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270 million gallons, or more than enough by 57 millions to fill the reser- voir. A stream giving approximately 100,000 gallons per day flows down the valley all the year round, and there are likewise two small perrennial nullahs which would be of some help in replenishing the volume of stored water after all rain drainage had ceased.
Owing to the very low site of its outlet culvert and its consequent inability to accommodate the upper town, the Aberdeen project, if adop- ted, would necessitate two distinct sets of water-works. Those parts of Victoria lying above the outlet level would have to be fed from Pok- foolum by a high level conduit, while the lower town would have to be provided for by a low level conduit from Aberdeen leading into a low level service reservoir to be built at some convenient site on the 200 feet level in the centre of the city. The line of demarcation between the two water services would be a little below the level of the Bonham and Caine Roads and Government House grounds.
The conveyance of the last mile and a quarter of the Aberdeen supply would have to be made in cast iron 24 inch mains as it would be injudicious to expose it to the chances of pollution by the percolation of town drainage, and indeed, at intervals along its whole length struc- tural precautions would have to be taken to make the cover of the conduit impervious to the filtration of sewage irrigation and other impurities, for its low level would compel it to pass through many frequented places and occasionally below the level of cultivated patches of land.
But it is mainly the inadequate height of delivery which so seriously detracts from any advantage that a water supply from Aberdeen might possess. It makes the project like the Pokfoolum triple reservoir scheme rank as an alternative plan, to be reverted to only when anything better has been found impracticable."
The cost of gravitation works at Aberdeen was found to come to £250,000. The inability of this project to deliver water at as high a level and in the quantity that was needed, led to the conception of an alternative Aberdeen scheme for the creation of a reservoir as described, without any conduit but with steam pumping-works to pass the water over the Aberdeen Hills into the present Pok- foolum reservoir, but this alternative scheme when brought to the test of figures- had also finally to be dismissed and I need not therefore dwell on it here.
The topographical examination of the island having exhausted the Southern districts, now passed along the northern slope from the valley above Causeway Bay as far as Mount Parker without any satisfactory results, and was finally brought to'a close in the Tytam Valley, where the nearest approximation to the required conditions was found. The main objection to gravitation works in the Tytam Valley lay obviously in the fact that the latter was on the wrong side of the island and that in order to bring the water into town it would be necessary to pierce the dividing ridge of mountains by means of a short direct tunnel or to adopt the alternative of following the hill contours along the surface by an unduly long and circuitous route passing round the hill-spurs overlooking Deep Water Bay and Repulse Bay with short tunnels. For the rest, the topography of the valley was favourable beyond measure to the construction of large works capable of expansion in the future if desired. The Tytam gorge was found to be so narrow as to admit of the formation of a deep lake over 28 acres in extent, impounding nearly 300 millions of gallons by means of a dam only about 400 feet long. The gathering ground above comprised 700 statute acres yielding under a minimum rainfall of 50 inches, 316 million gallons of surface drainage, by far the largest water yield in the Colony, and the point of delivery could be kept up as high as 400 feet above the level of the sea, an elevation sufficiently high to serve nine tenths of the houses in Victoria. The valley was also found to contain tributary streams amounting collectively to nearly 150,000 gallons a day and promising to make together with the impounded water an aggregate storage of considerably over 300 million gallons for the long dry season between October and March. The closer the capabilities of the site were compared with those of the other places that had been surveyed, the clearer and the more obvious it became in spite of the intervening ridge of mountains, that it was the only locality to which the Colony could look for the supply of the future, and in this conviction, when there remained no other sources to explore, plans for gravitation works at Tytam including an earth and puddled clay dam, were elaborated and submitted to the Colonial Government together with the estimate of the cost which amounted to £259,000.