Los Angeles daily herald., 1888-07-30
LETTERS FROM THE PEOPLE.

II hOM L GO1 hEs
The tenor of communications appearing in
this column is not necessarily endorsed by the
editors of the HERALD. The writer who desires
screed with his full name, not necessarily for
publication but as guarantee of good faith.l
The OutfaIl Sewer.
EDITORS HERALD A plan for an
outfall sewer has been lately laid
for adoption before the Council of the
City of Los Angeles, by the City Sur
veyor, and this plan is so defec-
tive in design that feel it duty to di-
rect public attention to it. ! do not write
in spirit of carping.criticism. do not
wish to criticise another engineers work,
but in justice to the public interests OF
this rapidly growing city, feel bound to
warn the public and the City Council
against the construction of sewer which
in its very design carries its own destruc-
ton.
A defective outfall sewer will give
bad reputation to the whole sewerage of
the city, and initiate against the claims
of Los Angeles as health resort.
In his report on the outfall sewer the
City Surveyor states that "the sewer will
discharge %, 100000 gallons in twenty
four hours" One section OF the sewer,
having length of over one and three
quarter miles, is egg-shaped, being 2
feet inches wide, by feet inches
high, and it's mean velocity is 6-10 feet
per second. This sewer is to be con-
structed of brick. In all properly de-
signed brick sewers the mean velocity is
kept we'll below five feet per second.
Rankine an authority, who is followed
by Baldwin Latham, another authority,
states that the velocity in sewer should
mot be more than four feet and one-half
per second"
Trautwine states that a velocity of
"about feet per second is as great as
can be adopted in practice" to prevent
the lower parts of the sewers from wear
ing away too rapidly by the debris car
ried along by the water. could cite
numbers of other hydraulic engineers to
the same effect, but refrain from doing
so, as 1 do not want to make this letter
too long and tedious. would remind
the readers of this letter that the bricks
referred to by the authorities quoted are
good, sound, well-burnt bricks. 1t is
we'll known that bricks suitable for sewer
construction, especially in sewers having
a high velocity, are not manufactured
in Los Angeles and its vicinity.
We must accept facts, and the facts are,
that good brick for sewer construction
are not manufactured here, and that
with good bricks the maximum velocity
allowed in a sewer, according to the rec
ognized authorities, is five feet per Sec
ond.
In the face of all this we have design
for the outfall sewer of this city SUBJ
mitted for adoption, said sewer to have
velocity of six and six-tenths feet per
second and to be built of the soft, porous
brick of Los Angeles.
In the design OF the former City Sur
veyor, Eaton, which design has been al
ready adopted by both the former and
present Councils. he has limited the We
locity of the outfall sewer to four feet per
second. He acknowledges the fact, that
to ensure permanence in the sewer four
feet per second should be the maximum
velocity. With velocity of four feet
per second the sewer, under the usual
conditions, may be regarded as perma-
nent structure. But can the sewer be re-
garded as safe structure when it's velo
city is increased from to 6-10 feet per
second? do not believe so.
To the reader not acquainted with
hydraulic engineering, it may appear
that with the increase of velocity from A
to 66-10 feet per second, that the increase
in the abraiding or wearing power of the
current is in the same proportion. Such
however, is not the case. The abraiding
power increases much faster than the
velocity. The abraiding power is as the
square of the velocity. For instance, in
two sewers having respectively velocities
of 6 6-10 and feet per second, the wearing
power will be as the squares of the
velocities, that is, as 43 56-100 to 16 or as
2 7-10 to l, so that the sewer with
ye,,ccoity of 6-10 feet per second will be
subjected 70 2 7-10 times, that is about
times the wear and tear of the same
sewer with a velocity Of 4 feet per
second.
Hydraulic miners are well aware of
the destructive effect of. high velocities,
and an experienced hydraulic miner, ac-
customed to the abralding and destruc-
tive power of water, at hicn veloeities.
would place little faith for utility or per
manence in q sewer having velocity of
, o.IO feet per second, and built of the in
ferior brick of Los Angeles.
The reply to this will probably be,
that in the separate system of sewerage
very little sand or silt will be delivered
into the sewers. This no doubt is true
for small area, but it does not hold
good in this instance, for the reason that
this sewer is to receiye the drainage OF
over 3.3 square miles, and however care
fully the house connections are made, it is
reasonable to believe that from such an
extensive drainage area a large amount
of silt will be carried to the outfall sewer.
In addition to broken glass, crockery and
other hard substances are frequently car
ried into the sewers through the house
connections. These substances in addi.
ton to the sand and silt will, with the
high velocity, act as triturating materials
to wear away the invent Of the sewer and
cause its destruction.
| Mr.. Lambie's sewer is intended to flow
full bore and any obstruction to its flow
will place it under pressure and cause
flooding above the obstruction. Such
flooding may entail the payment oi
heavy damages by the city.
Should the sewer cave in or be
preached III any part there would be
great difficulty and expense in carrying
out repairs in water having such veloc-
ity as 6-10 feet per second.
In the adopted design the outfall sewer
flows only two-thirds of it's full depth,
/ and aho,11d H. upt Ohatructod from on "