Citation
Hydrologic conditions in the vicinity of Levee 30

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Title:
Hydrologic conditions in the vicinity of Levee 30 northern Dade County, Florida ( FGS: Report of investigations 24, pt.1 )
Series Title:
( FGS: Report of investigations 24, pt.1 )
Creator:
Klein, Howard
Sherwood, C. B. ( joint author )
Place of Publication:
Tallahassee Fla
Publisher:
[s.n.]
Publication Date:
Language:
English
Physical Description:
v, 24 p. : map. diagrs. ; 24 cm.

Subjects

Subjects / Keywords:
Groundwater -- Florida -- Miami-Dade County ( lcsh )
City of Miami ( local )
City of Tallahassee ( local )
Levees ( jstor )
Canals ( jstor )
Conservation areas ( jstor )
Genre:
non-fiction ( marcgt )

Notes

General Note:
"Prepared by the United States Geological Survey in cooperation with the Central and Southern Florida Flood Control District."
General Note:
"References" : p. 23-24.
Statement of Responsibility:
by Howard Klein and C. B. Sherwood.

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University of Florida
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University of Florida
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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:
022573978 ( aleph )
01745370 ( oclc )
AES1348 ( notis )
a 61009620 ( lccn )

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Full Text
STATE OF FLORIDA
STATE BOARD OF CONSERVATION
FLORIDA GEOLOGICAL SURVEY
Robert O. Vernon, Director
REPORT OF INVESTIGATIONS NO. 24
PART I
HYDROLOGIC CONDITIONS IN THE VICINITY
OF LEVEE 30, NORTHERN DADE COUNTY, FLORIDA
By
Howard Klein and C. B. Sherwood United States Geological Survey
Prepared by the UNITED STATES GEOLOGICAL SURVEY in cooperation with the CENTRAL AND SOUTHERN FLORIDA FLOOD CONTROL DISTRICT
TALLAHASSEE, FLORIDA 1961
/




FLORIDA STATE BOARD a
OF tm
CONSERVATION
FARRIS BRYANT
Governor
TOM ADAMS RICHARD ERVIN
Secretary of State Attorney General
J. EDWIN LARSON RAY E. GREEN
Treasurer Comptroller
THOMAS D. BAILEY DOYLE CONNER
Superintendent Public Instruction Commissioner of Agriculture
ii




LETTER .OF TRANSMITTAL
Tiorikt geoloqical Surveqj
ZaIlakassee
June 1, 1961
Honorable Farris Bryant, Chairman Florida State Board of Conservation Tallahassee, Florida
Dear Governor Bryant:
The Florida Geological Survey is publishing as Report of Investigations No. 24, Part I, a report on the hydrologic conditions in the vicinity of Levee 30, northern Dade County, which was prepared by Howard Klein and C. B. Sherwood of the U. S. Geological Survey. This report was prepared in cooperation with the Central and Southern Florida Flood Control District, and this department is publishing the report in its regular series of water resources papers.
The formations that underlie Levee 30 are a part of the very permeable sediments that underlie the southern tip of Florida. The opportunity to make this study has provided important data relative to the transmissibility of the sediments and will assist in design of control structures and in-the development of the water resources of southern Florida.
Respectfully yours,
Robert O. Vernon, Director
iii




Completed manuscript received
February 27, 1961 -Published by the Florida Geological Survey
E. O. Painter Printing Company
DeLand, Florida
iv




CONTENTS
Abstract 1 Introduction -1
General statement and purpose 1 Previous investigations 3 Acknowledgments 3 D escription of area __....... ......... .... ... ..... .... 4
Geology ...........---5--------------------- -------------------_ 5
Drainage features 7 Hydrology ----- 9
Water levels and movement 9--- 9 Relation between ponded water and ground water 12 Underflow along Levee 30 16 Conclusions .....22 References-- ___ 23
ILLUSTRATIONS
Figure Page
1 Map of northern Dade County showing the area of investigation __ 2
2 Map of area of investigation showing the location of the test area
and the location of selected observation stations ------ 4
3 Cross section A-A' showing details of the near-surface geology near
the north end of Levee 30 _.5
4 Map of test area showing locations of observation stations and test
sites ------- ------ 6
5 Contour map of the area investigated showing the altitude and configuration of the water level on January 21, 1960 8
6 Hydrographs of groups of observation stations for 1959 and the
early part of 1960 ----- 11
7 Hydrograph of station G72 for the period 1940-59 and the annual
rainfall at the Miami Airport __12
8 Profile showing the relation between the ponded water and the
piezometric surface at site A-A', January 21 and February 8, 1960 13
9 Profile showing the relation between the ponded water and the
piezometric surface at site B-B', January 21 and February 8, 1960 14
10 Profile along site C-C' showing lines of equal potential, April
19, 1960 - -_-15
11 Graph showing the relation between the head difference across Levee
30 and the head difference between the pool and the piezometric
surface at the toe of the levee -_---- --- 21







HYDROLOGIC CONDITIONS IN THE VICINITY OF LEVEE 30,
NORTHERN DADE COUNTY, FLORIDA By
Howard Klein and C. B. Sherwood
ABSTRACT
Thin layers of dense limestone of low permeability that occur near the top of the Biscayne aquifer in the vicinity of the north end of Levee 30 in Dade County, Florida are of hydrologic importance because they retard the downward infiltration of ponded water in Conservation Area No. 3. This retarding effect frequently results in high head differentials across the levee. Tests made in a small area adjacent to Levee 30 indicate that the coefficient of transmissibility of the aquifer is 3,600,000 gpd (gallons per day) per foot, and the coefficient of vertical permeability of the dense limestones is 13 gpd per square foot. If ground-water flow beneath the levee is laminar, the total inflow to the Levee 30 Canal from Conservation Area No. 3 will be about 350 mgd (million gallons per day), or 540 cfs (cubic feet per second), per mile length of levee when the head difference across the levee is 10 feet.
INTRODUCTION
GENERAL STATEMENT AND PURPOSE
One of the major responsibilities of the Central and Southern Florida Flood Control District is to minimize flood damage in urban and agricultural areas west of the coastal ridge in southeastern Florida. A second function is to protect areas of potential urban development. A large area of anticipated growth in Dade County (shown as Area B in fig. 1) is west of Miami and extends about 10 miles eastward from Levees 30 and 31.
The initial project of the Central and Southern Florida Flood Control District was the construction of an east-coast protectivelevee system west of the Atlantic Coastal Ridge, extending from Lake Okeechobee southward into Dade County. Levees 33, 30, and 31 form the southern terminus of this levee system and are shown in figure 1. Its primary purpose was to alleviate flooding in urban and agricultural land, along and adjacent to the ridge, by retarding the overland eastward flow of floodwaters from the Everglades. When the flood-control system is completed, part of these excess floodwaters will be impounded in conservation areas west of the
1




2 FLORIDA GEOLOGICAL SURVEY
HOLLYWOOD
ES AREA
BROWARD -.#/_gU1TY CREEK
)6
DADE COUNTY
/ ,AREA B AREA A
36 t.Street
- ontrol
S/ /1 /
MIAMI
EXPLANATION N
REPORT AREA
CANAL AND CONTROL SCALE IN MILES 012345 6
Figure 1. Map of northern Dade County showing the area of investigation.
levee. Regulated releases of water will be conveyed by canals from conservation areas to coastal areas to replenish ground-water reservoirs during periods of drought.
This report is one of a series prepared in cooperation with the Central and Southern Florida Flood Control District. The general purposes of these investigations are (1) to define the hydrology of certain areas within the Flood Control District, (2) to determine the effectiveness of existing flood-control and water-control measures, and (3) to furnish hydrologic data that will be used in the design and operation of proposed and existing structures and works.




REPORT OF INVESTIGATIONS No. 24 3
The purpose of this investigation is to define the hydrologic characteristics of the water-bearing materials in the vicinity of Levee 30 in northern Dade County, in order to determine the feasibility of controlling water levels in Area B for maximum flood protection. Included is an analysis of the relation between the impounded water west of Levee 30 and the ground water in the area. From this relationship estimates of ground-water underflow along Levee 30 can be computed under existing conditions and under anticipated water-level conditions. Midway in the data-gathering stage of the investigation, major road construction altered the canal system in the immediate area and caused changes in water levels and discharge of canals. This resulted in curtailing of the field work; therefore the results of this investigation should be considered preliminary.
The work was done under the general supervision of P. E. LaMoreaux, chief, Ground Water Branch, Washington, D. C., and under the immediate supervision of M. I. Rorabaugh, district engineer, Tallahassee, Florida.
PREVIOUS INVESTIGATIONS
A comprehensive report by Parker and others (1955) presented fairly complete information on the geology and hydrology of southeastern Florida, and Parker (1951) gave estimates of the availability and adequacy of the ground-water supplies of the Biscayne aquifer which underlies southeastern Florida. Schroeder and others (1958) summarized additional data on the Biscayne aquifer collected since 1950. Stallman (1956) made theoretical computations on the effect of drainage in the area west of Miami and gave estimates of the amount of seepage that might occur beneath Levee 30 under certain assumed conditions. A mimeographed report by the U. S. Army Corps of Engineers (1953) described the results of permeability tests along different levees within the Flood Control District.
ACKNOWLEDGMENTS
The writers are indebted to personnel of the Surface Water Branch, U.S. Geological Survey, Miami, Florida, for making discharge measurements in the Levee 30 Canal and furnishing waterlevel information along the Miami Canal. Gratitude is expressed also to the Public Works Department of metropolitan Dade County for the record of water-level stages for several observation stations in the area. The office of the Central and Southern Florida Flood




4 FLORIDA GEOLOGICAL SURVEY
Control District furnished complete information on the location, the construction details, and the layout of the Corps of Engineers test sites near Levee 30. The writers benefited from technical discussions with F. A. Kohout of the Miami office, and H. H. Cooper, Jr, and N. D. Hoy of the Tallahassee office, U. S. Geological Survey.
DESCRIPTION OF AREA
The area described in this report comprises 60 square miles chiefly in northern Dade County, Florida (fig. 1). Figure 2, which is a large-scale map of the report area, delineates the test site within the area, locates certain water-level observation stations, and shows the drainage features. The western part of the area is traversed by Levees 30 and 33. These levees separate Conservation Area No. 3, which normally contains ponded water, from Area B which is swampy during much of the year. The altitude of the land surface is about 5 feet above msl (mean sea level).
Ex~R 9 E R 40E
z95XRVAT O AT ION
r -x L. :.-'mON '3 \ \ I 4
, \ u, %%oum o. --,
ZANAL ANDl CONTROL 2 9TO
M. 2\i \ \ 21, ,l' ,
EC- ROING GAGE
AND NUMBER
RSSERVATION, ST.TION
_OWD -RECT"\CN/ \ GLEN GLG7ES CANAL
____"___ II 3
,'_ N FEET,,
,,~ A / i! ,
\ 3 4
33E
TN30 TE
A'73RUSSIAN C--OONY CAA V4974 G973
3-E R40E
Figure 2. Map of area of investigation showing the location of the test area and the location of selected observation stations.




REPORT OF INVESTIGATIONS NO. 24 5
GEOLOGY
The area of investigation is underlain to a depth of 55 feet by the Biscayne aquifer, a body of highly permeable limestone. The Biscayne aquifer is underlain by relatively impermeable silt, marl, and fine sand which retard downward seepage from the aquifer or upward seepage from deeper materials.
The cross section in figure 3 gives details of the near-surface geology near the north end of Levee 30 in Dade County, as determined from shallow test holes drilled at site A-A' (fig. 4). The area is blanketed by 3 to 5 feet of muck and marl that is underlain by a layer of solution-riddled Miami oolite, a part of the Biscayne aquifer, 1 to 2 feet thick. Figure 3 shows two thin layers of very hard, dense limestone at depths ranging from 0.5 foot above msl to 3.0 feet below msl. In contrast to the high permeability of the underlying limestones, these thin layers appear to be relatively impermeable; and the vertical flow of water through them is many times less than the horizontal flow of water through the deeper, more permeable rocks. By effectively retarding the downward infiltration of water, the thin layers act as a confining
A 30 DISTANCE IN FEET A
3@0 2 00 0 100 200 300
4 LEVEE
3
_EXPLANATION L
< --
- - -E- -LAO -- ---PERMEABLE LIMESTONE
wlMEsTONE.HARD: MARL AND MUEK TO 50 FEET BELOW M SL
LOW PERMEABILITY LOW PERMEABILITY
LIMESTONESOFT. FILL;LOW ~
HIGH PERMEABILITY PERMEABILITY
Figure 3. Cross section A-A' showing details of the near-surface geology near the north end of Levee 30.




6 FLORIDA GEOLOGICAL SURVEY
Mil 27 10
h3
DADECANAL AND CONTROL G7A M2
Qg/'(J RECORDING GAGE 030
30 W C-CG LINE OF PROFILE
-Q2
L4 M 2
STREAM-GAGING STATION
A M 2
OBSEXPLAATIONTIO
30E AND NUMBER
0 W 30E LINE OF PROFILE <- Q02
STREAM-GAGING STATION SCALE IN FEET
0 2500 5000
Figure 4. Map of test area showing locations of observation stations and test sites.




REPORT OF INVESTIGATIONS NO. 24 7
unit that separates the ponded water in Conservation Area No. 3 from the water contained in the permeable limestone.
Geologic information from test wells and shallow borings, and reported information obtained in connection with canal excavations, indicate that the hard layers of dense limestone occur throughout most of Area B and in southern Dade County, and that they occur at about the same altitude. Each of the wells (prefixed by letter G) shown in figure 2 penetrated the impermeable layers approximately at sea level. Similar layers were noted in wells near the southern terminus of Levee 31 (fig. 1), and in wells south of the Tamiami Canal and west of Levee 31. It is reasonable to assume that the relatively impermeable zones underlie much of Conservation Area No. 3 and that their confining characteristics are widespread. In places, the dense limestones probably contain openings through which rainfall can infiltrate rapidly; however, the overall continuity and the blanketing effect of these layers in general tend to retard infiltration. In the Miami area to the east, the Biscayne aquifer thickens and contains much sand. The thin, dense limestones either thin and disappear or they occur deeper in the aquifer near the coast.
DRAINAGE FEATURES
During the past 10 years the improved canal system that provides gravity drainage to Biscayne Bay, as shown in figure 1, has effectively reduced flooding in Area A, the urbanized part of eastern Dade County. The system, as designed, can remove large quantities of excess runoff during rainy seasons and can lower ground-water levels in order to furnish storage in the aquifer to accommodate anticipated heavy recharge by rainfall. The controlled discharge of the canals has furnished good flood protection in Area A and at the same time has maintained adequate water levels in most coastal areas to retard the inland movement of salt water.
Area A must be at least partially drained before any depletion in storage can be effected in Area B; consequently, Area B normally remains inundated or swampy during long periods. Also, the eastward seepage beneath Levee 30 tends to maintain high water levels in the western part of Area B. Area B is drained chiefly by the Miami and Tamiami canals and to a lesser extent by the Snake Creek and Snapper Creek canals. Their capacities are not adequate to drain Area B by gravity during the rainy seasons.
Figure 2 shows the drainage features of the report area and indicates the normal directions of flow in the major canals. The




8 FLORIDA GEOLOGICAL SURVEY
discharge of the Miami Canal is regulated by a control located at 36th Street, Miami, 6 miles inland from Biscayne Bay (fig. 1). The control normally is opened a few weeks before the rainy season and remains open throughout the rainy season to facilitate the discharge of excess water. During open periods the effect of tides extends upstream to a point beyond the Pennsuco Canal (fig. 2). After the rainy season the control is closed in order to conserve water for heavy municipal and irrigation use during the following dry months and to maintain high water levels along the coast as a protective measure against salt-water encroachment.
The main tributaries of the Miami Canal in northern Dade County are the Levee 30 and 33 canals, the Pennsuco Canal, and the Russian Colony Canal. Flow in some canals is controlled by use of earth dams or manually operated sluice gates as located in figure 2. The Levee 30 Canal is controlled at the Dade-Broward Levee and its flow to the Miami Canal is maintained by seepage to the northeast around the control and by ground-water inflow between the control and the Miami Canal. The control in the Levee 30 Canal usually remains closed. The flow in the reach of the Levee 30 Canal upstream from the control is so small that
X 7iLA CT N R 39E R40E
- 1._43 CONTCL _$_RONARD OUNT r N .4.c CANL
A-5
RECORDING GAG
Fiur Cotu a of.th araivstgtdsown h lttd n
OBScER'ATICN STAT IOth w
G372 STAION NUMBER 5.7 WTER LEVEL
4.6
I NE SHOWING ALTITUDE 0 C
GF WATER LEVELING FEET GOLDEN GLADES C,1vat
AOVE MEAN SEA LEVEL .85
SCALE- 114 A F-T /
3 5000 i0500 XC4(:.: I
I _8F
(3 0 0 0 0 b
P39E R4OE
Figure 5. Contour map of the area investigated showing the altitude and
configuration of the water level on January 21, 1960.




REPORT OF INVESTIGATIONS No. 24 9
ordinarily it cannot be measured. Probably there is a very low water divide along the north-south reach of the canal from which there is a slight southward gradient toward the Tamiami Canal and northward gradient toward the Miami Canal.
The southward flow in the Levee 33 Canal is controlled at the Miami Canal. Operation of this control depends upon the ability to maintain water stages of 3.0 to 3.5 feet above msl at station M3, in the Miami Canal where it is joined by the Pennsuco Canal. When the stage is below this level, the control is opened and water is released into the Miami Canal to replenish supplies in the downstream reaches.
The southern part of the area is drained by the Pennsuco Canal, which extends westward to the Dade-Broward Levee, and by the Russian Colony Canal; however, effective drainage by the Russian Colony Canal extends only about 31/ miles west of its confluence with the Miami Canal. The westward extension of this canal is shallow and unimproved and therefore is effective only during flood periods. Partly effective drainage probably takes place along the shallow diagonal canal north of the Pennsuco Canal.
HYDROLOGY
WATER LEVELS AND MOVEMENT
Widespread fluctuations of water levels in Dade County are due to recharge by rainfall, to discharge into drainage canals and Biscayne Bay, and to evapotranspiration. Water levels in this part of northern Dade County are regulated also by the operation of the control in the Miami Canal at 36th Street, Miami, and by operation of controls in the Levee 30 and Levee 33 canals.
Figure 5 is a contour map of water levels in the area on January 21, 1960. The contours are based on water-level measurements obtained from observation points in canals that cut through the dense limestones and from observation wells. Water levels in the area were relatively high at that time and the control at 36th Street was open. The configuration shows that the drainage effect extended along the entire uncontrolled reach of the Miami Canal and its main tributaries and along the short reach of the Levee 30 Canal downstream from the Dade-Broward Levee. The pattern of the contours indicates the effectiveness of drainage by deep canals (Miami, Levee 30, and Pennsuco canals, and the lower reach of the Russian Colony Canal) and the lack of effective drainage by the shallow canals. High heads are maintained above the




10 FLORIDA GEOLOGICAL SURVEY
control in the Levee 33 Canal and the control in the Levee 30 Canal; however, the close spacing of the contours at these controls indicates that there is considerable seepage through the aquifer around the controls.
It is important to compare the pattern of the contours east of the Dade-Broward Levee with that adjacent to Levee 30 between the Dade-Broward Levee and the Miami Canal. The distribution of the heads east of the Dade-Broward Levee indicates that the shallow diagonal canal and the Dade-Broward Levee borrow canals do not have an appreciable drainage effect. In contrast, the steep gradient on the northwest side of Levee 30 and the low gradient on the southeast side indicate that the Levee 30 Canal is intercepting nearly all the underflow along Levee 30.
High water levels prevailed throughout this part of northern Dade County during 1958-59 and the early part of 1960. On May 8, 1958, the 36th Street control was opened and drainage of the area proceeded until January 5, 1959, when the control was closed. The control again was opened on June 23, 1959, and remained opened throughout the first half of 1960. During the entire period the eastern part of Conservation Area No. 3 was inundated to depths ranging from 1 foot to more than 4 feet. The area between Levee 30 and the Dade-Broward Levee also was flooded during the period, but the depth of the water was less than that in Conservation Area No. 3. Flooding east of the Dade-Broward Levee probably was intermittent and corresponded with periods of heavy rainfall.
Figure 6 shows hydrographs of groups of observation stations in the area for 1959 and the early part of 1960. The locations of these stations are shown in figures 2 and 4. The hydrographs show the relation between canal stages and ponded-water stages in the area adjacent to the Levee 30 and 33 canals and the Miami Canal.
The hydrographs of stations 30TW and 30TE show the variation in head differential between the pool in Conservation Area No. 3 (3OTW) and the stage in the Levee 30 Canal south of the DadeBroward Levee. During dry periods, such as March-May 1959, the head differential across Levee 30 at this point was very small and a temporary reversal of gradient (east to west) occurred at the end of April and in early May. During the dry months, the eastward underflow of water from Conservation Area No. 3 probably was negligible as compared to that during periods of high water stages (July 1959-January 1960).
The persistent high head differential represented by the hydrographs of stations 30W and 30E show the effectiveness of the control in the Levee 30 Canal at the Dade-Broward Levee. This




REPORT OF INVESTIGATIONS NO. 24 11
S"1959 1960
. AR. A JUNE JULY AUG. SEPT. CT. EB
O2 IfT N0 10 20 102 0 109 0 I0 8 fl 020
10
8
3 T fPOND_ TE
f0
_to
early- pato 90
loe ec of-th Leve.30.anal
<
En
Lij
J
09
L 3ee the atl his dV enEt, an ifrt t flo ding a7 relative dr p to m 4 f d h
An outtaninfetr i --o th yrgah infiur "-6 is h
iL 6 /
hgeddifferential badsetesttinos M9aag(pondefdoM (Levee :30 Canal); ;this, differential -ranged from 2.2 feet during a relatively dry period to more, than 4.5 feet during high water




12 FLORIDA GEOLOGICAL SURVEY
stages. Also shown in figure 6 are the heads maintained behind the control in the Levee 33 Canal (station 33) and the control in the Miami Canal at the Dade-Broward Levee (station M11). A comparison of the hydrographs of stations 30E and M8 shows the low gradient through the downstream reach of the Levee 30 Canal.
A continuous record of water-level fluctuations has been obtained from station G72 since 1940. A hydrograph of this station and the annual rainfall at the Miami Airport are shown in figure 7. The highest water level of record at station G72 was 9.4 feet above msl in October 1947, and the lowest of record was 1.1 feet above msl in June 1945. The hydrograph for the long period of record gives a comparison between water levels before the levee system and water-control practices were in effect (before 1952), and water levels after the water-control measures were in operation (195259). It can be seen that water levels during the drought period of 1955-56 did not decline as much as they did during the comparable drought periods of 1944-45 and 1950-52. Also, it is apparent that the unusually heavy rainfall of 1957-59 did not produce water levels as high as those during the wet years 1947-48. These facts demonstrate that the proper placement and operation of the existing controls in canals can decrease flood damage during rainy seasons and can maintain relatively high water levels during droughts.
RELATION BETWEEN PONDED WATER AND GROUND WATER
Three test sites were established adjacent to the Levee 30 Canal downstream from the Dade-Broward Levee (fig. 4). The purpose
19391940.1941.1942 1943 1944194519461947 1948 1949 1950 1951 19521953 19541955 1956,1957.1958 I5
5 MIAMI AIRPORT
-1
1- PRIOR TO WATER CONTROL A ER CONTROLG72 1 IN EFFECT
UA
z -Z
-U
>L 4 0
0 SEA LEVEL
19391940 1941 19421943 1944 1945 1946 1947 1948 1949 19501951 1952195319541955 1956195719581959
Figure 7. Hydrograph of station G72 for the period 1940-59 and the annual rainfall at the Miami Airport.




REPORT OF INVESTIGATIONS NO. 24 13
of studies at these sites was to determine the relation between the impounded water in Conservation Area No. 3 and ground water in the area. When this relationship is known, the amount of underflow occurring beneath Levee 30 can be calculated for the existing water-level conditions, and estimates of underflow can be made for various assumed water-level conditions.
Each of the test sites consists of a line or lines of. test wells perpendicular to Levee 30; these sites are shown in the profile sections in figures 8, 9, and 10. The wells at site A-A' (fig. 8) are the shallowest, but they penetrate the entire thickness of the dense limestones and terminate in the upper section of the highly permeable part of the aquifer. Site B-B' (fig. 9) was drilled by the Corps of Engineers and consists of a line of nine wells extending northwestward from Levee 30 and one well on the berm between Levee 30 and the Levee 30 Canal. These wells range in depth from 17 to 40 feet.
The wells at site C-C' (fig. 10) also were drilled by the Corps of Engineers and were used as observation wells during a pumping test to determine the permeability of the aquifer. The site consists of groups of multiple-depth wells extending northwestward into Conservation Area No. 3. Figure 10 shows the layout of the lines
300 200 DISTANCE IN FEET A'
A 0 0 00 0 t00
iu 8 o s in o t 300
Pon d level JO ri 8, 960 LEVEE
4 Pjiezometric su fac ,160
LEVEE
11- 30
CANAL
o
Figure 8. Profile showing the relation between the ponded water and the piezometric surface at site A-A', January 21 and February 8, 1960.




14 FLORIDA GEOLOGICAL SURVEY
DISTANCE IN FEET 1o
S Fe a LEVEE i

. I I : _Z4 30
cH
Jaur 21an Februa:1ry 8,16.Fiue8an 9 sho tewaer II CANAL
it
Figure 9 Profile showing the relation between the ponded water and the
piezometric surface at site B-B, January 21 and February 8, 1960.
of wells with reference to Levee 30 and the Levee 30 Canal and indicates the altitude of the bottom of each well.
Water-level measurements were made at A-A' and B-B' on January 21 and February 8, 1960. Figures 8 and 9 show the waterlevel profiles at the two sites on the dates the measurements were made At site A-A' (fig. 8) the gradient of the piezometric surface on the northwest side of the levee toward the Levee 30 Canal was 3.1 feet in 270 feet, or 0.0041 foot per foot. Within the 270foot distance the head differential between the ponded water and the piezometric surface increased toward the levee and ranged from 3.1 feet at the end well of the profile to 3.6 feet at the levee' The gradient of the piezometric surface along the profile in figure 9 was 3.17 feet in 650 feet, or 0.049 foot per foot. The head differential between the ponded level and the piezometric surface ranged from 1.2 feet at the end well of the profile to 3.5 feet at the levee. The average gradient of the piezometric surface during the 3-week test period was 0.0045 foot per foot toward the Levee 30 Caial. The aquifer was being replenished by the downward leakage of ponded water, at a rate dependent upon the head differential, and no depletion of aquifer storage was occurring northwest of Levee 30.
Water-level measurements made during the drilling at site A-A'




DISTANCE N FEE 4
+10o 0 .n0 14 I 00 0 1 o ?, Goo 4Q 20 0 r~~~~~ POFO IFF30
I .PIEZOMETRIPN 6,9/
>i "-RLAND SURFACE.J 0,,Wee 0 -- ------- .-- A
.e rt.@.34 sa ,ssa sp st;. s
0-0<
0 EPAA1 LU 7
. *, W634 E93557.02 3.30.54 040.
U.198 0u
.,-3 EXPLANATION -0
"lBOTTOM OF CASED WELLt 504
74II LWTER LEVEL 6..4 5 5 1 1 5
LINEO ,0QUA POETIL"1"';
F figure 10. Profile along site 0-0' showing lines of equal potential, April lb, 1960.




16 FLORIDA GEOLOGICAL SURVEY
showed that there was no head difference between the ponded level and the water level of wells bottomed in the Miami oolite. This indicates that the confining characteristics of the marl and muck blanket are of much less significance than those of the dense limestones.
No appreciable ponding occurred in the area immediately southeast of the Levee 30 Canal. Figure 8 shows also that the northwestward gradient of the piezometric surface on the southeast side toward the Levee 30 Canal was 0.40 foot in 250 feet, or 0.0016 foot per foot. Therefore, the quantity of inflow from the southeast was equivalent to approximately 40 percent of the inflow occurring from the northwest at the A-A' site during the period January 21February 8, 1960. The profile in figure 8 indicates a slight depletion of ground-water storage immediately southeast of the Levee 30 Canal. It is important to recognize that the contribution of water from the area southeast of the Levee 30 Canal to the canal was diminishing as shown on the contour map (fig. 5) by the decrease in ground-water gradient along the lower reach of the canal. It is estimated that the average gradient of the piezometric surface on the southeast side along the uncontrolled reach of the canal was 0.0010 foot per foot. Therefore, the total inflow to the Levee 30 Canal from the southeast was equivalent to approximately 20 to 25 percent of the total from the northwest.
UNDERFLOW ALONG LEVEE 30
During periods when the control in the Levee 30 Canal is closed, discharge along the downstream reach of the Levee 30 Canal represents a composite of the following: (1) leakage by underflow around the control, (2) ground-water inflow from the thick permeable section of the aquifer, and (3) seepage of ponded water through the levee fill and through the thin layer of permeable Miami oolite that occurs between the fill and the dense limestone layers. At high water stages, such as those which prevailed from July through November 1959, the water level of the downstream reach of the canal was above the canal bank and sheet flow occurred toward the Miami Canal. Most of the discharge of the Levee 30 Canal was maintained by ground-water inflow from the northwest.
By January 21, 1960, water stages had lowered and discharge measurements were made at points 1 mile apart in the Levee 30 Canal (Q, and Q2 in fig. 4), downstream from the control. Following is a tabulation of the discharge and water-level data obtained during the January 21 test:




REPORT OF INVESTIGATIONS No. 24 17
A. Discharge measurements in Levee 30 Canal
At Q1 -_ ___ -__.. .... .. .. 76 cfs (49 m gd)
At Q2 --- ------------------------------------ 252 cfs (163 mgd)
Q2 ---- ---------- ------------------ 176 cfs (114 mgd)
Estimated seepage (visible) through the levee
fill, across the berm to the canal (Qs) -- 10 cfs (7 mgd)
Net pickup by ground-water inflow (Qg)
Qg=Q2-Q-Qs -----------------------------166 cfs (107 mgd)
B. Gradients (I) of piezometric surface toward
Levee 30 Canal (fig. 8, 9).
Northwest of canal
A-A' site --------------------- 0.0041 foot per foot
B-B' site .---------------------- 0049 foot per foot
Southeast of canal
A-A' site .---------------------- 0016 foot per foot
Estimated average for area
southeast of canal ------------ .0010 foot per foot
By Darcy's law the rate of flow of a fluid through a porous medium is directly proportional to the hydraulic gradient and can be written as follows (Wenzel, 1942, p. 3-7):
Q=--PIA
where Q is the discharge rate, P is the coefficient of permeability of the material being tested, I is the hydraulic gradient, and A is the area of the cross section through which the fluid moves. If it is assumed that the permeable section of the aquifer beneath the dense limestone layers is isotropic and that underflow through this section is laminar, then the quantity of ground water discharging into the Levee 30 Canal is directly proportional to the gradient of the piezometric surface; therefore, about 80 percent of Qg or 86 mgd, represents underflow from the northwest along the 1-mile reach of the canal. (See tabulation above.)
In order to make computations that involve the entire thickness of an aquifer as a unit, Darcy's law may be written:
Q=TIL
in which Q is the quantity of water, in gpd (gallons per day), T is the coefficient of transmissibility, in gallons per day, for each vertical strip of the aquifer 1 foot wide; I is the hydraulic gradient,




18 FLORIDA GEOLOGICAL SURVEY
in feet per foot; and L is the length of section, in feet, through which the quantity (Q) flows. By substituting in the above equation the hydrologic data obtained during the January 21 test, a determination of the coefficient of transmissibility of the aquifer can be made as follows:
Q=TIL
Q (gpd)
T (gpd per foot)= (gpd)
I (foot per foot) xL (feet)
T 86,000,000
0.0045 x 5,280
T 3,600,000 gpd per foot, or 5.6 square feet per second
This computed coefficient of transmissibility compares very closely with the value of 5.76 square feet per second determined by the Corps of Engineers for the highly permeable part of the aquifer adjacent to Levee 30 (U.S. Army Corps of Engineers, 1953, p. D-6).
Dry weather prevailed during the spring of 1960, and by the middle of April the water stage in Conservation Area No. 3 had declined so that the multiple-depth wells along site C-C' were accessible. On April 19, 1960, water-level measurements were made in all wells in this test site. The profile in figure 10 shows the relation between the pool in Conservation Area No. 3 and the piezometric surface on that day and shows also, by equipotential lines, the approximate head distribution in the aquifer along the profile. The gradient of the piezometric surface within 1,000 feet of the Levee 30 Canal was 0.0017 foot per foot, but for the remaining 800 feet of the section the gradient decreased to 0.0011 foot per foot. The head differential between the ponded water and the piezometric surface ranged from 0.32 foot at the northwestern end of the profile to 1.57 feet near the toe of the levee.
The equipotential lines, shown in figure 10, indicate that flow through the highly permeable part of the aquifer (depths more than 5.0 feet below msl) toward the Levee 30 Canal is virtually horizontal, except for the section adjacent to and beneath the canal where the flow direction has an upward component. The distribution and pattern of the lines suggest that about 75 percent of the loss in head occurs within 1,000 feet of the levee. The horizontality and the close spacing of the lines at depths between 0.5 foot above and 3.0 feet below msl indicate a large vertical head loss caused by




REPORT OF INVESTIGATIONS No. 24 19
vertical flow through the dense limestone of low permeability at that interval (fig. 3). The flow through the shallow materials immediately beneath the levee is virtually horizontal and probably occurs chiefly through a thin layer of the permeable Miami oolite beneath the fill.
Detailed information on head distribution through a part of the aquifer, as shown in figure 10, makes it possible to estimate the amount of surface water that was seeping downward through the confining layers to the thick permeable part of the aquifer. The amount of ground water moving toward the canal in 1 day, across a section of the aquifer 1 mile long at a distance of 800 feet from the edge of the canal, may be computed as follows:
Q=TIL
0.4 foot x 5,280 feet
Q=3,600,000 x400 feet
400 feet
Q=19 mgd per mile, or 29 cfs per mile
A similar computation for a distance 400 feet from the canal is as follows:
0.59 foot x 5,280 feet
Q=3,600,000 x 0 feet
400 feet
Q=28 mgd per mile, or 43 cfs per mile.
The 9-mgd difference in flow represents approximately the amount of surface water picked up by leakage through the confining beds to the permeable flow section within the rectangular area 1 mile long between 400 and 800 feet from the levee.
Inasmuch as the appSroximate amount of downward infiltration in a given area has been determined, a computation of the coefficient of vertical permeability of the confining layers can be made. The coefficient of permeability is defined as the rate ,of flow through a cross section of 1 square foot, under a gradient of 1 foot per foot. The computation of the coefficient of vertical permeability of the dense limestone is as follows:
Rectangular area used in computation :_5,280 feet x 400 feet, or 2.1 million square
feet
Downward leakage ----9 nigd, or 4.3 gpd per square foot




20 FLORIDA GEOLOGICAL SURVEY
Altitude of piezometric surface 600
feet from levee 5.93 feet above msl
Altitude of ponded level _6.91 feet above msl
Head differential 600 feet from levee
(assumed average for area 400 to
800 feet from levee) 0.98 foot
Thickness of confining layers 3.0 feet
Gradient across confining layers .------0.33 foot per foot
Q
P=
IA
4.3 gpd
0.33 foot per foot x 1 square foot
P= 13 gpd square foot, or 2.0 x 10-1 foot per second
A proposed method of flood control in Area B is to reduce ground-water storage by means of a network of canals and a series of large pumping stations. The pumps would be placed at selected locations along Levees 30 and 31 and would pump water from the interconnected canal system of Area B westward into Conservation Area No. 3. Initially, it was proposed that the water stage in Area B be maintained at mean sea level in order to give maximum protection during all major storms. It is probable that water levels along the levee side of Area B will be lowered temporarily below mean sea level in order to provide adequate gradients toward the pumping stations.
Reducing the water stage in Area B would result in gradients across Levee 30 that would greatly exceed those shown in the profiles of figure 9. There might be times when the head differential between the pool in Conservation Area No. 3 and the stage in the Levee 30 Canal would be as much as 10 feet. It is extremely important, therefore, to determine the amount of water that would move from Conservation Area No. 3 to the adjacent canals in order that adequate pumping stations be provided.
To make a determination of the anticipated underseepage it is necessary to determine the relation between the head across the levee and the head differential at the toe of the levee at different water stages. Figure 11 is a graph showing this relationship; and the plotted points are based on the water-level profiles of figures




REPORT OF INVESTIGATIONS NO. 24 21
HEAD DIFFERENCE,IN FEET, BETWEEN POOL AND LEVEE 30 CANAL
3 4 5 6 7 8 I 0
8
6I
N /
w 07
z 6
-Jb
0>J
o/ uw/
0 Wl
,.n- JAN.21,1960 -DEC. 17,1959
2 U Li .
W 0
o <
LL
Wi U)
Z 2 _w
/,APRIL 19,1960
LLf
=:0
Figure 11. Graph showing the relation between the head difference across Levee 30 and the head difference between the pool and the piezometric surface at the toe of the levee.
9 and 10 and on a series of measurements made on December 17, 1959. The projection of the graph indicates that, if a 10-foot head were held across the levee, the head difference between the pool and the piezometric surface at the toe of the levee would be 7.8 feet; thus the gradient of the piezometric surface across the 150-foot width of the levee would be 2.2 feet.
Following is a computation of the amount of underflow that would be intercepted along a 1-mile reach of the canal (Q1 to Q2 in fig. 4) when the head differential across the levee was 10 feet:
Q=TIL
Q=3,600,000 gpd per foot x 2.2 feet x 5,280 feet 150 feet
Q-279 mgd per mile, or 432 cfs per mile
In order to determine the total quantity of water that Would be intercepted jby the Levee 30 :Canal along the 1-mile reach,




22 FLORIDA GEOLOGICAL SURVEY
consideration must be given to the seepage that would occur through the levee materials and through the thin permeable layer of Miami oolite that underlies the levee fill. This approximate determination is shown by the following tabulation:
Composite estimate of coefficient of
permeability of levee fill and
Miami oolite 20,000 gpd per square foot
Length of flow section 5,280 feet
Thickness of flow section
(10-foot head differential) 10 feet
Q=PIA
10 feet
Q=20,000 gpd per square foot x 150 feet x 5,280 feet x 10 feet 150 feet
Q= 70 mgd per mile, or 108 cfs per mile
The estimated coefficient of permeability used in the above computation probably is high and compares with a well sorted gravel that contains only small quantities of fine material (Wenzel, 1942, p. 13). However, the estimate was made in consideration of the probable high permeability of the layer of Miami oolite through which much of the direct seepage may occur.
The total quantity of water that would be intercepted along the 1-mile reach of Levee 30 Canal when the head difference across the levee was 10 feet is computed to be 349 mgd, or 540 cfs. These results were obtained by assuming that water movement beneath Levee 30 occurs by laminar flow. If there is turbulence through the large openings in the aquifer beneath the levee, the underflow would be less. For laminar flow the underflow to the canal would be directly proportional to the head difference across the levee, and for turbulent flow the underflow would be directly proportional to the square root of the head difference; in the transitional zone underflow would vary exponentially between the first and one-half powers of the head difference.
CONCLUSIONS
Water-level measurements and geologic data obtained from test wells indicate that the upper part of the Biscayne aquifer in the vicinity of Levee 30 in northern Dade County contains dense layers of limestone of relatively low permeability that retard downward




REPORT OF INVESTIGATIONS No. 24 23
infiltration to the thick permeable parts of the aquifer. The coefficient of transmissibility of 3,600,000 gpd per foot, or 5.6 square feet per second, as determined from water-level profiles taken Normal to Levee 30 and from discharge measurements made in
the Levee 30 Canal, compares closely with the coefficient determined by the Corps of Engineers by pumping-test methods. The computed coefficient of permeability of 13 gpd per square foot, or 2.0 x 10-5 foot per second, for the thin dense layers indicates that these layers form a fairly effective confining unit which separates the ponded water in Conservation Area No. 3 from the ground water. Geologic information obtained from the surrounding areas suggests that the thin, dense limestones probably are widespread, and therefore
that the blanketing effect occurs throughout a large area.
Conservation Area No. 3 generally is flooded for several months
-'of each year, the result being high head differentials across Levee
30. When the plan for the development of Area B is in effect, there may be times when the differential of head across the levee will be as much as 10 feet. When this condition occurs, it is estimated that the inflow to the Levee 30 Canal from Conservation Area No. 3 will be about 350 mgd per mile, or 540 cfs per mile.
This estimate was made by computing separately (1) the underflow through the main permeable section at the aquifer and (2) the seepage through the levee fill and the thin layer of permeable
limestone that immediately underlies the levee fill.
When the road construction is completed in the area it would be
desirable to obtain additional data to define more accurately the relation between head difference across the levee and discharge in
the Levee 30 Canal.
The coefficient of transmissibility of the aquifer, the coefficient
of vertical permeability of the confining layers, and the estimated rates of inflow from Conservation Area No. 3, as determined from this study, may be valid only for the north end of Levee 30. It is probable that hydrologic conditions vary along the entire length of Levee 30, and therefore similar studies will be required for the southern reaches in order to' determine total leakage along the
levee system.
REFERENCES
Ferguson, G. E. (see Parker, G. G.)
Love, S. K. (see Parker, G. G.)
Parker, G. G.
1951 Geologic and hydrologic factors in the perennial yield of the
Biscayne aquifer: Am. Water Works Assoc. Jour., v. 43, p. 817834.




24 FLORIDA GEOLOGICAL SURVEY
1955 (and Ferguson, G. E., Love, S. K., and others) Water resources
of southeastern Florida, with special reference to the geology and ground water of the Miami area: U. S. Ge6l. Survey WaterSupply Paper 1255, 965 p.
Schroeder, M. C.
1958 (and others) Biscayne aquifer of Dade and Broward counties,
Florida: Florida Geol. Survey Rept. Inv. 17, 56 p.
Sta lman, R. W.
1956 Preliminary findings on ground-water conditions relative to Area
B flood-control plans, Miami, Florida: U. S. Geol. Survey OpenFile Rept., Tallahassee, Florida, 42 p.
U.S. Army Corps of Engineers
1952 Test levee investigations: Partial Definite Project Report, Central
and Southern Florida Project, pt. 1, supp. 5, mimeograph
Rept., March 28.
1953 Agricultural and conservation areas, design memorandum, permeability investigations by well-pumping tests: Partial Definite Project Report, Central and Southern Florida Project, pt. 1,
supp. 7, Mimeograph Rept., February 16.
1954 Design memorandum, Hydrology and hydraulic design canals in
Greater Miami area (C-2 through C-9) (revised); Partial Definite Project Report, Central and Southern Florida Project, pt. 5, supp.
12, mimeograph Rept., March 23.
Wenzel, L. K.
1942 Methods for determining permeability of water-bearing materials,
with special reference to discharging-well methods, with a section on direct laboratory methods and bibliography on permeability and laminar flow, by V. C. Fishel: U. S. Geol. Survey WaterSupply Paper 887, 192 p.




Full Text

PAGE 1

STATE OF FLORIDA STATE BOARD OF CONSERVATION FLORIDA GEOLOGICAL SURVEY Robert O. Vernon, Director REPORT OF INVESTIGATIONS NO. 24 PART I HYDROLOGIC CONDITIONS IN THE VICINITY OF LEVEE 30, NORTHERN DADE COUNTY, FLORIDA By Howard Klein and C. B. Sherwood United States Geological Survey Prepared by the UNITED STATES GEOLOGICAL SURVEY in cooperation with the CENTRAL AND SOUTHERN FLORIDA FLOOD CONTROL DISTRICT TALLAHASSEE, FLORIDA 1961 /

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FLORIDA STATE BOARD Zte OF CONSERVATION FARRIS BRYANT Governor TOM ADAMS RICHARD ERVIN Secretary of State Attorney General J. EDWIN LARSON RAY E. GREEN Treasurer Comptroller THOMAS D. BAILEY DOYLE CONNER Superintendent Public Instruction Commissioner of Agriculture ii

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LETTER OF TRANSMITTAL §Tiorika geoloqical Survej Zallakassee June 1, 1961 Honorable Farris Bryant, Chairman Florida State Board of Conservation Tallahassee, Florida Dear Governor Bryant: The Florida Geological Survey is publishing as Report of Investigations No. 24, Part I, a report on the hydrologic conditions in the vicinity of Levee 30, northern Dade County, which was prepared by Howard Klein and C. B. Sherwood of the U. S. Geological Survey. This report was prepared in cooperation with the Central and Southern Florida Flood Control District, and this department is publishing the report in its regular series of water resources papers. The formations that underlie Levee 30 are a part of the very permeable sediments that underlie the southern tip of Florida. The opportunity to make this study has provided important data relative to the transmissibility of the sediments and will assist in design of control structures and in-the development of the water resources of southern Florida. Respectfully yours, Robert O. Vernon, Director iii

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Completed manuscript received February 27, 1961 Published by the Florida Geological Survey E. O. Painter Printing Company DeLand, Florida iv

PAGE 5

CONTENTS Abstract ___ ;1 Introduction -------__ 1 General statement and purpose -___ ____1 Previous investigations ___ 3 Acknowledgments ___-.______ 3 Description of area ___----..--...----_.--____.--_.--________-...____-. 4 Geology ......---------....... ------. ---------_._ -----------_________ 5 Drainage features __ -------7 Hydrology ---------____ 9 Water levels and movement ------__________ 9 Relation between ponded water and ground water 12 Underflow along Levee 30 _-___16 Conclusions c_______ 22 References -_-__ ________ __23 ILLUSTRATIONS Figure Page 1 Map of northern Dade County showing the area of investigation __ 2 2 Map of area of investigation showing the location of the test area and the location of selected observation stations _--_-___ 4 3 Cross section A-A' showing details of the near-surface geology near the north end of Levee 30 __ -5 4 Map of test area showing locations of observation stations and test sites----------~-----_ ---6 5 Contour map of the area investigated showing the altitude and configuration of the water level on January 21, 1960 8 6 Hydrographs of groups of observation stations for 1959 and the early part of 1960 ____ ___---11 7 Hydrograph of station G72 for the period 1940-59 and the annual rainfall at the Miami Airport ----12 8 Profile showing the relation between the ponded water and the piezometric surface at site A-A', January 21 and February 8, 1960 13 9 Profile showing the relation between the ponded water and the piezometric surface at site B-B', January 21 and February 8, 1960 14 10 Profile along site C-C' showing lines of equal potential, April 19, 1960 !--_5-------------_ 15 11 Graph showing the relation between the head difference across Levee 30 and the head difference between the pool and the piezometric surface at the toe of the levee -21 *V .^ ,*

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HYDROLOGIC CONDITIONS IN THE VICINITY OF LEVEE 30, NORTHERN DADE COUNTY, FLORIDA By Howard Klein and C. B. Sherwood ABSTRACT Thin layers of dense limestone of low permeability that occur near the top of the Biscayne aquifer in the vicinity of the north end of Levee 30 in Dade County, Florida are of hydrologic importance because they retard the downward infiltration of ponded water in Conservation Area No. 3. This retarding effect frequently results in high head differentials across the levee. Tests made in a small area adjacent to Levee 30 indicate that the coefficient of transmissibility of the aquifer is 3,600,000 gpd (gallons per day) per foot, and the coefficient of vertical permeability of the dense limestones is 13 gpd per square foot. If ground-water flow beneath the levee is laminar, the total inflow to the Levee 30 Canal from Conservation Area No. 3 will be about 350 mgd (million gallons per day), or 540 cfs (cubic feet per second), per mile length of levee when the head difference across the levee is 10 feet. INTRODUCTION GENERAL STATEMENT AND PURPOSE One of the major responsibilities of the Central and Southern Florida Flood Control District is to minimize flood damage in urban and agricultural areas west of the coastal ridge in southeastern Florida. A second function is to protect areas of potential urban development. A large area of anticipated growth in Dade County (shown as Area B in fig. 1). is west of Miami and extends about 10 miles eastward from Levees 30 and 31. The initial project of the Central and Southern Florida Flood Control District was the construction of an east-coast protectivelevee system west of the Atlantic Coastal Ridge, extending from Lake Okeechobee southward into Dade County. Levees 33, 30, and 31 form the southern terminus of this levee system and are shown in figure 1. Its primary purpose was to alleviate flooding in urban and agricultural land, along and adjacent to the ridge, by retarding the overland eastward flow of floodwaters from the Everglades. When the flood-control system is completed, part of these excess floodwaters will be impounded in conservation areas west of the 1

PAGE 8

2 FLORIDA GEOLOGICAL SURVEY HOLLYWOOD TEST AREA BROWA /RD 'C 'JTY CREEK 7 )6^ < '.' / / T ^ / V ,' / ;' //' I; \g^ I ^ / ;,/AREA B/J AREA A S/ :/I / /11' CANAL AND CONTROL SCALE IN MILES V0 1 2 3 4 5 6 Figure 1. Map of northern Dade County showing the area of investigation. levee. Regulated releases of water will be conveyed by canals from conservation areas to coastal areas to replenish ground-water reservoirs during periods of drought. This report is one of a series prepared in cooperation with the Central and Southern Florida Flood Control District. The general purposes of these investigations are (1) to define the hydrology of certain areas within the Flood Control District, (2) to determine the effectiveness of existing flood-control and water-control measures, and (3) to furnish hydrologic data that will be used in the design and operation of proposed and existing structures and works.

PAGE 9

REPORT OF INVESTIGATIONS No. 24 3 The purpose of this investigation is to define the hydrologic characteristics of the water-bearing materials in the vicinity of Levee 30 in northern Dade County, in order to determine the feasibility of controlling water levels in Area B for maximum flood protection. Included is an analysis of the relation between the impounded water west of Levee 30 and the ground water in the area. From this relationship estimates of ground-water underflow along Levee 30 can be computed under existing conditions and under anticipated water-level conditions. Midway in the data-gathering stage of the investigation, major road construction altered the canal system in the immediate area and caused changes in water levels and discharge of canals. This resulted in curtailing of the field work; therefore the results of this investigation should be considered preliminary. The work was done under the general supervision of P. E. LaMoreaux, chief, Ground Water Branch, Washington, D. C., and under the immediate supervision of M. I. Rorabaugh, district engineer, Tallahassee, Florida. PREVIOUS INVESTIGATIONS A comprehensive report by Parker and others (1955) presented fairly complete information on the geology and hydrology of southeastern Florida, and Parker (1951) gave estimates of the availability and adequacy of the ground-water supplies of the Biscayne aquifer which underlies southeastern Florida. Schroeder and others (1958) summarized additional data on the Biscayne aquifer collected since 1950. Stallman (1956) made theoretical computations on the effect of drainage in the area west of Miami and gave estimates of the amount of seepage that might occur beneath Levee 30 under certain assumed conditions. A mimeographed report by the U. S. Army Corps of Engineers (1953) described the results of permeability tests along different levees within the Flood Control District. ACKNOWLEDGMENTS The writers are indebted to personnel of the Surface Water Branch, U.S. Geological Survey, Miami, Florida, for making discharge measurements in the Levee 30 Canal and furnishing waterlevel information along the Miami Canal. Gratitude is expressed also to the Public Works Department of metropolitan Dade County for the record of water-level stages for several observation stations in the area. The office of the Central and Southern Florida Flood

PAGE 10

4 FLORIDA GEOLOGICAL SURVEY Control District furnished complete information on the location, the construction details, and the layout of the Corps of Engineers test sites near Levee 30. The writers benefited from technical discussions with F. A. Kohout of the Miami office, and H. H. Cooper, Jr, and N. D. Hoy of the Tallahassee office, U. S. Geological Survey. DESCRIPTION OF AREA The area described in this report comprises 60 square miles chiefly in northern Dade County, Florida (fig. 1). Figure 2, which is a large-scale map of the report area, delineates the test site within the area, locates certain water-level observation stations, and shows the drainage features. The western part of the area is traversed by Levees 30 and 33. These levees separate Conservation Area No. 3, which normally contains ponded water, from Area B which is swampy during much of the year. The altitude of the land surface is about 5 feet above msl (mean sea level). z_ V X T1AT ION ZANAL AND CONTROL 2 A9TO -E-CROING GAGE AN NUMBER S 'SERVAION, T9 GTIN A 11 4 -i i M 3i Figure 2. Map of area of investigation showing the location of the test area and the location of selected observation stations. \ 3 4 4974 G973 3-E R40E Figure 2. Map of area of investigation showing the location of the test area and the location of selected observation stations.

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REPORT OF INVESTIGATIONS NO. 24 5 GEOLOGY The area of investigation is underlain to a depth of 55 feet by the Biscayne aquifer, a body of highly permeable limestone. The Biscayne aquifer is underlain by relatively impermeable silt, marl, and fine sand which retard downward seepage from the aquifer or upward seepage from deeper materials. The cross section in figure 3 gives details of the near-surface geology near the north end of Levee 30 in Dade County, as determined from shallow test holes drilled at site A-A' (fig. 4). The area is blanketed by 3 to 5 feet of muck and marl that is underlain by a layer of solution-riddled Miami oolite, a part of the Biscayne aquifer, 1 to 2 feet thick. Figure 3 shows two thin layers of very hard, dense limestone at depths ranging from 0.5 foot above msl to 3.0 feet below msl. In contrast to the high permeability of the underlying limestones, these thin layers appear to be relatively impermeable; and the vertical flow of water through them is many times less than the horizontal flow of water through the deeper, more permeable rocks. By effectively retarding the downward infiltration of water, the thin layers act as a confining A DISTANCE IN FEET A 0. 20o T)00 0 00 200 300 Z ESLEVEEV -EXPLANATION ----------I-O I PERMEABLE LIMESTONE ME NE.ARDMARL AND MUK TO 50 FEET BELOW M SL LOW PERMEABILITY LOW PERMEABILITY LIMESTONE.SOFT; FILLLOW HIGH PERMEABILITY PERMEABILITY Figure 3. Cross section A-A' showing details of the near-surface geology near the north end of Levee 30.

PAGE 12

6 FLORIDA GEOLOGICAL SURVEY 10 |" 1< 0 h3 SPIN-RD COUNTY --------W1 SDCANAL AND CONTROL A M2 Q RECORDING GAGE 30W G-G' LINE OF PROFILE <-Q2 STREAM-GAGING STATION SCALE IN FEET 0 2500 5000 Figure 4. Map of test area showing locations of observation stations and test sites. OW V iG LIN ;F ^] O3i

PAGE 13

REPORT OF INVESTIGATIONS NO. 24 7 unit that separates the ponded water in Conservation Area No. 3 from the water contained in the permeable limestone. Geologic information from test wells and shallow borings, and reported information obtained in connection with canal excavations, indicate that the hard layers of dense limestone occur throughout most of Area B and in southern Dade County, and that they occur at about the same altitude. Each of the wells (prefixed by letter G) shown in figure 2 penetrated the impermeable layers approximately at sea level. Similar layers were noted in wells near the southern terminus of Levee 31 (fig. 1), and in wells south of the Tamiami Canal and west of Levee 31. It is reasonable to assume that the relatively impermeable zones underlie much of Conservation Area No. 3 and that their confining characteristics are widespread. In places, the dense limestones probably contain openings through which rainfall can infiltrate rapidly; however, the overall continuity and the blanketing effect of these layers in general tend to retard infiltration. In the Miami area to the east, the Biscayne aquifer thickens and contains much sand. The thin, dense limestones either thin and disappear or they occur deeper in the aquifer near the coast. DRAINAGE FEATURES During the past 10 years the improved canal system that provides gravity drainage to Biscayne Bay, as shown in figure 1, has effectively reduced flooding in Area A, the urbanized part of eastern Dade County. The system, as designed, can remove large quantities of excess runoff during rainy seasons and can lower ground-water levels in order to furnish storage in the aquifer to accommodate anticipated heavy recharge by rainfall. The controlled discharge of the canals has furnished good flood protection in Area A and at the same time has maintained adequate water levels in most coastal areas to retard the inland movement of salt water. Area A must be at least partially drained before any depletion in storage can be effected in Area B; consequently, Area B normally remains inundated or swampy during long periods. Also, the eastward seepage beneath Levee 30 tends to maintain high water levels in the western part of Area B. Area B is drained chiefly by the Miami and Tamiami canals and to a lesser extent by the Snake Creek and Snapper Creek canals. Their capacities are not adequate to drain Area B by gravity during the rainy seasons. Figure 2 shows the drainage features of the report area and indicates the normal directions of flow in the major canals. The

PAGE 14

8 FLORIDA GEOLOGICAL SURVEY discharge of the Miami Canal is regulated by a control located at 36th Street, Miami, 6 miles inland from Biscayne Bay (fig. 1). The control normally is opened a few weeks before the rainy season and remains open throughout the rainy season to facilitate the discharge of excess water. During open periods the effect of tides extends upstream to a point beyond the Pennsuco Canal (fig. 2). After the rainy season the control is closed in order to conserve water for heavy municipal and irrigation use during the following dry months and to maintain high water levels along the coast as a protective measure against salt-water encroachment. The main tributaries of the Miami Canal in northern Dade County are the Levee 30 and 33 canals, the Pennsuco Canal, and the Russian Colony Canal. Flow in some canals is controlled by use of earth dams or manually operated sluice gates as located in figure 2. The Levee 30 Canal is controlled at the Dade-Broward Levee and its flow to the Miami Canal is maintained by seepage to the northeast around the control and by ground-water inflow between the control and the Miami Canal. The control in the Levee 30 Canal usually remains closed. The flow in the reach of the Levee 30 Canal upstream from the control is so small that -X rXL, TiON R 939E R40E -C.1L 1.43 CONTrCL -._ o RDo_.t_ __ OUN .D rlNiCud K C_,L A t le u L REZORDING GAG" E C : .. ^ ^5.32 OBSERVATICN STATION G372 STATnION UMBER 5.7 WTER LEVEL X S4.60 LINE SHOWING ALTITUDE 0 V GF WATER LEVEL.IN FEET GOLDEN GLIDES CI1VL a8OVE MEAN SEA LEVEL -SCAL11 F--T # \ \' S 500co Iiac 0 J SG973 91 o -o4 I39E __ R40E Figure 5. Contour map of the area investigated showing the altitude and configuration of the water level on January 21, 1960.

PAGE 15

REPORT OF INVESTIGATIONS No. 24 9 ordinarily it cannot be measured. Probably there is a very low water divide along the north-south reach of the canal from which there is a slight southward gradient toward the Tamiami Canal and northward gradient toward the Miami Canal. The southward flow in the Levee 33 Canal is controlled at the Miami Canal. Operation of this control depends upon the ability to maintain water stages of 3.0 to 3.5 feet above msl at station M3, in the Miami Canal where it is joined by the Pennsuco Canal. When the stage is below this level, the control is opened and water is released into the Miami Canal to replenish supplies in the downstream reaches. The southern part of the area is drained by the Pennsuco Canal, which extends westward to the Dade-Broward Levee, and by the Russian Colony Canal; however, effective drainage by the Russian Colony Canal extends only about 31/ miles west of its confluence with the Miami Canal. The westward extension of this canal is shallow and unimproved and therefore is effective only during flood periods. Partly effective drainage probably takes place along the shallow diagonal canal north of the Pennsuco Canal. HYDROLOGY WATER LEVELS AND MOVEMENT Widespread fluctuations of water levels in Dade County are due to recharge by rainfall, to discharge into drainage canals and Biscayne Bay, and to evapotranspiration. Water levels in this part of northern Dade County are regulated also by the operation of the control in the Miami Canal at 36th Street, Miami, and by operation of controls in the Levee 30 and Levee 33 canals. Figure 5 is a contour map of water levels in the area on January 21, 1960. The contours are based on water-level measurements obtained from observation points in canals that cut through the dense limestones and from observation wells. Water levels in the area were relatively high at that time and the control at 36th Street was open. The configuration shows that the drainage effect extended along the entire uncontrolled reach of the Miami Canal and its main tributaries and along the short reach of the Levee 30 Canal downstream from the Dade-Broward Levee. The pattern of the contours indicates the effectiveness of drainage by deep canals (Miami, Levee 30, and Pennsuco canals, and the lower reach of the Russian Colony Canal) and the lack of effective drainage by the shallow canals. High heads are maintained above the

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10 FLORIDA GEOLOGICAL SURVEY control in the Levee 33 Canal and the control in the Levee 30 Canal; however, the close spacing of the contours at these controls indicates that there is considerable seepage through the aquifer around the controls. It is important to compare the pattern of the contours east of the Dade-Broward Levee with that adjacent to Levee 30 between the Dade-Broward Levee and the Miami Canal. The distribution of the heads east of the Dade-Broward Levee indicates that the shallow diagonal canal and the Dade-Broward Levee borrow canals do not have an appreciable drainage effect. In contrast, the steep gradient on the northwest side of Levee 30 and the low gradient on the southeast side indicate that the Levee 30 Canal is intercepting nearly all the underflow along Levee 30. High water levels prevailed throughout this part of northern Dade County during 1958-59 and the early part of 1960. On May 8, 1958, the 36th Street control was opened and drainage of the area proceeded until January 5, 1959, when the control was closed. The control again was opened on June 23, 1959, and remained opened throughout the first half of 1960. During the entire period the eastern part of Conservation Area No. 3 was inundated to depths ranging from 1 foot to more than 4 feet. The area between Levee 30 and the Dade-Broward Levee also was flooded during the period, but the depth of the water was less than that in Conservation Area No. 3. Flooding east of the Dade-Broward Levee probably was intermittent and corresponded with periods of heavy rainfall. Figure 6 shows hydrographs of groups of observation stations in the area for 1959 and the early part of 1960. The locations of these stations are shown in figures 2 and 4. The hydrographs show the relation between canal stages and ponded-water stages in the area adjacent to the Levee 30 and 33 canals and the Miami Canal. The hydrographs of stations 30TW and 30TE show the variation in head differential between the pool in Conservation Area No. 3 (30TW) and the stage in the Levee 30 Canal south of the DadeBroward Levee. During dry periods, such as March-May 1959, the head differential across Levee 30 at this point was very small and a temporary reversal of gradient (east to west) occurred at the end of April and in early May. During the dry months, the eastward underflow of water from Conservation Area No. 3 probably was negligible as compared to that during periods of high water stages (July 1959-January 1960). The persistent high head differential represented by the hydrographs of stations 30W and 30E show the effectiveness of the control in the Levee 30 Canal at the Dade-Broward Levee. This

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REPORT OF INVESTIGATIONS NO. 24 11 1959 1"960 S APR. MAY JUNE JULY AUG. SEPT. OCT NOV. DEC. FEB. 102 I b IN l p0 10 020 I02 0 109 0 0 $ 8 I 16 0 020 S33 WPONDE -9 (PONDED II l -prI I 1 __ lo r o-te3e...C. 0 0 w-8---w ..-i i I i '"--^ Lid ,6 ---------J---?oE I i -"-----Figure 6. Hydrographs of groups of observation stations for 19e9 and the S 30 early part of 1960. a(Leveea:30 Caa!)d ptis differentialan4ge from 2.2feet during ja reltivelydry peod to more than45 feet during high water 8 -____I _____ ____ Figure 6. Hydrographs of groups of observation stations for 1959 and the early part of 1960. differential in head suggests continuous leakage by underflow around the control which tends to maintain, in part, the flow in the lower reach of the Levee 30 Canal. An outstanding feature of the hydrographs in figure -6 is the high head differential between stations M9 (ponded) and M8 (Levee 30 Canal); this, differential -ranged from 2.2 feet during a relatively dry period to more, than 4.5 feet during high water

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12 FLORIDA GEOLOGICAL SURVEY stages. Also shown in figure 6 are the heads maintained behind the control in the Levee 33 Canal (station 33) and the control in the Miami Canal at the Dade-Broward Levee (station Mil). A comparison of the hydrographs of stations 30E and M8 shows the low gradient through the downstream reach of the Levee 30 Canal. A continuous record of water-level fluctuations has been obtained from station G72 since 1940. A hydrograph of this station and the annual rainfall at the Miami Airport are shown in figure 7. The highest water level of record at station G72 was 9.4 feet above msl in October 1947, and the lowest of record was 1.1 feet above msl in June 1945. The hydrograph for the long period of record gives a comparison between water levels before the levee system and water-control practices were in effect (before 1952), and water levels after the water-control measures were in operation (195259). It can be seen that water levels during the drought period of 1955-56 did not decline as much as they did during the comparable drought periods of 1944-45 and 1950-52. Also, it is apparent that the unusually heavy rainfall of 1957-59 did not produce water levels as high as those during the wet years 1947-48. These facts demonstrate that the proper placement and operation of the existing controls in canals can decrease flood damage during rainy seasons and can maintain relatively high water levels during droughts. RELATION BETWEEN PONDED WATER AND GROUND WATER Three test sites were established adjacent to the Levee 30 Canal downstream from the Dade-Broward Levee (fig. 4). The purpose 19391940.1941.1942 1943 1944194519461947 1948 1949 1950 1951 1952 1953 1954 1955 1956 1957.1958 I1 z MIAMI AIRPORT 10 G PRIOR TO WATER CONTROL WAT ER CONTROLS G72. IN EFFECT zUS 0 -SEA LEVEL 19391940 941 1421943 194441945 1946 1947 1948 1949 19501951 1952195319541955 19561957 1958 195 Figure 7. Hydrograph of station G72 for the period 1940-59 and the annual rainfall at the Miami Airport.

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REPORT OF INVESTIGATIONS NO. 24 13 of studies at these sites was to determine the relation between the impounded water in Conservation Area No. 3 and ground water in the area. When this relationship is known, the amount of underflow occurring beneath Levee 30 can be calculated for the existing water-level conditions, and estimates of underflow can be made for various assumed water-level conditions. Each of the test sites consists of a line or lines of. test wells perpendicular to Levee 30; these sites are shown in the profile sections in figures 8, 9, and 10. The wells at site A-A' (fig. 8) are the shallowest, but they penetrate the entire thickness of the dense limestones and terminate in the upper section of the highly permeable part of the aquifer. Site B-B' (fig. 9) was drilled by the Corps of Engineers and consists of a line of nine wells extending northwestward from Levee 30 and one well on the berm between Levee 30 and the Levee 30 Canal. These wells range in depth from 17 to 40 feet. The wells at site C-C' (fig. 10) also were drilled by the Corps of Engineers and were used as observation wells during a pumping test to determine the permeability of the aquifer. The site consists of groups of multiple-depth wells extending northwestward into Conservation Area No. 3. Figure 10 shows the layout of the lines SDISTANCE IN FEET A' S 300 200 10000 200 300 a Pon d level J"O2"bl, 960 LEVEE U4 Pi ezomeric urfac .960 LEVEE 230 CANAL I i ,-4 -| r\-------\ -8 Figure 8. Profile showing the relation between the ponded water and the piezometric surface at site A-A', January 21 and February 8, 1960.

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14 FLORIDA GEOLOGICAL SURVEY SDI STANCE IN FEET ;I ;CANAL We ard level, ea1 mt 9 1 at A 1A ad Ja Febre 9 LE E i o td 30 >as 11 Feet B219 IF I I e 27 i t Figure 9 Profile showing the relation between the ponded water and the piezometric surface at site B-B', January 21 and February 8, 1960. of wells with reference to Levee 30 and the Levee 30 Canal and indicates the altitude of the bottom of each well. Water-level measurements were made at A-A' and B-B' on January 21 and February 8, 1960. Figures 8 and 9 show the waterlevel profiles at the two sites on the dates the measurements were made. At site A-A' (fig. 8) the gradient of the piezometric surface on the northwest side of the levee toward the Levee 30 Canal was 1.1 feet in 270 feet, or 0.0041 foot per foot. Within the 270foot distance the head differential between the ponded water and the piezometric surface increased toward the levee and ranged from 3.1 feet at the end well of the profile to 3.6 feet at the levee' The gradient of the piezometric surface along the profile in figure 9 was 3.17 feet in 650 feet, or 0.049 foot per foot. The head differential between the ponded level and the piezometric surface ranged from 1.2 feet at the end well of the profile to 3.5 feet at the levee. The average gradient of the piezometric surface during the 3-week test period was 0.0045 foot per foot toward -the Levee 30 Caial. The aquifer was being replenished by the downward leakage of ponded water, at a rate dependent upon the head differential, and no depletion of aquifer storage was occurring northwest of Levee 30. Water-level measurements made during the drilling at site A-A'

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D I ISTANCE IN FEET +10o 0 .no 14 00 00 1, ? Goo 4Q 2 0 1 PN O6.9 L30 "J I .-PIEZOMETRIG SURFAGCE > "-i R LAND SURFACE.J 0LEVEE J0, L _____ C-A -/ C4NAL -0,0--------0 --s.>> .sas .ss ssa I u.6 .LJ e or S34Si 55l ..34 U 0 6 .3.4 .95 7 ,s 5.? s 5. 1 1,. 74II L0 ko k < o rn -30 1EXPLANATION BOTTOM OF CASED WELL *04. .6-74 5 E6.30 5 58 4 SWTER LEVEL .6 JO. 5 ../ LINE OF EQUAL POTENTIAL 40 __ ._,..... ....._ ... -.._ ... Figure 10. Profile along site C-C' showing lines of equal potential, April 1b, 1960. I enr

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16 FLORIDA GEOLOGICAL SURVEY showed that there was no head difference between the ponded level and the water level of wells bottomed in the Miami oolite. This indicates that the confining characteristics of the marl and muck blanket are of much less significance than those of the dense limestones. No appreciable ponding occurred in the area immediately southeast of the Levee 30 Canal. Figure 8 shows also that the northwestward gradient of the piezometric surface on the southeast side toward the Levee 30 Canal was 0.40 foot in 250 feet, or 0.0016 foot per foot. Therefore, the quantity of inflow from the southeast was equivalent to approximately 40 percent of the inflow occurring from the northwest at the A-A' site during the period January 21February 8, 1960. The profile in figure 8 indicates a slight depletion of ground-water storage immediately southeast of the Levee 30 Canal. It is important to recognize that the contribution of water from the area southeast of the Levee 30 Canal to the canal was diminishing as shown on the contour map (fig. 5) by the decrease in ground-water gradient along the lower reach of the canal. It is estimated that the average gradient of the piezometric surface on the southeast side along the uncontrolled reach of the canal was 0.0010 foot per foot. Therefore, the total inflow to the Levee 30 Canal from the southeast was equivalent to approximately 20 to 25 percent of the total from the northwest. UNDERFLOW ALONG LEVEE 30 During periods when the control in the Levee 30 Canal is closed, discharge along the downstream reach of the Levee 30 Canal represents a composite of the following: (1) leakage by underflow around the control, (2) ground-water inflow from the thick permeable section of the aquifer, and (3) seepage of ponded water through the levee fill and through the thin layer of permeable Miami oolite that occurs between the fill and the dense limestone layers. At high water stages, such as those which prevailed from July through November 1959, the water level of the downstream reach of the canal was above the canal bank and sheet flow occurred toward the Miami Canal. Most of the discharge of the Levee 30 Canal was maintained by ground-water inflow from the northwest. By January 21, 1960, water stages had lowered and discharge measurements were made at points 1 mile apart in the Levee 30 Canal (Q, and Q2 in fig. 4), downstream from the control. Following is a tabulation of the discharge and water-level data obtained during the January 21 test:

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REPORT OF INVESTIGATIONS No. 24 17 A. Discharge measurements in Levee 30 Canal At Q1 __..__ -__...--__ -_____ ---_ 76 cfs (49 mgd) At Q2 -..-----.--------------------------252 cfs (163 mgd) Q2-Q ----, -------------------176 cfs (114 mgd) Estimated seepage (visible) through the levee fill, across the berm to the canal (Qs) -10 cfs (7 mgd) Net pickup by ground-water inflow (Qg) Qg=Q2-Q-Qs -----------------------------166 cfs (107 mgd) B. Gradients (I) of piezometric surface toward Levee 30 Canal (fig. 8, 9). Northwest of canal A-A' site ------------------0.0041 foot per foot B-B' site--------.0049 foot per foot Southeast of canal A-A' site----------.0016 foot per foot Estimated average for area southeast of canal---------.0010 foot per foot By Darcy's law the rate of flow of a fluid through a porous medium is directly proportional to the hydraulic gradient and can be written as follows (Wenzel, 1942, p. 3-7): Q=PIA where Q is the discharge rate, P is the coefficient of permeability of the material being tested, I is the hydraulic gradient, and A is the area of the cross section through which the fluid moves. If it is assumed that the permeable section of the aquifer beneath the dense limestone layers is isotropic and that underflow through this section is laminar, then the quantity of ground water discharging into the Levee 30 Canal is directly proportional to the gradient of the piezometric surface; therefore, about 80 percent of Qg or 86 mgd, represents underflow from the northwest along the 1-mile reach of the canal. (See tabulation above.) In order to make computations that involve the entire thickness of an aquifer as a unit, Darcy's law may be written: Q=TIL in which Q is the quantity of water, in gpd (gallons per day), T is the coefficient of transmissibility, in gallons per day, for each vertical strip of the aquifer 1 foot wide; I is the hydraulic gradient,

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18 FLORIDA GEOLOGICAL SURVEY in feet per foot; and L is the length of section, in feet, through which the quantity (Q) flows. By substituting in the above equation the hydrologic data obtained during the January 21 test, a determination of the coefficient of transmissibility of the aquifer can be made as follows: Q=TIL Q (gpd) T (gpd per foot)= (g I (foot per foot) x L (feet) T -86,000,000 0.0045 x 5,280 T = 3,600,000 gpd per foot, or 5.6 square feet per second This computed coefficient of transmissibility compares very closely with the value of 5.76 square feet per second determined by the Corps of Engineers for the highly permeable part of the aquifer adjacent to Levee 30 (U.S. Army Corps of Engineers, 1953, p. D-6). Dry weather prevailed during the spring of 1960, and by the middle of April the water stage in Conservation Area No. 3 had declined so that the multiple-depth wells along site C-C' were accessible. On April 19, 1960, water-level measurements were made in all wells in this test site. The profile in figure 10 shows the relation between the pool in Conservation Area No. 3 and the piezometric surface on that day and shows also, by equipotential lines, the approximate head distribution in the aquifer along the profile. The gradient of the piezometric surface within 1,000 feet of the Levee 30 Canal was 0.0017 foot per foot, but for the remaining 800 feet of the section the gradient decreased to 0.0011 foot per foot. The head differential between the ponded water and the piezometric surface ranged from 0.32 foot at the northwestern end of the profile to 1.57 feet near the toe of the levee. The equipotential lines, shown in figure 10, indicate that flow through the highly permeable part of the aquifer (depths more than 5.0 feet below msl) toward the Levee 30 Canal is virtually horizontal, except for the section adjacent to and beneath the canal where the flow direction has an upward component. The distribution and pattern of the lines suggest that about 75 percent of the loss in head occurs within 1,000 feet of the levee. The horizontality and the close spacing of the lines at depths between 0.5 foot above and 3.0 feet below msl indicate a large vertical head loss caused by

PAGE 25

REPORT OF INVESTIGATIONS No. 24 19 vertical flow through the dense limestone of low permeability at that interval (fig. 3). The flow through the shallow materials immediately beneath the levee is virtually horizontal and probably occurs chiefly through a thin layer of the permeable Miami oolite beneath the fill. Detailed information on head distribution through a part of the aquifer, as shown in figure 10, makes it possible to estimate the amount of surface water that was seeping downward through the confining layers to the thick permeable part of the aquifer. The amount of ground water moving toward the canal in 1 day, across a section of the aquifer 1 mile long at a distance of 800 feet from the edge of the canal, may be computed as follows: Q=-TIL 0.4 foot x 5,280 feet Q=3,600,000 x40 400 feet Q=19 mgd per mile, or 29 cfs per mile A similar computation for a distance 400 feet from the canal is as follows: 0.59 foot x 5,280 feet Q=3,600,000 x 400 feet Q=28 mgd per mile, or 43 cfs per mile. The 9-mgd difference in flow represents approximately the amount of surface water picked up by leakage through the confining beds to the permeable flow section within the rectangular area 1 mile long between 400 and 800 feet from the levee. Inasmuch as the approximate amount of downward infiltration in a given area has been determined, a computation of the coefficient of vertical permeability of the confining layers can be made. The coefficient of permeability is defined as the rate, of flow through a cross section of 1 square foot, under a gradient of 1 foot per foot. The computation of the coefficient of vertical permeability of the dense limestone is as follows: Rectangular area used in computation __-5,280 feet x 400 feet, or 2.1 million square feet Downward leakage .__ ----9 nigd, or 4.3 gpd per square foot

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20 FLORIDA GEOLOGICAL SURVEY Altitude of piezometric surface 600 feet from levee 5.93 feet above msl Altitude of ponded level __6.91 feet above msl Head differential 600 feet from levee (assumed average for area 400 to 800 feet from levee) ___ 0.98 foot Thickness of confining layers _3.0 feet Gradient across confining layers ..-----. 0.33 foot per foot Q P= IA 4.3 gpd 0.33 foot per foot x 1 square foot P= 13 gpd square foot, or 2.0 x 10-5 foot per second A proposed method of flood control in Area B is to reduce ground-water storage by means of a network of canals and a series of large pumping stations. The pumps would be placed at selected locations along Levees 30 and 31 and would pump water from the interconnected canal system of Area B westward into Conservation Area No. 3. Initially, it was proposed that the water stage in Area B be maintained at mean sea level in order to give maximum protection during all major storms. It is probable that water levels along the levee side of Area B will be lowered temporarily below mean sea level in order to provide adequate gradients toward the pumping stations. Reducing the water stage in Area B would result in gradients across Levee 30 that would greatly exceed those shown in the profiles of figure 9. There might be times when the head differential between the pool in Conservation Area No. 3 and the stage in the Levee 30 Canal would be as much as 10 feet. It is extremely important, therefore, to determine the amount of water that would move from Conservation Area No. 3 to the adjacent canals in order that adequate pumping stations be provided. To make a determination of the anticipated underseepage it is necessary to determine the relation between the head across the levee and the head differential at the toe of the levee at different water stages. Figure 11 is a graph showing this relationship; and the plotted points are based on the water-level profiles of figures

PAGE 27

REPORT OF INVESTIGATIONS NO. 24 21 HEAD DIFFERENCE,IN FEET, BETWEEN POOL AND LEVEE 30 CANAL 2 3 4 5 6 7 8 10 6w -IO 0> N / W / S6-JAN.21,1960 EC. 171959 oUEJ /1960 U U) / Z 2X w ~ "-APRIL 19,1960 LL 0 0 Figure 11. Graph showing the relation between the head difference across Levee 30 and the head difference between the pool and the piezometric surface at the toe of the levee. 9 and 10 and on a series of measurements made on December 17, 1959. The projection of the graph indicates that, if a 10-foot head were held across the levee, the head difference between the pool and the piezometric surface at the toe of the levee would be 7.8 feet; thus the gradient of the piezometric surface across the 150-foot width of the levee would be 2.2 feet. Following is a computation of the amount of underflow that would be intercepted along a 1-mile reach of the canal (Q1 to Q2 in fig. 4) when the head differential across the levee was 10 feet: Q=TIL Q=3,600,000 gpd per foot x 2.2 feet x 5,280 feet 150 feet Q=279 mgd per mile, or 432 cfs per mile In order to determine the total quantity of water that would be intercepted :by the Levee 30 :Canal along the 1-mile reach,

PAGE 28

22 FLORIDA GEOLOGICAL SURVEY consideration must be given to the seepage that would occur through the levee materials and through the thin permeable layer of Miami oolite that underlies the levee fill. This approximate determination is shown by the following tabulation: Composite estimate of coefficient of permeability of levee fill and Miami oolite _20,000 gpd per square foot Length of flow section 5,280 feet Thickness of flow section (10-foot head differential) _. 10 feet Q=PIA 10 feet Q=20,000 gpd per square foot x -150 x 5,280 feet x 10 feet 150 feet Q=70 mgd per mile, or 108 cfs per mile The estimated coefficient of permeability used in the above computation probably is high and compares with a well sorted gravel that contains only small quantities of fine material (Wenzel, 1942, p. 13). However, the estimate was made in consideration of the probable high permeability of the layer of Miami oolite through which much of the direct seepage may occur. The total quantity of water that would be intercepted along the 1-mile reach of Levee 30 Canal when the head difference across the levee was 10 feet is computed to be 349 mgd, or 540 cfs. These results were obtained by assuming that water movement beneath Levee 30 occurs by laminar flow. If there is turbulence through the large openings in the aquifer beneath the levee, the underflow would be less. For laminar flow the underflow to the canal would be directly proportional to the head difference across the levee, and for turbulent flow the underflow would be directly proportional to the square root of the head difference; in the transitional zone underflow would vary exponentially between the first and one-half powers of the head difference. CONCLUSIONS Water-level measurements and geologic data obtained from test wells indicate that the upper part of the Biscayne aquifer in the vicinity of Levee 30 in northern Dade County contains dense layers of limestone of relatively low permeability that retard downward

PAGE 29

REPORT OF INVESTIGATIONS No. 24 23 infiltration to the thick permeable parts of the aquifer. The coefficient of transmissibility of 3,600,000 gpd per foot, or 5.6 square feet per second, as determined from water-level profiles taken Snormal to Levee 30 and from discharge measurements made in the Levee 30 Canal, compares closely with the coefficient determined by the Corps of Engineers by pumping-test methods. The computed coefficient of permeability of 13 gpd per square foot, or 2.0 x 10-5 foot per second, for the thin dense layers indicates that these layers form a fairly effective confining unit which separates the ponded water in Conservation Area No. 3 from the ground water. Geologic information obtained from the surrounding areas suggests that the thin, dense limestones probably are widespread, and therefore that the blanketing effect occurs throughout a large area. Conservation Area No. 3 generally is flooded for several months -'of each year, the result being high head differentials across Levee 30. When the plan for the development of Area B is in effect, there may be times when the differential of head across the levee will be as much as 10 feet. When this condition occurs, it is estimated that the inflow to the Levee 30 Canal from Conservation Area No. 3 will be about 350 mgd per mile, or 540 cfs per mile. This estimate was made by computing separately (1) the underflow through the main permeable section at the aquifer and (2) the seepage through the levee fill and the thin layer of permeable limestone that immediately underlies the levee fill. When the road construction is completed in the area it would be desirable to obtain additional data to define more accurately the relation between head difference across the levee and discharge in the Levee 30 Canal. The coefficient of transmissibility of the aquifer, the coefficient of vertical permeability of the confining layers, and the estimated rates of inflow from Conservation Area No. 3, as determined from this study, may be valid only for the northend of Levee 30. It is probable that hydrologic conditions vary along the entire length of Levee 30, and therefore similar studies will be required for the southern reaches in order to' determine total leakage along the levee system. REFERENCES Ferguson, G. E. (see Parker, G. G.) Love, S. K. (see Parker, G. G.) Parker, G. G. 1951 Geologic and hydrologic factors in the perennial yield of the Biscayne aquifer: Am. Water Works Assoc. Jour., v. 43, p. 817834.

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24 FLORIDA GEOLOGICAL SURVEY : 1955 (and Ferguson, G. E., Love, S. K., and others) Water resources of southeastern Florida, with special reference to the geology and ground water of the Miami area: U. S. Geol. Survey WaterSupply Paper 1255, 965 p. Schroeder, M. C. 1958 (and others) Biscayne aquifer of Dade and Broward counties, Florida: Florida Geol. Survey Rept. Inv. 17, 56 p. Stallman, R. W. 1956 Preliminary findings on ground-water conditions relative to Area B flood-control plans, Miami, Florida: U. S. Geol. Survey OpenFile Rept., Tallahassee, Florida, 42 p. U.S. Army Corps of Engineers 1952 Test levee investigations: Partial Definite Project Report, Central and Southern Florida Project, pt. 1, supp. 5, mimeograph Rept., March 28. 1953 Agricultural and conservation areas, design memorandum, permeability investigations by well-pumping tests: Partial Definite Project Report, Central and Southern Florida Project, pt. 1, supp. 7, Mimeograph Rept., February 16. 1954 Design memorandum, Hydrology and hydraulic design canals in Greater Miami area (C-2 through C-9) (revised) ; Partial Definite Project Report, Central and Southern Florida Project, pt. 5, supp. 12, mimeograph Rept., March 23. Wenzel, L. K. 1942 Methods for determining permeability of water-bearing materials, with special reference to discharging-well methods, with a section on direct laboratory methods and bibliography on permeability and laminar flow, by V. C. Fishel: U. S. Geol. Survey WaterSupply Paper 887, 192 p.

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-FLORIDA-GEOLOGICAL-SURVEY COPYRIGHT NOTICE [year of publication as printed] Florida Geological Survey [source text] The Florida Geological Survey holds all rights to the source text of this electronic resource on behalf of the State of Florida. The Florida Geological Survey shall be considered the copyright holder for the text of this publication. Under the Statutes of the State of Florida (FS 257.05; 257.105, and 377.075), the Florida Geologic Survey (Tallahassee, FL), publisher of the Florida Geologic Survey, as a division of state government, makes its documents public (i.e., published) and extends to the state's official agencies and libraries, including the University of Florida's Smathers Libraries, rights of reproduction. The Florida Geological Survey has made its publications available to the University of Florida, on behalf of the State University System of Florida, for the purpose of digitization and Internet distribution. The Florida Geological Survey reserves all rights to its publications. All uses, excluding those made under "fair use" provisions of U.S. copyright legislation (U.S. Code, Title 17, Section 107), are restricted. Contact the Florida Geological Survey for additional information and permissions.


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