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Interim report on salt-water encroachment in Dade County, Florida ( FGS: Information circular 9 )
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 Material Information
Title: Interim report on salt-water encroachment in Dade County, Florida ( FGS: Information circular 9 )
Series Title: ( FGS: Information circular 9 )
Uncontrolled: Salt-water encroachment in Dade County, Florida
Physical Description: 17 p. : maps, diagrs. ; 23 cm.
Language: English
Creator: Klein, Howard
Publisher: s.n.
Place of Publication: Tallahassee
Publication Date: 1957
 Subjects
Subjects / Keywords: Groundwater -- Florida -- Miami-Dade County   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
General Note: "Prepared by U. S. Geological Survey in cooperation with Dade County, the cities of Miami and Miami Beach, the Central and Southern Florida Flood Control District, and the Florida Geological Survey."
Funding: Digitized as a collaborative project with the Florida Geological Survey, Florida Department of Environmental Protection.
 Record Information
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management:
The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.
Resource Identifier: aleph - 001692732
oclc - 01744734
notis - AJA4806
lccn - a 57009579
System ID: UF00001069:00001

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Table of Contents
    Title Page
        Title Page
    List of Illustrations
        List of Illustrations
    Salt-water encroachment in Dade County, Florida, by Howard Klein
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Copyright
            Copyright
Full Text




STATE OF FLORIDA
STATE BOARD OF CONSERVATION
Ernest Mitts, Director

FLORIDA GEOLOGICAL SURVEY
Herman Gunter, Director



INFORMATION CIRCULAR NO. 9




INTERIM REPORT

ON

SALT-WATER ENCROACHMENT

IN


DADE COUNTY, FLORIDA



By

HOWARD KLEIN


PREPARED BY U. S. GEOLOGICAL SURVEY
IN COOPERATION WITH DADE COUNTY, THE CITIES OF MIAMI
AND MIAMI BEACH, THE CENTRAL AND SOUTHERN FLORIDA
FLOOD CONTROL DISTRICT, AND THE FLORIDA GEOLOGICAL SURVEY







Tallahassee, Florida
1957





ILLUSTRATIONS


Figure Page
1. Maps showing progressive salt-water
encroachment in the Miami area,
1904-53. . ... . . ... 3
2. Map of Dade County showing approximate
position of the 1, 000-ppm isochlor 4
3. Contour map showing the altitude of the
water table in the Silver Bluff area,
June 17, 1954 . . .. . 6
4. Contour map showing the altitude of the
water table in the Silver Bluff area,
November 29, 1955 . ..... 7
5. Contour map showing the depth of the
1, 000-ppm isochlor surface in the
Silver Bluff area, July 20, 1953 . 8
6. Contour map showing the depth of the
1, 000-ppm isochlor surface in the
Silver Bluff area, April 4, 196. . 9
7. Graph showing fluctuations of chloride
content in the open-hole part of well
F-198, compared with water-level
fluctuations. ................. 11
8. Graph showing fluctuations of chloride
content in the open-hole part of well
G-519A, compared with water-level
fluctuations. . . .. . .12
9. Graph showing fluctuations of chloride
content in the open-hole part of well
F-160, compared with water-level
fluctuations. . . . . 13
10. Graph showing fluctuations of chloride
content in the open-hole part of well
F-202, compared with water-level
fluctuations. . . .. . 14
11. Diagrammatic cross section of coastal
area, showing theoretical positions of
the fresh-water salt-water interface 15
12. .Contour map showing the average altitude
of the water table in Dade County,
1940-50. ............. . 17








SALT-WATER ENCROACHMENT IN


DADE COUNTY, FLORIDA

By

HOWARD KLEIN


Recently there has been much activity in reclaiming the
low-lying coastal areas of Dade County for residential use,
by the addition of fill. The fill is obtained by digging canals
both normal to and parallel to Biscayne Bay. The canals
serve the additional purpose of providing an access to the
Bay for boats. A problem needing to be considered is the
effect that these canals will have on the ground-water re-
sources. It is expected that the canals will have little effect
on ground water in parts of the county distant from the coast,
but their effect in coastal areas is a matter of concern. In
order to predict what, may happen in the vicinity of these
new canals if they are not equipped with adequate control
structures, it is instructive to review what has happened in
the vicinity of similar canals in the past.

The U. S. Geological Survey, in cooperation with Dade
County, the cities of Miami and Miami Beach, the Central
and Southern Florida Flood Control District, and the Florida
Geological Survey has collected water-level and salinity
data on wells and canals in Dade County since 1939. Some
of the agencies named, and others, collected similar data
before 1939. Analysis of all the data shows that sea water
in the Atlantic Ocean and Biscayne Bayis the sole source of
salt-water contamination in the Biscayne aquifer of the Dade
County area.

According to the Ghyben-Herzberg principle, a head of
fresh water one foot above mean sea level indicates that fresh
water extends to a depth of about 40 feet below mean, sea
level. Present studies in the Miami area indicate that this
principle is valid but is modified (greatly in certain areas)
by field conditions, particularly the movement of.ground
water.





FLORIDA GEOLOGICAL SURVEY


A report byParker and others 1/ presents a fairly com-


1/ Parker, G. G., Ferguson, G. E., Love, S. K., and
others, 1955, Water resources of southeastern Florida: U.S.
Geol. Survey Water-Supply Paper 1255.


plete history of salt-water encroachment in the Miami area.
Figure 1, adapted from figure 169 of that report, shows
successive stages of salt-water encroachment in the Miami
area from 1904 through 1953. The stippled areas in the
figure represent the zones in which wells 80 to 100 feet deep
would have tapped ground water having a chloride concen-
tration of 1,000 ppm (parts per million) or more. Figure 2
shows the extent of salt-water encroachment in Dade County
in 1951.

Uncontrolled or inadequately controlled tidal canals have
been the chief cause of salt-water contamination in the Bis-
cayne aquifer, the principal aquifer of southeastern Florida.
Such canals cause salt-water encroachment in two ways:

1. They drain off fresh ground water, thereby reducing
the fresh-water head that opposes the inland movement of
salt water; and,

2. They provide a path for sea water to move readily
inland during dry periods. A tongue of salty ground water
extends several miles inland along each principal tidal canal.

A comparison of the maps in figure 1 shows that the
greatest inland movement of salt water occurred between
1943 and 1946, as a result of the severe drought during 1944
and 1945. Much of the aquifer near the Miami, Little River,
and Biscayne canals, and also a large part of the aquifer
underlying Coral Gables, became contaminated. The map
for 1950 indicates the effectiveness of temporary control
structures in the several canals in retarding overdrainage
of ground water from storage and in retarding inland move-
ment of salt water in open canals. In the vicinities of Bis-
cayne, Little River, and Miami canals, the salt-water front























$arARCH e A ANO ItSC.a r Ce NL ARCmH /Ar Arf A "a'I 'm AH A
cn'n'err eCRI. .i Cl



*rr f R IVE .a."r R. ER .



.7..- A I.. .. DT >
*araI v.A va
0

.!,,98, 5 I~, ,J .I .
aov 0 I MAAVE.E D R -I- TM Al A















Figure 1. Maps showing progressive salt-water encroachment in the Miami area,
OM AV. 9 4-5) 41 Q













198 04-53. -








C i
4 B 4

1 p / I 4 r P






FLORIDA GEOLOGICAL SURVEY


BROWARD COUNTY


- I










I-

I-




rFcOat. C,,.

r- - -


a I SI "i *iL i ,


MAP OF
DADE COUNTY
SHOWING
4APPoximArg POSITION
OP t.O00-PPM ISIOCHLO
1991
U.S OLOLOGICAL SURVEY MIAMI, .LA


Figure 2.


Map of Dade County showing approximate

position of the 1, 000-ppm isochlor.





INFORMATION CIRCULAR NO. 9


retreated seaward approximately to the control structures,
but along the Coral Gables and Tamiami canals it migrated
farther inland, almost to Red Road. The continued en-
croachment in the vicinities of the Coral Gables and Tamiami
canals canbe attributedto the fact that the control structures
were placed too far upstream to be effective in retarding the
inland movement of salt water.
/
One of the most intensively studied areas in Dade County
is the Silver Bluff area, where Garald G. Parker, during
early years of the cooperative study, and Nevin D. -Hoy and
Francis A. Kohout, in recent years, have correlated the
movements of salt water with ground-water levels. An
opportunityto expandthese studies came in August 1954 when
the State Road Department began excavation of an open-trench
storm sewer beneath 27th Avenue. This excavation, in re-
ality, was an uncontrolled tidal drainage ditch, because the
altitude of its bottom ranged from three feet below mean sea
level at the Bay to sea level at a distance of about 9, 000 feet
from the outlet. On June 17, 1954, prior to the ditching
operations, measurements of water levels were made in
various wells in the Silver Bluff area and these were used
to draw the water-level contours in figure 3. On November
29, 1955, something like a year after the completion of the
ditching operations, the water levels in the wells were meas -
ured again, and these measurements were used to draw the
water-level contours in figure 4. The most prominent change
in the patterns shown by figures 3 and 4 is the realignment
of the contours along 27th Avenue. This realignment indi-
cates that ground water drains continuously into the storm
sewer and thence to Biscayne Bay. Figure 4 shows that by
November 1955 the effects of this drainage had extended over
a considerable area on both sides of 27th Avenue and to a
point north of 16th Street.

In addition to the water-level measurements, water
samples from many wells in the Silver Bluff area were
analyzed for chloride content. Figure 5 is a contour map
of the surface below which the chloride content exceeded
1, 000 ppm on July 20, 1953, prior to the excavation of the
t-ench. This is to be compared with figure 6, a contour
map of this surface on April 4, 1956. In the 1956 map the
contours curve northward along 27th Avenue, indicating that





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area, June 17, 1954.
Figure 3. Contour map showing the altitude of the water table in the Silver Bluff
area, June 17, 1954.


































Figure 4. Contour map showing the altitude of the water table in the Silver Bluff
area, November 29, 1955.































Figure 5.


Contour map showing the depth of the 1, 000-ppm isochlor surface in the
Silver Bluff area, July 20, 1953.


































Figure 6. Contour map showing the depth of the 1, 000-ppm isochlor surface in the
Silver Bluff area, April 4, 1956.





FLORIDA GEOLOGICAL SURVEY


the chloride content in the ground water in that area had in-
creased as a result of the drainage of ground water. How-
ever, the encroachment had occurred only in a relatively
narrow area parallel to the trench.

Figures 7 to 10 show the water level and the chloride
content of the water in wells in the immediate vicinity of
27th Avenue. The graphs show that the chloride content
decreases when the water level is high and increases when
the water levels low. The increase in chloride content that
began in December 1954 can be attributed chiefly to the
lowering of the water table as a result of the drainage of
ground water into the trench and out to the Bay.

As shown in figure 2, salt-water encroachment has
occurred throughout coastal Dade County and farther inland
along tidal canals. This does not mean, however, that fresh
water is not available in these areas. Moderate quantities
of fresh water can be obtained at shallow depths throughout
the area affected by encroachment, except in areas immedi-
ately adjacent to the Bay or tidal canals and in low-lying
coastal marshes that are periodically covered bytidal water.

Data on the salinity of water in wells in the coastal areas
indicate that the interface between the fresh water and salt
water moves fairly rapidly in response to changes in ground-
water levels. Figure 11-A shows, in profile, the position
that the interface would assume according to the Ghyben-
Herzberg principle. It rises and moves inland whenever the
water table is low, and falls and moves seaward when the
water table is high. Also shown in figure 11-A are two
supply wells, each of which will yield fresh water under the
stated conditions.

Figure 11-B assumes the same conditions as those in
figure 11-A, except that a network of uncontrolled tidal
canals has been added. The position of the interface in the
immediate area of the canals is shown to have shifted inland
by a distance approximately equal to the maximum inland
extension of the canals. As a result of this shift, well 1
would yield salty water at all times and well 2 would do so
during low-water conditions.



















1953 1954 1955
Jan Feb Mar Apr May June Jly Aug Sep Oct No Dec Jam Feb Mar Apr May Ame July Aug Sep Oct No0 D e Jan F~ Mar Apr May J.me July Aug Sep Oct Nov Dec
100 102 0 1020 10 0 100 10 20 1020 1020 1020 10 0 1020 1020 100 1030 1Z 20 1020 10P 20 1020 10 0 1020 10 20 lo 1020 1020 1020 10 1020 o 100 1020 o10 0 iol10a 10o2 10o0


COLLECTED AT -54.3' MS


IIIl!


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1953


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Figure 7.


Graph showing fluctuations of chloride content in the open-hole part of

well F-198, compared with water-level fluctuations.


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Figure 8. Graph showing fluctuations of chloride content in the open-hole part of
well G-519A, compared with water-level fluctuations.


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Figure 9.


Graph showing fluctuations of chloride content in the open-hole part of

well F-160, compared with water-level fluctuations.


100,000


10.001


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a. sep Oct nO DKe J3, De Mar Ap Ar y Jam jS Au Sep Oct MB Dc J3m Feb M1W Apr May
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Figure 10. Graph showing fluctuations of chloride content in the open-hole part of
well F-202, compared with water-level fluctuations.


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INFORMATION CIRCULAR NO. 9


Figure 11. Diagrammatic cross section of coastal
area, showing theoretical positions.of the
fresh-water salt-water interface.





FLORIDA GEOLOGICAL SURVEY


Where a series of closely spaced, uncontrolled tidal
canals has been excavated, the ultimate position of the inter-
face would be nearly the same as if an arm of Biscayne Bay
extended as far inland as the canals. A network of canals,
all connected with the Bay, would cause salt water to move
inland over a broad front. The intercanal areas might be
underlain to shallow depth by freshwater, but during droughts
some or all of the wells in these areas would yield salty
water.

The sole source of fresh ground water in the Biscayne
aquife- is the rainfall in the area. However, only a part of
the water that falls as rain becomes ground water. Much of
it runs off or is evaporated and transpired before it reaches
the water table. Of that which reaches the water table some
is also evaporated and transpired, and the rest flows into
Biscayne Bay and the tidal canals or is pumped from wells.
Obviously, if a series of uncontrolled tidal canals were dug
to the bay, the rate of ground-water outflow would increase,
and the water table would fall. A lowering of the water table
along the coast will inevitablybe accompanied by an advance
of the salt-water interface.

Figure 2 indicates that there has been little encroach-
ment in the vicinity of Cutler (south of Snapper Creek), near
the center of a coastal reach that has not yet been dissected
by canals. The reason that the salt water has not moved
inland is probably that the water table is high locally (fig. 12).
The nearest drainage canal (Snapper Creek) has little effect
on ground-water levels in the Cutler area.

In summary, it is to be stressed that one of the chief
causes of the encroachment of salt water in the underlying
rocks in the Miami area is the system of uncontrolled or
inadequately controlled tidal drainage canals. It has been
shown that water-control structures, properly placed, have
retarded encroachment and, in some places, have caused
the salt water to retreat seaward. In some canals, however,
the controls have been placed too far upstream to be effective
in retarding or preventing encroachment. The effects of un-
controlled tidal canals between Biscayne Bay and the coastal
ridge would be the same as if arms of the Bay extended to
the ridge; the salty ground water would occur farther inland
over a broad front.







INFORMATION CIRCULAR NO. 9


BROWARD COUNTY


SCALI IN MILES
0 It. 4 7 8. ,


Figure 12. Contour map showingthe average altitude

of the water table in Dade County, 1940-50.










FLRD GEOLOSk ( IC SUfRiW


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