The Salt Lake herald. [volume] (Salt Lake City [Utah]) 1870-1909, 1889-08-22
THE RESERVOIR QUESTION.
The Objections Urged Against Making Small
Ones in Adjacent CANYONS.

!
, Messrs. Sturges & Bryant hand in the
} following: ''Will you kindly allow US to
! criticise your editorial upon reservoirs that
J appeared in Wednesdays HERALD?
Designing reservoir dams is our speciality,
so that we would criticise it from pro
fessional standpoint. You must certainly
be mistaken in your statement as to what
Major Powell considers necessary to water
certain tract of land. You state that
twenty acres ten feet deep will water 800
acres and allow evaporation. From many
experiments and reports we have adopted
five feet as the depth of water over a
reservoir that may, on an average, be ex-
pected to be taken by evaporation and
seepage. In confirmation we will state
that the evaporation in Denver through
period of ten years, was 2T9 inches an
nually. Upon water surface, this dryer
climate may easily, then, claim five feet
for both evaporation and sub-seepage.
On our reservoir ten feet deep then we
must allow five feet for evaporation and
seepage practically the same as on resor-
voir ten times as deep, and we have sixty
inches Ton five feet of water over twenty
acres left.
ALL ENGINEERS AGREE
in allowing twenty inches of water per
acre as the necessary amount for irrigation
during the season, then sixty inches-three
times twenty inches = or one reservoir
will actually water three times twenty
acres, which is sixty acres. You will
readily see that 300 acres, five times this,
would come from some misunderstanding
as to what the Major really said. Now, let
US suppose that some town, Salt Lake city
for example, followed your advice, and
built series of small reservoirs in City
Creek CANON We will, for illustration, say
there were ten of them built at different
points in the canon. Let US imagine that
reservoir No. 10, up the canon, should be
faulty in some point in construction, and
some day it bursts; the reservoirs are all
full below, but we will not suppose any
storm in connection with them. When
reservoir No. 10 bursts, its waters, ten feet
deep (if not more, for dam always prac-
tically gives way at once) its waters, ten
feet deep, rush down to reservoir No be-
low, of the same size. Wewill imagine
THE MOST FAVORABLE CONDITIONS
that the dam at each reservoir is placed in
the broad canon, and hence as long as the
reservoir is wide, then a flood of water ten
feet deep rushes over the top of the entire
dam of reservoir No. 9, and it could not
help but take out that dam unless it were
made entirely of large slabs of rock bolted
together, which is too costly a type to in
troduce in any ordinary case in Utah.
With dam No. 9 taken out the increased
food would likewise run over the top of
, and wash out every dam in the canon, the
accumulated flood rushing down upon Salt
Lake city then JohnstoWn No. 2. These
statements show the danger of building one
dam above the other, no matter how small,
unless many miles apart; for one dam de-
stroyed, means also the sure destruction of
| every dam beneath it. u.
Now, as to the advisabilft% of building
. small reseryo irs The facts stated as 10
/ hot a
voir twenty feet deep will deliver three
times the useful water that dam ten feet
deep will.
THE GREAT DANGER
in reservoir dams lies in the faulty construc-
ton of some one little place anywhere in
the dam; and for that reason we never de-
sign dam that has not at least two differ
ent materials that safely resist water, to
be built by two different sets of workmen,
that if fault be at any one point, SINH
lar fault be not found at the same point in
the other imperviouS material, and thus no
one fault will allow water to go through
the dam. For if one drop goes through
dam, that dam is doomed.
Now with ten small reservoirs, thereis
TEN TIMES THE DANGER
of one being faulty and unsafe. while
workmen would not place as good work ON
a small dam as they would on larger one
We have then, by building small reser-
voirs, increased the danger ten-fold
The foundation work is the really import
ant work in a dam, that there may be no
opportunity for water to get through be-
tween the former ground and the material
of the dam. The expense in providing a
safe foundation for small dam is a large
proportion of the expense in providing a
safe foundation for large dam. AS to the
destructive
| INFLUENCE OF CLoUD-BURsT,
we would say that if the reservoir were
full there would be no shock to the dam,
and if it were empty the dam would be filed
by the water, and the slight shock would
never effect decently built dam. If there
were an engineer in charge of the construc-
ton, the waste-way would be made ample
to carry off the food without it running
over the top of the dam, which is the only
way flood can attack the dam. Also, if
an eglneer were in charge of construction,
he would recommend no site to be built
upon which was not ample enough to take
in all the mud and rubbish and the total
debris be but very small part of the
capacity of the dam, the rubbish can then,
at leisure, be afterwards used in strength
ening the dam by making the dam thicker.
1t is seldom that any canon contains over
one or two
that, on economic principles, could be re
commended by competent engineer. A
large majority of so-called reservoir sites
could never be constructed and yield any
return for the expense incurred. Up to
40 feet depth of water, reservoir dams
can be constructed quite cheaply, if they
are properly designed and built. As rule
they can be built, amply safe, for less
money than is supposed by many persons.
| OF course, as we have said before in THE
HERALD, no simple earth dam is safe, and
any citizen living below a dam thus con
structed, could enioin its use and easily
prove in court by any engineer that such
| dam is very unsafe.
| Likewise, any damin which is stick of
timber in any form, lying crosswise OF the |
dam, not used in the spillway, is built con-
trary to engineering practice.
uradvice is to consider dams of forty |
to fifty feet as the economical dams When |
above fifty feet the expense Of building a
safe dam increases very rapidly.
We will illustrate by stating that the !
dam we
LATELY DESIGNED FOR sPRISGvLLE |
has forty feet depth of water and contains |
some 200, 000,0 900 gallons, enough to water |
5000 acres two inches deep; for it is de- |
signed to be used, if built, only during a |
drought. to save the crops of the commu- |
nifty by giving one or two waterings when |
most needed. This dam has very bad |
foundation to rest upon, yet the total ex- |
Dense of building it, perfectly safe and first |
class, is only Sl1 600, of which 8, 600 is cash
and 50, 000 home labor.
CONFIRMED.
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