Water control vs. sea-water intrusion, (FGS: Leaflet no.5)

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Material Information

Title:
Water control vs. sea-water intrusion, (FGS: Leaflet no.5)
Physical Description:
15 p., 13 fig. illus.; color
Language:
English
Creator:
Sherwood, C.B.
Grantham, R.G.
Publisher:
Tallahassee, FL pub. for the Florida Geological Survey
Publication Date:

Notes

Abstract:
Residents in coastal areas are aware of the perpetual battle between man and the sea. Reports of beach erosion, destruction of property, damage to ships, and loss of cargos are of common knowledge. However, one .battle between man and the sea is a silent struggle that receives little publicity because it 1s invisible and not spectacular. This invisible struggle is waged to protect fresh-water supplies in coastal areas from inroads by the sea. This leaflet tells in general terms how the problem of sea-water intrusion in the aquifer in Broward County came about, what has been done to control the intrusion and what must be done to conserve the fresh water and keep the ocean where it belongs . Although the leaflet deals specifically with conditions in Broward County, the principles described are valid in any coastal area having a similar hydrology. For this reason, this leaflet is of interest to people living in other coastal areas of Florida.
General Note:
Series: Florida Geological Survey. Leaflet; 5 revised
General Note:
Subjects: Salt, Broward County Florida
General Note:
http://purl.fcla.edu/fcla/dl/UF00001173.pdf http://publicfiles.dep.state.fl.us/FGS/FGS%5FPublications/L/L5revSherwoodGrantham1966.pdf http://publicfiles.dep.state.fl.us/FGS/FGS%5FPublications/L/Leaflet5-rev1.pdf
General Note:
Call number: FGS Leaflet 5 rev

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
All rights reserved by the source institution.
System ID:
AA00013465:00001


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Table of Contents
    Front Cover
        Page 1
    Title Page
        Page 2
    Preface
        Page 3
    Water control vs. sea-water intrusion, Broward County, Florida
        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
    References
        Page 17
Full Text
Florida Bureau of Geology Library
903 W. Tennessee Street
Tallahassee, Florida 32304


WA TER


CO TROL


VS.


SEA WATER


IN TRUSIOC


LEAFLET NO. 5











STATE OF FLORIDA
STATE BOARD OF CONSERVATION
DIVISION OF GEOLOGY


FLORIDA GEOLOGICAL SURVEY
Robert O. Vernon, Director










SECOND EDITION




LEAFLET NO. 5


WATER CONTROL VS. SEA-WATER
INTRUSION, BROWARD COUNTY,
FLORIDA

By
C. B. Sherwood and R. G. Grantham

















Prepared by the
UNITED STATES GEOLOGICAL SURVEY
in cooperation with
BROWARD COUNTY
and the
FLORIDA GEOLOGICAL SURVEY

TALLAHASSEE


1966
















PREFACE


Residents in coastal areas are aware of
the perpetual battle between man and the sea.
Reports of beach erosion, destruction of pro-
perty, damage to ships, and loss of cargos are
of common knowledge. However, one battle
between man and the sea is a silent struggle
that receives little publicity because it is
invisible and not spectacular. This invisible
struggle is waged to protect fresh-water sup-
plies in coastal areas from inroads by the sea.
This leaflet tells in general terms how the
problem of sea-water intrusion in the aquifer
in Broward County came about, what has been
done to control the intrusion and what must
be done to conserve the fresh water and keep
the ocean where it belongs.
Although the leaflet deals specifically with
conditions in Broward County, the principles
described are valid in any coastal area having
a similar hydrology. For this reason, this leaf-
let is of interest to people living in other coas-
tal areas of Florida.




















WATER CONTROL VS. SEA-WATER
INTRUSION, BROWARD COUNTY, FLORIDA

By
C.B. Sherwood and R.G. Grantham

Broward County abounds in water--both
fresh and salt. With careful management, the
supply of fresh water is adequate for the present
and future needs of the area. The wealth of
salt water is a major asset--good for shipping
and recreation, such as swimming, boating,
and fishing. However, the ever present problem
is keeping salt water in its place. In fact, the
primary threat to the invaluable fresh-water
resources of the county is intrusion of sea water
into coastal streams and into subsurface water-
bearing materials. Sea-water intrusion is a
silent menace. It can spread without raising
alarm; it can contaminate domestic wells and
destroy city water supplies; and it can kill
crops and render soils unusable for agriculture.
It not only can, but has. However, studies
indicate that with proper detection and control
measures, sea-water intrusion can be halted,
and with time the sea water can be flushed out.
Broward County is underlain by the Bis-
cayne aquifer, a highly productive water-bearing
system of limestone, sandstone, and sand that
extends from land surface to depths of as much
as 200 feet near the coast. The aquifer yields
copious supplies of fresh water to municipal
well fields in the area, but the porous nature
of the materials exposed to the sea make it
also especially vulnerable to sea-water intru-
sion.
The inland extent of sea-water and salty-
water intrusion in Broward County in 1964 is
shown by red and pink shading on the map and
cross section below. Salty water as distin-
guished from sea water is a mixture of fresh
and sea water. The salty water body in the
aquifer is wedge-shaped, being thickest at the
coast, and thinning inland to an edge where it
underlies the fresh ground water at depths from
160 to 200 feet below the land surface.










EXPLANATION
AI Sea water
SSalty ground
SFresh water
"a Canol and cC
) Well field
GENERAL;
E
A CROSE S SEC
WELL FIELD
' - -


I


I -


A
I "


7,
i .


I i'->
-j I <







SVA C- --rj
sV-3W~ _gf; F ^-*^ ^ : ~


,H


Sea-water intrusion in Broward County in 1964 is
shown by pink shading. The salty water in the
aquifer is wedge shaped (see cross section), thick-
est at the coast and thinning inland where it under-
lies fresh ground water at depths of 160 to 200 feet.
Greatest inland penetration is in the vicinity of
tidal canals.






Because sea water contains large amounts
of dissolved salts, it is slightly heavier than
fresh water. A 41-foot column of fresh water
is required to balance 40 feet of sea water.
Thus, sea water moves inland unless fresh-water
levels are appreciably higher than sea level.
In coastal streams and in porous subsurface
materials, there is a constant balancing between
the two. If fresh-water levels are high, sea water
is held near the coast. If fresh-water levels are
low, sea water moves up the tidal streams and
inland in the aquifer beneath the fresh ground
water. Theoretically, in a coastal aquifer, each
foot of fresh water above sea level would indi-
cate 40 feet of fresh water below sea level.


7-7


r^


1










HIGH FRESH-WATER LEVELS



i ,


LOW FRESH-WATER LEVELS


Seo .-.,:


I_ L
--
I .
II J
I _ 1 - *-r __ _



Because sea water is heavier than fresh water it
tends to move inland unless balanced by higher
fresh-water levels. When fresh water is abundant,
stream flow and water levels are high and the sea
water is held near the coast. During drought, when
stream flow and fresh water levels are low, salty
water moves up tidal streams and inland beneath
the fresh ground water.









Prior to drainage improvements in Broward
County the existing streams were shallow and
relatively ineffective as drainage channels.
Therefore, fresh-water levels were high and
little or no salt water intruded. In fact, old-time
residents reported flowing wells in salt-water
bays and inlets. Later, as deep, effective drain-
age canals were cut far inland to reduce flooding
of farms and urban areas, coastal water levels
were lowered greatly and salt-water intrusion
began almost unnoticed. In addition, the rapid


Sea water and fresh water in coastal area before
construction of canals.


The construction of
sea-water intrusion
water levels, a,;nd
convey sea water ii
*er sbifts inland ad~ t


ntiroied tidal canals c
wo vvays: it, lowers
providess open channel
The salt front in the
to the new canal.


fresh
is tc
aqui-
.qu









urbanization of the area brought an increased
demand for drainage and for coastal canals to
create attractive waterfront property. The de-
sirable aspects of these developments were
clearly apparent; the undesirable aspect--salt
intrusion--was difficult to detect until domestic,
industrial or irrigation supplies began to be
contaminated. Uncontrolled tidal canals influ-
enced the position of salt-fresh water contact
in two ways--they lower fresh ground-water
levels, thus reducing the opposition to inland
movement of salt water and they provide a
channel for sea water to move inland. The inland
penetration of the salt front in the New River
area of Fort Lauderdale was caused chiefly by
extensive construction of canals. Fortunately,
this type of intrusion can be corrected if a
salinity control structure is built near the coast
to raise the level of fresh water and to prevent
the upstream movement of salt water. Salinity











. -




Salinity control structures serve to hold sea water
out, prevent excessive drainage of fresh water, and
hold fresh-water levels high near the coast.


control structures have been constructed in
coastal reaches of all primary canals of the
Central and Southern Florida Flood Control
Project to combat sea-water intrusion and to
control water levels on an area-wide basis. In
the older canals the controls were located as
far seaward as the existing land use and marine
interests permitted--in the newer canals they
are placed very close to the coast.























ML -


Salinity control structure S-37A on Cypress Creek
Canal (C-14) near Pompano Beach helps to prevent
the intrusion of sea water into the Fort Lauderdale
Prospect well field. When heavy rainfall occurs the
gates are opened to prevent flooding in the inland
areas. During dry periods the gates are closed to
conserve fresh water.


.- -*" -i








In Broward County the inland movement of
the salt front is accelerated by the lowering of
fresh-water levels near the coast as a result of
large withdrawals of ground water. When esta-
blished, the municipal well fields generally
were located an appreciable distance inland.
However, the westward expansion of urbaniza-
tion necessitated drainage of larger areas by
canals which in many instances passed within
the area where ground-water levels were being


An uncontrolled canal that extends into an area
of heavy pumpage can convey salt water inland to
contaminate fresh water supplies.

lowered by well fields. In an area of heavy
pumpage the ground-water flow is toward the
well field, thus the combined effects of the
canal and the pumpage can induce salt water
to move into the well field. In contrast, a con-
trolled canal can provide a perennial source of
fresh water to replenish the well field and to
prevent salt intrusion by bringing in additional
fresh water from outside the area. Water-control
structures as correction measures are presently
being constructed in some critical areas where
municipal supplies are threatened.


'~5T~-














I I.,N










In contrast a controlled canal can provide a peren-
nial source of fresh water to prevent salt-water intru-
sion and to replenish the well field by bringing in
fresh water from outside the area.



The map sequence below shows successive
adjustments to the salt front pattern, which have
occurred since 1941 in response to canal con-
struction, large scale pumping, and salinity
control works in the Middle River Prospect
well field area, near Fort Lauderdale.
In the early 1940's pumpage of ground
water was negligible and existing streams were
shallow and drained very little water; conse-
quently, fresh-water levels were high and salt-
water intrusion was confined to areas adjacent
to natural tidal channels. By the mid 1950's the
primary canals had been constructed, the Pros-
pect well field had been established, and exca-
vation of an extensive secondary canal system
by land developers was underway. Coastal
water levels were being lowered and a very
significant inland adjustment of the salt-front
pattern resulted.
In 1963 the effects of the construction of
the canal and control which integrated Cypress
Creek into the flood control system are shown.
Although pumpage had increased threefold,
ground-water levels remained high and the salt
front was essentially stabilized in the area
north of the well field. In contrast, south of the












1941


it--




In 1941, prior to canal construction, fresh-water
levels were high and sea-water intrusion was con-
fined to areas adjacent to natural tidal channels.



- - - "

1956-

'4"

















By 1956 the primary canals had been constructed,
the Prospect well field had been established, and
the excavation of an extensive system of secondary
drainage canals was underway. Coastal water levels
had been lowered excessively and the salt front
had moved appreciably inland.












S 1"") -.63

i_


The canal and control which connected Cypress
Creek into the flood-control system tended to sta-
bilize the salt front in that area despite a three-
fold increase in pumpage. In contrast, the uncon-
trolled reach of the North Fork of the Middle River
permitted the salt front to move inland into the
well field.


------ .- ----- --,





1.-




I "
.. .. ... ...... ~ I _ . .:







--p


Predicted effects of a proposed fresh-water feeder
canal and salinity control designed to halt sea-water
intrusion and furnish fresh-water replenishment to
the Prospect well field.








well field the salt front adjacent to the tidal
portion of the North Fork of the Middle River
moved steadily inland into the well field. The
feeder canal shown in the fourth map has been
proposed to provide higher fresh-water levels
for the control of salt intrusion and for recharge
to the well-field area.
Although the salinity-control structures in
major canals have retarded intrusion in some
areas, the rapidly increasing urbanization and
water use create an urgent need for legislation
to provide salinity control area wide. During
1963, the increased threat to ground-water
supplies, accentuated by the contamination of
a major well field, resulted in legislation to
prevent the construction of additional salt-water
canals and to require salinity control structures
where needed in existing canals.
Expansion of the secondary drainage sys-
tem and increased water use to keep pace with
continued rapid development of coastal Broward
County will lower water levels and will increase
the danger of salt intrusion in the future. By the
year 2000 water use for municipal supplies
alone is predicted to exceed one-half billion
gallons per day or more than ten times the
present use. Hydrologic studies indicate that
these water needs can be met by preventing
the construction of new avenues for salt intru-
sion and by making the maximum use of the
regional water-management system (see below).
The primary water-control system of the
Central and Southern Florida Flood Control
District is designed to alleviate the effects of
both flood and drought. This is accomplished
by draining a part of the flood waters to the
sea and storing a part in conservation areas
for release during droughts. This system, sup-
plemented by a controlled secondary drainage
network and by proper water-management can
provide the solution to Broward County's salt-
intrusion problem and can assure the county of
a long-term water supply.
The hydrologic data which made possible
the long-term delineation and monitoring of the
salt front were collected in cooperation with
the City of Fort Lauderdale. The collection of
additional data in northern Broward County was



































The Central and Southern Florida Flood Control
Project is designed to alleviate the effects of both
flood and drought on a regional basis. This is accom-
plished by draining a part of flood waters to the
sea and storing the remainder in conservation areas
for releases during droughts. This system, when
supplemented by a network of controlled secondary
drainage canals, can provide control of sea-water
intrusion and assure a long-term water supply for
Broward County.

begun in 1960 in cooperation with the City of
Pompano Beach and in 1963 with the City of
Deerfield Beach.
The cooperative investigation of the water
resources of Broward County by the U.S. Geolo-
gical Survey includes several salinity and hydro-
logic studies designed to aid in detecting and
countering salt intrusion. Among these are: (1)
a continuing program of water level and salinity
data for observation wells and sampling points
on canals to monitor the movement of salt in
the aquifer and canals; (2) a test drilling pro-
gram to determine the extent of intrusion in the
aquifer; (3) electrical analog model studies to
determine the effects of proposed changes in
the canal system and increase in pumpage; and









(4) hydrologic studies to determine the water
levels required at salinity controls in canals
and the amount of fresh water flow required in
canals to stop salt intrusion.
The results of these cooperative studies
will be published by the Florida Geological
Survey and the U.S. Geological Survey. Reports
and data are currently available from the U.S.
Geological Survey, 51 S.W. First Avenue, Miami,
Florida. Further information on the mechanics
of salt intrusion in the southeastern coastal
area of Florida may be found in the references
listed below.













REFERENCES


Cooper, H.H., Jr.
1964 (and Kohout, F.A., Henry, H.R., and
Glover, R.E.) Sea water in coastal aqui-
fers: U.S. Geol. Survey Water-Supply
Paper 1613-C.

Klein, Howard
1957 Interim report on salt-water encroachment
in Dade County, Florida: Fla. Geol. Sur-
vey Inf. Circ. 9.

Kohout, F.A.
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 encroach-
ment caused by a storm sewer in the
Miami area, Florida: Am. Water Works
Assoc. Jour., v. 53, no. 11.

Parker, G.G.
1955 (and others) Water resources of south-
eastern 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.
1959 Ground-water resources of the Oakland
Park area of eastern Broward County,
Florida: Fla. Geol. Survey Rept. of Inv.
20.

1963 (and Klein, Howard) Use of analog plotter
in water-control problems: National Water
Well Assoc., Ground Water Journal, v.
1, no. 1.

Tarver, G.R.
1964 Hydrology of the Biscayne aquifer in
the Pompano Beach area, Broward County,
Florida: Fla. Geol. Survey Rept. of Inv.
36.

Vorhis, R.C.
1948 Geology and ground water of the Fort
Lauderdale area, Florida: Fla. Geol.
Survey Rept. of Inv. 6.




Full Text

PAGE 1

1 I Florida Bureau of Geology library 903 w Tennessee Street Tallahassee, Florida 3 2304 WATER CONTROL vs. / SEA YfATEH INTRlJSION I lEAFlET N 0. 5

PAGE 2

STATE OF FLORIDA STATE BOARD OF CONSERVATION DIVISION OF GEOLOGY FLORIDA GEOLOGICAL SURVEY Robert 0. Vernon, Director SECOND EDITION LEAFLET NO. 5 WATER CONTROL VS. SEA-WATER INTRUSION, BROWARD COUNTY, FLORIDA By C B. Sherwood and R. G. Grantham Prepared by the UNITED STATES GEOLOGICAL SURVEY in cooperation with BROWARD COUNTY and the FLORIDA GEOLOGICAL SURVEY TALLAHASSEE 1966 0 z .0 0 ..,

PAGE 3

PREFACE Residents in coastal areas are aware of the perpetual battle between man and the sea. Reports of beach erosion, destruction of property, damage to ships, and loss of cargos are of common knowledge. However, one .battle between man and the sea is a silent struggle that receives little publicity because it 1s invisible and not spectacular. This invisible struggle is waged to protect fresh-water supplies in coastal areas from inroads by the sea. This leaflet tells in general terms how the problem of sea-water intrusion in the aquifer in Broward County came about, what has been done to control the intrusion and what must be done to conserve the fresh water and keep the ocean where it belongs. Although the leaflet deals specifically with conditions in Broward County, the principles described are valid in any coastal area having a similar hydrology. For this reason, this leaflet is of interest to peopl e living in other coastal areas of Florida.

PAGE 4

WATER CONTROL VS. SEA-WATER INTRUSION, BROWARD COUNTY, FLORIDA By C.B. Sherwood and R.G. Grantham Broward County abounds in water--both fresh and salt. With careful management, the supply of fresh water is adequate for the present and future needs of the area. The wealth of salt water is a major asset--good for shipping and recreation, such as swimming, boating, and fishing. However, the ever present problem is keeping salt water in its place. In fact, the primary threat to the invaluable fresh-water resources of the county is intrusion of sea water into coastal streams and into subsurface waterbearing materials. Sea-water intrusion is a silent menace. It can spread without raising alarm; it can contaminate domestic wells and destroy city water supplies; and it can kill crops aru:l render soils unusable for agriculture. It not only can, but has. However, studies indicate that with proper deteclion and control measures, sea-water intrusion can be halted, ahd with t ime the sea water can be flushed out. Broward County is underlain by the Biscayne aqui fer, a h ighly productive water-bearing system of limest o ne, sandstone, and sand that extends from land surface to depths of as much as 200 feet near the coast. The aquifer yields copious supplies of fresh water to municipal well fields in the area, but the porous nature of the materials exposed to the sea make it also especially vulnerable to sea-water intrusion. The inland extent of sea-water and saltywater intrusi o n in Broward County in 1964 is shown by red and pink shading on the map and cross section below. Salty water as distinguished f rom sea water is a mixture of fresh a n d sea water. The salty water body in the aquifer i s wedge-shaped, being thickest a t the coast, a n d t hin n ing i n l and to an e dge whe r e i t underlies th e f resh gr oun d wate r at depths f ro m 160 t o 200 feet below t he l and s u r face. J

PAGE 5

EXPLANATI O N !lill Sea water C=:J Sol l y ground water c::J Fresh water -t-Cortalondcontrol ()Well fiel d GEN ERALIZ E D CROSS SECTION A' . Sea-water intrusion in Broward County in 1964 is shown by pink shading. The salty water in the aquifer is wedge shaped (see cross section), thickest at the coast and thinning inland where it underlies fresh ground water at depths of 160 to 200 feet. Greatest inland penetration is in the vicinity of tidal canals. Because sea water contains large amounts of dissolved salts, it is slightly heavier than fresh water. A 41-foot column of fresh water is required to balance 40 feet of sea water. Thus, sea water moves inland unless fresh-water levels are appreciably higher than sea level. In coastal streams and in porous subsurface materials, there is a constant balancing between the two. If fresh-water levels are high, sea water is held near the coast. If fresh-water levels are low, sea water moves up the tidal streams and inland in the aquifer beneath the fresh ground water. Theoretically, in a coastal aquifer, each foot of fresh water above sea level would indicate 40 feet of fresh water below sea level.

PAGE 6

HIGH FRESH -WATER LEVELS Seo level LOW FRESH-WATER LEVELS Seo level Because sea water is heavier than fresh water it tends to move inland unless balanced by higher fresh-water levels. Whe n fresh water is abundant, stream flow and water levels are high and the sea water is held near the coast. During drought, when stream flow and fresh water levels are low, salty water moves up tidal streams and inland beneath the fresh ground water.

PAGE 7

Prior to drainage improvements in Broward County the existing streams were shallow and relative ly ineffective as drainage channels. Therefore, fresh-water levels were high and little or no salt water intruded. In fact, old-time residents reported flowing wells in salt-water bays and inlets. Later, as deep, effective drainage canals were cut far inland to reduce flooding of farms and urban areap, coastal water levels were lowered greatly and salt-water intrusion began unnoticed. In addition, the rapid Sea water and f resh water in coastal area before construction of canals. The construction of uncontrolled tidal canals c?.uses sea-water intrusion in two ways: it lowers freshwater levels, and it provides open channels to convey sea water inland. The salt front in the aquifer shifts inland adjacent to the new canal.

PAGE 8

urbanization of the area brought an increased demand for drainage and for coastal canals to create attractive waterfront property. The desirable aspects of these developments were clearly apparent; the undesirable aspect--salt intrusion--was difficult to detect until domestic, industrial or irrigation supplies began to be contaminated. Uncontrolled tidal canals influenced the position of salt-fresh water contact in two ways--they lower fresh ground-water levels, thus reducing the opposition to inland movement of salt water and they provide a channel for sea water to move inland. The inland penetration of the salt front in the New River area of Fort Lauderdale was caused chiefly by extensive construction of canals. Fortunately, this type of intrusion can be corrected if a salinity control structure is built near the coast to raise the level of fresh water and to prevent the upstream movement of salt water. Salinity Salinity control structures serve to hold sea water out, prevent excessive drainage of fresh water, and hold fresh-water levels high near the coast. control coastal Central structures have been constructed in reaches of all primary canals of the and Southern Florida Flood Control Project to combat sea-water intrusion and to control water levels on an area-wide basis. In the older canals the controls were located as far seaward as the existing land use and marine interests permitted--in the newer canals they are placed very close to the coast.

PAGE 9

Salinity control structure S-37 A on Cypress Creek Canal (C-14) near Pompano Beach helps to prevent the intrusion of sea water into the Fort Lauderdale Prospect well field. When heavy rainfall occurs the gates are opened to prevent flooding in the inland areas. During dry periods the gates are closed to conserve fresh water.

PAGE 10

In Broward County the inland movement of the salt front is accelerated by the lowering of fresh-water levels near the coast as a result of large withdrawals of ground water. When established, the municipal well fields generally were located an appreciable distance inland. However, the westward expansion of urbanization necessitated drainage of larger areas by canals which in many instances passed within the area where ground-water levels were being An uncontro !led canal that extends into an area of heavy pumpage can convey salt wate r inland to contaminate fresh water supplies. lowered by well fields. In an area of heavy pumpage the ground-water flow is toward the well field, thus the combined effects of the canal and the pumpage can induce salt water to move into the well field. In contrast, a controlled canal can provide a perennial source of fresh water to replenish the well field and to prevent salt intrusion by bringing in additional fresh water from outside the area. Water-control structures as correction measures are presently being constructed in some critical arefl,s where municipal supplies are threatenl')d.

PAGE 11

In contrast a controlled canal can provide a per e n nial source o f fres h w a t e r to prevent s a l t -water intrusion and t o r eplenis h t h e w ell field by bring ing in fres h w a t e r from outside the area The map sequence below shows successive adjustments to the salt front pattern, which have occurred since 1941 in response to canal construction, large scale pumping, and salinity control works in the Middle River Prospect well field area, near Fort Lauderdale. In the early 1940's pumpage of ground water was negligible and existing streams were shallow and drained very little water; consequently, fresh-water levels were high and saltwater intrusion was confined to areas adjacent to natural tidal channels. By the mid 1950's the prilT)ary canals had been constructed, the Prospect well field had been established, and excavation of an extensive secondary canal system by land developers was underway. Coastal water levels were being lowered and a very significant inland adjustment of the salt-front pattern resulted. In 1963 the effects of the construction of the canal and control which integrated Cypress Creek into the flood control system are shown Although pumpage had increased threefold, ground-water levels remained high and the salt front was essentially stabilized in the area north of the well field. In contrast, south of the

PAGE 12

1941 I l EXPLANATION CANAL A N D CONTROL NUNICIPAL SUPPLY WELL In 1941, prior to canal construction, fresh-water levels were high and sea-water intrusion was confined to areas adjacent to natural tidal channels. I l PROSPECT WELL FIELD 10 M G D . EXPLANATION CANAL AND CONTROL MUNICIPAL WELL SCALE IN FEET By 1956 the primary canals had been constructed, the Prospect well field had been established, and the excavation of an extensive system of secondary drainage canals was underway. Coastal water levels had been lowered excessively and the salt front had moved appreciably inland.

PAGE 13

1963 ... I I EXPLANATION _._, C A NAL AND CONTROL MUNICIPAL SUPPLY WELL The canal and control which connected Cypress Creek into the flood-control system tended to stabilize the salt front in that area despite a threefold increase in pumpage. In contrast, the uncontrolled reach of the North Fork of the Middle River permitted the salt front to move inland into the well field. c:, CANAL C/3 \;:: I I E XPLANATI ON _._, "'< CANAL AND CONTROL 2 MUNICIPAL SUPPLY WELL t < zoOOCAL O INz:OE:000 Predicted effects of a proposed fresh-water feeder canal and salinity control designed to halt sea-water intrusion and furnish fresh-water replenishment to the Prospect well field.

PAGE 14

well field the salt front adjacent to the tidal portion of the North Fork of the Middle River moved steadily inland into the well field. The feeder canal shown in the fourth map has been proposed to provide higher fresh-water levels for the control of salt intrusion and for recharge to the well-field area. Although the salinity-control structures in major canals have retarded intrusion in some areas, the rapidly increasing urbanization and water use create an urgent need for legislation to provide salinity control area wide. During 1963, the increased threat to ground-water supplies, accentuated by the contamination of a major well field, resulted in legislation to prevent the construction of additional salt-water canals and to require salinity control structures where needed in existing canals. Expansion of the secondary drainage system and increased water use to keep pace with continued rapid development of coastal Broward County will lower water levels and will increase the danger of salt intrusion in the future. By the year 2000 water use for municipal supplies alone is predicted to exceed one-half billion gallons per day or more than ten times the present use. Hydrologic studies indicate that these water needs can be met by preventing the construction of new avenues for salt intrusion and by making the maximum use of the regional water-management system (see below). The primary water-control system of the Central and Southern Florida Flood Control District is designed to alleviate the effects of both flood and drought. This is accomplished by draining a part of the flood waters to the sea and storing a part in conservation areas for release during droughts. This system, supplemented by a controlled secondary drainage network and by proper water-management can provide the solution to Broward County's saltintrusion problem and can assure the county of a long-term water supply. The hydrologic data which made possible the long-term delineation and monitoring of the salt front were collected in cooperation with the City of Fort Lauderdale. The collection of additional data in northern Broward County was

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The Central and Southern Florida Flood Control Project is designed to alleviate the effects of both flood and drought on a regional bas is. This is accomplished by draining a part of flood waters to the sea and storing the remainder in conservation areas for releases during droughts. This system, when supplemented by a network of controlled secondary drainage canals, can provide control of sea-water intrusion and assure a long-term water supply for Broward County. begun in 1960 in cooperation with the City of Pompano Beach and in 1963 with the City of Deerfield Beach. The cooperative investigation of the water resources of Broward County by the U.S. Geological Survey includes several salinity and hydrologic studies designed to aid in detecting and countering salt intrusion. Among these are: (1) a continuing program of water level and salinity data for observation wells and sampling points on canals to monitor the movement of salt in the aquifer and canals; (2) a test drilling pro gram to determine the extent of intrusion in the aquifer; (3) electrical analog model studies to determin(:l the effects of proposed changes in the canal system and increase in pumpage; and

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( 4) hydrologic studies to determine the water levels required at salinity controls in canals and the amount of fresh water flow required in canals to stop salt intrusion. The results of these cooperative studies will be published by the Florida Geological Survey and the U S Geological Survey. Reports and data are currently available from the U.S. Geological Survey, 51 S.W. First Avenue, Miami, Florida. Further information on the mechanics of salt intrusion in the southeastern coastal area of Florida may be found in the references listed below.

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REFERENCES IU1., Jr. Cooper, 1964 (and Kohout, F.A., Henry, Il.R., and Glover, R.F:.) Sea water in coastal aqui fers: U .S. Ceo l. Survey Water-Supply Paper 1613-C. Klein, Howard 1 957 Interim report on Sillt-water encroachment in Dade County, Florida: Fla. Geol. Sur vey Inf. Circ. 9. Kohout, F.A. 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 sal t-water encroachment caused by a storm sewer in the Miami area, Florida: Am. Water Works Assoc. Jour., v 53, no. 11. Parker G .G. 1 !-l55 (and others) Water resources of southeastern Florida, with special reference to the geology and ground water of the Miami area: U.S. Geol. Survey WaterSupply Paper 1255. Sherwood, C.B. 1959 Ground-water resources of the Oakland Park area of eastern Broward County, Florida: Fla. Geol. Survey Rept. of Inv. 20. 1963 (