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The leading features of the Pokfoolum project having been cursorily described, its merits and defects may be summed up in a very few words, While the necessities of the city during long droughts exact a minimum of 330 million gallons, the triple reservoir could only yield 184 millions.
This quantity, divided among the population, would afford an allowance only of eight gallons per day. This allowance could however be increased to nine gallons by the absorption of the nullahs between Pokfoolum and Victoria which the conduit would intercept.
The project is incapable of further enlargement or extension, owing to the steep slope of the valley, which does not admit of a repetition of reservoirs in steps higher up and to the inability of its drainage area to fill more basins.
The upper basin could only be formed by a height of dam entailing an outlay totally disproportionate to the small number of gallons to be impounded by it.
The lower basin, containing 60 million gallons, would be very shallow, accordingly the loss by evaporation would be excessive. The constant temperature of the water would be high, and its purity towards the end of the dry season questionable. The lowest layer of ten feet containing 10 million gallons would scarcely be available."
The idea of an increased water supply from the Pokfoolum Valley having thus had to be dismissed, the examination of the ground passed on to the East, but it is unnecessary to refer here to the country eastward of Pokfoolum, searched without avail, until the Aberdeen Valley was reached. At the Aberdeen Valley however I pause for a moment as it also became the subject of a subsequent somewhat detailed investigation. Again I quote from a former official report of mine on the subject of this valley as a possible site for supplementary water-works,
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"A little above the village of Aberdeen to the right of the bridle path which leads over the mountains to Victoria, there is a large valley possessing an area of nearly 600 statute acres. This valley is flanked by precipitous hills narrowing towards a gorge 500 feet wide, in which is an admirable site for a dam.
Nearly every condition for the formation of a store reservoir which had been so fruitlessly sought for in the narrow and contracted valley of Pokfoolum, would appear at first sight to be here fulfilled. Its great natural basin seemed as it were expressly shaped to afford every facility for the easy realization of an abundant water provision, and the con- figuration of the upper valley appeared equally favourable for a small subsidiary reservoir had such been required. At the back of this again, were hills stretching out to a height of nearly 1,500 feet, promising a rain drainage in excess of the requirements of Victoria. Issuing fresh from the difficulties which had beset the preceding surveys at Pokfoolum, and the questionable expedient of a triple reservoir, which had to be resorted to in order to devise a water-supply however scant, the marked contrast presented by the generous dimensions of the Aberdeen Valley could not but be a gratifying sight.
On closer examination however, the bed of the valley scarcely appeared to have a sufficiently high elevation to provide water to the higher portions of the town. The subsequent surveys were productive of the most disappointing results, for although it was proved that the formation of an inland lake of twenty-two acres was perfectly feasible, it was also discovered that the exit of the water could not be effected at a greater elevation than 240 feet above mean sea level.
Aberdeen water,
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if brought by gravitation into town, could therefore only serve those districts below that level.
A dam at Aberdeen 90 feet high in its deepest part and 520 feet long would form an impounding reservoir of 213 million gallons. This quantity gives 93 gallons per day and together with the present Pokfoo- lum supply, would make a total storage of 287 million gallons, or a total daily allowance of 14 gallons per head of population.
The area of the gathering ground above the reservoir site is 600 acres yielding in years of the smallest rainfall, say 50 inches, a drainage of 680 million gallons, which after a deduction of sixty per cent. for percolation into the ground and evaporation would leave a balance of