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112
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