The Austin weekly statesman. (Austin, Tex.) 1883-1898, 1891-11-12
IMPORTANT REPORT.
THE FEAR OF INJURIOUS DEPOSITS IN
THE GREAT POND GROUNDLEss.
Engineers Agree That the Accommodations of
sedimennt Will Not Impair the Value
Of The Water POwer-A Com
prensive Review of the Subject.

'"SS0SlihS lne possibility OF
sediment accommodating in the pond to
be created by the dam to such an ex-
tent as to impair its usefulness. Fears
too, have been expressed by many
citizens that such will be the case,
and to set the matter at rest. THE
STATESMAN this morning publishes
the following report.
1t will be observed that the Board
of Public Works have given the sub
ject careful attention and the report
below by Engineer Frizell was made
at the request of the Board.
THE REPORT.
The apprehension appears to be
felt by several members that deposits
will occur in the pond to an extent
sufficient to impair its usefulness, and
that this difficulty may be met by
sluices in the dam.
That much sediment will be depos-
tied in the dam is unquestionable.
The waters of the stream are
heavily charged with sediment in
time OF flood, and the slackening of
the current in passing through
the pond is condition very favorable
to its precipitation.
WILL NOT DO INJURY.
Nevertheless vast accumulation of
sediment can take place without the
slightest degree impairing the value
OF the water power. The pond Gre
ated by the dam is not "a storage
reservoir. The dam is built to create
a waterfall. The pond is only an in
cident Of that waterfall. 1t is to be
used as Il reservoir, only to Il very
limited extent. During low water the
flow Of nights and holidays will be
retained in it for use during working
hours. In extraordinary low water it
is in contemplation to draw upon the
pond as a storage reservoir to the eX-
tent Of five feet. Fight feet is the ut
most limit to which it can be drawn
consistently with arrangements now
in contemplation. These arrange
ments being dictated by consideration
relating to depth of sluices and means
of operating them, depth and
cost OF canal, and general
conformity to the ordinary
methods of supplying water power
we may therefore affirm with entire
confidence that all that part of
the pond lying more than eight feet
below the crest of the dam might be
filled solid without in the least affect
ing the value Of the water power.
WORK or FLOODS.
! Assuming the pond to be filled to
this extent, would the deposit be
likely to 90 on iucrC asing? | answer
confidently, No. The condition which
determines deposits has Disappeared,
J largely in time Of high water, wholly
} in time of great floods. In such Il
food, for instance, as occurred in 1869
the water, as I estimate, would go
sixteen feet over the dam. This would
MAKE 1t tWenty-four feet deep in the
broadcast part of the pond near the
dam, where the pond is some 1900 feet
wide. It's cross section there would
be ., 800 square feet. The natural
| cross section at the site Of the dam, in
such a flood would be %, 7G0 feet. The
velocity in the pond, therefore, would
not be slackened and the
water would be in no condition to pre-
| ciptate sediment.
sLUICES OF No BENEFIT.
/ Granting that accumulatiOns, to an
| injurious extent, might occur, | am
not able to see how sluices could he
expected to remedy that evil. ! will
suppose, for argument, that we have
three sluices, each consisting of a pipe
seven feet two inches in diameter, |
put them at this size, as the gates
would be about as heavy as we could
manage, under a head of sixty feet.
Each gate requiring a dead lift OF
forty tons to raise it.
With full pond these sluices would
discharge 1000 cubt feet per second,
being seven times the low water flow
of the Colorado. They would dis
charge the low water flow of the
stream under head of little over
one foot. How is it proposed to effect
the removal Of deposits by means Of
such sluices? Are they to be opened
while the river is in flood?
They would have no effect, except
in the immediate vicinity Of the dam.
A hundred yards above the dam the
effect would be absolutely null. No
number of such sluices that could be
introduced would have any marked
effect in securing the channel so long
as they did not lower the level Of water
in the pond. The securing action OF
water at any point in the channel de-
ponds solely upon its velocity, and SO
far as the velocity is concerned, it is OF
no consequence whether the water
goes over the dam or under it, so long
as the pond remains full.
NOT TO BE THOUGHT OF.
Is it proposed to draw off the water
and empty the pond? The slightest
consideration will disclose fatal objec-
tions to that method. To empty
the pond with the proposed
system of sluices would re-
quire ten days. TO operate on
the sedimentary accumuIations would
require a period of time which | need
not attempt to specify. TO refill the
pond in ordinary low water would re-
quirc twenty-five days. During all
this time the pump works and all IN
dustrial establishments dependent