Title: General Summary, Draft
Full Citation
Permanent Link: http://ufdc.ufl.edu/WL00002253/00001
 Material Information
Title: General Summary, Draft
Physical Description: Book
Language: English
Spatial Coverage: North America -- United States of America -- Florida
Abstract: General Summary, Draft
General Note: Box 10, Folder 12 ( SF Water Rights-Water Crop - 1973, 1976-77 ), Item 17
Funding: Digitized by the Legal Technology Institute in the Levin College of Law at the University of Florida.
 Record Information
Bibliographic ID: WL00002253
Volume ID: VID00001
Source Institution: Levin College of Law, University of Florida
Holding Location: Levin College of Law, University of Florida
Rights Management: All rights reserved by the source institution and holding location.

Full Text



Water Crop is simply the amount of water that is annually available,

'in a given area'e .ia ie -.3 ,;ef-it; c the total amount of i-c ,

? j at t r less the amount of evapotranspiration (P-Et) -wras the

water yield of an area (Langbein and Iseri, 1960).

4 {c4E#i1sr e. investigations in west-central Florida conducted

from 1964-1966 indicate that the water crop for a"500-square mileac*

aee-43 18 inches. In this particular area, water-inflow consisted

entirely of rainfall (57 inches total). Outflow or discharge from the

area consisted of runoff (17 inches); evapotranspiration (39 inches);
o /*
and ground-water4flow (1-inch) (Cherry, Stewart and Mann, 1970).

T, jIE. fiaOu9 TA OG P lt.f /,t f -G LI. 1 -'A/I'
By conservatively estimating/ iarea.-wtsr= wap planners can

L sure-taI t an adequate supply of water is available for mae2~6 a e 3h A

SowdiftsM-. conservative estimates/ 1ab protectXagainst ti

Si extensive reductionsin ground water storage, even during periods of

Si prolonged drought. A f~ to. .

SThe water crop conceptef-eae illustrated W pWI*F gure
t W AV44 V-64e 'R e JI. BZ V
1 The bucket represents te aquifers and lakes within the Districtv
-wh 4eh- ve an estimated 52 inches of precipitationA* year. Of this

total, 39 inches arejlost to evapotranspiration ( ich -tit ~ .sp 4on

F evaporation and transpiration tiegh plants to the atmosphere). The
At I t < AaL-4 TV "A/
remaining 13 inches resent-the amount that s.an -' ,eenem t a4 and this is

.what-I~ called the water crop.

When working with the water crop concept, two important facts must

be noted. First, the actual amount of evapotranspiration varies with

temperature and with the availability of water. But, because the rate

of evapotranspiration varies directly with rainfall, the water crop

tends to remain constant. Second, man's demand for water does not
a coincide with of rainfall. Consequently, to capture the
a~wes oincide' with A:



;* "" :'- 2

/, /"'.' ..,'r; /< o
-2- ^ Ij -

entire 13 inches! the -wner level in.the bucket must be lowered. In

this way a storage area is provided in which totn the 13-inch

surplus until is needed.

(4)A/tA L L X rts- t.-jPoYZRsp;Aio/.o; 5 L iAL R IVL O
Walterr rp and the SWWM .
Within the District rainfall has averaged 52 inches annually in

recent years. The average evapotranspiration rate is about 39 inches,

and the average discharge from the area--primarily through surface-water

runoff--is approximately 13 inches. This 13 inches it the District

staff's estimate of the water crop, or the amount of water annually

available for man's use. It ha bn adopted by th Ditr- t C v--ng

Board as a guideline w.he-n making water manfgmcnt dLecisins

When Water is Used .

If water is removed from the District "bucket" (that is, from

-|naiinl f storage within the District), and used consumptively (lost

to evapotranspiration, pumped into the Gulf of Mexico after use, or
otherwise made unavailable for man's re-use), then the amount of water
ThkAi ,'O-'7 O'lfrJ 4-i orn- P.-bof~ / ri hJ4-e-astae. diS hargged from the area is reduced. ~-aLet wJdraw&
exceed an area's watr crop, aeter is., .in effee., ,being mIed and thi:
,,, -"^ i IA -- "owari* ....A'V ,ievelS.

De eass in discharge and in t--.. r"flect-d in many ways.
ffiU.^'-T IY ^ OLF txkIv tom C'
WIe the amount of water in storageli-medm.i4, water levels in streams,
S^ IffOArt T L-Y 7,/,;,/sP IS C-A"/ Rn
lakes and aquifers are lowered. W 'dei s i

., bR'y .wae.,. the /
,k' amount of water in storage should not be allowed to decline for long

periods of time and short-term declines should occur only during periods
when the water crop is less than the 13 inches. -o '-' **

4/ occur if/ti ulter crcp i4 fncrteaA ad* .r' rr. ..
i/-.P^ "" 4r Lf $ 7 P" TO _P CCc-
vwater" p-a ga e- g-lfe_ evapotranspiratipon, .

aS4doGs .4rae,4 however, doing so.4 P.1 tain w e ajreatt /7
SL. ./ al
aegwliasB ** Reuse of water -- such as ~ irrig ion purposes --
CPihi %B- /U^ TP s L/^.^F S.. .< C.w. r-m T- i 7y...&,e s-r-,tem
has the net effect of- incrsin the rechar the system

e7 4 A"Ur a.$ 0- /,- tA mmo y1, '

. .. t


The water c p concept considers only the i ow or recharge to an

area dal pr does not consider ground, or..

surface-water inflow or o flo Under the concept, if water in one

area is allocated or co med, here is no outflow to another area.

Therefore, if wa is to be made ailable for consumptive use in all

areas, onlyhe water crop should be co idered as available and inflow

fro ne area to another must be excluded for location purposes.

The Hydrologic System .

To fully understand the water crop concept, it's important to first

have a.geBEs understanding ofkthe hydrologic system. Thisisystem,/
,',. ^' 15 tmpiASL or op pl -m*"aP ivTo
Qeufps la-'ll waterifrom where it falls as rainto/either/the Gulf of
11r.w.nA'tP pwfo
Mexico ortb the atmosphere. All streams, lakes, springs, sinkholes and

aquifers are part of it.

From wherever it falls as rain, water moves downgradient through

the various interconnected water-conveying components of the hydrologic


ar-p~e te a he Forelmae, in one iate the principal conveying unit

may be streams, while in another it may be aquifers; in a third, it

could be a combination of the two. The water may pass from stream to

aquifer, or from aquifer to stream, or it may evaporate into the atmosphere

while enroute to the Gulf.

Whatever its route, water enters the conveying system as rainfall

and is temporarily stored in streams, lakes or aquifers while enroute to

discharge points. During periods of heavy rainfall, the rate of recharge

S(or replenishment) to an area usually exceeds its rate of discharge and

water levels rise accordingly. When there is little or no rainfall, the

discharge rate exceeds the recharge rate, the volume of water in storage

declines, and water levels fall accordingly.

Within the District .

The quantity of water stored or in transit within the hydrologic

system varies gslet t-ypartcua The characteristics and

r I ()

i;1 I ki J II


4.pit- ase of the water-conveying components vary regionally and optimum

management of the water resource depends ti e on an/understanding
pPaKMgA0 CICc fC 7a 4- y/r-o ** / VA/1 A r42 r1c.- 4a ..
of the- ,
S In the northern part of the District,,the aquifer system glseas
Y C, ciit, *LIC- ,,
f a water-table aquifer consisting primarily of sand, and fe* artesian
/ ^4 l~iai dar quiferd W limestone-~eEHfigure 2>. Th two/are commonly

separated by/layers of clay. In some places#*nWl *, the clay layers

are thin, leaky or altogether absent and water is readily tnsm
.truei V ArV P
des-s-a-r0d the water-table t the underlying Floridan Aquifer.

smmi- in the southern portion of the District ,the aquifer system

tends to be more complex. (see figure 3). Here the Floridan Aquifer

consists of several layers of limestone of varying thicknesses and

water-transmitting caractcrstis. The limestone ones are separated by

S clay or other limestone with low water-transmitting abilitywv1/wc-
\ resulting in minimal -3%m recharge to the lower aquifers. This idsiau

4~.- recharge, combined with the considerable number of large WNS2-

withdrawal facilities in the deeper water-bearing zones, has caused

widespread declines in ground water levels.

Some Special Management Concerns. '

A-..?M.S 4. A -tfouh t he water cropf0 1 r 0 a lur area-maLy

ut b o to insure tdgat -b r zope or aquifer from which water is to
J ,) c..* rI, -Quw y L" I/.Nf 44)r I^/H /'- t -i /I <-t-4"1 f" / -Pi^ 1
% wi thdrawnjxna be recharged. a.is..ers whe.R=6--e-
,A b # 10jc! OZ aQL4Ta^S f I)' S k- Sf 00f A-. ^ $AAr t 4n 4 ~7Tw)ptJrf'
watr crop o r. en a lc:ssr,. but nevertheless subst-.ntil' m.unt of
1 A -41-,k~., ,-0- t^b.- .. jI, A_ ,t?. A4 ,S !. 0 U) .i.d -- -- e--J I .A"'eTiS'J
r.-i .is is TII k, bI' Wa, -7-~o; 4.Aioy 7i.xi ..-y-
S2oundwar mang d-water withdrawals tonnr neot onlf which
/4/ 7*/s ^^n fsh. ntr f, T Jifvq4'ig AiE. S ir/v-/,Q.-
a3.abilty of water inevels to declaine in zon, es from twhich largethod by withdrawals
70are made .but which met recharg44Y te nr 'b annually
~th ^~ i- 4 it9rOiMn. rw- minmigciment practttof murt :ithrr

1. Artificially recharge' zones which awwmIrecharge oftaly

a-s4ei rageoogy.iofv-tbeo'gt ; or
2. Restrict ground-water withdrawals to zones or ecmpenents which

can annually replenish or recharge themselves; or

3. Allow water levels to decline in zones from which large withdrawals

are made ,but which oGmot rechargeA Iale4 annually.



Ints is necessary to.preven a reduction in s age or a decline in
water levels. Fortunately, ost of District is in a recharge area

The water level of the sha &aifer is at a Ireater elevation than

the potentiometri surface of the Flor n Aquifer throughout most of

Sthe Dis ct and this allows the recharging aa on to occur, although at

lower rates in the southern portions than in the no ern ones).


S -be water within the Floridan Aquifer comes, p*i4arily from downward "
' seepage from the shallow aquiferX the pot _ima f

--- -- _Where the potentiometric surface is lower than the

^ water table/ recharge can take place /eeet4y. In-ekth case the rate
of movement of water from the shallow aquifer to the Floridan Aquifer

(or vice versa) depends on both the water-transmitting characteristics

MV of the clay unit separating the two and the differing water levels

within them.

4 When water is w4-thdraw from an' aquifer, the water level/is lowered

and a cone of depression n = around _
Po).Y T f ^nH^^^A, ,F OAr'. A*1TM>Ao *0ote -lr, i w A _EI/ 4*-
the di4sharging we ll. As -a-esult na second, more subtle cone of depression '

forms in the water table of the overlying shallow aquifer. (see figure

4). The difference in the elevations of the water level in the shallow

aquifer and the potentiometric surface of the Floridan Aquifer A greatest

at the point of withdrawal; other condti i. g -, leakage frto

the watertable aquifer to the Floridan Aquifer is also greatest at the

point th wirga'w" i
tYheom iA riA Cg A V- D i**y C0 7 CArd6A4A/ 8SAL I- P

By monitoring the two elevations, the potentiometric surface can be
ht.WM~9vLTCS BY 4-*vr T betweenIT ^
controlled via pumpage rg**tign -so=tfatthe head difference between

IT 1. .20-O t* ~' ai ,'

"~ management practicesG4d aa. that the withdraw of

water from an aquifer be limited to the water crop in recharge are,


the two aquifers (that is, the difference in the water pressures within
S1e^ f ,,A V .&tA D, fV.1 f h~.Q ,'-- T4 '-7 ,ni-
them) 19i1 allow no more than the volume of the water crop to move

downward from tht shallow aquifer to the Floridan Aquifer. This ,in turn/

prevents a continual lowering of water levels in the shallow aquifer

outside the immediate vicinity of the well field.

In effect, this type'of management plan allows the water level in
-pWAA46 Y */l* sAeG
the shallow aquifer to be lowered, during dry periods v aprovidA storage
W/IL- I/6
for the annual water cropj atjat the same time, 4L assure) that runoff '. )

vitl=etr from aR areas outside the 6 h._ _ateacrt P-is.

Figure 5 shows the estimated quantities of water/that will leak

from4te shallow aquifer to the Floridan Aquifer as a result of pumping

from a deep well. The estimates assume that the well field consists of

one well withdrawing 15,000,000 gallons per day (mgd); that the transmissivity

( of the Floridan Aquifer i 300,000 gallons per day per foot)(gpd/ft);
&MC"- OL, -
and that the leakance coefficientAof the confining layer which overlies

the Floridan Aquifer is .0015 gallons per day per square foot per foot
Ig A14 TWSA. 4'01,Ve4A 4)Lb C;^ w c
(gpd/ft3). This figure shows that/over 60% of the water is=derC4ed from

the shallow aquifer within a radius of about 4 miles of the well.

Larger quantities are derived from wnts nearer the well than from tme

more distant. ( \

In areas where only a water-table or unconfined aquifer exists,

water management regulations should limit water withdrawals to the water

crop of the area. Otherwise, reduction in storage accompanies water-

level declines in the area and mining of water occurs -- that is, more

water is taken out of the system than Nature puts in. If such practices

were allowed to proceed unchecked, the water supply would eventually be


Limited Withdrawals .

Even though the calculated water crop of a given area may indicate

that the amount of water requested by an applicant is available forhis


i H ..I j 4,1 I al L i ,I ,1, 14 4 11


aW, it may be necessary to limit his withdrawal to a lesser amount

because the method of wiutdrawal may induce salt-water encroachment or

result in other damage to the resource.

In some coastal areas, for example, the salt-water/fresh-water

balance is so delicate that withdrawal of the water crop could cause the

interface to move Uadwed and result in the contamination of tIe potable
I" 7AAJ.Mr "'t C
water supplA by'increasing '4s/chlorid eisNt beyond the 250 parts per

million considered safe for human consumption. (To avoid or minimize)

(T s iimbalancm)something less than the water crop

Utilization Of The Shallow Aquifer..

The Floridan Aquifer is an excellent source of water because of its

high transmissivity. Yields of as much as 5,000 gallons per minute

(gpm) are not uncommon, and some wells yielding 7,000 gpm are currently
in use. However, through the use of/networkl of sandpoint wells, large
40V& P
volumes of water uRn also be developed from the shallow aquifer.

Tests have shown that the permeability of the shallow aquifer is

about the same as the Floridan Aquifer. Water from the shallow aquifer

can readily be used for lawn irrigation, and, in some areas, for domestic

supply. Large withdrawalsjwould probably necessitate the use of multiple-
well manifold systems. For example, where one Floridan Aquifer well

might yield 5,000 gpm, it would require 200 sand-point wells drawing 25
4' -.X ^^ e-.p-' Mi 7rCA^iI h3'7 e rWb.
gpm to produce the same quantity. -^Alth gh W ...i ht -m p-r bhltii+aly
jwpas the 4 4 -of ami m-w -9 is, eCletvly che p, and in9-6 Aa4
izL (i-OWI6, -Vo y f/1'eo-a< M -r r-'qF^S S1tm.

Recharge Facilities. .

In areas where the water Crop isAsufficient to meet demands, MiaugmeL .

-a -rie i-Seu certain practices~ ino ure -4t mot eCffet- e deverpmr t.

For instance, if large withdrawals of water are to be made from deeper

zones some form of augmentatio -- such as recharge wells -- may be

-s--.(.ed W 9 Precharge. iso. M we e. _.-e
0mMe such practices ly ha n-a re.h a-.-rge wate-4 he proese

iust be closely monitored to insure *tbd the aquifer is protected against



Planned Declines For A Limited Period .

Provided that adequate safeguards against salt-water encroachment

and damage to other users are assured, water levels may be allowed to
decline for certain periods. In large areas such as the Peace and Alafia
a- 4LM'r/jAP 7/M 'C-
Basins, water level declines may be allowed for certain uses for-fdyrj r/

qidsf. For instance, phosphate mines require large quantities of

water for the life expectancy of the mine which is generally about 20

years the/wi thdraw may be within the -u& athe water crop o

the area but eenemies di4tate thatwater/be withdrawn from zones which

cannot be readily or locally recharge. Based on aquifer characteristics,
withdrawal rates, and recharge potential, the rate of water-level decline

in the area can be projected. If the projections indicate that no

potential salt-water encroachment or damage to other users is likely,

the water-level declines sae. may be permitted for specified

periods of time.

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