The Roanoke times. [volume] (Roanoke, Va.) 1890-1895, 1891-10-22
THE lMTERcEPToR.
Mr. Hering's Reasons For its
Recommendation.

& III f.
of the largo storm water interceptor.
ROANOKE, VA, April Is, 1891.
To the Chairman of Sewerage Commit
tee, Roanoke, Va.
DEAR Sh:-The following prelimi-
mary. report is sent to you concerning
the design for system of sewerage in
the central part of the city, some sewers
OF which you contemplate building this
year. j regret that this preliminary, as
well as the final, report is DELAYED be-
yond what expected. The insufficient
information held me back for o long
time, and then other matters had
crowded in. The design is. moreover,
, one which requires great doal of study,
as 1T is by no means simple. Not only
the present must be provided for ccono-
mically, but the works must DO so ar
ranged that the future additions will
also be economical.
Tho most important matter to be con-
sidered was the removal of tho storm
water from the city. 1t presented the
key to the treatment of the sewage
question and therefore had to BIO CON
sidered first. The main part of the
city lies quite low, some Of 1t below
the Roanoke river.
The natural outlet for the creeks
passing through the city is Tinker
OtSChS OhO ulIlO OClOWs On0rlHp DuG q
very light slope to the sewers Before
q city was built on tho ground the sur,
face was porous and covered with vege-i
tation. Comparatively little water,
therefore, accumulated in the creeks
during the short time of heavy showers
to flood the territory. AS tho surface
became more impervious through build
ings and pavements, change took
place. The rainwater now runs off
quickly in the lower channels and accu-
mulates in large quantities before
tho rain has ceased. This increase will
continue in proportion to the growth of
the city. In cities like philadelphia,
where probably less than a five foot
sewer might once have answered in
certain depression, twenty foot sewer
is now needed to carry off tho storm
water from the same area.
We have at the present day enough
information to proportion the sizes of
sewers with sufficient accuracy for all
ordinary purposes. TO do this, we must
know the greatest rainfall, the proper
ton which runs off and tho greatest
accumulation a any moment.
Regarding the greatest rainfalls, /
append the following table, which l
have compiled from the best data avail
able. For future constructions, (which
Will become necessary TO intercept the
rainwater, it would be an economical
matter for you to have rainfall observa-
'tions within your own city, showing the
greatest intensity of the storm. l
would recommend to you that the neces-
sary instruments be obtained for this
purpose.
OFrom the data in the above mentioned
/ table and the relation of the topography
Of Roanoke to that of other localities, /
a OF
rainfall at the rate of three inches per
hour is necessary.
Using Burkli-Ziegler's formula for
determining the reduction of this
amount in accordance with the size,
slope and character of the area, we
obtain the best available information
for ascertaining The proportion OF water
running off and its accumulation at any
moment, and which should be provided
for in the sewers and drains. The nee.
essary tables for these quantities will
he given in the final report.
The water which will be shed from
the natural drainage area, upon which
most of the city is now located is too
great, when the surface is paved and
rooted in, to be made to pass down the
bed Of Lick run without mourning a
very large expense at present. For
tunately it has been found practicable
to intercept the stormwater all around
the central and low part OF the city and
to carry it directly into the Roanoke
river on one side and into Tinker crock
on the other, thus preventing its &C
cumulation where it already gives
trouble. Tho remaining area. Which
cannot be intercepted, is sufficiently re-
duced in size, so that in the future the
water from the heaviest showers can be
economically carried down the present
channel OF Lick run.
At the present time it is necessary to
build only one of the aforementioned
interceptors, namely, that which pre-
vents the wafer of Trout run from
passing through the city, and discharges
It into the Roanoke River instead.
Tbe.relief given by it will be suffl-
cient until the valley of Lick run. or
the upper part of the valley of Tout
many years. The accompanying plan
shows tho position of the intorceptor,
according to Mr.. Dunlap's surveys,
from Trout run to the river. 1t pre-.
vents all water west of it from passing
through the city, and will discharge its
waite: freely into the river when its
height is fourteen feet above low water,
or 9nS feet above tide.
When the river reaches greater ele-
walton, which I am informed it seldom
does, it then becomes necessary to shut
down gates provided for the purpose. to
prevent tho water from flowing into
Trout run. When the gates are down
the interceptor can no gradually emp
tied through the relief sewer at Taze-
we'll street. Should it rain when the
river stands over fourteen feet above
low water there will be then sufficient
stoI age capacity in the interceptor for