DRAINAGE OF AUCKLAND.

New Zealand Herald, Volume LXVII, Issue 20519, 21 March 1930, Page 15

DRAINAGE OF AUCKLAND.

HANY, PROBLEMS AHEAD.

THE orakei outfall**

POSITION ON THE MANUKAU.

ENGINEER'S TOUR ABROAD. The return of Mr. H. H. Watkins., engineer to the Auckland and Suburban Drainage Board, who is expected here next week/' after an 11 months' tour abroad, will revive the movement to deal comprehensively with the drainage of tho whole Auckland urban area.

Drainage matters came under public { notice this' week when the Boyal New Zealand Yscht Squadron protested against the nuisance caused by sewage near the main sewer outfall at Orakei. Actually, this nuisance, although rather conspicuous at times, is only one, and not the greatest, of the problems with which Mr. Watkins and the Auckland local authorities will have to deal. These prpblems have been receiving very earnest consideration from local bodies, medical officers of health and others during the past two years, and it was in order to gain fresh expert knowledge with which to meet them that- Mr. Watkins was sent abroad early last May. H 9 has visited Canada, the United States, Great Britain, Belgium, Germany, France and Italy, concluding with several weeks in the chief cities of Australia.

The Original Scheme. When the Auckland and Suburban Drainage Board, was formed more than 20 years ago, it was expected that the main drainage system then planned would suffice the city for a very long time. The scheme, which began to operate in 1914, provided unified main drainage for the whole Waitemata watershed of the Auckland isthmus. Now it is only too apparent that the drainage of the Manukau. watershed will'also have to be dealt with in a comprehensive way. Possibly it may even.be necessary to link both watersheds and provide a singlo outlet in the lower reaches of the Manukau Harbour, an obviously the volume of sewage discharged from Orakei cannot be allowed to increase to an indefinite extent. On the Manukau side au acute problem has arisen.' There are three sewage outfalls" aloug the southern shore of the isthmus, draining Onehunga, part of Mount Roslviil and New Lynn. These are fairly satisfactory, but the Health Department has drawn attention to pollution of the water? just below the Mangere Bridge. Where the real trouble occurs is in the upper reaches of the harbour, opposite Westfield and-Otahuhu. Here the effluent from the freezing works, the municipal abtfttohs and other industrial plants is discharged into shallow water, which is becoming more shallow every year. The ebb tide lacks strength to carry it far, and the flood, often aided by a westerly wind, takes it back to ihe point of origin. Change in Conditions.

This creates a particularly offensive nuisance in a lagoon beside the Great Soath Road at St. Anne's Bridge. As •-? the Westfield and Penrose districts seem 'destined to become the home of Auckland's " heavy" industries, the systematic drainage of the whole area will soon become imperative. Another difficulty is provided by Ellerslie, where very insanitary conditions exist whenever there is heavy rain, which cannot be properly drained except into the Manukau.

When the Auckland main drainage

scheme was launched the question of an . outlet to the open ocean at Hanukau Heads was considered and dismissed on account of its enormous cost. Orakei was selected for the outfall because exhaustive float testi gave satisfactory results, and it seemed likely to meet all needs for many years to come. Since then, however, conditions have radically changed. The eastern and western tide deflectors and the waterfront road embankment across Hobson Bay have changed the course of the tide currents. The Orakei native reserve. formerly a sort of no-man's-land, is now becoming a residential suburb of the first rank/ A scenic road is being built along the shore from the city to St. HeJiers Bav, passing actually over the outfall tanks" and past the plant which screens the sewage. Greater Volume of Sewage.

Owing to the growth of population and the laying of sewers in new districts the volume o£ sewage has greatly increased, and will continue to do 60. In wet weather great quantities of storm-water are admitted lo the sowers, and the outflow is then enormous, although heavily diluted. At every ebb-tide a large area of water off the Orakei Wharf is rendered highly offensive. It should not he supposed that there is necessarily any danger to health from the discharge of sewage in this way. Analyses of water samples taken early last year by Dr. T. J. Hughes, medical officer of health, showed that pollution existed only in the area of discharge. Even in the Rangitoto Channel, at a time when the sewage could he presumed to hie on its way out into the gulf, the tests gaVe a normal result for harbour water owing to heavy dilution. The same was true of samples taken in the neighbourhood of Orakei and Mission Bav, outside the area of noticeable discoloration. A Greater Evil.

Nevertheless the nuisance is admitted and is certain to increase. The unfortunate part is that apparently _a plant for treating the sewage at Orakei so as to give a harmless effluent would ,bo more offensive still in the neighbourhood. Such plants, it seems, create unpleasant odours which in this case would be wafted up the valleys of Orakei by every sea breeze to the homes on the heights. Tn short, Auckland will soon find itself with a sewerage outlet at its very front door. , Carrying the outfall pipe further out to sea will do no good, for the simple rpason that the sewage will then be discharged nearer the track of shipping. On the North Shore drainage reticulation presents few difficulties. The chief question for consideration is whether a multiplicity of outfalls should be allowed. There are.about five at present, one being from a septic tank at Northcote, one at North Head, one at Narrow Neck and two on the Takapuna foreshore.