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THE POKFULUM CATCHMENT AREA AND WATER WORKS.
Note by Mr. A. H. Hollingsworth, A.M.I.C.E. Executive Engineer in charge of the Water Branch, Public Works Department.
"The Pokfulum reservoir is situated in the valley to the South of Victoria Gap and has a watershed of some 416 acres in extent.
The Reservoir is formed by an earthen Dam across the valley forming a basin capable of impounding about 70 million gallons of water.
The Dam is provided with an overflow at one end over which flood waters pass without damage to the main embankment.
The top water level is about 554 feet above mean sea level.
The hillsides forming the catchment area are composed chiefly of granite and syenite on which the fir tree grows up to a level of about 700 feet above sea. On the upper parts of the hillsides the vegetation consists principally of scrub and coarse grass.
The tops of the hills to the East and West of Victoria Gap are occupied by the European community as residential areas and some of the houses have been built within the catchment area of the Pokfulum Reservoir as well as the roads which open up the. different areas that have been built upon,
The distance of the houses from the Reservoir is considerable and the greatest care. has been taken that all sewage waters are intercepted by properly constructed drains and are led away and discharged outside the catchment areas.
There is also one road that leads from the Victoria Gap through the centre of the catchment area and past the Reservoir joining up with the lower road leading from the City of Victoria to the village of Aberdeen.
This road is not greatly used, indeed, with the exception of those who walk for pleasure, and few natives employed by the Dairy Farm to carry milk to the residences on the hills, there is practically no traffic.
There are very few animals in the Island so that from the point of view of possible contamination of the catch grounds they may be disregarded entirely.
The water from the Reservior is led to filter beds situated at West Point by a conduit l' 6" x 1' 6" built of brickwork and covered with granite slabs, which contours the Western slopes of High West and in its course intercepting certain streams whereby some additional catch grounds are secured.
There is an arrangement at the Reservior by which all the water from the catch grounds enters the Reservoir, or some part can be diverted from the Reservoir and led into the conduit direct,
It has been found that heavy rains are apt to bring a good deal of sand into the Reservoir and that the water is liable to become turbid and charged with a considerable quantity of muddy matter derived chiefly from the disintegrated granite. Under these circumstances the water must be allowed to rest for a while until the matter has sub- sided.
The streams however clear rapidly and these are led past the Reservoir to the filter beds during the time of heavy rain.
The filter beds at West Point are six in number having au individual area of 330 square yards or a total of 1,980 square yards.
The beds are fitted with controlling valves whereby the speed of filtering may be regulated.