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Salt-water study of the Miami River and its tributaries, Dade County, Florida ( FGS: Report of investigations 45 )

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Title:
Salt-water study of the Miami River and its tributaries, Dade County, Florida ( FGS: Report of investigations 45 )
Series Title:
( FGS: Report of investigations 45 )
Creator:
Leach, Stanley D
Grantham, Rodney G
Geological Survey (U. S.)
Geological Survey (U. S.) -- Water Resources Division
Place of Publication:
[Tallahassee]
Publisher:
Florida Geological Survey
Publication Date:
Language:
English
Physical Description:
36 p. : illus. ;

Subjects

Subjects / Keywords:
Saline waters -- Florida -- Miami River ( lcsh )
Geology -- Florida -- Miami-Dade County ( lcsh )
Water-supply -- Florida -- Miami-Dade County ( lcsh )
City of Miami ( local )
Miami River ( local )
Biscayne Bay ( local )
City of Hialeah ( local )
City of Coral Gables ( local )
Canals ( jstor )
Dams ( jstor )
Chlorides ( jstor )
Saltwater ( jstor )
Aquifers ( jstor )
Genre:
bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Bibliography:
Bibliography.
Statement of Responsibility:
by S. D. Leach and R. G. Grantham. Prepared by the United States Geological Survey in cooperation with Dade County and the Florida Geological Survey.

Record Information

Source Institution:
University of Florida
Rights Management:
The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.
Resource Identifier:
000957327 ( aleph )
01722582 ( oclc )
AES0063 ( notis )

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Full Text
STATE OF FLORIDA
STATE BOARD OF CONSERVATION
DIVISION OF GEOLOGY
FLORIDA GEOLOGICAL SURVEY
Robert O. Vernon, Director
REPORT OF INVESTIGATIONS NO. .15
SALT-WATER STUDY OF THE MIAMI RIVER
AND ITS TRIBUTARIES, DADE COUNTY, FLORIDA
By
S. D. Leach and R. G. Grantham
U. S. Geological Survey
Prepared by the UNITED STATES GEOLOGICAL SURVEY
Sin cooperation with DADE COUNTY
and
THE FLORIDA GEOLOGICAL SURVEY 1966




FLORIDA STATE BOARD OF,
CONSERVATION
HAYDON BURNS
Governor
TOM ADAMS EARL FAIRCLOTH
Secretary of State Attorney General
f
BROWARD WILLIAMS FRED O. DICKINSON, Jr.
Treasurer Comptroller
FLOYD T. CHRISTIAN DOYLE CONNER
Superintendent of Public Instruction Commissioner of Agriculture
ii1




LETTER OF TRANSMITTAL
Jorida j7e oloyi caI Suveyj
at'aass~ee
August 16, 1966
Governor Haydon Burns, Chairman State Board of Conservation Tallahassee, Florida
Dear Governor Burns:
Messrs. S. D. Leach and R. G. Grantham, of the Water Resources Division of the U. S. Geological Survey, have completed a study of the Miami River and its tributaries in Dade County, and the relationships of these tributaries to salt-water intrusion in the area. The report will be published as Report of- Investigations No. 45. The study was done in cooperation with the Division of Geology, of the State Board of Conservation, and Dade County, and outlines the main trend of the water resources of the Miami area.
The Biscayne aquifer, which is composed of highly permeable limestone, is being intruded upon by salt water along any canal or stream that connects the aquifer to salt water. It has been found that this intrusion could be prevented and reversed by careful management of the water resources of the area by the construction of salinity control dams near the coast, and through the judicious development of water.
Respectfully yours,
Robert O. Vernon
Director and State Geologist
ooo1i




Completed manuscript received
August 16, 1966
Published for the Florida Geological Survey
By Rose Printing Company
Tallahassee
1966




CONTENTS
Page
Abstract ...........-------- ..-----.-----------------------................... 1
Introduction ........----------.......... ................. ------------------------------------------2
Area of investigations .........---------.............--.............--------------------------- ................--.................. 4
History of salinity-control dam operation in the Miami Canal ...........--------- 6
Rainfall in the Miami River drainage basin ....--...-------..............--------------.... 8
Long-term hydrology ................... ........... ...........---------------------------------------- 9
Discharge in the Miami Canal ........................ ......................---------------------------------- 9
Water levels in the area of investigation .................................................. -------------------------10
Water-level comparison between Miami River and Biscayne Bay .........------ 11
Salt-water movement in the Miami River -------------------------------- 14
Short-term comparison of chloride with water levels and discharge ------- 19 High and low tide salt-water movement ................................ ------------------- 23
Chloride concentration extremes ...............................----------------------------------- 23
The 1945 drought ... ............. ...------------------------------------------. .. ....... 25
Chloride concentration in the aquifer .......... ..-------------------------. .._ 25
Discharge at selected locations ...............-----------------------------------.. 28
The effects of wind on water movement ................ ................---------------------------- 31
Summary ..........................................----------------------------------------------------- 33
References ....................--------------------------------------------------------... 35
ILLUSTRATIONS
Figure Page
1 Map of the Greater Miami area showing the major canals and the
area investigated ..............................................................................------------------------------------------ 4
2 Map of the Miami River and its tributaries showing data-collection
sites in the area investigated ...........................................................----------------------- 5
3 Photographs of successive salinity-control dams in the Miami Canal
at N.W 36th Street ................................................ -------------------------- - 7
4 Graph of monthly mean rainfall, monthly extremes, and the year
the extremes occurred based on the averages of Hialeah, Pennsuco, and Pennsuco 5 N.W. (Broken Dam) rain gages for the period
1944 through 1963 ............ ............... ....................------------------------------....-- ----- 8
5 Graphs showing monthly and annual mean discharge in the Miami
Canal above N.W. 36th Street control dam and the total annual and monthly rainfall for the three rain gages in the Miami
Canal drainage basin .............................................................------------------------- ----- ..... 9
6 Graphs of water levels at three selected Miami Canal stations and
one Biscayne Bay Station, from 1944 to 1963 -- --------------------- 11
7 Hydrographs of monthly high, low, and average water elevations in
the Miami Canal at N.W. 27th Avenue and at Biscayne Bay, based
on 18 years of record '1946 to 1963 ...............-------------............................--- 12
8 Graphs showing a mean water-level elevation, mean high and low
water from the N.W. 36th Street control dam to the mouth at Biscayne Bay, based on 18 years of record 1946 to 1963 ................... -------------13
9 Graph showing percentage of time water containing 1,000 ppm
chloride was at or above various locations in the Miami Canal for
the period May 1945 to March 1958 .......... .........................- ---------. 15
V




ILLUSTRATIONS
Figure Page 10 Graphs showing position of the 1,000 ppm chloride content in the Miami Canal for the period January 1940 to March 1958 ................ 16
11 Graph showing relation between monthly mean discharge in cfs and the location of water containing 1,000 ppm chloride in the Miami
Canal .......................................................................................................---------------------------------------------------.. 17
12 Graphs showing chloride concentration in the Miami Canal during a typical wet year (1948) and a typical dry year (1956) .............. 18
13 Graphs showing the effect of changes of the N.W. 36th Street control dam on discharge,water levels, and chloride content at selected
locations in the Miami Canal from July 12 to 19, 1964 .................... 20
14 Graphs showing the effect of changes of the N.W. 36th Street control dam on discharge, water levels, and chloride content at selected locations in the Miami Canal during the period August 14 to 19,
1964 .....................................................................................................----------------------------------------------------. 21
15 Profile of chloride content in the Miami Canal on July 16, 1964 at
low and high tide when the N.W. 36th Street control dam was partially open ..................................... .........----------------------------------------------................... 22
16 Graphs showing chloride extremes at high tide in the Miami River and the Miami Canal at various sampling locations ...............---------....... 24
17 Graphs showing an extreme chloride concentration in the Miami
Canal above the N.W. 36th Street control dam on May 31, 1945 .... 26
18 Map showing salt-water encroachment at the base of the Biscayne
aquifer 1904-62 (Parker and others, 1955, p. 589), (Kohout, 1961)
updated ...--.......................................................................................-----------------------------------------------. 27
19 Graphs showing monthly mean discharge at selected locations in
the Miami and Tamiami Canals, October 1960 through September
1963 .........................................................................--------------------------------------.................................... 29
20 Graph showing monthly mean discharge from or into the aquifer
below the control dams in the Miami River and its tributaries,
April 1961 through September 1963 -----------------..............................--------..................... 30
21 Graphs showing the effects of Hurricane Cleo's winds at selected
discharge and water-level stations in the Miami Canal and Biscayne Bay, August 26-27, 1964 ........................................------------------------------ 32
vi




SALT-WATER STUDY OF THE MIAMI RIVER AND ITS TRIBUTARIES,
DADE COUNTY, FLORIDA
By
S. D. Leach and R. G. Grantham
ABSTRACT
The main threat to water resources in the Miami area is saltwater intrusion into the highly permeable Biscayne aquifer. Saltwater pollution of the aquifer may be held at its present location or moved seaward by raising the fresh-water levels in the ground by increasing fresh-water heads behind the control dams, or by moving the controls farther downstream in the canals.
Analysis of available data indicates that water containing 1,000 parts per million or more of chloride in the Miami Canal is immediately downstream from the salinity-control dam at N.W. 36th Street approximately 23 percent of the time and at N.W. 27th Avenue about 60 percent of the time. Also, an analysis of flow data indicates that when the discharge of the Miami Canal at N.W. 36th Street is approximately 280 cubic feet per second or less, the salt-water wedge is located at the downstream side of the control dam at N.W. 36th Street. With the present location of the control dams a minimum discharge of 550 cubic feet per second would be required to hold the salt-water wedge downstream from N.W. 27th Avenue.
The fresh-water discharge from 60 percent of the aquifer in the Miami River and its tributaries below the control dams would be salvaged by moving the controls downstream from the confluence of the Tamiami Canal.
With reference to proposed downstream locations of controls, it was determined that during dry years, as experienced in 1961-62, there would be a discharge of about 55 cubic feet per second available for boat lockages in the Miami Canal at N.W. 27th Avenue and about 30 cubic feet per second in the Tamiami Canal at LeJeune Road.
When a severe hurricane is imminent for the lower southeast coast of Florida, the salinity controls in the major canals in Dade County are generally fully opened before the hurricane strikes to
1




2 FLORIDA GEOLOGICAL SURVEY
reduce the possibility of flooding. High storm tides as a result of strong easterly winds push large quantities of salt water upstream. This invasion of salt water above the opened controls may contaminate the aquifer as well as increase the threat of flooding. If the salinity controls were redesigned so that they could be closed when the flow starts to reverse during hurricanes, they could more effectively protect the area from floods, salt-water encroachment, and better conserve the fresh-water resources of the area.
The chloride records indicate the present controls in the Miami and Tamiami Canals have proven to be barely adequate in protecting the City of Miami's Hialeah-Miami Springs well field from salt-water contamination during the dry years. If the extreme conditions that were experienced in the early sixties were to recur along with increased withdrawals from the fresh-water supply for public use, the salt water might move inland to the extent that it could cause some reduction in the capacity of the Hialeah well field to supply the fresh-water needs of the area.
INTRODUCTION
The Miami River has the largest discharge of all rivers in southeastern Florida, and serves as the outlet for the Miami and the Tamiami Canals. The widening and deepening of the Miami River and the construction of the Miami and Tamiami Canals have been beneficial in flood control but have increased the threat of salt-water encroachment. The primary purpose of the investigation is to present a study of the salt-water movement in the Miami River and Canal and its effect on the fresh-water supply of the area.
The rapid growth of population and industry in Dade County has placed an ever-increasing demand on the available freshwater supply. A major part of the water supplies come from the City of Miami's Hialeah-Miami Springs well field, and it is essential that contamination by salt water continues to be prevented. Two possible ways to accomplish this are to (1) hold higher heads of fresh water behind the controls; or, (2) relocate the controls downstream. However, holding higher heads of water behind the controls may not be practical because much valuable low land would be flooded. Relocating the control dams farther downstream would furnish additional protection against salt-water




REPORT OF INVESTIGATION No. 45
encroachment in the Biscayne aquifer and provide a widening of the fresh-water safety zone between the salt water and the Hialeah-Miami Springs well field. As the metropolitan area places an ever-increasing demand on the available fresh-water supply, there is a need to conserve as much fresh water as possible. In connection with this conservation the study of the movement of the salt-water wedge in the Miami River and its tributaries will provide one additional tool to better understand and manage the water resources of the area.
Salt-water intrusion historically has been the chief threat to the water resources of the Miami area. This report, prepared in cooperation with Dade County, gives detailed attention to the movement of salt water in the Miami River and its tributaries. The major hydrologic features in greater Miami and the area investigated are shown in figures 1 and 2. Salt water in the canal moves in response to the operation of salinity-control dams located in the Miami and the Tamiami Canals (fig. 1). Other factors that affect movement of the salt water in the Miami River and its tributaries are as follows: Fresh-water discharge through the controls; seaward movement of water in the aquifer downstream from the controls; rainfall and evaporation; tidal cycles, and seasonal changes in the tidal oscillations in Biscayne Bay. Of the above factors, only the fresh-water discharge can be easily controlled by man. Even in the operation of the control dams he is limited by the available supply of fresh water. In this endeavor hydrologic knowledge is a prerequisite to conserving as much of the available fresh water as is safely possible without inland flooding.
The investigation was made in cooperation with Dade County and was under the general supervision of A. O. Patterson and K. A. MacKichan, Ocala District Engineers of the Surface Water and Quality of Water Branches, and subsequently, R. W. Pride, acting District Engineer, Surface Water Branch, and C. S. Conover, District Chief, Water Resources Division of the U.S. Geological Survey.
Thanks are extended to F. D. R. Park and M. C. Brooks, Water Control Engineeers of the Water Control Department, Public Works Department of Dade County, for furnishing the operation log of the Miami Canal salinity-control dam and the chloride concentrations during 1961-62. C. F. Wertz, Director, Department of Water and Sewers, City of Miami, furnished photos of the salinity dams in the Miami Canal.




4 FLORIDA GEOLOGICAL SURVEY
HOLLYWOOD
BROWARD OUNTY DADE COUNTY BROKEN DAM
BISCAYNE CANAL
uPENsuco
V LITTLE RIVER CANAL
MIAMI HIALEAH WELL FI1A
EXPLANATION 13J
0
WATIR LEVEL RECORDING GAGE .K
lT~ER LEVEL RECORDING GAGE
ANDWDSCHARGE
r A
RAIN G8
CANAL, CONTROL DAM
LEVEE MILES O 2 4
Figure 1. The Greater Miami area showing the major canals and the area investigated.
AREA OF INVESTIGATION
The area investigated in this report is the Miami River which extends from Biscayne Bay to N.W. 27th Avenue, the Miami Canal from N.W. 27th Avenue west to Levee 30, and the lower reach of the Tamiami Canal (See figs. 1 and 2).
Samples of the fresh water taken between 1946 and 1958 in the




AIRPORT EXPY
N.W. 36 th ST.,W I A M
MIAMI INTERNATIONAL 1WT
0- CHLDRDER SAML R ING T TAMIAMI TRAI C-1
LASCHARGE \ MI CA N, 3! N.W Oi ZSBz i
- CONTROL D AM S TA.AM T
igr -. CNii eCrDn G uae
0.5 0 0.5 I
Figure 2. Miami River and its tributaries showing data-collection sites in the area investigated.
AIRP




6 FLORIDA GEOLOGICAL SURVEY
Miami Canal west of the salinity-control dam indicate that chloride concentration generally ranges between 10 and 15 ppm (parts per million). This small amount of salt contamination comes from the fresh-water contact with the rock aquifer and the soil materials in the Everglades. The chloride concentration of the fresh water varies slightly with seasonal changes in rainfall and runoff from the area, and averages about 12 ppm for the Miami Canal west of the salinity-control dam.
The main area covered in this report is the diluted zone between the average chloride concentrations of 12 ppm in the fresh water to the west of the salinity-control structures and the average chloride concentrations of about 19,000 ppm in Biscayne Bay. The area between these ranges is undergoing an evercontinuing battle between the fresh water and its higher heads and sea water and its density current. The greatest degree of variability in salt-water content occurs in this reach. Therefore, the main emphasis of the report is on this section.
HISTORY OF SALINITY CONTROL-DAM OPERATION IN THE MIAMI CANAL
In 1945 salinity-control dams were installed in most of the canals in the Miami area as barriers against further encroachment of salt water in the Biscayne aquifer. The dams were constructed across the canals by driving sheet-steel piles into the limestone aquifer.
On the Miami Canal four salinity control dams in the vicinity of N.W. 36th Street have been in operation during various periods. Their purpose was to furnish protection to a Miami municipal well field located upstream. The first control dam of sheet-piling was in operation from December 1939 to June 1942, when it was replaced by a pneumatic dam. The pneumatic dam remained in operation until it failed in March 1945. The high rise in chloride concentration at that time may be noted in the figure on page 16. Ten days later a temporary sheet-piling dam was installed and remained in operation until 1946 when the present sheet-piling control dam was constructed. The present control dam in the Miami Canal is operated by removing alternate steel piles (called needles) during the wet periods and replacing them during the dry periods. Photographs of various salinity-control dams in the Miami Canal at N.W. 36th Street are shown in figure 3.




Original sheet-piling dam (1939-42)
Pneumatic dam (1942-45)
Temporary sheet-piling dam (1945-46) Figure 3. Successive salinity-control dams in the Miami Canal at N.W. 36th Street.




8 FLORIDA GEOLOGICAL SURVEY
RAINFALL IN THE MIAMI RIVER DRAINAGE BASIN
The area depends chiefly on rainfall for its available freshwater supply. The rainfall in the Miami River drainage basin averages 57 inches per year. Extremes range from 74 inches in 1959 to 38 inches in 1951. The average and extremes are based on 20 years of record (1944 through 1963) from three rain gages. The rain records used in this report (fig. 1) are Hialeah, Pennsuco 5 N.W. (Broken Dam), and Pennsuco. The monthly mean rainfall for the above period is shown in figure 4. Rainfall for the wet period, May through October, averages 44 inches or 71 percent of the average annual rainfall; rainfall for the dry season, November through April, averages 13 inches per year. Also shown in figure 4 are the monthly extremes and the year in which they occurred.
1958 1957 1959 1957 1958 1962 1946 1956 1948 1952 1959 1957
18
1 -- - . . ..
14 .......... *........
MEAN
12 ...... ...... ...._oL1
S00
1951 1944 1956 1946 1945 1952 1963 1954 1961 1962 1952 1961 Jon Feb Mar Apr May June July Aug Sept Oct Nov Dec
Figure 4. Monthly mean rainfall, monthly extremes, and the year the extremes occurred based on the averages of Hialeah, Pennsuco, and Pennsuco 5 N.W. (Broken Dam) rain gages for the period 1944 through 1963.
A.




REPORT OF INVESTIGATION No. 45 9
LONG-TERM HYDROLOGY
DISCHARGE IN THE MIAMI CANAL
The discharge of the Miami Canal depends on rainfall and the operation of the salinity-control dam at N.W. 36th Street. The monthly mean discharges of the Miami Canal at the salinitycontrol dam, shown in figure 5, were determined from the gaging stations located in the Miami Canal opposite the City of Miami's water plant, and at N.W. 36th Street (figs. 1 and 2). The station at the water plant was operated prior to February 1959, and the N.W. 36th Street station was operated thereafter. A comparison of overlapping records from the two stations indicates that the discharge measured at the water plant exceeds that at N.W. 36th
STATUS OF THE CONTROL DAM
..I I I I I I
200
o I vl) 3,20
2. c -1 DM ULL OPEN OR OUT _E2f1O t DAM PARTLY OPEN I M M ANAL ABOVE DAM I DAM CLOSED
S800 4
2 1.4L :- .. ... .. .. TOTAL ANNUAL RAINFALL N I S
z 12 - -. --
- I. ..i
10
,.,I--
20 .-~~!7 TOT- L AUL ANAL -- C E - -- -- _
6
z 4 12
6 -W_ iwi
944 1945 194 97 194 949 195 1951 952 195395 954 1955 1956 1957 ... 1959 1 96 1962 1963
Figure 5. Monthly and annual mean discharge in the Miami Canal above N.W. 36th Street control dam and the total annual and monthly rainfall for the three rain gages in the Miami Canal drainage basin.




10 FLORIDA GEOLOGICAL SURVEY
Street by about 5 percent. As the difference in discharge between the two stations was small, the records were considered comparable without adjustments and were used consecutively in figure 5. The total monthly rainfall in figure 5 is the average of three rain gages in the drainage basin. The total annual rainfall, the annual mean discharge, and the operation of the salinity-control dam are also shown. The annual discharge (runoff) from the drainage basin does not correlate with the annual rainfall during wet periods because the excessive runoff lasts several months into the next year. On the other hand, the discharge shown in figure 5 does compare with the movement of salt water (see figure on page 16) in the Miami Canal. During times of peak discharge the 1,000 ppm chloride front is downstream in the canal, and in periods of low flow the 1,000 ppm chloride front moves upstream to the salinity-control dam. Further comparison of figures 5 and 10 indicates that there is very little lag in the salt-water movement in relation to fresh-water discharge.
WATER LEVELS IN THE AREA OF INVESTIGATION
Long-term monthly mean water-level fluctuations in three selected Miami Canal recording stations are shown in figure 6. The Miami Canal at Broken Dam and Miami Canal at N.W. 36th Street recording stations are located above the salinity-control dam as shown in figures 1 and 2. The slope in the Miami Canal may be determined from figure 6 by comparing the water levels at Broken Dam gage (located to the west and 2 miles downstream from Levee 30) and with those at the N.W. 36th Street gage (just upstream from the salinity-control dam). An examination of the records of the past 20 years (figs. 5 and 6) shows that wet and dry cycles have lasted for several years.
When the discharge is high, the slope in the upper reaches of the Miami Canal above the salinity-control dam is greatest, as shown during the wet years 1947-49, 1953-54, and 1958-60. During the dry years, when the mean annual discharge is less than 600 cfs (cubic feet per second) at the N.W. 36th Street salinity control, the difference in water level betwiveen Broken Dam and N.W. 36th Street gages is less-indicating a decrease in the slope of the canal during these years. A comparison of the monthly mean water level in the Miami Canal at N.W. 27th Avenue and at Biscayne Bay (fig. 6) shows they closely follow




REPORT OF INVESTIGATION NO. 45 11
MIAMI CANAL AT BROKEN DAM
- -54
IAMI CANAL AT NW 3 STREET (ABOVE DAM)
2
--J
1LI L 1.I t Ii 1L
Ii MIAMI CANAL AT NW 27th AE I I I
BISCAYNE BAY
3 ,, t '' I 194194811949 1'0 1" 5-!I"---111[I 1 9L 11 I J ,r --r o
9 s 946 1947 948 949 1910195 1 952 19 9 1954 1 955 1956 1957 956 19 960 1961 962 1963
Figure 6. Water levels at three selected Miami Canal stations and one Biscayne Bay station, from 1944 to 1963.
each other except during the extremely wet years when the runoff was high.
WATER LEVEL COMPARISON BETWEEN MIAMI RIVER AND BISCAYNE BAY
Graphs of the mean monthly high, low, and average water elevations of the Miami Canal at N.W. 27th Avenue and of Biscayne Bay are based on 18 years of record from 1946 through 1963 as shown in figure 7. The seasonal changes in the average elevations of Miami Canal at N.W. 27th Avenue and of Biscayne Bay (fig. 7) are generally low around the beginning of the year, rise gradually until October, and then decline rapidly until the end of the year.
Comparison of the monthly mean elevations of the record shows that the Miami River always has a seaward gradient. This indicates that even when the flow at the control in the Miami




19 FLoRmA GEOLOGICAL SURVEY
MIAMI CANAL AT N. W. 271h AVE. BISCAYNE SAY
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Figure 7. Monthly high, low, and average elevations in the Miami Canal
at N-W. 27th Avenue and at Biscayne Bay based on 18 years of record f rom
1946 through 1963.
and Tamiami Canals is nil, there is generally a discharge from the
aquifer to the Miami and Tamiami Canals in the reaches below
the present controls, except during extremely dry 'periods. The
fresh-water discharge from 60 percent of the aquifer could be
saved by moving the control downstream in the Miami Canal
below the confluence with the Tamiami Canal. The total monthly.
mean flow from or into the Biscayne aquifer downstream of the
.1




REPORT OF INVESTIGATION NO. 45 13
control dams from April 1961 to September 1963 is shown in the figure on page 30.
If past conditions are repeated in the future, the mean high, mean low, and average water levels shown in the Miami Canal at N.W. 27th Avenue (fig. 7) would be experienced below any control constructed at that location.
The annual mean high water, mean low water, and average water-level elevations are shown in figure 8. By the use of figure 8, the mean high water, mean low water, and the mean water-level elevations may be determined throughout the lower reaches in the Miami Canal below the N.W. 36th Street control
LiiI
>- Lj Z
o o
-JJ X 0pf<
3 2 3l 4 5L 6
Ear o 1 to 1
U.
0
LL Z z 0) z Uz
ED MEAN HIGH WATER r
0
I
MEAN ELEVATION
tI
IL
W
z
IdI
MEAN LOW WATER,
I 6
W1
DISTANCE UPSTREAM FROM BISCAYNE BAY, IN MILES
Figure 8. Mean water-level elevation, mean high and low. water from the N.W. 37th Street control dam to the mouth of Biscayne Bay, based on 18 years of record, 1946 to 1963.




14 FLORIDA GEOLOGICAL SURVEY
dam. The average annual gradient from the N.W. 36th Street control dam to Biscayne Bay is about 0.6 foot in 5.5 miles. The mean annual water-level elevation of Biscayne Bay is 0.48 foot above msI (mean sea level) datum of 1929, based on 18 years of record (1946-63).
SALT-WATER MOVEMENT IN THE MIAMI RIVER
The Geological Survey has collected chloride data in the Miami River and Canal from 1940 to June 1958 and from 1962 to 1964. The chloride samples were collected bi-weekly or monthly from the bottom of the canal at or near high tide when the upstream advance of salt water was at its greatest penetration. The location of the sampling sites were in most cases bridges from which the sampler could be lowered by a line to the deepest section of the canal. The accessibility of these bridges by car enabled the field men to move rapidly from station to station in order that all samples might be taken as near high tide as possible.
Prior to this study the objective was to determine the location of the 1,000 ppm chloride concentration by collecting salinity samples in the canals. Frequently, it was possible to determine the location of the 1,000 ppm chloride concentration by taking a relatively few samples. Thus all sampling stations were not visited each sampling period.
The locations of periodic salinity sampling stations and their distance, in miles, from the mouth of the Miami River at Biscayne Bay are shown in the following tabulation:
Locations Miles from Biscayne Bay Miami River at Brickell Avenue 0.10 Miami River at Miami Avenue 0.40 Miami River at West Flagler Street 1.10 Miami River at N.W. 7th Avenue 1.57 Miami River at N.W. 12th Avenue 2.11 Miami River at N.W. 17th Avenue 2.65 Miami Canal at N.W. 27th Avenue 3.83 Miami Canal at Seaboard
Airline Railway Bridge 5.32 Miami Canal below
N.W. 36th Street control dam 5.45




REPORT OF INVESTIGATION No. 45 15
Locations (Continued) Miles from Biscayne Bay (Con't) Miami Canal above
N.W. 36th Street control dam 5.48 Miami Canal at N.W. 36th Street 5.56 Miami Canal at N.W. 54th Street, (Hialeah) 7.06
In addition, two continuous conductivity recorders were placed in the Miami Canal at N.W. 27th Avenue and below the N.W. 36th Street control dam. These recorders were used to indicate the continuous movement of the salt-water wedge during tidal oscillations of the Miami Canal. Also, hydrologic data were collected from eleven water-level recorders, six discharge stations, and three rain gages at the locations shown in figures 1 and 2.
Beginning in January 1940 and continuing for a period of 18 years, chloride samples were taken bi-weekly at selected points on the Miami River. The data were arranged to show the percentage of time that the chloride content was 1,000 ppm at selected points in the Miami River. Figure 9 shows that water containing 1,000 ppm or more of chloride was at N.W. 27th Avenue
100 I
NW12 AVE
NW17AVE *
U. NW 27 AVE
0
~-50
z
W
W NW36 ST nL DAM
0 1 2 3 4 5 6
DISTANCE UPSTREAM FROM BISCAYNE BAY, IN MILES
Figure 9. Percentage of time water containing 1,000 ppm chloride was at or above various locations in the Miami Canal for the period 1945 to March 1958.




16 FLORIDA GEOLOGICAL SURVEY
60 percent of the time, and extended as far upstream as the control dam at N.W. 36th Street 23 percent of the time. The location of the 1,000 ppm isochlor is shown in figure 10. During
SHEET PILE DAM I P MTC DAM
M JA ONDJ MAM4JAS ND JJA OND FMAM ASO D A 10 - - 1 T -TTT r- T 7 T 1 -" -T r-- F-T -1 1 1 T .i ,r( ,i
N. W 27 AVE.
I t:4:~N Ift.W AVE.
'J--L'iM: E 0" Nl''v 'JN.,I: -- -- . --1; lii: rAN, I~ Vi! i.: 4N:b S1i!;~! fl
L AM. o nJ AS oiN A JLFU A'M A A SO N D 1 FM A M J AISO NIIJ F MA M J A SO ND IFIMA JAI SO NDA
-940 ,4 z 4 943 94
. EMPORRY DA M PE PRESEHEET PILE DAM
, --_ NLW. 2T AVE.
oW IA AVE.
kILL4I44441 4I4+ IZZIIJ1
14s 1956 1947 1994
PRESENT SWEET PILE DAMU
0 T T r r na T to March 1958 I L .... .. .. WATER WAAD P
front wasatheDAM.36tSteec. DAma p o i1n Aresen 9 DWAs
NW r IN AV :1E AI I
inaled,.Psino the 1,000 ppm chloride t oasraet one Mamiv Cana
c t o da 1951 1952 t 1953 1954 SE .NT SHEET PILE DAM .
10 L I i I I L I I T FL([~ I I_ Z Z
5o the id d and by Marc5 1953 ST DA ha ir
dought0 ppm.iAs, 194-4 Mach 19502,orml 1,000 pptoidepe
frontfasatthe N control dama o ia fmc 1geater e re o eam. Sing Nh 1 W. Ze AV the 10946 p md d N W 12 AVE fP f m 18
S 1
Figure 10. Position of the 1,000 ppm chloride contend in the Miami Canal for the period January 1940 to March 1958.h as1 pm
drought periods, 1943-45 andy M 1950-52, the 1,000 ppm chloride
front was at the N.W. 36th Street control dam a much greater
installed, the 1,000 ppm chloride front has rarely gone above the control dam. On May 18, 1951 the chloride was 1,550 ppm just above the dam, and by May 25, 1951 the chloride had increased to 4,000 ppm. Also in March 1962 abnormally high tides topped
the salinity-control dam in the Miami Canal and caused salt water to move upstream. During the 18 years of record the 1,000 ppm chloride front reached the dam at least once during most years; the exception was in 1954 when the canal discharge remained relatively high all year. Most of 1954 the 1,000 ppm chloride front remained below 27th Avenue. Records show that prior to building the present 36th Street dam it was normal for the 1,000 ppm chloride front to extend into and even beyond the Hialeah area during dry years.




REPORT OF INVESTIGATION NO. 45 17
When fluids of different density meet, they remain relatively unmixed. The difference in density between fresh and salt water affects the movement of water in the tide-affected reach of a river. When the tide is rising in the Miami Canal the denser salt water moves upstream as a wedge beneath the seaward-moving fresh water. The salt-water wedge continues to move upstream until the tidal force is equalized by the force of the discharging fresh water or until the tide reverses. During dry periods, when there is little or no discharge, salt water may move far enough upstream to contaminate the fresh ground-water supply.
The salt-water wedge advances farthest inland along the bottom of a tidal canal at or near high tide. At high tide the salt-water wedge is relatively blunt, and the distance it moves inland along the bottom of the canal is comparable to the 1,000 ppm chloride shown in the figure on page 22. Therefore, the movement of the 1,000 ppm chloride was used as an index to determine the movement of the salt-water wedge (fig. 10). The distance in miles above the mouth of the Miami River at Biscayne Bay that the monthly average of 1,000 ppm chloride remained (fig. 10), was compared with the monthly mean discharge (fig. 5) to determine the distance downstream from the salinity-control dam that various discharges move the salt-water wedge. This relation shown in figure 11 was developed from data collected from January
I .N;6 36 'CONTROL DAM
-o oI
tlo
%000 MIAMI CANAL
0 o
9 -NW. 27h -AVENUE
-0 0
on
0 o o
I1 Io
I~ ~ ~ ~ 0 ___ __ __ 0
O- MONTHLY MEAN POSRION OF THE 000 PPM CHLORIDE
0 I I I I I I i J i, .
0 200 400 600 800 1,000. 1,000 1,400 16o00 1,800 2p000 2,200 2,400 DISCHARGE, IN CUBIC FEET PER SECOND
Figure 11. Relation between monthly mean discharge in cfs and the location of water containing 1,000 ppm chloride in the Miami Canal.




18 FLORIDA GEOLOGICAL SURVEY
1940 through February 1958, and suggests that a minimum discharge of 280 cfs is required to move the salt-water wedge away from the base of the salinity-control dam at N.W. 36th Street. Also the graph indicates that approximately 550 cfs is required to hold the salt-water wedge as far downstream as N.W. 27th Avenue. Discharge from the Tamiami Canal and flow from the aquifer to the canal downstream from the controls.also contributes to holding the salt-water wedge downstream. During the period
__ _N__W 36st. DAM SSEABOARD R.R.
5 0
4.0
.NW 27 AVE
19481
- 3 5 . ...-
g0
2.5
NW 17 AVE
20
5.5 NW 36st. DAM
5 05 -- --
.,,..,SEABOARD R.R.
0m 4.5 -.0 AVE
3.0
z
3,0
0
1NW 7 AVE
2.5
2.5NW 12 AVE
2.0
JAN FES MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC
Figure 12. Chloride concentration in the Miami Canal during a typical wet year (1948) and a typical dry year (1956).




REPORT OF INVESTIGATION No. 45 19
1940 to 1958, when the salinity samples were taken in the canal, the Tamiami Canal discharge was measured only from January 1940 through June 1943. Therefore, discharge of the Miami Canal was taken as an index of the hydrologic conditions and was used to determine the position of the inland extent of the salt water wedge in the canal.
Chloride concentration during a typical wet and dry year is shown in figure 12. The wet year 1948 was selected as it was the only year in which discharge remained above 400 cfs throughout the year and was above 1,900 cfs at the beginning and end of the year. The dry year 1956 was used because, except for January and February, the discharge remained generally below 400 cfs all year. During the wet year 1948 the 1,000 ppm chloride remained downstream from the N.W. 36th Street control but, during the 1956 dry year water containing 1,000 ppm or more of chloride was at the bottom of the canal at the dam from March through August, with 5,000 ppm on the downstream side of the control in April, June, and August, and 10,000 ppm chloride in May. A comparison of figures 5 and 12 shows a close relation between discharge at the N.W. 36th Street control and the movement of chloride in the Miami Canal.
SHORT-TERM COMPARISON OF CHLORIDE WITH WATER LEVELS AND DISCHARGE
A comparison of water levels, discharge, and chloride content at selected stations is shown in figures 13 and 14. At noon on July 14 (fig. 13) the Miami Canal at N.W. 36th Street control was reduced from 4 full needles and 4 one-half needles open to 4 one-half needles open; the mean daily discharge dropped from about 300 cfs to 100 cfs. The stage above the control rose from about 1.0 foot above msl on July 13 to about 1.75 feet on the 14th. During that period the chloride content at N.W. 27th Avenue increased from less than 1,000 ppm to 3,000 ppm. On July 15 at 2:30 p.m. the control opening was increased by 4 full needles and the discharge increased to more than 200 cfs. Water levels above the control declined to about 1.25 feet above msl and the chloride dropped below 1,000 ppm. It is noted that when the discharge through the control ranged from about 400 cfs at low tide to about 200 cfs at high tide, the chloride of the water at 27th Avenue remained generally below 1,000 ppm. However, when




20 FLORIDA GEOLOGICAL SURVEY
ILLY. 964
a A-- - .,. 0 2 0
.. I r + r-+ z-- - - "I -- -- T - + -- I --,'
I I ___ I
... __-_/_ _1___._400 M A 2" VME(60 AA AT NW 361 STREET 0 (AOVMCNTOL
-- ----- .__0
IAMI CANAL AT NW 27 AVM
30 3000
Figure 13. The effect of changes of the N.W. 36th Street control dam on discharge, water levels, and chloride content at selected locations in the Miami Canal from July 12 to 19, 1964.
the discharge ranged from 300 cfs to 275 cfs at low tide to between 130 cfs and 100 cfs at high tide, the chloride content generally rose above 1,000 ppm during each high tide. The hydrographs also show that small changes in the control at N.W. 36th Street have a negligible effect on water levels at N.W. 27th Avenue.
A representative period of relatively low discharge, August 14-19, 1964 (fig. 14) has been selected to demonstrate the relation between the discharge, water levels, and chloride concentration in the Miami Canal. During August 14-16 when the discharge generally declined, the chloride content below the salinity control at N.W. 36th Street increased. When the control opening was increased from 2 half needles to 1 full needle and 4 half needles
2-0 2.0




REPORT OF INVESTIGATION NO. 45 21
400
300 W . r N.W. . .. S T . . . .
SMIAMI CANAL at NW 36 ST
4200,
1 00 __________0
coo AMIA ABOVE CONTROL) __at 3S(ELCOTL
3.0.
.5
MIAMI CANAL at NVE
1.0 4-
Figure 14. The effect of changes of the N.W. 36th Street control dam on discharge, water levels, and chloride content at selected locations in the Miami Canal during the period August 14 to 19, 1964.
at 10:30 a.m. on August 17, the salt-water front was forced downstream, as shown by the decline in chloride below the control and
at N.W. 27th Avenue (fig. 14.) Even when the control structure
was changed to 4 half needles open at 2:00 p.m. on August 18, the chloride remained downstream at N.W. 36th Street through August 19. On the other hand the chloride content at N.W. 27th Avenue again began to increase on August 19. The maximum chloride advances occurred about high tide on each cycle as shown in the N.W. 27th Avenue salinity and stage hydrographs. At low tide when the gradient in the Miami Canal is at its greatest, the discharge increases and the salt water again moves in a seaward direction. The anomaly in water levels at N.W. 27th Avenue at mid-rising tide is caused when the upstream movement of the
tid wenthegrdint n heMIAMI CANa i at its gratst theWOTRL
direction. ~ ~ ~ MAM TheA anmlonwtefeesa N.W. 27t Avenu
atFidrising tie isec cae whe the ups 3trea mteeomntoofdathe
salt-water wedge started passing this location (fig. 14). It was most pronounced on the afternoon of August 19.




II 9 9
. I
a --- ---- - --- ----- .-- ..- -.__
_ _90 C I MIAMI* CANAL PROFILE ,70 s wo CHLORIDE IN PPM
es0 LOW TIDE
8 . .. ... .. .. . ... .. .00 .*. .*.**- -5,000.. .
"IRS........ . . . . . .-oo.... L / /
,.o_ ,00MIAMI CANAL PROFILE .....000- CHLORIDE IN PP P2 I
14 0
DISTANCE UPSTREAM FROM ISCAYNE AY, IN MILES
Figure 15. Profile of chloride content in the Miami Canal on July 16, 1964 at low and high tide when the N.W. 86th Street control dam was partially open.




REPORT OF INVESTIGATION NO. 45 28
HIGH AND LOW TIDE SALT-WATER MOVEMENT
On July 16, 1964, two chloride profiles were made along the Miami Canal. The first was made near low tide between 8:00 and 9:00 a.m. Canal water was sampled for chloride content at 2-foot intervals from the bottom to the water surface at each of the stations named in figure 15. Another profile was made at high tide, between 2:30 and 3:30 p.m. using the same procedure.
The lower profile of figure 15 shows the most inland advance of the salt-water wedge. It may be noted that the seaward discharge in the Miami and Tamiami Canals at high tide was 52 cfs and 180 cfs, but at the same time the peak inland flow at Brickell Avenue was 480 cfs. This combined flow of 712 cfs at that time was going into storage in the Miami Canal, the Tamiami Canal, several man-made lakes, and into the aquifer. The salt-water wedge moved upstream in the Miami Canal during this period because Biscayne Bay with its high chloride concentration was supplying about 70 percent of the water going into storage at that time. The low-tide profile (fig. 15) shows the isochlor positions moved seaward. The discharge through the controls in the Miami and Tamiami Canals was 90 cfs and 225 cfs downstream and 2,370 cfs seaward in the Miami Canal at Brickell Avenue. The peak discharge affecting the downstream movement of the salt-water wedge indicated that 2.055 cfs was coming out of storage below the controls just prior to low tide. A comparison of the two profiles shows the change in location of the salt-water wedge in the Miami Canal between high and low tide. The above discharges represent only the extremes of the high and low-tide cycle; they do not determine the runoff for the tide cycle. Data indicate these would be typical high and low tide profiles for any period of average discharge and normal tides.
CHLORIDE CONCENTRATION EXTREMES
The chloride concentration extremes in the Miami River and Canal are shown in figure 16 for the period of record 1942 to 1964. The water samples were taken at the bottom of the canal at or near high tide when the salt-water wedge was at its most inland advance. The chloride concentration reached 13,200 ppm just above the temporary control dam located at N.W. 36th Street and extended inland past the Hialeah water plant, and was meas-




24 FLORIDA GEOLOGICAL SURVEY
DSTANCE UPSTREAM FROM BISCAYNE BAY, IN MILES
7 6 5 4 3 2
-.o -- I / {t -- . . I . /
70 - --- r- - . .' -- -..' . . ..,
16000 MAXIMUM
1Io -. 1942-1945 14,000 1946-1964 13,000 I
It
1 20 -- t- tci.00010
9n 0 80
7000MINIMUM -6 0 .
1942 -1964
a --- 50
50 /-[ -t-- 40
4000 3o
Figure 16. Chloride extremes at high tide in the Miami River and the Miami Canal at various sampling locations.
ured at 2,800 ppm in the Miami Canal as far as Red Road during the period 1942 to 1945.
The present sheet-steel piling control dam constructed in 1946 has proven adequate during all but the very dry periods. These dry periods coupled with withdrawals of fresh water from the Miami Canal by the adjacent Hialeah well field in the 1960's and the drought experienced in the latter part of 1961 through May 1962, there was not enough fresh water available in the drainage basin to provide high enough heads in the canal upstream from the control dam to prevent the salt-water seepage around the closed control dam. This salt water then moved upstream in the Miami Canal for more than eight-tenths of a mile. At the end of May 1962 the chloride concentration was measured at 7,200 ppm just above the control and 790 ppm at a point eight-tenths of a mile upstream. This water of high chloride content was very near the influence of the Hialeah well field's
02
0 0
O x < 0
Mim Cana at vaiu apiglctos
ured at 2,800 ppm in the Miami Canal as far as Red Road during the period 1942 to 1945.
The present sheet-steel piling control dam constructed in 1946 has proven adequate during all but the very dry periods. These dry periods coupled with withdrawals of fresh water from the Miami Canal by the adjacent Hialeah well field in the 1960's and the drought experienced in the latter part of 1961 through May 1962, there was not enough fresh water available in the drainage basin to provide high enough heads in the canal upstream from the control dam to prevent the salt-water seepage around the closed control dam. This salt water then moved upstream in the Miami Canal for more than eight-tenths of a mile. At the end of May 1962 the chloride concentration was measured at 7,200 ppm just above the control and 790. ppm at a point eight-tenths of a mile upstream. This water of high chloride content was very near the influence of the Hialeah well field's




REPORT OF INVESTIGATION NO. 45 25
cone of depression. This condition was improved in June 1962 when above normal rainfall, 14.54 inches, fell in the Miami Canal drainage basin. This rainfall provided enough fresh water to permit the opening of the control dam and to flush the salt water seaward.
THE 1945 DROUGHT
Control structures in the Miami Canal area will effectively hold back the intrusion of salt water, provided that the fresh water behind the dams is maintained at a high enough level. However, the problem of maintaining high fresh-water levels is complicated by the highly permeable limestone through which the canals were constructed. During times when the water table approaches msl, the denser salt water will move around the closed control structures through the aquifer and contaminate the fresh-water supply upstream.
On March 17, 1945, the pneumatic dam in the Miami Canal failed, and the salt water moved upstream to a point more than half-a-mile above the Hialeah water plant. Ten days later a temporary sheet-steel piling dam was constructed. Additional salt water moved around this closed temporary dam through the aquifer because the water levels above this dam were lower than the downstream mean tidal levels. Figure 17 shows the inland extent of this salt-water penetration along the bottom of the Miami Canal on May 31, 1945. Since the only samples taken at that time were from the bottom of the canal, the isochlor lines in ppm were estimated from these bottom samples and from an isochlor profile made on May 15, 1945. The upstream advance of the salt-water wedge was relieved when the rain gages in the basin average 3.85 inches and 6.77 inches during June and July, respectively. The rain was sufficient to move the salt water downstream from the N.W. 36th Street control structure during July.
CHLORIDE CONCENTRATION IN THE AQUIFER
The history of the City of Miami's fresh-water supply has been a problem of moving westward when their well fields were contaminated by the high chloride concentration from Biscayne ,ay and the Miami River. In later years when several uncon'rolled canals were constructed through the coastal ridge to develop the low-lying lands in the Everglades for urban and agri-




. ... . .... .. O IS T A N C E U P S T R E A M F R O M *S C A Y C E B A Y IN U IL E S . . . ... .
9 ? 7
g g 7 6 .j 4-- -
MEAN OAILY
- ~. ....- --- WATER LEVEL
0 14 ft 0.23 ft.
a --- -- -- - -
5/__ ..#_ _.._M IA M I C A N A L P R O F IL E S00 MAY 31I, 1945 .. ; --- -- -- -.................-oo o" I 1'____ ,
,0:. -000-
F urW 1 E m c
F ig u re _. E
Figur 17. xtrem chloide oetainith imCaaabvth ..6tStetctrldmoMk31195




REPORT OF INVESTIGATION No. 45 27
cultural use, the canals provided flood protection for the lowlands except during extremely wet periods when the drainage system was overburdened. The uncontrolled canals caused overdrainage during dry periods which resulted in lowering the water table and permitted salt water to move upstream in the canals and into the highly permeable Biscayne aquifer, the fresh-water bearing formation from which Miami obtains its water supply.
Hydrologic data collected to date shows the salt front at depth in the Biscayne aquifer has tended to move slowly, but progressively, inland from the Tamiami Canal toward the Miami well field, thereby flanking the control structure on the Miami Canal at N.W. 36th Street. The proximity of the salt-water intrusion to the Hialeah-Miami Springs well field's cone of depression is indicated by the map for 1962 in figure 18. The inland ex190482(Parkr an other 1955 589,., 16 undate
N
...... ,,AA~ I ..'AJ.
MIAMI MIAMI MIAMI MIAMI
190 1918 194.
..-. \
...I IAH .. 4
199
Figure 18. Salt-water encroachment at the base of the Biscayne aquifer 1904-62 (Parker and others, 1955, p. 589), (Kohout, 1961) updated.




28 FLORIDA GEOLOGICAL SURVEY
tent of the 1,000 ppm chloride located at depth in the Biscayn( aquifer is about 1 mile from the southeast edge of the cone of depression. During extreme dry periods the canals act as inland extensions of the sea, carrying salt water several miles upstream and allowing it to leak out and contaminate the aquifer all along its course. During these periods the low water table enables the salt water to move inland toward the Miami well field. During wet periods discharge in the canals rapidly moves the salt water in the canals downstream and the overall higher water levels tend to move the salt front in the aquifer seaward and toward the Bay. Examination of the past records of the position of the salt-water front in the ground has shown a very slow but a steady movement toward the Miami well fields as the increasing population places an ever-increasing demand on the available water supply.
DISCHARGE AT SELECTED LOCATIONS
The past threats of salt intrusion and the expected increase in withdrawals from the Hialeah well field show that the threat of intrusion toward the well field will become progressively more imminent with the present locations of the controls in the Miami and Tamiami Canals. A control structure in the Miami Canal below the confluence of the Tamiami Canal would reduce the threat of salt-water encroachment to the well field from both canal systems. A structure at such a location would move the salt water in the canal more than 1 mile downstream in the Miami Canal, and eliminate recurrence of the intrusion such as that of 1962. The resulting rise in fresh-water levels attendant with the downstream relocation would blunt the lobe of salt water in the aquifer and cause it to move seaward and thereby create a larger buffer zone of fresh water between the well field and the salt-water front. In addition, the deep rockpits within the area, which presently contain water of high chloride concentration at depth, probably would become progressively fresher, thus adding to the area of fresh-water storage.
A lock and dam site in the Tamiami Canal at LeJeune Road coupled with the present control structure in the Miami Canal would be less effective than a single control structure downstream in the Miami Canal below the confluence of the Tamiami Canal. The mean monthly discharge, shown in figure 19, shows the water that would be available for boat lockages at Tamiami Canal at Le-




REPORT OF INVESTIGATION NO. 45 29
Ioo -Fl I11f T FT I I I I I I I II I ii I TITTlF
1,400
1,300 ----- MIAMI CANAL at NW 27 AVE.
---- -MIAMI CANAL at N.W. 36 ST.
-,-oo TAMIAMI CANAL at LeJUNE RD.
Z 1,1000
oo ----|\
0
0 0
1,000
9 I 900
_\ __ : ___,_ i i 'oo _- -._ ....\ _1i_1.771 _o ,. 3001
Io -- \ .. I \.- I
sNJMAMJJdA SON J dF IRA MJJASON IJ FM AM JJdAS
1960 1961 D 1962 D 1963 __U
S oo!
400 ________
0 ,--.- J I
< 960 0 910192 0 16
Figure 19. Monthly mean discharge at selected locations in the Miami and Tamiami Canals, October 1960 through September 1963.
Jeune Road, Miami Canal at N.W. 36th Street, and Miami Canal at N.W. 27th Avenue. The discharge shown for Miami Canal at N.W. 36th Street was taken directly from published records. Because the Geological Survey at present has no discharge stations at the other two locations, the discharge was computed as follows: The discharge for Tamiami Canal at LeJeune Road is the summation of the three discharge stations (Tamiami Canal near Coral Gables, North Line Canal near Coral Gables, and Coral Gables Canal near Coral Gables) plus 30 percent of the flow difference between the total of the above stations plus the discharge at Miami Canal at N.W. 36th Street from the total flow of the Miami River at Brickell Avenue. The computed discharge for Miami Canal at N.W. 27th Avenue is the flow of Tamiami Canal at LeJeune Road plus the discharge of the Miami Canal at N.W. 36th Street plus 30 percent of the flow difference between Tamiami Canal at LeJeune Road plus Miami Canal at N.W. 36th Street from the total discharge of the Miami River at Brickell Avenue.




30 FLORIDA GEOLOGICAL SURVEY
Locations of the above discharge stations are shown on the map in figures 1 and 2. The mean monthly discharge for Miami Canal at N.W. 36th Street indicates that during extreme dry periods there would not be water available for lockages at this location. On the other hand, the Tamiami Canal at LeJeune Road would have a minimum flow during a dry period, such as that experienced early in 1962, of about 30 cfs, and the Miami Canal at N.W. 27th Avenue would have a minimum flow of about 55 cfs
1.200
1.100
1.000
900
go 700 600
2400!
i!
Uj 300
a loo_ ..
0v
-100 JIFIMIAIMIJIJiAISOINIDOJIFIMIAIMIJIJAISiOINIDJIFIMIAIMIJJIAISoQ
1961 1962 1963
Figure 20. Monthly mean discharge from or into the aquifer below the control dams in the Miami River and its tributaries, April 1961 through September 1963.
available for boat lockages. This minimum flow also takes into account the additional storage of fresh water that could be used for boat lockages that would become available in the aquifer and several lakes with the relocation of the controls downstream from their present location.
The discharge from or into the Biscayne aquifer from the Miami River and its tributaries below the control dams during the dry period April 1961 through September 1963 is shown in figure 20. Even during this dry period the aquifer was discharging to the Miami River at all times except for March 1962 when ab-




REPORT OF INVESTIGATION NO. 45 81
normally high tides occurred, and again in April and May 1963.
The most important factors that will control the ultimate effectiveness of the proposed lock and dam structure are: (1) the precautions taken to prevent the movement of salt water beyond the structure during locking operations; and (2) the amount of fresh water used for locking boats during prolonged drought. If, in the future, the amount of fresh water used in locking plus that required to maintain safe water levels at the control were to exceed the quantity available in the canal system, the effectiveness of the control of salt intrusion would be negated and a readvance of the salt front would occur.
THE EFFECTS OF WIND ON WATER MOVEMENT
The effects of wind on water levels and canal discharge are shown in figure 21. When Hurricane Cleo passed through the Miami area on August 26-27, 1964, the hydrologic effect was recorded on all gages in the study area and the tidal gages in Biscayne Bay. Discharge illustrated in the upper graph shows the flow through the salinity control in the Miami Canal at N.W. 36th Street. Early in the morning on August 26 the discharge at the control was averaging 170 cfs with 4 half needles open. In anticipation of the impending hurricane and possible flooding, the control was opened to 22 full and 6 half needles at 11:00 a.m. The flow then increased to 580 cfs at 3:00 p.m. on August 26, but fell off rapidly to a negative (upstream) flow of 62 cfs at 11:00 p.m. when the strongest easterly winds hit the area and pushed the water in the Miami River at Brickell Avenue to a higher level than that above the open control dam as shown in the center hydrographs from 10:00 p.m. to 11:30 p.m. on August 26. After the eye of Hurricane Cleo passed, the strong westerly winds increased in intensity until a westward gradient of more than 3.5 feet existed across Biscayne Bay. That effect is markedly shown in the lower hydrograph when the Biscayne Bay at Coconut Grove tide gage recorded a minimum of -1.4 feet (referred to msl) at 3:00 a.m. on August 27, while the Biscayne Bay tide gage located in the Key Biscayne Marina recorded a high of 2.55 feet at 3:20 a.m. on August 27. Hurricane Cleo was a relatively dry storm. The average rainfall recorded at the three rain gages in the basin was 0.77 inch on August 26, and 4.61 inches on August 27.
When a severe hurricane is imminent for the lower southeast coast of Florida, the present type of salinity controls in the major




82 FLORIDA GEOLOGICAL SURVEY
oo- 1-- -MIAMI CANAL at N W. 36 ST
oo- -- -- -- I -! ,I--- I ..
too- 1- \ I
o
0 100)STERLY WIND- WESTERLY WINDI
- I I
MIAMI CANAL at N. W. 36 ST-ABOVE CONTROL
o- -- -,---- ------ -- ...--
,.,.~ ~ ~~~~'.0 I 4 IX/l ',/1', I .
cc-' I I .5- MIAMI RIVER at BRICKELL AVENUE
as- 1 1
BISCAYNE BAY at COCONUT GROVE
2.0-- 4- I I .
J
>o 111D. 5 I. I ( |

'o-U -+- - .* -- -- -10
I** I BISCAYNE BAY ot KEY ISCiYNEI
I I
SAM 12NOON 6PM 6AM 12NOON 6PM AUGUST 26, 1964 AUGUST 27, 1964 Figure 21. Effects of Hurricane Cleo's winds at selected discharge and water-level stations in the Miami Canal and Biscayne Bay, August 26-27, 1964.




REPORT OF INVESTIGATION NO. 45 33
canals in Dade County are generally fully opened before the hurricane strikes to reduce the possibility of flooding. High storm tides as a result of strong easterly winds push large quantities of salt water upstream. This invasion of salt water above the opened controls may contaminate the aquifer as well as increase the threat of flooding. If the salinity controls were redesigned and operated so that they could be closed when the flow starts to reverse during the hurricane, much better protection of the fresh-water supply and from flooding would be assured. During the period August 26-27, 1964, the control in the Miami Canal at N.W. 36th Street was open in anticipation of Hurricane Cleo. Following the passage of Hurricane Cleo which brought very little rainfall to Dade County, it was necessary to discharge valuable fresh water from the reserve supply in order to push the salt water downstream from the salinity controls. An example of the magnitude of reverse flow caused by storm tides was that of September 10, 1960, during Hurricane Donna, when a peak flow of 1,220 cfs moved upstream through the open salinity control in Snapper Creek Canal. These typical examples demonstrate the need for salinity controls that can be operated during hurricanes to more effectively protect the area from floods, salt-water encroachment and to conserve the fresh-water supply.
SUMMARY
Salt-water intrusion historically has been the chief threat to the water resources of the Miami area. The early history of the City of Miami's fresh-water supply has been that of moving westward when the well fields were contaminated by the high-chloride concentration from Biscayne Bay and the Miami River. In later years several uncontrolled canals were constructed through the coastal ridge to develop the lowlying lands in the Everglades for urban and agricultural use. The canals provided flood protection for the lowlands except during extremely wet periods when the drainage system was overburdened. These canals were the chief factor in salt-water contamination of the aquifer in two ways. First, during dry periods the uncontrolled canals were avenues for salt water to travel inland for several miles to contaminate the aquifer. Second, the overdrainage lowered water levels in the ground and permitted denser salt water to move inland through the aquifer. The chloride contamination in the aquifer can be halted or pushed back by holding higher water levels behind con-




34 FLORIDA GEOLOGICAL SURVEY
trol dams in the canals, or by moving the control dams further downstream.
The average chloride content of water in the Miami Canal ranges from about 12 ppm above the controls to about 19,000 ppm in Biscayne Bay. The data show that the salt-water wedge in the Miami Canal was located at N.W. 27th Avenue about 60 percent of the time and at the downstream side of the present control dam 23 percent of the time. It was determined that a discharge of at least 550 cfs from the area is required to hold the salt-water wedge downstream as far as N.W. 27th Avenue and at least 280 cfs in the canal system would be required to move the salt-water wedge away from the base of the N.W. 36th Street control dam. During wet years the salt water will remain downstream from the salinity-control dam all year, but during dry years water containing 1,000 ppm chloride or more will remain just below the control dam for several months. The freshwater discharge from 60 percent of the aquifer below the controls in the Miami River and its tributaries would be saved by moving the present controls below the confluence of the Miami and Tamiami Canals.
If a lock and dam were located in the Miami Canal in the vicinity of N.W. 27th Avenue there would be about 55 cfs available for boat lockage during dry periods, such as early in 1962. Records indicate that at times there would be no discharge available in the Miami Canal at N.W. 36th Street and about 30 cfs at Tamiami Canal at LeJeune Road. Isochlor profiles indicate that the salt-water wedge is very sensitive to tidal cycles and changes in discharge. It moves upstream during rising and high tide when the seaward flow in the canal is at a minimum and moves seaward during falling and low tide when the flow in the canal is at a maximum.
When a severe hurricane is imminent, the controls in major canals in Dade County are generally left full open before the hurricane strikes to reduce the possibility of flooding. During the hurricane high storm tides as a result of strong easterly winds may push large quantities of salt water upstream. Hurricane Cleo brought very little rain to Dade County, so it was necessary to discharge fresh water from storage in order to again push the salt water below the salinity controls. If the salinity controls were redesigned so that they could be closed when the flow starts to reverse during the hurricane, much better protection




REPORT OF INVESTIGATION No. 45 85
of the fresh-water resources and flooding of the area would be assured.
The present control in the Miami Canal has protected the water supply of a City of Miami well field but if the extreme conditions such as experienced in the early 1960's were to recur, accompanied by increased withdrawals from the well field, the salt-water wedge in the aquifer could move into the cone of depression and contaminate the fresh-water supply. Considerable reduction in the well field's pumping rate would be required to control the salt-water intrusion.
The continuing changes in water control and the increasing withdrawals for water supply will alter the flow system and greatly increase the quantity of water required to maintain the desired levels in the Miami Canal to hold back the salt-water front in the aquifer. This study was limited in scope to data collected since 1940 and to hydrologic conditions existing at this time. However, the data presented will provide a basis for the analyses of the effects of any major changes in the flow system in the future.
REFERENCES
Chambers, A. C. (see Dole, R. B.)
Cooper, H. H., Jr.
1964 (and Kohout, F. A.; Henry, H. R.; and Glover, R. E.) Sea water
in coastal aquifers: U. S. Geol. Survey Water-Supply Paper
1613-C.
Dole, R. B.
1918 (and Chambers, A. C.) Salinity of ocean water at Fowey Rocks,
Florida: Carnegie Inst. Washington Pub., v. 9, rept. 213. Glover, R. E. (see Cooper, H. H., Jr.) Henry, H. R. (see Cooper, H. H., Jr.) Klein, Howard (also see Sherwood, C. B.)
1957 Interim report on salt-water encroachment in Dade County, Florida: Florida Geol. Survey Inf. Circ. 9. Kohout, F. A. (also see Cooper, H. H., Jr.)
1960 Flow pattern of fresh water and salt water in the Biscayne
aquifer of the Miami area, Florida: Internat. Assoc. Sci. Hydro.,
no. 52.
1961 A case history of salt-water encroachment caused by a storm
sewer in the Miami area, Florida: Am. Water Works Assoc.
Jour., v. 53, no. 11.
1964 (and Leach, S. D.) Salt-water movement caused by control-dam
operation in the Snake Creek Canal, Miami, Florida: Florida
Geol. Survey Rept. of Inv. 24, pt. 4.




36 FLORIDA GEOLOGICAL SURVEY
Leach, S. D. (also see Kohout, F. A.)
1963 (and Sherwood, C. B.) Hydrologic studies in the Snake Creek
Canal area, Dade County, Florida: Florida Geol. Survey Rept. of
Inv. 24, pt. 3.
Parker, G. G.
1955 (and others) Water resources of southeastern Florida; with
special reference to the geology and ground water of the Miami
area: U.S. Geol. Survey Water-Supply Paper 1255. Sherwood, C. B.
1962 (and Leach, S. D.) Hydrologic studies in the Snapper Creek Canal area, Dade County, Florida: Florida Geol. Survey Rept. of
Inv. 24, pt. 2.
1963 (and Klein, Howard) Surface and ground-water relation in a
highly permeable environment: Internat. Assoc. Sci. Hydro.,
no. 63.