CO882-(3-4) — Page 492

PUBLIC RECORD OFFICE

للسانين

Reference:

CO. 882

ALLY WITHOUT PERMISSION OF THE BE REPRODUCED PHOTOGRAPHIC-

COPYRIGHT PHOTOGRAPH-NOT TO

PUBLIC RECORD OFFICE, LONDON

Method of

laying concrete

to facili-

tate repairs.

A hard surface

which finds its way into the

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195. The execution of repairs is difficult, for the new concrete joins but indifferently with the old. This may be to some extent obviated by marking off the surface by When a repair to gas or water- means of grooves into rectangles about one foot square. pipes is necessary, one or more of these squares can be broken up and relaid. When the work is finished, the regular boundaries of the old and new work prevents its having patchy appearance. The junction of the new with the old is facilitated, for the joints are vertical, or may be undercut, thus preventing separation of the two.

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196. The provision of a hard surface for streets is most desirable, for it will greatly reduces the silt diminish the amount of silt and sand washed into the sewers during the rain. It does away with the necessity for catch-pits at the gulley-holes. These are a common source of nuisance on account of the organic matter deposited in them, along with the sand and mud washed from the road.

drains.

uitfalls of present sewers cause a Dui-

Bance.

An outfall ren note from the town is the

"

PART II. SECTION 4. STREET SEWERS.

197. The outfalls of the present sewers are through the Praya wall into the harbour. Here the tidal current is weak at all times. No steps have been taken to carry out the The inverts of sewage beyond and below low-water mark, or to reach the tidal current. the sewer outlets are usually at, or near the level, of low-water ordinary springs. Hence on a warm still day, at low water, the stench along the Praya is most offensive. At low water also, the huge mouths of the sewer are uncovered, and exposed to the full force of the northerly winds, and at such times it is probable that the pressure of the wind forces the sewer gas up them, which makes its escape by gulley-holes, and no doubt also, by the untrapped house drains.

198. The complete remedy for the nuisance caused by the discharge of sewage in front of the Praya wall, is to construct an intercepting sewer, collecting the sewage, and remedy for this conveying it to some distant point, where it may be discharged without causing

inconvenience.

nuisance.

Land for irrigation does not exist. Sea outfall.

Study of tidal

currents.

Results of current obser- vations.

The outfall Newer a minor improvement

to others.

199. A glance at the map of the island, will show that, there is no suitable land for the utilisation or purification of sewage. This question, therefore, needs no discussion, and we may assume that the sea must receive the sewage.

200. The first step towards the solution of the problem of interception is the determi- nution of the position of the outfall. To do this a careful study of the tidal currents of the harbour must be made. The direction of the currents at different states of the Inasmuch as the tides differ tide and different points must be carefully observed. greatly in their character, summer and winter, the day tide being the greatest in one instance, the night in the other, and as observations can only be made in the day time, it Hence, it was is absolutely necessary that sets of experiments be made at both seasons. impossible for me to obtain complete data during my stay in Hong Kong. I thought it desirable, however, to make some observations which night at least indicate the direction of future experiments. Thanks to Captain Carpenter, R.N., of H.M.'s survey-vessel "Magpie," who placed the able services of Lieutenant Frederick, R.N., at my disposal for the purpose, I was enabled to collect the data which are given in the Appendix.

201. The results of these experiments are briefly as follows:-

(1.) That no material benefit will ensue from the concentration of the sewage at outfalls, anywhere within the length of the town.

(2.) That towards the eastern extremity of the town there is but little hope of finding a satisfactory outlet.

(3.) The experiments, so far as they go, tend to show that the most desirable position for the outfall will be in Sulphur Channel, which divides Green Island from the main island. Objects put in at this point do not seem, at any state of the tide, to be carried immediately in front of the city.

202. Until the position of the outfall is finally determined, it is premature to discuss the construction of an intercepting sewer. There are many other improvements in the in comparison general drainage system which can meanwhile be made, which will be on the whole more beneficial to the general health of the community. An intercepting sewer is but the last step in the process of filth removal. Unless provision be made for removal from the house and the street, it will be of little use. It will abate a local nuisance, that is all.

203. Owing to the level nature of the land close to the foreshore the whole of the sewage Never- cannot be converted to any one outfall by gravitation. The fall is insufficient.

Whole of

sewage cannot

be removed

to outfall by

gravitation

only,

• Witness Brighton.

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theless, it is possible to intercept the sewage of by far the greater part of the town, that above Queen's Road, and carry it off by gravitation. That of the remaining portions of the town must, either be pumped into the intercepting sewer, or discharged into the harbour by improved outlets. Their effluent will be relatively small, so that not much nuisance will be caused by this arrangement.

rainfall cannot

204. It is out of the question to attempt to make an intercepting sewer to carry off the The whole

To remove the quantity of be removed in whole of the rainfall; 14 inches have fallen in one day. water that then fell on Victoria and the slopes above it in 24 hours, would require a pipe intercepting at least 12 feet in diameter. The intercepting sewer, therefore, should be constructed to deal with the dry-weather flow or true sewage only, leaving storm water to find its way to the sea as at present.

sewer.

unobjection-

205. As it does not seem expedient to utilize the sewage by irrigation, a certain Partial dilation amount of dilution by rainwater up to the capacity of the intercepting sewer is harmless. by rain water This permits the use of the present sewers to be continued for the conveyance of sewage ble.

Arrangements as well as rainwater, some minor improvements only being required. Thus the expense of for intercepting a complete duplicate system of sewers proper will be avoided. The dry-weather flow sewage. can be diverted at their lower end by means of a tumbling bay or low weir, constructed across them as shown in Figs. 45, 46, 47, 48, Sheet VI. The height of the weir must be so calculated as to turn aside the whole dry-weather flow. When the contents of the sewer is augmented by heavy rains it will over-top the weir, and the surplus will pass direct to the harbour. In this case the effluent will be so diluted as to be inoffensive.

interception

below low-

206. The arrangement of the diverting weir, just described, would serve to carry off Temporary the summer flow of a sewer through a small cast-iron pipe, which could be extended sewage to below low-water mark, an arrangement which might serve as a temporary, or partial conduct it out

The effluent of several drains might water mark, means of abating the nuisance in the harbour. easily be united and carried out below low-water mark by a single pipe. The generation so as to abate

in the large sewers at their lower ends, from matter deposited there, would by this special nu gas means be prevented.

of

BATIOO

ocive scwage.

207. The upper portions of the existing sewers, those above Queen's Road, are, thanks Preparation to their great fall, rather than to their design and construction, almost wholly free from of drains to re deposit. Nevertheless, it would be well to render their inverts watertight, and to accelerate the dry-weather flow through them, by concentrating it in a semicircular tile, laid on the invert. Concrete should be filled in on either side of it, the surface of which should be rendered with cement. This work could be executed in lengths, the flow being temporarily diverted by a trough. See Fig. 38, Sheet IX.

sewers in lower

208. Permanent manholes are much required. At present the street must be broken Manholes up whenever a sewer has to be entered for repairs or inspection.

They should be required. provided at all junctions. As there is so little carriage traffic, they may, in most instances, he made direct over the sewer, thus saving the expense of side entrances.

209. Much inconvenience and expense is caused, by the necessity for cleaning out Deposit in periodically, the portions of the sewers where they cross the low district about Bonham districts. Strand. The deposit in them is due to silt and sand, brought down from the ravines above the city. In one case, that of the large drain running near the Harbour-Master's office, the deposit which takes place therein, is mainly derived from a plot of waste ground in which its intake is situated, and which is used as a rubbish tip. This sewer should be extended above this ground, which should be levelled and laid out for building.

heads of orwert.

210. To remedy the inconvenience caused by the deposition of silt in the sewers, they construction of should be provided at their upper ends with catchpits, in which such substances would capitat be deposited and from which they could be easily removed. These catchpits might be formed by constructing masonry dams across the ravines, and they could be so designed as to promote ventilation also, as will be presently described.

of sowers.

ventilating

drains.

211. The question of the ventilation of sewers is now attracting great attention. Ventilation Loud complaints are made of the stenches which proceed from the ventilating grating. of The real cause of the nuisance may almost invariably be traced to imperfect house nine from drainage, for recent town sewers have been constructed with great skill. The sewage, coming to to owing to deposit and stagnation in imperfect house drains, enters the sowers in a state of found in im active putrefaction, and much gas of an offensive and dangerous character is evolved. perfect house This gas will escape somewhere. The construction of ventilating shafts is but a palliation, not a remedy, of the evil. They merely remove the nuisance a little farther Where the house drains as well as the sewers are thoroughly well constructed, complete removal takes place before putrefaction commences, and little or no gas is evolved. In Chapel Brampton, a village recently drained completely, houses as well as streets, there is no nuisance whatsoever from the ventilating openings. A visit to the

E

off.

R 3727.

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