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    Title Page
        Page i
        Page ii
    Table of Contents
        Page iii
        Page iv
    Introduction
        Page 1
    Factors that influence lake levels
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
    Fluctuations in lake levels
        Page 10
        Page 11
        Page 12
    Effects of lake-stage control
        Page 13
        Page 14
    Summary
        Page 14
        Page 15
        Copyright
            Main

STATE OF FLORIDA
STATE BOARD OF CONSERVATION
DIVISION OF GEOLOGY


FLORIDA GEOLOGICAL SURVEY
Robert 0. Vernon, Director





INFORMATION CIRCULAR NO. 47


CONTROL OF LAKE


LEVE LS IN ORANGE COUNTY,
FLORIDA


By
Warren Anderson, W. F. Lichtler, and B. F. Joyner





Prepared by the
UNITED STATES GEOLOGICAL SURVEY
in cooperation with the
FLORIDA GEOLOGICAL SURVEY
and the
BOARD OF COUNTY COMMISSIONERS OF ORANGE COUNTY



TALLAHASSEE


1965






4 4 L



AGCR
CULTURAL
LOBRARY







































Completed manuscript received
December 8, 1964
Printed by the Florida Geological Survoy-22
Tallahassee
1968












Introduction ............. .... .... ... ... .... .......... 1
Factors that influence lake levels ............... ... ............ 2
Rainfall ................... .... ...... ..... .... 2
Evaporation .................... .... ................. 2
Relationship of rainfall and evaporation to changes in lake
levels ........................... .. ......... ......... 4
Surface inflow ................................. .... ..... 4
Surface outflow .......... ................................ 4
Underground inflow and outflow ..... .......... ...... ....... 7
Fluctuations in lake levels ....... ............................. 10
Control of lake stages.......................................... 10
R ainfall ....................................... ........ 10
Evaporation .................................. ........... 10
Surface inflow........ .............. ....................... 10
Surface outflow ............................ ..... ... ....... 11
Underground inflow and outflow ........ ...... .............. 11
Effects of lake-stage control .......... ......... ... ............. 13
Summary ........................................ ........... 14

ILLUSTRATIONS

Figure
1 Bar graph of rainfall at Orlando, Florida, showing monthly
averages, maximums and minimums ............ ........... 3
2 Bar graph of lake evaporation in Orange County, Florida,
showing monthly averages................................. 5
3 Bar graphs showing comparison of average monthly change
in stage of three lakes in Orange County, Florida (upper
graph), and average monthly difference in rainfall and
evaporation at Orlando, Florida (lower graph) .............. 6
4 Cross section of a lake perched above the water table ...... 8
5 Cross section of a water-table lake ..................... 8
6 Cross section of an artesian lake ........................ 9
7 Map of Orange County, Florida, showing the range in fluctua-
tion of selected lake levels and the decline in the piezome-
trio surface from September 1960 to May 1962 .............. 12









CONTROL OF LAKE LEVELS IN ORANGE COUNTY, FLORIDA


By
Warren Anderson, W. F. Lichtler, and B. F. Joyner



INTRODUCTION

The many lakes in Orange County are a valuable natural re-
source. The lakes are of great value as recreational facilities,
as settings for homesites, and as sources of water for the irriga-
tion of more than 20,000 acres of citrus and truck crops on the
mucklands adjacent to several of the lakes. Air temperatures near
lakes are moderated by the lakes. The elevation and fluctuation
of the water surface in lakes are of concern to all persons using
the lakes for any purpose. The value of the lakes is reduced if
their levels fluctuate excessively. Flooding caused by high lake
levels damages homes, roads, and crops, and interferes with trans-
portation. Low lake levels render boat houses and docks useless,
cause loss of fish and wildlife, curtail aquatic recreation, increase
the cost of irrigation, reduce the moderating effect of the lakes on
the air temperature, and usually reduce the amount of recharge to
underlying aquifers. These undesirable effects of extremes in
lake levels could be reduced or even eliminated if the lake levels
were controlled to reduce the range between extremes.
If a lake is used for more than one purpose, there is some-
times disagreement as to the optimum level of the lake. Before
taking measures to control the level of a lake, the effect that
those measures will have on other areas and on municipal and
industrial water supplies must be considered. Effective plan-
ning for the control of lake levels requires an understanding of
the factors that affect lake levels, the methods that can be used
to control them, and the effects of the control measures on the
lake and its environment.
The purpose of this report is to provide information that will
increase this understanding and thereby bring about better use of
lakes in Orange County.





FLORIDA GEOLOGICAL SURVEY


FACTORS THAT INFLUENCE LAKE LEVELS

Lake levels are influenced by rainfall, evaporation, surface
inflow, surface outflow, underground inflow, and underground out-
flow. All lake levels are influenced by rainfall and evaporation
but the influence of one or more of the other factors may be ab-
sent.

RAINFALL

Rainfall, the source of water in Orange County lakes, is ex-
tremely variable. Variation in rainfall is the main reason lake
levels fluctuate. The annual rainfall at Orlando, which averages
51.37 inches, has been as little as 33.76 inches and as much as
68.74 inches. Extremely low lake levels are usually the result
of several successive dry years. The lowest lake levels of record
occurred near the end of the drought period, 1954 to 1956, during
which rainfall was deficient by 20 inches. On the other hand, high
lake levels can be caused by excessive rainfall during a much
shorter period such as August and September 1953, when rainfall
was 10 inches above normal.
On the average, 57 percent of the annual rainfall in Orange
County falls during the rainy season from June to September.
Occasionally more rain falls during the dry than during the rainy
season, as in 1958 when only a third of the year's rain fell during
the rainy season. Figure 1 shows the maximum, minimum, and
average monthly rainfalls at Orlando.

EVAPORATION

The average annual evaporation from lakes in Orange County
was computed to be 51.07 inches, based on the normal pan evapo-
ration reported by the U. S. Weather Bureau at Orlando, and ad-
justed by coefficients determined from evaporation studies at Lake
Okeechobee between 1940 and 1946.1 This amount is only 0.3 inch
less than the average annual rainfall at Orlando.
Evaporation is much less variable than rainfall. The annual
evaporation at the Belle Glade station has departed from the nor-

lU. S. Geological Survey, 1954, Water Loss Investigations: Lake Hefnel
Studies, Technical Report: U. S. Geological Survey Prof. Paper 269, p. 128.






INFORMATION CIRCULAR NO. 47


J F M A M J J A S O N D
Figure 1. Bar graph of rainfall at Orlando, Florida showing monthly
averages, maximums and minimums.






FLORIDA GEOLOGICAL SURVEY


mal by more than two inches in only three of the 36 years of record.
The maximum difference was only seven and one half inches.
Evaporation varies seasonally from a minimum rate in December
and January to a maximum rate in May. Figure 2 shows the ave-
rage monthly evaporation from lakes in Orange County.

RELATIONSHIP OF RAINFALL AND EVAPORATION TO CHANGES
IN LAKE LEVELS

The direct exchange of water between lakes and the atmos-
phere is accomplished by rainfall and evaporation. Rainfall and
evaporation determine the seasonal trend in lake levels. Figure
3 shows the differences in the average monthly rainfall and eva-
poration in comparison with the average monthly change in stage
of three lakes in Orange County. When the difference is negative
(rainfall less than evaporation), the lake levels fall, and when the
difference is positive (rainfall more than evaporation), the lake
levels rise. The reaction of some lake levels to an excess of rain-
fall over evaporation is delayed at the beginning of the rainy
season by storage of water in the ground. The levels of lakes
with surface outlets normally decline in October despite a slight
excess in rainfall over evaporation because of the large surface
outflow when the lakes are high.

SURFACE INFLOW

Surface inflow occurs when it rains so much the soil becomes
saturated or when it. rains so hard the soil cannot absorb the rain
fast enough to keep it from running off. The volume of inflow to
a lake depends on the amount of rainfall rejected by the soil and
the size of the area that. drains to the lake. The change in a lake
level caused by a given volume of surface inflow depends on the
area of the lake and the volume of water lost from the lake during
the period of inflow. The inflow will cause the lake level to rise
if its volume is more than the volume lost, but the lake level will
fall if the volume of inflow is less than the volume lost.

SURFACE OUTFLOW

Surface outflow occurs when the level of a lake rises above
the lowest point on its rim. Many lakes in Orange County do not







INFORMATION CIRCULAR NO. 47


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showing monthly averages.


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3 JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT OCT. NOV. DEC.

Figure 3. Bar graphs showing comparison of average monthly change in stage of three lakes in Orange County,
Florida (upper graph), and average monthly difference in rainfall and evaporation at Orlando, Florida (lower graph).






INFORMATION CIRCULAR NO. 47


have surface outflow because their levels never rise above their
rims. Some lakes would have to rise more than 40 feet for surface
outflow to occur.
Surface outflow normally increases as the level of a lake
rises; however, sometimes the outflow is decreased by water
backed up in the outlet channel even though the level of a lake is
rising.
There is very little surface outflow from lakes in Orange
County during extreme droughts.

UNDERGROUND INFLOW AND OUTFLOW

These two factors will be considered together because they
are closely related. Indeed, it is possible for both processes to
occur in the same lake at the same time. Figures 4, 5, and 6 show
the relationships that lakes can have to aquifers. Three aquifers
exist in Orange County; the water-table aquifer, the shallow ar-
tesian aquifer, and the Floridan or deep artesian aquifer. The
water-table aquifer is the zone of saturated earth above the rela-
tively impermeable layer that confines the artesian aquifers. The
artesian aquifers are zones of saturation beneath impermeable
layers that confine the water under greater than atmospheric pres-
sure. The artesian pressure surface, which is called the piezome-
tric surface, is the height to which water will rise in a tightly
cased well that is drilled into the aquifer. The levels and fluc-
tuations of the water table and the piezometric surface are more
or less independent of each other, depending on the permeability
of the confining bed.
Figure 4 depicts a lake that is perched above the water-table
aquifer. There can be no underground inflow to this type of lake
as its level is higher than the surrounding water table nor can
there be much underground outflow from it because of its imper-
meable bottom.
Figure 5 shows a cross section of a water-table lake. This
type of lake forms where the land surface dips below the water
table. Under the conditions shown in the illustration, there is no
exchange of water between the lake and the aquifer because the
lake surface and the water table are at the same level. This con-
dition seldom exists and most of the time the lake level is either
below the water table, at which times water seeps into the lake,






FLORIDA GEOLOGICAL SURVEY


Figure 4. Cross section of a lake perched above the water table.


Figure 5. Cross section of a water-table lake.






INFORMATION CIRCULAR NO. 47


Figure 6. Cross section of an artesian lake.


or the lake level is above the water table, at which times water
seeps out of the lake. A cross section of an artesian lake is shown
in figure 6. This type of lake is connected directly to the artesian
aquifer and reflects the piezometric surface. Two lakes in Orange
County Emerald Springs and an unnamed lake near Rock Springs -
are definitely known to be of this type and there may be others.
Water from the water-table aquifer probably seeps into these lakes
and recharges the artesian aquifer continuously. It is possible,
however, for the opposite process to occur if the piezometric
surface becomes higher than the water table around the lake.


Land Surfae


_ __






FLORIDA GEOLOGICAL SURVEY


FLUCTUATIONS IN LAKE LEVELS

All of the lakes in Orange County tend to fluctuate seasonally
because the factors that affect lake levels seasonally rainfall
and evaporation affect all of the lakes similarly. On the other
hand, the range in the fluctuations of the lakes varies widely
because the factors that control the range in fluctuation topo-
graphy and geology vary widely from lake to lake. The observed
range in stage of Lake Susannah is only 2.4 feet, but a range in
stage of 20 feet has been observed for Lake Sherwood (fig. 7).

CONTROL OF LAKE STAGES

The logical approach to control of lake levels is through con-
trol of the factors that affect them. These factors are: rainfall,
evaporation, surface inflow and outflow, and underground inflow
and outflow.

RAINFALL

No way has been devised to prevent rain, so it is not possible
to prevent the rise of lake levels in this way. Some success in
causing rainfall by cloud seeding, under favorable cloud condi-
tions, has been claimed. However, there is still doubt as to these
claims and, because favorable conditions seldom exist in Orange
County during droughts, rainmaking can be eliminated at this time
as a practical means for preventing low lake levels.

EVAPORATION

No practical way of increasing the rate of evaporation has
been devised, so this method of lowering lake stages can be eli-
minated. Some progress has been made in the use of chemical and
plastic films to reduce evaporation but the techniques are still
in the research stage.

SURFACE INFLOW

Control of lake levels through control of surface inflow has
been practiced in Orange County for years. For example, water






INFORMATION CIRCULAR NO. 47


that would normally drain from Colonial Plaza into the south
Orlando lakes is diverted to Lake Sue through a pipe line. Much
water that would otherwise enter lakes from street drainage is
diverted to the artesian aquifer through drainage wells. However,
during extremely wet years, such as 1960, flow down these wells
when added to the normal recharge builds up the piezometric sur-
face so that the wells in some lakes refuse to take water and
some wells even discharge water into the lakes.

SURFACE OUTFLOW

Surface outflow from a lake may be conveyed in open channels
and culverts or pumped out through pipes. Open channels can be
used to drain any of Orange County's lakes. However, it would
be extremely expensive to dig open channels to many of the land-
locked lakes because of the very deep cuts required and the long
distances to discharge points on stream systems at elevations
lower than the levels of the lakes. For instance, to drain Lake
Sherwood through an open channel would require a channel more
than 10 miles long with cuts up to 45 feet. The channel would,
of course, provide drainage for those intervening lakes through
which it could be routed, but might drain some of them dry.
Open channels require considerable maintenance, wide rights-
of-way, are often unsightly, and they break up the continuity of
the land and interfere with transportation.
A combination of open channels, culverts, and pumps can often
be used to advantage.

UNDERGROUND INFLOW AND OUTFLOW

Artesian wells can be used to remove water from or to put
water into a lake. If the lake level is higher than the piezometric
surface, water will flow down the well; if the piezometric surface
is higher than the lake level, water will flow out of the well. The
natural direction of flow can, of course, be reversed by using
pumps (however, pumping water down drainage wells is prohi-
bited by State Board of Health regulations). Figure 7 gives the
periods of record, maximum and minimum elevations, in feet above
mean sea level, and the fluctuations, in feet, of selected lakes in
Orange County. Also shown are contour lines representing the









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Figure 7. Map of Orange County, Florida, showing the range in fluctuation of selected lake levels and the decline
in'the piezometric surface from September 1960 to May 1962.






INFORMATION CIRCULAR NO. 47


piezometric surface of the Floridan aquifer during high water in
September 1960 and the decline in the elevation of the piezometric
surface between September 1960 and May 1962.
The ability of a well to take or to yield water is dependent
on the permeability of the aquifer into which it is drilled and the
difference between the level of the lake and the piezometric sur-
face. Wells are relatively cheap; they are unobtrusive; and they
can be used either to supply water or to remove water from a lake.
On the other hand, wells have less capacity than open channels
and they may pollute the artesian aquifer when used for drainage.
Also, many drainage wells become less effective during wet wea-
ther when they are needed most. This is because the piezometric
surface rises more rapidly than lake levels during wet periods,
causing a reduction in the difference between the levels of the
lakes and the piezometric surface.

EFFECTS OF LAKE-STAGE CONTROL

The methods used to control lakes in Orange County nearly
always fail to remedy the problem of lake-level fluctuation, but
merely transfer the same problem to a lower elevation. This is
because the control projects are usually directed at reducing high
lake levels without regard to the effect on low lake levels. In-
creasing the outflow from a lake to prevent high levels without
providing a means to prevent the loss of an equal amount of water
or a means to replace the extra outflow causes the lake's level
to become lower than normal during drought so that the range in
fluctuation is virtually unchanged.
Most lakes in Orange County are water-table lakes whose
levels are above the piezometric surface. In general, the water
table conforms to the land surface and usually slopes downward
toward the lakes, causing water to seep into the lakes from the
surrounding water-table aquifer. When the level of a lake is arti-
ficially lowered by increasing surface outflow, the slope of the
water table toward the lake is increased, causing an increase in
the rate of seepage from the water-table aquifer into the lake. If
the lower lake level is maintained, the increased outflow from the
water-table aquifer will lower the water table until equilibrium is
re-established between the outflow and inflow of the lake. Thus,






FLORIDA GEOLOGICAL SURVEY


lowering the level of a lake not only reduces the amount of water
stored in the lake; it also reduces the amount of water stored in
the water-table aquifer surrounding the lake.
In areas where the water table is higher than the piezometric
surface, the rate that water percolates from the water-table aquifer
to the artesian aquifer depends on the permeability of the inter-
vening material and the height of the water table above the pie-
zometric surface. When the levels of a lake and the surrounding
water table are lowered, their heights above the piezometric sur-
face are decreased and the rate of recharge to the artesian aquifer
is decreased.
When drainage wells are used to lower lake levels, the effect
is the same as that caused by surface removal except that recharge
to the artesian aquifer is increased rather than reduced. The water
is not lost, but stored in the artesian aquifer where no losses by
evaporation occur. However, when water is put into the artesian
aquifer by drainage wells, the slope of the piezometric surface is
increased unnaturally, causing more than normal outflow from the
aquifer. If ground water use increases to the point where the pie-
zometric surface is permanently lowered, drainage of excess
surface water to the Floridan aquifer may be beneficial, provided
no polluted water is allowed to enter the aquifer.

SUMMARY

Lakes are one of the most valuable natural resources in
Orange County. The usefulness of some of these lakes is reduced
because their levels fluctuate excessively. These fluctuations
occur because of differences in the rates that water enters and
leaves the lakes. Water enters the lakes as a result of rainfall,
surface inflow, and underground inflow. Water leaves the lakes
as a result of evaporation, surface outflow, and underground out-
flow. Lake levels cannot be effectively controlled through control
of rainfall and evapotranspiration. Lake levels can be controlled
by altering the surface inflow and outflow and the underground
inflow and outflow. Control of the levels of many of the lakes
cannot be effected at all times by altering the underground outflow
because the artesian aquifer will not accept this surplus water
during wet periods.






FLORIDA GEOLOGICAL SURVEY


lowering the level of a lake not only reduces the amount of water
stored in the lake; it also reduces the amount of water stored in
the water-table aquifer surrounding the lake.
In areas where the water table is higher than the piezometric
surface, the rate that water percolates from the water-table aquifer
to the artesian aquifer depends on the permeability of the inter-
vening material and the height of the water table above the pie-
zometric surface. When the levels of a lake and the surrounding
water table are lowered, their heights above the piezometric sur-
face are decreased and the rate of recharge to the artesian aquifer
is decreased.
When drainage wells are used to lower lake levels, the effect
is the same as that caused by surface removal except that recharge
to the artesian aquifer is increased rather than reduced. The water
is not lost, but stored in the artesian aquifer where no losses by
evaporation occur. However, when water is put into the artesian
aquifer by drainage wells, the slope of the piezometric surface is
increased unnaturally, causing more than normal outflow from the
aquifer. If ground water use increases to the point where the pie-
zometric surface is permanently lowered, drainage of excess
surface water to the Floridan aquifer may be beneficial, provided
no polluted water is allowed to enter the aquifer.

SUMMARY

Lakes are one of the most valuable natural resources in
Orange County. The usefulness of some of these lakes is reduced
because their levels fluctuate excessively. These fluctuations
occur because of differences in the rates that water enters and
leaves the lakes. Water enters the lakes as a result of rainfall,
surface inflow, and underground inflow. Water leaves the lakes
as a result of evaporation, surface outflow, and underground out-
flow. Lake levels cannot be effectively controlled through control
of rainfall and evapotranspiration. Lake levels can be controlled
by altering the surface inflow and outflow and the underground
inflow and outflow. Control of the levels of many of the lakes
cannot be effected at all times by altering the underground outflow
because the artesian aquifer will not accept this surplus water
during wet periods.






INFORMATION CIRCULAR NO. 47 15

If the level of a lake is controlled by merely removing excess
water during wet periods, the range in its fluctuations will be
virtually unchanged, its average level will be lower, and its level
will be lower than normal during droughts.
Lowering the level of a lake causes more water to seep into
the lake from the surrounding water-table aquifer. Thus, not only
is the amount of water stored in the lake reduced by lowering its
level, but the amount stored in the adjoining water-table aquifer
is also reduced.
Except when drainage wells are used to increase flow to the
artesian aquifer, lowering lake levels and the water table reduces
the rate of recharge to the artesian aquifer. Increasing recharge
to the artesian aquifer causes the rate of water loss from the
aquifer to increase.
Withdrawal of water from the artesian aquifer increases the
rate of recharge to the aquifer and improves the effectiveness of
drainage wells.










FLRD GEOLOSk ( IC SUfRiW


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