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dam in a depression to the South of the main dam. Both dams are constructed of masonry and concrete.
The main dam is curved on plan with a radius of 240 feet. Its length on top is 600 feet, its height from the lowest part of the foundation to the top 112 feet and its maximum thickness 72 feet. Four draw-offs, fitted with the necessary valves, are provided at the levels of 375, 395, 415 and 435 feet above Ordnance Datum respectively, (permanent overflow level being 448 feet above Ordnance Datum), and are connected with a 10" cast iron stand-pipe fixed in a well which is formed in the dam. From the bottom of the well, a culvert extends to the outer face of the dam, in which are laid a 10" main which is joined up to the stand-pipe and a 12" scour pipe which served the purpose of enabling the height of the water to be controlled during construction and is now available as a wash-out for the reservoir.
The dam is composed almost entirely of cement concrete, faced on the inner side with granite ashlar masonry and on the outer side with granite rubble masonry. In the top 21 feet and at both ends, where the dam extends well into the hillsides, lime concrete has been substituted for cement concrete. Immediately behind the ashlar masonry of the inner face, cement concrete of special quality, (proportions 1, 1, 3), varying from 5' 0" thick at the bottom to 20" thick at the top, has been used for the purpose of ensuring water-tightness. As an old pathway across the hills to Sheng Mun and Tai Po crossed the site of the reservoir and therefore became submerged, it was necessary to make other provision for it and this has been done by forming a path, 9 feet wide, on top of the dam, which is at a level of 454 feet above Ordnance Datum.
The following are the quantities of material used in the construction of the dam :-
Cement concrete, 36,740 cubic yards. Lime concrete, 4,420 cubic yards. Ashlar masonry, 64,520 cubic feet. Rubble masonry, 1,750 cubic yards.The overflow dam is 140 feet long and 23 feet high from the lowest part of its foundation to overflow level, the path already referred to being carried across it on a bridge 9 feet wide supported on granite ashlar piers. The overflow comprises 10 openings, each 10 feet wide, all of which are provided with iron sluices, by means of which an additional depth of 2 feet of water in excess of that held up by the dam can be impounded. Below the overflow dam are two "water cushions" to break the fall of the water and beyond them a channel, varying in width from 120 feet to 60 feet, has been cut for a distance of 300 feet and lined with concrete and masonry. Clock-work recording gear has been provided to register the extent of any overflow which may occur.
In addition to the provision made for it in the case of the two dams, the diversion of the old pathway necessitated the formation of 1 mile of new path, varying in width from 6 feet to 4 feet. It
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should be kept as is at the top and bottom as per rule 11. The rest of the corrections are made according to the given rules. I corrected "re- spectively" to "respectively", added a table for the quantities, and made minor spacing adjustments. The text is now formatted in HTML as requested.P 51
dam in a depression to the South of the main dam. Both dams are constructed of masonry and concrete.
The main dam is curved on plan with a radius of 240 feet. Its length on top is 600 feet, its height from the lowest part of the foundation to the top 112 feet and its maximum thickness 72 feet. Four draw-offs, fitted with the necessary valves, are provided at the levels of 375, 395, 415 and 435 feet above Ordnance Datum re- spectively, (permanent overflow level being 448 feet above Ordnance Datum), and are connected with a 10" cast iron stand-pipe fixed in a well which is formed in the dam. From the bottom of the well, a culvert extends to the outer face of the dam, in which are laid a 10" main which is joined up to the stand-pipe and a 12" scour pipe which served the purpose of enabling the height of the water to be controlled during construction and is now available as a wash- out for the reservoir.
The dam is composed almost entirely of cement concrete, faced on the inner side with granite ashlar masonry and on the outer side with granite rubble masonry. In the top 21 feet and at both ends, where the dam extends well into the hillsides, lime concrete has been substituted for cement concrete. Immediately behind the ashlar masonry of the inner face, cement concrete of special quality, (proportions 1, 1, 3), varying from 5' 0" thick at the bottom to 20" thick at the top, has been used for the purpose of ensuring water-tightness. As an old pathway across the hills to Sheng Mun and Tai Po crossed the site of the reservoir and therefore became submerged, it was necessary to make other provision for it and this has been done by forming a path, 9 feet wide, on top of the dam, which is at a level of 454 feet above Ordnance Datum.
The following are the quantities of material used in the con- struction of the dam :-
Cement concrete,
Lime
})
Ashlar masonry, Rubble
19
36,740 cubic yards.
4,420
产
64,520 cubic feet.
1,750 cubic yards.
The overflow dam is 140 feet long and 23 feet high from the lowest part of its foundation to overflow level, the path already referred to being carried across it on a bridge 9 feet wide supported on granite ashlar piers. The overflow comprises 10 openings, each 10 feet wide, all of which are provided with iron sluices, by means of which an additional depth of 2 feet of water in excess of that held up by the dam can be impounded. Below the overflow dam are two "water cushions" to break the fall of the water and beyond them a channel, varying in width from 120 feet to 60 feet, has been cut for a distance of 300 feet and lined with concrete and masonry. Clock- work recording gear has been provided to register the extent of any overflow which may occur.
In addition to the provision made for it in the case of the two dams, the diversion of the old pathway necessitated the formation of 1 miles of new path, varying in width from 6 feet to 4 feet. It
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