Title: Reprint from AGE OF CHANGING PRIORITIES FOR LAND AND WATER
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Abstract: Jake Varn Collection - Reprint from AGE OF CHANGING PRIORITIES FOR LAND AND WATER (JDV Box 43)
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Reprinted from


AGE OF

CHANGING

PRIORITIES

FOR LAND

AND WATER






Irrigation and Drainage Division Specialty Conference
SPOKANE, WASHINGTON
September 26-28,1972
Sponsored by
Irrigation and Drainage Division
American Society of Civil Engineers
Co-Sponsor
Pacific Northwest Region,
American Society of Agricultural Engineers
Co-operating Organization
American Meteorological Society



Published by
American Society of Civil Engineers
345 East 47th Street
New York, N. Y. 10017


I -
















HYDROGEOLOGY OF FLORIDA'S LARGEST CITRUS GROVEa

By William E. Wilson1



INTRODUCTION

In 1968, land clearing was begun for a citrus grove in north-
eastern DeSoto County, Florida (Fig. 1), in a geographic setting that
contrasted with what had generally been considered the most desirable
for citrus production in the State. The site of the new grove was a


referred to in text

A-A'
Line of geologic section,
figure 3


FIG. 1.--LOCATION OF STUDY AREA SHOWING WELLS AND LINE OF GEOLOGIC
SECTION

lPublication authorized by the Director, U. S. Geological Survey.
Hydrologist, U.S. Geological Survey, Tampa, Florida.

293
WILSON


I~










practically treeless poorly drained flatland dotted with shallow de-
pressions and covered with palmettos and wire grasses. The traditional
citrus belt of Florida lies in the hilly sandy well-drained ridge
sections of the State. Nonetheless, the new grove, when fully planted,
will be the largest single citrus grove in Florida under one manage-
ment; it will cover 42 square miles and will require a source of irri-
gation water capable of yielding nearly 200 million gallons per day.
For decades the development of water resources in DeSoto County
proceeded gradually and without significant hydrologic consequences.
New wells were drilled each year for irrigating vine crops, citrus,
and pasture, but population growth was slow, and extensive areas of
flatland remained uncultivated. The establishment of the large new
grove was one of several developments that could significantly affect
the area's water resources. The county adjoins populous coastal
counties to the west and south, and pressures are being felt as they
look inland for potential water supplies for their burgeoning popula-
tions. To the north, in Hardee and Polk Counties, water levels have
been lowered markedly owing to large ground-water withdrawals by phos-
phate mining and processing industries, in combination with pumpages
for irrigation, citrus processing, and municipalities. Large mineral
leases are being held in reserve in DeSoto County until mining of phos-
phate there becomes economically feasible. As the sand hills of the
citrus belt become urbanized, successful production of citrus in the
flatlands takes on added importance. If the large grove in DeSoto
County succeeds, probably others on a similar scale will be established
in the area.
In 1969 the U.S. Geological Survey began a water-resources inves-
tigation of DeSoto and Hardee Counties, in cooperation with the South-
west Florida Water Management District. The District has jurisdiction
over the water resources of the river basin in which the two counties
lie, and the investigation is intended to provide information that the
District can use in regulating and managing the resources. This paper
presents some results of the hydrogeologic studies made as part of the
two-county study. The author gratefully acknowledges the cooperation
and assistance of officials of American Agronomics Corporation and
American International Food Corporation.


DESCRIPTION AND IRRIGATION

The grove forms a vast geometric pattern that dominates the land-
scape when viewed from the air (Fig. 2). By mid-1972, more than 21,000
acres were under cultivation and about 2.3 million trees had been set.
The trees are planted in rectangular 10-acre tracts, and the grove is
criss-crossed by roads and an extensive 660-mile network of ditches.
The checkered pattern is interrupted only by numerous shallow depres-
sions, or flag ponds, that are too poorly drained to be planted in
citrus.
Average annual rainfall is abundant (51 inches). However, about
60 percent comes during 4 months, June through September, and for much
of the remainder of the year, irrigation of citrus is beneficial. Irri-
gation requirements at the grove, as projected by agricul -ralenieer-
ing consultants call for a capacity of 5 pym_ er ace (gallons per
minute per acre), or 193 mgd (mliion gallons per day) for the 42


WILSON


r



































FIG. 2.--AERIAL VIEW OF FLORIDA'S LARGEST CITRUS GROVE, DESOTO COUNTY,
FLORIDA

square miles. Irrigation water is pumed fm n dir v
'nto the ditches that con levin h 1 m. i^
w pan s The ditches also lower the initially high shallow
water table and carry away excess runoff during non-irrigating periods.
As the trees mature, irrigation will be by mobile high-pressure guns
that discharge water pumped from the ditches through rotating sprink-
ler heads. Grove operators hope that irrigation requirements can be
reduced by as much as 40 percent by efficient management and through
the development of new irrigation methods now being tried in central
Florida.
At the grove, pumpage is greatest during the dry winter and spring
and least during the wet summer (Fig. 3). Pumpage has been monitored
at various intervals since the first wells were pumped in the fall of
1969. Each well was rated to determine a relation between discharge
and electric power consumption, and total grove pumpage was computed
from total kilowatt-hours consumed. The highest average dailvDumiae
during t-h intervals was 3 e sprin of 1971 On May 19,
171, 21 wells were pumping at 53.5 mgd, the highest daily rate of re-
cord. Average daily pumpage in 1971 (12.6 mgd) was more than twice
that n197 ( m ), reflecting the expansion of the grove during
1971. During the first half of 1972, however, the average daily pump-
age was less than that during 'the first half of 1971, owing both to
more efficient operation of the irrigation system and to greater pre-
cipitation during the first half of 1972.

HYDROGEOLOGIC CONDITIONS


Geologic Setting.--The surficial sand of the area is underlain by a


WILSON


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40 i-- | --------|----------
40





0o 30

eo.
W




-4l

wz

L J N I VI. N ld
0 20
















thick sequence of gently dipping carbonate and elastic rocks of Ter-
tiary age. As shown in Fig. 4, a north-south cross section at the
grove, two artesian aquifer have been designated in the upper 1,500
feet--the Floridan aquifer and the secondary aquifer. The highly
transmissive Floridan aquifer underlies all of Florida and in this
area includes the Lake City Lm stone, Avon Park Limestone, Ocala
Group, and Suwannee Limestone The aquifer is about 1,000 feet thick
and consists of zones of highly permeable cavernous limestone and dolo-
mite separated by layers of marl and dense limestone of low permeabil-
ity. The most productive zone is a cavernous section in the hard
brown dolomite of the Lake City Limestone.
Underlying the Floridan aquifer are limestone, dolomite, and
evaporite deposits of low permeability. Overlying the aquifer is about
150 feet of predominantly elastic deposits, tentatively assigned to the
Tampa Formation, which consists principally of clay but includes beds
of sand, marl, and limestone. These deposits serve as a confining
layer for water in the Floridan aquifer.
The secondary artesian aquifer consists of permeable limestone
beds in the upper part of the Hawthorn Formation. Water in this aqui-
fer is confined by overlying marl and clay.

Well Construction and Yields.--Irrigation wells at the grove are
being drilled on a 1-mile grid. Well construction is illustrated
diagrammatically in Fig. 4. The wells are bout 1,340 feet deep on
the average; most have 150-200 feet of 12-inch upper casing, followed
2The nomenclature used is that of the Florida Bureau of Geology.
thick sequence of gently dipping carbonate and elastic rocks of Ter-
tiary age. As shown in Fig. 4, a north-south cross section at the
grove, two artesian aquifers have been designated in the upper 1,500

transmissive Floridan aquifer underlies all of Florida and in this
area includes the Lake City L iestone, Avon Park Limestone, Ocala
Group, and Suwannee Limestone The aquifer is about 1,000 feet thick
and consists of zones of highly permeable cavernous limestone and dolo-









layer for water in the Floridan aquifer.









2 The nomenclature used is that of the Florida Bureau of Geology.


WILSON


r


I II- --












A A'
200
20 22 23 24

Sand, clay, and marl
Secondary
OPEN Aquifer
Hawthorn Formation CASING HOPLE Aquifer
0 200 Confining
Tampa Formation bed

0 400
m- L Suwannee Limestone OPEN .
< HOLE
- 600
. Ocala Group
w<
Un W
z 800

.0
z O Avon Park Limestone
W 1000 -
I-

> 1200 -
J Lake City Limestone

1400

0 I 2 MILES
1600 I I I
FIG. 4.--GEOLOGIC SECTION AND WELL CONSTRUCTION (SEE FIG. 1 FOR LOCA-
TION)

by an interval of about 100 feet of open hole in the secondary aquifer.
From 200 to 300 feet of 10-inch lower casing seals off part of the
lower Hawthorn Formation and the plastic rocks of the Tampa Formation.
Below 400 to 500 feet, the wells are open hole in the Floridan aquifer.
Drilling generally continues until the highly permeable zone in the
Lake City Limestone is penetrated, usually at depths greater than 1,100
feet. The wells thus tap both aquifers and are open to 900-1,100 feet
of rock. This method of construction is characteristic of large diameter
wells used for irrigating citrus, pasture, and vine crops in the
area. Many 2-inch and 4-inch wells used for domestic, stock-watering,
and small-irrigation purposes tap only the secondary aquifer.
Turbine pumps with 75 horse power electric motors have been in-
stalled in the wells. Pumping rates range from 1,000 to 2,240 gpm and
average 1,800 gpm. Field specific capacities computed for 15 wells
range from 13 to 121 gpm/ft and average 62 gpm/ft. As of mid-1972, 37
wells had been drilled; capacity of the well field at that time was
estimated to be 100 mgd.

Potentiometric Surface.--In 1969, the potentiometric surface in
this area sloped to the southwest at 1.2 ft per mile (5). Water levels
measured periodically in wells at the grove since 1969 have confirmed


WILSON


I











the gentleness of the gradient. In September 1971 the average water-
level elevation in 30 wells was 51 feet above sea level (about 38 feet
below land surface); in only three of the wells were the water-level
elevations lower than 50 feet above sea level. Measured water levels
in irrigation wells at the grove represent an average value of the
hydraulic head in both the secondary and Floridan aquifers. However,
the head difference between the two aquifers at the grove is probably
small.
The pattern of seasonal fluctuations of the potentiometric sur-
face in Hardee and DeSoto Counties reflects the synchronous effects of
the rainfall distribution and irrigation pumpage. The range in season-
al fluctuation in 1971 was less than 10 feet in most of DeSoto County
and more than 20 feet in most of Hardee County. At the grove, the
average water level rose 6 feet between measurements in May and Septem-
ber 1971. At the Marshall observation well, 12 miles west of the
grove (Fig. 5), annual water-level minima during 1962-72 had a wide

4 i ii i i I i
w
< 8







W 20 MARSHALL
I' 3 OBSERVATION -
< WELL
24 -
I-_
w
LL 28 I




FIG. 5.--HYDROGRAPH OF MARSHALL OBSERVATION WELL, DESOTO COUNTY,
FLORIDA

range in elevation, probably owing to year-to-year differences in the
timing and amounts of spring rainfall and irrigation withdrawals. With
the onset of heavy summer rains and the general cessation of pumping
for irrigation, the potentiometric surface recovered rapidly and nearly
to the same level each year.
In most of Polk, Hardee, and DeSoto Counties, the potentiometric
surface showed a net decline between 1964 and 1969 (5). In north-
eastern DeSoto County this decline was about 5 feet. Declines of more
than 20 feet occurred in Polk County, a center of heavy year-round
industrial ground-water withdrawals in addition to agricultural and
municipal pumpages. The lowering is reflected in the general downward
trend of the autumnal peaks in the hydrograph of the Marshall observa-
tion well (Fig. 5). The declines in DeSoto County can probably be
attributed to a combination of increased irrigation pumpage and a de-
ficiency in rainfall. During 1964-71, rainfall at nearby Arcadia was


WILSON


~ I~ ~











18.65 inches below normal, based on the 1941-70 mean.

Water Quality.--Water pumped from the grove wells is of a calcium
magnesium sulfate type and is satisfactory for citrus irrigation.
Temperature ranges from 260C to 32C and averages about 300C; total
hardness averaged 497 mg/l (milligrams per liter) and sulfate content
averaged 368 mg/l in samples from five of the wells.
Chemical characteristics of water in the Floridan aquifer are
different from those in the secondary aquifer, as suggested by the
analyses in Table 1. Well TB-1, used at one of the grove equipment

TABLE 1.--CHEMICAL ANALYSES OF WATER FROM WELLS

WELL 17 WELL TB-1

Aquifer Secondary and Secondary
Floridan
Date sampled 4-6-71 10-26-71
Temperature (degrees C) 31.0 25.5
Specific conductance
(micromhos per centimeter at 250C) 1060 670
pH 8.0 8.3

Dissolved solids (determined) 875 398
Dissolved solids (calculated 761 384
Silica (SiO 20 51
Calcium (Ca 134 36
Magnesium (Mg) 46 26
Sodium (Na) 18 54
Potassium (K) 3.0 3.5
Bicarbonate (HCO ) 139 224
Sulfate (SO ) 429 5.4
Chloride (Ci) g 22 97
Fluoride (F) 1.5 2.0
Nitrate (NO ) 0.0 1.4
Phosphate ( PO) r .01
Hardness (Ca, Mg) ) 545 208
Hardness (non-carbonate) r 431 24
Alkalinity 0 114 184


sheds, taps only the secondary aquifer; well 17 is open to both aqui-
fers, but derives its major supply from the Floridan aquifer. Water
in the secondary aquifer is cooler and less mineralized than that in
the Floridan aquifer. The secondary aquifer does contain higher con-
centrations of chloride and fluoride, the latter probably derived from
the abundant phosphorite in the Hawthorn Formation and younger deposits
The higher temperature and higher sulfate content of water in the Flor-
idan aquifer probably reflect a deeper circulation pattern and contact
with evaporite deposits known to occur in the Lake City Formation and
underlying Oldsmar Formation (4).
Highly mineralized water is reported to lie at about 1,500 feet
below sea level in much of the interior of central Florida (3). Many
irrigation wells in Polk, Hardee, and DeSoto Counties, including some


WILSON


I











at the large new grove, have been drilled to 1,400-1,500 feet below
sea level. None of these is known to pump salt water, even though the
potentiometric surface has been lowered 40-60 feet in the last 20 years
in parts of Polk County (5). Such a substantial lowering should result
in the upward movement of salt water, but this encroachment has
probably been retarded by rocks of low permeability underlying the
Floridan aquifer. In addition, the salt water in these counties may
occur considerably deeper than reported. At the grove, no significant
differences in chloride and sulfate contents and specific conductance
were observed among seven samples collected periodically from well 17
during 1970-72 (Table 2), suggesting that no deterioration in chemical
quality of ground water occurred during this time.

TABLE 2.--CHEMICAL CHARACTERISTICS OF MULTIPLE WATER SAMPLES FROM
WELL 17

Date Specific Conductance Sulfate Chloride
Sampled (micromhos per centi- (milligrams per
meter at 25'C) liter)

7-2-70 998 359 27
4-6-71 1,060 429 22
4-22-71 1,050 474 22
5-10-71 1,070 -- 22
6-4-71 1,070 476 22
4-27-72 1,030 -- 22
5-24-72 1,020 440 25

HYDRAULIC PROPERTIES OF THE AQUIFER SYSTEM

Aquifer Model.--The hydrogeologic conditions at the grove can be
represented by Hantush's mathematical model for leaky artesian systems
(2, p. 325-326). The general system is composed of a semipermeable
layer confining a main artesian aquifer resting on an impermeable bed.
In the case applicable to the grove, the system is overlain by a satu-
rated sand bed in which the head distribution is not influenced by
pumping in the artesian aquifer. The discharge of wells is supplied
from local storage in the artesian aquifer and from leakage through
and storage in the confining bed.
Representation of the field conditions at the grove is complicated
by the presence of two artesian aquifers, the secondary and Floridan.
In the model, these were treated as a single main artesian aquifer,
because data are insufficient to consider them separately. The clay
and marl beds of the Tampa Formation and those overlying the Hawthorn
Formation act as semipermeable confining beds. Results of aquifer
tests, described below, indicate that some water is derived from stor-
age in these confining beds. The shallow water table at the grove is
controlled at a relatively constant level, and the rocks underlying
the Floridan aquifer act as an impermeable bed.

Aquifer Tests.--Analyses of data from aquifer tests made at the
well field indicate the aquifer system has a high transmissivity and
has a storage coefficient in the artesian range. In one test, a well
was pumped at a constant rate of 2,075 gpm for 4.1 days. Net water-


WILSON


----











level change was 0.6 foot in an observation well 1 mile away. In an
effort to increase the drawdown due to pumping, a second test was made
in which seven wells were pumped at an initial combined rate of 12,530
gpm, and water-level changes were observed in four observation wells.
During the first day of pumping, the seven wells were cut off in a
series of power failures caused by lightning. These wells were turned
back on, but the test was terminated after about 30 hours because of
additional lightning strikes.
A reasonably good fit can be made between the observed data and
a modified leaky-aquifer type curve plotted from the tables of Hantush
(1,2), as shown in Fig. 6 for one of the observation wells. In the
analysis the distance from each observation well to an effective center
of pumpage, r, was computed as follows: the products of the logarithm
of the distance to each pumping well and the discharge of each well
were summed and divided by total discharge; r equals the antilog of
that quotient. A revised value was computed at each time of change in
discharge rate, and drawdown, s, was divided by discharge, Q, to
account for the variable pumping rates. Average values of aquifer and
confining-layer characteristics determined from the tests are as
follows: 5 2 -
Aquifer transmissivity, T = 2.7 x 10 ft gay ;
Aquifer storage coefficient, S = 3.0 x 10 ; and
Confining-bed hydraulic conductivity divided by thickness,
K'/b' = 1.5 x 10 day .

PROJECTED DRAWDOWNS

The aquifer and confining-layer characteristics 7:re used to
project anticipated drawdowns in the vicinity of the well field for
various pumping rates and durations, as shown in Fig. 7. The values
of aquifer and confining-layer characteristics determined from the
tests were used in the analysis. In addition, the storage coefficient
of the confining bed, S', was assumed to be 5.0 x 10-2. In the analy-
sis, the pumpage was considered to be coming from a single well at the
center of the well field. During actual irrigation operations, the
drawdown distribution near the well field would differ slightly from
that shown whenever the effective center of pumpage differed from the
well-field center.
The equations of Hantush (1, 2) for computing drawdowns are appli-
cable only within certain time ranges that depend on the magnitude of
the confining-layer characteristics. Drawdown solutions were obtain-
able for times less than 33 days and more than 670 days. Following
the procedures suggested by Hantush (1, 2), drawdowns for intermediate
times were obtained by constructing from inspection a smooth curve
between the two plotted segments (Fig. 7).
The graph shows, for example, that if the well field were pumped
at 100 mgd for 100 days, drawdown in the aquifer 5 miles from the grove
center would be less than 5 feet, and at 10 miles drawdown would be
about 2 feet. If the full projected well-field capacity of about 200
mgd were pumped for 10 days, drawdown at 5 miles would be about 4 feet.
Fig. 7 also indicates that after pumping at any constant rate up to 200
mgd for about 2 years (670 days), no further drawdown of the potentio-
metric surface would occur as long as that rate were maintained. Under
these conditions, water derived from storage in and leakage through


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r











































0
0 00


TYPE CURVE


MATCH POINT


H (,D) I
I *I
O *.tS100-

I/At 7.IlOI


EXPLANATION
* 1971 tulflelr tst, Q0 12,530 wgp
A 1971 iqulfr tt., 0 vrioble
0 1I70-71 Well-field pmpage, QvorMe


-It Ill 10o10


10' lO-1 10-7
TIME / DISTANCE I, I/Ot, IN DAYS/FEiT


FIG. 6.--PLOT OF t/r2 VERSUS s/Q, AND MATCHING MODIFIED LEAKY-AQUIFER TYPE CURVE FOR WELL 18


-- 0-----
,_,--a


I



z


0-7L
10


1


1 I I I I I I


_ o .




































,, 8 -


z 10

z
0
0 2 --- ---------


02 Q`Ioo

AT 10 MILES I --
4 _-__


6



I 2 5 10 20 50 100 200 500 1000
TIME SINCE PUMPING STARTED, IN DAYS
FIG. 7.--PROJECTED DRAWDOWNS AT 5 MILES AND 10 MILES FROM THE GROVE CENTER








304


the confining beds would be sufficient to supply the amount pumped.
Pumpage at the citrus grove is cyclic, not constant, and there-
fore Fig. 7 cannot be used to predict drawdowns resulting from long-
term grove operations. In order to assess the magnitudes of drawdowns
that might be expected over a period of several years, a hypothetical
annual pattern of pumpage was assumed and drawdown at 5 miles computed
(Fig. 8). The pattern consists of 155 days of fall and winter pumping
O>




w




















(E O I 2 3 Q






at 50 mgd, 90 days of spring pumping at 100 mgd, and 120 days of













stations, resulting fro pumpage at the grove, would be superposed
Z 5
z o-
W -
0c




W o





a-
< M 100

W -




0 2 3 4
TIME, IN YEARS
FIG. 8.--PROJECTED LONG-TERM CHANGES IN POTENTIOMETRIC SURFACE DUE TO
HYPOTHETICAL PATTERN OF GROVE PUMPAGE

at 50 mgd, 90 days of spring pumping at 100 mgd, and 120 days of
summer shutdown. The durations and ratios of pumping correspond
approximately to those of 1970-71; the magnitudes are probably reason-
able for fully operational conditions. Average daily pumpage for the
year with this pattern would be about 46 mgd.
Fig. 8 shows that pumping according to the hypothetical schedule
would result in a lowering of the potentiometric surface to approx-
imately the same elevation at the end of each spring pumping period.
At the end of the first year's recovery period, the potentiometric
surface would show a small net decline, but in succeeding years addi-
tional net declines would be negligible. The initial net decline
represents water removed from aquifer storage; in succeeding pumping
cycles, water would be obtained from leakage. These water-level fluc-
tuations, resulting from pumpage at the grove, would be superposed
upon the seasonal fluctuations that occur each year.


WILSON







305


Reliability of Results.--The aquifer model is a simplified
representation of a complex and really extensive multi-aquifer system.
A meaningful test of the applicability of the model in the area of the
grove would require extensive pumpage and water-level history before
and after the installation of the well field at the grove. Such data
are not available, but some indication of the degree of reliability
can be obtained by analyzing nearly a year's record of well-field
pumpage and the corresponding water-level fluctuations at two observa-
tion wells--one (well 18) at the margin of the grove and the other
(Foster Farms observation well) about 17 miles southwest of the grove
(Fig. 9).

0
'\ FOSTER FARMS /
S\ OBSERVATION
C\ WELL
z 2 /8







W'\

3 WELL 18 -' I


1970 1971
1 NID J I FI M I A M I J A S

0 100 200 300
TIME, IN DAYS


FIG. 9.--GROVE PUMPAGE AND WATER-LEVEL CHANGES IN OBSERVATION WELLS,
1970-71

In the analysis, the well-field pumpage was treated as a 335-day
aquifer test with variable discharge. Drawdown at well 18 caused by
this pumpage was estimated by subtracting the measured water-level
changes at the Foster Farms observation well from those at well 18.
Fluctuations in the Foster Farms observation well were considered to
represent the regional seasonal changes unaffected by pumpage at the
new grove. As in the short-term aquifer tests, revised values of r
and s/Q were computed each time average well-field discharge changed.
The data points, shown in Fig. 6, plot in a scatter about the type
curve, but fall within the log cycles that would be expected from an
extension of the short-term aquifer-test data. Considering the many
variables involved in comparing and analyzing water-level fluctuations


WILSON











in observation wells, these results suggest that the model, while
imperfect, is a reasonable representation of the aquifer system at the
grove.


CONCLUSIONS

Florida's largest citrus grove has been established in an area of
complex hydrogeologic conditions that can be generally represented by a
mathematical model for leaky artesian aquifer systems. Results of
aquifer tests and analysis of early well-field history suggest that
ground-water withdrawals for irrigation will probably result in small
drawdowns near the grove, on the order of feet rather than tens of
feet. Pumping rates may exceed 100 mgd during spring irrigation
periods, but, during non-irrigating seasons, the potentiometric surface
will probably recover nearly fully from the effects of pumping. Thus
long-term net declines due to grove pumping will probably also be small
The effects of pumping must be considered in the perspective of
other current and prospective ground-water developments in the area.
In addition, in the analyses areal variations in aquifer and confining-
bed properties in the region surrounding the grove were not assessed.
If present, these boundary conditions could significantly affect the
magnitude of drawdowns at and near the grove. Monitoring of pumpage,
water-level changes, and water quality would be necessary to provide
the Southwest Florida Water Management District with the background
data necessary for sound management, but the model can be used for
preliminary resource-management purposes.




APPENDIX I.--REFERENCES



1. Hantush, M.S., "Modification of the Theory of Leaky Aquifers,"
Journal of Geophysical Research, Vol. 65, No. 11, Nov., 1960,
pp. 3713-3725.
2. Hantush, M. S., "Hydraulics of Wells," Advances in Hydroscience,
V. T. Chow, ed., Vol. 1, Academic Press, New York, 1964, pp.
281-432.
3. Pride, R. W., Meyer, F. W., and Cherry, R. N., "Hydrology of Green
Swamp Area in Central Florida," Report of Investigations 42,
Florida Geological Survey, Tallahassee, Florida, Feb., 1966.
4. Stewart, H. G., "Ground-water Resources of Polk County," Report of
Investigations 41, Florida Geological Survey, Tallahassee, Florida
Aug., 1966.
5. Stewart, J. W., et al., "Potentiometric Surface and Areas of
Artesian Flow, May 1969, and Change of Potentiometric Surface 1964
to 1969, Floridan Aquifer, Southwest Florida Water Management
District, Florida," Hydrologic Investigations Atlas 440, U. S.
Geological Survey, Washington, D. C., 1971.


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I













APPENDIX II.--NOTATION




The following symbols are used in this paper:

b' = uniform thickness of a semipervious confining bed of leaky
systems;
H(u,0) = well function for leaky aquifers;
K' = hydraulic conductivity of a semipervious confining bed;
Q = constant discharge rate of a well or well field;
r = weighted logarithmic mean radial distance from center of a
pumping well or well field to an observation well;
s = drawdown in an observation well;
S = storage coefficient of an artesian aquifer;
S' = storage coefficient of a semipervious confining bed;
T = transmissivity of an artesian aquifer;
t = time since beginning of pumping of a well or well field;
t = weighted logarithmic mean time since beginning of pumping of
a well or well field;
u = r2S/4Tt;
S= parameter in formulas pertaining to leaky systems with
storage in semipervious confining bed, defined in Hantush (2).


WILSON


C




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