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Dam B.B.
Dain C.C.
Dam D.D.
Dam 2A.
Catch- waters
Filter Beds
24" Pipe
Line.
Owing to the great fluctuation of the annual rainfall, from a minimum of 46 in. to a max. of 120 in., the quick run off of this catchment area and the fact that this is gravity water it would appear desirable up to a point to get as large storage capacity as possible.
Or
With this object in view and also to eliminate if possible Dam No. 1 Sing Mun Village Dam owing to its excessive cost, I have taken out estimates for Dams at the Gorge on Lines B.B., C.C. & D.D. shown on Drawings Nos. 2 & 3 and each having a Top Water Level of 600 A.O.D.
Dam on line B.B. would have a maximum depth of water of 200 ft. a max. depth to bottom of foundations of 270 ft. and impound approx. 2,000 mill. galls. I estimate it would cost $4,700,000 to construct or at the rate of $2,350 per mill. gulis.
Dam on Line C.C, slightly above Dam B.B. would have a max. depth of water of 190 ft. a max. depth to bottom of foundations of 245 ft. and impound approx. 2,000 mill. galls. I estimate it would cost $4,400,000 to construct or at the rate of $2,200 per mill. galls.
Dam on Line D.D. is slightly above Dam C.C. and is just outside the gorge. This dam would have a max. depth of water of 182 ft. have a max. depth to bottom of foundations of 220 ft. and would impound a little less than 2,000 mill. galls. I estimate the cost of construction would be $4,550,000 or at the rate of $2,275 per mill. galls.
As the level of line Apple Pass is 542 A.O.D. I have included in the above estimates $250,000 which I estimate as the cost of the necessary dam at that print.
It would appear from the above figures that it would be much cheaper to eliminate the Village Dam Reservoir and raise the Gorge Dam to a Top Water level of about 600 A.0.1), and thus secure the 2,000 mill. galls, storage in one reservoir.
With storage of 2,000 mill. galls, and taking the direct drainage Area only.
a supply of 6 mill, galls. per day would be ensured throughout the driest known period. As the existing temporary intake works produce approx. 2 mill. galls. per day, this would mean an addition of approx. 4 mill, galls. of gravity water per day to the Colony's supply.
Of the three Dam Sites discussed above, from the information now avail- able I would favour the Site on Line D.D., although this does not work out the cheapest Dam.
Dam No. 24 or Needle Hill Dam. With the raising of the Top Water Level of the Gorge Dam to about 600 A.0.D). a large portion of the basin of Needle Hill Reservoir is included in the Gorge Dam Reservoir.
For this reason and also owing to the fact that on closer investigation this Site has not proved so favourable as at one time hoped for, I would recommend that this dam be abandoned.
The catchwaters discharging through Lead Mine Pass present no particular difficulties apart from their being situated at a very high level and are therefore somewhat inaccessible. They should be put in hand while the Reservoir is under construction, but are not so urgent.
The filter beds will be an extension of the existing plant and should be dealt with early. The existing plant has been designed to allow of extension when necessary.
A second pipe line should not be required until the Reservoir is almost com- pleted, so need not be considered at the moment.
Reservoir.
Shing Mun Scheme-Fifth Section. With a view to getting some little idea of Gin Drink- the possibilities of the Gin Drinkers Bay Reservoir Site, I have had a series of bore ers Bay, holes put down along the line of the Lower Dam Site, but with very disappointing results.
The bores show that bedrock is only reached at a depth of about sixty feet, and that, over a large section of the Damn. The cost of a dam on this site would appear excessive.
Borings are proceeding on the upper site which it is hoped will prove more favourable.
It is not improbable. however, that both sites at Gin Drinkers Bay may prove unfavourable, thus cutting out large potential storage.
It would appear, therefore, that the upper Shing Mun Valley should be developed to the utmost and, to do this, the Gorge Dam should be made of as great a height as is consistent with safety.
Drawings accompanying this report.
R. M.
HENDERSON,
M.I.C.E., M.I.M.E., M.I.W.E Asst. Director of Public Works.
(1) Shing Mun Valley Scheme and existing Works in Kowloon. (2) Contours of Upper Shing Mun Valley Reservoir Sites.
(3) Contours of Shing Muin Gorge Pineapple Pass. (4) Sections of Village Dam Site A-A. & Gorge Dam Site B-B. (5) Sections of Gorge Dam Site C-C & D-D.
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