124
which it is proposed should eventually be intercepted by catchwaters. A masonry channel will conduct the overflow water clear of the toe of the dam and of the gauge basin. On the overflow provision will be inade for inserting planks, by means of which an additional two feet of water may be impounded in favourable seasons, as is now done at Tytam and Pokfulam. The hill road, which crosses the valley in the neighbourhood, will be diverted and carried across the overflow by means of a bridge.
The outlet works will consist of a culvert built in a trench excavated in the solid ground at the northern end of the dam, this will be connected to a valve tower containing the usual stand pipe and three outlet valves at different levels. A small bridge above top water level will give access to the valve tower.
The lowest draw off will be 395 feet above Ordnance datum, top water level at the existing Yau-Ma-Ti service reservoir is 215 feet. Advantage will be taken of the ample head thus available to construct the gauge basin at such a distance below the dam as to intercept all probable leakage.
Catchwater. The catchwater will be constructed to carry a rainfall of 11⁄2 inch an hour on the drainage area intercepted by it. This amount is seldom exceeded in dry years, and in wet years, when the rainfall is excessive, the surplus will be carried away by suitable overflows. The bottom will be pitched with stone and a small cemented channel left at one side to carry the dry weather flow and prevent its loss by evaporation and leakage. The bank alongside the catchwater will be raised a foot above the level of the overflows on straight lengths, and two feet where sand pits overflows or sharp bends occur. A connection will be provided from the catch water to the gauge basin below the dam by means of a cast iron pipe, so that it may serve as a clearwater cannel after times of heavy rain.
Main to Filter Beds. From the gauge basin below the dam the water will be conveyed to the Filter Beds by means of a 12-inch cast iron pipe laid along the hill side. This pipe when new will be capable of carrying 1.600,000 gallons a day, and will therefore serve for delivering the entire supply estimated to be obtainable when the whole of the sources described in the first portion of this report are made available. Near the Filter Beds a branch will be left for a future connection to Reservoir No. 2. All available streams will be intercepted en route.
Filter Beds.-The only suitable site for Filter Beds appears to be on a comparatively level spot north of the point where the new Táipó Road passes behind the hills above Cheung Sha Wan.
To filter 590,000 gallons a day-making the usual allowance for cleaning beds-an area of about 1,300 square yards will be necessary, and in order to take advantage of the site in an economical manner the beds will be arranged at different levels, which can be done without undue loss of head, owing to the comparatively high level of the storage reservoir. A caretaker's bungalow will be required alongside the beds. If, on detailed surveys being made, the site is found to be large enough, it will be laid out with a view to the addition of further filter beds to deal with the water from the proposed reservoir on site No. 2. Should this, however, be found impracticable, a suitable site for this purpose must be found elsewhere.
Main to Service Reservoir.-From the Filter Beds either a short tunnel will be driven through the ridge, or a pipe carried round it, as may be found the more economical when detailed surveys are made, and a 12′′ main will then be laid partly below and partly along the new Táipó Road and up the hill to the large service reservoir about to be described.
Service Reservoirs.-The existing service reservoirs are capable of containing only 250.000 gallons, a quantity which has on several occasions been found inadequate to tide over a breakdown, and provision on a much more extensive scale for the storage of water after filtration is urgently required. There is no suitable site for a large service reservoir near the centre of the district to be served, and it has therefore been found necessary to select one on a hill to the north of the village of Kowloon Tong. The reservoir will be circular, 150 feet in diameter and 20 feet deep having a capacity of about 2,000,000 gallons.
At Kowloon City a small reservoir only, say 150,000 gallons capacity, will be required; it will be similar to the existing ones and situated on the hill above the walled city.
Connection to existing Distribution System.-From the Kowloon Tong service reservoir a 12′′ main will be laid through Mong-Kok-Tsui to connect with the existing 7" main at Yau-Ma-Ti, and a 5" main with 3" and 4" branches will supply Tai-Kok-Tsui and Sham-Shui-Po. On the eastern side of the Peninsula a 6" main will be carried along the new road to Kowloon City with 3" and 4" branch mains to the large villages of Too-Kwa-Wan and Ma-Tau-Wai. All new mains will have hydrant- brauches at distances of 300 feet apart where building is at all probable, and hydrants will be fixed
in all built districts.
Fire Hydrants on existing System.In the original waterworks scheme fire hydrants were omitted, partly on account of the limited supply and partly because most of the houses were situated near the harbour. When the proposed new supply is obtained fire hydrants should be fixed at intervals of