Heavy Pollution By Sewage In Lyttelton Harbour

Press, Volume CI, Issue 29783, 28 March 1962, Page 20

Heavy Pollution By Sewage In Lyttelton Harbour

Lyttelton Harbour, especially in its upper reaches, is ; among the most heavily ! polluted of New Zealand’s coastal waters, according to a recent general Health Department survey of the pollution of harbours and beaches. The senior inspector of health, Christchurch (Mr J. B. Snoad), said the cause was partly the sewage from harbourside communities, partly the effluent from the Lyttelton borough abattoir, and partly the discharge from ships. At present, the sewage from the Lyttelton borough went into the harbour at the end of Gladstone quay, but because of the construction of the new docks the outfall was being diverted two-thirds of a mile further down towards the sea, said Mr Snoad. This would be an improvement, but the sewage would still be much better dealt with by a treatment plant The discharge from the abattoir at Cass Bay was not now so objectionable as formerly, since the larger solids were screened out by a “save-ell,” but in his opinion the waste should be taken into a common treatment plant with the town sewage, Mr Snoad added. The sewage from Diamond Harbour went into the lower harbour through a sedimentation tank at the west foreland of Purau Bay. Although this system was not entirely

satisfactory, it was tolerable as located.

All sewage from ships in dock was discharged into the harbour basin, whence it was washed into the outer harbour by the tides. The pollution discharged into the harbour from all these sources tended to be swept back into the upper reaches by the tide, and stranded on the mudflats when the tide receded. This was why the upper harbour was probably the most highly polluted part, Mr Snoad added.

Mr Snoad thought that all ships should carry holding tanks or treatment plants so that untreated sewage need not be discharged into harbours. Some of the newer ships had such arrangements, he said.

The engineer-in-chief to the Lyttelton Harbour Board (Mr J. A. Cashin) confirmed that some of the world’s oceangoing ships now had sewage holding tanks or similar devices. Shipowners had begun to make such a provision when health authorities in certain overseas ports with enclosed docks had begun to insist that ship toilets should be locked while the shifts were in port. The necessity of going to a shore toilet had proved most inconvenient. Where the tanks were fitted, one or more toilets were diverted to these as soon as the ship berthed, and the rest sealed.

Mr Cashin added, however, that the locking of toilets was a practice generally restricted to ports where docks were normally sealed off from the tides. In New Zealand, with a relatively low tidal range, the docks were always directly open to the sea. The inner harbour at Lyttelton, for example, had a 500 ft-wide opening which gave the tides full rein. “In these circumstances, I personally do not see any immediate need for action at Lyttelton to prevent the ships discharging sewage into the harbour,” said Mr Cashin. “If figures can be produced, however, to show that serious pollution is being caused in

any part of the harbour by the ships in port, then of course we shall have to take a closer look at the position.” An engineer of the Union Steam Ship Company said that, as far as he knew, none of his company’s ships had any way of disposing af sewage except by jettisoning it straight into the water. There was provision, however, for rubbish and galley refuse to be held on board until the ship was in the open sea, as port regulations forbade this to be emptied in enclosed waters.

A Railway Department spokesman said that the new inter-island car and rail ferry would have a sewage disposal plant designed to retain solid material (but not liquid) while the vessel was in harbour.