Sacramento daily record-union. [volume] (Sacramento [Calif.]) 1875-1891, 1880-03-13

from which only comparatively small por
ton of the top gravel has been removed.
Below San Juan the gravel body has q sur
face width of over 600 feet and is. say, lao
feet deep. From Badger Hill to Bloomfield
it is for the greater portion very much
wider and deeper At Columbia Hill its
surface width varies from 5000 or 4, 600 to
s. 600 feet, and is from 800 to 600 feet deep.
The gravel at Lake City is probably
300 or 400 feet deep. At North Bloomfield
it is opened to the bedrock, showing depth
of more than 500 feet. Roughly estimating
the average width of the remaining gravel
range at 400 yards, and after allowing for the
portion worked off, placing its average depth
at 20 yards, the SUN is an average of 50,000,-
600 yards per mile, or for II miles say 100, 600,
600 yards. There are, so far as is known, nc
means of estimating the contents of other
gravel deposits in the drainage basin Of tue
Sacramento, nor is it necessary for the pur-
poses of this report that this amount be now
known. What is fairly known is sufficient
to justify conclusion"
The preceding description enables Us To
forecast with certainty, In every respect but
time the disasters which impend over the
yalleys and their water courses. The great
gravel deposits on the tanks Of the Sierra
Nevada occupy the channels of an ancient
drainage system, which was obliterated by
an enormous movement Of gravel and
boulders brought from higher regions, per-
haps, by glacial action. New drainage lines
were in time eXcavated by erosion, and these,
In turn, are now undergoing a process of OBJ
liberation which, if less magnificent in the
scale Of movement of material than the
ancient natural action, is no less certain in
Its results.
1t is hardly necessary here to say anything
as to the probable alignment of the third and
last drainage system which will replace that
which now exists 1t is sufficient to appre-
ciate that the result, be what it may, viii
bring disaster to a large portion of the State
STORAGE or MINING DETRITUs
II is then Of the first importar ce to know
what can be done to remedy or mitigate these
evils that have been described This descIip'
ton has been directed mainly toward showing
the injuries to which the rivers are exposed
There are other features that are only second
airy in importance. The elevation of the bed
raises the food line and gives to an ordinary
freshet the terrors of food.
The riparian strips of country is constantly
threatened with overflow, ana ali the country
which depends on the rivers for communica-
ton finds The efficiency of navigation i'm
paired
Relief from the certain increase Of evil that
must result from continuance of the pres
ent system of mining can be giveH only by q
restraint of the mining detritus by storing in
places where it can do little harm. This
mass of material must be stored in reservoirs.
the best place for which is in the foothills Of
the Sierra Nevada. The reservoirs must be
made by placing dams across the beds of the
streams into which the material is discharged
from the mines.
MATERIAL FOR DAM CONSTRUCTION.
Well up in the foothills there is an abund-
auce of stone This is the material Of which
to make the dams, which will be mass of
rip-rap, the pieces being of sufficient weight
not to be moved by the freshets. The dam
will therefore not be water-tight, and being
composed of stones without bond, we are en-
abled to found it on the gravel without the
necessity of going to bedrock below. 1t is,
therefore, an obstruction rather than dam.
The slopes of the mass will depend upon the
size of the material With large stones Of
several tons weight the lower slope may be
one base. The only disaster that can come
to such structure is settlement If it should
be undermined at the foot of the slopes, it
will settle, and can be restored by the addi-
ton of stone. The construction is mex
pensive, involving no skilled labor.
Now suppose such an obstruction placed
across the bed of the Yuba, the storage ca
pacity will depend upon the slope the ma
terial takes under the action of the freshets.
The slope of the detritus now in the bed at
this point, as it was left by last winters
freshet. is about % feet to the mile. II we
assume this as the slope when the reservoir is
full, the estimate of the storage, based upon
the surveys of the State Engineers, show that
a. hight of one or more obstruction, making
total of 30 feet, placed just above Deer creek
would hold back about thirty million cubic
yards. Taking the slope of 10 feet to the
mile, the same obstruction would hold back
seven and a half million yards.
If you suppose the material mined on the
Yuba to be stored, it would not be two years
before the larger capacity here mentioned
would be exhausted.
1t cannot be expected, however. that all
the detritus will be stored. The slickens and
some proportion of the sand will escape.
What that proportion may be, experience
must determine. We can safely say that
very large proportion will be retained and
that in this respect, the condition will be i'm
proved.
When the necessity for more storage APP
proaches, let us suppose another dam built of
suitable hight placed further up stream, and
so on in succession as may prove to be peces-
sary. The width of the bed of the Yuba at
the dam site is 800 feet. There is deposit
in the bed of 80 feet of sand, gravel and
stones. The side slopes Of the mountains rise
to hight of perhaps 1,500 feet, and have an
inclination of So to the horizon,
The base of the first dam is 800 feet. Fifty
feet higher the width of TIE valley will be
40 feet, and each succeeding hight of 80 feet
would widen the stream 40 feet. The hight
that it may be prudent to give to these dams
depends so much on the material and circum-
stances in each case that it must be left for
future consideration.
The following table gives the storage Ca
pacity for different nights on the assumption
that the material takes a slope of ten feet to
the mile. The quantities in this table are
used as a basis for an approximate estimate:
Table showing the quantities of material in dams
and quantity that can be impounded at different
nights, the present width of bed being assumed at
300 feet and side slopes at 35 degrees: