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earthen embankment proposed in 1873, and the point raised by Mr. CHADWICK having been referred by the EARL OF KIMBERLEY to the Consulting Engineer, Sir ROBERT RAWLINSON replied that as far as he was concerned, it would not be possi- ble for him to recommend to the Government any embankment for the Tytam Valley that was not a stone or cement concrete one.
This point finally decided in favour of masonry, and absolute security thus guaranteed, the following natural question arose out of the decision. "If the proposed new dam is now to be of masonry and therefore capable of being increased to any height without jeopardy to its stability, why not raise it at once by another twenty feet, and thus enable it to impound an increased volume of water, one sufficiently large to yield 19 gallons a day for a population of 125,000, to which number the increasing water consumers of Victoria are rapidly attaining?" This proposition was to be commended not alone on the ground of public sanitation and convenience, but on the score of economy, since it would cost less to superpose the extra height of twenty feet now that a working establishment was to be opened on the spot, than later when all the expense of obtaining mechanics from England and other expenses of installation would have to be gone through over again. Accordingly after due consideration of the matter, it was resolved to increase the height of the dam to 110 feet. These increased dimensions coupled with the radical change in the style of structure sent up the estimate for the dam from its original figure submitted in 1875 i.e., £64,800 to the larger sum of £99,000.
It is obvious however that if the Colony cannot afford a dam of this height at £99,000, a lower and less expensive one-one in fact not exceeding the original £64.800-can be adopted always provided that the top of the structure is left sufficiently wide to admit of its being increased in height hereafter, if it should be decided to relegate to the future the realization of a complete water supply. This precaution as regards a sufficiency of width has of course been taken in respect of the fabric at present in course of erection at Tytam.
There have been other departures from the former abridged project which explain other minor additions to the aggregate estimate of cost.
The most important of these changes is the reversion to the original scheme of a surface conduit running along the contours of the hills overlooking the Happy Valley and Wantsai, in lieu of the cheaper, but less desirable expedient of an underground pipe down the Wong-nei-Chung Valley and under the Race Course meadows, to which recourse was bad in 1875 only in order to avoid initial expense.
The superiority of a surface conduit over an iron pipe is obvious. An iron pipe would rust and perish in the course of a few years while there is no reason why the conduit should not endure for many generations. An iron pipe buried in the earth is incapable of augmenting the town supply in any way, while a conduit winding along the surface of the ground is able to convert into tributaries all the mountain streams that cross its path, and thus to augment the supply by wayside feeders. There is an additional advantage special to the conduit, which is that in case of a breakdown at the outlet works in Tytam, or in the event of any tem- porary stoppage for repairs-a most serious thing for a town--the supply can be continued for a day or two from the conduit. The conduit is not being built in an even or gradual incline or fall from the tunnel mouth to the town, like the bed of a flowing stream, but in a series of flats or level steps resembling a concatenation of narrow elongated tanks, each tank about a quarter of a mile long, and each lower than its neighbour by about one foot. These water-compartments may therefore in case of emergency, be converted into temporary sources of supply and their contents retained or eked out at will by means of stop-planks or water-gates, until the main supply is re-opened from the fountain head."
The foregoing modifications of design all tending to the ultimate efficiency of these water-works when completed, account in the main for the increased cost, but there have been also, though of course to an infinitely less extent, certain other contributory factors and causes of excess of actual over estimated expenditure not due to any modifications in the design, but which it is none the less necessary to set forth in these pages without reserve.
The preliminary estimate for the construction of the Tytam tunnel was an approximate estimate which allowed a margin for the uncertainties and difficulties that attend, more or less, all undertakings of this class, but that estimate did not allow any margin for an unexpected source of expense that has arisen in the ever constant presence of sickness on the works. Almost from the beginning, the disease known as Hongkong fever has haunted both tunnels with unremitting