Title Page
        Page i
        Page ii
    Letter of transmittal
        Page iii
        Page iv
    Table of Contents
        Page v
    List of Illustrations
        Page vi
    List of Tables
        Page vii
        Page viii
    Abstract and introduction
        Page 1
        Page 2
        Page 3
        Page 4
    Hydrologic setting
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
    East Glades salinity studies
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
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        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
    Sea-water intrusion and saline soils
        Page 34
        Page 35
    Alternatives
        Page 36
    Summary
        Page 37
    References
        Page 38
        Page 39
    Copyright
        Copyright

STATE OF FLORIDA
DEPARTMENT OF NATURAL RESOURCES
Randolph Hodges, Executive Director



DIVISION OF INTERIOR RESOURCES
Robert O. Vernon, Director



BUREAU OF GEOLOGY
Charles W. Hendry, Jr., Chief





Report of Investigation No. 66



SALINITY STUDIES IN EAST GLADES AGRICULTURAL AREA

SOUTHEASTERN DADE COUNTY, FLORIDA



By
J. E. Hull and F. W. Meyer


Prepared by the
U.S. GEOLOGICAL SURVEY
in cooperation with
CENTRAL AND SOUTHERN FLORIDA FLOOD CONTROL DISTRICT
and the
BUREAU OF GEOLOGY
FLORIDA DEPARTMENT OF NATURAL RESOURCES

Tallahassee, Florida

1973







DEPARTMENT
OF
NATURAL RESOURCES



REUBIN O'D. ASKEW
Governor


RICHARD (DICK) STONE
Secretly of State




THOMAS D. O'MALLEY
Treasurer




FLOYD T. CHRISTIAN
Commissioner of Education


ROBERT L. SHEVIN
Attorney Generrl




FRED O. DICKINSON, JR.
Comptroller




DOYLE CONNER
Commissioner of Agriculture


W. RANDOLPH HODGES
Executive Director






LETTER OF TRANSMITTAL


Bureau of Geology
Tallahassee
September 24, 1973


Honorable Reubin O'D. Askew, Chairman
Department of Natural Resources
Tallahassee, Florida

Dear Governor Askew:

The Department of Natural Resources, Bureau of Geology, is publishing as its
Report of Investigation No. 66 the report entitled, "Salinity Studies in East
Glades Agricultural Area, Southeastern Dade County, Florida, by J. E. Hull
and F. W. Meyer, of the U. S. Geological Survey.

The nearly frost-free climate and rich, marly soils are ideal for raising winter
vegetables for northern markets. However, farming of some fields is periodically
prevented by salt accumulation in the soil. This report is the result of the
investigation to determine the cause of the saline soils. The results indicate there
will be no improvement in saline soil problems unless land use changes
significantly, permitting maintenance of higher water levels along the coast to
halt the inland movement of sea water.

Respectfully yours,



Charles W. Hendry, Jr., Chief
Bureau of Geology






















































Completed manuscript received
August 24, 1973
Printed for the Florida Department of Natural Resources
Bureau of Geology
by Ambrose the Printer
Jacksonville, Florida
Tallahassee
1973
iv










Abstract . . .
Introduction . .
Purpose and scope .
Previous studies . .
Acknowledgments .
Hydrologic setting .....
Climate . . .
Topography and drainage
Ground water ......
Sea-water intrusion .
Land use . . .
Soils . . .
East Glades salinity studies .


Site A East Glades Experiment Station
Description . . .
Water levels and water movement
Distribution and source of salts .
Site B Peterson Farm .........
Description . . .
Water levels and water-movement
Distribution and source of salts .
Sea-water intrusion and saline soils . .
Alternatives ................
Summary ..................


References ................... ..... ............


CONTENTS


Page
1
1
1
4
4
5
5
5
8
10
13
15
15
15
15
19
23
25
25
28
32
34
36
37


j


. . . .
.. . . .
. . . .






ILLUSTRATIONS

HFgre Page
1. Map of Dade County showing locations of East Glades Agricultural Area
and study area ............................... 2

2. Map of study area showing locations of special study sites, data-collection
points, topography, and the positions of the 1970 and 1971 salt fronts 3

3. Graphs of monthly rainfall and temperature, July 1970 June 1971 .. 6

4. Map of Dade County showing contours on the average water table, 1959 -
1971 . . . . . . . . . 9

5. Hydrograph for well G-1183 at Homestead Air Force Base, 1961 72 10

6. Water-table map of study area, April 14-15, 1971 . . .... 11

7. Map of Dade County showing the approximate position of the 1,000
milligrams per liter chloride line at the base of the Biscayne aquifer, 1946
and 1971 .................................. 12

8 Chloride content in water from well S-529 at Site A, 1945 72 . 13

9. Map showing land use in southeastern Dade County, February 1971 14

I1. Soils map of study area ................... ..... ... 16

11. Map of site A showing locations of data-collection points and topography 17

12. Graphs of water levels in Canal 103 in Biscayne Bay, and in well G-1515;
and local rainfall; July 1970 -June 1971 . . . ... 20

13. Generalized cross section A-A' through site A showing water movement
and chloride content ................... ......... 22

14. Graphs of chloride content in soils at site A, in Canal 103 at SW 117
Avenue and above S-20F, July 1070- June 1971; and chloride content in
water from selected depths in well G-1515, January June 1971 . 23

15. Graphs of chloride content in ground water in wells G-1514 through
G-1517 at selected depths, April 15, 1971 . . . ..... 24

16. Map of site B showing locations of data-collection points and topography 26

17. Graphs of water levels in Canal 102 above S-21A, in Biscayne Bay, and in
well G-1506; and local rainfall, July 1970 June 1971 . .... 29
18 Generalized cross section B-B' through site B showing water movement and
chloride content ......... ................... 31
vl








Figure
19.


ILLUSTRATIONS continued


Graphs of chloride content in soil at site B, in Canal 102 at SW 107th
Avenue and above S-21A, July 1970-June 1971; and chloride content in
well G-1506 at selected depths, January -June 1971 . . .


20. Graphs of chloride content in ground water in wells G-1505 through
G-1508 at selected depths, May 18, 1971 . . . . .








TABLES


Table


Page


Page


1. Record of wells at Site A ............................ 18

2. Record of wells at site B ................... ....... 27







SALINITY STUDIES IN EAST GLADES
AGRICULTURAL AREA, SOUTHEASTERN
DADE COUNTY, FLORIDA


By
J. E. Hull and F. W. Meyer


ABSTRACT

Saline soils in the East Glades Agricultural Area are caused chiefly by
brackish ground water moving upward from the water table during dry periods.
Brackish ground water is caused by infiltration of salt water from nearby
coast-normal canals and by inland movement of salt water through the deep
parts of the Biscayne aquifer during droughts. The soils most prone to salt
accumulation generally occur within the area affected by sea-water intrusion.
The outlook for the East Glades is for no improvement in saline soil problems
unless land use changes significantly, permitting maintenance of higher water
levels along the coast to halt the inland movement of sea water.

INTRODUCTION

The East Glades Agricultural Area, located east of Homestead in
southeastern Dade County (fig. 1), is part of the nation's "winter breadbasket."
The nearly frost-free climate and rich marly soil are ideal for raising winter
vegetables for northern markets. Studies by the U. S. Geological Survey and the
U. S. Department of Agriculture indicate that part of the East Glades is
underlain by salty ground water, and that farming of some fields is periodically
prevented by salt accumulations in the soil. Local agriculturalists believe that the
saline soil problem might be related to operations of salinity controls at the
mouths of major canals that cross the area.

In July 1970, the C&SFFCD (Central and Southern Florida Flood Control
District) which is the agency responsible for regional water management,
requested the U. S. Geological Survey to conduct an investigation to determine
the cause of the saline soils.

PURPOSE AND SCOPE

The purposes of this investigation were to determine the source of salts in
the soil and the process by which the salts accumulate. Data collected by Dr. J.
D. Dalton of the Dade County Agricultural Extension Office indicates that
repeated crop failures occur in the area east of Homestead due to saline soils.






BUREAU OF GEOLOGY


Figure 1. Dade County showing locations of East Glades Agricultural Area
and study area.
After discussions with Dr. Dalton and U. S. Department of Agriculture
personnel, it was decided that the investigation be centered in a 20-square mile
area near the Homestead Air Force Base and that two affected areas (sites A and
B on fig. 2) would be studied intensively. Site A, a 20-acre plot known locally as
the East Glades Experiment Station, is about 1 mile southeast of the base; and
site B, an 80-acre plot known locally as the Peterson Farm, is 0.25 mile
northeast of the base.

Observation wells and piezometers were drilled to depths ranging from 1
to about 60 feet, in order to periodically collect data concerning water-levels and









REPORT OF INVESTIGATIONS NO. 66


salinities at different depths in the soil and in the underlying Biscayne aquifer.
Water-level and salinity data were also collected in nearby canals and ditches.


1971 -1970
INLAND EXTENT OF SALT-WATER INTRUSION
AT BASE OF BISCAYNE AQUIFER 1000
MILLIGRAMS PER LITER

STUDY SITES

MANGROVE
LOCATION OF CROSS SECTION


EXPLANATION G-Il
WELL AND NUMBER
SOIL SAMPLING SITE
A
CANAL SAMPLING SITE

RAIN GAGE

CONTOUR INTERVAL I FOOT
DATUM IS MEAN SEA LEVEL


Figure 2. Study area showing locations of special study sites, data-collection

points, topography, and the positions of the 1970 and 1971 salt
fronts.







BUREAU OF GEOLOGY


PREVIOUS STUDIES

During the drought years 1943-45, the U. S. Geological Survey
investigated extensive salt contamination in canals east of Homestead. Parker,
Ferguson, Love and others (1955, p. 679-682) reported salt contamination of
crop land due to intrusion of sea water from nearby east-west canals. In 1945,
they found that sea water had moved inland in both controlled and uncontrolled
canals. Chloride concentration (which is commonly used as an indicator of
sea-water intrusion) in some canals was higher than in normal sea water. Because
of high evapotranspiration rates in the agricultural area, they concluded that the
salty canal water seeped laterally from the canals into the porous limestone and
contaminated the underlying ground water in nearby fields. They also presented
a map of eastern Dade County showing the inland extent of sea-water intrusion
in 1946 (1955, fig. 200). Since then the U. S. Geological Survey has mapped the
approximate position of the salt front for 1951 (Klein, 1957, fig. 2), 1961
(Kohout, 1964, fig. 1), 1968 (Hull, 1970, fig. 35), 1969 (Hull, 1971, fig. 39),
and 1970 (Hull, 1972, fig. 38).

The sea-water intrusion maps cited above indicate that the east half of the
East Glades Agricultural Area is underlain by ground water whose chloride
content is more than 1,000 mg/1 (milligrams per liter) at depths ranging from a
few feet near the coast to about 70 feet about 3 miles inland.

During 1967-69, E. H. Stewart and R. R. Alberts, of the U. S. Agricultural
Research Service, studied the occurrence of saline soils at the East Glades
Experiment Station (site A) in cooperation with the University of Florida
Tropical Experiment Station and the Florida Agricultural Extension Service.
Data concerning grain-size of soils, hydraulic conductivity, soil depth,
ground-water levels, rainfall, leaching tests, and the distribution of chloride in
the soil, were presented in the 1967-69 annual reports by the Plantation Field
Laboratory, Fort Lauderdale, Florida. Data concerning the effects of crop
density and water-table depth on evapotranspiration rates were reported by E.
H. Stewart and W. C. Mills (1967).

ACKNOWLEDGMENTS

This report was prepared by the U. S. Geological Survey as part of the
cooperative water resources program with the Central and Southern Florida
Flood Control District.

The authors thank the following people for providing data and assistance
during the investigation: Mr. William V. Storch, Chief Engineer of the Central
and Southern Florida Flood Control District; Dr. J. D. Dalton of the Florida







REPORT OF INVESTIGATIONS NO. 66


Agricultural Extension Service; Messrs. E. H. Stewart and R. R. Alberts of the U.
S. Agricultural Research Service; and Dr. P. G. Orth of the Florida Agricultural
Experiment Station.

HYDROLOGIC SETTING

CLIMATE

The climate of the East Glades Agricultural Area is humid sub-tropical.
The average annual temperature at the Homestead Experiment Station 3 miles
north of Homestead is 73.70F; and the average annual rainfall is 64.69 inches.
Rainfall is usually greatest during June through November and least from
December through May.

During the investigation (July 1970 June 1971) the average temperature
was 73.30F., a departure of 0.4F. below normal. The coldest months, January
and February, averaged about 660F. with 1 day below freezing (fig. 3). The total
rainfall was 32.95 inches, a departure of 31.74 inches below normal. Rainfall
was greatest from July through October 1970 and May through June 1971, and
least from November 1970 through April 1971. Because the investigation was
conducted during one of the most severe droughts in south Florida's history, the
soil salinities probably were above normal.

TOPOGRAPHY AND DRAINAGE

Land surface slopes gently southeastward from the Homestead Air Force
Base toward the shore of Biscayne Bay (fig.2). The elevation of the land along
Tallahassee Road, on the west side of the area is generally less than 5 feet above
msl (mean sea level of 1929), except for the area within Homestead Air Force
Base which is partly filled. East of the base, the land is generally less than 3 feet
above msl. The actual shoreline of Biscayne Bay probably lies slightly west of a
band of mangrove trees shown on figure 2. The crest of Levee 31E, which was
constructed in 1966 to prevent tidal flooding, is about 8 feet above msl. Because
of the low elevation and marly soil, the East Glades is subject to flooding during
the wet periods. Tidal flooding occurs infrequently when hurricane driven tides
top the levee. For example, a hurricane flood tide at the Homestead Bay Front
Park tide gage (see location on figure 2) on September 8, 1965 reached a height
of 9.82 feet above msl.

Drainage canals and ditches were excavated through a bed of marl, ranging
from about 1 to 6 feet in thickness, into the permeable Miami Oolite, the upper
unit of the Biscayne aquifer. Water levels in the ditches and canals compare
closely with nearby ground-water levels.









BUREAU OF GEOLOGY


15






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1970 1971


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Figure 3. Monthly rainfall and temperature, July 1970 June 1971.








REPORT OF INVESTIGATIONS NO. 66


Most of the area shown in figure 2 is drained by Canal 102, Military Canal,
and Canal 103. Canal 102 connects the inland drainage system, which consists of
Canal 111 and Levee 31N Borrow Canal with the coast (fig. 1) and water levels
are controlled by strategically placed gated structures designed to hold
increasingly higher water levels inland from the coast. Locally, the Levee 31E
Borrow Canal receives drainage from the ditched area northeast of the base
between Military Canal and Canal 102, and empties into Canal 102 just upstream
of salinity control structure S-21A.

Military Canal drains only the Homestead Air Force Base, and water levels
there are controlled by salinity control structure S-20G. The Levee 31E Borrow
Canal is separated from Military Canal by earthen plugs.

Canal 103 (Mowry Canal) drains the area south and east of the base. The
canal also connects the inland drainage system (Canal 111) with the coast, and
water levels there are controlled by strategically placed gated structures designed
to hold higher water levels inland from the coast. Locally, the Levee 31 E Borrow
Canal receives drainage from Florida City Canal, North Canal, and the ditched
area southeast of the base and empties it into Canal 103 just upstream of salinity
control structure S-20F.

Before Canals 102 and 103 were constructed by the C&SFFCD in the mid
1960's, water levels in the East Glades area were controlled by high-capacity
low-lift pumps above dams in Florida City Canal, North Canal, Military Canal,
Mowry Canal, and Goulds Canal.

Salinity controls S-21A and S-20F near the bay in Canals 102 and 103 (fig.
2) are operated by the C&SFFCD to provide drainage for the agricultural area
and to abate sea-water intrusion. The operational range of the controls varies
with the growing season. Usually the controls are set low (average 1.2 feet above
msl) from November 15 to January 15 (the beginning of the winter growing
season); and the controls are set high (average 2.0 feet above msl) during the
remainder of the year. Unfortunately, certain crops, such as potatoes, require
low water levels from November through April, which nearly corresponds to the
annual dry season, November through May, when fresh-water levels should be
held high. As a result the control settings are frequently changed during
January April in an attempt to accommodate the needs of a particular crop and
to conserve fresh water at the same time. This procedure often results in
insufficient fresh-water head above the controls to prevent sea-water intrusion
during the latter part of the dry season.

At this point it is important to distinguish between msl (mean sea level)
and present day sea, or bay level. Mean sea level is a datum based on mean sea







BUREAU OF GEOLOGY


level of 1929 and it is used for determining relative elevations for surveys. Since
1929, mean sea level has risen at a rate of about 0.01 foot per year so that
present day mean sea level averages about 0.3 foot above msl (Schneider, 1969,
p. 13).
GROUND WATER
The Biscayne aquifer (Parker, 1955, and Schroeder and others, 1958) is the
sole source of fresh ground water in the East Glades Agricultural Area. The
aquifer, or ground-water reservoir, is composed chiefly of highly permeable
lmestone and locally underlies a thin bed of marl to a depth of about 60 feet
below msl. The ground water is obtained from local rainfall and from rainfall on
topographically higher areas to the west. The water table rises chiefly in response
to infiltrating rainfall and declines in response to evapotranspiration and seepage
losses.

Ground water moves generally southeastward (down gradient) across the
East Glades Agricultural Area, as shown by the configuration of the water table
contours in figure 4. The average position of the water table during 1959-71
ranged from about 2.8 feet above msl along the west side of the area to about a
foot above msl on the east side.

The average yearly highest water level during 1959-71 was about 5.5 feet
above msl along the west side of the area and about 3 feet above msl along the
east side; and the average yearly lowest water level was about 1 foot above msl
along the west side and slightly below msl along the east side.

Generally the water table is less than 3 feet below land surface. The
capacity to store additional ground water in the East Glades is therefore
relatively small and heavy rains often cause the water table to rise above land
surface inundating the area. Rapid drainage of the area is achieved, however, by
a network of ditches and canals which discharge into Biscayne Bay.

Because of the shallow water table the evapotranspiration loss is high. The
water table, in the southeast part of the East Glades, as shown by the
hydrograph for well G-1183 (fig. 5) often declines below bay level during the
dry season due to high evapotranspiration and to inadequate recharge from
rainfall and the canals. During April and May 1971, water levels in the south half
of the East Glades area declined below bay level and an extensive water-level
depression developed in the area south of Canal 102. The contour pattern in the
study area for April 14-15 (fig. 6), shows that fresh water was moving south
toward the center of the depression, and that salt water was moving westward
toward the center from Biscayne Bay. Within the large water-level depression are
three smaller depressions, which indicate locally higher ground-water loss; and a
ground-water mound which indicates recharge.








REPORT OF INVESTIGATIONS NO. 66


The water-level depressions near sites A and B (as shown by the
minus 0.3-foot contours) are a result of evapotianspiration; and the cone of
depression within Homestead Air Force Base, as shown by the minus 0.1-foot
contour, is a result of well-field pumpage. The ground water mound about
Military Canal is a result of infiltration of effluent from the base sewage
treatment plant.


800 05


Figure 4. Dade County showing contours on the average water table, 1959-71.












8


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LJ
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LJ
Ln 4
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2

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BUREAU OF GEOLOGY


1960


70 1972


FiSge 5. Hydrograph for well G-1183 at Homestead Air Force Base, 1961-72.


SEA-WATER INTRUSION


The salinity of water in the East Glades Agricultural Area varies seasonally.
During the wet season, water levels are usually higher in the interior and fresh
water moves generally eastward through the canals and aquifer to flush salts
toward Biscayne Bay. During the dry season, water levels in the interior are
usually low and fresh-water flow to the coast is generally insufficient to sustain
coastal water levels high enough to prevent inland movement of sea water into
both the canals and aquifer.


Sea-water intrusion is commonly detected by high chloride concentration
in the water. Chloride concentrations in fresh ground water or surface water are
generally less than 20 mg/l. The concentration of chloride in water in Biscayne
Bay averages about 20,000 mg/l.

During the 1943-45 drought, sea water had moved inland through
controlled and uncontrolled coastal canals almost to Homestead and, in some
cases, the chloride content in water in the canals exceeded that in normal sea
water by 30 percent (Parker, 1955, p. 679-682, fig. 188). Analyses of water
from test wells about 3 miles southeast of Homestead indicated in 1941 that
round water at depts of 70 feet contained more than 20 mg/1 of chloride.


I I I I II
















AVERAGE BAY
LEVEL


| | i J i ] i I I i i I







REPORT OF INVESTIGATIONS NO. 66 11
80025' 22'30" 80020'
25 32 3d i
Coconut J Polm Drive CUL A i.


/ v ... J1 ,

00 y Ur ve 1
0-. .,0
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30. .

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2527 30d-



EXPLANATION
0.2
WATER-LEVEL CONTOUR STUDY SITES A AND B
MEASURED APRIL 14-15, 1971
CONTOUR INTERVAL 0.1 FOOT
DATUM IS MEAN SEA LEVEL DIRECTION OF GROUND-WATER FLOW
Figure 6. Water-table map of study area, April 14-15, 1971.




In December 1946, G. G. Parker, R. H. Brown, D. B. Bogart, and S. K.
Love, of the U. S. Geological Survey, mapped the approximate inland extent of
the 1,000 mg/1 chloride line (salt front) at the base of the Biscayne aquifer in
eastern Dade County (p. 709). From 1946 to 1971 the salt front moved only
slightly farther inland beneath the East Glades area (fig. 7). The greatest inland
movement occurred south of Canal 102 in the vicinity of Homestead Air Force
Base in 1971 as a result of drought conditions and wellfield pumpage. Data are
insufficient to determine the position of the salt front prior to development and
drainage, but the low altitude of the area and close proximity to the bay suggest
that the salt front was inland from the coastline before any of the area was
drained.







BUREAU OF GEOLOGY


Variations in chloride content in water from well S-529 at site A during
1945-72 (fig. 8) indicate the advance and retreat of the salt front. Inland
movement is indicated by increasing chloride content and bayward movement
by decreasing chloride content. Inland movement was caused chiefly by the
droughts of 1943-45, 1956-57, and 1970-71 and by tidal inundation from severe
hurricanes in 1946 and 1965. Bayward movement was caused chiefly by heavy
rains and associated high water levels during 1947-48, 1958-60, and 1968-69.


Figure 7. Dade County showing the approximate position of the 1,000
milligrams per liter chloride line at the base of the Biscayneaquifer,
1946 and 1971.








REPORT OF INVESTIGATIONS NO. 66


3000
or
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SITE A
SAMPLING DEPTH 19 FEET








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345 1950


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1955 1960 1965 1970 1972


Figure 8. Chloride content in water from well S-529 at site A, 1945 72.

During 1965-67, Levee 31E was constructed to protect the East Glades
area from hurricane tides; and water-control facilities were constructed to
improve drainage. Prior to construction of these works the chloride
concentration in water from well S-529 decreased at a relatively rapid rate
following heavy rains. Only slight reductions in chloride content have occurred
under similar conditions since completion in 1967. The apparent reduction in
flushing capability is believed by the authors to be related to the reduction in
peak water levels which formerly provided the necessary fresh-water head to
move the salt front toward Biscayne Bay.

Studies by Klein (1957) and Kohout (1964) in canals north of East Glades
suggest that water levels upstream from salinity controls should be maintained at
least 2 feet higher than present sea level, or about 2.3 feet above msl, in order to
prevent sea-water intrusion. However use of this criterion would cause
inundation of a large part of the area of investigation.

LAND USE

The East Glades Agricultural Area is farmed extensively. Principal crops
are tomatoes, potatoes, snap beans, pole beans, squash, cabbage, peppers, celery,


. I I


' ' "


' "


III I








14 BUREAU OF GEOLOGY

and corn. Malanga and yucca were recently introduced to the area due to their
popularity with the growing Latin population. During early stages of
development before 1940 most of the area east of U. S. Highway 1 was cropped
except for the mangrove and tidal marsh areas along the coast. During recent
years, the Homestead Air Force Base and urban development have encroached
upon the area from the west and cropland along the coast has been abandoned
due to poor drainage, salt-water contamination, and saline soil conditions. The
current (1971) distribution of agricultural land east of U. S. Highway 1 is shown
on the land use map (fig. 9).


eo'0' 222' 30" eo'2







I. '- .... ... .i 4 _j .... . .4

..i .. .
















EXPLANATION DATA FROM NASA FLIGHT 6

a M
CULTIVATED AIR FORCE BASE
M 0
UNCULTIVATED MANGROVE AND
SALT WATER MARSH

Figure 9. Land use in southeastern Dade County, February 1971.







REPORT OF INVESTIGATIONS NO. 66


SOILS

The dominant soil in the East Glades agricultural area is the Perrine marl
(Leighty and others, 1958).It is composed chiefly of unconsolidated finely
divided calcareous sediments that are mainly of fresh-water origin. The marl
contains slightly more silt than clay. The hydraulic (saturated) conductivity of
the soil is very low and the water retentivity is high. Capillary conductivity of
the soil is high; therefore upward movement of water from the water table
occurs during dry periods. The porosity of the soil is about 50 percent.

Generally the Perrine marl has a silty loam texture and varies in thickness
from a few inches on the limestone ridge near U. S. Highway 1 and Homestead
Air Force Base to about 6 feet along the coast. The soil is alkaline and low in
organic matter, nitrogen, available phosphorus, and potassium. The lack of
mineral nutrients necessitates frequent fertilize applications. The marl occurs
chiefly in flat areas only a few feet above sea level and frequently becomes
waterlogged during the rainy season unless drained. During the dry season, the
soils often become either too friable and (or) too salty for plant growth.
Therefore, drainage irrigation, and heavy fertilized applications are required in
order to farm this soil.

The soils map of the study area (fig. 10) shows that the Perrine marl
feathers out against the limestone ridge (designated as Rockdale soils) in the
vicinity of the Homestead Air Force Base. The marl deposit is thickest in a band
parallel to the coastline.

EAST GLADES SALINITY STUDIES

SITE A EAST GLADES EXPERIMENT STATION

DESCRIPTION

Site A, locally referred to as the East Glades Experiment Station, is east of
Homestead and about 2.2 miles west of Biscayne Bay on the west side of SW
112 Avenue extended between SW 328 Street (North Canal Drive) and SW 324
Street extended (see location on figs. 2 and 11). The site is about 20 acres and it
is used extensively as an experimental farm by personnel of the Florida
Agricultural Experiment Station in Homestead.

Land surface at site A ranges in altitude from 1.4 to 2.6 feet; most of it is
above 2.0 feet. The surface is pockmarked by numerous small depressions which
are only a few tenths of a foot lower than the surrounding land. Some of the
depressions appear to be surface expressions of similar features on the








BUREAU OF GEOLOGY


2sa'd'" f I P


R / Pk R L







P. I 0" ,I pc-}^\


SHOMESTEA C
r y lR FORCE Bc '



P LhowRO CON tC C,
2 /30'\ c / R
Pc Re 1 PC \_ ,<











AFTER LIroHTY AND OTHERS, 19r

Rc ROCKDALE FINE SANDY LOAM, Pc PERRINE MARL, 2-6 FEET THICK.
LEVEL PHASE.
Ph PERRINE MARL LESS THAN I FOOT
THICK. Mb MANGROVE SWAMP
P. PERRINE MARL,.r-2 FEET THICK. [ STUDY SITES A AND B
Figure 10. Soils map of study area.



underlying limestone surface, thereby suggesting relatively recent sinkhole
development.









The Perrine marl underlies the site to a maximum depth of 3 feet. The
average thickness of the marl is about 2.5 feet and the marl feathers out to the
west against the limestone ridge near Homestead Air Base. Ditches on the north
and east side of the site convey excess water northward about one-quarter mile

to Canal 103 (Mowry Canal). Fields to the east have been abandoned for farming
due to salinity and drainage problems. Salt accumulation in the soil has been a
long-term problem at site A.
underlying limestone surface, thereby suggesting relatively recent sinkhole








REPORT OF INVESTIGATIONS NO. 66


2----;----
CONTOUR, FEET
MEAN SEA LEVEl

0
DEPRESSION

0
MOUND


SOURCE: U.S. AGRICULTICAL
EXPLANATION RESEARCH SERVICE, 1968
G-iiSi
WELLAND NUMBER
L A


DITCH AND CANAL
SAMPLING SITE
QG-1515A
PIEZOMETER AND NUMBER

SOIL SAMPLING SITE


Figure 11. Site A showing locations of data collection points and topography.








Table 1. Records of wels at dite A.


WeO Number Lattered number me for piezometes.

Water Lvel: Measured on AprI 15, 1971.

Cloride: Sample collected at bottom of weU on April 15, 1971.

Depth Caing Caing Elevation Water Level
Well (feet, (feet, Diamete Land Surface (feet Chloride
Number ml) nul) (inches) (feet, mld) mel) (mg/I) Remrks

G-1514 -58.28 2.72 6 2.72 -0.36 11,800 Continuous water-level record
G-1515 -57.45 2.54 6 2.46 -0.35 11,400 Continuous water-level record
G-1515A + 0.34 + 0.34 9 2.46 Dry Dry Continuous water-level record
G-1515B 1.11 0.61 2 2.50 -0.38 910
G-1515C -12.82 -12.32 2 2.50 -0.40 1,225
G-1515D -17.14 -16.64 2 2.50 -0.37 1,400
G-1515E 8.59 8.09 2 2.50 -0.37 920
G-1515F -22.28 -21.78 2 2.50 -0.38 1,550
G-1515G -11.38 -10.88 2 2.50 -0.38 1,125
G.1516 -55.00 2.62 6 2.38 -0.39 11,900 Continuous water-level record
G-1517 -56.05 + 1.05 6 3.05 -0.35 11,000






REPORT OF INVESTIGATIONS NO. 66


Descriptions of wells and piezometers at site A are presented in table 1.
Data on water levels, soil salinity, and water salinity were collected at the points
shown on figure 8. Most of the data were collected during January through June
1971. Rainfall data at the site were obtained from Dr. P. G. Orth of the Florida
Agricultural Experiment Station. Soil salinity data were obtained from Dr. J. D.
Dalton of the Dade County Agricultural Extension Office. Supplementary
water-level and salinity data were collected at selected points in the vicinity of
site A as shown on figure 2. Results of intensive studies of saline soils at the site
by E. H. Stewart and R. P. Albert during 1967-69 were used to help determine
cause-and-effect relationships.

WATER LEVELS AND WATER MOVEMENT

The water table at site A normally is about 0.8 foot below land surface, or
about 1.5 feet above msl. The water table rises when recharge by infiltrating
rainfall and canal water exceed losses by drainage and evapotranspiration. During
the wet season it frequently rises above land surface; and during the dry season it
often declines below bay level. The water table at site A is closely related to the
water levels in Canal 103 and other nearby canals because the hydraulic
connection between the Biscayne aquifer and the canals is good.

Semidiurnal water-table fluctuations resembling tidal fluctuations are
frequently observed during wet periods. These fluctuations are caused by the
reduction in flow when the automatic tide gates in salinity control S-20F in
Canal 103 close in response to high tides in Biscayne Bay, thereby producing a
pulse effect. Evapotranspiration during daylight hours causes a diurnal
fluctuation in the water table during dry periods.

A comparison of the water level in Canal 103 upstream from the salinity
control structure S-20F with the water level in Biscayne Bay at Homestead
Bayfront Park (fig. 12) indicates that the automatic gate control was set to hold
upstream water levels at about 1.8 feet above msl during July through October
1970. During late October the setting was lowered about one-half foot and
upstream water levels held at about 1.3 feet above msl until January 1971 when
the water level in the canal began to decline more rapidly. By February 6 the
water level fell to 0.7 foot above msl but rose sharply to 1.3 feet above msl by
February 14 due to local heavy rainfall. As a result of the rain, the automatic
gates in S-20F opened and part of the timely rainfall was discharged to the bay.
During March through mid-May the water level in Canal 103 declined due chiefly
to evapotranspiration losses in the surrounding area. By mid-March the water
level declined below bay level and the normal bayward hydraulic gradient was
reversed. As a result bay water began to seep inland around S-20F to
contaminate parts of Canal 103, the Levee 31E Borrow Canal, North Canal, and







BUREAU OF GEOLOGY


3
2
JOw O

)Z a
w-
Z 0
.a < -I
4 2-2


I 7 I
_z 6 EAST GLADES EXPERIMENT STATION
5
Z- J
U. 3
S2- .

J A S O N D J F M A M J
1970 1971
Figure 12. Water levels in Canal 103 in Biscayne Bay, and in well G-1515; and
local rainfall; July 1970 June 1971.


Florida City Canal. By May 11 the water level had declined to 0.95 foot below
msl (or about 1.2 feet below bay level) and parts of the canals were highly
contaminated by salt water. Heavy rains in late May and in June caused water
levels to rise to 1.8 feet above msl at the end of June thus ending the 1971
drought.

Early in March the water table, as shown by the water level in well G-1515
on figure 12, began to decline below the bottom of the marl in a small area at
the west side of site A and by May 11 the water table declined below the marl.
The hydraulic continuity between the water table and the marl was reduced and
capillary flow from the water table to the surface probably decreased.

The water-table map for April 14-15, 1971 (fig. 6) shows that site A was
within a shallow depression (as shown by the minus 0.3-foot contour), the
center of which was slightly west and south of site A. Ground-water movement,
though slight, was chiefly westward beneath site A from Biscayne Bay. The
principal direction of regional ground-water movement was, however, upward to
the surface as a result of evapotranspiration.

Evapotranspiration is high because the ground altitude is low and the
water table is near land surface, and the Perrine marl and the water table are


I i I I I I I I I I I
CANAL 103 ABOVE S-20F F WELL G-1515 AND CANAL 103
ABOVE S-20 F


BISCAYNE BAY AT
HOMESTEAD BAYFRONT PARK
SAT WELL G-ISIS LAND SURFACE IS
S I I I I 2.5 FEET ABOVE MEAN SEA LEVEL
I I I I I I I I i






REPORT OF INVESTIGATIONS NO. 66 21

usually in contact, thereby providing excellent capillary flow to the surface.

In order to more clearly describe the flow pattern at site A a cross section
(fig. 13) was constructed along line A-A' located on figure 2. The data for April
15, 1971 were selected to show the position of the water table and the
distribution of chloride. The general direction of water movement is shown by
arrows, and the number of arrows represent the relative amounts of flow.

Flow upward through unsaturated soil is generally greatest where the
water table is nearest to land surface, provided all other things are equal. On this
basis, flow would be slightly greater on the east side of site A than on the west
side. Because the salt content in ground water is also greater on the east side, a
higher salt accumulation would be expected there.

The decline in water levels at site A during February May was caused
chiefly by evapotranspiration. The water table at site A declined at an average
rate of 0.029 foot per day during April 1971, according to the hydrograph for
well G-1515 on figure 12. The approximate evapotranspiration from aquifer
storage was computed by using the equation:

ETs = RP

where ETs is the average daily evapotranspiration loss,
in feet per day, from ground water storage.

R is the rate of water-level decline, 0.029 foot
per day.

P is the aquifer porosity, 0.25.

By substitution,

ETs = 0.029 foot per day x 0.25
= 0.0072 foot per day, or about 2,400 gallons
per day per acre.

In addition to the storage depletion estimated above, total
evapotranspiration would include return of precipitation and transfer of
incoming ground water to the air. Rainfall in April 1971 was very small and may
be neglected. Based on approximate water table gradients in figure 6 and a
transmissivity of 400,000 feet squared per day, a crude estimate of transfer of
ground-water inflow to the air in April 1971 amounted to 0.006 foot per day, or
about 2,000 gallons per day per acre. The net ET is therefore about 0.013 foot







BUREAU OF GEOLOGY


EXPLANATION


EVAPOTRANSPIRATION
f1


GROUND-WATER FLOW


U --2-50--
CAPILLARY FLOW LINE OF EQUAL
CHLORIDE CONCENTRATION,
MILLIGRAMS PER LITER
Fgwe 13. Geeralzed ers section A-A' through site A showing water
movement and chloride content.






REPORT OF INVESTIGATIONS NO. 66


per day, or about 4.7 inches per month. This estimated value does not include
the small amount of rainfall in April and effects of salt content on hydraulic
gradients, thus the estimated value is lower than the true value. But the value
compares well with estimates of 4 inches for April, based on average
evapotranspiration from fully sodded, fine sand, evapotranspirometers in which
the water table was about 3 feet below the surface (Steward and Mills, 1967).

DISTRIBUTION AND SOURCE OF SALTS

At site A, chloride concentrations were highest in the top two inches of
soil and in the ground water at the base of the Biscayne aquifer (fig. 14). In the
extracts from soil samples obtained from the southeast corner of the site,
chloride concentrations ranged from about 200 mg/l in October 1970 to 15,000
mg/l in May 1971. Soil samples obtained at the east edge of the field (outside)
within a tree line during August 1970 through February 1971, contained about
the same amount of chloride as that inside the field; however, samples obtained
there during March through May 1971 contained only minor amounts of salt
compared to the samples taken from inside the field. A comparison of the
chloride concentrations in the soil with the concentration in water from Canal


J A S O N D J F M A M J
1970 1971
Figure 14. Chloride content in soils at site A, in Canal 103 at SW 117 Avenue
and above S-20F, July 1970-June 1971; and chloride content in
water from selected depths in well G-15 IS, JanuaryJune 1971.







BUREAU OF GEOLOGY


103 suggests that during March through May the soil salt was related to the
increase in salt content in the canal water. Rains during late May and June 1971
effectively leached most of the salt from the soils at both locations and flushed
salt water from Canal 103.

The effect of the 1971 drought was more subtle in the aquifer than in the
canals and soils, because salt concentrations there increased less spectacularly as
shown by the concentration in water at selected depths from well G-1515 (fig.
14). The chloride content in water from well G-1515 near the center of the site
increased only a few hundred milligrams per liter at all levels.

A comparison of the vertical distribution of chloride in water from wells
G-1514 through G-1517 on April 15, 1971 (fig. 15) shows that chloride content

0 II I I

APRIL 15, 1971


LOCATION SKETCH
10-
G-I514



G-15 -1 516
-J


G-1517
300
3 or to SCALE




40




50




60
O 2 4 6 8 10.
CHLORIDE CONTENT, THOUSAND MILLIGRAMS PER LITER

Figure 15. Chloride content in ground water in wells G-1514 through G-1517
at selected depths, April 15, 1971.







REPORT OF INVESTIGATIONS NO. 66


in ground water at 5 feet below msl was higher in wells G-1514 and G-1516 than
in wells G-1515 and G-1517, thereby suggesting that the source of salt-water
intrusion was located northeast of site A; or in the vicinity of Canal 103.

Data collected on April 15, 1971 were selected to show the dry season
chloride (salinity) distribution at site A. The chloride content in the soil extract
(inside field) was 12,000 mg/l. The chloride content of water in the unsaturated
soil zone was not determined because samples of soil water were not obtained
there. Water in nearby ditches contained 1,200 mg/1 chloride. Chloride content
in ground water at mean sea level ranged from 400 mg/1 in wells G-1515 and
G-1517 to 1,100 mg/1 in wells G-1514 and G-1516; chloride content in these
four wells at elevation -10 feet msl was about 1,100 mg/1, and below elevation
-40 feet msl was more than 5,000 mg/l. Chloride content of the water at the
bottom of North Canal adjacent to site A was 3,800 mg/l; in water at the
bottom of Canal 103 at SW 117 Avenue was 2,800 mg/l, and upstream from the
control S-20F it was 12,400 mg/1.

The amount of salt (as NaC1) carried to the surface daily by capillarity and
osmosis was computed to be about 64 pounds per acre, based on an
evapotranspiration rate of 0.013 foot per day and a sodium chloride content of
1,800 mg/1 (1,100 mg/1 chloride).

Thus the distribution of chloride in water at site A suggests that the saline
soil was formed chiefly by evapotranspiration of brackish ground water that
moved upward from the water table by capillarity and osmosis to the surface.

SITE B- PETERSON FARM
DESCRIPTION

Site B, an 80-acre plot locally referred to as the "Peterson Farm" is
northeast of Homestead Air Force Base and about 1.8 miles from Biscayne Bay,
on the north side of SW 280th Street between SW 107th and 112th Avenues (see
location on figs. 2 and 16). Land surface there ranges in altitude from about 2.5
and 3.5 feet above msl and averages about 3 feet (fig. 16). The site is completely
underlain by Perrine marl to a depth of about 2 feet. The Perrine marl feathers
out to the west against the limestone ridge in the vicinity of Homestead Air
Force Base. Soil in the southeast corner of the site, the area of lowest altitude,
has periodically become too saline for farming. Adjacent fields are cropped
except those to the east which have been abandoned due to salinity and drainage
problems. Ditches on the north and south sides of the site convey excess water
eastward about 1 mile into the Levee 31E Borrow Canal. A ditch on the west
side of SW 112 Avenue conveys excess water northward about 1 mile to Canal
102.











G-15


EXPLANATION
SG-1507
WELL AND NUMBER
Q
PIEZOMETERS
A
DITCH SAMPLING
POINT

SOIL SAMPLING
SITE
0 00 FEET
*L -1 l 1 l


NOTE:
CONTOURS WITH INTERVAL OF 0.25 FOOT FROM
TOPOGRAPHIC SURVEY BY
E.H. STEWART AND W.H. SPEIR, U.S. AGRICULTURE
RESEARCH SERVICE 1968


tj


S3.25

3.25--% miTrc


325


Figue 16. Site B showing locations of data-collection points and topography.





Table 2. Records of wells at site B.


Well Number: Lettered well numbers are for piezometers.

Water Level: Measured on April 14, 1971.


Chloride: Sample collected at bottom of well on April 14, 1971, in milligrams per liter (mg/I).


Depth Casing Casing Elevation Water Level
Well (feet, (feet, Diameter Land Surface (feet Chloride
Number msI) msl) (inches) (feet, msl) msl) (mg/1)

G 1505 -41.28 + 0.42 6 2.42 -0.13 3200
G 1506 -28.20 2.50 6 2.50 -0.20 1350 Continuous water-level record
G 1506A 1.08 0.58 2 2.50 -0.21 1/
G 1506B 7.56 7.06 2 2.50 -0.21 660
G 1506C -19.50 -19.00 2 2.50 0.00 104 Plugged
G 1506D -12.45 -11.95 2 2.50 -0.20 620
G 1506E 2.91 2.41 2 2.50 -0.21 360
G 1506F -12.68 -12.18 2 2.50 -0.16 114 Partially plugged
G 1507 -47.12 + 1.28 6 3.28 -0.16 3700
G 1508 -43.20 2.28 6 2.72 -0.15 1840 Continuous water-level record
G1508A -26.77 -26.27 2 2.72 -0.12 475
G 1508B -11.48 -10.98 2 2.72 -0.14 285
G 1508C -17.22 -16.72 2 2.72 -0.14 370
G 1508D 0.50 0.00 2 2.72 -0.15 1/
G 1508E 3.78 3.28 2 2.72 -0.15 265
G 1508F 7.15 6.65 2 2.72 -0.15 270

!/ Insufficient water for analysis


'i


0

0
oZ

P\
0r







BUREAU OF GEOLOGY


Descriptions of wells and piezometers at site B are presented in table 2.
Data on water levels, soil salinity, and water salinity were collected during
January through June 1971 at the points shown on figures 2 and 16. Rainfall
data were obtained from Homestead Air Force Base. Soil salinity data were
obtained from Dr. J. D. Dalton of the Dade County Agricultural Extension
Office.
WATER LEVELS AND WATER MOVEMENT

The water table at site B normally is about 1 foot below land surface, or
slightly less than 2 feet above msl. The water table rises when recharge by
infiltrating rainfall and canal waters exceed losses by drainage and
evapotranspiration, and falls when losses exceed replenishment. During the wet
season the water table frequently rises above land surface; and during the dry
season it often declines below bay level. The water table at site B is closely
related to the water levels in nearby ditches and canals. Semidiurnal fluctuations
of the water table resembling tidal fluctuations are produced by the opening and
closing of automatic tide gates in salinity control S-21A at the mouth of Canal
102 in response to the tides in Biscayne Bay during wet periods. Diurnal
fluctuations of the water table during daylight hours are produced chiefly by
evapotranspiration during dry periods.

A comparison of the water level in Canal 102 upstream from the salinity
control S-21A with the water level in Biscayne Bay at Homestead Bayfront Park
(fig. 17) indicates that during June through November 1970 the automatic gate
control was set to hold upstream water levels at a stage of about 2 feet above
msl. During December 1970 the gate setting was lowered and the canal's water
level began to decline. During April and May the water level above S-21A
declined below the bay level thereby reversing the normal bayward gradient. As
a result, bay water seeped inland around the control and contaminated parts of
Canal 102 and the Levee 31E Borrow Canal. By May 11 the upstream water level
had declined to 0.11 foot below msl, or about 0.5 foot below bay level. Heavy
rains in late May and June caused the upstream water level to rise to 2 feet above
msl by the end of June 1971.

At site B the water table, as shown by the water level in well G-1506 on
figure 17, was generally below the water level in Canal 102 during January
through June 1971, except following heavy rains when the water table peaked
higher. The relationship indicates that usually there is a hydraulic gradient from
Canal 102 toward site B and that seepage from Canal 102 sustains water levels
there. Comparisons of the two water levels during the recession from March 1
through May 11 shows that the water level in well G-1506 declined at a slightly
faster rate, thereby suggesting that evapotranspiration at site B exceeded the
recharge from the canal.









REPORT OF INVESTIGATIONS NO. 66


-j

-r2
W

Wv

0 4, 0
U LzJ

w
W -2
W
LL .2


(n
w

.-z
z-J
o-J
2


65



3

J


A S O N D J F M A M J
1970 1971


Figure 17. Water levels in Canal 102 above S-21A, in Biscayne Bay, and in well
G-1506; and local rainfall, July 1970 June 1971.


In January the water table was about 0.3 foot below the marl at the west
side of site B, and by early March it had declined below the marl on the east
side. In mid-March the water table had declined below the bay level, and by May
11 it was 0.8 foot below msl, or about 1 foot below bay level.

During January through June 1971, water levels in wells G-1507, and
G-1508 (Hydrographs not shown) were only slightly higher than that in well
G-1506 the record for which is shown on figure 17. The hydraulic gradients
between wells and the water-table map for April 14-15, 1971 (fig. 6) indicate
that some ground-water moved southward beneath site B toward the center of
the depression, as indicated by the closed minus 0.3-foot contour south of site
B. The principal direction of ground-water movement was, however, upward to
the surface as a result of evapotranspiration. The depression at site B was a result
of inadequate recharge and a high rate of evapotranspiration.


Ground-water flowed toward the center of the depression south of site B
chiefly from Military Canal, Canal 102, and Biscayne Bay. Flow of fresh ground
water toward the center was greatest from Military Canal because the aquifer
was being recharged by effluent from the Base sewage treatment plant. Flow of
fresh ground water from the west (inland) was least. The contours east of site B
indicate inland movement of salt water from Biscayne Bay.


CANAL 102 aBOVE S-2A I I I




BISCaYNE BAY AT .
HOMESTEAD BAYFRONT PARK WELL G-1506 -
LAND SURFACE 2,5 FEET
S I I I I ABOVE MEAN SEA LEVEL







BUREAU OF GEOLOGY


Water levels in the shallow piezometers at site B during January through
May 1971, were a few hundredths of a foot lower than water levels in the deep
riezometers; therefore some ground water moved upward from the lower part of
the aquifer to replace losses in the upper part.

In order to more fully describe water movement at site B a cross section
(fig. 18) was constructed along line B-B' located on figure 2. The data for April
14, 1971 were selected to show the position of the water table and distribution
of chloride. The arrows indicate the general direction of water movement and
the number of arrows suggest the relative amounts of flow.

Capillary flow through unsaturated soil is generally greatest where the
water table is nearest to land surface, provided all other things are equal. On this
basis, upward flow would be slightly greater on the east side of site B than on
the west side. Because salt content in the ground water is greater on the east side
a higher salt accumulation would be expected there.

The decline in water levels at site B during April 1971 was chiefly caused
by evapotranspiration. An approximation of the magnitude of
evapotranspiration was made by assuming that evapotranspiration was equivalent
to the loss in ground-water storage.

The water table at site B declined at an average rate of 0.022 foot per day
during April 1971, according to the graph of the water level in well G-1506 on
figure 17. The approximate evapotranspiration from aquifer storage (ETs) was
computed by using the equation as described earlier in the section dealing with
site A.

By substitution in the equation ET = R P

ETs = 0.022 foot per day x 0.25
= 0.0055 foot per day, or 1,800 gallons
per day per acre.


In addition to the storage depletion estimated above, the transfer of
incoming ground water to the air was estimated to be 0.011 foot per day, based
on approximate water table gradients in figure 6 and a transmissivity of 400,000
feet squared per day. The net ET is therefore about 0.016 foot per day, or about
5.8 inches per month. This estimated value does not include the small amount of
rainfall in April, thus the estimated value is lower than the true value. But the
value compares well with estimates of 4 inches based on studies by E. H.
Steward and W. C. Mills (1967).








REPORT OF INVESTIGATIONS NO. 66


APPROXIMATE WIDTH OF THE
SALINE SOIL ZONE


t
EVAPOTRANSPIRATION


CAPILLARY FLOW


EXPLANATION


q====
GROUND-WATER FLOW

---250--
LINE OF EQUAL
CHLORIDE CONCENTRATION,
MILLIGRAMS PER LITER


Figure 18. Generalized cross section B-B' through site B showing water
movement and chloride content.









32 BUREAU OF GEOLOGY


DISTRIBUTION AND SOURCE OF SALTS


At site B the concentrations of chloride were highest in the top two inches
of soil and in the ground water at the base of the aquifer. Extracts from samples
of soil near well G-1506 in the southeast corner of the site (see location on fig.
16) contained chloride in concentrations ranging from 1,000 mg/1 in October
1970 to 17,500 mg/1 in April 1971 (fig. 19). Concentrations in the soil decreased
during the wet season and increased during the dry season. Significant reductions
in chloride occurred during the dry season, however, as a result of leaching
following heavy rains in February and March.


The concentration of chloride in ground water generally increased with
increasing depth in the aquifer and with decreasing distance from Biscayne Bay.
For example, in April 1971 the chloride content in water from well G-1506 was
about 600 mg/l at 5 feet below msl and 1,400 mg/l at 28 feet below msl. A
water sample from the lower part of the aquifer probably would have contained
more than 5,000 mg/1 chloride.


LL 7
1-2
cz 6
za.


z2



3
cr

r z
0^4



0Z2
_I-
uolt=

r3


J A S O N D J F M A M J
1970 1971


OW
l&J


-J c


=^0.

Z V)
F-


I-
Z0


u


I-



Oc.

a.


Figure 19. Chloride content in soil at site B, in Canal 102 at SW 107th Avenue
and above S-21A, July 1970- June 1971: and chloride content in
well G-1506 at selected depths, January June 1971.








REPORT OF INVESTIGATIONS NO. 66


1000 2000 3000 4000
CHLORIDE CONTENT, MILLIGRAMS PER LITER


Figure 20. Chloride content in ground water in wells
at selected depths, May 18, 1971.


G-1505 through G-1508


Chloride content was generally higher in water at equivalent depth in wells
G-1505 and G-1506 on the east side of site B than in wells G-1507 and G-1508
on the west side (fig. 20). The concentrations at depths below 40 feet at site B
greatly exceed 1,000 mg/l, therefore the 1,000 mg/l chloride line at the base of
the aquifer lies considerably west of site B.

Data collected on April 14, 1971 were selected to show the dry season
chloride (salinity) distribution at site B. The chloride content in the extract from
the soil in the southeast corner of the site was about 17,000 mg/l. The chloride
content in soil at the west side was not determined; however, it was assumed to
be low based on the excellent condition of crops there. The chloride content in
the unsaturated zone was unknown because samples of soil water were not


0




IO
10i

..J
ULi
_J
-j
< 20
2
w

z
Li


o 30





40
I-'


40


50
0


5000







BUREAU OF GEOLOGY


obtained. Most of the nearby ditches were either dry or ponded and chloride
content of the water there was about the same as the chloride content of the
ground water. Chloride contained in ground water at altitude -5 feet msl ranged
from about 300 mg/1 in wells G-1507 and G-1508 on the west side of site B to
about 600 mg/1 in wells G-1505 and G-1506 on the east side. Chloride content
of the water in the bottom of canal 102 (at approximately altitude -10 feet msl)
ranged from 750 mg/l upstream from the control S-21A to 600 mg/l at SW 107
Avenue; and chloride content 1 foot below the canal's water surface at the same
locations was 350 mg/l and 120 mg/1. In the southeast corner, the amount of
salt (as NaCI) carried to the surface daily by capillarity and osmosis was
computed to be about 43 pounds per acre, based on an evapotranspiration rate
of 0.016 foot per day and a sodium chloride content of 990 mg/l (600 mg/l
chloride).

SEA-WATER INTRUSION AND SALINE SOILS

The sea-water intrusion and saline soil problems are interrelated because
the saline soils cannot exist without a source of relatively salty ground water.
Salty ground water is chiefly caused by inland movement of bay water during
dry periods; however, infrequent inundation by hurricane tides also contribute
to sea-water intrusion.

Data collected by the U. S. Geological Survey and the U. S. Department of
Agriculture since the early 1940's indicate that both are long-term problems.
Data collected during this investigation at sites A and B support previous
findings and conclusions. The movement of ground water and the distribution of
chloride content (salt) at both sites indicate that the soil salinity is caused by
evapotranspiration of relatively brackish ground water that moves upward from
the water table by capillarity and osmosis during dry periods.

The supporting data for this report were collected during an unusual
drought; however water-level conditions in the East Glades have reached almost
the same proportions on several occasions since the early 1940's. Records of
water levels prior to drainage in the 1940's are lacking; however, water levels
have declined below sea level on several occasions in undrained low-lying areas
near the East Glades and in Everglades National Park, south of the East Glades
area. Figure 7 shows that the salt front is inland about 5 miles from Florida Bay
in the eastern part of Everglades National Park. Because of the close similarity
between the two areas, it is apparent that in East Glades the present (1971)
position of the salt front probably is only slightly farther inland from its natural
position. Thus saline soils are for the most part a natural occurrence in the East
Glades except when sea-water intrusion can be traced to man-made causes, such
as, salt-water seepage from a canal or increased inland movement due to lowered
water levels (this could be related to pumpage or to increased drainage).







REPORT OF INVESTIGATIONS NO. 66


At site A the chloride content in the ground water near the water table
appears to be caused chiefly by infiltrating salt water from nearby canals; and at
site B it appears to be caused by upward movement of salty ground water from
deeper parts of the aquifer.

Comparison of the chloride content in extracts from the upper 2 inches of
soil at sites A (fig. 14) and B (fig. 19) shows a wide variation in peak
concentration and in rates of buildup and leaching. Peak concentration was
higher at site B than at site A. There is no simple explanation for these
variations; but according to the chloride concentrations in the ground water and
the position of the water table with respect to the bottom of the soil (Perrine
Marl) and to the land surface, the reverse of the situation would be expected.
Therefore one can only speculate on the cause of the variations in soil salinity at
the two sites.

Stewart and Albert (1968) found that salt concentrations varied widely in
soils at site A. They found very little correlation between the depth to the water
table and soil salinity. The data collected at sites A and B for this investigation
suggests that partially shading at site A would cause variations in the local soil
salinity by reducing evapotranspiration and that differences in permeability,
ground cover, and rainfall would also account, for variations in concentration.
Therefore the variations in soil salinity at sites A and B could be caused by local
conditions, but in each case only a slightly brackish ground-water source was
needed to produce unfavorable salt buildup in the soil.

Infiltration of salt water from coastal canals during extended dry periods
helps to sustain high chloride concentrations in the ground water. Infiltration of
salt water from canals is chiefly man made and movement of salty ground water
inland through deep parts of the aquifer are both natural and man made. Both
types of intrusion are related to the inability to hold fresh water levels high
during drought. Based on existing data it is not possible to clearly separate the
parts of intercanal areas affected by natural intrusion from parts affected by
man. Apparently a large part of the coastal part of the East Glades was underlain
by salt water prior to drainage; however, recent intrusion is indicated since the
late 1960's as a result of increased water use and reduction of peak water levels.

Studies by the U. S. Geological Survey indicate that water levels along the
eastern and southern sides of East Glades Agricultural Area often decline below
bay level during dry periods thereby causing a reversal in the normal bayward
hydraulic gradient. As a result salt water moves inland through the aquifer and
up the canals. The inland advance of the salt front during the dry season is
usually reversed by seaward moving fresh water during the wet season; however,
the advance during a drought, such as that in 1971, would require an event of







BUREAU OF GEOLOGY


opposite but equal magnitude to return the salt front to the original position.
Current land use in the area does not permit widespread flooding, therefore the
chances of returning the salt front to the pre-drought position without raising
water levels is remote.

The long-term solution to the saline soil problem would be to prevent
further intrusion from coastal canals by holding water levels higher there during
dry periods. The fact that the winter growing season generally corresponds with
the annual dry season poses a special problem to the Central and Southern
Florida Flood Control District because the respective water-level needs are
conflicting. Agriculturalists in East Glades require that water levels in coastal
canals be held sufficiently low to farm low-lying fields while water managers
require that coastal water levels be held sufficiently high to prevent sea-water
intrusion.

Keeping water levels low during the dry season is a short-term benefit to
agriculture because the practice often leads to increased sea-water intrusion
which is a long-term detriment to agriculture. Thus the outlook for the East
Glades Agricultural Area is for no improvement in sea-water intrusion and saline
soil problems unless there are significant changes in land use that will permit the
maintenance of higher water levels upstream from the coastal salinity control
structures.

ALTERNATIVES

Current land use and farming practices in the East Glades are in conflict
with the need to maintain water levels upstream from coastal controls high
enough to prevent sea-water intrusion. The Perrine marl is of major agricultural
and economic importance and the need to utilize this valuable resource to the
fullest will become more apparent as the need for future food supply and "green
areas" increase. The solution to the problems of sea-water intrusion and saline
soils presents a challenge to those responsible for land and water management.
The data collected thus far indicates that the problems are related and that the
solution will require changes in land use as water levels are raised to optimum
levels to halt sea-water intrusion and to reclaim lands already affected by
sea-water intrusion.

One method of changing the land use would be to mound the marl deposit
in low-lying fields so that water levels can be raised. Another method would
involve the complete removal of the marl deposit from all low-lying lands along
the coast and the distribution of the deposit on higher areas to the west. The
denuded fields could be filled with crushed limestone for urban development
and the raised fields could be used for agriculture and parks. Both methods







REPORT OF INVESTIGATIONS NO. 66


would permit holding higher water levels above the coastal controls and
continued use of the marl for agriculture.

SUMMARY

Saline soils in the East Glades Agricultural Area are caused chiefly by
evapotranspiration of brackish ground water during dry periods. Salt
concentration in soils are highest where the underlying ground water contains
high concentrations of salt and the flow upward from the water table is greatest.
Salt content in the ground water is caused by sea-water intrusion (infiltration of
salt water from nearby canals and by inland movement of salt water through the
aquifer, both occurring during dry periods). Upward flow from the water table is
greater through the Perrine marl than through the limestone of the Biscayne
aquifer because the soil moisture content and capillary conductivity of the
Perrine marl is higher. Upward flow is also greater in areas where the water table
occurs nearest land surface.

Salt concentrations in soils can vary considerably within short distances
depending upon the local variations in the above mentioned conditions;
however, the area most prone to development of soil salinity generally coincides
with the zone affected by sea-water intrusion along the coast. The zone of
intrusion is caused by man-made and natural factors.

The problems of sea-water intrusion and saline soils are partly related to
the need to control water levels sufficiently low in the coastal reaches of canals
that cross the area so that low-lying fields can be farmed. The need to maintain
low water levels during the winter growing season conflicts with the need to
maintain high water levels for prevention of sea-water intrusion during the same
period; however, to date the needs of agriculture have had priority. Therefore,
the outlook for the East Glades is for no improvement in sea-water intrusion and
saline soil problems unless there are significant changes in land use which will
permit maintenance of higher water levels upstream from the salintiy controls in
the major coastal canals.





BUREAU OF GEOLOGY

REFERENCES


Galliher, C. F. and Hull, J. E.
1969 Hydrologic conditions during 1967 in Dade County, Florida: U. S. Geol
Survey open-file report.

Hull, E. and Galliher, C. F.
1968 Hydrologic conditions during 1966 in Dade County, Florida: U. S. GeoL
Survey open-file report.

1970 Hydrologic conditions during 1968 in Dade County, Florida: U. S. Geol
survey open-file report.

1971 Hydrologic conditions during 1969 in Dade County, Florida: U. S. Geol
survey open-file report.

1972 Hydrologic conditions during 1970 Dade County, Florida: U. S. GeoL survey
open-file report.

Israelson, O. W, and Hansen, V. E.
1962 Irrigation principles and practices: John Wiley and Sons, Inc., New York, New
York.

Klein, Howard
1957 Salt--wter encroachment in Dade County, Florida: Florida Geol. Survey Inf.
Cir 9.

Kohout, FA., and Leach, S. D.
1964 Salt-water movement caused by control-dam operation in Snake Creek Canal,
Miami, Florida: Florida GeoL Survey Rept Inv. 24, part 4.

Leighty, R. G., Henderson, J. R. and others
1958 Soil Survey (Detailed-Reconnaissance) of Dade County, Florida: U. S. Dept
of Agriculture, Soil Survey Series 1947, No. 4.

Parker, G. G, Ferguson, G. E., and Love, S. K.
1955 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, 935 p.

Richards, L A., and others
1954 Diagnosis and improvement of saline and alkali soils: U. S. Dept. of
Agriculture, Handbook No. 60.

Schneider, J. J.
1969 T-ual relations in the south Biscayne Bay area Dade County, Florida: U. S.
GeoL Survey open-file report.

Schroeder, M. C., Klein, Howard and Hoy, N. D.
1958 Biscayne aquifer of Dade and Broward Counties, Florida: Florida Geol. Survey
Rept Inv. 17.





REPORT OF INVESTIGATIONS NO. 66 39

Stewart, E. H., Albert, R. R., and others
1967 'Salinity status and water relationships of marl soils in southern Florida: U. S.
Dept. of Agriculture, Agricultural Research Service, Everglades Project Annual
Report.

1968 Salinity status and water relationships of marl soils in southern Florida: U. S.
Dept. of Agriculture, Agricultural Research Service, Everglades Project
Annual Report.

Stewart, E. H., Albert, R. R., and others
1969 Salinity status and water relationships of marl soils in southern Florida: U. S.
Dept of Agriculture, Agricultural Research Service, Everglades Project Annual -
Report

Stewart, E. H., and Mills, W. C.
1967 Effect of depth to water table and plant density on evapotranspiration rate in
southern Florida: Am. Soc. Agr. Engineers Trans. Vol. 10, no. 6, pp. 746-747.

U. S. Weather Bureau
1970 Climatological Data, Florida: v. 74, No. 13.










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