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THE HONGKONG GOVERNMENT GAZETTE, 10TH JULY, 1875.

In both projects the advantage of wayside feeders between Tytam and Wong-nei-chung is relin- quished for the sake of economy of cost, these sources being only obtainable by the cutting of a surface conduit along the hillsides to intercept their contents, and this conduit from its serpentine course, and therefore great length, would necessarily entail a very great outlay. In the Low Level Project the water trough between the reservoir and Wong-nei-chung following the hill contours would be 3 miles long, while the same taken direct under the hill as now proposed has only a length of 2,445 yards, a difference of 2 miles in favour of the direct route. In the High Level Project the difference is almost as great. The loss of nullah water by the adoption of this short underground channel is considerable, but it must be borne in mind that the professed intention of the present studies is no longer the largest water supply possible for Victoria, but rather the attainment of a moderate provision at a minimum cost and that this has entailed the sacrifice.

The most practical way to judge of the true money-value of the water to be had under the two schemes now before us, and therefore the best way to test their respective merits, is not to rush at once to the lump sums shewn in the estimates, but to take the gallon and find what this measure will stand us at under each. The upper project gives us 72 million gallons for £39,000, the lower 283 million gallons for £122,600, that is to say, under the first we pay 0.52 of a farthing per gallon, under the second 0.41 of a farthing, a saving of 0.11 in favour of the Low Level Project notwithstanding that its total cost is nearly three and a half times as great as that of its less pretentious competitor.

But there is another recommendation in favour of the larger scheme which must have great weight, and that is the facility of realizing it by piecemeal, spreading it over as many years as need be, according to the resources of the Colony, without detracting from its final utility and completeness. By the High Level Project we lead away a mountain stream from a distant valley into the city, and this work accomplished we cannot in future years increase the supply by a single additional pint should the requirements of the people demand it, because there is no room for storage works on the 500 foot level. By the Low Level Project we bring the same stream into the city tanks, and if the means of the Colony do not at present allow the cost of storage works, viz., a dam and reservoir, these may be reserved for a future occasion, when they may be made on the sites now selected, and be the means of more than doubling the single stream supply. It is true that the selection of the lower project would entail a loss of height in the point of delivery, for it is laid out nearly one hundred feet below the higher scheme, but this defect may be provided for by falling back upon the Pokfoolum subsidiary supply for the service of all houses in the highest districts, and these are not many.

Mr. RAWLINSON, Consulting Hydraulic Engineer to Her Majesty's Government, who has on three distinct occasions had under consideration the water requirements of the Colony, has suggested what may be termed a variation of the Low Level Project in the shape of a low embankment fifteen or twenty feet in height to dam the water of the stream to that depth, the embankment to be of such a width as to enable it eventually to be carried up to its full height of 96 feet; I have only been prevented from acting upon this suggestion by the difficulty of providing a suitable bye-wash. From the configuration of the gorge the immense volume of water brought down by summer freshets would have to be carried over the brim of the embankment itself entailing the construction of a stone paved flooring over its top and slopes to prevent the entire structure being washed away; the laying of a masonry skin upon a fresh made bank would be unadvisable from the risk of subsidence or shrinkage in the latter. Mr. RAWLINSON's suggestion is naturally based upon the feasibility of some convenient escape channel for flood waters, elsewhere than over the top of the embankment, but the ground shows no such favourable outlet and this so alters the case as to entail the abandonment of the dwarf dam. In dealing with the Low Level Project, we have, therefore, but two courses open to us as regards storage works; either to postpone the construction of the embankment It is the latter altogether, or else to carry it up to its full height if possible in one dry season. alternative that is strongly to be urged if the attendant outlay can be met, for the stream supply of itself will be found to afford but very partial relief.

The very expensive item of a service reservoir in town is dispensed with in the present designs, and acting upon the suggestion of Mr. RAWLINSON, the conduit both in tunnel and in the open has been converted into a sort of elongated tank to act as a service reservoir, further water accumulation to meet the maximum hourly demand being also provided by the utilization of the present tanks in the new system of distribution.

Between Wong-nei-chung and the Syphon head, the open conduit will be made to intercept and take in all the hill drainage available in the manner described in my preliminary Report with certain modifications since suggested by Mr. RAWLINSON.

Pokfoolum Subsidiary Works.-The necessity of tapping the reservoir at Pokfoolum through a larger artery than the present 10 inch main laid under the carriage road, has long been admitted, and independently of any action hereafter to be taken in regard to the Tytam project, it should be decided as soon as conveniently possible to lay down a surface conduit of adequate dimensions, along the 500 foot contour from the Pokfoolum guage-basin to the Albany Tanks in Victoria.