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STATE OF FLORIDA
STATE BOARD OF CONSERVATION





DIVISION OF GEOLOGY

Robert O. Vernon, Director







REPORT OF INVESTIGATIONS NO. 48








ANALYSIS OF THE WATER-LEVEL
FLUCTUATIONS OF LAKE JACKSON NEAR
TALLAHASSEE, FLORIDA

By
Gilbert H. Hughes
U. S. Geological Survey










Prepared by the
UNITED STATES GEOLOGICAL SURVEY
in cooperation with the
DIVISION OF GEOLOGY
FLORIDA BOARD OF CONSERVATION
Tallahassee, Florida
1967










FLORIDA STATE BOARD

OF

CONSERVATION






CLAUDE R. KIRK, JR.
Governor


TOM ADAMS
Secretary of State




BROWARD WILLIAMS
Treasurer




FLOYD T. CHRISTIAN
Superintendent of Public Instruction


EARL FAIRCLOTH
Attorney General




FRED O. DICKINSON, JR.
Comptroller




DOYLE CONNOR
Commissioner of Agriculture


W. RANDOLPH HODGES
Director








LETTER OF TRANSMITTAL


JVivison of eoloqy

CaIlahzassee
June 15, 1967

Honorable Claude R. Kirk, Jr., Chairman
State Board of Conservation
Tallahassee, Florida


Dear Governor Kirk:

One of the most pressing problems relating to water resources
management is that of flood plain control and zoning. A study of
all of our flood plain problems is now being completed by the
Corps of Engineers, personnel of the State Board of Conservation,
and the U. S. Geological Survey.
A study on Lake Jackson has just been completed in which it
was recorded that the 1966 high record level of water in the basin
has established a base line for future planning. A report on the
"Analysis of the Water-Level Fluctuations of Lake Jackson near
Tallahassee, Florida," has been prepared by Gilbert H. Hughes of
the U. S. Geological Survey and is being published as Report of
Investigations No. 48. It is anticipated that the data presented in
this report will be valuable to the planning departments of the
City of Tallahassee and Leon County, and will serve as an example
for State studies.
Respectfully yours,
Robert O. Vernon
Director and State Geologist
























































Completed manuscript received
June 15, 1967
Printed for the Division of Geology
By the E. O. Painter Printing Company
DeLand, Florida

iv











TABLE OF CONTENTS


Introduction .....-....----------- -------..-....... .-.-----------..............- 1
Available data .......................... .... ................------------ ... .......... ..... 1
Lake levels ---..............---..------.....-..-.....-- ----- ..-.--..-..-..-- 1
Rainfall -.-......--...---.........-.-.-... --... --... .--- --.. ---- .--..- -...- ..------ ... 2
Evaporation ..............---.......- -- -------------................---.........- 4
Surface water ....................................-------------- ------. --.... -............- 5
Ground-water levels ....--...-.....--..------...-...-...-...- ...-----...-- 6
Ground-water movement .--....--.......-....---------.......... --------.. ......-..--.-- 8
Analysis of data .......-...-...-------.---........... --------...----- ..--- .----- 9
Rainfall versus rise of the lake level .....----..........--..--- ..-.--.........--...-- 9
Long-term fluctuations of the lake level .....-.............-.................-................. 14
Comparison of lake level and ground-water level .-......---...-..-......-....---.--- 15
Comparison of lake levels and rainfall .-..-......-...................---.....---.. 15
Analysis of the yearly change of the lake level ..--.......--..---........---....-- ...... -- 17
Control of the lake level -...--...-....--......--.........-------------------...... 22
Rising lake level -..--...----.....---.... ------------....----- 23
Declining lake level ....----....-.......--.....---------. --. ------...-..-.......---- 24
Summary --..---..-.......--...-- --...------------------------- 25
References ...-------.....---.....~ ......................-------....------------ 25




Illustrations

Figure Page
Frontispiece. Lake Jackson at high water March 1966. --.--...----.-----...--.-..... viii
1 Location of Lake Jackson ........----....... .......----- ----- .--.......---...... 2
2 Month-end water level of Lake Jackson ---.............. ............-- -----..-- 3
3 Stage-duration curve for Lake Jackson ..........------.......----..---.. ...-.. 4
4 Yearly rainfall at Tallahassee, Fla., 1886-1965 .--......-..-- ....-- .....-- ....--- 5
5 Relation between cumulative rainfall at Tallahassee, Florida
and that at Monticello, Florida; and Quincy, Florida .---_ ---- 6
6 Yearly average water level of Lake Jackson and selected wells ..---- 8
7 Lake Jackson when dry in 1932 --.............---.. --... --- .-._ _____.- 10
8 Water-level rise of Lake Jackson during selected storm periods -.. 11
9 Months for which water-level recorder chart record for Lake
Jackson was complete ---..........................................---- ... --... 12
10 Monthly rainfall estimated for Lake Jackson versus the cumu-
lation of all rises of the lake level during the month .--.......-----..--.... 13
11 Double-mass relation between estimated rainfall at Lake Jack-
son and the resulting rise of the lake level ...--.........----......--...---.. 14
12 Three-year moving average of rainfall at Tallahassee, Florida ...--- 16
13 Relation between the average of yearly rainfall at Quincy,
Monticello, and Tallahassee, and the net yearly change of the
level of Lake Jackson .-.--.---- ----------....-..-..-.. ........ --...............-........... 20







14 Relations of net yearly lake-level change and yearly rainfall at
Quincy, Monticello and Tallahassec, Florida ................................. 21
15 Cumulative frequency curve for average of rainfall at Quincy,
Monticello, and Tallahassee, Florida .................................................... 22
16 Cumulative frequency curve for net yearly lake-level changes of
Lake Jackson .---....... ............. ........-.........-..... ... ..........................-- .-- 23

TABLES
able Page
1 Monthly evaporation from Class A pan at Woodruff Dam,
1959-65 .. ........ .. ... ................ ......................... ............ ...................... 7
2 Net yearly change in water level of Lake Jackson,
1950-65 .-- -....-..-...-...- ...... .................... ... .... .............. ........... 17













































1


Lake Jackson at high water March 1966.







ANALYSIS OF THE WATER-LEVEL
FLUCTUATIONS OF LAKE JACKSON NEAR
TALLAHASSEE, FLORIDA
By
Gilbert H. Hughes

INTRODUCTION

Lake Jackson, near Tallahassee, currently (1966) is at a
record-high level and is flooding parts of adjacent residential areas.
The apparent disregard of the hazard of developing the adjacent
flood plain areas is partly understandable as the lake was almost
dry as recently as 1957.
The wide fluctuations of the lake level concern those who have
an interest in the overall utility and scenic attractiveness of the
lake as well as those whose property may be flooded. The purpose
of this report is to summarize the hydrologic data that pertain to
the fluctuations of the lake level so that the cause of the fluctua-
tions can be more easily understood. Such understanding is
required of those responsible for making decisions relative to lake
control and land development.
Lake Jackson occupies a closed depression in an area of expand-
ing population within the environs of Tallahassee, the State Capital.
The lake is a valuable asset to the residents of the county and
state, providing a convenient recreational area for boating, fishing,
and bird hunting.
The approximate center of the somewhat irregularly shaped
lake is about 7 miles north of the center of Tallahassee, figure 1.
The altitude of the lowest point on the rim of the ridge that
separates Lake Jackson drainage basin from the Ochlockonee River
is about 115 feet. Lake Jackson recently rose to a maximum alti-
tude of 96.5 feet. At altitude 90 feet, Lake Jackson covers about
9.8 square miles (6,300 acres) or about 23 per cent of its 43.2
square mile drainage area.

AVAILABLE DATA

LAKE LEVELS
The altitude of the water level of Lake Jackson has been
measured by a continuous water-level recorder since March 1950
except at times when the water level dropped below the operating





REPORT OF INVESTIGATIONS NO. 48


Figure 1.-Location of Lake Jackson.


limit of the gage. During these periods monthly measurements of
the water level were obtained from an auxiliary staff gage. The
monthly hydrograph for Lake Jackson is shown by figure 2. Figure
3 shows for the period of record the per cent of time that the
lake was at or above a particular level.

RAINFALL

Rainfall has not been measured at Lake Jackson but rainfall
at, or near, Tallahassee has been recorded since 1886. The
average yearly rainfall for Tallahassee for all years of record
through 1965 is 57.32 inches. The variation in annual rainfall at
Tallahassee is shown by figure 4.
Rainfall at Quincy, Florida and Monticello, Florida (fig. 1)
has been recorded since 1917 and 1906, respectively; however, the
record for Monticello is incomplete for several years prior to 1920.
The long-term average of yearly rainfall for all years of complete
record through 1965 is 55.33 inches for Quincy and 56.82 inches
for Monticello. Figure 5 compares the cumulative yearly rainfall
at Tallahassee with that at both Quincy and Monticello. In each




4 FI I;m I I mII


_j 96
w
w
j 94


w 92
f)

z 90
W

2 88


S86
0

84
I--
W
W 82


i 80
U.
W

-i 78

W
76

74
74


F1950gue 2- 1955 Mo d w r 1960d w r 1 965 1 Jc1970

Figure 2.-Month-end water level of Lake Jackson.


I I I I


I I I I


1111


I I I I


- 80


78


, 76






REPORT OF INVESTIGATIONS No. 48


92

96 S-- ---



. ..i. \ i

RECORD USED- WATER LEVEL ON 51th, 0Ith, 151h,2Oth,25th AND END
90 -- ---- OF EACH MONTH, JANUARY 1950 TO SEPTEMBER 1966
<


-J
'f i









and Sept 1956 through Aug. 1958. Most of the estimated record

84
was below 76 5 ft. (especially during 1957) and therefore the
duration curve is less accurate for this portion.



0 10 20 30 40 50 60 70 O0 90 100
PERCENT OF TIME INDICATED LAKE LEVEL WAS EQUALLED OR EXCEEDED
Figure 3.-Stage-duration curve for Lake Jackson.

case, only the data for complete years common to both of the
involved stations were used.
The graph indicates that yearly precipitation at the three
stations is almost equal and that there is no appreciable long-term
deviation between the stations. Thus, the average of rainfall at
these three stations should be reasonably representative of that
falling at Lake Jackson.

EVAPORATION

Evaporation from Lake Jackson has not been measured directly,
but the yearly rate may be estimated with reasonable accuracy
from measurements of evaporation from the United States Weather
Bureau Class A Pan at Woodruff Dam (fig. 1). Records of pan
evaporation for years 1959-65 are summarized in table 1.






ANALYSIS OF WATER-LEVEL-LAKE JACKSON


70 ..
-6 J -- 60





o 0 ,






Figure 4.-Yearly rainfall at Tallahassee, Florida, from 1886 to 1965.



According to Kohler and others (1959, Plate 3), a yearly pan
coefficient of 0.77 is applicable to Class A pan evaporation in the
vicinity of Tallahassee. Thus, on the basis of this coefficient and
records of pan evaporation in table 1, yearly lake evaporation
averages about 50 inches or 4.2 feet per year.


SURFACE WATER

Most of the time there is little or no surface-water inflow to
Lake Jackson; however, following periods of above average rain-
fall substantial inflow may occur from intense rainstorms. Small
rivulets fed by ground water or by drainage from small ponds and
lakes also contribute inflow to Lake Jackson during unusually wet
periods, however, no measurements of surface-water inflow have
been made.
There is no surface-water outflow from Lake Jackson. The lake
can spill into the Ochlockonee River only when the lake level is
above about 115 feet. This altitude is almost 19 feet above the
present record-high level of the lake.
present record-high level of the lake.





REPORT OF INVESTIGATIONS NO. 48


RAINFALL AT TALLAHASSEE HUNDREDS OF INCHES


Figure 5.-Relation between cumulation rainfall at
Monticello and Quincy.


Tallahassee, and that at


GROUND-WATER LEVELS

Periodic measurements have been made of the water level in
well Leon 115 since 1950. This well which is near the shoreline
of Lake Jackson (fig. 1), is 194 feet in depth, and penetrates
the artesian aquifer which underlies Florida and parts of Georgia
and Alabama. Wells Leon 5 and Leon 7 (fig. 1), drilled as supply
wells for the City of Tallahasse, penetrate the same artesian
aquifer. The water level in well 5 was measured from 1932 to
1950, and that in well 7 has been measured from 1945 to present.
Hydrographs in figure 6 show that the level in well 115 differs
in altitude from that in well 7, but the two fluctuate in the same












TABLE 1.-MONTHLY EVAPORATION FROM CLASS A PAN AT WOODRUFF DAM, 1959-65. o

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Year

Maximum 3.09 3.80 5.66 7.28 9.11 8.84 7.85 7.77 7.53 6.28 3.74 3.04 69.17
Average 2.42 3.28 5.14 6.64 7.88 7.50 7.44 7.12 6.67 5.27 3.45 2.71 65.51
Minimum 2.00 2.69 4.09 5.28 7.33 6.47 6.71 6.43 5.58 3.31 3.26 2.35 57.47







z






REPORT OF INVESTIGATIONS NO. 48


100


95


90___
LAKE JACKSON

85





75


40
well 115
35 ________ -




A A I
25 ---- "-"i, 5-F-
I'
20
well 5 well 7


15
0 0 0 0 C
Figure 6-Yearly average water level of Lake Jackson and selected wells.
Figure 6.-Yearly average water level of Lake Jackson and selected wells.


general manner. The hydrographs for wells 5 and 7
the same during the period of concurrent record,
expected from their proximity to each other.


are basically
as might be


GROUND-WATER MOVEMENT

The rate of ground-water movement into, or out of, Lake
Jackson has not been determined. The level of Lake Jackson
consistently is about 50 to 55 feet above the level of the piezometric






ANALYSIS OF WATER-LEVEL-LAKE JACKSON


surface in the underlying limestone aquifer. Active sinkholes have
existed in the lake bottom (Sellards, 1914 p. 128) and, with the lake
at a low level, the downward movement of lake water has been
visible. Thus, some water probably always moves from the lake to
the limestone aquifer system through sinkholes. A sink-hole depres-
sion, exposed when the lake was dry in 1932, is shown in figure 7.
In addition to the limestone aquifer there is a surficial, sandy-
clay aquifer with a water table that probably approximates the
lake level in areas adjacent to the lake. During years of greater-
than-average rainfall the surficial aquifer probably contributes
significantly to the lake, but during dry periods its contribution
to the lake is probably small.
Net ground-water movement to or from the lake may vary
depending on the relative amounts contributed by the surficial
aquifer and lost to the limestone aquifer. Evidence developed later
in this report indicates that net ground-water movement is into
the lake during most years having greater-than-average rainfall
and out of the lake during most years having less-than-average
rainfall.

ANALYSIS OF DATA

RAINFALL VERSUS RISE OF LAKE LEVEL

Much of the rainfall at Lake Jackson is from thunderstorms
that are intense but of brief duration. The rise of the lake level
due to such storms is illustrated by graphs in figure 8. During
these brief periods of rise, loss of water by evaporation or ground-
water outflow is small. Thus, the rise of the lake level should be at
least as great as the rainfall; any inflow from the tributary area
during the storm adds to the lake-level rise.
The over-all effect of inflow from the tributary area can be
evaluated by comparing the lake-level rise to the rainfall. Rain-
fall was not recorded at Lake Jackson and thunderstorm intensities
vary greatly over wide areas, therefore, such a comparison cannot
be made on a daily basis. However, the variability of rainfall at
different points in the area tends to decrease as the measurement
period is increased.
Thus, to evaluate the effect of inflow to Lake Jackson from its
tributary area, the rise of the lake level was determined for all
detectable storm periods. All rises whether abrupt or gradual were
included, but only the months for which the recorder record was





















,p t V, ho.s


V,


v0
1 z
i'1 :ii.!ai ;0
I ?. i.: 00


Figure 7.-A sink hole depression in Lake Jackson when dry in 1932.







ANALYSIS OF WATER-LEVEL--LAKE JACKSON


0.


(a)



Apr. 27, 1950 Apr. 28, 1950


0.5
(d)



May 30,1952 My 31,1952
May 30, 1952 May 31, 1952


Dec. 4, 1964 Dec.5, 1964


Nov. 15, 1961 Nov. 16,1961

Figure 8.-Water-level rise of Lake Jackson during selected storm periods.



complete and accurate were included. These months are identified
by bar graphs in figure 9.
Figures 10 and 11 show the accumulation of all individual rises
during a month compared to the average of monthly rainfall at
Quincy, Monticello, and Tallahassee.
The plot of points in figure 10 indicates that for monthly rain-
fall of less than about 0.6 foot the rise of the lake level is less
than the rainfall while with greater rainfall the rise of the lake
level exceeds the rainfall. Part of the scatter of the plot can be
attributed to the fact that the measured rainfall was not always
representative of rainfall on Lake Jackson. Scatter due to this
cause, however, should tend to be centered about the equal-value
line.


1


O.






REPORT OF INVESTIGATIONS NO. 48


950 i..... i...... i







57

S... ...... I iiiiiiiiiiiiiiiiiiii iiiii
196 : .:. ::.






JAN FEB MAR APR MAY JUN JUL AUG SEPT OCT NOV DEC

EXPLANATION
Period of complete record


Figure 9.-Months for which water-level recorder chart record for Lake
Jackson was complete.

The tendency for the lake-level rise to be smaller than monthly
rainfall for amounts less than about 0.6 foot may be due partly to
evaporation and ground-water outflow and partly to mechanical
lag of the water-level recorder. If the recorder is following a down-
ward trend, the water level must rise about 0.01 foot before a trace
of the rise is recorded. This effect is a cumulative one if only the
rises are considered as has been done on this analysis. The total
effect is appreciable for months having several rises.
The tendency of the lake-level rise to exceed rainfall when
monthly rainfall is greater than about 0.6 foot is probably due to
surface-water inflow from the more intense storms during the
month.
The data shown in figure 10 are plotted on a cumulative basis
in figure 11. Monthly values of each parameter were summed in
chronological order for months when the data were complete.
(See fig. 9).
The over-all slope of the graph in figure 11 shows that measured
rainfall generally exceeded the recorded rise of the lake level. As






ANALYSIS OF WATER-LEVEL-LAKE JACKSON


I J.*. *

g** a 0

:** .*

0 0.2 0.4 0.6 0.8 1.0
MONTHLY RAINFALL


1.2
FEET


1.4 1.6 1.8 2.0


Figure 10.-Plot of monthly rainfall estimated for Lake Jackson
cumulation of all rises of the lake level during the month.


versus the


mentioned above, this tendency may be due to the use of nonrepre-
sentative rainfall data, mechanical lag of the recorder, loss of water
from the lake by evaporation, or by ground-water outflow during
storm periods.
The breaks in the slope of the graph are generally related to
rising and declining trends of the lake level. Periods of increasing
slope, which correspond to rising trends of the lake level, indicate
that surface-water inflow probably contributed appreciably to the
lake-level rise during these periods. This interpretation is consis-
tent with the fact that rising trends of the lake level are related
to periods of greater-than-average rainfall when maximum surface
runoff occurs.
Urbanization alters the pattern of runoff from an area and may
alter the total yield of the area. The effect of progressive urbani-
zation would be manifested in a cumulative relation involving






REPORT OF INVESTIGATIONS NO. 48


0 5 10 15 20 25 30 35 40 45 50 55 60
CUMULATIVE RAINFALL, FEET
Figure 11.-Double mass relation between estimated rainfall at Lake
Jackson and the resulting rise of the lake level.

runoff, and by a tendency for the relation line, as shown in figure
11. to drift persistently in one direction. In figure 11, however,
the relation line shows no such tendency, indicating that to date
the total runoff from the lake basin has not been altered appreci-
ably by urbanization.

LONG-TERM FLUCTUATIONS OF LAKE LEVEL

The hydrologic significance of the recent water-level fluctua-
tions of Lake Jackson may be appraised by considering past
fluctuations. Unfortunately, systematic observations of the water
level of Lake Jackson, or of any comparable lake, were -not made
prior to 1950. Other hydrologic parameters, such as rainfall and
ground-water levels, have been observed for longer periods of






ANALYSIS OF WATER-LEVEL-LAKE JACKSON


time. Thus, if similarities can be established between lake-level
fluctuations and variations of other hydrologic parameters, the
probable range of the past lake-level fluctuations may be inferred.

COMPARISON OF LAKE LEVEL AND GROUND-WATER LEVEL

Although lakes and ground-water bodies differ in many ways,
the two have at least one important factor in common. Both derive
their water from rainfall. Thus, if the recharge area for the
ground-water body is in the general area of the lake, the fluctua-
tions of the two must follow the same long-term trend.
The recharge area for the limestone aquifer underlying Lake
Jackson though not precisely delineated is known to be widespread.
As indicated by rainfall records for Quincy, Monticello, and Talla-
hassee, the variations in rainfall at Lake Jackson would apply
to a broad area. Therefore, the long-term water-level fluctuations
of Lake Jackson should be similar to those of wells 7 and 115.
Although the hydrograph for Lake Jackson shown in figure 6 is
not entirely similar to those shown for wells 7 and 115, the
graphs do follow the same over-all trends.
The fluctuations of the ground-water levels between 1933 and
1947 are smaller than those for subsequent years (fig. 6). Thus,
though records of lake-level fluctuations prior to 1950 are lacking,
the graphs of ground-water levels suggest that the fluctuations of
Lake Jackson between 1933 and 1947 were much less pronounced
than those for subsequent years. A longer period of record is
needed for comparison, in order to establish which set of fluctua-
tions might be considered the more unusual.

COMPARISON OF LAKE LEVELS AND RAINFALL

Extreme levels of natural water bodies normally result from
successive years of greater-than-average or less-than-average rain-
fall rather than from a gross excess or deficiency of rainfall in any
one year. The cumulative effect of two or more years of rainfall
can be appraised by use of a moving average of rainfall.
The moving average is computed by averaging rainfall data for
a specified number of consecutive years, progressively discarding
data for the first year of the period as data for each successive
year is included. Thus, in a sense, the period represented by the
average moves through the entire period of record. Figure 12
shows the moving average of rainfall at Tallahassee for 3-year






REPORT OF INVESTIGATIONS NO. 48


Figure 12.-Three-year moving average of rainfall at Tallahassee, Florida.


periods, the average being plotted at the end of the last year of the
period represented.
Although the rainfall graph (fig. 12) and the water-level
graphs for Lake Jackson and wells 5 and 7 (fig. 6) differ in
detail, in a gross sense the graphs are similar. The rainfall record
for Tallahassee was used to compute the moving average because
the period of continuous record for this station was appreciably
longer than that for either Quincy or Monticello.
The rainfall graph suggests that the 3-year periods preceding
1948. 1956, and 1965 were periods of hydrologic significance. The
graph further suggests that the level of Lake Jackson was higher
in 1965 than at any time during the preceding 75 years. The same
conclusion is indicated by moving average graphs for 4- and
10-year periods. The graph for 5-year periods shows the average
for the period ending 1948 to be slightly higher than that for 1965.
Lake Jackson was dry during the early part of 1957, coincident
with the low shown on the graph of rainfall. The lake is quite
shallow, however, and leakage through its bottom may vary. Thus,
the lake could have been dry during less severe drought periods
than 1954-56. Sellards (1914, p. 129) reported the lake to be "dry,
or nearly so, in the early spring of 1907." He also mentioned the
existence of two active sinks in the lake bottom. Local residents
report that the lake was dry in 1932, 1935, and 1936. Thus, inter-
preted in light of this information, the rainfall graph indicates
that the lake may have been dry a number of times.






ANALYSIS OF WATER-LEVEL-LAKE JACKSON


ANALYSIS OF THE YEARLY CHANGE OF THE LAKE LEVEL

The level of Lake Jackson declines because of evaporation from
the water surface, transpiration by aquatic vegetation, and ground-
water outflow. The lake level rises because of precipitation on the
water surface and inflow from the tributary area. Whether there
is a net decline or a net rise for a given period depends on the
degree of balance between these different factors. Separate analy-
sis of years of net decline and of years of net rise provides a
broader basis for understanding the behavior of the lake.
During years 1950-56, 1962-63, the lake level declined an
average of 2.2 feet per year (table 2). Evaporation from the water
surface as computed from table 1 was 4.2 feet per year, and it is
arbitrarily assumed that any transpiration by aquatic vegetation
was the same. Yearly rainfall at Lake Jackson may be assumed
equal to the average of rainfall at Quincy, Monticello, and Talla-
hassee, which during these particular years (table 2) was 4 feet
per year. Thus, the net decline that may be attributed to the
difference between precipitation and evaporation was only 0.2 foot.
The remaining 2.0 feet of the decline represents ground-water

TABLE 2.-NET YEARLY CHANGE IN WATER LEVEL OF LAKE
JACKSON, 1950-65
[Minus (-) indicates decline; plus (+) indicates rise]

Average lake Net yearly Estimated rain-
Year level, in feet change, in feet fall*, in inches

1950 92.5 -1.7 45.1
1951 90.2 -1.9 54.1
1952 88.8 -2.3 46.1
1953 86.4 -1.4 60.9
1954 83.0 -5.0 30.4
1955 79.1 -3.2 41.8
1956 76.9 -1.8 51.7
1957 .... +2.2 66.3
1958 80.2 +2.4 52.9
1959 83.4 +5.0 73.7
1960 87.2 +3.2 64.8
1961 89.1 +0.2 51.8
1962 88.4 -1.0 47.9
1963 87.3 -1.6 51.3
1964 88.8 +4.7 92.0
1965 94.2 +3.9 73.4


Quincy, Monticello, and Tallahassee.


*Average of rainfall at






REPORT OF INVESTIGATIONS NO. 48


outflow in excess of ground-water and surface-water inflow from
the tributary area. If such inflow were zero-and it probably was
minimal during these relatively dry years-the decline of 2.0 feet
per year would be a measure of the ground-water outflow.
During years 1957-61, 1964-65, the lake rose an average of
3.1 feet per year. Precipitation at Quincy, Monticello, and Talla-
hassee during these years averaged 5.6 feet. Evaporation and
transpiration again may be assumed to be 4.2 feet per year. Thus,
only 1.4 feet of the 3.1 feet average yearly rise may be attributed
to the difference between precipitation and evaporation. The
remaining 1.7 feet of the rise represents the difference between
gound-water and surface-water inflow from the tributary area and
ground-water outflow. In other words, inflow from the tributary
area apparently was greater than ground-water outflow through
the lake bottom by an amount equivalent to 1.7 feet per year.
The relative distribution of inflow from the tributary area
between surface-water inflow and ground-water inflow cannot be
determined. The small lakes and ponds within the tributary area
are influenced by the same factors that cause Lake Jackson to
fluctuate, and they contribute inflow to Lake Jackson only at the
height of unusually wet periods. In addition their combined surface
area is small relative to that of Lake Jackson. Therefore, the
drainage of surface water from lakes and ponds would not be likely
to noticeably affect the average yearly rise of Lake Jackson.
The preceding analysis of the lake-level rise due to rainfall
shows that at times during and immediately after storms, surface-
water runoff contributed substantially to the water-level rise of
Lake Jackson. This effect does not appear to have exceeded from
I to 1.5 feet per year during the wettest years (fig. 11). Thus,
during wet years ground-water inflow may have exceeded ground-
water outflow.
Ground-water outflow during dry years was equivalent to a
lake-level decline averaging at least 2 feet per year, and it could
be about the same during wet years. If so, ground-water inflow
contributed substantially to the over-all lake-level rise during the
wet years.
The years of net rise all occurred after the lake was almost
dry in 1957, when one active sink reportedly was filled with dirt.
Therefore, ground-water outflow during years after 1957 may have
been less than indicated by data for preceding years.
This possibility is partly substantiated by data given in table 2.
During years 1952-53 and 1962-63 the lake was declining from






ANALYSIS OF WATER-LEVEL--LAKE JACKSON


about the same level. The over-all decline was 3.7 feet in 1952-53
compared to only 2.6 feet in 1962-63; yet, rainfall at Quincy,
Monticello, and Tallahassee was 0.7 feet greater in 1952-53. No
conclusion regarding ground-water outflow can be made based on
this evidence, however, because rainfall at Quincy, Monticello, and
Tallahassee is not necessarily always truly representative of rain-
fall at Lake Jackson. Future observations during a prolonged
drought period may indicate whether ground-water outflow has
changed appreciably, but such observations likewise may not be
conclusive because sinkholes may develop at any time.
Figures 10 and 11 show that the rise of the lake level is closely
related to areal rainfall. Thus, if yearly evaporation and seepage
are virtually constant, the yearly net lake-level change should be
directly related to yearly rainfall. Data given in table 2 suggest
that such a relation exists but the plot of these data in figure 13
does not expressly define the relation.
The scatter of the data in figure 13 is not unusual for hydrologic
correlations of this type but part of the data appear to be grouped
in a way that is not independent from the sequence of years. This
type of grouping suggests that the required underlying assump-
tions may not have applied uniformly during the entire period
under consideration. For example, such an effect might result
from a pronounced change in seepage.
In figure 14 similar data are plotted separately for the individ-
ual rainfall stations involved. The scatter of these plots more
nearly conforms to that which might be due primarily to the non-
representativeness of the rainfall data with respect to Lake
Jackson. Thus, the apparent grouping that results when these data
are averaged may be only coincidental.
A more adequate measurement of rainfall at Lake Jackson
would be required to evaluate the inconsistencies which abound in
figures 13 and 14. Some scatter still would persist, however,
because the effects of variations in the seasonal distribution of
rainfall are not entirely compensating within the period of a year.
If, tentatively, the relation between yearly rainfall and net
yearly lake-level change shown in figure 13 can be presumed to be
defined, further speculations can be made regarding the relative
frequency of a given yearly lake-level change. The relative fre-
quency of areal rainfall, as represented by the average of rainfall
at Quincy, Monticello, and Tallahassee, is shown on a cumulative
basis by the graph in figure 15. By means of 'the relation between





REPORT OF INVESTIGATIONS NO. 48


RAINFALL, INCHES
Figure 13.-Relation between the average of yearly rainfall at Quincy, Monti-
cello and Tallahassee, and the net yearly change of the level of Lake Jackson.


rainfall and lake-level change given in figure 13, the rainfall fre-
quency curve can be converted into a frequency curve for lake-level
change as shown in figure 16.
Figure 16 can be used to approximate the probability of occur-
rence of a yearly lake-level change of a specified magnitude. The
reality of the approximation rests on the validity of three assump-
tions: (1) that yearly rainfall is a random event; (2) that the
relative frequency of rainfall has been established by records of
past rainfall; (3) that the relation between rainfall and lake-level
changes shown in figure 13 adequately represents the true relation.
If the factors controlling the lake level are in basic equilibrium,
the frequency curve in figure 16 should be symmetrical about the
line of zero change. As drawn, the frequency curve suggests a







I-


,>+6 -6 +6




-.4 +4





6 -- -- -6 L
I I




S 20 40 60 0 00 10 20 40 60 80 00 0 20 40 60 0 1
& 0 0
U. -2 -2 -












rainfall at Quincy, Monticello, and Tallahassee.






REPORT OF INVESTIGATIONS NO. 48


S70








30


0 10 20 30 40 50 60 70 80 90 100 110
PERCENT OF TIME THAT INDICATED YEARLY
RAINFALL WAS EQUALLED OR EXCEEDED
Figure 15.-Cumulative frequency curve for average of rainfall at Quincy,
Monticello, and Tallahassee, Fla.


slight tendency for the lake to dry up. This tendency probably is
real, as the lake has been dry several times, but the tendency may
be greater or less than indicated because part of the basis for the
frequency curve was not explicitly defined.
The foregoing analyses may be affected by variations in evapo-
ration during wet and dry years. The pan evaporation record at
Woodruff dam was available only for the years 1959-65. However,
yearly pan evaporation for 1962-63, which were relatively dry
years, averaged only 0.6 inch more than that for 1964-65, which
were relatively wet years. Thus, it is doubtful that variations in
annual evaporation are an important factor.


CONTROL OF THE LAKE LEVEL

Lake Jackson is currently flooding adjacent residential areas
which, as lakeshore properties, offer scenic and recreational advan-
tages. Although to date the behavior of the lake apparently has






ANALYSIS OF WATER-LEVEL--LAKE JACKSON


PERCENT OF TIME LAKE-LEVEL RISE EQUALLED
OR EXCEEDED THAT INDICATED
Figure 16.-Cumulative frequency curve for net yearly lake-level change of
Lake Jackson.

not been affected by urbanization within its tributary area, con-
tinued urbanization may increase the total inflow to the lake.
The threat of increased damage by future floodings leads to the
consideration of methods of maintaining the lake below a given
maximum level. However, the diversion of water from the lake
to control high levels during wet periods will tend to decrease the
utility of the lake during dry periods. Thus, methods of maintain-
ing the lake level above a given minimum level during dry periods
also may be considered.


RISING LAKE LEVEL

The design of an outflow system to maintain the lake level
below a given maximum level should be based on data representa-
tive of the maximum rise that probably will occur. The outstanding
rise of Lake Jackson, within the period of record, occurred from
December 1, 1964 to April 30, 1965, when the net rise was 1.6 feet
for the month of December alone and 5.2 feet for the 5-month
period. Preventing any appreciable cumulative rise of the lake
level during this prolonged and unusually wet period would have
required the removal of a volume of water each month equivalent






REPORT OF INVESTIGATIONS NO. 48


to a rise of about 1 foot. Some fluctuation of the lake level would
result, of course, because inflow does not occur at a uniform rate.
Most of the net rise of the lake for December 1964, for example,
was due to a rise of 1.1 feet within a 24-hour period (figure 8,
graph (e)).
The volume of water equivalent to a 1-foot rise of the lake
level depends on the surface area of the lake which, in turn, varies
with the lake level. The higher the lake level, the greater the
surface area and the greater the volume of water corresponding
to a given rise.
The level of the lake prior to the outstanding rise beginning
in December 1964 was slightly below the altitude of 90 feet. At this
level the surface area of the lake is about 6,300 acres. The volume
of water corresponding to a 1-foot rise at this level is about 6,300
acre-feet. Removal of this volume of water within a period of
30 days would require an average outflow of 106 cfs (cubic feet
per second) or 48,000 gpm (gallons per minute).
Flow by gravity past the controlling feature of the outflow
system would vary with the height of the water above the level
of the controlling feature. Thus, flow would not occur at an average
rate but, rather, would be greater than average part of the time
and less than average part of the time. To accomplish an average
flow of 106 cfs, therefore, the controlling feature of the outflow
system must be designed to pass a maximum flow substantially
greater than the average. A lower rate of outflow could be used
if more time were allowed to lower the lake to the desired level.
In this case, however, the cumulative lake rise would be greater,
thus requiring a greater allowance for the zone subject to flooding.

DECLINING LAKE LEVEL

During years having less-than-average rainfall the level of
Lake Jackson usually declines. If the decline could be decreased
by adding water to the lake during dry years, the utility of the
lake for some purposes would be increased.
The decline of the lake level averaged 2.2 feet per year for
the 9 years of net decline since 1950 (table 2). The required
inflow to offset such a decline with the lake level at an altitude
of 90 feet, for example, would be equivalent to a continuous inflow
of about 20 cfs or 9,000 gpm. As a matter of comparison, this
amount is about 50 per cent greater than the pumpage for the
City of Tallahassee, which during 1965 averaged about 6,200 gpm.






ANALYSIS OF WATER-LEVEL--LAKE JACKSON


SUMMARY

The present high level of Lake Jackson is due to the occurrence
of an unusual number of successive years of greater-than-average
rainfall. Total rainfall at Tallahassee during the 3-year period
1963-65 exceeded that for any 3-year period since at least 1885.
By way of contrast, the drought at Tallahassee during 1954-56 was
the most extreme that has occurred since at least 1885. Oddly
enough, this severe drought occurred within the decade (1956-65)
having the highest average rainfall since at least 1885.
Rainfall on the lake and surface-water inflow to the lake during
and immediately after storms basically are the only factors causing
the lake level to rise, rainfall being the predominant factor.
Ground-water inflow apparently contributes appreciable water to
the lake during years of greater-than-average rainfall. Ground-
water inflow contributes to the over-all rise of the lake by retarding
the lake-level decline due to evaporation and ground-water outflow
during the interval between storms.
The level of Lake Jackson can be stabilized within reasonable
limits. However, facilities for doing so must be designed to remove
large amounts of water from the lake during years of unusually
'great rainfall and to return large amounts of water to the lake
during most years of less-than-average rainfall.


REFERENCES

Kohler, M. A.
1959 (and Nordenson, T. J. and Baker, D. R.) Evaporation maps for
the United States: U. S. Weather Bureau Tech. Paper No. 37.
Sellards, E. H.
1914 Some Florida lakes and lake basins in Sixth Annual Report:
Florida Geological Survey.