SEW
417
SEW
as a e P’Pe approximates much more to its surface-velocity,rn asg Cf *p ta ^ n ed by a float, than does the velocity of the wholeMo ■ ,' vater in the sewer approximate to its own surface-
!> 1 j tJ ® v ® ra l experiments in this pipe were also made, to deter-°W i P ro P u lsive force exerted by the water in removingMec e C 6S ’ ani ^ '*■ was iound that quantities of sand, mud, andth e 8 °f brick and stones, were carried from the inlet throughtvi t j l ent * re i en gtb °f tb e pipe, where they were discharged'#Ve r j° ns '^ era ble force, and carried some distance along theeflg °f the original sewer. All these experiments wereMt er d w ' len the pipe was only or less than half-full of^ ie period of year at which the experiments weref <V ,VVas principally during the month of October, and theiti n ln S is the detailed daily account of the depth of water^ 8 pipe :—
t ' 1 er|p tern * 5er 28 and 29. Very wet both days and nights;1 * le n - ' VaS a ^ iin® period 96 hours’continuance of rain, and0„! p ® Was never observed to be more than half-filled.
“ft er ,, er if*- Morning, depth of water in pipe 3 inches ;f-*ct°? n ’ 3e P tb 2 inches.
i and . r 21- Heavy rain all day; depth of water in pipe0 0 indies.
hii n :* er 23. Morning, 3 inches ; afternoon, very heavyQ ct o|| en the pipe filled.
"ft,
0ot°? n ’ *' rom t0 3 inches,
er 24. Morning, depth varied from 2 to 21 inches;
to 2)'* K ' r 2o. During the day, depth of water varied from
“ft
0 M V nches S afternoon from 24 to 3 inches,t-tobe- "". 1
er 26. Morning, depth varied from 4 to 3 inches ;M| i'ee (] un ’ ^"rom 21 inches to 3 inches. During the aboveMioti^' 3 - tbe wea tber was mostly fine. The considerable■^Ses- 113 are ^ ue to f * ie i'™ 03 °f the water being on at the'“ci-s ’ |* ,e sewage at such times is much clearer, as well as, 0 ut ,, in quantity.
V, ber 27. On tlii
this day a storm occurred, which, for a
° ft lie .-
!°s e was very violent; the waters filled the pipe, and
/Ml a * e it 18 inches, but did not reach the top of thele igl lt "* len tbe waters had reached this maximum
3 ntv , tbe y receded
o<2><
utes.
er 28.
to nearly the level of the pipe inDepth during day varied from 3 inches toDepth during day varied from 2 inches to
inches to 24
2. Variation of depth from 2 inches to 2-1
'n ncl ‘es.
2 u c S, ei ' 3 °-
0 U| es.
^ i^che s er -^pf* 1 during day varied from 11 inches toI'f’er 1. Variation of depth from 11
ser ies of experiments was very carefully super-t^'Strppt ^ r - ^ oy ick, Surveyor to the Commission, inl^Qriai ’ Marylebone; the original sewer presenting aap M i n ar ? a °f 15 feet, and having a flat segmental invert!* 8 ’°00 c ' V , ldth > in which deposit accumulated at the rate1 jMr \v ;)s 4 C feet in 31 days. The area draining into thisC- Hn 3-656 acres ; and the number of houses drained,V^'Mu-p 10 ” <be ’ nvev,; °f Ibis sewer, a 15-inch glazedtfM'umr was Hid for a length of 115 feet, and having'‘n tl ° f 1 in 153 -
l'C S ’ Ut "pti * eSe ex P ei 'inients, it appeared that the averagetjij, diiy j Q a bf water was about 5.7 gallons per individual"bth’ . °1-| gallons per house per day; the average
of ": l,ar S e d when there was no rain, and no freshv l| ‘e d a ," ater ’ vvas 44^ gallons per house per diem ; andH.. ii 8 " ben the water was supplied to the houses,5 o
209 gallons per house per day. Thus the mean flow on thedays when water was supplied to the houses by the watercompanies, was nearly 4f times greater than the mean flowon ordinary days, or days when there was no supply.
The annexed table, deduced from those experiments, willgive a correct idea of the several conditions of discharge onordinary and water days :—
Days.
Quality of Flow.
Cubic feetper minute.
Sectionalarea of flowin pipe.
Diameter ofcircles, equalin area to thesectional areaof flow.
f
Least .
1.78
Inches.
3.05
Inches.
2.00
On ordinaryJ
2.10
_
_
Mean .
5.64
8.57
3.4
days. |
Mean Greatest ...
16.90
18.14
4.9
Greatest.
46.50
__
—
(
Least .
1.07
1.66
1.5
On water 1
Mean .
26.46
27.94
6.00
days. 1
Mean Greatest ...
106.00
—
—
Greatest.
150.00
109.79
11.8
The maximum being greater than the minimum, on thewater days 140 times, and on ordinary days 26 times.The experiment was continued for 30 days, 16 of whichwere water days, and the remaining 14 ordinary days, andthe period of the year at which it took place was during themonths of February and March. The leastflow in the abovetable, refers to the least flow which occurred at any one timeduring the range of observations ; the mean least , to theaverage of the lowest discharges of every day ; the mean, tothe average of the mean of all the observations ; so also ofthe greatest and mean greatest.
As an evidence of the false principles on which the oldsystem was based, the same surveyor states that the sectionalarea of the drains in this block of houses, was 596 feet,whereas the sectional area of the outlet sewer was only 15feet, or about one-fortieth the aggregate sectional area ofthe house-drains. He also states, as the result of his experi-ence generally, that blocks of houses drained with 3, 4, 6,and 9-inch pipes, have been more efficiently drained thanunder the old system.
The same opinion, with reference to the size of sewers,was given by Mr. Phillips, also Surveyor to the Metropo-litan Commission and the late Westminster Commission, inhis examination before the Sanitary Commissioners ; but heconsiders a constant supply of water indispensable, if smallersizes be adopted. In answer to the question—
“ Have you at all considered the capacities of sewersnecessary for draining the different areas of ground ?” hereplies, “ Yes ; I have given the subject much attention. Ifthe consideration of the sizes of sewers was confined solelyto the carrying off the water supplied by the several water-companies, then I apprehend that pipes somewhat larger insize than the supply-pipes themselves, would suffice ; butprovision has to be made for receiving and carrying awaythe waters of heavy rains. In London , continuous heavyfalls of rain are not of long duration, lasting seldom morethan from one to four hours. About one-fifth of the quan-tity that falls, is absorbed partly by the dryness of the sur-face of the roofs, the paving, and the ground, and partly bythe porosity of the ground itself. A farther proportion isalso prevented from flowing to the drains and sewers at allby hollows in the surface, and again reascends into the atmo-sphere as vapour. There is also a small quantity that entersinto the composition of animal and vegetable bodies. Thee