The record-union., 1893-09-19

and had engaged NJ eSSrS. StrelQengef anu
Won Geldern, civil engineers, to pass
upon the sufficiency OF the restraining
works proposed to be erected by the
miners applying for permission to mine.
The reports are as follows:
YUBA CANAL COMPANY.
SAN FRANCISCO, Sept l, 1898.
Mr.. Robert T. DeULln. AttOyaey-dt Lar,
Anti Debris association = DEAR SIR:
Having been called upon by you to make
certain examinations Of a technical char
acter Of the petition of the Eureka Lake
and Yuba Canal Company Consolidated,
to operate certain mining land in Nevada
County, Cal, hydraulically, we beg leave
TO submit the following report:
The petitioners propose to wash 5.25
acres Of placer mining land situated at
Columbia Hill.
The hight of the bank, it is claimed,
ranges from 80 10 4S feet, with an average
hight of 40 feet from bedrock to surface.
with covering Of from five to six feet OF
1oam, and mixture Of sand and Tree
gravel thence to bedrock, with little or
no pipe clay. The gravel is very fine and
we'll washed.
The outlet or drainage OF said land is
into the head of Shady Creek, and thence
into the South Yuba River, a distance OF
about fourteen miles.
1t is proposed to use 400 24-hOur min
ers' inches of water under 75-foot pres
sure.
The amount of material to be handled
is placed at $40 cubic yards of gravel In
each twenty-foUr hours, or 151 cubic
yards per hour.
AS an impounding reservoir it is pro-
posed to use an old hydraulic pit, formed
by the closing of the Lewis cat, by dam
600 feet long. Into this basin tailings
H1afol1a6 a g tho
filling continued the dam was extended
along point of unwOrked ground.
The present water area is 25.9 acres with
a water shed of I53 acres-the area Of the
old diggings. The water spreads over
this area in thin sheet, being thirteen
inches deep at the waterways, and eX-
tending southeasterly 600 feet.
1t is claimed that there is probably not
over 500 Neutrality-suspicious. inches of
water at any time in the reservoir.
The sides of the settling basin are
bordered by sand and gravel; to the south
it extends to the high bedrock, distance
OF $50 TO 800 feet the gravel lying on a
grade of six feet in 100 feet horizontal.
The dam across Lewis cut was built of
logs, 80 to 40 feet long, forming crib
bing within which the tops and branches
OF the trees were laid and well packed
with earth and ground. The dam at
Lewis cut shows a perpendicular
wall OF timber 10 feet high. The dam
was extended along ledge OF unwOrked
ground, 217 feet, making total length of
dam of 337 feet. Along this ridge q gravel
wall was built with brush. placed on the
outer toe, two to three feet thick, the levee
being also extended over the timber dam.
Along the water line on the inner slope
pine boughs were placed, to resist the ac-
ton of any waves that might arise.
A cross-section of the timber dam
shows the levee to be 2.S feet wide on top,
% above the Water-line when in opera
tion, and 2.3 above the deposited sedi-
ment, and nine feet thick at the water
line.
The wasteway is built of plank eight
feet wide, 3.S feet high at the water edge,
3.6feet long, and four feet wide atIthe dis
charge, and extending 24 feet from the
dam.
With an area of .25 acres, and estimat-
ing the average depth at % feet, will give
Oil ,94S cubic yards to be washed. 1t is
assumed that IS per cent. Of the bank will
be slickens, and with that assumption the
settling basin is calculated to be covered
1.30 feet deep.
There is no stream or natural water in
said pit other than the rainfall on the sur
face, and there is no water to carry off the
debris when the water is shut off at the
head of the supply-pipe.
All debris when deposited in the set
Ting pool will be permanently at rest
when the water is drawn off from the res
ervoir.
San ample waste weir is the safety of a
reservoir embankment."
1.-The outside slope of an earth embank-
ment is the weakest part, and if flood
overtops the embankment and reaches
the outer slope it will be cut away like a
bank of snow before Jet of steam.''
Acting upon these words Of sound ad-
vice, we begin in examining the waste
weir question in reference to the proposed
settling basin for hydraulic mining de-
tritus, and find:
That there is discrepancy between the
drawings accompanying the petition and
the text of the petition itself. The draw
ing shows two waSte-WayS, while only
one is mentioned in the petition.
Neither are there any provisions made
to prevent the water from undermining
or washing out the waste weir, nor for
raising the outfall proportionately as the
reservoir fills with debris. And again,
the waste weir, as proposed, lacks the re-
quired width TO provide for the simulta-
neous discharge of fume and storm wa
ters at low depth on overfall.
Although the sections a, B and C D
shown on the maps were taken in the
angles of the proposed levee, and for this
reason distorted, giving Halter slopes and
greater Jhicknesses than normal Sec
tion would show, yet, even with this ex-
aggeration, the slopes assumed are en-
tirely too steep for the intended gravel
embankment And then again, the alb
sence of q bernie on top of the crib and
in front of the gravel levee adds another
element of weakness to the embankment.
There is a discrepancy between the
first statement, that the hight of the
bank to be mined ranges from 80 to Is
feet, with an eyerage of 10 feet from bed
rock to surface; and the second state
ment, 1.-THE ground proposed TO be washed
contains 5.25 acres, estimating the average
depth at % feet.
Adopting the first statement for oul
calculation we obtain 33S, 500 cubic yards
of detritus as against 2II, $50 cubic yards