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‛།། ༄། །
I PUBLIC RECORD OFFICE
Reference:
C.O. 882
4PUBLIC RECORD OFFICE, LONDON
ALLY WITHOUT PERMISSION OF THE BE REPRODUCED PHOTOGRAPHIC- COPYRIGHT PHOTOGRAPH~~~NOT TO
Special
mechanism
ur systems
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*
house, as well as in the street, the evils just described have undoubtedly occurred, though on the whole, in the majority of cases it may safely be asserted, that improvement of health, often very marked, has resulted from the execution of drainage works.
131. Methods and appliances are kuown, and have stood the test of experience, whereby the danger in question may be wholly obviated. They are neither expensive nor not requisite. complicated, and require little or no special mechanism, but only the skilful application of certain principles to the use of well-known and generally available materials and appliances, coupled with good workmanship.
General prio- riples guiding construction
of sewers.
Deposit in all cases to be prevented.
""
132. The general principles guiding the construction of both house drains and sewers are: first, they must have such proportions and such fall or gradient as will produce a If the level of current in them sufficient to prevent the deposition of suspended matter. the outfall is too high to admit of a natural fall adequate to produce this velocity, then the sewage must either be conducted to some lower point which will admit of sufficient flushing must be fall, from which it must be raised to the outfall by pumping, or “ resorted to. This expedient depends upon the principle that the gradients or slope of Permanent the channels being the same, large volumes of fluid flow faster than small.* deposit may therefore in some cases be prevented by artificially augmenting the natural stream from time to time, thereby increasing the velocity, so as to sweep away sediment. This operation is known as flushing. The selection of the method to be employed in any given case must depend on circumstances.
133. Whatever be the plan adopted, it is essential that no deposit requiring occasional hand removal, should take place in sewer or house drain, for if it does, the principles laid Hand removal down in paragraph 124 are violated. The cost of hand-cleansing is great, and from a purely economical point of view, it will be cheaper to construct works so as to obviate any necessity for it.
costly.
Ventilation, disconnexion, and trapping.
Importance of proper bouse draina. 'Their imper- fection is the cause of ob. jections to
water carriage. Failure of drainage pro-
jects may be traced to de- fective house
drainage.
134. Secondly, it is necessary that both sewers and drains be ventilated, so as to prevent accumulation of foul gas within them, and further, that house drains be 80 trapped and disconnected, that gas cannot enter the dwelling through them. Experience shows that it is practically impossible to confine sewer gas, even water traps cannot be relied on to prevent its passage, for the water which forms the obstruction frequently. escapes, either by evaporation, or by some fragment of cloth forming a syphon, and tbus emptying the trap. Indeed it has been proved that sewer gas will actually pass through Hence sewers the water in a trap, being absorbed at one side and given off at the other, require ventilating orifices, so that gas may more easily escape in the streets, where it is comparatively harmless, on account of excessive diffusion, than in the house, where, owing to confinement, it is positively dangerous. For the same reason the bouse drains require ventilation and disconnexion. For ventilation, an inlet as well as an outlet is required. Therefore, immediately on the house side of the trap, an opening to the air should be provided, whereby not only fresh air may enter, but also any gas which passes the trap may escape. The provision of a free opening to the air, on the house side of the trap, is called "disconnexion." In a complete and well-constructed system of drainage there will be little sewer gas. If the whole of the works, in the house as well as in the street, are properly made, so as absolutely to prevent deposit, the emanations from these various openings will be innocuous, if not imperceptible. As no accumulation takes place, all being removed before putrefaction commences, little effluvium will be evolved, and that of a harmless nature.
135. The importance of proper house drains is paramount. They are the first link in the chain without which the remainder is comparatively useless. The failures of drainage projects to realise the advantages expected from them, and the greater part of the objections raised against the system of water carriage, may be traced to the neglect of the internal drains and appliances within the house.
136. Municipal bodies, whilst they have constructed admirable street sewers, have shrunk from the expense and interference with private property which the improvement of house drains involves. They have been connected to the sewers as they were, or their construction has been left to the proprietor, directed only by the builder and the plumber, and having been badly designed and worse executed, deposit has taken place in them. The emanations from these putrid accumulations escape into the house, and the sub-oil is polluted by infiltration from leaky pipes. The sewage, instead of coming out fresh from the house, oozes slowly through the drains, and enters the sewer in an already putrid condition. Therefore noxious and dangerous gases are given off in the
* This principle is not mathematically correct. Strictly speaking the velocity varies as the square root of the hydraulic men depth which is the sectional area of the stream divided by the length, the border of the channel wetted. For the purpose of illustration, the statement is sufficiently accurate,
sewer, escaping by the ventilating orifices or returning through the untrapped drains to the dwelling.
The
137. Open channels instead of pipes have been advocated for house drains, because Open channels. they cannot convey gas, and can be more easily freed from obstruction. Unfortunately they are rarely applicable. It is not possible to carry an open drain through a house, as will often be necessary; open channels like pipes, to produce a current, must have a certain fall, hence in level ground they must be inconveniently deep at one end. Their application, even if desirable for slop water, will be limited. By proper construction most, if not all, their advantages can be realised by the proper use of pipes, and at no greater cost. conveyance of sewage, even when free from fæcal matter, by open channels by the side of the street, would hardly be satisfactory, unless there were an almost unlimited supply of water for its dilution, a condition rarely found, except perhaps in some Swiss town, having The question of the admission or a glacier or a snow-capped mountain close at hand. exclusion of the rainfall from the sewers depends chiefly on local circumstances. The principal argument for its admission is that downpours of rain clean the sewers. worthless; for, firstly, there should be no deposit, and if there were, some regular means should be contrived for its removal, and it should not be left to accumulate till rain falls, which may not happen for several months, especially in the tropics. The admission of rainfall greatly increases the difficulty of disposing of sewage by application to the land, for it augments the volume to be dealt with in an irregular manner, and at uncertain intervals, and the augmentation takes place at the times when it is most inconvenient, during wet weather when the land requires no moisture. With this question we have little or nothing to do.
This is
suitable by
138. I hope to show that the existing sewers of Victoria may be improved so as to Existing sewers fit them for the conveyance of sewage, besides serving to carry the storm water to the may be made harbour, as they do at present, and further, that the sewage, during dry weather, may modification. be diverted from their lower extremities, and carried to some distant outfall, where it will
be innocuous.
earth system.
necessity for
139. I will now proceed to the general discussion of the dry-earth system, examining Objects of dry its general objects and effects, leaving its special application to Hong Kong to be treated it does not do under the head of scavenging. I propose to show that the dry-earth system does not away with affect a complete solution of the problem of sanitation, and that it does not obviate the drains. necessity for drainage.
140. Complete information on this subject will be found in the Minute of the Army Information Sanitation Committee, dated 19th October 1881, on the comparative advantages as system. regards health, cost, and convenience of the dry-earth and water-sewage systems for cleansing barracks and hospitals, and I shall freely quote from it such passages as seem applicable to the requirements of a city.
on dry-earth
141. The dry-earth system is based on the fact that dry humus (garden soil), mixed Principle of
dry-earth with human excreta renders them inodorous, to some extent innocuous, enabling the system. inixture to be kept for considerable periods near habitations, without danger to health or causing a nuisance. In a previous minute on the same subject quoted by them, in the minute referred to, the Commissioners thus define a dry-earth latrine: "This com- prehends the introduction of special arrangements into latrines, including suitable "vessels, and some mechanical contrivance by which a sufficiency of dry humus (garden soil)--not sand, which is of no use, nor clay or other tenacious material-is discharged " over the excreta each time the latrine is used by each man."
affect
for drainage
use of dry- earth systemu.
142. After stating that no complaints have been made as regards health, as to either The necasity class of latrines (dry-earth and water), from which we may infer that the dry-earth is not done system satisfactorily performs the work for which it is intended, they proceed to say: away with by "But there are other considerations as to the use of dry-earth latrines which may “the health of barracks and camps injuriously, and which require notice.
"The latrine matter of a barrack is about one part in 190 of the total putrescable Now it is clear that if the latrine matter alone is dealt with, and the other sewage matter of the population, including, of course, that of animals, is left to itself, "serious disease may be the result.
« refuse.
"One advantage of the water conservancy is that it affords an oulet for the entire "barrack sewage. This is not the case with dry-earth conservancy, and it follows that "whichever systein is adopted, the cost of draining the barracks must be incurred. "Absence of drainage is the main cause of unhealthiness of Indian stations; but all, or nearly all, have dry-earth conservancy; and nevertheless all these stations, with incon- "siderable exceptions, have suffered year after year from cholera, and enteric fever. As a matter of fact, it would be safe to state that wherever in India there are dry-earth "latrines these diseases show their presence; and yet this fact affords no argument
R 3797.
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