778
Drains as
often sources
of nuisance
as sewers.
As to the
outfall
4. All observations made, during my visit, tend to a belief that nuisances are as often, even more often, traceable to drain gulleys and openings as to sewer gulleys or manholes. The drain and sewer gulleys are normally close to each other and the one gets blamed for what is due to the other.
are indeed
5. The gradients of the low-level sewers--those below Queen's Road- low-level and somewhat flat, but not so flat that they could not keep themselves free from deposit if there were a copious flow through them, and if road-detritus and other improper substances were excluded from them. Indeed they do actually keep free from sewage-deposit, properly so called.
sewers- their gra- dients.
The levels of the outfalls are lower than I intended them to be. I proposed that the centre line of the sewer, at its outlet on the Praya, should be at mean sea level, so that each sewer would be only filled to one-half its diameter for one-half of the year and during the remaining half there would be a free and unchecked flow of sewage through it, sufficient to remove any deposit which might precipitate, during the times at which the flow was checked by the rise of the tide.
The following are the levels of the inverts of the sewers at the several outfalls :-
Outfall No.
INSTHIS CO
Centre Line below Mean Sea Level
Locality.
Juvert Level at Outfall (or near it) above Ordnance
Diameter of Pipes in Inches.
in Feet.
Datum.
Belchers Point, French Street,..
Eastern Street, Wing Lok Street,
2.10
15
0.98
1.66
1.67
0.67
15
2.41
0.98
21
1.85
Hillier Street, .
1.71
21
1.12
Queen Victoria Street,
2.43
18
0.52
The levels of
utfalls too Jow, and
ents too
The annexed plans Nos. 1 to 6 show the extent to which the various low-level sewers are tide-locked at mean high-water and mean sea level, lines being drawn to show respectively the distance to which the pipes are entirely filled and half filled by tidal water.
It is but right to say that the outfall sewers laid on the Praya Reclamation are temporary only, pending consolidation of the ground. In one or more cases, a 9′′ pipe receives the flow of one or more 18′′ or 21". This cannot fail to check the flow of sewage, and thus promote deposit. Under these circumstances the low- level sewers cannot be said to have had fair play up to the present, and will not until the Praya Reclamation is finally completed and consolidated.
6. I will freely admit that, were I to design the sewerage system over again, I should make the outfalls more numerous, place them at a higher level and give, if sewer gradi possible, steeper gradients to the low-level sewers. I do not, however, consider that it is necessary to make any alteration at present, certainly not until the Praya Reclamation is completed and consolidated.. The sewers on the New Praya Re- clamation will for the most part surely require re-laying, and when the time comes for so doing, the question may be re-opened. By that time, the effect of copious flushing at low-water will have been settled by experiment.
Flushing the low-level
sewers.
7. As soon as pipes of the full diameter have been laid, temporarily or otherwise, across the Reclamation, the effect of vigorous flushing should be tried. This experi- mencing ment should be made on the sewers along Des Voeux and Connaught Roads running
from the eastward to the outfall at Queen Victoria Street,
l'oint of com-
work.
A flushing tank containing say 3,000 gallons should be constructed beneath the Parade Ground near to the urinal now under construction. This should be filled, daily during the dry season, from a well, or from the sea by pumping. In the case of a well, a centrifugal pump driven by an electric motor would probably be the most economical means of pumping. Possibly the electric motor