Changes in the Ground Water Systems

GROUND WATER I N V E S T I G A T I O N O F THE
MOUNTAIN HOME PLATEAU, IDAHO

by

M a r c A.

Norton

William O n d r e c h e n
and
J a m e s L.

Baggs

Idaho D e p a r t m e n t o f W a t e r Resources
Boise, Idaho

A u g u s t 1982

T A B L E O F CONTE.STS

ACKNOWLEDGEMENTS
L I S T O F FIGURES

.................................
..................................

...................................
I N T R O D U C T I O N .....................................
P u r p o s e and O b j e c t i v e s ......................
D e s c r i p t i o n of the S t u d y A r e a ...............

L I S T O F TABLES

Previous Studies
HYDROGEOLOGY

Geology
Aquifer

............................

.....................................
.....................................
D e s c r i p t i o n .........................

.............................
G r o u n d Water F l o w ..............

Data C o l l e c t i o n
Direction of

Water Level Fluctuations

....................

.........
.............................

Changes i n the Ground Water S y s t e m s

WATER SUPPLY AND USE

.................................
L a n d s .............................

Basin Y i e l d
Irrigated

..........
...............................

Consumptive l r r i g a c l o n R e q u i r e l n e l ~ t
Water Balance

........................
CONCLUSTnNS ......................................
RECOMMENDATIONS ..................................
REASONABLE PUMPING LEVELS

i

ii

iii

ACKNOWLEDGEMENTS

The authors would 'Like t o thank
Mountain

Home

Plateau

i n v e s t i g a t i o n by

for

allowing

their
access

t h e r e s i d e n t s of t h e

cooperation
to

IDWR

during

field

the

personnel

and t o Charles Cook of t h e Mountain Home I r r i g a t i o n D i s t r i c t
f o r h i s help concerning t h e i r r i g a t i o n d i s t r i c t .

would

also like

t o thank

DeWayne McAndrew,

1J.S

T h e authors

Bureau of

Reclamation, for the maps of i r r i g a t e d land c l a s s i f i c a t i o n .
The authors

would

Like

to

thank

the

following I D W R

personnel :

........ review & imported w a t e r s e c t i o n
......... d a t a c o l l e c t i o n and r e v i e w

Alan Robertson
S t a n Szczepanowski
Lee Sisco
J a n Grover
EIal Anderson
Mark Gross

............. d a t a c o l l e c t i o n - s t r e a m gaging
............................
........................ c r od pa t da i cs torlilbeuc tt ii oo nn

Water

.......................... c r o p d i s t r i b u t i o n
A l l o c a t i o n S c c t i o n ........ water r i g h t s reoearch

L I S T OF F I G U R E S

Page
S t u d y A r e a L o c a t i o n - ----------------------------M o u n t a i n Home P l a t e a u S t u d y A r e a ----------------Major G e o l o g i c U n i t s a n d L o c a t i o n s of C r o s s
S e c t i o n s on M o u n t a i n H o m e P l a t e a u ------------Cross S e c t i o n A
-------------------- ---C r o s s S e c t i o n B ---------------------------------C r o s s Section C
-------------

--------

-----

------------------------------------~ ~ c a t i oo fn P e r c h e d A q u i f e r ---------------------L o c a t i o n s o f Wells M e a s u r e d i n 1982 -------------W a t e r L e v e L s o f the R e g i o n a l A q u i f e r
i n F a l l of 1 9 7 6 ------------------------- -- ---Water L e v e l s of the R e g i o n a l A q u i f e r
i n F a l l of 1 9 8 1 -------------------------- - ---W a t e r L e v e l s of the P e r c h e d A q u i f e r , 1 9 7 6 -------Water L e v e l s of the P e r c h e d A q u i f e r , 1981 -------H y d r o g r a p h s o f W e l l s o n t h e M o u n t a i n Home
Plateau
--------------- -------------------em----

Gross S e c t i o n D

-----

-

H y d r o g r a p h s o f W e l l s o n t h e M o u n t a i n Home
------------ ----Plateau
H y d r o g r a p h s o f Wells o n the M o u n t a i n Home
p l a t e a u --- -----------------------------------H y d r o g r a p h s of W e l l s o n t h e M o u n t a i n Home
Plateau
H y d r o g r a p h s o f W e l l s o n t h e M o u n t a i n Home

Plateau ----------------H y d r o g r a p h s o f W e l l s o n t h e M o u n t a i n Home
P l a t e a u --------------------------------------H y d r o g r a p h s o f Wells o n t h e M o u n t a i n Home
----P l a t e a u --------- --------

------------------------------------------------------------

-----------------

Change i n W a t e r Levels i n the R e g i o n a l

A q u i f e r From 1 9 7 6 t o 1 9 8 1 i n F e e t ------------Change i n W a t e r L e v e l s i n the P e r c h e d
A q u i f e r From 1 9 7 6 t o 1 9 8 1 i n F e e t
I r r i g a t e d Lands o n M o u n t a i n Home P l a t e a u ,
1980
I n d i c e s o f P r i c e s P a i d and P r i c e s R e c e i v e d
by F a r m e r s , U . S . , 1 9 7 3 - 1 9 8 1
Per A c r e E l e c t r i c i t y C o s t Comparisons
f o r Ground Water Pumping i n I d a h o

------------------------------------------------------------------------

-------------

R e c u ~ ~ u n e r t d eC
d r i t i c a l Groundwater A r e a

Boundaries

------------------------------------

LIST OF TABLES

Page
~ e s c r i p t i o na n d W a t e r - B e a r i n g c h a r a c t e r i s t i c s
of Geologi r IJni ts i n t h e M o u n t a i n Home
P l a t e a u Area (Young, 1977) -------------------A n n u a l P r e c i p i t a t i o n a n d D e p a r t u r e From N o r m a l
f o r S t a t i o n s i n V i c i n i t y o f ljlountain H o m e
P l a t e a u in I n c h e s
u e v e l o p e d , A p p l i c a t i u r i s f o r , and P e r m i t t e d
Lands, Mountain H o m e S t u d y Area ( a c r e s )
R o w Crop and Small G r a i n Classification

----------------

Water Balance f o r Mountain Home Study
A r e a , 1980 C o n d i t i o n s ------------------------P e r A c r e C r o p E n t e r p r i s e a n d Farm Budget
Summaries f o r M o u n t a i n Home A r e a With
C e n t e r P i v o t I r r i g a t i o n ----------------------P e r A c r e C r o p E n t e r p r i s e a n d Farm B u d g e t
Summaries f o r M o u n t a i n H o m e A r e a W i t h
Hand L i n e S p r i n k l e r I r r i g a t i o n

----------------

---- --------------------------Annual C o s t of Pumping G r o u n d Water I d a h o P o w e r S e r v i c e A r e a as of
March 1, 1982 --------------------------------Annual C o s t o f Pumping Ground W a t e r Farm Rl]dget---------

I d a h o P u w e r S e r vica Area n s of
March 1, 1 9 8 2 ---------------------------------

GROUND WATER INVESTIGATION OF THE
MOUNTAIN HUME PLA'YEAU, IUAHU

INTRODUCTION
Purpose and Objectives
On May 7 ,
Mountain

Home

1981,
was

a 128 square mile
designated

as

the

.

C r i t i c a l Grouna Water A r e a ( c . G . w . A )
the

response by

Water Resources

the D i r e c t o r

of

area

the

Cinder

northwest
Cone

of

Butte

T h i s declaration w a s

Idaho Department

of

t o declining ground water l e v e l s and

(IDwR)

a possibly over-appropriated system.
This study was i n i t i a t e d on May 19, 1981 t o review the
hydrogeology of a l a r g e r area including ana surrounding the
Cinder Cone Butte C . G . W . A .

The r e s u l t s of

the combined a r e a s .

to m o t l i f y t-he boundaries

develop

and t o develop a water budget for
the study w i l l be used

of t h e C.G.W.A.,

reconmendat ions

for

management

i f warranted, a n d
of

the

region ' s

ground water resource.
The objectives of t h e study a r e :
1)

Determine the recharge f o r t h e study a r e a ,

2)

Determine the a q ~ l i f e r ( s )and grolind water move-

ment f o r the study a r e a ,
3)

Determine
opment

and

the
the

net

withdrawal

potential

net

from e x i s t i n g develwithdrawal

study area by water r i g h t permits and
f o r ground w a t e r development p r o j e c t s ,

from t h e

applications

4)

Propose changes i n the C . G .W.A.

boundaries, i f

w a r r a n t e d , and

5)

Recommend management provisions such a s w e l l spacing,
c a s i n g requirements.

s script ion of t h e Study Area
i n southwestern Idaho

Located

( F i g u r e I ) , much of t h e

s t u d y a r e a is p a r t of a g e n e r a l l y broad,
slopes gently Cowards the s o u t h w e s t .

by v o l c a n i c s t r u c t u r e s
s h i e l d volcanoes.

---

f l a t p l a t e a u which

T h e plateau

c r a t e r rings,

i s broken

c i n d e r c o n e s , and

The northern boundary of

the study area

i s formed by t h e Danskin Mountains while t h e s o u t h e r n boundary i s t h e r i m of t h e Snake River Canyon ( ~ i g u r e2 ) .

Local

ground

river

conditions

waLtjr

t h e canyon a l o n g

within

a r e n o t addressed by t h i s

study.

t h e study a r e a was s e l e c t e d t o

the

e a s t e r n boundary of

The

include

e s s e n t i a l l y a l l of

t h e p l a t e a u e a s t of Mountain Home which c o u l d be c o n s i d e r e d
t o have a source of recharge s i m i l a r t o a r e a s t o t h e west.
The

boundary

north-south

is

a

topographic

approxirnately

divide

one m i l e

east

running
of

generally

Reverse.

The

northwestern boundary was similarly c h o s e n t o i n c l u d e a r e a s
w h e r e t h e ground water recharqe

source ( F i g u r e 2 ) .

i s c o n s i d e r e d t o be a common

T r i b u t a r i e s of I n d i a n Creek which flow

westward t o t h e Boise River were excludecl.
The study a r e a

varies

i n elevation

from 6694 f e e t a t

Danskin Peak t o about 2330 f e e t near t h e Snake R i v e r .
streams d r a i n i n g t h e p l a t e a u a r e e p h e m e r a l ,
toward

the

Snake R i v e r .

The

larger

flowing

All

south

streams draining

the

'-1

II
I

- -1 I

BOUNDARY

I

L-- I

I

BONNER

II

IDAHO

F i g u r e I. Study A r e a L o c a t i o n

-3-

Danskin Mountains

a r e fed by s p r i n g s i n t h e T e r t i a r y vol-

c a n i c ~and Cretaceous g r a n i t e s .
sutruners

and

cold

semi-arid.

winters,

the

Characterized by hot, dry
climate

of

Average annual p r e c i p i t a t i o n

the p l a t e a u
ranges

is

from nine

i n c h e s on t h e p l a t e a u t o about 2 3 inches i n t h e mountains.
Previous S t u d i e s
Two s t u d i e s were made by Ralston and Chapman
1 9 7 0 ) before t h e m a j o r i t y

place.
water

Those
system

is

Plateau

studies
in

the

Limited

of ground water development took

found

eastern

due

(1968 and

to

that

recharge

portion

low

01

amounts

to

Mvuntain Home

tile

of

the ground

precipitation,

r e l a t i v e l y impermeable m a t e r i a l i n t h e a r e a of most p r e c i p i t a t i o n , and high e v a p o t r a n s p i r a t i o n r a t e s .
state:

"The l a c k of evidence of

The a u t h o r s f u r t h e r

recharge and d i s c h a r g e i n

t h e a r e a i n d i c a t e s a very l i m i t e d r e s o u r c e . "
By

1977, development

of

t h e ground water

resource had

caused water l e v e l s t o d e c l i n e i n a r e a s south and west of
Mountain Home (Young, 1 9 7 7 ) .
additional
grubably

large

result

scale
in

The conclusion was drawn t h a t

ground

water

development

economically prohibitive pumping

o r e x c e s s i v e uses of energy t o l i f t t h e water.
was

made

s y s tern.

of

the

volume

of

recharge

to

the

would
lifts

No e s t i m a t e
ground w a t e r

HYDROGEOLOGY

Geology

The major geologic u n i t s i n the Mountain Home P l a t e a u
1) alluvium

are:
River

5)

Group,

and

Idaho

3)

Idaho B a t h o l i t h .

terrace
4)

Group,

gravels,

Idavada

A d e s c r i p t i o n of

and i t s water bearing
(Young, 1977).

younger

Snake

2)

Volccrnics,

and

each g e o l o g i c u n i t

c h a r a c t e r i s t i c is

listed

i n Table 1

The a r e a l e x t e n t of t h e g e o l o g i c u n i t s and

t h e l o c a t i o n of t h e hydrogeologic cross

s e c t i o n s a r e shown

i n Figure 3 .
The c r o s s s e c t i o n s ,

based on w e l l

logs, show t h a t

the

b a s a l t s a r e considerably t h i c k e r i n the n o r t h e r n s e c t i o n of
the study a r e a ( ~ i g u r e s4 A - 4 D ) .

thin

Formation

to

the

south

rapidly

The b a s a l t s of t h e Bruneau

t o the

(cross sections

east ( c r o s s s e z t i o n A)
B,

C,

Two p a r a l l e l

D).

&

and

northwest trending f a u l t s c u t through t h e a r e a (Bond, 1 9 7 8 ) .
An

apparent

Butte,

third

bisects

Several

one

volcanic

including

fault,

Crater

of

trending

the

structures
Rings,

east

northwest
are

Cinder

frorn

faults

near

Cone

Cleft.

on

the

plateau

Butte,

and

Lockman

present
Cone

Cinder

Butte.
A deeper ground water system may e x i s t below t h e Glenns
Ferry

~orrnation.

10,000 f e e t of
1963).

If

Gravity

material

data

indicakc

that

above the basement

there

complex

may

he

(@ill,

a system e x i s t s , a r t e s i a n p r e s s u r e may be g r e a t

enough t o allow development (pumping) f o r i r r i g a t i o n .

Maximum

->

to

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'D

t h i c k n e s s of the Glenns Ferry Formation i s 2,000 f e e t w i t h
300 Lv 1100 S e c t of basalt abnve it.

Aquifer Description
In

addition t o

the

possible

a q u i f e r below

t h e Glenns

Ferry Formation, t h e r e a r e two mafn a q u i f e r s in the M o u n t a i n
Home

study

Mountain
perched

mapped

area:

Home

and

system

by

Young

ground water

1) a

in

2)

a

shallow,

perched

deeper,

regional

approximately

underlies

(1977)

( ~ i g u r e5 ) .

the perched

system

system i s

system.

38,000

For

beneath

the

The

acres

as

most p a r t ,

i n the clay,

sand, and gravel l a y e r s of the Quaternary Alluvium.

silt,

Basalts

of t h e Snake River G r o u p and b a s a l t s and fan d e p o s i t s of the
Brurtenu

water

Formation beneath

from

the

perched

shallow system can be
s i d e r a b l y along

the

the

a1 l u v i u m

systern.
less

limits

a l s o c o n t a i n qround

Depth

to

water

than 10 f e e t b u t
of

t h e perched

in

varies

system as

the

eonthe

water moves v e r t i c a l l y down t o t h e regional system.
Recharge t o the perched systein occurs from both R a t t l e snake and Canyon Creeks as well

as

seepage

from Mountain

Home Reservoir and the canals and l a t e r a l s t h a t d i s t r i b u t e
the

water.

I t has

been

estimated

by

the

Mountain H o m e

I r r i g a t i o n D i s t r i c t t h a t it takes a d i v e r s i o n t o t h e r e s e r v o i r
of approximately 2 8 c E s t o m a i n t a i n the reservoir a t

Fill1

stage with no r e l e a s e s (Charles Cook, personal communication).
Natural discharge from t h e perched system occurs mainly
as downward p e r c o l a t i o n t o t h e regional system and as s p r i n g
flow a t Rattlesnake Spring near t h e Snake River Canyon r i m .

LIMITS O F PERCHED

SYSTEM AS MAPPED
BY YOUNG- 1977

Figure 5. Location o f P e r c h e d A q u i f e r

-14-

The amount of f l o w from t h e spring i s n o t known.

There has

system a s

a domestic

been

some development of

the perched

supply and f o r small i r r i g a t i o n uses ( l e s s than 40 a c r e s ) .
deeper,

The

regional

to

aquifer s u p p l i e s ground water

t h e l a r g e i r r i g a t i o n wells and municipal wells f o r Mountain
Home

the A i r

and

basalts

of

Force

base.

The rnajor

the Bruneau Formation,

types

rock

Idaho Group

are

and poorly

c o n s o l i d a t e d d e t r i t a l material and minor b a s a l t flows of t h e
i;lenns Ferry Formation,

Idaho Group.

W e l l yields

from t h e

(Bruneau Formation) range from 1 0 t o 3500 gpm.

hasalts

range of

The

the well y i e l d s f o r t h e Glenns Ferry Formation i s

t h r e e t o 350 gprn.

The Bruneau Forrnation t h i n s r a p i d l y towards

t h e e a s t where the Glenns Ferry Formation becomes t h e major
source of ground water.
Recharge

to
of

lusses

from

the

regional

system

precipitation t h a t f a l l s

intermittent

otrcarn

flows,

from the perched system.

tation

occurs

f a l l i n g on a r e a s having

on t h e

downward

mountains,

from

and

Some of

little

as

downward

t h e precipi-

s o i l cover probably

a l s o reaches the a q u i f e r .
isc charge from t h e regional system o c c u r s as s p r i n g flow,

unaerflow to t h e

Srlakc

Rives,

estilnated t h a t 3000 a c r e - f t / y r

nild pumpage.

of

the

study

area.

(1977)

a r e d i s c h a r g e d through f o u r

springs i n the Snake River Canyon; o n e
west

Young

Pumpage

for

of

the

springs

irrigation

l a r g e s t discharge from t h e r e g i o n a l a q u i f e r system.

is

is
the

Data C o l l e c t i o n
Ground water l e v e l d a t a c o l l e c t e d by t h e U.S.

Geological

Sclrvey for t h e 1976-77 s t u d y , i n a d d i t i o n t o t h e o b s e r v a t i o n
well d a t a , were supplemented by a mass measuretnent i n t h e f a l l
of 1981.

The l o c a t i o n s of w e l l s measured i n 1981 a r e shown

i n Figure 6 .

wells

were

I n a d d i t i o n t o t h e mass measurement,
measured

~eriodically to

help

several

determine

the

amount and l o c a t i o n of recharge.
staff gage was

A

bridge

on F o o t h i l l

i n s t a l l e d on Canyon Creek

Road

(T.2S.

R.6E.

ments of Canyon Creek a t t h e o l d U . S .

See.

11).

above thc

Measure-

Highway 30 bridge w e r e

made t o determine channel l o s s between F o o t h i l l Road and the
highway

.

D i r e c t i o n of Ground Water Flow
Contour maps of t h e r e g i o n a l ground water system for the
f a l l of

1976 and 1981 a r e shown i n Figures 7 and 8 .

The

d i r e c t i o n of ground water flow i s p e r p e n d i c u l a r t o the contour

lines.

I n general,

t h e d i r e c t i o n of f l o w i s towards

t h e southwest with a s o u t h e r n component i n t h e s o u t h e a s t and
a western componerit

iri

t h e apparent east-west

the northwest.

t r e n d i n g f a u l t through C l e f t limits

t h e flow toward t h e n o r t h .
tn

Low pcrmcability a l o n g

The ground water e l e v a t i o n is 70

165 f e e t h i g h e r on t h e south s i d e of t h e f a u l t .

Due t o a

g r e a t e r number of w e l l s i n t h e Cinder Cone B u t t e a r e a now than
i n 1 9 7 6 , t h e e f f e c t s of t h e f a u l t a r e rnure r e a d i l y v i s i b l e .

The d i r e c t i o n of flow i n t h e perched ground water s y s t e m
i s towards t h e southwest ( F i g u r e s 9 and 10)

.

Note t h e change

LIMITS OF PERCHED
SYSTEM AS MAPPED
BY YOUNG- 1977

-00

01

Figure 9.

W a t e r L e v e l s o f t h e Perched A q u i f e r , 1976.

-20-

LIMITS OF PERCHED
SYSTEM A S MAPPED
B Y Y O U N G - 1977

01

Figure 10. Water L e v e l s

o f the

-21-

Perched A q u i f e r , 1981.

i n t h e 3200 foot contour between 1976 and 1981.
is in

response t o development

uf

the

T h i s change

y e r c f ~ e r l t j y s t e i ~ l a=r

a

d o m e s t i c supply of water.
Water Level Fluctuations
In

general,

a

ground

water

i n e q u i l i b r i u m when discharge

system

from,

can be

recharge

considered

to,

and

the

volume i n storage remain c o n s t a n t .

When development o c c u r s ,

the

direction

equilibrium i s

chanyed.

The

of

the

change

depends on the type of development; i f s u r f a c e w a t e r i r r i g a t i o n i s s t a r t e d , more water is made a v a i l a b l e f o r recharge
and w a t e r l e v e l s r i s e .

But i f pumpage from t h e ground water

system occurs, water is taken from s t o r a g e and w a t e r l e v e l s
w i l l decline.

Natural discharge from the system may I n c r e a s e

i n response t o recharge and may decrease with pumpage.
development reaches t h e new l e v e l , t h e
new

e q u i l ihri I

I

~or

steady

system i s

system w i l l reach a

s t a t e condition.

f l u c t u a t i o n s provide an i n d i c a t i o n of
r e a c t i n g t o changes

When

Water

level

h o w the ground water

i n recharge, discharge,

and

pumping
There are 15 observation w e l l s of the USGS
in the study area-

discontinued.

Two

other

-

X D W R network

observation w e l l s

have h p p n

Twelve wells have long term r e c o r d s (1967 t o

p r e s e n t ) while records for the f i v e remaining w e l l s began i n
1976.

Depth

to

water

ranges

from

less

than

three

(perched system) t o over 487 f e e t ( r e g i o n a l s y s t e m ) .

feet
Loca-

t i o n s of t h e s e wells a r e shown i n F i g u r e 6 and t h e hydrographs
a r e plotted i n Figures 11 through 1 7 .

Four of

t h e w e l l s do n o t

( ' 1 . R . ~ E , Sec.

1 0 D ~ D 1 and

s t a b l e ( F i g u r e s 12 and 1 5 ) .
feet

488

In

1967 t o

show s i g n s of
T.~s. R.~E.

Two

2 9 D ~ 1 )a r e

Sec.

One ( F i g u r e 11) h a s r i s e n Erorn
feet

482

decline.

in

1981 (T.1S.

R.4E.

Sec.

3 0 ~ ~ ~ w
1 h1i l,e t h e f o u r t h (E'igure 1 3 ) t o o k s e v e r a l y e a r s t o
r e c o v e r from

.

t e s t pumping i n 1973 (T.2S. R . 6 E .

Sec. 1 1 ~ ~ ~ 1 )

D e c l i n e s i n tine r e m a i n i n g o b s e r v a t i o n w e l l s h a v e v a r i e d
from l e s s t h a n one f o o t t o o v e r 35 f e e t .
level i n wellT.2S.

The g r o u n d w a t e r

S e c . 9DDD2 r o s e s e v e n f e e t f r o m 1 9 6 0

R.4E.

The u p a r d t r e n d t h e n r e v e r s e d and

t h r o u y h 1 9 7 7 ( F i g u r e 11).

t h e w a t e r l e v e l h a s d e c l i n e d t o t h e 1960 l e v e l o v e r t h e l a s t
f i v e years.

Well T . 2 s . R. 5 E . S e c , 26BDB1, l o c a t e d n o r t h w e s t

of

Home,

Plountain

(Figure 12).
BBBl

has

declined

one-half

foot

t r e n d i n w e l l T.2S.

An upward

s i n c e 1976

r e v e r s e d d u r i n g t h e w i n t e r of 1977 and d e c l i n e d a l m o s t

two f e e t by September 1 9 8 1 ( F i g u r e 1 2 ) .
d o m e s t i c w e l l T.3S.
from J u l y

through

The h y d r o y r a p h of

Sec. 7BDD1 shows a

R.5E.

January

(Figure 13).

steady

little u r

t h i s area.

1x0

rtlcllarye

Well T.3S.

R.6E.

Lu

the

Sec.

yrouild

decline

water level

The

r i s e s o n l y s l i g h t l y , i f a t a l l , d u r i n g the s p r i n g .
cates

See. 3 6

R.5E.

water

This indisysLe~n

in

13BBA1 i s i n the p e r c h e d

systern n o r t h oE Mountain Home and h a s d e c l i n e d o v e r 30 f e e t
s i n c e 1976 ( F i g u r e 1 4 )

.

The w a t e r l e v e l d e c l i n e s from ijlarch

t h r o u y h September i n r e s p o n s e t o pumpage

i n t h e a r e a , and

r e c o v e r y i n t h e w e l l o c c u r s d u r i n g the w i n t e r .

A

shallow

w e l l u s e d a s a d o m e s t i c source of w a t e r i n the l a t e 1 9 6 0 ' s
shows a s i m i l a r t r e n d

to

the previous w e l l

(T.3S.

R.6E.

T.3S. R . 6 E . S e c . 3 5 B C C l

T.4 S. R . 3 E . S e c . 2 3 CDDI

ELMORE

T.4 5.R . 3 E . S e c . 2 9 DDDI

F i g u r e 15.

Hydrographs o f W e l l s o n the Mountain Home Plateau

Sec.

35ABB1)

(Sec.

( ~ i g u r e1 4 ) .

35BCC1), b u t

second

A

i n the r e g i o n a l

well

i n the

section

s y s t e m h a s d e c l i n e d 18

f e e t o v e r t h e l a s t f i v e y e a r s and a l m o s t 31 f e e t s i n c e 1 9 6 7
(Figure 15).

Well T . 4 S .

S e c . 23CDD1 i s l o c a t e d nine

R.3E.

m i l e s w e s t of Mountain Home A . F . B .
t h e n e a r e s t production w e l l .

and o v e r two m i l e s f r o m

The w a t e r l e v e l h a s d e c l i n e d

o v e r f i v e f e e t s i n c e 1976 ( F i g u r e 1 5 ) .
a s t e a d y r a t e of

d e c l i n e w i t h l i t t l e o r no r e c h a r g e .

wells

observation

The h y d r o g r a p h shows

east

of

the

Mountain

shown a s t e a d y d e c l i n e s i n c e 1967 (T.4S.
and

Sec.

25BBC1)

(Figure

16).

The

d e c l i n e d 34 and 27 f e e t , r e s p e c t i v e l y .

Home A . F . B .

Two
have

R.5E. S e c . 24AAB1
water

levels

have

The pumping l e v e l a t

w e l l 25BBC1 i n 1975 w a s a p p r o x i m a t e l y 400 f e e t b e l o w L.S. D .
b u t by 1981,
T.4S.

R.7E.

t h e pumping

l e v e l was below 43-1 f e e t .

Well

Sec. 9DCC1 has d e c l i n e d a l m o s t n i n e f e e t since

1967 w h i l e w e l l T . 5 S .

R.4E.

S e c . 5CAA1 o v e r the sane p e r i o d

of t i m e declined 27 f e e t ( ~ i g u r c1 7 ) .

W e l l T.56. R.6E. S e c .

15BCD1 has d e c l i n e d f o u r f e e t s i n c e 1 9 7 6 ( F i g u r e 1 7 ) .
Changes i n t h e Ground Water S y s t e m s
The change i n ground w a t e r l e v e l s o v e r a 5 y e a r p e r i o d
was c o n t o u r e d t o show the a r e a s and t h e amount o f d e c l i n e
( F i g u r e ti))
data

.

collected

The
in

d i f f eret'lce b e t w e e n t h e Inass measurement
the

fall of

1976

(Young,

1 9 7 7 ) and the

mass measurement d a t a c o l l e c t e d i n t h e f a l l of 1 9 8 1 was u s e d
f o r t h e change map.

W e l l s w h e r e d a t a w e r e c o l l e c t e d from t h e

s p r i n g of b o t h y e a r s were also used f o r a l a r g e r number of
data points.

A l a r g e a r e a s o u t h of

Mountain Home d e c l i n e d

more than f i v e f e e t , with two depressions of 35 and 4 0 f e e t
inside

the -5

f o o t contour.

d e c l i n e s occurred

The second

largest

i n the Cinder Cone Butte

area of
with

Z.G.W.A.

d e c l i n e s of more than 3 5 f e e t over a large p o r t i o n of t h e
area.

Declines of more than 35 f e e t a l s o occurred west of

Mountain

Home

decline

appeared

beneath Mountain Home (-20 f e e t ) and n o r t h e a s t of

the c i t y

feet).

(-15

Small

A.F.B.

areas

of

Declines i n the regional systeln have occurred

i n areas where i r r i g a t i o n development has taken p l a c e ,

Declines

in

t h e perched

ground

water

system occurred

mainly i n the v i c i n i t y of Mountain Home where l a r g e domestic
development has occurred

(Figure 1 9 )

.

Declines

varied

in

amounts from over 50 f e e t t o no d e c l i n e a t a l l .

Two s m a l l

areas of

south and

decline of over f i v e feet were located

n o r t h e a s t of Mountain Home.
Declines i n both the perched and regional
syste~ils are due m a i n l y to dcvclopment
lower

amounts of

precipitation

of

the

ground w a t e r
resource, but

i n t h e mountains

l a s t several years have a l s o played a p a r t .

over t'ne

Table 2 shows

the annual p r e c i p i t a t i o n and the departure from normal for
precipitation stations
Dam, anB H i l l City.

located

a t Mountain Home,

Anderson

P r e c i p i t a t i o n at iJlountclin Womc f o r the

e i g h t years of record shown was above average f o r a l l b u t one
year and 14.35 inches above average f o r the period l i s t e d .
p r e c i p i t a t i o n f o r the s t a t i o n a t Anderson Dam was above average
only three times over t h e same time period, b u t p r e c i p i t a t i o n
f o r the three w e t years was almost equal t o the l a c k of p r e c i p i t a t i o n during the remaining f i v e y e a r s .

The s t a t i o n a t X i 1 1

LIMITS OF PERCHED
SYSTEM AS MAPPED
BY YOUNG- 1977

F i g u r e 19. C h a n c e i n W a t e r L e v e l s i n t h e
1976 t o 1981 i n Feet.

Perched

Aquifer

from

C i t y was below a v e r a g e f o r a l l b u t o n e y e a r a n d 1 9 . 2 1 i n c h e s
below

average

for

the period

l i s t ~ A .

Over

the l a s t - e i g h t

y e a r s , p r e c i p i t a t i o n was a b o v e a v e r a g e f o r t h e M o u n t a i n Home
P l a t e a u b u t was p r o b a b l y n e a r or b e l o w a v e r a g e i n the mount a i n s above t h e p l a t e a u .
averaye

yield

Creek b a s i n s .

from

T h i s would l e a d t o n e a r or b e l o w

Canyon

Creek,

Rattlesnake,

and D i t t o

Below a v e r a g e p r e c i p i t a t i o n would a1so a£f e c t

the i n t e r b a s i n t r a n s f e r of w a t e r from L i t t l e Camas R e s e r v i o r .

Table 2 .-

-

Date

*

Annual P r e c i p i t a t i o n a n d D e p a r t u r e from Normal
f o r S t a t i o n s i n V i c i n i t y o f M o u n t a i n Home
Plateau i n inches

- - -

Mountain Home
Annual
DeparPrecip
ture*

Anderson Dam
Annual
DeparPrecip
tuie*

Hill C i t y
D e-p a r -

Annual
Precip

ture*

D e p a r t u r e from a v e r a g e a n n u a l p r e c i p i t a t i o n b a s e d on p e r i o d
1941-1970.

WATER SUPPLY AND USE

Basin Y i e l d
~ e c h a r g e to

the

ground

water

is

systein

frorn

water

d e r i v e d from p r e c i p i t a t i o n both within and from o u t s i d e t h e
study

Imported

area.

irrigation w a t e r

from

Little

~ e s e r v o i rand the Snake River a r e the out-of-basin

Camas

components.

Recharge from within the basin i s mainly from p r e c i p i t a t i o n
f a l l i n q on the higher e l e v a t i o n s of t h e mountainous p o r t i o n
of t h e b a s i n .

This recharge can e i t h e r move d i r e c t l y through

t h e v o l c a n i c rocks from the source area t o the ground water
systein under the plateau p o r t i o n of t h e a r e a o r e n t e r stream
c h a n n e l s flowing out from the h i l l s o n t o the p l a t e a u .
water

i n t h e streams i s e i t h e r d i v e r t e d

The

for i r r i q a t i o n or

i n f i l t r a t e s t o the ground water t a b l e as the s t r e a m s c r o s s
the plateau.

As a r e s u l t ,

o n l y i n y e a r s of

l a r g e runoff

does s u r f a c e discharge reach t h e Snake R i v e r .
Recharge
lowlands of

from

precipitation

the plateau

falling

directly

(Young,

1977 and

Rawls

S o i l ~norphological c h a r a c t e r i s t i c s ,
survey data for t h e p l a t e a u

area,

and

f o r evapo-

others,

described

in

1973 )

the

where p r e c i p i t a t i o n

t o occur
f a l l s on

on p o r t i o n s
rock

.

soil

a l s o i n d i c a t e no s i g n i -

f i c a n t w a t e r m o v e m e n t b e l o w the r o o t zone (Nne, 1 9 A 2 ) .

recharge i s believed

the

i s thought t o be small due t o t h e

low amounts of p r e c i p i t a t i o n and high p o t e n t i a l
transpiration

on

outcrops.

of

Some

the plateau
An

estimate

of t h i s q u a n t i t y was developed from p r e v i o u s e s t i m a t e s made
f o r a similar purpose f o r the Snake P l a i n a q u i f e r .

Mundorff

and o t h e r s (1964) used a f i g u r e of 26 percent of

t h e annual

to

p r e c i p i t a t i o n on b a s a l t rock s u r f a c e s as k i n g recharged
t h a t aquifer.

This same f r a c t i o n of

tion

for

was

used

extreme

stoniness

plateau

area.

this

study.

amount

Recharge

tile a n n u a l p r e c i p i t a -

Areas of

to

about

from

this

rock

four

or

outcrop

of

percent

source would

the

be a b o u t

4400 a c r e f e e t per year over t h e plateau area.

Water

i s imported i n t o t h e Canyon Creek b a s i n

by the M u u r i t a i r i

Creek,

f r u i a Little C a r r x a s

Irriyatiorl District

Hurtle

a t r i b u t a r y of

t h e South Fork

for u s e

Boise R i v e r .

Flows

i n L i t t l e Camas Creek a r e stored i n L i t t l e Camas Reservoir
( c a p a c i t y 17,300 a c r e

Eeet)

and

released

into

the trans-

b a s i n L i t t l e Camas Canal which c a r r i e s the water
E a s t e-ork o f Long Tom creeit.

Long Tom Reservoir
creeks

form

Irrigation

Canyon

Company

before

T A e water

joining

Creek

from

diverts

to

then p a s s e s thrOUgfi

Syrup Creek.

which
its

into the

the

The t w o

Mountain

reservoir

Home

through

the

Mountain Home Feeder Canal.
Records

of

Little

Camas

Canal

kept from 1924-29 and 1932-73.

Average annual flow d u r i n g

t h a t period was 11,100 a c r e f e e t .
made

frnm April

flow records

or

'oelow

early May

provided

net

on

import.

Based

a

Diversions a r e g e n e r a l l y

thrntigh

Tunnel No.

Canyon Creek b a s i n ,

9,

a basis

Tunnel 9 with flows a t the head,

tni A - S ~ p t ~ m h e r . C a n a l

where

correlation

about 9500 a c r e f e e t per year.

i t s head were

flow a t

for
of

the

water

enters

determining
monthly

the

flows

at

t h e average n e t import

is

In

the s o u t h e r n p o r t i o n of

the study area,

t h e S n a k e R i v e r i s pumped up t o t h e p l a t e a u .

water from

Approximately

a r e d i v e r t e d f o r 1 4 , 6 5 3 a c r e s a t an a v e r a g e

37,800 a c r e - f t / y r

( S u t t e r , 1976).

d i v e r s i o n r a t e of 2 . 5 8 a c r e - f t / y r

T h e r e a r e v e r y l i t t l e d a t a o n r u n o f f of the s t r e a m s i n
t h e s t u d y area.

Measurements o f

I n t h e March-September

f o r a few mont'ns i n 1917.
that

year,

Rattlesnake

s e v e r a l s t r e a m s w e r e made

Creek

carried

p e r i o d of

f e e t and

1800 a c r e

Canyon Creek 35,760 a c r e feet, 9840 acre fcct of w h i c h
d i v e r t e d i n t o t h e b a s i n i n t h e L i t t l e Camas C a n a l .
however,

a

wetter

s o u t h F o r k of

than

normal

as

year

evidenced

was

I t was,

by

the

t h e B o i s e R i v e r n e a r L e n o x w h i c h had a n n u a l

r u n o f f of 1 4 1 p e r c e n t o f normal i n 1917.
Records

Canal

Of

provide

water y i e l d .
water

to

Ciiversions

thruuylt

the best basis

Uxa

for

Mountain H o m e Feeder

estimating

C a n y o n Creek

The f e e d e r c a n a l which t r a n s f e r s Canyon Creek

Mountain

Home

& e s e r v o i r and

the

Mountain

Home

irrigation D i s t r i c t c a r r i e d an a v e r a g e o f 2 3 , 2 0 0 a c r e f e e t

per y e a r d u r i n g a 43 y e a r d e r i o d e n d i n g i n 1969.
made by p e r s o n n e l

of

the

district,

it

From n o t e s

is e s t i m a t e d

that,

a n a v e r a g e of r o u g h l y 5 3 0 0 a c r e f e e t per year

i n addition,

passes the feeder

carial h e a d g a t e s and i s n o t d i v e r t e d .

Deduc-

t i n g t h e a v e r a g e L i t t l e Camas C a n a l i m p o r t of 9500 a c r e f e e t
r e s u l t s i n a y i e l d e s t i m a t e f o r Canyon C r e e k o t 19, UUU a c r e
f e e t p e r Year.
Similar

data

are

not

available

for

the

( ~ a t t l e s n a k eand D i t t o C r e e k s and a d j a c e n t a r e a s )

other

.

basins

To estimate

t h e i r y i e l d s , a c u r v e of

y i e l d v e r s u s tnean b a s i n e l e v a t i o n

was drawn from s k e t c h y d a t a f o r n e a r b y w a t e r s h e d s w h i c h , when
a p p l i e d t o Canyon Creek b a s i n , would r e p r o d u c e t h e e s t i m a t e d
y i e l d of 19,000 a c r e f e e t ( 5 . 1 i n c h e s ) f o r t h a t b a s i n .

This

c u r v e was t h e n used w i t h a r e a e l e v a t i o n c u r v e s f o r the t w o
basins t o estimate t h e i r yields.
C r e e k is

estimated t o y i e l d

By t h i s method, R a t t l e s n a k e

a n a v e r a g e of

3460 a c r e f e e t

( 4 i n c h e s ) p e r y e a r and D i t t o and a d j a c e n t a r e a s 3800 a c r e

f e e t ( 2 . 9 i n c h e s ) per y e a r .
I n October

1981,

a

gaging

s t a t i o n was

established

Canyon Creek a t t h e F o o t h i l l Road b r i d g e (T.~s. R.6E.
Eight

fl4)

October

discharge

1 9 8 1 and

March

measurements

1982 t o

were

establish

made

the

r e l a t l o n s h i p , and a s t a t ? g a g e w a s r e a d d a l l y .

on

S e c . l \ , SGNw%-

between

stage-flow

F l o w s ranged

from a b o u t two c f s d u r i n g t h e f a l l t o 400 c f s i n F e b r u a r y .
Runoff from O c t o b e r t h r o u g h March t o t a l e d 8 b o u t 3 0 , 0 0 0 a c r e
feet.

During t h i s period there w e r e no Ai versinns i n t o the

basin

from

Little

Camas

Creek.

Canyon

Creek

flow w a s

d i v e r t e d t o Mountain Home R e s e r v o i r u n t i l J a n u a r y 18.
During F e b r u a r y when Canyon C r e e k f l o w s r a p i d l y i n c r e a s e d
i n r e s p o n s e t o warn w e t w e a t h e r ,
H i g h w a y Q 4 bridge

and

c o n t i n u e d through

The flow a t t h e f o r m e r U . S .
downstream

from

1-84

f l o w r e a c h e d the I n t e r s t a t e

was

determine channel l o s s e s .

to the Snake R i v e r -

Highway 30 b r i d g e

measured

on

three

immediately

occasions

to

Canvon Creek Discharcre i n C F S
a t Foot'nil l

at Old
U.S. 30

Road

D i v e r s i on

Loss

February 18
March 11
April 1 9

On

February

18 l o c a l

runoff

was

entering

the

stream

between t h e two s i t e s , b u t none was occurring on March 11,
I t appears

t h a t about 6000 a c r e f e e t of Canyon Creek flow

was recnarged t o the y r w u n i l w a t e r s y s t e m s between m i d - F e b r u a r y
and t h e end of March.

Between January 19 and mid-February

about 4000 a c r e f e e t was recharged from t h e creek w i t h small
a m o u n t s occurring i n the f a l l and e a r l y w i n t e r .

On March 11 roughly h a l f

of

the

flow a t t h e U.S.

30

b r i d g e was passing Idaho Highway 6 7 , west of Mountain Home
A i r Force Base.

S u b s t a n t i a l amounts of a d d i t i o n a l recharge

undoubtedly occurred from D i t t o , Rattlesnake and o t h e r small
creeks which drain t h e f o o t h i l l s .
From notes by personnel of t h e Mountain Home I r r i g a t i o n
D i s t r i c t , it appears t h a t some canyon c r e e k water passes the
d i v e r s i o n works

t o Wountain Home Reservoir

i n most years.

Amounts which have occurred i n e a r l y 1 9 8 2 , however,
to be much

larger

than

at any

appear

time i n t h e p a s t 10 years.

Available data i n d i c a t e s t h a t accumulated p r e c i p i t a t i o n from
October through March i n t h e general a r e a was about 1 4 5 perc e n t of normal.

Based
s p r i n g of

on t h e

apparent

1982, a rough

losses

to

e s t i m a t e of

ground

water

the losses

i n the

from w a t e r

passing the d i v e r s i o n t o Mountain Home Feeder Canal was made
f o r the 1972 t o 1980 p e r i o d ,
wet year

escapement

O f t h e 5300 a c r e f e e t per y e a r ,

t o Snake River i s estimated t o be 1900

a c r e f e e t , with t h e remainder being recharged.
I r r i g a t e d Lands
I r r i g a t e d land i n t h e study a r e a was determined from 1975
maps of i r r i g a t e d l a n d s i n Ada and Elmore Counties; these w e r e
prepared by the Department of Water Resources and updated by
Bureau of Reclamation t o i n c l u d e 1979 acreages.

With the use

of a e r i a l photos, t h e acreage under c u l t i v a t i o n was a d j u s t e d
t o 1980 ( F i g u r e 2 0 ) .

Applications

and permits

f o r use of

ground water on f i l e with I D W R were a l s o determined (Table 3 )
Table 3 .

Developed, A p p l i c a t i o n s f o r , and
P e r m i t t e d Lands, Mountain Home
Study Area ( a c r e s )

Ground Water Permits (undeveloped, 1980)
Pending Applications
Developed

Canyon Creek
Canyon Creek ( G W s u p p l . )
Ground Water
Snake River
T o t a l Developed
Total

.

U t i l i z i n g image a n a l y s i s techniques the crop d i s t r i b u t i o n

The 1980 crops on i r r i -

was estimated for the study a r e a .
gated land were:

row crops ( 2 5 . 6 % ) ,

small grains ( 4 7 . 8 % ) ,

alfalfa ( 1 7 . 3 % ) , and p a s t u r e ( 9 . 3 % ) . The row crops and small
g r a i n c l a s s i E i e a t i o n s were f u r t h e r divided based on county
records

(1980 Idaho A g r i c u l t u r a l

statistics)

as

shown

in

Table 4 .
Table 4.

Row Crop and Small Grain C l a s s i f i c a t i o n
Small Grains

Row Crops

The

number

Winter Wheat
Spring Wheat,
Oats, Barley

8.5%
24.7%
20.2%
46.6%

Corn
Beans
Sugar Beets
Potatoes
of

acres

per

crop

type was

45.7%
54.38

c a l c u l a t e d by

multiplying t h e t o t a l number of acres i r r i g a t e d from Canyon
Creek,

Snake River,

and ground water by the percentage of

t h a t crop type for the s t u d y a r e a .

Consumptive I r r i g a t i o n Requirement
The number oE acres per

crop type was then multiplied

by the average annual consumptive i r ~ i y a l i o nrequirement for

that crop

(Sutter

&

Corey,

1970).

The t o t a l

consumptive

i r r i g a t i o n requirement was then determined f o r lands served
f r o m the t h r e e sources as follows:

Consumptive
Irrigation
Requirement
Acres
-

Canyon C r e e k (SW)

*

4,968"

Ground Water

22,290"

Snake R i v e r

14,653

I n c l u d e s h a l f of t h e l a n d s
Creek and ground w a t e r .
In

addition

to

(AC-~t/~r)

the a b o v e ,

supplied

irrigation

from b o t h

of

Canyon

approximately

1 5 0 0 a c r e s o f lawns and g a r d e n s i n M o u n t a i n Home and a t t h e
A i r Rase u s e s a b o u t 2500 a c r e f e e t p e r y e a r .

Water B a l a n c e
T h e w a t e r b a l a n c e f o r tine s t u d y area i s shown i n Table 5 .

Under 1980 c o n d i t i o n s of u s e ,
s u p p l y compared t o u s e .

t h e r e w a s a s l i g h t d e f i c i t of

T a b l e 5.

Water B a l a n c e f o r Mountain Home S t u d y A r e a ,
1980 C o n d i t i o n s

Total (rounded)
(ac/ft/ys)

Source
Canyon Creek Y i e l d
Little C a r n a s C r e e k

(imported)
R a t t l e s n a k e Creek y i e l d
D i t t o Creek &
A d j a c e n t Areas
Snake R i v e r Pumping
P r e c i p i t a t i o n on P l a t e a u
~ o c k ym e a s

Use
-

L o s s t o Snake R i v e r
U s e by Crops
Use by M u n i c i p a l ,
Air Base Irrigation
S o u r c e L e s s Use

Lands i r r i g a t e d by Canyon Creek w a t e r l i e n o r t h and s o u t h
of Mountain H o m e ( F i g u r e 2 0 ) .

a r e mainly
W e s t

of

Ground w a t e r i r r i g a t e d l a n d s

i n t h e C i n d e r Cone B u t t e C.G.W.A.

Mountain H o m e Air

Fvrce

Base

and e a s t and

( ~ i ~ u r t20).
z

rjround

w a t e r p e r m i t s n o t y e t d e v e l o p e d l i e m o s t l y i n t h e C i n d e r Cone
Butte

area

(Figure 20).

as

well

as

north

and

south

of

Mountain

Home

A p p l i c a t i o n s f o r qround w a t e r u s e a r e s c a t t e r e d

t h r o u g h o u t t h e s t u d y a r e a , but t h e l a n d s l i e m a i n l y n o r t t l w e s t

of the A i r Base.

If

the

15,517 a c r e s

of

ground

vlrater permits

not

yet

developed were i r r i g a t e d ( ~ i g u r e2 0 ) , t h e r e would be an addi27,500 a c r e f e e t per year i n the study

t i o n a l o v e r d r a f t of

a r e a o r a t o t a l o v e r d r a f t of 28,100 a c r e f e e t per year.
ground

water

applications

c u r r e n t l y pending

11,21/ a c r e s c o u ~ d be developed
tional

o v e r d r a f t of

If

a r e approved,

( ~ i g u r e2 0 ) with a n adai-

19,900 a c r e f e e t per year o r a t o t a l

p o t e n t i a l o v e r d r a f t of 48,000 a c r e f e e t per year.

REASONABLE PUMPING LEVELS

definite

No

standards

have

been

set

in

Tdaho

which

f u l l y define what the a p p r o p r i a t e measure of reasonableness
is

or

hdw

pumping

it

will

levels.

be

The

applied

statutes,

in

determining

however,

reasonable

do i n d i c a t e t h a t

economic f a c t o r s s31ould af f e e t t h e measure of reasonableness.
It

is

not

t h e purpose

of

this

s e c t i o n t o analyze the

multitude of f a c t o r s af Eecting the d e f i n i t i o n of reasonableness.

Rather

this

section w i l l

provide

information about the study area which
important

inputs

to

any

determination

certain

economic

is one of

the many

of

a

reasonable

~ J U I I I L - Ievts1.
' ~ ~ ~ ~

Idaho s t a t u t e s e x p l i c i t l y recognize two economic f a c t o r s
which

should a f f e c t reasonableness:

(1) p r o t e c t i n g

early

appropriators from water l e v e l d e c l i n e beyond t h e i r economic

c a p a c i t y t o c o n t i n u e t o p u m p , and ( 2 ) a c h i e v i n g f c l l l economic
Aevel opment

of

underground w a t e r r e s o u r c e s .

The f o l l o w i n g

i n f o r m a t i o n a d d r e s s e s o n l y t h e q u e s t i o n of economic c a p a c i t y
t o pump.
Economic c a p a c i t y t o pump i s d i f f e r e n t f o r e v e r y i n d i v i d ual even w i t h i n a r e l a t i v e l y n a r r o w l y d e f i n e d a r e a s u c h a s t h e

one under study;

it i s a l s o c o n s t a n t l y c h a n g i n g .

Examples

o f change i n i m p o r t a n t f a c t o r s i n £ l u e n c i n g e c o n o m i c c a p a c i t y
t o pump a r e shown i n F i g u r e s 2 1 and 2 2 .

Increases i n prices

paid i n e x c e s s of p r i c e s r e c e i v e d b y f a r m e r s l e s s e n a f a r m e r ' s

economic c a p a c i t y t o pump'.

A s c a n be s e e n i n F i g u r e 2 1 , t h i s

h a s been the case since l a t e 1979.

The i n c r e a s e d c o s t o f

e l e c t r i c i t y a l o n e i n t h e Mountain Home a r e a has h a d a dramat i c e f f e c t on ecorlomic c a p a c i t y t o pump.

Figure 22 t h a t

It is e v i d e n t f r O m

the e l e c t r i c i t y c o s t p e r a c r e t o pump from

200 f e e t t o d a y i s t h e sarne a s t h e cost p e r a c r e w a s i n 1 9 7 5

tu

~ U I L I L Jf

r o m 3 0 0 fcct.

T a b l e 6 shows a r e p r e s e n t a t i v e farm b u d g e t summary for a
farin w i t h
area.

All.

center pivot
crops,

sprinkler

irrigation

except potatoes,

t o r i s k and w a t e r .

i n the s t u d y

show a n e g a t i v e r e t u r n

T h i s v a l u e r e p r e s e n t s the amount a v a i l -

able, a f t e r a l l utlltr

costs are paid,

a n d electricity c o s t s .

On a

to pay w e l l . m o t o r , pt~rnp

farm with t h e crop r o t a t i o n

assumed i n l i n e one of T a b l e 6 , the o v e r a l l r e t u r n t o r i s k
and water

i s $-36.50

per

acre.

Table 7

is identical

to

Table 6 e x c e p t

t h a t h a n d l i n e s p r i n k l e r s a r e assumed t o be

t h e method

irrigation.

of

Again,

potatoes

a r e t h e only

1982
Power
Rates
/
#-

/
/
'

/
/
/

/
/

/

/

/

/

/

,
'
/

/

/

/

/

197 5
Power
Rates

DEPTH TO W A T E R ( F T . )
Figure 22. Per Acre E l e c t r i c i t y C o s t C o m p a r i s o n s for Ground Water
Pumping i n I d a h o Power S e r v i c e A r e a . 1975 a n d 1982.

d rd6 l

" 2 4c

4

arn:
1

LI

8s

G 5 M

2 .$ 2

2w

rl

4

.-

m

fd

w

3

E : . - w
o C O - 3

J

J

.

\

o

a,

.

r

-

c

i

l r ) % r I n m
CY
m
ui

c r o p w i t h a p o s i t i v e r e t u r n t o r i s k a n d water a n d t h e o v e r a l l
f a r m r e t u r n i s $-26.53

An example of t h e budgets

per acre.

u t i l i z e d t o form summary T a b l e s 6 and 7 i s shown i n Table 8 .
The a n n u a l c o s t p e r a c r e of pumping ground w a t e r from
various depths i n the

study area,

t i o n g i v e n i n T a b l e s 6 and 7 ,
g i v e n i n column f o u r o f

assuming t h e

c r o p rota-

is given i n Table 9.

Values

t h e t a b l e a r e those which must be

compared w i t h a f a r m e r ' s a b i l i t y t o p a y f o r i r r i g a t i o n water.
1f

t h e s e Values exceed a f a r m e r ' s a b i l i t y t o pay a t a g i v e n

depth then t h a t farmer
pump.

is beyond h i s

capacity to

economic

For example, a f a r m e r growing 1 0 0 % p o t a t o e s and using

c e n t e r p i v o t i r r i g a t i o n would have a n economic c a p a c i t y t o
pump

froin a t l e a s t 8 0 0 f e e t .

This

rotation,

infeasible from a t e c h n i c a l s t a n d p o i n t .

however, i s

I n c o n t r a s t , a farmer

growing t h e c r o p r o t a t i o n assumed i n T a b l e 6 has a negative
return t o risk

and w a t e r

and

t h e r e f o r e does

economic capacity to prmp at a l l .

n o t have t h e

An in t ~ n s i v ec r n p r o t a t i o n

o f 50 p e r c e n t wheat would y i e l d a r e t u r n t o risk a n d water of
$126.74 u s i n g c e n t e r p i v o t

irrigation.

The pumping c o s t s

associated w i t h t h i s r o t a t i o n a r e g i v e n in Table 10.
be s e e n Erom t h e t a b l e ,
farmer

growing

the

As can

t h e e c o r ~ o m i c c a p a c i t y t o pump of a

wheat

and

potatoes

rotation

i s between.

450 and 500 f e e t below l a n d s u r f a c e .
I t i s i m p o r t a n t t o r e c o g n i z e t h a t t h e r e a r e a multitude

of

assumptions i n h e r e n t i n any r e p r e s e n t a t i v e

a n a l y s i s such a s t h e ones p r e s e n t e d
assumptions w i l l

lead

to a different

above.

farm budget

Any change i n

economic capacity to

T a b l e 8.
Crop:

Farm Budget
County:

Potatoes

Elmore

-- -----------Per
Times Over

Operation or I t e m

Acre-------C o s t s or
Receipts

- - --Unit

Total

T o t a l Revenue
Potatoes

350.00 C w t

Production Costs:
Plow S t u b b l e (Moldboard)
D i s c and Harrow
C h i s e l a n d Mark
Planting Potatoes
Seed P o t a t o e s
F e r t i l i z i n g Broadc