow from the Everglades by
canals and by underflow, and (3) operation of the control.







REPORT OF INVESTIGATIONS NO. 24


1959


WELL SF .0,






_Z W S/ 71 "




LC
w I I WEL F- LE -V
U11
< | I I I I I





a:
SSNAPPER REEK CANAL AT













*.-*RE ROAD










--CONTROL SCON WURE
S"HALF A.IE m
SEAST C .ALLOWAY RV.











o / I I I ri










40 U -- /R- -
2 I l I !
.










." 1 'I I I '


142 _-- -tALLOmr ROAO -




__ __ __ ------
at selected stations July 1-26 1959.









CIO f






Figure 9. Hydrographs of ground-water levels and canal stage and discharge
at selected stations July 17-26. 1959.


J uLY
iT iI ,P O






16 FLORIDA GEOLOGICAL SURVEY


Figure 10. Hydrographs of canal stage and discharge at selected stations
July 21 and 24, 1959.






REPORT OF INVESTIGATIONS No. 24


Figure 7 shows fluctuations of the water levels and rainfall
for much of 1959, and includes also a graph of the daily mean
discharge of the Snapper Creek Canal at the control structure.
Each heavy rainfall caused a corresponding rise of the water table
and canal stage, except in the lower reaches of the canal where
levels were generally lowered by the opening of the control gates.
When the heavy rains of March 18-22 and June 17-21 occurred,
the control gates were opened; this caused a rapid decline of canal
stage at the dam and a large increase in discharge. These periods
can be noted readily in figure 7. The effectiveness of drainage by
the canal is shown by the rapid decline of peak ground-water
levels after these rains.
The quantity of inflow from the Everglades areas varies with
the ground-water gradient toward the coast. During flood periods
this gradient is initially slight because of high water levels under-
lying the coastal ridge, but as coastal ground-water levels decline,
large quantities of water enter the canal system and the aquifer
from the west. As a result, the control gates must be kept open
for long periods.
When the control is open a large part of the system is affected
by tides. The magnitude of the effect decreases upstream and
depends upon the magnitude of the gate opening and the rate of
discharge. Maximum discharge from the canal occurs 1 to 2 hours
before low tide, and minimum discharge occurs at high tide. Figure
11, from Parker and others (1955, fig. 127), is an idealized sketch
showing progressive changes of slope of the water surface, direc-
tions of flow, and storage in a tidal canal. Tidal changes in Snapper
Creek during' the test periods were similar to those shown in figure
11 except that the seaward flow in the canal was sufficient to
prevent reverse flow at high tide. A comparison of the tidal
fluctuations in the canal east of Galloway Road and in wells F451,
S1271, and S1432 in figure 9 shows the lag in time and decrease in
magnitude of the fluctuations with increased distance from the
canal. The tidal fluctuation in the canal was about 1 foot, while in
wells F451, 2,900 feet south of the canal, S1432, 1,100 feet north
of the canal, and S1271, 600 feet north of the canal, the fluctuation
was about 0.0, 0.10, and 0.25 foot, respectively.
The changes caused by opening or closing the control gates
during the tests correspond generally with the changes caused by
a falling or rising tide, except in rate and magnitude. The extent
of the changes within the flow system depends chiefly on the length
of time the control gates remain open or closed, and the antecedent
hydrologic conditions. The hydrographs in figure 9 indicate that a







18 FLORIDA GEOLOGICAL SURVEY


EXPLAMATIOM

-1ECTOtFLOW *

C *NE OGF OIWEL S1TORAG- GAMS

O E VD ODWSEL ST AME-L3OHG
NCJM SniE


Figure 11. Idealized sketch showing progressive changes of slope, directions
of flow, and storage in a tidal canal (Parker and others, 1955, fig. 127).






REPORT OF INVESTIGATIONS NO. 24


period of several days is required for water levels throughout the
area to adjust to a given control setting.
The test of July 17-24 presents fairly complete data on
fluctuations of water levels and discharge within the flow system.
This test was complicated by heavy rainfall that began July 22 and
caused a sharp rise in water levels, necessitating a slight opening
of the control gates. The control change is indicated by the increase
in discharge at the control and the stabilizing of canal stage in
the hydrographs (fig. 9). A comparison of the hydrographs
suggests that ground water moved away from the canal in the
area near wells S1271 and S1432 during the period after the
closing of the control. The slight opening of the control on July 22
caused a reversal of this gradient and ground water began to flow
toward the canal. The changes in the flow system caused by the
closing and opening of the control on July 21 and 24, respectively,
are shown in detail by the hydrographs in figure 10, the flow pat-
terns and canal profiles in figure 12, and the water-level contours in
figures 13 and 14. Figure 12 shows canal profiles and the flow
regime of the canal at selected times before and after the closing
and opening of the control. Figures 13 and 14 show water-levil
contours under relatively stable conditions before the closing and
opening of the control.
As seen in detail on figure 10, the closing of the control gates
at high tide on July 21 extended the flow pattern established
previously by the rising tide. A comparison of the discharges
measured immediately before the closing (fig. 10, 12) shows that
water was entering the aquifer from the canal in all reaches
east of Galloway Road except the section along Red Road. In the
Red Road section, ground water was flowing into the canal because
of the steep gradient of the water table in the area west of the
canal (fig. 13). The sharp rise in canal level after the closing of
the control caused recharge to the aquifer in all coastal reaches.
The flattening of the stage and discharge curves about 5 hours
after the closing reflects the increase in channel and bank storage
and the decrease of seaward gradient in the canal. The computed
rates of increase in channel storage 5 hours after the closing of
the control, shown in figure 12, indicate that most of the canal
discharge was entering the aquifer. At this time more than half the
flow passing Galloway Road was entering the aquifer in the Red
Road reach of Snapper Creek Canal and Ludlum Drain. In this
area the canals run in a north-south direction and the ground-
water gradient is steep toward the sea.
The discharges measured in the canal immediately before the

























NOTEL
SNOTIE COONTIROL OPEN
1:10 P.M. CONTROL CLOINO


JULY 21.1959


N O T E y s o o .o ,rn o .ton
ooT1001. ,ONrilOL CLOSIO
Io'OOA M. CONTROL OP9N
""-' |r w t.L


JULY 24,1959


3SP M N .CLOSED 9:0A












Figure 12. The flow regime and water-level profiles in Snapper Creek Canal
at selected times on July 21 and 24, 1959.







































Figure 18. Contour map showing water levels in the Snapper Creek area
July 21, 1959.































1 a


)1104





EXPLANA3PN
WATI9-TAILE CONTOUR.IN FEET N d
AsOVi MEAN ILFA LEVEL i

OBIERVAVICW WELL
STAFF IMAGE
WATERALIVIL RECORDING GAGE E

HCN BIW


Figure 14. Contour map showing water levels in the Snapper Creek area
July 24, 1959.







REPORT OF INVESTIGATIONS NO. 24


full opening of the control on July 24 (9:00 a.m.) were relatively
high in spite of the small (50 square feet) opening at the control
structure. As seen in figure 9, the mean discharge at the control
was only slightly less than the mean discharge shown when the
control was completely open. Measurements made before the full
opening (fig. 12) show that the discharge at Galloway Road was
about the same as that measured at the control. These discharge
measurements and the gradients shown by the contours in figure
14 indicate that the inflow to the canal within the coastal ridge
area was considerably greater than the losses to the bay. The rate
at which the discharge at the control structure reached 1,575 cfs,
after the opening of the control gates, suggests that most of this
initial flow was from channel storage in Snapper Creek Canal and
Ludlum Drain. The much smaller increase in flow at Palmetto
Road shows the effect exerted on the system by the inflow from
Ludlum Drain.
The sharp reversals in stage and discharge rates about an hour
after the opening of the control on July 24 reflect the damming
effect of the incoming tide. This tidal action also caused a reversal
in the direction of ground-water flow adjacent to the canal in most
reaches. The sharp change in slope in the canal profiles at Palmetto
Road during periods of high flow (fig. 12) is caused by a
constriction in the canal at that point. This change in the cross-
sectional area of the canal may have affected the accuracy of the
discharge measurements at this station.
The changes in the water table shown by the contours in figures
13 and 14 indicate the increase in storage in the aquifer during the
period the control structure was closed. The hydrographs for this
period indicate that an appreciable part of the increase in storage
in inland areas was caused by the rain on July 22; however, in the
coastal areas the effects of the rainfall were largely overcome by
drainage to the canal. The large changes shown by the contours
indicate the effectiveness of the control structure in lowering or
raising water levels. The system is especially effective near the
coast where Snapper Creek Canal and Ludlum Drain extend in a
north-south direction.

AQUIFER COEFFICIENTS

The principal hydraulic properties of an aquifer are its capacity
to transmit and store water. These properties may be expressed as
the coefficients of transmissibility (T) and storage (S). The
coefficient of transmissibility is defined as the amount of water






FLORIDA GEOLOGICAL SURVEY


in gpd (gallons per day), at the prevailing temperature, transmitted
through a 1-foot strip of saturated thickness of the aquifer under
a hydraulic gradient of 1 foot per foot. The coefficient of storage
is defined as the unit volume of water released from or taken into
storage per unit surface area of aquifer per unit change in the
component of head normal to that surface.
When water is pumped from a well in the Biscayne aquifer,
the unwatering of the adjacent materials causes the water table
to slope toward the well, thus forming a cone of depression. The
slope or hydraulic gradient of the cone causes ground water to
move from the surrounding areas to the well. The movement of
water through the aquifer follows a law developed experimentally
by Darcy, which may be modified for use with the tranmissibility
coefficient and written as:

Q = TIW
where Q = the average pumpage from a well field, in gpd
T = the transmissibility of the aquifer, in gpd per foot
W = the circumference of a cylinder through the aquifer at a given
radius from the center of pumping, in feet
I = the average slope of the cone of depression around this cylinder, in
feet per foot.

Approximate values for the coefficient of transmissibility of
the aquifer were computed from the ground-water gradients caused
by pumping in the Alexander Orr and Southwest well fields.
Using gradients shown in the contour maps of April 22, 1958, and
May 12, 1960 (fig. 15) for the two fields and the corresponding
average pumping rate for each well field, the computations indicate
a coefficient of transmissibility of 8.6 mgd per foot in the vicinity
of the Southwest field and 5.5 mgd per foot in the vicinity of the
Orr field.
The coefficient of storage of a water-table aquifer approximates
the specific yield, which may be expressed as the ratio of the volume
of water that the saturated material will yield by gravity to the
volume of the material. A calculation was made of the approximate
storage coefficient of the aquifer in the area adjacent to the canal
between Palmetto and Galloway roads by measuring the quantity
of water required to replenish a section of the aquifer, as shown
in the profiles in figure 16, during the 5 hours after the closing of
the control gates on July 21. The difference between the discharge
measured at Galloway Road and that at Palmetto Road during the
period, minus the change in channel storage, indicates that approxi-
mately 650,000 cubic feet of water were introduced to the 1-mile



































Figure 15. Contour map showing water levels in the Southwest and Alexander
Orr well fields on April 22, 1958 and May 12, 1960, respectively.






























Figure 16. Diagram showing water-level profiles along Palmetto Road and
Galloway Road on July 21, 1959.







REPORT OF INVESTIGATIONS No. 24


section of the aquifer from the canal. In addition to this, computa-
tions using the transmissibility coefficient obtained for the vicinity
of the Alexander Orr well field and ground-water gradients shown
in the profiles and the contour map (fig. 13) indicate that about
420,000 cubic feet of ground water flowing toward the canal
entered the test area.
The product of the average rise of the water table (between the
low and high water profiles in figure 16) and the area within the
test site indicates that the volume of material filled during this
period was approximately 9,700,000 cubic feet. Thus, the storage
coefficient is about 0.11. This coefficient is in the proper order of
magnitude for an aquifer under water-table conditions but is lower
than the average storage coefficient of 0.20 as determined from
pumping tests in the Miami area. The storage coefficient in the
vicinity of the canal probably is lower than in most of the Miami
area because of the presence of shallow marls throughout most of
the transverse glade (fig. 2) along the test section.

GROUND-WATER MOVEMENT AND CANAL FLOW

Of primary importance in the study of the canal area are the
accretions to and withdrawals from ground-water storage and the
corresponding changes in canal stage and discharge under different
hydrologic conditions. Under controlled drainage conditions
ground-water flow is toward the canal and canal flow increases
toward the bay. Any reduction of canal flow caused by the opera-
tion of the control structure raises canal stages and reduces or
reverses the ground-water gradients in areas adjacent to the canal.
If a given head is maintained at the control, the contours in
figure 14 indicate that the losses from the canal would occur
chiefly around the control structure, and eastward from the canal
and from Ludlum Drain. The magnitude of these losses is pro-
portional to the gradient between the canal system and the bay, but
the thickness of the seaward flow section near the canal system
and the bay and around the control structure is greatly reduced by
the salt-water wedge extending inland in the lower part of the
aquifer. If it is assumed that the base of the fresh-water flow sec-
tion is near the depth of the 5,000 ppm (parts per million) isochlor
(Kohout, 1960), salinity data in the Snapper Creek Canal area
indicate that the flow section underlying the edge of the coastal
ridge is only about 35 feet thick.
The only complete streamflow and water-level data available
for a period of low-water conditions are shown in figures 17 and






FLORIDA GEOLOGICAL SURVEY


Figure 17. Contour map showing water levels in the Snapper Creek area and
flow at selected points in the canal on March 21, 1951.

18, prepared during 1951 by Nevin D. Hoy of the U. S. Geological
Survey. Figure 17 shows the discharge measured at different points
in the canal and the water-table contours on March 21, 1951. A
sheet-steel dam, in use at that time, was closed during January
1-September 1, 1951, except for a partial opening April 10-13, and
only 0.06 inch of rain had occurred in the 30 days that preceded
the measurements. These data show the same general pattern of
canal discharge and ground-water inflow as that indicated by
the high-stage discharge measurements and contour map of July 24,
1959. Most of the water lost from the eastern reaches of the
canal came from the aquifer in the western part of the coastal
ridge.
It is apparent that under both high and low ground-water con-
ditions the flow in the canal was being maintained by ground-water
inflow from the western part of the coastal ridge. This inflow was
sufficient to balance losses along the lower reaches of the canal.
The point in the flow system where losses by outflow from the canal
exceed the quantity of ground-water inflow to the canal moves up-
stream as water levels in the area decline.
No flow was observed in the canal near Miller Drive at the time
of the 1951 measurements. Downstream from Miller Drive the
flow increased to 18 cfs at Palmetto Road, then decreased to zero






REPORT OF INVESTIGATIONS NO. 24


Figure 18. Contour map showing water levels in the Snapper Creek area on
June 12, 1951.

at the control structure. Ludlum Drain was not in existence in
1951, but by superimposing this drainageway on the contour map
of figure 17 and estimating the change in eastward losses through
the area from the ground-water gradients and the transmissibility
of the aquifer, the total losses from the flow system east of Palmetto
Road under these hypothetical conditions can be calculated. Sub-
stituting a coefficient of transmissibility of 5 mgd per foot, the
average ground-water gradient in area (fig. 17), and the length
of Ludlum Drain in the formula Q = TIW, the eastward loss on
March 21, 1951 was computed to be about 15 cfs. On the assump-
tion that the water level in Ludlum Drain would have been equal
to that at its junction with Snapper Creek Canal (2.9 feet above
msl), it is estimated that eastward losses from Ludlum Drain
would have been about 25 cfs, thus the increase in losses due to
the presence of Ludlum Drain would have been about 10 cfs and
the total loss from the canal system downstream from Palmetto
Road would have been about 28 cfs. If the same. canal levels were
maintained under prolonged drought conditions, the losses east of
Palmetto. Road would remain about the same, but additional losses
would occur from the western reaches when ground-water levels
declined to a level lower than that maintained in the canal.






FLORIDA GEOLOGICAL SURVEY


An estimate of maximum losses was made by superimposing
the canal levees of March 21, 1951 (2.75 feet above msl at the con-
trol structure, 3.71 feet above msl near Miller Road), on the low
stage water-table contour map of June 12, 1951 (fig. 18), which
shows near record low ground-water levels for controlled condi-
tions. If the canal levels were maintained constant, the losses from
the canal system east of Palmetto Road would be about equal to the
28 cfs estimated at the time of the March 21 measurements but the
contours in figure 18 indicate that additional losses would have oc-
curred from the canal west of Palmetto Road. On the basis of
average ground-water gradients estimated from the assumed canal
levels and the low stage water-table contour map, the computed
losses from the canal between Palmetto Road and the bend near
Miller Road were about 25 cfs. Thus the total losses from the
canal system would have been about 53 cfs.
During low-water periods large additional losses from the canal
may be caused by pumping in the large municipal well fields. It is
possible that more than 50 percent of the water withdrawn from
the Orr well field (49 mgd) and the Southwest well field (80 mgd)
may be derived from the canal. This loss would increase with any
increase in well field pumpage and could be more than twice the
magnitude of all other losses from the canal system.

SUMMARY

The Snapper Creek Canal drains the southernmost part of the
Greater Miami area and also a large part of the lower Everglades
west of the city. Flow in the canal is maintained chiefly by inflow
of ground water, but considerable surface runoff is introduced
from low areas on the coastal ridge and from the Everglades during
periods of heavy rainfall. Canal discharge is regulated by a control
structure near Biscayne Bay, in order to provide maximum flood
protection during periods of heavy rainfall and to maintain water
levels high enough to retard salt-water encroachment during dry
periods. The maximum discharge of record, 2,010 cfs, was recorded
at the control structure during the hurricane of September 9-10,
1960.
The area is underlain by permeable limestone, sandstone, and
sand of the Biscayne aquifer, which extend from the surface to a
depth of about 85 feet in the western part of the ridge and to about
120 feet at the coast. Geologic sections show that the deeper sub-
surface materials are relatively uniform throughout the area. In
several places the shallow limestone of the coastal ridge is cut by






REPORT OF INVESTIGATIONS NO. 24


natural drainageways which are bottomed by a few feet of marl
or silt of relatively low permeability. The coefficient of trans-
missibility of the aquifer ranged from about 8.6 mgd per foot at
the Southwest well field of the city of Miami to about 5.5 mgd per
foot at the Alexander Orr well field. The average coefficient of
storage of the aquifer as determined by pumping tests in the Miami
area was about 0.2. The storage coefficient computed for the
Snapper Creek Canal area was about 0.1.
Water-level data indicate that by manipulation of the control
structure, ground-water levels can be effectively raised or lowered
throughout the drainage area, especially adjacent to the north-
south reach of the canal near the coast. However, during severe
floods high-water levels in lower reaches of the system temporarily
reduce the effectiveness of the canal in lowering ground-water levels
within the ridge area.
Discharge data indicate that when the control gates are open,
ground water flows toward the canal and canal flow increases
toward the bay. When the control gates are closed canal levels
near the coast are generally higher than ground-water levels and
appreciable losses from the canal occur. Under all but the lowest
ground-water levels, however, these losses are balanced by ground-
water inflow in the western part of the coastal ridge.
By using water-level and discharge information collected during
1951 as an index of low-water conditions, it was calculated that
about 53 cfs would have to be brought into the system to maintain
a 2.75-foot stage at the control structure during severe drought.
In addition to this, a large part of the water withdrawn from the
Orr and Southwest well fields would probably be derived from the
canal. This loss could amount to more than 50 percent of the
current capacity of the well fields (129 mgd) and would increase
with future enlargement of the fields.
Because of the changes in the canal system since 1951, it is
important that further hydrologic data be obtained throughout the
Snapper Creek flow system during forthcoming low-water periods.
Analysis of these data will provide more accurate determinations
of the quantity of water needed to maintain the desired water levels
in the Snapper Creek Canal.

REFERENCES

Kohout, F. A.
1960 Cyclic flow of salt water in the Biscayne aquifer of southeastern
Florida: Geophys. Research Jour., v. 65, no. 7, p. 2133-2141.







32 FLORIDA GEOLOGICAL SURVEY

Parker, G. G.
1951 Geologic and hydrologic factors in the perennial yield of the
Biscayne aquifer: Am. Water Works Assoc. Jour., v. 43, p. 817-
834.
1955 (and others) Water resources of southeastern Florida, with special
reference to geology and ground water of the Miami area: U. S.
Water-Supply Paper 1255.
Schroeder, M. C.
1958 (and others) Biscayne aquifer of Dade and Broward counties,
Florida: Florida Geol. Survey Rept. Inv. 17.
Stallman, R. W.
1956 Preliminary findings on ground-water conditions relative to Area
B flood-control plans, Miami, Florida: U. S. Geol. Survey open
file report release, Tallahassee, Florida.




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