TANGIWAI RAIL BRIDGE

Press, Volume XC, Issue 27303, 20 March 1954, Page 8

TANGIWAI RAIL BRIDGE

‘Not Well Designed Or Located”

ENGINEER’S VIEWS ON DISASTER

(New Zealand Press Association) WELLINGTON, March 19. Mr James Patterson Porter, chief engineer of the Auckland Metropolitan Drainage Board, fold the Tangiwai Board of Inquiry today that in his opinion the Tangiwai railway bridge was not ’well designed or located in the first instance, but even if he were wrong in that view, a review of the design in the light of increased knowledge would long since have revealed defects. Mr Porter holds the degree of B.Sc. from London University, and is a member of the Institution of- Civil Engineers and of the New Zealand Institute of Engineers. He was called by Mr L Macarthur, counsel for the relatives of those who lost their lives in the disaster. Mr Porter said he had had more than 32 years’ experience in the design and construction of maior public works, for the most part in tne United Kingdom. His daughter and granddaughter were lost in the Tangiwai tragedy. In his opinion, Mr Porter said, any important structure which could be destroyed by flood or other more or less predictable catastrophe, should be designed or strengthened, if its failure was likely to result in a serious loss of life, to withstand the worst foreseeable catastrophe likely within 100 years, with a probability of not more than one in IPO in any given year. Mr Pojter in his view, some <rStoipe was available in 1906 which thX7d warned the designing engineer. Much more evidence had become available since then. Precautions Against Floods "I am of the opinion that, quite apart from possible failure of the ice barrier at the Ruapehu crater lake, the capacity of this bridge should have been adjusted to take a heavily siltladen discharge of at least 50,000 cusecs as a possible maximum flood within a frequency of one year in 100,” he said. “In my opinion, the probable rate of discharge on the night of the disaster was 30,000 to 40,000 cusecs at the ‘ipstantar ecus peak,’ when there was no longer a difference between uostream and downstream levels at the bridge.” Mr Porter said he considered piers 4 and 5 of the bridge were undermined by violent “scouring vortices.” The depths and design details of the foundations of the piers were completely inadequate. “I am of the opinion that this bridge was wrongly located with reference to this river. There were no suitably J designed guide banks which would have minimised the defects in location,” he said. To Mr Macarthur, Mr Porter said that the scouring detected under pier 4 after the 1925 floods was a warning signal. At that time, there was a substantial amount of knowledge as to the methods of assessing quantities. Mr Macarthur: You mean assessing flood discharges that might reasonably be expected from a given catchment area?—Yes. Damming of River Later, at the invitation of Judge Stilwell, chairman of the board, the Chief Civil Engineer of the Railways Department (Mr A. H. Murison) and the department’s research engineer (Mr P. B. Bryden) joined counsel around a map. <n which Mr Porter indicated a place where he said the river had been partly damned. After pointing out where he thought the damming took place, Mr Porter said: “The river level upstream of the bridge would rise by at least Bft, and I assume that at that time pressure on the temporary dam was too great and the dabris forming the dam was washed a way very quickly. There was a very substantial scour, and pier 4 was carried away.” The board today adjourned its sittings till March 29, to enable members and counsel to study the technical evidence already given. „ •*