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Economic Aspects of the Conjunctive Use of Ground and Surface Water
347
ECONOMIC ASPECTS OF THE CONJUNCTIVE USE OF GROUND AND SURFACE WATER
And& S a h u q u i l l o , P o l y t e c h n i c a l V a l e n c i a Spain
University
o f Valencia, c / de Vera s/n,
46071
ABSTRACT The d i f f e r e n t s t r u c t u r e o f t h e c o s t s o f ground and s u r f a c e w a t e r and t h e d i f f e r e n t and complementary c h a r a c t e r i s t i c s o f b o t h k i n d s o f r e s o u r c e s make i t p o s s i b l e t o s o l v e t h e s p e c i f i c needs o f w a t e r q u a n t i t y and q u a l i t y more adequately and e c o n o m i c a l l y i f b o t h r e s o u r c e s a r e used c o n j u n c t i v e l y . Higher d i s c o u n t r a t e s f a v o u r t h e i n c l u s i o n o f elements i n v o l v i n g l o w e r initial investment and g e n e r a l l y w i t h h i g h e r groundwater components. Lower d i s c o u n t r a t e s favour a higher p a r t i c i p a t i o n o f surface water. The e x t e r n a l f a c t o r s produced by groundwater pumping must be t a k e n i n t o c o n s i d e r a t i o n i n any economic a n a l y s i s . Examples o f e x t e r n a l f a c t o r s a r e w a t e r l e v e l descents, s u r f a c e w a t e r f l o w r e d u c t i o n , d e g r a d a t i o n o f w e t l a n d s and e c o l o g i c a l issues, w a t e r qua1 i t y d e t e r i o r a t i o n and l a n d subsidence. T h i s paper discusses t h e economics o f a r t i f i c i a l recharge and i t s r o l e i n t h e d i f f e r e n t t y p e s o f c o n j u n c t i v e use. I t s importance i s c r u c i a l i n some cases and secondary o r m a r g i n a l i n o t h e r s . The amount o f s t o r e d ground w a t e r i n many cases i s s e v e r a l t e n s o r hundreds o f t i m e s t h e mean annual groundwater recharge 1eve1 . P1 anned overpumping a1 1ows c o s t l y p r o j e c t s r e q u i r i n g 1a r g e dams o r t r a n s f e r s t r u c t u r e s t o be postponed. The u n c e r t a i n t y i n h e r e n t i n r i v e r f l o w p r e d i c t i o n and demand v a r i a b i l i t y o r inadequate i n f o r s a t i o n o f t h e h y d r o l o g i c a l parameters o f t h e system can be c o u n t e r a c t e d by t h e f l e x i b i l i t y i n t h e seasonal and y e a r l y use o f ground w a t e r which c o n j u n c t i v e use schemes p r o v i d e s . I n many cases t h i s r e p r e s e n t s a k i n d o f i n s u r a n c e a g a i n s t adverse h y d r o l o g i c a l o r economic s i t u a t i o n s .
1. INTRODUCTION Growing w a t e r needs, of w a t e r development
t h e c o n s t r a i n t s caused by w a t e r
projects, i n c l u d i n g t h e c o s t
p o l l u t i o n and t h e c o s t
o f responding t o
s o c i a l and
F o r t h e s e reasons, i t has
environmental concerns, a r e i n c r e a s i n g d r a m a t i c a l l y .
become i m p e r a t i v e t o t a k e i n t o c o n s i d e r a t i o n a l l w a t e r sources and f a c i l i t i e s i n o r d e r t o s a t i s f y p r e s e n t and f u t u r e w a t e r demands. obtained i f a
water
system i s
resource
A d d i t i o n a l b e n e f i t s w i l l be
planned and/or
operated t a k i n g
into
c o n s i d e r a t i o n t h e advantage o f f e r e d by t h e c o n j u n c t i v e use o f ground and s u r f a c e water.
If
the
alternatives for
multiplicity achieving
of
objectives
this,
i n t e r r e l a t i o n s h i p seem e v i d e n t , i t r e c o u r s e t o c o n j u n c t i v e use; scarce.
and is
i n water the
advisable
planning, t h e d i f f e r e n t
ground i n most
and
surface
situations t o
water have
and n o t o n l y i n a r i d areas o r those where w a t e r i s
Ground w a t e r management
cannot e x i s t w i t h o u t s u r f a c e w a t e r management;
and surface w a t e r cannot be managed o p t i m a l l y i f t h e groundwater r e s e r v o i r s a r e
348 n o t included (Fowler, 1981). These p o s s i b i l i t i e s are f a r conjunctive use has been
from
carried
being
recognised unanimously and
out i n
few areas and
is
p r a c t i c e i n the water resources planning agencies o f most o f the decisions and a t t i t u d e s o f water s p e c i a l i s t s o f them favour surface water
utilization.
not
i n fact
a
customary
countries.
Analysis
indicate
t h a t the m a j o r i t y
Very o f t e n groundwater resources are
n o t taken i n t o consideration even i n regions where in-depth and r e l i a b l e studies have confirmed the existence o f positive results.
formations
whose u t i l i z a t i o n would c r e a t e very
This u n j u s t i f i e d disregard o f
q u a l i f i e d by Wiener (1972) as an evidence and defined as "hydroschizophrenia"
by
of
groundwater resources has been
a deep, unpremeditated prejudice,
Nace
(1972)
and
analysed by
Llamas
(1974). I n some countries the
r e s p o n s i b i l i t y f o r water
by the c e n t r a l government, projects.
at
planning has been taken over
l e a s t when making
final
decisions
on major
Large p r o j e c t s u s u a l l y have g r e a t e r f i n a n c i a l resources a v a i l a b l e and
have more favourable f i n a n c i a l terms
as w e l l ; these considerations, i n a d d i t i o n
t o p o l i t i c a l motivations, tend t o favour the l a r g e r more spectacular engineering projects. The a t t i t u d e s r e l a t e d above ground water occurrence
are due, i n part, t o a l a c k
and movement.
experience i n ground water studies education i n
hydrogeology,
even
Most
o f understanding o f
h y d r a u l i c engineers
have
and many planners have n o t had though an
appeal
to
increase
limited
any formal hydrogeology
studies has f r e q u e n t l y been made (Llamas 1974, Howell and Warman 1982). The i n c l u s i o n o f courses d e a l i n g w i t h the i n the
water resources
technical and
departments
scientific
of
d i f f e r e n t aspects o f ground water
universities,
accomplishments
can
and
co-operate
the to
diffusion change
of
those
a t t i t u d e s i n the near f u t u r e .
2. GROUND WATER COST STRUCTURE The main economic d i f f e r e n c e between t h a t i n general
i n i t i a l investment i s
contrary operation and maintenance i n i t i a l investment per
unit
of
chemical s
.
urban
much lower i n ground
costs are
higher.
r e s u l t i n g product
operation and maintenance cost small. treatment needs f o r
ground and surface
The
is
exception
uses u s u a l l y r e q u i r e
higher
water
projects i s
water
and on the
I n surface water u s u a l l y high is
that
costs
and
this to
the
surface water f o r energy
The c l a s s i c way t o compare t h e d i f f e r e n c e o f occurrence i n time between and b e n e f i t i s by reducing
the
a present value through a discount
and cost
factor.
The s e l e c t i o n o f the discount r a t e t o be used i n h y d r a u l i c p r o j e c t s has been t h e subject o f arduous debates.
A
lower
greater component o f surface water.
rate
favours t h e
projects
A r a t e which i s more i n keeping
involving a with
the
349
real price o f construction.
money favours
deferring
the
more
costly
investments
for
For example, t h e present value o f a d o l l a r which w i l l be spent i n
t e n years time
is
i f a 12% d i s c o u n t
0.322
expenditure were t o be made
i n 20 years.
rate i s applied
a r a t e o f 8% i s
the
used then
the
a,nd a p p l y i n g a 4% d i s c o u n t r a t e
the
If
r e s p e c t i v e values would be 0.463 and 0.215;
and 0.104 i f
See Table I .
r e s p e c t i v e values would be 0.676 and 0.456. TABLE I
Present value o f a d o l l a r t o be spent i n t h e f u t u r e Discount r a t e % 10 years 20 years
12
10
0.322 0.104
0.386 0.149
8
4
0.463 0.215
0.676 0.456
Groundwater p r o j e c t s o f f e r t h e advantage o f r e q u i r i n g s m a l l e r investments f o r which reason they are a more
hand,
i n v o l v e d are smaller, the
the
risk
is
marketing u n c e r t a i n t i e s involved; staggered, m o d i f y i n g
as t h e
it
i n which t h e r e i s
f i t t i n g a l t e r n a t i v e f o r cases
l i m i t e d c a p i t a l and h i g h i n t e r e s t r a t e s ; on t h e o t h e r lower i n view o f and
as
the
hydrogeological
exploitation
demand f o r water
investments can be reduced t o a minimum.
as t h e investments of
water
develops, then
On t h e c o n t r a r y ,
and
can be
unproductive
a scaled economy
is
one o f the obvious, c l a s s i c advantages o f s u r f a c e water. I n t h e 1950s most
countries
was s i g n i f i c a n t l y lower than
a p p l i e d a s o c i a l l y o r i e n t e d discount r a t e which
the
discount r a t e was applied, as
market
rate.
I n t h e 1970s
the c o s t o f money
had
a much
higher
a l s o increased (James and
I t apparently seems t h a t t h e energy c r i s i s works a g a i n s t t h e use
Rogers, 1976).
o f ground water although, i n f a c t , t h e
increased
d i s c o u n t r a t e compensates f o r
t h e increased c o s t o f energy (Gomez de Pablos, 1974). Comparisons a r e f r e q u e n t l y made between t h e metre o f water i n a accuracy, t h e
reservoir
have t o be taken i n t o account, which c l e a r l y France where t h e
of
r e g u l a t i n g one
and o b t a i n i n g i t from a w e l l .
cost o f transport, d i s t r i b u t i o n
o n l y c o s t comparison known
cost
t o be made on
F o r t h e sake o f
and water treatment tends t o f a v o u r
cubic
would
also
ground water. The
a n a t i o n a l l e v e l was c a r r i e d o u t i n
gross p r o d u c t i o n c o s t p l u s water treatment o f a r i v e r i s 0.14
FF/m3 and o n l y 0.09 FF/m3 f o r ground water (Erhard-Cassegrain and Margat, 1983). The comparison would be
even more unfavourable i f
regulating
dams were t o
be
the l o s s i n
the
constructed. Other economic aspects t o be taken i n t o water t r a n s p o r t
consideration
are
and d i s t r i b u t i o n networks, which i s g e n e r a l l y
more s i g n i f i c a n t
i n the case o f surface water, and evaporation from t h e r e s e r v o i r s .
I n t h e USSR,
350 the t o t a l loss
a t t r i b u t e d t o evaporation
U.S. and 75% i n t h e Carpentras
I f ground
total
Canal i n Provence (Erhard-Cassegrain and Margat,
and s u r f a c e
l i n i n g canals t o t a l l y recharges an
quoted as 10% o f t h e
Loss i n i r r i g a t i o n networks has been quoted as 16.4% i n t h e
c o n t r o l l e d volume. 1983).
has been
or
water
a r e used
partially i s
conjunctively,
not evident
the
if
Different
a1 t e r n a t i v e s
of
Water Resources 1957,
e x p l o i t e d a q u i f e r ( C a l i f o r n i a Department o f
Morel-Seytoux e t a1 , undated).
the b e n e f i t
i n f i l t r a t e d water
must be
simulated
to
compare t h e i r appropriateness and economic i m p l i c a t i o n s . The v a r i a b l e s a f f e c t i n g t h e c o s t o f Lopez-Camacho (1974).
w e l l was s t u d i e d by
water pumped from a
As a general r u l e t h e most i n f l u e n c e f a c t o r i s t h e annual
volume o f water pumped.
A l l t h e o t h e r f a c t o r s b e i n g equal, e.g. y i e l d o f w e l l s ,
water l e v e l s , drawdown,
pump e f f i c i e n c y
. . .; water
c o s t s more
for
irrigation
purposes than f o r urban and i n d u s t r i a l uses, as t h e former system operates fewer hours a n n u a l l y .
I n many
i r r i g a t i o n needs o f
aquifers
the y i e l d
t h e Mediterranean coast
of Spain where i t i s
farmers owning and o p e r a t i n g a w e l l . t h e need t o
of
individual wells
individual plots o f i r r i g a t e d
share
the
risk
of
It
is
groundwater development. c o n s t r u c t i o n techniques f o r
This i s
the
on
normal t o have
an a s s o c i a t i o n o f
probably
an i n h e r i t a n c e o f
drilling
obvious
exceeds t h e
l a n d T h i s o f t e n happens
costs
that
the
achieving greater s p e c i f i c
also n
the
early
improvement yields
days of
of well
and t h e c o r r e c t
design of pumping and e l e c t r i c a l i n s t a l l a t i o n s can reduce groundwater c o s t . 3. EXTERNAL FACTORS PRODUCED BY GROUNDWATER ABSTRACTION
Groundwater e x p l o i t a t i o n produces e x t e r n a l f a c t o r s such as r e d u c t i o n i n water levels, reduction
i n r i v e r discharges, sea water
wetland o r e c o l o g i c a l degradation i r r i g a t i o n areas.
Piezometric d e c l i n e
cases leads t o w e l l s
being
abandoned
Pumping o f coastal a q u i f e r s can cause w e l l s life.
I n the
o r l o n g term
induces
intrusion,
land
increases energy c o s t s and and
the
to
the
need f o r
built.
a r t i f i c i a l recharge,
can
Conjunctive help
to
reduce
extreme
advancement o f t h e s a l i n e wedge which
overdraft, a r t i f i c i a l
b a r r i e r s have t o be
in
r e b u i l d i n g them.
t o be abandoned and t h e consequent r e d u c t i o n o f case o f
subsidence,
v a r i a t i o n s i n water q u a l i t y i n
recharge
use,
t h e i r economic
facilities o r injection
whether
piezometric
or
not this
decline
or
includes seawater
intrusion. The e f f e c t o f pumping on
s u r f a c e water
flows
occurs w i t h
a
delay
which
depends on t h e geometry and hydrodynamic parameter o f t h e a q u i f e r s concerned and on t h e l o c a t i o n o f t h e w e l l s . e f f e c t has been used
Even i n t h e
t o operate a q u i f e r s
f l o w o f t h e r i v e r s i n c o n j u n c t i v e use periods.
narrow f l u v i a l a q u i f e r s t h i s delayed as
storage elements t o r e g u l a t e t h e
schemes when w e l l s a r e pumped i n low f l o w
The s t u d i e s made i n t h e a q u i f e r - r i v e r systems o f
and South P l a t t e
in
Colorado, USA, have
the Rivers
Arkansas
become c l a s s i c s (Moulder and Jenkins,
351 1963; Morel-Seytoux e t a l , Young, 1983).
And
in
systems w i t h a q u i f e r s
1973,
Young
and Bredehoeft,
t h e U n i t e d Kingdom
1972,
conjunctive
use
Bredehoeft and
i n aquifer
river
o f r e l a t i v e l y small dimensions i s being c a r r i e d o u t i n
a
very s t r i c t and pragmatic way (Downing e t a l , 1974, B i r t l e e s and Reeves, 1979). Intense a q u i f e r
pumping
can
temporarily
or
permanently
modify
the
a q u i f e r - r i v e r r e l a t i o n s h i p a l l o w i n g some water volume t o i n f i l t r a t e through i t s bed and thus increase t h e a q u i f e r storage.
The
on a l a r g e
the Ganges
scale
has been
suggested
a r t i f i c i a l recharge i n u n l i n e d canals a l , 1979).
in
a p p l i c a t i o n o f induced recharge basin conjunctively w i t h
t o r e g u l a t e t h e r i v e r f l o w (Chaturvedy e t
Economic l o s s caused by l a n d subsidence i s
o f major
urban o r coastal areas and minor i n r u r a l environments. o f clay consolidation
is
n o t a r e v e r s i b l e one,
b u t n o t a l l e v i a t e d i f piezometric l e v e l s
are
importance
in
As t h e p h y s i c a l process
l a n d subsidence can be stopped
raised
b y means o f
artificial
recharge o r decrease o f groundwater pumping. The small i n f l u e n c e o f t h e decisions made by on t h e
future
water l e v e l d e c l i n e i n
i n f l u e n c e o f h i s own users I , produces
extractions
his
on h i s
an i n d i v i d u a l groundwater u s e r
own w e l l , water
divergences between p r i v a t e
To c o r r e c t such divergencies adequate l e g a l
and
t h e small n e g a t i v e
costs, although
n o t on
other
and s o c i a l b e n e f i t s (Burt, 1964). and a d m i n i s t r a t i v e r e g u l a t i o n s must
be drawn up. 4. WATER QUALITY PROBLEMS Ground water i s u s u a l l y more s a l i n e than s u r f a c e water although i n some cases t h e opposite i s t r u e .
The water imported v i a t h e Colorado
Aqueduct t o Southern
C a l i f o r n i a i s s a l t i e r than t h e
ground water from c o a s t a l a q u i f e r s w i t h which i t
i s recharged.
from t h e K i n n e r e t Lake recharged i n t h e
I n I s r a e l water
and limestone a q u i f e r i s more
saline
than
ground water.
s a l i n i t y are sewage waters, d i f f u s i o n through t h e i n t e r f a c e between and the i n t r u d e d sea water and leakage increase 1980).
Another p o s s i b i l i t y o f
obtaining
an
coastal
Other sources
of
f r e s h water
from adjacent a q u i f e r s (Mercado acceptable water q u a l i t y
is
by
m i x i n g p r i o r t o i t s use. I r r i g a t i o n can increase ground water i s
c h l o r i n e and
n i t r a t e content
pumped f o r i r r i g a t i o n purposes, t h e
i n ground water.
If
depression o f g r a d i e n t s t o
t h e aquifer o u t l e t s r e s u l t s i n a drop o f water and s a l i n i t y f l u s h . I r r i g a t i o n w i t h surface water water and pumping. i n the
soil salinization
i n d r y areas very o f t e n c r e a t e s
The most spectacular example i s t h e Indo a l l u v i a l
plain
i n Pakistan
Punjab where
i r r i g a t i o n system i n t h e w o r l d i s located, c o v e r i n g hectares.
drainage and
problems which c o u l d be m i t i g a t e d by groundwater i r r i g a t i o n system l o c a t e d the an
largest
concentration
extension o f 13 m i l l i o n
Aquifer recharge as a r e s u l t o f excessive i r r i g a t i o n , and f i l t r a t i o n s
along the 65,000 km o f
canals,
which are u n l i n e d i n most cases,
has produced
352 very serious drainage and s a l i n i z a t i o n problems.
two m i l l i o n hectares had
Over
t o be abandoned and each year t h i s problem a f f e c t s an a d d i t i o n a l 25,000 hectares (Chaudry e t al, 1979).
This case was studied i n g r e a t d e t a i l and a proposal made
t o construct 30,000 w e l l s 70.10'
m3
o f water per
with
sufficient
annum.
The
aims
capacity t o pump i n of this
piezometric surface and e l i m i n a t e p a r t o f
the
proposal are
order
to
of
lower t h e
the s a l t water, thus a l l e v i a t i n g t h e
drainage and s a l i n i z a t i o n problems. I n Soviet Central annually through
Asia
an
estimated 25.109 m3
of
a g r i c u l t u r a l drainage systems i n
Conjunctive use o f surface and
water
the zone
are
under
discharged irrigation.
ground water has been proposed t o u t i i z e these
resources (Kats, 1975), 5. ARTIFICIAL RECHARGE
A r t i f i c i a l recharge i s an e f f e c t i v e d e c l i n i n g piezometric encroachment.
levels,
Nevertheless
or
way t o
protect should
it
be
a r t i f i c i a l recharge are n o t synonymous, as problems w i t h a r t i f i c i a l requires, i n
addition
recharge to
the
It
reduce against
said
that
we s h a l l
i s that
is
discuss l a t e r .
advisable
to
by t a k i n g advantage o f n o t d e l i b e r a t e l y planned l e a k i n g dams,
unlined
use
and
One o f the
i s costly
derivation,
stop
seawater
since
transport
it
and
Furthermore the operating and maintenance take
p o s s i b i l i t i e s o f f i n d i n g a cheap way t o recharge water cases o f
or
conjunctive
very o f t e n i t
recharge elements
sedimentation or treatment elements. costs are u s u a l l y high.
s t o r e water,
coastal a q u i f e r s
canals,
into
consideration
the
by a r t i f i c i a l means,
recharge,
as
induced recharge
happens i n or
or the
incidental
o v e r i r r i g a t i o n (Custodio, 1986). I n the course o f the a r t i f i c i a l recharge process, the w a t e r ' s physicochemical and b i o l o g i c a l p r o p e r t i e s are transformed zone and, as
as i t passes through a non-saturated
a r e s u l t , bacteria, virus, organic m a t e r i a l , heavy metals and many
t o x i c compounds are eliminated o r are g r e a t l y reduced. p o l l u t e d surface
water i s
European countries. ground water i s
u t i l i z e d extensively
This method o f t r e a t i n g
i n many
c e n t r a l and northern
There a l s o e x i s t many instances throughout the world
recharged
using
reclaimed waste water
(Asano
1985),
growing i n t e r e s t i s emerging i n research t o reduce pre-treatment needs. mentioned before t h a t
artificial
recharge
has a l s o been used as
where and
a
We have
a means
of
blending i n the a q u i f e r waters w i t h d i f f e r e n t chemical p r o p e r t i e s . The economic
effects
of
r a i s i n g water
seawater i n t r u s i o n and a q u i f e r storage a l l
levels, a q u i f e r p r o t e c t i o n against need t o be analysed
through a q u i f e r
and water system simulation. 6. INFORMATION UNCERTAINTY AND FORECASTING Wiener (1972) has b r i l l i a n t l y noted the f o l l o w i n g p o i n t s concerning t h e need
353
f o r i n f o r m a t i o n and
the
u n c e r t a i n t i e s which
exist
at
the
time
of
making
d e c i s i o n s r e l a t e d t o s u r f a c e and ground w a t e r use. I n t h e m a j o r i t y o f cases, stream f l o w r e p r e s e n t s a r a p i d response t o c l i m a t i c phenomena.
Normally, t h e
c o l l e c t e d over a
information
derived
few y e a r s i s more r e l i a b l e ,
from
ground-water r e l a t e d d a t a
i f p r o p e r l y analysed,
than t h a t
p r o v i d e d by s u r f a c e - w a t e r r e l a t e d d a t a c o l l e c t e d o v e r a l o n g e r p e r i o d o f t i m e . The i n e r t i a o f
the
a q u i f e r s , caused by
the large
amounts
o f water
i n t e g r a t e s a l o n g p e r i o d o f h y d r o m e t e o r o l o g i c a l phenomena and
stored,
short-term
data
c o l l e c t i o n can p r o v i d e much b e t t e r o v e r a l l i n f o r m a t i o n . F l u c t u a t i o n s i n t h e magnitude o f t h e f l o w a r e g r e a t e r i n s u r f a c e i n ground w a t e r .
made.
water than
M i d o r l o n g t e r m p r e d i c t i o n s o f s t r e a m f l o w d i s c h a r g e cannot be
Streamflow d i s c h a r g e i s s t o c h a s t i c b y n a t u r e so i t s b e h a v i o u r can o n l y b e
t r e a t e d i n terms o f p r o b a b i l i t y . more d e t e r m i n i s t i c as a
Groundwater b e h a v i o u r i s much l e s s e r r a t i c and
r e s u l t o f the normally
close
r e l a t i o n s h i p between t h e
s t o r e d w a t e r and t h e a q u i f e r ' s average recharge. Groundwater e x p l o i t a t i o n operational costs are
requires
high.
low,
Surface
initial
water
investment;
exploitation
however,
requires a
the large
investment, w h i l e o p e r a t i o n a l c o s t s a r e n o r m a l l y l o w e r . I n t h e case o f s u r f a c e water, t h e i n v e s t m e n t r e q u i r e d i s u s u a l l y i n d i v i s i b l e , which a l s o e n t a i l s
a lengthy
i n o p e r a t i v e p e r i o d d u r i n g t h e study, c o n s t r u c t i o n
and d e c i s i o n making process.
I t may t a k e
years
a c t u a l l y e f f e c t i v e i n o p e r a t i o n a l terms.
for
The l a r g e
imposes g r e a t e r demands on t h e i n f o r m a t i o n r e q u i r e d . investment r e q u i r e d much s h o r t e r .
for
ground w a t e r i s
the
project t o
become
investment involved a l s o C o n t r a r y t o t h e above, t h e
d i v i s i b l e and t h e
inoperative period
T h i s i n t r o d u c e s t h e a d d i t i o n a l advantage o f i t s
being
much more
adaptable t o i n c r e a s i n g w a t e r demands. For the
cases,
common
throughout
t h e world,
i n f o r m a t i o n i s i n c o m p l e t e and f o r those where t h e c o n s i d e r a t i o n s mentioned
above
recession experienced i n the
last
are
where
the
hydrological
f u t u r e w a t e r needs a r e u n c e r t a i n ,
crucially
important.
The
economic
few y e a r s has had a
d e c i s i v e i n f l u e n c e on
r e d u c i n g expected w a t e r needs i n many p a r t s o f t h e w o r l d .
Ground w a t e r can p l a y
a more i m p o r t a n t r o l e i f t h e w a t e r r e s o u r c e s system i s conceived d y n a m i c a l l y and t h e u n c e r t a i n t i e s which e x i s t i n t a k e n i n t o account
r a t h e r than
r e l a t i o n t o t h e w a t e r r e s o u r c e s and demand a r e r e s o r t i n g t o a system
which
is
statistically
conceived and s t r u c t u r a l l y o r i e n t a t e d . I n t h e l a s t few y e a r s t h e r e have been some i m p o r t a n t changes i n t h e and management o f w a t e r resources. questioned, g r e a t e r
interest
is
The u t i l i t y o f s t r u c t u r a l s o l u t i o n s has been being
shown
i n an
optimum u t i l i z a t i o n
e x i s t i n g f a c i l i t i e s r a t h e r t h a n i n i n v e s t i n g i n new ones, t h e e r a o f c o n s t r u c t i n g l a r g e dams
planning of
and i n many c o u n t r i e s
has p r o b a b l y come t o an end ( W i l l e k e e 1979).
A l t h o u g h v e r y few f i n a n c i a l e v a l u a t i o n s
have been made o f t h e
results o f
some
354
these
projects, there i s s u f f i c i e n t evidence t o question whether the r e s u l t s o f l a r g e construction p r o j e c t s have l i v e d up o f government subsidies f o r major water
t o expectations o r not.
The problem
p r o j e c t s has been f r e q u e n t l y questioned
and the f i r s t step towards determining a s o l u t i o n should
be an a n a l y s i s o f
the
various a1 t e r n a t i v e s a v a i l a b l e . 7. ECONOMIC ASPECTS OF DIFFERENT CONJUNCTIVE USE TYPOLOGY O f the d i f f e r e n t functions u s u a l l y i d e n t i f i e d i n
source o f water, treatment
-
we
storage have
and
regulation,
n o t analysed i n
a water resources system
transport,
t h i s paper
-
d i s t r i b u t i o n and water
the a q u i f e r
as a v e h i c l e t o
t r a n s p o r t water since an a q u i f e r i s g e n e r a l l y u n s u i t a b l e f o r t h i s f u n c t i o n .
The
cases i n which
not
the a q u i f e r
serves as a means o f water
included e x p l i c i t l y e i t h e r , as t h i s f u n c t i o n i s r o l e as a means o f
storage.
Aquifers
d i s t r i b u t i o n and substantial
savings
distribution
usually closely related
provide
alternate
surface
distribution
in
are
means
to i t s
for
water
systems.
In
previous paragrahs we have mentioned the p o s s i b i l i t i e s o f a r t i f i c i a l recharge as a means o f water treatment and t h e mixing o f d i f f e r e n t kinds o f water. I n a d d i t i o n t o an aquifer's be u t i l i s e d ( r e f e r r e d t o
e x p l o i t a b l e resources, i t s stored water can a l s o the
as
"one
time"
reserve)
causing
a
temporary
overexpl o i t a t i o n . I n spite o f
the
serious
economic
and
s o c i a l problems
the
overdraft
of
aquifers can cause, i t i s n o t necessary t o r u l e o u t o v e r d r a f t as a general r u l e . I n f a c t , the reasons f o r
overexploitation
o f ground water i n
i t s p r o s p e r i t y which
consequently created costly projects
the
such as
facilitated
propitious
its
California economic
i s one o f
development
conditions f o r carrying out
interbasin transfers
from
areas
with
other the
the and more
heaviest
r a i n f a l l i n the northern p a r t o f the s t a t e ( C a l i f o r n i a State Department o f Water Resources, 1957). The a v a i l a b i l i t y o f l a r g e q u a n t i t i e s o f water proposals f o r the well-planned u t i l i s a t i o n o f d e f e r r i n g c o s t l y construction p r o j e c t s . such a
methodology was
proposed f o r
in
the
a q u i f e r s has prompted
o f the a q u i f e r - s reserves as a means This
has
subsequent
been done i n I s r a e l where modelling
and
economic
o p t i m i s a t i o n (Schwartz, 1980). I n actual f a c t Planned Overdraft i s n o t but rather a
first
conjunctive use o f
stage which one
type
or
can
be
a separate type o f c o n j u n c t i v e use, followed
another.
by
successive
O v e r e x p l o i t a t i o n has
stages also
of been
suggested i n successive stages, followed by successive surface water development and conjunctive use
(Schwartz
1980), o r
as a permanent
component d u r i n g
the
e n t i r e planning period. I n the type
o f conjunctive
use we
r e s e r v o i r s release more water i n r a i n y
have
termed
Alternative
periods o r years
and
Use,
surface
the a q u i f e r s are
355
pumped more i n d r y periods. be made a v a i l a b l e
by
The e x p l o i t a b l e
storage
piezometric o s c i l l a t i o n s .
c a p a c i t y t o be used would
I n this
way, an
underground
storage area o f 37.109 m3 would become a v a i l a b l e f o r use i n C a l i f o r n i a ' s Central i n c o n t r a s t t o t h e 27.109
V a l l e y w i t h r e l a t i v e l y small piezometric o s c i l l a t i o n s m3 t o be
provided by surface storage
(California
State
Department
of
Water
Resources, 1957). I n La Plana de C a s t e l l h , on o s c i l l a t i o n s represent
t h e Mediterranean coast o f
an a q u i f e r storage o f 500.106 m3,
Spain, three
piezometric
times
greater
than t h e e x i s t i n g surface storage. I n t h e A l g a r a q u i f e r p e r i o d i c l e v e l drawdowns represent 40.106 m3
o f storage as compared t o
and Amadorio dams can
store.
Also
in
t h e 30.106 m3 t h a t t h e Guadalest
Spain
large scale
developments
are
p o s s i b l e and have been suggested (Sahuquillo, 1986). These type o f
schemes
require
that a part
o f the
demand
i n d i s t i n c t l y by two sources and i n some cases t h e water l e v e l be high.
When
distribution o f
this
is
the
the
case,
different
in
addition t o
components,
recharge elements, t h e o p e r a t i o n o f t h e
the
can
depends on t h e s t a t e o f t h e system, t h e water
i s crucial. stored
in
served
oscillations
design
including wells
system
be
can
and p h y s i c a l
and
artificial
Optimal
operation
dams, t h e p i e z o m e t r i c
l e v e l s , the s u r f a c e water i n p u t s and water q u a l i t y . Improvements i n mid o r s u b s t a n t i a l economic gains
long
term
h y d r o l o g i c a l f o r e c a s t i n g would
i n reservoir
operation o f
conjunctive
lead
to
use schemes
(Jaquette 1981). Greater use o f ground water
can
be made d u r i n g
drought
European c o u n t r i e s took advantage o f t h i s i n t h e summer o f 1976.
periods.
Many
I n California,
i t helped reduce t h e e f f e c t s of low-water i n 1976-77 t o a s i g n i f i c a n t e x t e n t .
Owing t o t h e
i n i t i a t i v e taken by p r i v a t e i n d u s t r y
government a c t i o n , t h e
effects o f
e a r l y e i g h t i e s were m i t i g a t e d
in
the drought some
and, t o a
Spain was
areas.
l e s s e r degree,
experiencing i n the
I n fact,
the e f f e c t s o f
the
drought were lessened i n t h e areas where g r e a t e r u t i l i z a t i o n o f ground water was made and a methodology
to
this
effect
has
been
proposed f o r
subsequent
a p p l i c a t i o n t o c o n j u n c t i v e use o f surface and ground water ( S a h u q u i l l o 1983). When l o c a l s u r f a c e waters a r e l e s s important,
a q u i f e r s can be used t o
and d i s t r i b u t e imported and l o c a l surface water A r t i f i c i a l recharge i s c r u c i a l Terminal o r L a t e r a l i t s role i s only use are I s r a e l and
to this
Ground Water
complementary. Southern
l e s s important than i n t h e
artificial
C l a s s i c examples In
we c a l l
t o a l t e r n a t i v e use where
o f t h i s type this
store
recharge.
t y p e o f c o n j u n c t i v e use which
Storage, as opposed
California.
v a r i a t i o n s of imported water
through
type
of
o f conjunctive scheme
annual
a r e minimum o r r e l a t i v e l y low and i n any case a r e
so c a l l e d a l t e r n a t i v e use.
important than t h e p h y s i c a l d i s t r i b u t i o n
of
recharge and water t r a n s p o r t and d i s t r i b u t i o n .
wells
Here o p e r a t i o n i s
and elements o f
less
artificial
The C a l i f o r n i a S t a t e Department
356 o f Water Resources hydrological
,
o f systems.
in
the
sixties
hydrogeological
developed
, operational
I n these s t u d i e s
a
large
a
methodology f o r
working
on
and economic s t u d i e s f o r these types
number o f a l t e r n a t i v e s
were simulated,
a l s o t a k i n g i n t o account t h e d i f f e r e n t values o f water i n terms o f i t s s a l i n i t y . ( C a l i f o r n i a S t a t e Department o f Water Resources 1966, 1971). The A q u i f e r - r i v e r
Systems can
be considered a
I n t h i s the aquifer-river relationship i s o f o p e r a t i o n i s very
important,
mainly
prime importance, a l s o
function o f
of
t h e system
o f t h e ground water component whereas t h e
a r t i f i c i a l recharge i s o f secondary importance. use a l a r g e r use
subgroup o f a1 t e r n a t i v e use.
With t h i s
type o f
conjunctive
s u r f a c e water can be obtained, g i v i n g t h e ground water t h e
complementing
the
deficit
in
the
driest
years
or
seasonally
throughout t h e y e a r . Operating ground water i n t h i s way ( S a h u q u i l l o 1983).
Bredehoeft
insurance t h e farmers
represents
an insurance a g a i n s t
and Young (1983) a l s o analysed t h e
o f t h e South P l a t t e make
drought
role of
the
o f ground water where t h e y have
i n s t a l l e d a w e l l c a p a c i t y almost s u f f i c i e n t t o i r r i g a t e t h e e n t i r e area, u s i n g a s i m u l a t i o n model system t o an
which
1i n k s
economic model
the
hydrology o f a
which i n c o r p o r a t e s
r e s u l t s o f t h e model c o i n c i d e w i t h t h e w e l l t h i s has two
conjunctive
the
stream-aquifer
farmers’ behaviour.
Doing
b e n e f i t s : i t maximises t h e expected n e t b e n e f i t s and minimises t h e
v a r i a t i o n i n annual income. t h e value o f f l o w
By i n c r e a s i n g t h e pumping
f o r e c a s t i s diminished,
pumping more ground water.
capacity
counteracting
The r o l e o f r e d u c i n g
a
t o such value,
poor
forecast
by
t h e unwant economic e f f e c t s o f
u n c e r t a i n t y by u s i n g more ground water i s discussed a n a l y t i c a l l y I s s a r (1987).
The
capacity actually i n s t a l l e d .
by
Tsur
and
They p r o v i d e an e x p l i c i t expression f o r t h e v a l u e o f u s i n g ground
water i n t h i s way i n terms o f t h e marginal p r o d u c t i v i t y o f water, t h e p r o d u c t i o n f u n c t i o n and t h e v a r i a b i l i t y o f s u r f a c e water. 8. APPLICATIONS
OF SYSTEM ANALYSIS TECHNIQUES
The d e t a i l i n which methods.
The s i m p l e s t
aggregated parameters.
a q u i f e r behaviour way
is to
i s analysed v a r i e s
c o n s i d e r a q u i f e r s as
The commonest
way i s
to
i n the
elements
assimilate
different
with
them
a
to
few
linear
r e s e r v o i r s r e l e a s i n g a f l o w associated l i n e a r l y w i t h a volume o f water s t o r e d i n t h e a q u i f e r (Buras 1963, 1967, Sanchez m u l t i c e l l u l a r n o n l i n e a r models
with
s i m p l i f i c a t i o n i s used i n
higher
the
1983). a
few
Birtles non
hierarchical
associated w i t h o p t i m i z a t i o n methods (Schwartz 1980). been used w i t h d e t a i l e d a q u i f e r
models
using
and
Reeves (1979) use
linear cells.
dynamic
levels
Usually and
very
this often
O p t i m i s a t i o n methods have programming, l i n e a r and
non l i n e a r programming ( G o r e l i c k 1983). Nevertheless, f o r complex systems, when t h e i n t e r a c t i o n between
surface
and
ground water and when s t o c h a s t i c s u r f a c e flow v a r i a t i o n s have t o be taken i n t o
357 consideration,
o r where more
than
one
s i m u l a t i o n techniques i s v i r t u a l l y
surface
reservoir exists, the
unavoidable.
This i s p a r t i c u l a r l y
t h e a l t e r n a t i v e use type, o r when q u a l i t y problems have t o l a r g e number simulated.
o f a1 t e r n a t i v e s
or
synthetic
use
of
true i n
be considered, and a
h y d r o l o g i c a l sequences
have t o be
I n t h i s case
t h e eigenvalue method (Andreu and S a h u q u i l l o 1987) i s I t s most i n t e r e s t i n g aspect i s t h a t e x t e r n a l a c t i o n s and
t h e most a p p r o p r i a t e .
i n i t i a l c o n d i t i o n s are e x p l i c i t l y
transformed f o r a q u i f e r s i n t o a s t a t e v e c t o r .
From t h i s , piezometric head f l o w s and surface-ground water interchanges a r e a l s o e x p l i c i t l y computed t o s i m u l a t e c o n j u n c t i v e use systems. 9. CONCLUSIONS A1 though ground water has v e r y o f t e n been overlooked by p l a n n i n g s p e c i a l i s t s , i t can o f f e r t e c h n i c a l and economic advantages
worthy o f c o n s i d e r a t i o n .
water can p r o v i d e a d d i t i o n a l resources as w e l l as d i s t r i b u t i o n and
treatment, which can
water resources.
Likewise, ground water can p r o v i d e o t h e r
i t s adaptability t o possibility o f
a
temporary
construction projects, drainage problems. t h e insurance
progressive to
be
t h e means f o r water
mitigate
combined advantageously w i t h s u r f a c e
increase
overexploitation the
Ground storage,
in as
a
effects
the
means of
advantages
demand
for
for
such
water,
as the
deferring costly
droughts
and
alleviate
Another v i r t u e o f ground water i n c o n j u n c t i v e use schemes i s
role i t
supplies
t o o f f s e t the
uncertainty
concerning s u r f a c e
flow, h y d r o l o g i c a l parameters o r demand. 10. REFERENCES Andreu, J. and Sahuquillo, A. 1987. E f f i c i e n t A q u i f e r S i m u l a t i o n i n Complex Systems: J. Water Resour. Planning Mgmt Div. A.S.C.E. Vol. 113 No. 1, Jan 1987, 110, 129. Asano, T. E d i t o r , 1985. A r t i f i c i a l Recharge o f Ground Water. Butterworth Pub1 i s hers. B i r t l e s , A.B. and Reeves, M.J., 1977. A Simple E f f e c t i v e Method f o r t h e Computer S i m u l a t i o n o f Ground Water Storage and i t s A p p l i c a t i o n i n t h e Design o f Water Resource Systems. J. o f Hydrology No. 34, 77-96. Bredehoeft, J.D. and Young, R.A., 1983. Conjunctive Use o f Groundwater and a Surface Water f o r I r r i g a t e d A g r i c u l t u r e : Risk Aversion. Water Res. Res., Vol. 19, NO. 5, 1111-1121. Buras, N., 1963. Conjunctive Operation o f Dams and Aquifers. Journ. of H y d r a u l i c D i v i s i o n , ASCE, Vol. 89, HY6, November, 111-131. Buras, N., 1967. Operation o f a Complex Water Resources U t i l i z a t i o n System. Conference on Water f o r Peace. Washington D.C. Burt, O.R., 1964. The Economics o f Conjunctive Use o f Ground and Surface Water. H i l g a r d i a . Vol. 3G, No. 2, December 1964. C a l i f o r n i a S t a t e Department o f Water Resources, 1957. The C a l i f o r n i a Water Plan. B u l l . Number 3. C a l i f o r n i a S t a t e Department o f Water Resources, 1965. Planned U t i l i z a t i o n of Ground Water Basins: Coastal P l a i n o f Los Angeles Country. Appendix C. Operation and Economics, B u l l . No. 4. C a l i f o r n i a S t a t e Department o f Water Resources, 1971. Planned U t i l i z a t i o n o f Water Resources i n t h e San Juan Creek Basin Area, B u l l . Nos. 104-7. Chaturvedy, M.C. and Srivostava, V.K., 1979. Induced Ground Water Recharge i n
358 t h e Ganges Basin, Water Resources Research, 15 ( 5 ) 1156-1166. H a l l , W.. and Abberston, M.L, 1974. Optimal Chaudry, M.T., Labadie, J.W., Conjunctive Use Model f o r Indus Basin, Journal o f t h e H y d r a u l i c D i v i s i o n A.S.C.E. , 100 HY5) 667-678. Avances y Realizaciones. Custodio, E. , 1986. Recarga a r t i f i c i a l de a c u i f e r o s . S e r v i c i o Geoldgico de Obras Pu'blicas. Bol. I n f . y Estudios, No. 45. M i n i s t e r i o de Obras Pu'blicas. Madrid. 176 pages. Wilkinson, W.B. and Wright, C.E., 1974. Regional Downing, R.A., Oakes, D.B., Develppment o f Groundwater Resources i n Combination w i t h Surface Water, Journal o f Hydrology, 22 (1-2) (June) 155-177. Erchard-Cassegraom, A. and Margat, J. 1983. I n t r o d u c t i o n 'a 1'Economie Ge'ne'rale de 1 'Eau. Masson, 1983. Fowler, L., 1981. Case Study U.S.A. Santa Clara V a l l e y D i s t r i c t . Proceedings o f the NATO Advanced Study I n s t i t u t e , Operation o f Complex Water Resource Systems, Erice, I t a l y , May. Conferencia Nacional sobre H i d r o l o g i a Gdmez de Pablos, M., Ponencia I . , 1974. General y Aplicada, Saldn Monogrdfico d e l Agua. Zaragoza, Spain, 45-55. Gorelick, S.M., 1983. A Review o f D i s t r i b u t e d Parameter Groundwater Management Modeling Methods. Water Resources Research. Vol. 19, No. 2, 305-319. Howell, O.H. and Warmann, J.C., 1982. Ground-Water Management i n t h e Southeast, A.S.C.E., Journal o f t h e Water Resources Planning and Management D i v i s i o n . Vol. 8 WR3, 321-328. James, D.L. and Rogers, J.R., 1976. Economics and Water Resources Planning i n America. Journal o f t h e Water Resources Planning and Management D i v i s i o n A.S.C.E., Vol. 105, No. WR1, March, 47-64. Jaquette, D.J., 1981. E f f i c i e n t Water Use i n C a l i f o r n i a : Conjunctive Management o f Ground and Surface Reservoirs I n : R. Beard Guest E d i t o r , Water f o r S u r v i v a l . J. Hydrol, 51, 187-204. Combined Use o f Ground and Surface Waters f o r I r r i g a t i o n . Kats, D.M., 1975. S o v i e t Hydrology, Selected Papers, Published by American Geophysical Union, I n t e r n a t i o n a l Water Resources Association, American Water Resources Association, 190-194. Ldpez-Camacho, B., 1974. A n i l i s i s del c o s t e d e l agua s u b t e r r i n e a mediante un prograrna de ordenador. I Conferencia Nacional Sobre H i d r o l o g i a General y Aplicada. Zaragoza. Llamas, M.R., 1974. Non-economic Motivation in Groundwater Use: Hydroschizofrenia. Groundwater, 13 ( 3 ) , 196-300. Mercado, A., 1980. The Coastal A q u i f e r i n I s r a e l : Some Q u a l i t y Aspects o f Groundwater Management I n : Water Q u a l i t y Management under Conditions of S c a r c i t y . I s r a e l as a Case Study. H.J. Shuval E d i t o r , Academic Press. Morel-Seytoux, H.J., Young, R.A., Radosevich, G.E., 1973. Systematic Design o f Legal R e g u l a t i o n f o r Optimal Surface Groundwater Usage - PHASE 1. Colorado S t a t e U n i v e r s i t y Environmental Resources Center, Report No. 53, August, 81 pages. Illangasekare, T. , B i t t i n g e r , M.W., Evans, N.E. (undated). Morel-Seytoux, H.J., The Impacts o f Improving Efficiency o f I r r i g a t i o n Systems on Water A v a i l a b i l i t y i n t h e Lower South P l a t t e R i v e r Basin. Colorado Water Resource Research I n s t i t u t e . I n f o r m a t i o n Series No. 33. 1963. Methods f o r C o n t r o l l i n g t h e Groundwater Moulder, E.A. and Jenkins, C.T., Regime E x p l o i t a t i o n and Conservation. Assembly o f Berkeley, Pub. NO. 64. I n t e r . Assoc. S c i e n t . Hydrol. Nace, L.R., 1972. Water Problems and Developments o f t h e Past. Water Resources B u l l e t i n . Vol. 8, No. 1. Sahuquillo, A., 1983. La u t i l i z a c i d n c o n j u n t a de aguas s u p e r f i c i a l e s y subterrdneas como D a l i a t i v o de l a s e w f a . Proceedings I11 Simposio Nacional de Hidrogeologia, Madrid, Spain, May,' 1983, 253-270.Sahuquillo, A., 1986. Las aguas subterrsneas en l a p l a n i f i c a c i d n de recursos h i d r d u l i c o s : e l us0 conjunto. R e v i s t a de Obras Pu'blicas. Madrid. December, 927-936. En: U t i l i z a c i d n c o n j u n t a de aguas Modelo de optimizacio'n. Sinchez, A., 1983. S e r v i c i o Geoldgico de Obras Pu'bl i c a s y s u p e r f i c i a l e s y subterrbneas.
359 Universidad Pol i t e c n i c a de Valencia. Schwarz, J . , 1980. A Systems Approach t o t h e S t r a t e g y o f I n t e g r a t e d Management o f Surface and Groundwater Resources. I n : Water Q u a l i t y Management under Conditions o f S c a r c i t y . I s r a e l as a Case Study. H.I. Shuval E d i t o r . Academic Press. Taylor, O.J. and Luckey, R.R., 1974. Water Management Studies o f a Stream A q u i f e r System, Arkansas R i v e r Valley, Colorado. Groundwater, Vol. 12, No. 1, January, 22-38. Tsur, Y. and I s s a r , A., ,1987. The B u f f e r Role o f Ground Water when Supply o f Surface Water i s Uncertain. Paper presented a t t h e UN-Spain Symp. on Ground Water Economics, Barcelona, October, 1987. Wiener, A., 1972. The Role o f Water i n Development. McGraw H i l l Book Company, 1972. Willekee, G.E., 1979. Social Aspects o f Water Resources Planning. Journal o f the Water Resources Planning and Management D i v i s i o n A.S.C.E., Vol. 105, No. 1 WR1, March, 79-90. Young, R.A., Bredehoeft, J.D., 1972. D i g i t a l Computer S i m u l a t i o n f o r S o l v i n g Management Problems o f Conjunctive Ground Water and Surface Water Systems. Water Resources Research, Vol. 8, No. 3, June, 533-558.
ECONOMIC ASPECTS OF THE CONJUNCTIVE USE OF GROUND AND SURFACE WATER
And& S a h u q u i l l o , P o l y t e c h n i c a l V a l e n c i a Spain
University
o f Valencia, c / de Vera s/n,
46071
ABSTRACT The d i f f e r e n t s t r u c t u r e o f t h e c o s t s o f ground and s u r f a c e w a t e r and t h e d i f f e r e n t and complementary c h a r a c t e r i s t i c s o f b o t h k i n d s o f r e s o u r c e s make i t p o s s i b l e t o s o l v e t h e s p e c i f i c needs o f w a t e r q u a n t i t y and q u a l i t y more adequately and e c o n o m i c a l l y i f b o t h r e s o u r c e s a r e used c o n j u n c t i v e l y . Higher d i s c o u n t r a t e s f a v o u r t h e i n c l u s i o n o f elements i n v o l v i n g l o w e r initial investment and g e n e r a l l y w i t h h i g h e r groundwater components. Lower d i s c o u n t r a t e s favour a higher p a r t i c i p a t i o n o f surface water. The e x t e r n a l f a c t o r s produced by groundwater pumping must be t a k e n i n t o c o n s i d e r a t i o n i n any economic a n a l y s i s . Examples o f e x t e r n a l f a c t o r s a r e w a t e r l e v e l descents, s u r f a c e w a t e r f l o w r e d u c t i o n , d e g r a d a t i o n o f w e t l a n d s and e c o l o g i c a l issues, w a t e r qua1 i t y d e t e r i o r a t i o n and l a n d subsidence. T h i s paper discusses t h e economics o f a r t i f i c i a l recharge and i t s r o l e i n t h e d i f f e r e n t t y p e s o f c o n j u n c t i v e use. I t s importance i s c r u c i a l i n some cases and secondary o r m a r g i n a l i n o t h e r s . The amount o f s t o r e d ground w a t e r i n many cases i s s e v e r a l t e n s o r hundreds o f t i m e s t h e mean annual groundwater recharge 1eve1 . P1 anned overpumping a1 1ows c o s t l y p r o j e c t s r e q u i r i n g 1a r g e dams o r t r a n s f e r s t r u c t u r e s t o be postponed. The u n c e r t a i n t y i n h e r e n t i n r i v e r f l o w p r e d i c t i o n and demand v a r i a b i l i t y o r inadequate i n f o r s a t i o n o f t h e h y d r o l o g i c a l parameters o f t h e system can be c o u n t e r a c t e d by t h e f l e x i b i l i t y i n t h e seasonal and y e a r l y use o f ground w a t e r which c o n j u n c t i v e use schemes p r o v i d e s . I n many cases t h i s r e p r e s e n t s a k i n d o f i n s u r a n c e a g a i n s t adverse h y d r o l o g i c a l o r economic s i t u a t i o n s .
1. INTRODUCTION Growing w a t e r needs, of w a t e r development
t h e c o n s t r a i n t s caused by w a t e r
projects, i n c l u d i n g t h e c o s t
p o l l u t i o n and t h e c o s t
o f responding t o
s o c i a l and
F o r t h e s e reasons, i t has
environmental concerns, a r e i n c r e a s i n g d r a m a t i c a l l y .
become i m p e r a t i v e t o t a k e i n t o c o n s i d e r a t i o n a l l w a t e r sources and f a c i l i t i e s i n o r d e r t o s a t i s f y p r e s e n t and f u t u r e w a t e r demands. obtained i f a
water
system i s
resource
A d d i t i o n a l b e n e f i t s w i l l be
planned and/or
operated t a k i n g
into
c o n s i d e r a t i o n t h e advantage o f f e r e d by t h e c o n j u n c t i v e use o f ground and s u r f a c e water.
If
the
alternatives for
multiplicity achieving
of
objectives
this,
i n t e r r e l a t i o n s h i p seem e v i d e n t , i t r e c o u r s e t o c o n j u n c t i v e use; scarce.
and is
i n water the
advisable
planning, t h e d i f f e r e n t
ground i n most
and
surface
situations t o
water have
and n o t o n l y i n a r i d areas o r those where w a t e r i s
Ground w a t e r management
cannot e x i s t w i t h o u t s u r f a c e w a t e r management;
and surface w a t e r cannot be managed o p t i m a l l y i f t h e groundwater r e s e r v o i r s a r e
348 n o t included (Fowler, 1981). These p o s s i b i l i t i e s are f a r conjunctive use has been
from
carried
being
recognised unanimously and
out i n
few areas and
is
p r a c t i c e i n the water resources planning agencies o f most o f the decisions and a t t i t u d e s o f water s p e c i a l i s t s o f them favour surface water
utilization.
not
i n fact
a
customary
countries.
Analysis
indicate
t h a t the m a j o r i t y
Very o f t e n groundwater resources are
n o t taken i n t o consideration even i n regions where in-depth and r e l i a b l e studies have confirmed the existence o f positive results.
formations
whose u t i l i z a t i o n would c r e a t e very
This u n j u s t i f i e d disregard o f
q u a l i f i e d by Wiener (1972) as an evidence and defined as "hydroschizophrenia"
by
of
groundwater resources has been
a deep, unpremeditated prejudice,
Nace
(1972)
and
analysed by
Llamas
(1974). I n some countries the
r e s p o n s i b i l i t y f o r water
by the c e n t r a l government, projects.
at
planning has been taken over
l e a s t when making
final
decisions
on major
Large p r o j e c t s u s u a l l y have g r e a t e r f i n a n c i a l resources a v a i l a b l e and
have more favourable f i n a n c i a l terms
as w e l l ; these considerations, i n a d d i t i o n
t o p o l i t i c a l motivations, tend t o favour the l a r g e r more spectacular engineering projects. The a t t i t u d e s r e l a t e d above ground water occurrence
are due, i n part, t o a l a c k
and movement.
experience i n ground water studies education i n
hydrogeology,
even
Most
o f understanding o f
h y d r a u l i c engineers
have
and many planners have n o t had though an
appeal
to
increase
limited
any formal hydrogeology
studies has f r e q u e n t l y been made (Llamas 1974, Howell and Warman 1982). The i n c l u s i o n o f courses d e a l i n g w i t h the i n the
water resources
technical and
departments
scientific
of
d i f f e r e n t aspects o f ground water
universities,
accomplishments
can
and
co-operate
the to
diffusion change
of
those
a t t i t u d e s i n the near f u t u r e .
2. GROUND WATER COST STRUCTURE The main economic d i f f e r e n c e between t h a t i n general
i n i t i a l investment i s
contrary operation and maintenance i n i t i a l investment per
unit
of
chemical s
.
urban
much lower i n ground
costs are
higher.
r e s u l t i n g product
operation and maintenance cost small. treatment needs f o r
ground and surface
The
is
exception
uses u s u a l l y r e q u i r e
higher
water
projects i s
water
and on the
I n surface water u s u a l l y high is
that
costs
and
this to
the
surface water f o r energy
The c l a s s i c way t o compare t h e d i f f e r e n c e o f occurrence i n time between and b e n e f i t i s by reducing
the
a present value through a discount
and cost
factor.
The s e l e c t i o n o f the discount r a t e t o be used i n h y d r a u l i c p r o j e c t s has been t h e subject o f arduous debates.
A
lower
greater component o f surface water.
rate
favours t h e
projects
A r a t e which i s more i n keeping
involving a with
the
349
real price o f construction.
money favours
deferring
the
more
costly
investments
for
For example, t h e present value o f a d o l l a r which w i l l be spent i n
t e n years time
is
i f a 12% d i s c o u n t
0.322
expenditure were t o be made
i n 20 years.
rate i s applied
a r a t e o f 8% i s
the
used then
the
a,nd a p p l y i n g a 4% d i s c o u n t r a t e
the
If
r e s p e c t i v e values would be 0.463 and 0.215;
and 0.104 i f
See Table I .
r e s p e c t i v e values would be 0.676 and 0.456. TABLE I
Present value o f a d o l l a r t o be spent i n t h e f u t u r e Discount r a t e % 10 years 20 years
12
10
0.322 0.104
0.386 0.149
8
4
0.463 0.215
0.676 0.456
Groundwater p r o j e c t s o f f e r t h e advantage o f r e q u i r i n g s m a l l e r investments f o r which reason they are a more
hand,
i n v o l v e d are smaller, the
the
risk
is
marketing u n c e r t a i n t i e s involved; staggered, m o d i f y i n g
as t h e
it
i n which t h e r e i s
f i t t i n g a l t e r n a t i v e f o r cases
l i m i t e d c a p i t a l and h i g h i n t e r e s t r a t e s ; on t h e o t h e r lower i n view o f and
as
the
hydrogeological
exploitation
demand f o r water
investments can be reduced t o a minimum.
as t h e investments of
water
develops, then
On t h e c o n t r a r y ,
and
can be
unproductive
a scaled economy
is
one o f the obvious, c l a s s i c advantages o f s u r f a c e water. I n t h e 1950s most
countries
was s i g n i f i c a n t l y lower than
a p p l i e d a s o c i a l l y o r i e n t e d discount r a t e which
the
discount r a t e was applied, as
market
rate.
I n t h e 1970s
the c o s t o f money
had
a much
higher
a l s o increased (James and
I t apparently seems t h a t t h e energy c r i s i s works a g a i n s t t h e use
Rogers, 1976).
o f ground water although, i n f a c t , t h e
increased
d i s c o u n t r a t e compensates f o r
t h e increased c o s t o f energy (Gomez de Pablos, 1974). Comparisons a r e f r e q u e n t l y made between t h e metre o f water i n a accuracy, t h e
reservoir
have t o be taken i n t o account, which c l e a r l y France where t h e
of
r e g u l a t i n g one
and o b t a i n i n g i t from a w e l l .
cost o f transport, d i s t r i b u t i o n
o n l y c o s t comparison known
cost
t o be made on
F o r t h e sake o f
and water treatment tends t o f a v o u r
cubic
would
also
ground water. The
a n a t i o n a l l e v e l was c a r r i e d o u t i n
gross p r o d u c t i o n c o s t p l u s water treatment o f a r i v e r i s 0.14
FF/m3 and o n l y 0.09 FF/m3 f o r ground water (Erhard-Cassegrain and Margat, 1983). The comparison would be
even more unfavourable i f
regulating
dams were t o
be
the l o s s i n
the
constructed. Other economic aspects t o be taken i n t o water t r a n s p o r t
consideration
are
and d i s t r i b u t i o n networks, which i s g e n e r a l l y
more s i g n i f i c a n t
i n the case o f surface water, and evaporation from t h e r e s e r v o i r s .
I n t h e USSR,
350 the t o t a l loss
a t t r i b u t e d t o evaporation
U.S. and 75% i n t h e Carpentras
I f ground
total
Canal i n Provence (Erhard-Cassegrain and Margat,
and s u r f a c e
l i n i n g canals t o t a l l y recharges an
quoted as 10% o f t h e
Loss i n i r r i g a t i o n networks has been quoted as 16.4% i n t h e
c o n t r o l l e d volume. 1983).
has been
or
water
a r e used
partially i s
conjunctively,
not evident
the
if
Different
a1 t e r n a t i v e s
of
Water Resources 1957,
e x p l o i t e d a q u i f e r ( C a l i f o r n i a Department o f
Morel-Seytoux e t a1 , undated).
the b e n e f i t
i n f i l t r a t e d water
must be
simulated
to
compare t h e i r appropriateness and economic i m p l i c a t i o n s . The v a r i a b l e s a f f e c t i n g t h e c o s t o f Lopez-Camacho (1974).
w e l l was s t u d i e d by
water pumped from a
As a general r u l e t h e most i n f l u e n c e f a c t o r i s t h e annual
volume o f water pumped.
A l l t h e o t h e r f a c t o r s b e i n g equal, e.g. y i e l d o f w e l l s ,
water l e v e l s , drawdown,
pump e f f i c i e n c y
. . .; water
c o s t s more
for
irrigation
purposes than f o r urban and i n d u s t r i a l uses, as t h e former system operates fewer hours a n n u a l l y .
I n many
i r r i g a t i o n needs o f
aquifers
the y i e l d
t h e Mediterranean coast
of Spain where i t i s
farmers owning and o p e r a t i n g a w e l l . t h e need t o
of
individual wells
individual plots o f i r r i g a t e d
share
the
risk
of
It
is
groundwater development. c o n s t r u c t i o n techniques f o r
This i s
the
on
normal t o have
an a s s o c i a t i o n o f
probably
an i n h e r i t a n c e o f
drilling
obvious
exceeds t h e
l a n d T h i s o f t e n happens
costs
that
the
achieving greater s p e c i f i c
also n
the
early
improvement yields
days of
of well
and t h e c o r r e c t
design of pumping and e l e c t r i c a l i n s t a l l a t i o n s can reduce groundwater c o s t . 3. EXTERNAL FACTORS PRODUCED BY GROUNDWATER ABSTRACTION
Groundwater e x p l o i t a t i o n produces e x t e r n a l f a c t o r s such as r e d u c t i o n i n water levels, reduction
i n r i v e r discharges, sea water
wetland o r e c o l o g i c a l degradation i r r i g a t i o n areas.
Piezometric d e c l i n e
cases leads t o w e l l s
being
abandoned
Pumping o f coastal a q u i f e r s can cause w e l l s life.
I n the
o r l o n g term
induces
intrusion,
land
increases energy c o s t s and and
the
to
the
need f o r
built.
a r t i f i c i a l recharge,
can
Conjunctive help
to
reduce
extreme
advancement o f t h e s a l i n e wedge which
overdraft, a r t i f i c i a l
b a r r i e r s have t o be
in
r e b u i l d i n g them.
t o be abandoned and t h e consequent r e d u c t i o n o f case o f
subsidence,
v a r i a t i o n s i n water q u a l i t y i n
recharge
use,
t h e i r economic
facilities o r injection
whether
piezometric
or
not this
decline
or
includes seawater
intrusion. The e f f e c t o f pumping on
s u r f a c e water
flows
occurs w i t h
a
delay
which
depends on t h e geometry and hydrodynamic parameter o f t h e a q u i f e r s concerned and on t h e l o c a t i o n o f t h e w e l l s . e f f e c t has been used
Even i n t h e
t o operate a q u i f e r s
f l o w o f t h e r i v e r s i n c o n j u n c t i v e use periods.
narrow f l u v i a l a q u i f e r s t h i s delayed as
storage elements t o r e g u l a t e t h e
schemes when w e l l s a r e pumped i n low f l o w
The s t u d i e s made i n t h e a q u i f e r - r i v e r systems o f
and South P l a t t e
in
Colorado, USA, have
the Rivers
Arkansas
become c l a s s i c s (Moulder and Jenkins,
351 1963; Morel-Seytoux e t a l , Young, 1983).
And
in
systems w i t h a q u i f e r s
1973,
Young
and Bredehoeft,
t h e U n i t e d Kingdom
1972,
conjunctive
use
Bredehoeft and
i n aquifer
river
o f r e l a t i v e l y small dimensions i s being c a r r i e d o u t i n
a
very s t r i c t and pragmatic way (Downing e t a l , 1974, B i r t l e e s and Reeves, 1979). Intense a q u i f e r
pumping
can
temporarily
or
permanently
modify
the
a q u i f e r - r i v e r r e l a t i o n s h i p a l l o w i n g some water volume t o i n f i l t r a t e through i t s bed and thus increase t h e a q u i f e r storage.
The
on a l a r g e
the Ganges
scale
has been
suggested
a r t i f i c i a l recharge i n u n l i n e d canals a l , 1979).
in
a p p l i c a t i o n o f induced recharge basin conjunctively w i t h
t o r e g u l a t e t h e r i v e r f l o w (Chaturvedy e t
Economic l o s s caused by l a n d subsidence i s
o f major
urban o r coastal areas and minor i n r u r a l environments. o f clay consolidation
is
n o t a r e v e r s i b l e one,
b u t n o t a l l e v i a t e d i f piezometric l e v e l s
are
importance
in
As t h e p h y s i c a l process
l a n d subsidence can be stopped
raised
b y means o f
artificial
recharge o r decrease o f groundwater pumping. The small i n f l u e n c e o f t h e decisions made by on t h e
future
water l e v e l d e c l i n e i n
i n f l u e n c e o f h i s own users I , produces
extractions
his
on h i s
an i n d i v i d u a l groundwater u s e r
own w e l l , water
divergences between p r i v a t e
To c o r r e c t such divergencies adequate l e g a l
and
t h e small n e g a t i v e
costs, although
n o t on
other
and s o c i a l b e n e f i t s (Burt, 1964). and a d m i n i s t r a t i v e r e g u l a t i o n s must
be drawn up. 4. WATER QUALITY PROBLEMS Ground water i s u s u a l l y more s a l i n e than s u r f a c e water although i n some cases t h e opposite i s t r u e .
The water imported v i a t h e Colorado
Aqueduct t o Southern
C a l i f o r n i a i s s a l t i e r than t h e
ground water from c o a s t a l a q u i f e r s w i t h which i t
i s recharged.
from t h e K i n n e r e t Lake recharged i n t h e
I n I s r a e l water
and limestone a q u i f e r i s more
saline
than
ground water.
s a l i n i t y are sewage waters, d i f f u s i o n through t h e i n t e r f a c e between and the i n t r u d e d sea water and leakage increase 1980).
Another p o s s i b i l i t y o f
obtaining
an
coastal
Other sources
of
f r e s h water
from adjacent a q u i f e r s (Mercado acceptable water q u a l i t y
is
by
m i x i n g p r i o r t o i t s use. I r r i g a t i o n can increase ground water i s
c h l o r i n e and
n i t r a t e content
pumped f o r i r r i g a t i o n purposes, t h e
i n ground water.
If
depression o f g r a d i e n t s t o
t h e aquifer o u t l e t s r e s u l t s i n a drop o f water and s a l i n i t y f l u s h . I r r i g a t i o n w i t h surface water water and pumping. i n the
soil salinization
i n d r y areas very o f t e n c r e a t e s
The most spectacular example i s t h e Indo a l l u v i a l
plain
i n Pakistan
Punjab where
i r r i g a t i o n system i n t h e w o r l d i s located, c o v e r i n g hectares.
drainage and
problems which c o u l d be m i t i g a t e d by groundwater i r r i g a t i o n system l o c a t e d the an
largest
concentration
extension o f 13 m i l l i o n
Aquifer recharge as a r e s u l t o f excessive i r r i g a t i o n , and f i l t r a t i o n s
along the 65,000 km o f
canals,
which are u n l i n e d i n most cases,
has produced
352 very serious drainage and s a l i n i z a t i o n problems.
two m i l l i o n hectares had
Over
t o be abandoned and each year t h i s problem a f f e c t s an a d d i t i o n a l 25,000 hectares (Chaudry e t al, 1979).
This case was studied i n g r e a t d e t a i l and a proposal made
t o construct 30,000 w e l l s 70.10'
m3
o f water per
with
sufficient
annum.
The
aims
capacity t o pump i n of this
piezometric surface and e l i m i n a t e p a r t o f
the
proposal are
order
to
of
lower t h e
the s a l t water, thus a l l e v i a t i n g t h e
drainage and s a l i n i z a t i o n problems. I n Soviet Central annually through
Asia
an
estimated 25.109 m3
of
a g r i c u l t u r a l drainage systems i n
Conjunctive use o f surface and
water
the zone
are
under
discharged irrigation.
ground water has been proposed t o u t i i z e these
resources (Kats, 1975), 5. ARTIFICIAL RECHARGE
A r t i f i c i a l recharge i s an e f f e c t i v e d e c l i n i n g piezometric encroachment.
levels,
Nevertheless
or
way t o
protect should
it
be
a r t i f i c i a l recharge are n o t synonymous, as problems w i t h a r t i f i c i a l requires, i n
addition
recharge to
the
It
reduce against
said
that
we s h a l l
i s that
is
discuss l a t e r .
advisable
to
by t a k i n g advantage o f n o t d e l i b e r a t e l y planned l e a k i n g dams,
unlined
use
and
One o f the
i s costly
derivation,
stop
seawater
since
transport
it
and
Furthermore the operating and maintenance take
p o s s i b i l i t i e s o f f i n d i n g a cheap way t o recharge water cases o f
or
conjunctive
very o f t e n i t
recharge elements
sedimentation or treatment elements. costs are u s u a l l y high.
s t o r e water,
coastal a q u i f e r s
canals,
into
consideration
the
by a r t i f i c i a l means,
recharge,
as
induced recharge
happens i n or
or the
incidental
o v e r i r r i g a t i o n (Custodio, 1986). I n the course o f the a r t i f i c i a l recharge process, the w a t e r ' s physicochemical and b i o l o g i c a l p r o p e r t i e s are transformed zone and, as
as i t passes through a non-saturated
a r e s u l t , bacteria, virus, organic m a t e r i a l , heavy metals and many
t o x i c compounds are eliminated o r are g r e a t l y reduced. p o l l u t e d surface
water i s
European countries. ground water i s
u t i l i z e d extensively
This method o f t r e a t i n g
i n many
c e n t r a l and northern
There a l s o e x i s t many instances throughout the world
recharged
using
reclaimed waste water
(Asano
1985),
growing i n t e r e s t i s emerging i n research t o reduce pre-treatment needs. mentioned before t h a t
artificial
recharge
has a l s o been used as
where and
a
We have
a means
of
blending i n the a q u i f e r waters w i t h d i f f e r e n t chemical p r o p e r t i e s . The economic
effects
of
r a i s i n g water
seawater i n t r u s i o n and a q u i f e r storage a l l
levels, a q u i f e r p r o t e c t i o n against need t o be analysed
through a q u i f e r
and water system simulation. 6. INFORMATION UNCERTAINTY AND FORECASTING Wiener (1972) has b r i l l i a n t l y noted the f o l l o w i n g p o i n t s concerning t h e need
353
f o r i n f o r m a t i o n and
the
u n c e r t a i n t i e s which
exist
at
the
time
of
making
d e c i s i o n s r e l a t e d t o s u r f a c e and ground w a t e r use. I n t h e m a j o r i t y o f cases, stream f l o w r e p r e s e n t s a r a p i d response t o c l i m a t i c phenomena.
Normally, t h e
c o l l e c t e d over a
information
derived
few y e a r s i s more r e l i a b l e ,
from
ground-water r e l a t e d d a t a
i f p r o p e r l y analysed,
than t h a t
p r o v i d e d by s u r f a c e - w a t e r r e l a t e d d a t a c o l l e c t e d o v e r a l o n g e r p e r i o d o f t i m e . The i n e r t i a o f
the
a q u i f e r s , caused by
the large
amounts
o f water
i n t e g r a t e s a l o n g p e r i o d o f h y d r o m e t e o r o l o g i c a l phenomena and
stored,
short-term
data
c o l l e c t i o n can p r o v i d e much b e t t e r o v e r a l l i n f o r m a t i o n . F l u c t u a t i o n s i n t h e magnitude o f t h e f l o w a r e g r e a t e r i n s u r f a c e i n ground w a t e r .
made.
water than
M i d o r l o n g t e r m p r e d i c t i o n s o f s t r e a m f l o w d i s c h a r g e cannot be
Streamflow d i s c h a r g e i s s t o c h a s t i c b y n a t u r e so i t s b e h a v i o u r can o n l y b e
t r e a t e d i n terms o f p r o b a b i l i t y . more d e t e r m i n i s t i c as a
Groundwater b e h a v i o u r i s much l e s s e r r a t i c and
r e s u l t o f the normally
close
r e l a t i o n s h i p between t h e
s t o r e d w a t e r and t h e a q u i f e r ' s average recharge. Groundwater e x p l o i t a t i o n operational costs are
requires
high.
low,
Surface
initial
water
investment;
exploitation
however,
requires a
the large
investment, w h i l e o p e r a t i o n a l c o s t s a r e n o r m a l l y l o w e r . I n t h e case o f s u r f a c e water, t h e i n v e s t m e n t r e q u i r e d i s u s u a l l y i n d i v i s i b l e , which a l s o e n t a i l s
a lengthy
i n o p e r a t i v e p e r i o d d u r i n g t h e study, c o n s t r u c t i o n
and d e c i s i o n making process.
I t may t a k e
years
a c t u a l l y e f f e c t i v e i n o p e r a t i o n a l terms.
for
The l a r g e
imposes g r e a t e r demands on t h e i n f o r m a t i o n r e q u i r e d . investment r e q u i r e d much s h o r t e r .
for
ground w a t e r i s
the
project t o
become
investment involved a l s o C o n t r a r y t o t h e above, t h e
d i v i s i b l e and t h e
inoperative period
T h i s i n t r o d u c e s t h e a d d i t i o n a l advantage o f i t s
being
much more
adaptable t o i n c r e a s i n g w a t e r demands. For the
cases,
common
throughout
t h e world,
i n f o r m a t i o n i s i n c o m p l e t e and f o r those where t h e c o n s i d e r a t i o n s mentioned
above
recession experienced i n the
last
are
where
the
hydrological
f u t u r e w a t e r needs a r e u n c e r t a i n ,
crucially
important.
The
economic
few y e a r s has had a
d e c i s i v e i n f l u e n c e on
r e d u c i n g expected w a t e r needs i n many p a r t s o f t h e w o r l d .
Ground w a t e r can p l a y
a more i m p o r t a n t r o l e i f t h e w a t e r r e s o u r c e s system i s conceived d y n a m i c a l l y and t h e u n c e r t a i n t i e s which e x i s t i n t a k e n i n t o account
r a t h e r than
r e l a t i o n t o t h e w a t e r r e s o u r c e s and demand a r e r e s o r t i n g t o a system
which
is
statistically
conceived and s t r u c t u r a l l y o r i e n t a t e d . I n t h e l a s t few y e a r s t h e r e have been some i m p o r t a n t changes i n t h e and management o f w a t e r resources. questioned, g r e a t e r
interest
is
The u t i l i t y o f s t r u c t u r a l s o l u t i o n s has been being
shown
i n an
optimum u t i l i z a t i o n
e x i s t i n g f a c i l i t i e s r a t h e r t h a n i n i n v e s t i n g i n new ones, t h e e r a o f c o n s t r u c t i n g l a r g e dams
planning of
and i n many c o u n t r i e s
has p r o b a b l y come t o an end ( W i l l e k e e 1979).
A l t h o u g h v e r y few f i n a n c i a l e v a l u a t i o n s
have been made o f t h e
results o f
some
354
these
projects, there i s s u f f i c i e n t evidence t o question whether the r e s u l t s o f l a r g e construction p r o j e c t s have l i v e d up o f government subsidies f o r major water
t o expectations o r not.
The problem
p r o j e c t s has been f r e q u e n t l y questioned
and the f i r s t step towards determining a s o l u t i o n should
be an a n a l y s i s o f
the
various a1 t e r n a t i v e s a v a i l a b l e . 7. ECONOMIC ASPECTS OF DIFFERENT CONJUNCTIVE USE TYPOLOGY O f the d i f f e r e n t functions u s u a l l y i d e n t i f i e d i n
source o f water, treatment
-
we
storage have
and
regulation,
n o t analysed i n
a water resources system
transport,
t h i s paper
-
d i s t r i b u t i o n and water
the a q u i f e r
as a v e h i c l e t o
t r a n s p o r t water since an a q u i f e r i s g e n e r a l l y u n s u i t a b l e f o r t h i s f u n c t i o n .
The
cases i n which
not
the a q u i f e r
serves as a means o f water
included e x p l i c i t l y e i t h e r , as t h i s f u n c t i o n i s r o l e as a means o f
storage.
Aquifers
d i s t r i b u t i o n and substantial
savings
distribution
usually closely related
provide
alternate
surface
distribution
in
are
means
to i t s
for
water
systems.
In
previous paragrahs we have mentioned the p o s s i b i l i t i e s o f a r t i f i c i a l recharge as a means o f water treatment and t h e mixing o f d i f f e r e n t kinds o f water. I n a d d i t i o n t o an aquifer's be u t i l i s e d ( r e f e r r e d t o
e x p l o i t a b l e resources, i t s stored water can a l s o the
as
"one
time"
reserve)
causing
a
temporary
overexpl o i t a t i o n . I n spite o f
the
serious
economic
and
s o c i a l problems
the
overdraft
of
aquifers can cause, i t i s n o t necessary t o r u l e o u t o v e r d r a f t as a general r u l e . I n f a c t , the reasons f o r
overexploitation
o f ground water i n
i t s p r o s p e r i t y which
consequently created costly projects
the
such as
facilitated
propitious
its
California economic
i s one o f
development
conditions f o r carrying out
interbasin transfers
from
areas
with
other the
the and more
heaviest
r a i n f a l l i n the northern p a r t o f the s t a t e ( C a l i f o r n i a State Department o f Water Resources, 1957). The a v a i l a b i l i t y o f l a r g e q u a n t i t i e s o f water proposals f o r the well-planned u t i l i s a t i o n o f d e f e r r i n g c o s t l y construction p r o j e c t s . such a
methodology was
proposed f o r
in
the
a q u i f e r s has prompted
o f the a q u i f e r - s reserves as a means This
has
subsequent
been done i n I s r a e l where modelling
and
economic
o p t i m i s a t i o n (Schwartz, 1980). I n actual f a c t Planned Overdraft i s n o t but rather a
first
conjunctive use o f
stage which one
type
or
can
be
a separate type o f c o n j u n c t i v e use, followed
another.
by
successive
O v e r e x p l o i t a t i o n has
stages also
of been
suggested i n successive stages, followed by successive surface water development and conjunctive use
(Schwartz
1980), o r
as a permanent
component d u r i n g
the
e n t i r e planning period. I n the type
o f conjunctive
use we
r e s e r v o i r s release more water i n r a i n y
have
termed
Alternative
periods o r years
and
Use,
surface
the a q u i f e r s are
355
pumped more i n d r y periods. be made a v a i l a b l e
by
The e x p l o i t a b l e
storage
piezometric o s c i l l a t i o n s .
c a p a c i t y t o be used would
I n this
way, an
underground
storage area o f 37.109 m3 would become a v a i l a b l e f o r use i n C a l i f o r n i a ' s Central i n c o n t r a s t t o t h e 27.109
V a l l e y w i t h r e l a t i v e l y small piezometric o s c i l l a t i o n s m3 t o be
provided by surface storage
(California
State
Department
of
Water
Resources, 1957). I n La Plana de C a s t e l l h , on o s c i l l a t i o n s represent
t h e Mediterranean coast o f
an a q u i f e r storage o f 500.106 m3,
Spain, three
piezometric
times
greater
than t h e e x i s t i n g surface storage. I n t h e A l g a r a q u i f e r p e r i o d i c l e v e l drawdowns represent 40.106 m3
o f storage as compared t o
and Amadorio dams can
store.
Also
in
t h e 30.106 m3 t h a t t h e Guadalest
Spain
large scale
developments
are
p o s s i b l e and have been suggested (Sahuquillo, 1986). These type o f
schemes
require
that a part
o f the
demand
i n d i s t i n c t l y by two sources and i n some cases t h e water l e v e l be high.
When
distribution o f
this
is
the
the
case,
different
in
addition t o
components,
recharge elements, t h e o p e r a t i o n o f t h e
the
can
depends on t h e s t a t e o f t h e system, t h e water
i s crucial. stored
in
served
oscillations
design
including wells
system
be
can
and p h y s i c a l
and
artificial
Optimal
operation
dams, t h e p i e z o m e t r i c
l e v e l s , the s u r f a c e water i n p u t s and water q u a l i t y . Improvements i n mid o r s u b s t a n t i a l economic gains
long
term
h y d r o l o g i c a l f o r e c a s t i n g would
i n reservoir
operation o f
conjunctive
lead
to
use schemes
(Jaquette 1981). Greater use o f ground water
can
be made d u r i n g
drought
European c o u n t r i e s took advantage o f t h i s i n t h e summer o f 1976.
periods.
Many
I n California,
i t helped reduce t h e e f f e c t s of low-water i n 1976-77 t o a s i g n i f i c a n t e x t e n t .
Owing t o t h e
i n i t i a t i v e taken by p r i v a t e i n d u s t r y
government a c t i o n , t h e
effects o f
e a r l y e i g h t i e s were m i t i g a t e d
in
the drought some
and, t o a
Spain was
areas.
l e s s e r degree,
experiencing i n the
I n fact,
the e f f e c t s o f
the
drought were lessened i n t h e areas where g r e a t e r u t i l i z a t i o n o f ground water was made and a methodology
to
this
effect
has
been
proposed f o r
subsequent
a p p l i c a t i o n t o c o n j u n c t i v e use o f surface and ground water ( S a h u q u i l l o 1983). When l o c a l s u r f a c e waters a r e l e s s important,
a q u i f e r s can be used t o
and d i s t r i b u t e imported and l o c a l surface water A r t i f i c i a l recharge i s c r u c i a l Terminal o r L a t e r a l i t s role i s only use are I s r a e l and
to this
Ground Water
complementary. Southern
l e s s important than i n t h e
artificial
C l a s s i c examples In
we c a l l
t o a l t e r n a t i v e use where
o f t h i s type this
store
recharge.
t y p e o f c o n j u n c t i v e use which
Storage, as opposed
California.
v a r i a t i o n s of imported water
through
type
of
o f conjunctive scheme
annual
a r e minimum o r r e l a t i v e l y low and i n any case a r e
so c a l l e d a l t e r n a t i v e use.
important than t h e p h y s i c a l d i s t r i b u t i o n
of
recharge and water t r a n s p o r t and d i s t r i b u t i o n .
wells
Here o p e r a t i o n i s
and elements o f
less
artificial
The C a l i f o r n i a S t a t e Department
356 o f Water Resources hydrological
,
o f systems.
in
the
sixties
hydrogeological
developed
, operational
I n these s t u d i e s
a
large
a
methodology f o r
working
on
and economic s t u d i e s f o r these types
number o f a l t e r n a t i v e s
were simulated,
a l s o t a k i n g i n t o account t h e d i f f e r e n t values o f water i n terms o f i t s s a l i n i t y . ( C a l i f o r n i a S t a t e Department o f Water Resources 1966, 1971). The A q u i f e r - r i v e r
Systems can
be considered a
I n t h i s the aquifer-river relationship i s o f o p e r a t i o n i s very
important,
mainly
prime importance, a l s o
function o f
of
t h e system
o f t h e ground water component whereas t h e
a r t i f i c i a l recharge i s o f secondary importance. use a l a r g e r use
subgroup o f a1 t e r n a t i v e use.
With t h i s
type o f
conjunctive
s u r f a c e water can be obtained, g i v i n g t h e ground water t h e
complementing
the
deficit
in
the
driest
years
or
seasonally
throughout t h e y e a r . Operating ground water i n t h i s way ( S a h u q u i l l o 1983).
Bredehoeft
insurance t h e farmers
represents
an insurance a g a i n s t
and Young (1983) a l s o analysed t h e
o f t h e South P l a t t e make
drought
role of
the
o f ground water where t h e y have
i n s t a l l e d a w e l l c a p a c i t y almost s u f f i c i e n t t o i r r i g a t e t h e e n t i r e area, u s i n g a s i m u l a t i o n model system t o an
which
1i n k s
economic model
the
hydrology o f a
which i n c o r p o r a t e s
r e s u l t s o f t h e model c o i n c i d e w i t h t h e w e l l t h i s has two
conjunctive
the
stream-aquifer
farmers’ behaviour.
Doing
b e n e f i t s : i t maximises t h e expected n e t b e n e f i t s and minimises t h e
v a r i a t i o n i n annual income. t h e value o f f l o w
By i n c r e a s i n g t h e pumping
f o r e c a s t i s diminished,
pumping more ground water.
capacity
counteracting
The r o l e o f r e d u c i n g
a
t o such value,
poor
forecast
by
t h e unwant economic e f f e c t s o f
u n c e r t a i n t y by u s i n g more ground water i s discussed a n a l y t i c a l l y I s s a r (1987).
The
capacity actually i n s t a l l e d .
by
Tsur
and
They p r o v i d e an e x p l i c i t expression f o r t h e v a l u e o f u s i n g ground
water i n t h i s way i n terms o f t h e marginal p r o d u c t i v i t y o f water, t h e p r o d u c t i o n f u n c t i o n and t h e v a r i a b i l i t y o f s u r f a c e water. 8. APPLICATIONS
OF SYSTEM ANALYSIS TECHNIQUES
The d e t a i l i n which methods.
The s i m p l e s t
aggregated parameters.
a q u i f e r behaviour way
is to
i s analysed v a r i e s
c o n s i d e r a q u i f e r s as
The commonest
way i s
to
i n the
elements
assimilate
different
with
them
a
to
few
linear
r e s e r v o i r s r e l e a s i n g a f l o w associated l i n e a r l y w i t h a volume o f water s t o r e d i n t h e a q u i f e r (Buras 1963, 1967, Sanchez m u l t i c e l l u l a r n o n l i n e a r models
with
s i m p l i f i c a t i o n i s used i n
higher
the
1983). a
few
Birtles non
hierarchical
associated w i t h o p t i m i z a t i o n methods (Schwartz 1980). been used w i t h d e t a i l e d a q u i f e r
models
using
and
Reeves (1979) use
linear cells.
dynamic
levels
Usually and
very
this often
O p t i m i s a t i o n methods have programming, l i n e a r and
non l i n e a r programming ( G o r e l i c k 1983). Nevertheless, f o r complex systems, when t h e i n t e r a c t i o n between
surface
and
ground water and when s t o c h a s t i c s u r f a c e flow v a r i a t i o n s have t o be taken i n t o
357 consideration,
o r where more
than
one
s i m u l a t i o n techniques i s v i r t u a l l y
surface
reservoir exists, the
unavoidable.
This i s p a r t i c u l a r l y
t h e a l t e r n a t i v e use type, o r when q u a l i t y problems have t o l a r g e number simulated.
o f a1 t e r n a t i v e s
or
synthetic
use
of
true i n
be considered, and a
h y d r o l o g i c a l sequences
have t o be
I n t h i s case
t h e eigenvalue method (Andreu and S a h u q u i l l o 1987) i s I t s most i n t e r e s t i n g aspect i s t h a t e x t e r n a l a c t i o n s and
t h e most a p p r o p r i a t e .
i n i t i a l c o n d i t i o n s are e x p l i c i t l y
transformed f o r a q u i f e r s i n t o a s t a t e v e c t o r .
From t h i s , piezometric head f l o w s and surface-ground water interchanges a r e a l s o e x p l i c i t l y computed t o s i m u l a t e c o n j u n c t i v e use systems. 9. CONCLUSIONS A1 though ground water has v e r y o f t e n been overlooked by p l a n n i n g s p e c i a l i s t s , i t can o f f e r t e c h n i c a l and economic advantages
worthy o f c o n s i d e r a t i o n .
water can p r o v i d e a d d i t i o n a l resources as w e l l as d i s t r i b u t i o n and
treatment, which can
water resources.
Likewise, ground water can p r o v i d e o t h e r
i t s adaptability t o possibility o f
a
temporary
construction projects, drainage problems. t h e insurance
progressive to
be
t h e means f o r water
mitigate
combined advantageously w i t h s u r f a c e
increase
overexploitation the
Ground storage,
in as
a
effects
the
means of
advantages
demand
for
for
such
water,
as the
deferring costly
droughts
and
alleviate
Another v i r t u e o f ground water i n c o n j u n c t i v e use schemes i s
role i t
supplies
t o o f f s e t the
uncertainty
concerning s u r f a c e
flow, h y d r o l o g i c a l parameters o r demand. 10. REFERENCES Andreu, J. and Sahuquillo, A. 1987. E f f i c i e n t A q u i f e r S i m u l a t i o n i n Complex Systems: J. Water Resour. Planning Mgmt Div. A.S.C.E. Vol. 113 No. 1, Jan 1987, 110, 129. Asano, T. E d i t o r , 1985. A r t i f i c i a l Recharge o f Ground Water. Butterworth Pub1 i s hers. B i r t l e s , A.B. and Reeves, M.J., 1977. A Simple E f f e c t i v e Method f o r t h e Computer S i m u l a t i o n o f Ground Water Storage and i t s A p p l i c a t i o n i n t h e Design o f Water Resource Systems. J. o f Hydrology No. 34, 77-96. Bredehoeft, J.D. and Young, R.A., 1983. Conjunctive Use o f Groundwater and a Surface Water f o r I r r i g a t e d A g r i c u l t u r e : Risk Aversion. Water Res. Res., Vol. 19, NO. 5, 1111-1121. Buras, N., 1963. Conjunctive Operation o f Dams and Aquifers. Journ. of H y d r a u l i c D i v i s i o n , ASCE, Vol. 89, HY6, November, 111-131. Buras, N., 1967. Operation o f a Complex Water Resources U t i l i z a t i o n System. Conference on Water f o r Peace. Washington D.C. Burt, O.R., 1964. The Economics o f Conjunctive Use o f Ground and Surface Water. H i l g a r d i a . Vol. 3G, No. 2, December 1964. C a l i f o r n i a S t a t e Department o f Water Resources, 1957. The C a l i f o r n i a Water Plan. B u l l . Number 3. C a l i f o r n i a S t a t e Department o f Water Resources, 1965. Planned U t i l i z a t i o n of Ground Water Basins: Coastal P l a i n o f Los Angeles Country. Appendix C. Operation and Economics, B u l l . No. 4. C a l i f o r n i a S t a t e Department o f Water Resources, 1971. Planned U t i l i z a t i o n o f Water Resources i n t h e San Juan Creek Basin Area, B u l l . Nos. 104-7. Chaturvedy, M.C. and Srivostava, V.K., 1979. Induced Ground Water Recharge i n
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