Water Manageement District
P. 0. BOX 457
DERRILL McATEER, Chairman, Brooksville
J. R. GRAW, Vice Chairman, Ocala
JOE E. HILL, Treasurer, Leesburg
July 26, 1976
BROOKSVILLE, FLORIDA 33512
THOMAS VAN DER VEER, Secretary, Yankeetown RONALD B. LAMBERT, Wauchula
S. C. BEXLEY, JR., Land O'Lakes ROBERT MARTINEZ, Tampa
N. BROOKS JOHNS, Lakeland LEWIS H. HOMER, Clearwater
C ? D Id R. Feaster, Executive Director
RJUL 2 1976
JUL 2 7 1976
By ------.... __ _--
Mr. L. M. Blain, Esquire
P. 0. Box 1363 "
Tampa, Florida 33601
The enclosed Water Crop slide presentation script
comments made by yourself and the staff. I would
your reviewing it by August 10th and returning to
ROBERT R. ATCHISON
Public Information Officer
cc: E. D. Vergara
T A OE CROP SLIDE SHOW Ii ... -
The first recorded instance of anyone having reasoned
that rainfall feeds lakes, rivers and springs occurred in
the late 1600's. Halley, the famous English astronomer,
totalled up the amount of water flowing in rivers that
lead to the Mediterranean Sea and discovered that their
combined flow ft roughly equal to the water in the rain
and snow that b)ih4 on the area drained by the rivers.
Almost simultaneously two Frenchmen, Perrault and Marriotte,
made very nearly the same discovery. They measured the
flow of rivers in their area and found that flow to be
about equal to the amount of rain and snow there.
In the late 17th century this correlation was almost earth-
shaking in nature. Now, nearly 300 years later, it's
almost common knowledge.
Water is constantly being exchanged between the earth and
the atmosphere. The "power source" for the exchange is the
heat of the sun and the pull of gravity. Water evaporates
from the ground, from vegetation, isw lakes, ponds, streams,
rivers and oceans. It is carried in the air as water vapor.
Eventually, the vapor cools and condenses, changing from
vapor to a liquid -- and then it falls again as rain.
The rain feeds the lakes and rivers. From there, the water
is carried to the ocean. From the ocean -- and other open-
surfaces -- it w|n and returns to the atmosphere,
once again to turn to rain in a continuous, unbroken cycle.
Water goes from earth to air, from atmosphere to earth
again and again. Consequently, the exchange is called
the hydrologic cycle -- hydro meaning "having to do with
water" and loge, the Greek work meaning "knowledge of."
The hydrologic cycle functions within the hydrologic system.
This system conveys all water from where it falls as rain
to the Gulf or to the atmosphere. All streams, lakes,
springs, sinks and aquifers are part of this water-conveying
Water enters the hydrologic system as rainfall and is
temporarily stored in streams, lakes or aquifers while
enroute to the area's discharge points. When the rainfall
has been heavy, the rate of recharge to the aquifers for
the area usually exceeds the rate of discharge from the
area. This means that more water will be stored in the
area -- usually within the aquifer--than will be released
from it. Consequently ground water levels will rise.
When the discharge rate exceeds the recharge rate -- the
volume of water in storage declines and ground water levels
The characteristics of the hydrologic system vary regionally
within the District, although its water-conveyance principal
remains the same.
The aquifer system in the northern District has two major
facets: the sandy, water-table aquifer and the limestone
Floridan Aquifer. The two are separated by a clay layer
which varies in thickness. Where this layer is thin,
leaky or altogether abset, water moves more readily into
the Floridan aquifer from the water table aquifer. In
these areas, the greatest amount of recharge takes place.
In the southern part of the District, the aquifer system
tends to be more complex. Here, the Floridan Aquifer consists
of several types of limestone in layers of various thickness
and water transmitting characteristics. These limestone zones
are separated by clay layers with low-water transmitting
characteristics. Consequently, recharge to the lower limestone
layers is more limited than it is in the northern part of the
Despite the structural differences of the hydrologic system
within the District, it nevertheless operates in the same
manner. A certain amount of rainfall is immediately absorbed
by the land surface. This amount -- which is really only a
very small percentage -- is the amount which enters the
ground water part of the hydrologic system. It filters
through the surficial sand and clay layers very slowly till
it reaches and eventually enters the Floridan aquifer. From
there it moves even more slowly toward discharge points in
springs or the Gulf.
The water which is not absorbed by the ground is either
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lost to evaporation, transpiration or to overland flow
called runoff, which drains into the nearest low area -- a
swamp, lake, stream, sink, or the Gulf. Most of this
water eventually evaporates or flows into the Gulf, although
a small portion filters into the aquifer and the ground water
Determining just how much water really enters the ground
water system, and just how much of that is available for
man's use, requires some fairly complex scientific thought.
The amount of water annually available for man's use is
referred to today as the "water crop" or the "water budget".
As an accepted theory, it's not really that new. Referring
to it by many different names, scientists have been working
with it for decades. For instance, as early as 1920 the
concept for determining this amount -- referred to then as
"safe yield" -- was used in a United States Geological
Survey technical paper. In that year, 0. E. Meinzer, a
scientist with the Survey, published his paper "Quantitative
Methods of Estimating Ground Water Supplies." He defined
safe yield as: "the rate at which ground water can be
withdrawn year after year without depleting the supply."
Meinzer's definition is based on ideas very similar to
today's concept of water crop -- the amount of water
annually available for man's use.
"Water Crop," referred to as part of the "water balance"
concept, was first used at the District shortly after It
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became a regulatory agency in 1969. Another USGS paper,
published in 1970 as part of the District's cooperative
program with the Survey, entitled "General Hydrology of
the Middle Gulf Area, Florida" refers to "the long term
availability of water, that is the amount of water that
can be developed. ."
But the water crop concept as a tool for water management
and regulation did not come into use at the District until
late 1974. At that time the District was involved in
establishing a code of rules and regulations to assure the
protection of the water resources as required by Chapter
373 of the Florida Statutes. Among other requisites, Ihe
District was to establish #minimum flow2A i-
.water .so. in _tha i _** That is, for e19 streamswerm(
"/ f L" *o 4e _
riversbtpmount of flow4wast be established such that
any further withdrawal ~f~ would be significantly
harmful to the water resources or the ecology of the area.
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minimum level was to be the level of ground water in an
aquifer and the level of surface water at which further
withdrawals would be significantly harmful to-the water
resources of the area.
To establish these levels, the statute directed the District
to use "the best information available." Accordingly, the
water crop concept came into its own.
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The water crop -- the amount of water anby available for
man's use -- is defined as precipitation less evapotranspiration.
That is, the total water crop for a given area is equal to
the amount of an lI precipitation after the processes of
evaporation and transpiration have taken place. How the
concept actually works is relatively easy to understand if
you compare it to a checking account.
In a checking account, you deposit cas and write checks on
the deposited amount.4 Hopefully, your withdrawals -- checks --
will not total more than theAdeposited amount. The same is
true with the water crop account. The deposit is equal to
the total amount of rainfall less what's lost to evaporation,
transpiration and runoff. If more water is withdrawn from
the aquifer than Nature puts into it, the water account will
Abe operating "in the red"., If that continues for any length
of time, it could result in a serious water situation.
'V BE. his could prove particularly seriously the District
is a hydrologic unit -- a complete entity unto iself. Its
boundaries were established on natural water shed lines, so
there is no appreciable ground or surface water inflow from
areas outside the District. Consequently, the only source
we have of fresh water is rainfall. Of that "income" a
great percentage is lost to runoff and to evapotranspiration.
Only a small portion is allotted to storage in the hydrologic
system -- and it is this stored amount that is tapped by
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Research and investigations conducted by the USGS and
the District staff have shown that in a typical year,
on a District-wide average, approximately 52 inches of
rain falls within our boundaries. Studies indicate that
of this total, 39 inches are lost to evapotranspiration.
The remaining 13 inches become runoff. This is the amount
of water that flows as either ground or surface water
into District rivers and streams and eventually to the
Gulf of Mexico.
Based on the water crop equation (P=Et + r), precipitation (P)
equals evapotranspiration (Et) plus runoff (R) -- this 13
inches of rain is the total potential water crop available
for man's use within the District. That means that a maximum
of about 2.3 trillion gallons of water is available annually
within the District.
If we then divide the total District water crop by its
10,000 square mile area, we find that a single square mile
of land has an annual water crop of about 233-billion gallons,
or a daily water crop of 640,000 gallons. This amounts to'mis a
1,000 gallons an acre each day.
Although this may seem like a lot of water, and assurredly,
there are many, many acres whose water crop is virtually
untouched, there are more and more places where water use
exceeds the water crop of the acreage involved.
This is what the District's program of Consumptive Use
Permitting is all about.
Unlike most other natural resources, water is not necessarily
destroyed by use. While coal and oil, for example, can only
be burned once, water can be used, returned to a river, lake
or aquifer, and then re-used again and again. Nature does
this constantly through the hydrologic cycle.
Man simulates this natural re-use in many ways. For instance
a family pumps water from the ground, uses it in their home,
and drains it into a septic tank. From there, it percolates
back into the aquifer and rejoins the natural system. This
use 'is considered non-consumptive because virtually no water
is removed from the site of pumpage, and none is lost to
On the other hand, if a municipal well field pumps water
from the ground, pipes it several miles away to individual
homes, businesses or water systems and then -- through a city
sewerage system -- dumps it into the Gulf or Bay, the use
is totally consumptive.
The difference between consumptive and non-consumptive use
of water, then, is whether it can be re-used by others. If
it is lost to evaporation or transpiration, if it is chemically
polluted, if it is dumped into salty water, it becomes useless
as fresh-water. That makes its use consumptive. If the
water flows back into the aquifer or is somehow retained
after its use, the water use is non-consumptive.
It is, of course, physically possible to "spend" more water
than Nature puts into the aquifer without immediately obvious
effects -- just as it's possible for an individual with
credit cards to spend more than he earns during any particular
year. In fact, the massive Floridan Aquifer acts much like a
savings account. It can be drawn down to a limited extent
during dry months -- and even dry years, if necessary -- as
long as comparable "deposits" are made during rainy months
and wet years. But constantly or extensively exceeding the
land's water crop -- called mining of the resource -- can
result in substantial adverse effects. Inevitably such
mining will upset the hydrologic balance of nature, the
delicate equilibrium between salt and fresh water and between
ground and surface water.
The hazards of upsetting this delicate balance are great.
First, as the water level in the aquifer begins to drop,
small domestic wells would gradually become less effective.
And because the water would have to be pumped from a greater
depth, more power would be required to lift less water.
Larger wells would remain functional for a longer period of
time, but only with expensive modifications -- and eventually
they too could go "dry."
Surface waters would begin to show the effects of the imbalance
too. As the aquifer level dropped, the difference in pressures
between the artesian and water table aquifers would increase
Surface water in lakes and streams would flow downward
to "fill the vacuum." The effect? Lake levels would drop,
vegetation would be placed in stress conditions, rivers
would be reduced to creeks and creeks to dry runs.
But perhaps the most serious consequence of mining the resource
is that eventually salt water would find its way into the
fresh water, both above and below ground level. Because
Florida is a peninsula, and becauseof its geologic formations,
the threat of salt-water encroachment is an ever present
problem. All along the coastline, the fresh water of'the
Floridan Aquifer meets the salt water of the Gulf and the
Atlantic. Salt water also underlies the Floridan Aquifer at
various depths through the peninsula. This salt water is
under constant pressure from the Gulf to rise to mean sea
level. It is only the counter-pressure from the fresh waters
in the portion of the Floridan Aquifer above sea level which
prevents that from happening. This fresh water "bubble" is
like an iceberg. If you chip off part of the "top," the
"bottom" begins to rise. If you keep chipping way, it is
If we begin massive mining of the water resource, thereby
reducing the pressure in the aquifer, the eventual result
would be massive salt-water intrusion. f-tJ ep wells
would go salty. Cities and counties would be forced to
switch to an expensive desalination process to supply water
to their residents. MIgqOettrus growers, farmers, ranchers
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and nurserymen would face a difficult and necessarily expensive
dilemma: irrigate with brackish water; pay for desalted
water; move their operation; or go out of business.
These are the reasons the District Governing Board regulates
the amount of water that can be withdrawn from the aquifer.
When the Board began its Consumptive Use Plan, no records
were available to establish with any degree of assurance how
much water was actually being used. In additi n, the law
gave all existing users ff urY, 7, bc, h
mS.a.p... So it will be several months before the District
will have an accurate inventory of the total amount of
water being used. In the meantime, applications keep coming
in for new or additional uses. Consequently, the District's
information on water use is continually being refined.
The Board has established the Consumptive Use rule so that all
applicants will know the yard stick being applied on a District-
wide basis. If everyone were to take his exact pro rata share of
the water crop, it would average 365,000 gallons per year per
acre. For the health, welfare, and best interests of the
public throughout the District, as well as for the protection
of the water resource, that 365,000 gallon annual total
water crop should not be exceeded. Applicants who desire
to withdraw more than this pro rata share must be prepared
to establish that the proposed use is for a reasonable,
beneficial purpose, that it will not interfere with any
presently existing legal use, and is consistent with the
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It must be remembered, however, that the water crop concept
is not in-and-of-itself an absolute rule or regulation of
the District. The concept is a water management tool, and
is used by the staff and the Board in determining the
appropriateness of a request for large-volume water use.
It is used as a guideline, and as such represents the
best information presently available for establishing the
total amount of water available, and t eAreguoa o level s4- a
a-b- ke cIt e a A Jas'r protecting the
public interest and the resource itself,.*aA"tis continually
Using the average water crop of 1,000 gallons per day per
acre as a basic guideline, coupled with an understanding of
the hydrologic system and cycle, the Board and its staff can
determine the average rate at which water can be pumped
from a given area over a long period of time without creating.
In this manner, the water crop remains a tool that is both
flexible enough to work with special types of water use
problems, public-supply well fields such as those involved
with agriculture and industry, and is strong enough to aid
the Board in determining which uses will "obtain the most
beneficial use of the water resources of the State and .
interests of the water users affected."
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