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Assuming the officer's salary would be £1,200, a sum the order of £4,000 for nine months would be required to cover salaries, allowances, labour, transport, etc. It would be reasonable to apply for assistance from the Colonial Development and Welfare Fund in meeting the cost of this Survey should such assistance be considered necessary.
Water Supply.
The particular aspects of water supply to which my attention was called were those relating to underground water resources, rural water supplies, and the Tai Lam Chung Dam Scheme.
The question has been raised as to whether the Tai Lam Chung Dam Scheme, estimated to cost $64,000,000 to $96,000,000 and to take seven to twelve years to com- plete, could be replaced by an underground water scheme on the Island or on the main- land, or both.
Since this scheme is expected to provide Hong Kong with an additional supply of about 20,000,000 gallons of water per day, there is in my opinion no prospect whatever of so large an amount of water being obtained from ground-water sources, and I see no prospect of obtaining the required supply except by means of a surface scheme such as that of Tai Lam Chung.
The Island is built up very largely of granite, which normally yields very small ground-water supplies. It will be recalled that the tunnels driven into this rock at Hong Kong and Kowloon in recent years yielded only a little water of negligible importance in relation to the town's demands.
On the mainland the rocks comprise various igneous rocks and some ancient sediments, which are normally capable of yielding supplies adequate for rural use or for small townships, but are of negligible importance from the point of view of sup- plying a town with the population of Hong Kong.
I discussed with the officers concerned the question of rural water supplies on the mainland. The problem is not yet clearly defined, since it depends largely on the unknown factor of the rate of increase of population in the near future. It ap- pears, however, that for the next few years demands on the lowland plains could be met from streams in the surrounding hills, and that with the aid of pipe-lines of small diameter branching off from the main line, most of the smaller distant villages could be supplied. Moreover, such a system would simplify the task of purifying the water.
Yet should it happen that owing to distance from the main line, or shortage of surface supplies, the outlying villages could not be economically supplied in this way, then there is a considerable reserve of ground water that could be drawn upon by means of dug wells lined with concrete and otherwise protected against pollution, and by bore-holes. Dug wells are already extensively used, but they are generally polluted and in some cases yield little or no water towards the end of the dry season; these conditions could easily be remedied by proper construction. The sinking of bore-holes to a depth of 200 to 300 feet would require an experienced driller and a light, portable, power-driven percussion drill capable of drilling to a depth of 600 feet. The drilling and well-sinking depths would need to be reduced with approach to the sea shore, since otherwise brackish water would be drawn in. Where surface supplies are not available, it may be necessary to bore for water, or to sink wells with the aid of power pumping-plant, to supply the needs of factories, etc.
In general, ground water supplies from bore-holes are adequate only for small-scale intensive cultivation, as for an acre or two of market garden, and not for irrigation on any considerable scale.
Water-boring operations should not be undertaken without geological advice, since the occurrence of water in rocks is essentially a geological problem. When bore- hole supplies are likely to be needed geological advice should be sought and trial bores put down. The required advice could normally be obtained by the brief secondment of a water-supply Geologist from a Colonial Geological Survey.
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