ENG-1969 — Page 231

PUBLIC WORKS AND UTILITIES

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To control plant and insect growth in Plover Cove reservoir until a natural fish population develops there, 636,500 fish, mainly silver, mud and common carp, have been introduced and their progress is being studied. Other ecological studies revealed that, in the early spring, with a greater depth of water in the reservoir, there developed in the lower levels stable layers of water at low temperature which would inhibit the mixing of this water with surface water. Water temperatures, chemical content and biological condition are being carefully observed to determine the effect of these layers on water quality.

At the beginning of the year the water stored in the Plover Cove reservoir had stabilised at a salinity a little over 500 ppm sodium chloride but with the influx of fresh water during the summer rains the salinity dropped to a minimum of 290 ppm sodium chloride at the draw off point, comparing very favourably with the normal taste threshold which is in the region of 330 ppm sodium chloride.

Coupled with site investigations in preparation for raising the Plover Cove spillway and dams by 12 feet was a proposal to acceler- ate flood discharge by means of a siphon spillway. This will enable the water retention level to be further increased and bring the total storage capacity up to about 50,000 million gallons without reducing the safety margin provided to allow for waves.

Tenders were invited from selected contractors for the supply of a 50,000-gallon-per-day experimental desalting plant designed to be installed and operated at several different sites to test various plant configurations and to assess the effect of sea water with differing chemical characteristics upon the various materials of construction --a prelude to providing and operating a desalting plant of higher output within the next decade or so.

Recommendations for investigations into detailed design work for the High Island Water Scheme were approved in July. This scheme, if proceeded with, will yield about 60 million gallons per day and include another large 'Plover Cove' type impounding reservoir at High Island. The scheme is designed to develop the water resources of the Sai Kung peninsula, possibly with other catchments. The High Island reservoir itself will be created by placing rock filled dams at each end of the shallow sea passage between the Sai Kung