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Particulars of the tunnel are as follows:-Length 2,034 lineal feet; gradient 1 in 2,700; width at invert 7′ 0′′; width 4′ 0′′ above invert 9' 0"; maximum height 7′ 6′′; radius of invert 12′ 6′′; radius of arch 4.65 feet; capacity 40 million gallons per day.
The approach cut to the North face, the lining and capacity of which are similar to those of the tunnels, has a length of about 140 feet between the end of the North Conduit and the tunnel portal.
South Conduit.
The South Conduit, which connects the North and South Tunnels, was com- menced early in 1925 and completed early in 1926. It has been constructed of cement concrete throughout, has a gradient of 1 in 1600, a length of 2,000 feet, and a capacity of 40 million gallons per day. In all other respects it is similar to the North Conduit.
A 2-span reinforced concrete bridge was constructed to carry the conduit and foot path across the stream from Smugglers Pass.
South Tunnel.
Work on the South Tunnel under Golden Hill, which receives the discharge from the South Conduit and passes it through the outlet cut and gauge basin into the Reception Reservoir, was commenced on the North face in February, 1925, and on the South face in April, 1925, the two headings meeting on July 4th, 1926, at a point 2,350 feet from the North end. The work was finally completed in Decem- ber, 1926.
The rock throughout was granite of a very good quality and no lining to the side walls or roof was necessary.
The invert is lined throughout in a manner similar to that adopted for the North Tunnel.
The tunnel portals have been finished in granite ashlar.
The tunnel is of the same dimensions and capacity as the North Tunnel and has a gradient of 1 in 2300 and a length of 4,654 feet.
The outlet cut to the Reception Reservoir, which has dimensions and lining similar to the tunnels, is 245 feet long and terminates at a gauge basin construct- ed of granite ashlar on a cement concrete foundation. The gauge basin is provided with a gauge to pass 40 million gallons per day, the cill level being 483.00 A.O.D.
Reception Reservoir.
This Reservoir, in addition to providing further storage, is designed to regulate the supply of raw water from the Shing Mun Valley which discharges directly into
it.
Work was commenced in December, 1924, and completed in December, 1926, the works being somewhat delayed by labour troubles. The Reservoir has a capacity of 33.15 million gallons, a direct drainage area of 96 acres, an area of 93 acres at a top water level of 480.00 A.O.D., and comprises a Draw-off Dam and Valve House, an Overflow Dam and Overflow Channel.
The Draw-off Dam, situated at the South end of the Reservoir, has an overall length of 228 feet, and a maximum height of 48 feet from foundation to path level. the latter being at 482.50 A.O.D.
The dam is of the gravity type constructed of mass concrete, and is composed of 4 to 1 cement concrete, faced on the up-stream side above 466.25 A.O.D. with coursed granite ashlar blocks and backed with 8 to 1 displacer cement concrete on the downstream side, the latter being faced with coursed granite rubble.