Hongkong, 26th January, 1904.
Kowloon Waterworks Gravitation Scheme.
Catchwater.
The honourable W. Chatham,
Director of Public Works.
Dear Sir,
We are now about to get out the contract for above and request instructions as to what length of catchwater we should provide for.
In our letter of 14th October, 1901, it was proposed to construct a sufficient length of catchwater to intercept the water from 400 acres, the channel to be of such sectional area and gradient as to carry 12-inch rain per hour from this area, this we estimated could be done for about $40,000.
Since this estimate was made Mr. Chadwick has advised that the catchwater be built of such a gradient as to give a velocity of 5 or 6 feet per second. The Tytan catchwaters on which our estimate was based have a velocity of 10 to 12 feet per second, decreasing the velocity by half would necessitate doubling the sectional area of the channel and consequently at least doubling the cost.
The advantages of the reduced velocity are:-
1. Decreased wear and tear in catchwater and
2. Increased carrying capacity, it being found that with a high velocity a channel did not actually carry the quantity of water which, judging by its sectional area and gradient it was expected it would carry, the wave action set up by the high velocity causing overflow before the channel was actually running full.
With