CO129-588-16 Water Supply- report on the Tai Lam Chung Valley Scheme 3-1-1941 - 3-1-1941 — Page 15

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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