Shoshone journal. [volume] (Shoshone, Idaho) 1884-1931, 1909-07-23
Trip Big Dam of the Idaho Irrigation Company by
Representative of the Journal is Full of Interest
To all Settlers the Companys Project
A MIGHTY FEAT OF CIVIL ENGINEERING
When Finished the Main Dam will be 500 Feet Long, 800 Feet
Thick, 14O High, with Three CoresLake will be Formed
Several Miles Wide in Places and Twelve Long

capable of conveying the entire cur
rent of the river during the period of
low water.
AT present two dams are being built
across the canyon, 800 feet apart, and
later the intervening space will be filled
to make one solid dam which will rise
140 feet above the bed of the river, and
extend 800 feet up and down the river
and 800 feet across the canyon. The
slope of the upper and lower walls will
be such that the top of the dam will
form roadway 40 feet broad. This
dam will rise above the top of the
promontory through which the tunnel
penetrates, and its wall viii be ex-
tended westward across the plateau
nearly three-fourths of a mile where
400-foot spillway will carry off all the
flood waters of the river which the
tunnel cannot handle. Not drop of
water will ever go over the dam or
through it.
The two walls of the dam now being
constructed are called the heel and toe,
and the space between them, nearly
800 feet, is being prepared for three
cores or cutoffs.
The center core will constitute the
exact center of the dam, and it will be
formed by driving heavy steel piles, 30
feet long, perpendicularly into the
gravel bed of the river, nearly to bed
rock, and extending across the canyon
from wall to wall This sheet piling is
so constructed that each couple are
joined together by steel web that is
grooved or dovetailed to match the
piling and is driven down the entire
length of the piling, binding it in a solid
wall of steel 800 feet long from bank to
bank, and reaching 80 feet to bedrock
Two other cores are located above
stream from the steel center, both be-
ing sunk to bedrock and made of native
clay cement, which hardens and be-
comes water tight. These cores will
not be constructed until the upper wall
of the dam becomes water tight and
the space between the two walls is
drained dry. When completed the up
river wall of the dam will be faced with
four feet of gravel covered by two feet
of large loose rock to prevent erosion
from water or ice, and between the
upper and lower walls the entire space
of nearly 800 feet up and down stream,
and 800 feet from canyon wall to can
yon wall, will be filled with dirt with
the three cores completely buried in
their midst.
Remember that the main dam is only |
300 feet long from canyon wall to can
yon wall, but as it rises higher than
the top of the promontory through
which the tunnel penetrates, fanking
lam is to be constructed westward
across the plateau, nearly three-fourths
IF a mile to higher ground. And it is
On this fianking dam that the spillway
IF 400 feet is to be located. The ordl-
lary flow of the river is sucked down
oy the tunnel while the flood waters
are carried off through the spillway.
With only 20 feet of water now in
The bottom of the canyon, the reser-
1oir holds some $1,000 acre feet of
water, sufficient for all needs of irriga-
ion this season. As the dam wall is
being built up the depth of water in
,reases daily, and by next season nearly
he full capacity will be reached, al
hough it may take all of next year to
ully complete the gigantic undertaking.
When completed, this dam will form
reservoir or lake several miles wide
n places and nearly twelve long with ,
otal capacity of 205. 900 acre feet.
The drainage area of the Big Wood I
iver which pours into the reservoir 3
overs 1850 square miles and the flood
vaters are sufficient to fill the reservoir /
nd irrigate the entire lands of the /
daho Irrigation system during the a
pring. This leaves a. brimming full t
eservoir to be used during the latter Q
art of the irrigation season only, and e
is sufficient to cover 205, 900 acres of
vel land ope foot deep. AS the tun a
el is located near the bottom of the t
anyon nearly all thewa of the res