KAIKORAI DRAINAGE.

Evening Star, Issue 14964, 26 August 1912, Page 3

KAIKORAI DRAINAGE.

For some months past the Dunedin Draiu. age Board engineer (Mr A. Slinger) has devoted considerable time to a survey of the Kaikorai Valley watershed and the preparation of plans and estimates for a drainage scheme for that district. These will, in due course, be submitted to the local authorities interested: —Roslyn Borough Council. Mornington Borough Council, Green Island Borough Council, Taieri County Council, and the City Council (whose abattoirs are situated in the area). The above plan shows the whole watershed area (as well as a considerable portion of the Dunedin drainage district). Within the Kaikorai watershed is shown the area which would be served by the scheme—i.e., the reticulated area.

ing Rcslyn from Maori Hill. It follows the Valley road fairly closely into Green Island, crosses under tho railway line, and then skirts the eastern shore of the lagoon, finally emerging through the coastal sandhummocks at an ocean outfall (B) on the Kaikorai Beach, a total length of 8J miles. Should it be thought preferable, tho sewer could be taken along the beach to Black Head fan additional 1-J miles), where. an ideal outfall in very deep water is obtainable. On the other hand, it would be pofsrbie to terminate the sewer at the point I), on the shore of the lagoon, septic tanks being installed there and the effluent flowing into the lagoon. The cost of construction from D to B would be saved, against which a sum of about £2,000 would bo required tor the septic tanks. It is believed that as a

temporary means of disposing of the sewago this would suffice for some years to come. When found advisable, the line could be continued to the ocean either near the Kaikorai mouth or at Black Head. The sewer line would consist of pipes 3ft to sft 4in in diameter, tho sewer trench averaging about 6ft depth below the surface of the ground, and the fall would be 1 in 2,000. The lengths of the various sections along the sewer line are: Balmacewen Golf Links to old railway tunnel 19,000 ft Railway tunnel to Grc-en Island ... 11,024 ft Green Island to Kaikorai Mouth... 14,505 ft Kaikorai Mouth to Black Head ... 9,431 ft It will be noticed from the above that the sehe.mp is purely a gravitation one, and the cost of pumping—hitherto thought

The main line of sewer would begin at the point A, on the Wakari road, separat-

MR SLINGER'S SCHEME. NO PUMPING REQUIRED.

inevitable in the drainage of the valley—is thus avoided. There is one very small lowlying area, in Green Island which could not be served by this scheme. This small portion as, however, not yet a residential area; but should it ever become so it could be connected to the above system, and its drainage lifted into the main sewer line by means of a small pumping plant operated on the automatic starting and stopping principle. The scheme provides for the storm water as well as the sewage of tho reticulation area on the "combined" eyetem—i.e., the same conduits beinc used for the carriage of both. The main sewer line would have overflow valves to discharge the surplus storm water into the Kaikorai stream.