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Large springs of Florida's "Sun Coast"...
FLRD GEOLOSk ( IC SUfRiW
[year of publication as printed] Florida Geological Survey [source text]
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LARGE SPRINGS OF FLORIDA'S
CITRUS AND HERNANDO COUNTIES
LEAFLET NO. 9
Prepared by the
UNITED STATES GEOLOGICAL SURVEY
in cooperation with the
BUREAU OF GEOLOGY
DIVISION OF INTERIOR RESOURCES
FLORIDA DEPARTMENT OF NATURAL RESOURCES
SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT
LARGE SPRINGS OF FLORIDA'S
CITRUS AND HERNANDO COUNTIES
J. A. Mann and R. N. Cherry
Florida has more first magnitude springs than any other
state in the nation. A first magnitude spring has an average
discharge (flow) of at least 100 cfs (cubic feet per second) or
64.6 mgd (million gallons per day). About 20 springs or spring
complexes within Florida are in this category. Four of the
large spring complexes are in Citrus and Hernando counties,
along the west-central gulf coast of Florida. These four spring
complexes provide almost the entire fresh-water flow of
Crystal, Homosassa, Chassahowitzka, and Weekiwachee Rivers,
figure 1. The combined flow of these rivers averages or exceeds
one billion gallons per day, which equals 1,000 mgd, and could
have supplied all of Florida's industrial and municipal water
used in 1967.
The four large spring complexes are of utmost importance
to the future development of the "Sun Coast" area because of
their value to tourists (the largest industry of the area) and
their esthetic and natural resource value.
GEOGRAPHIC SETTING OF THE SPRINGS
The four spring complexes near the head of the Crystal,
Homosassa, Chassahowitzka, and Weekiwachee Rivers occur
where the aquifer, in this case a water-bearing limestone, lies
near the land surface or is exposed in the headwaters or
channels of the rivers.
The lands along the springfed rivers abound in natural
beauty. For several miles the rivers wind through lowlands
containing lush tropical and semitropical growth, the habitat
of numerous varieties of animals and birds. The aquatic plants
and the associated invertebrate animals that thrive in the
crystal-clear, warm (about 740F year round) unpolluted waters
attract thousands of fresh and salt-water fish, including bass,
redfish, snook, tarpon, sheepshead, and spotted weak fish
(locally called trout). Thus, the springs form giant natural fish
bowls, figure 2, which are popular sites for sport fishing, skin
diving, and other recreational activities.
The area around the large springs and to the east is sparsely
populated. Most people live in the towns near the springs.
Many retirees have moved to the area, attracted by the mild
climate, natural beauty, and recreational opportunities.
Figure 1. "Sun Coast" springs area of Florida.
Figure 2. Thousands of fish of many kinds gather at "Nature's Giant
Fishbowl"-Homosassa Springs. The vertically striped fish are
sheepshead, a favorite of fishermen.
The springs at Homosassa and Weekiwachee are tourist
attractions of national and even international reknown, figures
3 and 4. Chassahowitzka Springs, however, remains in a nearly
natural setting and is used mostly by local swimmers and
fishermen. The area around Homosassa and Chassahowitzka
springs is well known for its excellent hunting. The
35,000-acre Chassahowitzka National Wildlife Refuge offers
seasonal hunting of wild turkeys, ducks, doves, squirrels, hogs,
The brackish conditions (semi-salty) caused by the discharge
of good quality fresh water into sea water provide an ideal
habitat for oysters and other mollusks. Shell mounds left by
the early Indian inhabitants of the Crystal River area attest to
the ready availability of this food supply. Commercial fishing
and the seafood industry flourish on the excellent salt water
fishing grounds nearby, figure 5. The abundance and variety of
seafood from this area is well known throughout Florida and
neighboring states. Crystal River was once mainly a fishing
village; but in recent years as tourism has grown, the town has
become a tourist recreational center and a retirement
Limerock is mined at several places, mostly south of
Bayport and near Crystal River, figure 6. Much of the mining
is done in conjunction with land development; limerock sold
for use in road building partially pays the cost of land
Figure 3. Homosassa Springs, "Nature's Giant Fishbowl"-underwater
observatory at the main springs openings at Homosassa River.
Figure 4. Weekiwachee Springs-"The Springs of Live
Mermaids"-underwater amphitheater and glass-bottom cruise boats at
the main springs openings at Weekiwachee River.
Figure 5. Commercial fishing and the seafood industry are important to
"Sun Coast" area.
WHAT IS THE FLOW OF THE SPRINGS?
The flow of the springs varies seasonally--during or
following a drought the discharge is much less than during or
following an exceptionally wet period. Although response to
seasonal variations in rainfall is apparent, the fluctuations of
flow are slower than those of normal streams. Time is required
for rainfall to infiltrate the soil and flow through the limestone
aquifer (called the Floridan aquifer) to the spring vent where it
is noticeable as an increase in discharge.
A comparison of flow from the four major spring complexes
can be made from the data of table 1. Hydrologic conditions
in the area during the period January 1964 to June 1966 were
near average for the long-term records of flow for Homosassa
and Weekiwachee Springs.
The flow from the spring complex at the head of Crystal
River is apparently the largest in the area. Because the springs
occur at various points in the headwaters of Crystal River, the
flow from the individual springs could not be measured. The
average flow represents that recorded at the gaging station
about three miles downstream from the town of Crystal River
(fig. 1) and includes most of the spring discharge to Crystal
River. The monthly mean flow of Crystal River at this location
is shown on figure 7. Maximum flow occurs during the dry
season of the year and minimum flow during the wet season,
whereas in most streams the maximum and minimum flow
I ;:t t
;:1: : --
:.: (.)-. i.:7j;L'
i ~~i- ,rlr
TABLE 1. DISCHARGE OF MAJOR COASTAL SPRINGS IN CITRUS AND HERNANDO COUNTIES
Discharge in million gallons per day
1January 1964 to June 1966
2Daily mean (negative sign indicates upstream flow)
-r g ~,- ,-... .
iv WT D GV~ Vi m"' ~ D
rnl r mill iy V Vit
Figure 6. Limerock mining near Crystal River, Florida.
normally coincides with the wet and dry seasons. The
anomalous timing of the flow of Crystal River is probably
caused by seasonal tides. The highest seasonal tides occur
during wet seasons, and impose a backwater condition which
decreases the river's flow; lowest tides occur during dry
seasons and allow water to flow out of storage, increasing the
river s flow. The minimum and maximum net daily flow to the
ocean at the gaging station on Crystal River occurred during
Hurricane Dor.a, September, 1964. On September 10, the
hurricane passed and wind tides carried sea water upstream, at
an average rate for the day of 1,520 cfs. The maximum daily
flow occurred the following day as the tides subsided and the
wind-blown water flowed seaward at 4,340 cfs.
The flow of Homosassa Springs has been measured
periodically since 1922. From 1932 through 1966 the flow
averaged 129 mgd on the basis of 25 discharge measurements.
The maximum measured flow occurred August 4, 1965, during
median hydrologic conditions. The minimum measured flow.
81 mgd, occurred April 3, 1946 during a severe drought. The
measured flows include the discharge of springs in the
Southeast Fork of Homosassa Springs. The average flow of
Homosassa River from January 1964 to June 1966 was about
The flow of Weekiwachee Springs has been measured
periodically since 1917. fhe average flow is 112 mgd, on the
basis of 300 measurements from 1917 to 1966. The maximum
measured flow occurred October 19, 1964, during median
SI i II I I I I I I-Ol i
to C STAL RIR
-- 25 100 --*---
.; 8 00------- -
E o 1 1I1 1 1 1 1 111 1 1 1 1 1 1 I l lIi l l
J F M A M J J A S 0 N O J F M A M J J A S 0 N D J FM A
1964 1965 1966
Figure 7. Monthly mean flow ofCrystal River and Weekiwachee River, January 1964 June 1966.
hydrologic conditions. The minimum measured flow, 65 mgd,
occurred July 24, 1956, during a severe drought. The flow of
Weekiwachee River is derived mainly from Weekiwachee
Springs. However, the flow of Little Weekiwachee Springs and
countless small springs in the channel along the entire length
of the river also contribute to the river's flow. The flow of the
river about 5 miles downstream from the main springs
averaged about 170 mgd from January 1964 to June 1966.
The flow of Chassahowitzka Springs is measured together
with the flow from several small springs in the headwaters and
the springs in Crab Creek (a small tributary of Chassahowitzka
River) at a point in Chassahowitzka River downstream from
Crab Creek. The average combined flow for the January
1964-June 1966 period was 90 mgd. The maximum measured
flow (127 mgd) occurred May 18, 1966 during median
hydrologic conditions. The minimum measured flow (21 mgd)
occurred July 8, 1964.
The flow of all the large springs, with the exception of
Weekiwachee Springs, is affected by tidal fluctuations in the
Gulf of Mexico. Weekiwachee Springs is unaffected because of
the high discharge per unit of channel cross sectional area and
the elevation of the springs which effectively blocks tidal
movement upstream to the springs.
Variation in specific conductance and discharge caused by
tidal flow, as measured at the gaging station on Crystal River,
is shown in figure 8. Specific conductance measurement is a
convenient and rapid way to determine the approximate
amount of dissolved solids in water. The greater the specific
conductance, the more dissolved solids (high mineral content).
Commonly, the amount of dissolved solids(in milligrams per
liter) is about 65 percent of the specific conductance (in
micromhos). The mineral content of water in Crystal River is
due mostly to sodium chloride from sea water; therefore, high
conductance indicates high concentration of sodium chloride.
The high values of conductance on September 10, 1964,
resulted from wind blown tides caused by Hurricane Dora
lle variation in mineral content of water from Homosassa and
Chassahowitzka springs caused by salt water migrating
upstream on flood tides are about the same as at Crystal River.
However, the mineral content of water from Weekiwachee
Springs maintains an almost constant value of about 150 mg/I
(milligrams per liter), or conductance of about 230
The flows of Crystal River and Homosassa, Weekiwachee,
and Chassahowitzka springs vary as shown by the correlation
in figure 9. The maximum rate of water movement and total
volume of water discharge by these spring-fed rivers is high
Figure 8. Variation in specific conductance and discharge for three-hour intervals at Crystal River near Crystal River, Florida, Septmeber 9-13. 1964.
FEET PER SECOND CRYSTAL R.
MEAN DISCHARGE, THOUSANDS -
FEET PER SECOND, CRYSTAL RU
Figure 9. Correlation of discharge of Homosassa, Weekiwachee, and
Chassahowitzka Springs with Crystal River.
4 -------- ______^___________
during tidal cycles. At Crystal River during normal tidal cycles
the maximum positive (downstream) and negative (upstream)
flow is about 4,000 cfs. During j Hurricane Dora! in
September, 1964, the maximum instantaneous negative flow
was estimated to be more than 10,000 cfs--largely caused by
WHERE DOES THE WATER COME FROM?
The vast flow of the springs is derived from rain-about 55
inches annually-that falls on about 2,300 square miles east of
the springs, figure 10. About 38 inches of the rain returns to
the atmosphere annually by the
evapotranspiration-evaporation from water, soil, and plant
surfaces and by transpiration by vegetation.
Very little water (as streamflow) leaves the area
immediately west of the western topographically defined
drainage divide of the Withlacoochee River (fig. 10). This 570
square mile area is almost devoid of surface drainage. Surface
runoff (runoff per square mile of topographic drainage area)
from the Withlacoochee River is low in comparison to adjacent
stream basins. Much of the rain that falls on the area enters the
Floridan (limestone) aquifer either by percolation through the
soil zone into the limestone or by drainage through sinkholes,
moves generally westward toward the large coastal springs, and
reappears as springflow and seepage into the coastal rivers.
The Floridan aquifer, which is composed of more than
1,000 feet of limestone and dolomite in the "Sun Coast" area,
is one of the most productive aquifers in the United States and
probably the world. The aquifer transmits water beneath the
area to the springs near the coast and is the source of virtually
all water used locally. Figure 11 shows the piezometric surface
of the Floridan aquifer in the coastal springs area. The contour
lines represent the height above mean sea level to which water
would rise in tightly cased wells that penetrate this aquifer,
and the arrows indicate the general direction of flow through
The top of the aquifer is about 60 to 80 feet below land
surface in the central part of the state but is at or near land
surface close to the coast. The gentle slope of the limestone
aquifer, its high calcium carbonate content and natural
porosity, the small amount of surface runoff, the dense
vegetation and humid climate, and active circulation of ground
water create an environment in this area of Florida- that is
most favorable for solution of the limestone. The results of
limestone solution is cavity formation and the development of
S- Boundory of area contri-
buting water to large
S Withlaocoochee River topo-
V / graphic drainage boundary
o 10 MILES
Figure 10. Water contributing area for large coastal springs and
topographic drainage divide of the Withlacoochec River.
high permeability. The springs orifices are elongated vertical
solution cavities that intersect an especially permeable part of
the aquifer at depth. Such orifices provide avenues for water
under pressure in the aquifer to escape from the aquifer thus
creating the big springs.
WHY ARE SOME SPRINGS
FRESH AND SOME SALTY?
Some springs in the coastal area discharge fresh water, some
salty water, and some at times discharge fresh or at other times
salty water. The mineral -content of water from the main
Contour represents the
height of the piezometric
surface, In feet above mean
Direction of Flow
Flow Is generally normal
to the contours as shown
0 I MILES
I I l
Figure 11. Plezomotric surface of the Floridan aquifer, Sun Coast area,
springs at the head of Crystal River varied from about 200 to
1,100 mg/l during the January 1964-June 1966 period, and
mineral content of water from the main springs at the head of
Chassahowitzka River varied from about 300 to 2,000 mg/l
during the August 1964-June 1966 period. Sodium chloride,
common table salt, was the principal dissolved mineral
constituent in the more mineralized water. The reason for the
variation in mineral content is complex and only partly
understood; it is probably controlled by a fluctuation of the
dynamic balance between the denser sea water and the level of
the fresh water above sea level and the dynamics imparted by
the diurnal tidal cycle. Because the density of sea water is
greater than that of fresh water, a 41-foot column of fresh
water is theoretically required to balance 40 feet of sea water,
figure 12. Thus, in theory, in a coastal aquifer each foot of
fresh water above sea level would indicate 40 feet of fresh
water below sea level. In the coastal area, the balance between
the two heads constantly changes: whenever fresh-water levels
at the coast decline to or near sea level, sea water moves
inland; if fresh-water levels are at or below sea level, salt water
moves up coastal streams and into the aquifer.
The zone in the aquifer between fresh and salt water that
exists because of this dynamic balance is known as the
fresh-salt water interface. Because of changes in hydrostatic
pressure in the aquifer, this interface can move both
horizontally and vertically within an aquifer. The interface is
normally not sharp but is a transitional zone of some
thickness. In the Miami, Florida area where it has been
extensively studied in great detail, Parker (1955, p. 620)
reports that the zone is about 60 feet thick.
Figure 13 illustrates how movement of this interface could
cause variation in quality of the water discharging from the
springs. During periods of high fresh water levels in the aquifer
(wet season) the fresh-salt-water interface is below the spring
vent as shown in figure 13-A, and discharge from the spring is
fresh. During low fresh water levels (dry season) the depth to
the interface decreases--the interface zone may be located
within the spring vent as shown in figure 13-B. Under this
condition, discharge from the spring would be salty to some
degree. The interface could remain relatively stationary for a
year or more, could change seasonally as illustrated, or could
change as a result of ground-water withdrawals in an area.
Depending on the location of the fresh-salt-water interface,
the quality of the spring flow could be changing seasonally or
as physical changes are imposed on the aquifer system.
he basic principle la that of balanced weights.
I cubic foot of soa water weilph 04,1.O lhs.
I cubic Ioot of fresh water weighs t2.5 lts.
Ihus salt water is t4.0 or 1,025 tilmni a s heavy ai
frxhs water and a column ol f s allt water 1. feot I n height
will halj nce a soltumn( of freshly water (1.025) 1 feet
(.'nnIct'l h eI all anl fresh water columns showt inI
A by :a connecting tube and addl a reservoir to the top
of the s lt water columnl. lheo result is shown above.
hen ca rxplaitned In A.
11 1.025 L.
or h t 1.025 L 1.025 h
(1.02S I) .025
When I 1. h 40.
iHence for every foot of fresh water love Iea level
there are 40 feet or fresh water below sea level.
Figure 12. The hydrostatic relationship between salt and fresh water,
known as the Chybcn-Herzbcrg Principle (Black, A.P., Brown, Eugene,
and Pearcc, J.M.. 1953, "Salt water intrusion in Florida, 1953": Fla.
State Board of Conservation water survey and research paper no. 9).
A. High fresh-water levels.
B. Low fresh-water levels.
Figure 13. Movement of fresh-salt water contact at a spring vent.
Records from an observation well in the Floridan aquifer
near the headwaters of Crystal River show that the water level
in the aquifer fluctuates with the tide. The water level remains
generally about one-half to one foot above mean sea level,
figure 14. The level of fresh water is sufficient to depress the
salt water at this point about 20 to 40 feet below mean sea
level. The rivers and springs tend to be fresher upstream from
the gulf, where water levels in the aquifer are generally higher.
Rivers and springs also tend to be fresher during the summer
and early fall when water levels in the aquifer are highest.
When the fresh-water level declines the salt water moves inland
during high tide and may mix with the fresh water flowing
upward toward the spring openings.
The Crystal, Homosassa and Chassahowitzka spring systems
are much more subject to variations in chemical quality of
water between extremes of fresh and salty than Weekiwachee
Springs. During the 1964-66 study period, the measured range
of dissolved solids in Crystal River was 300 to 15,000 mg/l; in
Homosassa River was 550 to 9,100 mg/l; in Chassahowitzka
River was 300 to 2,000 mg/1; and Weekiwachee Springs was
125 to 150 mg/1. The wider range in variation in chemical
quality occurs because the water level at the former springs is
about one foot above msl whereas the level at the main springs
at Weekiwachee is about 10 to 12 feet above mean sea level.
Any set of conditions, either natural or influenced by man,
that markedly decreases the level of the fresh water, decreases
the fresh water discharge and permits sea water to move
further inland. This can, in turn, cause increased salinity in
water discharging from the low-lying springs. For example,
excessive pumping from the fresh-water aquifer in the area
adjacent to the springs or extensive drainage by canals, or
deepening of natural river channels in and adjacent to springs
may permit reduction in the level of the fresh water and allow
more frequent discharge of salt water or saltier water from the
springs, figure 15.
Various state, county, water-management districts, and
citizen groups are aware of the fresh-salt water balance in the
area of the springs. Suggestions and proposals are under study
and data are being collected for realistic water-management
programs to safeguard the unique spring system for use by
EXTENT OF KNOWLEDGE ON THE SPRINGS
Completed elements of hydrologic investigations in the area
include: (1) extensive field reconnaissance to locate all springs
and points of potential spring flow under changing hydrologic
30 5 10 15 20 25 31 5 10 15 20
OCTOBER 1964 NOVEMBER
Figure 14. Comparison of water levels in the Floridan
aquifer, Crystal River and the Gulf of Mexico.
Fresh-salt water balance in a coastal area under natural
conditions altered slightly by gound-water withdrawal.
Inland migration of fresha-alt water interface as a result
of construction of an uncontrolled tidal canal which allows
increased discharge of fresh water from the aquifer and
inland movement of salt water through the canal.
Fresh-salt water Interface migrates farther inland as ground
water withdrawals increase and canal is extended. Can cause
saline contamination of a previously fresh supply.
Figure 15. Results of alerting the fresh-salt balance in the aquifer in a
conditions(2) detailed analysis of the amount and variation of
the salinity of water from wells in the Crystal River area; (3)
determination of the elevation of the piezometric surface in
the Floridan aquifer in the coastal area and approximate
location of the line where the ground-water level equals sea
level; (4) the continuous monitoring of the flow of Crystal
River; and (5) an extensive program of recording the discharge,
water level, and chemical quality of water from streams, lakes,
springs, sinkholes, and wells (part of the investigation of the
hydrology of the Middle Gulf area cooperatively planned and
financed by the Southwest Florida Water Management District
and the Bureau of Geology, Florida Department of Natural
Resources, and the U.S. Geological Survey).
Continuing hydrologic investigations in the area include: (1)
an expanded hydrologic-records program to determine
discharge, water level and chemical quality of water from
streams, lakes, springs, sinkholes, and wells, to monitor
changes in the hydrologic system brought about by accelerated
land development; (2) test drilling to determine the position of
the fresh-salt water interface in the aquifer and to obtain basic
geologic and other hydrologic data; and (3) studies to
determine the minimum level of fresh water required in the
area to prevent salt-water intrusion of the aquifer and saline
contamination of water supplies such as those of the cities of
Crystal River and Homosassa.
Additional hydrologic investigations needed in the area
include: (1)more detailed definition of the fresh-salt water
interface in the aquifer, the extent of its movement from year
to year, and its relation to natural events and to developmental
measures. Eventually key wells will be equipped with
electronic instruments which will continuously measure the
salinity and water level within the aquifer; and (2) definition
of the areas of major local recharge. Although the recharge
area for the springs includes a large area east of the springs,
some of the water that emerges from the springs is probably
recharged locally. Local recharge areas need to be defined so
that the spring flow will not be endangered by improper use of
The area surrounding the springs is attractive for land
development. However, caution should be used in land
development, so that damage to the springs, the hydrologic
system feeding them, and the potable water supplies in the
aquifer can be avoided or minimized.
WHERE CAN MORE INFORMATION BE OBTAINED?
Additional information on the hydrology and geology of
Citrus and Hernando counties and of coastal areas in general is
contained in the following reports:
Black, A.P., Brown, Eugene, and Pearce, J.M.,
1953 Salt water intrusion in Florida, 1953: Florida State Board
of Conservation Water Survey and Research Paper no. 9.
Cooper, H.H., Jr.,
1964 (and Kohout, F.A., Henry, H.R., and Glover, R.E.) Sea
water in coastal aquifers: U.S. Geol. Survey, Water-Supply
1947 (and Lingham, C.W., and Love, S.K., and Vernon, R.O.)
Springs of Florida: Florida Geol. Survey Bull. 31.
Florida Board of Conservation, Division of Water Resources,
1966 Florida land and water resources--southwest Florida.
Parker, Garald G.,
1955 The encroachment of salt water into fresh; in: The
Yearbook of Agriculture, p. 615-635; 723.
Sherwood, C. B., and Grantham, R.G.,
1966 Water control vs. sea-water intrusion, Broward County,
Florida: Florida Geol. Survey Leaflet 5.
1951 Geology of Citrus and Levy counties, Florida: Florida
Geol. Survey Bull. 33.
1964 Geohydrologic reconnaissance of Pasco and southern
Hernando counties, Florida: Florida Geol. Survey Rept.
1965 Reconnaissance of springs and sinks in west-central
Florida: Florida Geol. Survey Rept. Inv. 39.