CO129-598-2 Tai Lam Chung Reservoir Project 24-6-1948 - 3-3-1949 — Page 105

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In order to safeguard the water supplies for the future

it is important that the local sovore erosion of the hillsidos should be checked, and that afforcstation should be greatly

extended.

Tai Lam Chung Schome. I discussed with the Engincer (Construction), Mr. Jackson, the alternative sites that have boon proposed for the

main dam. The lower sito, would require the dam foundation to be

carried down to a maximum depth of 60 foet below the valley floor,

which is subject to tidal flow. Also, drilling has disclosed a

small area of weakness and fissuring at the lowest point; this

area of weakness is probably of some importance and thero is

evidenco that it is part of a line of weaknes that has

the site of the valley itself. Apart from this weak point the

foundation appears to be good, and the visible sides of the

valloy at the contro linc are of good strong granito free from

sorious fissuring.

The upper site, on the other hand, on the valley floor

and up the greater part of the valley sides, is wholly of good

fresh granite. The lowest section is well cxposed in the stream

bod and is strong and frosh throughout; it has somo slight

of

degree/horizontal jointing but no more than could be suitably

doalt with during construction.

Away from the valloy, the

extension of the dam at high levels in the form of a cut-off wall

would cut across woathored rock which would involve a few feet of

trenching down to the fresh rock.

The Engineer (Construction) in a statement dated Fobruary, 1948, has summarised the relative advantages and disadvantages of the two sites, and has shown that a dam of 190 feet at the upper

site, while storing as much water as one of a total height of 260

foot at the lower sito, would of for many advantages from the point of view of cost and difficulty of construction, tho amount

of concreto requirod, ctc. The object of this note is to record

my opinion as a Gcologist that the upper site is proforable in

that the foundation there is sound and woll exposed; moreover it