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23
HEAD WORKS.
First Instalment.
7† M.G. per diem Average: 10 M.G. per diem maximun
Main Dam and Cols.
95.
Estimates were prepared showing what would be the
cost if the main dam were carried out in two instalments.
96.
It would only be necessary to construct a dam about
140 feet in height above ground level to form a reservoir of
sufficient capacity to maintain a supply of 7 million gallons per diem, but as the dam would have to be subsequently heightened by 50 feet, the lower portion would have to be of sufficient thickness to stand the extra water pressure when its height was raised, nor could the foundations below ground level
be carried out in two instalments.
97. A dam decreases rapidly in thickness towards the top and although the top 50 feat beed not be constructed in the first instance, the amount of concrete which would be
saved would only be about one-tenth of that required to
construct the dam to its full height.
98.
Against this saving in concrete, it would be
necessary to dismantle the plant, which might either be kept in good working order until the dam was heightened, or sold,
and to maintain the camp, anti-malarial works, etc.
99. The cost of the plant and teels is a very heavy
item of expenditure if the work is to be carried out in the most expeditious and economical manner, that employed for the construction of the Gorge Dam representing over 20 per cent.
of the total cost of the work.
100. After weighing the advantages and disadvantages of
constructing the dam in two instalments, we came to the con-
clusion that it would be more economical to complete it to its
full height in the first instance, the cost being estimated at
13,300,000 including the subsidiary dams at the three cols,
191