14
43.
Calculations show that the available storage of
6,400 million gallons would be sufficient during both these
periods to permit of an average annual quantity of 30 million
gallons per diem being supplied when the run-off from 8,000
acres had been brought into the reservoir, and 15 million gallons
per diem when only the runoff from the natural catchment area
was contributing.
Outlet Tunnel.
44.
It will be seen from the Map which is appended to
this Report, that it is proposed to convey the water from the
reservoár by a pressure tunnel which would pass under the
ridge lying to the S. E. of the reservoir.
45. It would appear from a surface examination that
this tunnel would pass through granite for almost its entire
length similar to the rock through which the pressure tunnel
of the Lochaber Aqueduct was driven. Whers the granite is
sound and sufficient cover is provided, it would be of ample
strength to take the internal bursting pressure, but portions
would be decomposed or badly fissured, calling for steel
reinforcement of the concrete lining, which is also necessary
where the weight of the superincumbent rock is insufficient to
counterbalance the internal water pressure.
46. In preparing our estimate we have therefore assumed
that the tunnel is reinforced for a length which should be
ample judging by the experience gained during the construction
of the tunnel referred to above.
47.
This tunnel would serve dual purpose when the
catchwaters are constructed to convay water from the southern
slopes of the mountains to the reservoir, as it would be of
sufficient size to act as the channel by means of which that
water would enter the reservoir whan the discharge of the
catchwaters exceeded the amount being drawn off for supply.