SEW
418
SEW
there is the resistance the flow experiences from the frictionof the entire surface, being accelerated or detained in propor-tion as the surface is more or less inclined. To provide forthe discharge of a fall of rain of two inches in depth, hasbeen considered by Mr. Hawksby, C.E., the extreme datumupon which to proportion the capacities of town-sewersgenerally. Now I believe that, practically, the sizes in histable, although they may appear theoretically correct, are(excepting for the smallest sizes) too large for sewers inLondon . It is extremely violent rains alone, that producea depth of two inches per hour, and such rains occur onlyonce in four or five years, if so much. I am of opinion thatit is unnecessary to proportion the sizes of the sewers to meetan extraordinary occurrence that may probably happen onlyonce in so many years. My reason for not fearing any seriousdamage from an excess of rain at remote intervals, beingprovided for in surface - channels, excepting, perhaps, insituations peculiarly liable to inundation, (for instance, at thefoot of a long or steep declivity, or where the waters mayfrom any cause be suddenly congregated at one focus,) is,that I have observed, that in towns entirely destitute ofunderground drains, no such inconvenience is felt as wouldjustify the formation of enormously large sewers, or theexpenditure of large sums of money to provide against it.”
The evidence of Mr. Roe, late chief Surveyor to theMetropolitan Commission, and previously to the Holbornand Finsbury Sewers, will be deemed most valuable, if notconclusive on this subject, both on account of his long expe-rience, his straightforwardness, and unbiassed judgment ;he was also the first to pay attention to the subject, andintroduced many improvements, before it bad become thetopic of general consideration. In his evidence beforethe Sanitary Commission, he states as the result of hisexperience, that a cylindrical sewer, 48 inches in diameter,
with a fall of 1 in 240, is sufficient to drain 10® a sotown-area, allowing for a fall of rain unusually l ar S e ' e3 (fithat in a street 924 feet in length, containing 93 b° 1( , 9 jn
of
an area of 6 acres, 1 rood, 8 poles, a fall of rain
2 inC >
depth, producing 346 cubic feet of water per minj 1 e Jj nJ iti° nrequire a sewer of 2.44 feet capacity, with an 0 f fbof 1 in 480. Allowing further for a supply of vva ^pacWgallons per day to each house, he would add to the ^yjtbof the sewer .16 of a foot, making a total of 2.6 fee ‘ ^ fiverespect to uncovered land, he gives as the resui p 0l )ndmonths’observation, that the greatest amount that w j )0U r,to reach the invert from a fall of rain of J-inch in j 0 d °*averaged 3 cubic feet per acre per minute at the P fropithe greatest flow, and that that period was genera ra inthe greatest to one hour after the heaviest portionhad fallen.' . j ]g fleet
Mr. Roe’s observations on the flow of water in ^ , {g 0 jt'Sewer are of great practical value. This sewer, aS up er ”let into the city, is 12 feet high by 12 feet wide, wi geVf er 3 >ficial area of 120 feet; it receives the discharge of , feet)the total sectional area of which amounts to abou jn
and its inclination varies from 1 inch in 100 f eet grained by2 feet, while some parts are on a level. The area acr es 0it consists of 1,181 acres of town-area, and 2, 0 3 eT at° Tt ?rural district. During the unusually heavy p 1 * atwhich occurred on August 1, 1846, the area o. i^derst 01 ' 1 ^
an
d °°
in July, 1844 W the m = eaS f l - r< f V 06 feet ’ in a heavy 1 "““'an extraordinary ( 4 ,!° area of was f eet V' are*occupied Zs Z ff T’ fa!I of snow in 1841. the **
an area of lo feet 6 ’ W ll e ^ ie ordinary flow does not c
gentleman, are^from 6 ’ Ma< ^ unfJer the directions ofcharge and will ■■ £ au g ,n gs of several sewers undS ’ am *iU give a fair notion of the true state of the e^
Table of Gauging of Sewers.
Run of Water.
Area
No. of
Capacity.
Average
Area
When
Area
During great-
Distance
Height above
Inclination-
drained.
Houses.
common
occu-
Water let
OCCU-
est rain in
from the
Thames high-
run.
pied.
on from
pied.
1846, area
Thames.
water mark.
pipes.
occupied.
Acres.
Feet.
Inches.
Feet.
Inches.
Feet.
Feet.
Chains.
} Inch in 10 feet, a ®?|" tera l3 Inches in 50 feet, c
110
13
3
13.00
120
36
5
100
9.0
0.08
2
0.13
2.50
150
47.0
2.70
69
7.65
1
0.024
0.06
2.10
166
62.0
5 Inches in 100 feet.
5.15
104
9.65
4
0.11
2.70
145
47.0
1.09
49
9.09
...
H
0.33
1.43
265
120.0
0.25
32
...
l
0.04
0.33
157
110.0
1.36
41
7.65
...
n
0.23
1.40
151
46.0
S 2 Inches ’no^ e
( by height of water
2.16
4.16
50
120
7.65
9.65
...
...
i
3
0.034
0.23
1.13
4.17
160
140
51.0
49.0
0.25
19.10
16
482
9.09
9.09
3
0.23
i
0.03
0.30
6,33
155
140
102.0
50.0
5 Inches in 100Jeeb ^
j by height of water
1.00
22
7.65
0.03
1.13
147
47.0
1.36
37
0.05
1.25
149
47.0
1.08
31
...
0.04
. . .
1.20
151
46.0
12 Inches in 10°
5£ Inches in 1°° fe
3.42
65
3.14
0.09
1.60
180
118.0
0.84
40
1.22
0.17
...
1.22
92
48.0
Engine waste water.
In opposition to this evidence, we have the authority ofsuch names as Walker, Cubitt, and Brunei , names whichmay not be passed by unnoticed, although, with the previousstatements before us, it seems somewhat difficult to coincidewith their views. While, however, we pay due deference togentlemen of such high standing in their profession, we must
as Mr. Roe have probably u3
attempt fo slmniT , * Particular ''lass of works.
»>mp llty the question as :
* Alw
not forget that such men
greater experience in this particular c ^ a f® p ossi^ e ' - th^o Hnm rvf In oinanlifw tlio m, nation as much as F e> . e i-
The objection!^ “ le 9 <testiou _ _
!. he ? are unneeeas^i^ a & ainst the old system ore,
detent. Their rr,l ! y ex P ena ive—2n<lSy, that they ^ e f 0 re§ at expense arises from their size. th e