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The draw-off arrangements, which are designed to deal with the ultimate capacity of the Shing Mun Valley Scheme, are in duplicate and consist of two 18" diameter stand-pipes to each of which are connected two 18" diameter draw-off pipes each controlled by an 18" Penstock and a 15" Sluice Valve, one at 465.00 and the other at 472.00 A.O.D. The draw-offs are accommodated in a Valve Well surmounted by a Valve House from which they are controlled. An 18" wash- out pipe has been provided at 450.00 A.O.D.
The quantities of materials used in the construction of the dam and Valve Tower include 1,380 cubic yards of 4 to 1 cement concrete, 967 cubic yards of 8 to 1 cement concrete, 111 cubic yards of lime concrete, 218 cubic yards of ashlar masonry and 172 cubic yards of rubble masonry.
The Overflow Dam, situated in a gap at the Eastern end of the Reservoir, diverts the overflow into the Overflow Channel, which discharges into the Byewash Reservoir.
This dam has a total length of 87 feet, a maximum height of 16 feet from foundation to cope level--the latter at an elevation of 483.00 A.O.D.-and an over- flow 40 feet wide by 3 feet deep. It is faced on both sides with granite ashlar masonry having a hearting of 8 to 1 cement concrete.
In order to supply the Kowloon Filters with Shing Mun water which would be- come available on the completion of the Shing Mun Tunnels and the Reception Re- servoir, an 18" draw-off pipe controlled by an 18" penstock valve was provided in this overflow dam and a Temporary 18" main was laid thence to the Kowloon Filters.
In January, 1927, Shing Mun water was first brought into use through this connecting main, whence, after filtration at the Kowloon Filters, it was passed into the Kowloon supply. The main was removed 4 years later on the completion of the Byewash Reservoir as it was then no longer necessary.
Immediately below the Overflow Dam a water cushion and masonry gauge wall containing a 2′ 6′′ V. gauge were constructed, the latter being subsequently removed.
The Overflow Channel, which commences immediately below the gauge wall, was originally constructed down the hill side until a good rock bottom was encounter- ed. It was approximately 12′ 0′′ wide by 4'6" deep and was 265 feet long. The invert was of 8 to 1 cement concrete stepped to suit the slope, and the sidewalls were con- structed of similar concrete surmounted by a granite ashlar cope. Slight altera- tions to this work were necessitated by the construction of the Byewash Reservoir into which the overflow channel now discharges.
Filtration Plant and Erection.
This installation, situated adjacent to the Reception Reservoir, from which it is supplied, comprises the first section of the plant to deal with the filtration of the ultimate capacity of the Shing Mun Valley Scheme and consists of a battery of eight Paterson Rapid Gravity Filters, having a capacity of 5 million gallons per day, together with a chemical house which contains the plant and equipment for the treat- ment of a daily supply of 10 million gallons. Provision has been made in this installa- tion for the necessary connections for the addition of a similar battery of eight filters when the filtering capacity of the plant will be increased to 10 million gallons per
day.
A contract for the supply and erection of the chemical and mechanical apparatus was let through the Crown Agents to the Paterson Engineering Company in Eng- land at the end of 1925, but delivery in Hong Kong was not completed until the end of 1927.
In May, 1927, a contract for the erection of the buildings and structures was prepared locally and let on June 29th, 1927. This work, together with the erec- tion of the mechanical plant, was satisfactorily completed and tested by the end of 1928, and the plant was brought into service on June 10th, 1929.