H—3

Drainage League Schemes (5) {a) Alternative schemes for the drainage of the Central and Southern Districts were submitted by the Drainage League. These were prepared by Mr. R. P. Worley, of Auckland, a consulting engineer who has specialized in sewerage engineering. Mr. Worley gave evidence before us in support of his proposals, and they were also supported by another consulting engineer, Mr. Hugh Vickerman, of Wellington. The latter was requested by the league to give evidence some time after the sittings of the Commission had commenced. He arrived in Auckland on the evening of the 29th March (Tuesday), and gave his evidence on Monday, 4th April. He had no knowledge whatever of Auckland's drainage problems or of the matters being considered by the Commission until he arrived in Auckland, and he admitted that he had not studied the reports made by Mr. Porter which have been referred to. Mr. Vickerman did not claim to be a sewerage expert, but he has had a very wide experience as a civil engineer. It will be obvious that he was at a serious disadvantage. (6) Leaving out of consideration the treatment and utilization aspects, all the proposals of the Drainage League include provision for the whole of the sewage from the Central and Southern Districts to be treated at works on the southern side of the isthmus and for the effluent to be discharged into the Manukau Harbour. The following brief outline should give a sufficient explanation of the proposals. (c) The Orakei tanks would be used as storm-water balancing tanks as proposed by Mr. Porter. There would be a main pumping-station at Orakei to elevate the sewage so that it may be discharged into a proposed new trunk sewer from Orakei to Southdown. Main sewers would be constructed to carry the sewage, including trade wastes, from Onehunga, Penrose, and Papatoetoe to Southdown as proposed in Mr. Porter's Schema No. 2, and an additional main sewer (replacing Mr. Porter's proposed sewer from Panmure to West Tamaki Head) would be constructed from Glendowie to Southdown via Panmure. There would be treatment-works using the activated-sludge process at Southdown. If the league's proposals for an oxidation lake, the growing of waterhyacinths or other water plants, and for the 'composting of sludge and garbage and other municipal and trade wastes are not adopted, it is proposed that the sewage effluent would be discharged by a pipe from Southdown to the Purakau Channel on ebb tides only. (d) It should be mentioned that although the league criticized the discharge of excess storm-water at Orakei as being insanitary, its schemes do not include any different provision for the disposal of the storm-water from that proposed by the Drainage Board. In this connection we consider that the-Board's proposal is in accordance with normal sewerage-engineering practice and that the greatly diluted sewage that would flow into the harbour during periods of prolonged rainfall would not cause a nuisance. Estimate of Costs (6) (a) Estimates of costs for the various schemes proposed by the Drainage Board and the Drainage League respectively were given by the expert witnesses and were discussed and examined before us at considerable length. We have given careful consideration to the subject and have decided that we should not do more than make a few general observations and that no useful purpose would be served by examining the figures in detail in this report. In the first place it will, of course, be appreciated that our rejection of the oxidation lake and composting proposals has affected in many ways any consideration of the estimates. Further, it is plain that there are many uncertain and unknown factors which must have an influence on the reliability of the estimates. In addition to the effect of uncertain geological and other similar conditions, wages and other factors which affect construction costs in New Zealand and elsewhere have changed in certain respects since some of the estimates were prepared, and further changes are likely to occur before the works are executed. Again, the results of the investigations

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