-10-
15
48.
In order to fulfil this function, a shaft would be
constructed down which the water would fall to enter the tunnel.
In times of heavy rainfall the water would travel down the
catchwaters at high velocity carrying in suspension sand etc.
which had been washed into the channels from the flanks of the
mountains above or had entered from the streams which had been
intercepted.
49. When catchwaters discharge into a reservoir this sand
and silt is deposited and no trouble arises, but it would not
be permissible to allow this material to enter the pipes.
50. It is therefore proposed to construct a small settling
reservoir, provided with ample cleansing sluices, in which this
material would be deposited before the water entered the shaft,
this reservoir being located where the contours indicate that
it can be economically constructed (see map attached to this
Report).
51. An alternative to the proposals outlined above would
be (a) to lay the supply pipe down the valley to the road which
would be followed till the same point was reached: (b) to carry the catchwater round the flank of the mountain to discharge into
a stream entering the reservoir, and as this catchwater should
be capable of carrying about 1,000 cubic feet per second, its
construction would be an expensive matter.
52. Estimates were therefore prepared of the cost of the tunnel, shaft and rettling reservoir, and compared with the cost of the pipeline (a) and the catchwater (b), which comparison showed that a very considerable saving would be brought about
by adopting the tunnel.
Aqueduct:
General Layout of the Supply Scheme.
Reservoir to Filters.
53. It is proposed to convey the water by gravity from
the reservoir te filters situated to the East of the commencement