Sessional_Paper_1887-1888 — Page 329

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The size and gradients proposed for the new sewers have been the subject of careful calculation the aim and intention being to maintain a self cleansing velocity throughout the whole system. Considering the existence of large drains through- out the city and the facilities offered for getting rid over the surface of the storm- water in back yards during heavy rain-falls I am of opinion the sizes proposed for the new sewers will be found ample to meet the requirements of the increasing population.

The Separate System as designed contemplates the provision of overflows along the lines of the proposed intercepting sewers in order to relieve them in case it should be found impracticable for the present to exclude from them as much of the storm-water as I have specified. In many instances the rain from the back yards of private houses will be admitted into the proposed new sewers but, where back yards are continuous from one street to another such storm water can easily be diverted from the sewer by a continuous surface gutter from yard to yard, iron gratings being fixed in the communication holes at each partition wall. Some rain- fall from the backs of houses must, under any circumstances, be adinitted into the proposed new pipe sewers but the special method of providing for the carrying off of storm-waters from private premises is a detail that must be considered indivi- dually in each case,

The proposed sewers are intended to be laid out in straight lines and man- holes are provided at every change of direction in order to facililate inspection or the removal of obstructions should the latter at any time occur.

As a rule every

manhole will be furnished with a ventilating grating to be placed as near as possible in the middle of the street. Additional ventilators will also be provided wherever the interval between two manholes is longer than 350 feet. Flushing doors will also be provided in some of the manholes on the mains where the fall or inclination is small, and for the purpose of obtaining a rapid change of air in the sewer and of preventing a decided set of air therein to one point, traps and valves will be fixed in some of the manholes. The out-falls will be protected by tidal valves.

I have not considered it necessary to design any system of sewers for Kennedy- town situated at the extreme west of the city, as that suburb is at present very sparsely built over, and because sewers can at any time without difficulty be con- structed leading into the Sulphur Channel, the scour through the Sulphur Channel being sufficient to prevent any nuisance therefrom.

HOUSE-DRAINS.

As I am here dealing with the subject of main-drainage and not of house- drainage I need not enter very fully into the question of house-drains though I need scarcely add I have considered this matter very carefully before laying the scheme for the proposed main sewerage of the city before you. I would however state that in my opinion, Ordinance No. 24 of 1887 together with the Bye-Laws now before the Sanitary Board clearly define what a house-drain ought to be and only place such restrictions on house owners as are placed on them in England and as I have found necessary in my experience as a Sanitary Engineer.

Unless house-drains are properly constructed under such sanitary provisions as those contained in the Bye-Laws above referred to they will be practically worse than no drains at all, and considering their close proximity to buildings, house- drains obviously require even more careful supervision than main sewers.

I consider that it cannot be too strongly impressed upon the public mind that it is to the connexion with the Government main sewers, of badly laid out and badly built house-drains in private premises, wherein the house-sewage, is imprisoned for long periods, and therefore entirely decomposed before it leaves such private premises to pass into the Government mains, that is to be attributed the chief cause of foul emanations from the main sewer-openings in the streets and elsewhere, and that therefore the first or initial step towards sanitary reform is obviously the reconstruction of house-drains. It is therefore of the utmost importance that defective house-drains should be dealt with as soon as possible and I see no reason why this should not be done at once under the powers conferred by the Public