Arizona republican. [volume] (Phoenix, Ariz.) 1890-1930, 1902-04-27

from February p to December 81, 1901.
vas observed at the reservoir site and
requires no reduction
The storage Of food waters on Salt
river win not only utilize such waters
h. holding them until needed. but VIII
greatly increase the utility of he Hoods
Oh -" Nerde river by providing n much
larger irrigated area to receive such
floods. and at the same time holding
back the waters of The Salt as long as
the Verde is able to fill the require
ments. An examination of the records
shows that with such manipulation the
Verde will usually supply all require
ments during the four months of De
Cember. January. February and March.
and that a very large proportion of the
flood waters of the Verde which now
run to waste would be thus utilized.
The record since 1883 is taken in con-
nection with the proposed reservoir and
100000 acre-fee- annual consumption.
and from this a table has been con-
structed, showing what would take
place if the past experience should be
repeated after the construction OF the
reservoir.
This table shows that if the proposed
reservoir were operated in conjunction
with the natural flow of the Verde
river. and an annual supply OF GEO. 900
acre-feet were desired. this could have
been furnished every year in the record
except 1900. IN that year there would
have been shortage of about &c per
cent IL is believed that such a short
age is permissible i'm a storage project
if ii does not occur oftener than once
in. say 20 years. which is the fact in
the present case.
The duty of 100000 acre-feet per an
mum is that Of the combined Salt and
Verde rivers. with n reservoir on Salt
river operated in conjunction With the
Verde. the waters of Salt river being
held in the reservoir as long as the
waters Of the Verde are sufficient to
supply demands. If the flood waters
Of the Verde IRE to be stored and used
independent Of Salt river they will not
be available for this use, and the ma
nipul3tion Of Salt river reservoir viii
De radically different. Under these con-
GitiCns the draft on the reservoir be-
comes constant the year round: the re
Quirement for storage is lessened, and
the irrigation duty of Salt river alone
is of course much less. Our records in
dicate that a duty CT about $500
acre-feet can be depended upon by
using the rest of our storage capacity
fer reserve storage.
PLANS FOR THE DAM.
The gorge on Salt river is an espe-
cialiy favorable site for a masonry
dam, the most permanent, conservative
and secure form Of construction for y
high dam that is known to engineering
science. The formation is sedimentary.
with the strata inclined to an angle OF
about 80 degrees to the horizontal. dip
ping toward the reservoir most ia
Vorable condition for retaining stored
waters and for the stability Of the
dam. The foundation and abutment of
hard, tough, fine-grained sandstone are
all that could be desired. The building
stone, &C The same material is at hand.
and above the site. AS elsewhere SET
forth Sood Portland cement can be
made near the site. Sand for mortar
can be obtained from the river bed. but
will have 10 be washed and screened.
and 1t is thought that the best plan will
be to manufacture sand by crushing
quartZite. which occurs il abundance
near the site. This will provide an
ideal sand and as power is abundant its
cost viii not be great.
The dam must be so designed and
constructed as 10 be safe from destruc-
ton by any or all of the forces acting
upon it. 1t is possible for a masonry
dam to fall in any one of three ways:
/. BY Overturning.
,. By sliding on the base, or on any
/ horizontal joint.
| 3. BY crushing it's foundation or ma
/ sorry near the base.
\ factor CT safety Of at least two is
/ secured against oVerturning by so de-
! signing the dam that under all condi-
| tons the resultant of all the forces act
| ing will fall within the middle third OF
any horizontal joint. This also elini-
mates the possibility CT any tensile
strains in the masonry, a very desir-
able result. The same condition also
/ secures safety against sliding, which
/ is insured in a still greater degree by
constructing the masonry of random
rubble, and by the use of hydraulic
mortar, bonding it together and to its
| base, so that it becomes a true mono
/ Iith-a part of the solid rock to which
it is firmly joined. Under these condi-
tons the structure cannot slide with
/ out shearing the masonry which pro
Vides a large margin of safety. In adj
ditiOn to these precautions the dan
planned is to be built in the form of g
circular arch, which greatly increases
its safety against both sliding ant
overturning. In fact, neither can occur
without overcoming the gravity ant
cohesion of the masonry, and alsC
crushing the masonry or abutments
The total factor of safety against fail
ure by the first and second method:
cannot be exactly known. but it is un.
questionably very great. The thirt
method. that OF the crushing of tn
masonry. is not affected by the curved
plan, and there is room for considerable
( differ of opinion as to what ar,
safe limits Of pressure. The best guide
when intelligently followed, is the eX
perfence of the past. The following
IL bic gives pressures in some existing
structures:
/ PREssURES ON MASONRY IN En-
ISTING STRUCTURES.
Bridge Bont-y-Prydd. Wales; ma
terial. limestone rubble. lime, mortar