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DiscussionSir Hubert Walker referred to the statement in 8 14 that the completion date had been February 1956, but work had not started until January 1955 and it seemed to him that this must have been a very optimistic estimate indeed. From his own experience of getting work done in West Africa the 2 years in which the job had actually been done were in fact extremely creditable. 153.He asked if the Authors could give any more details as to the method of calculating the catastrophic flood level. From his own experience the determination of flood levels was one of the most difficult problems in the design of bridges in West Africa, because of the lack of reliable information. For some time before the war, in Northern Nigeria, where the country was somewhat similar to the Volta Valley, they had found that 70% of the Dunn 154. It would also be interesting to know whether the recent catastrophic floods in Rhodesia had given any cause for thought. Mr Pedder, in his Paper, had made some comparison of the rainfall/area/duration relations between Northern Nigeria and Rhodesia, and had come to the conclusion that in Northern Nigeria rather more than 65% of the Rhodesian rainfali could be expected.155. Usually, when faced with a complete lack of catchment data, a very fair indication of maximum flood level was the floor of the ferryman's house. The ferryman and his family would have been working there for possibly hundreds of years, and they would have built their hut just above the flood level, but not much.156. On what information had the wind speed of 80 m.p.h. been adopted as a basis for design? Most of the wind records in that part of the world were obtained from aerodromes, but it was always thought that the large river valleys were much more susceptible to gusts than the more open sites where the international airports were situated. During the construction of the Benue Bridge a gust anemometer had been installed and, to the best of his recollection, there had been one or two occasions during the period when gusts in excess of 80 m.p.h. had been recorded, and some years ago a gust of 100 m.p.h. had been recorded at Kano. 157.In 0 136 was given a list of the professional staff employed. There were eight engineers; the job had cost €682,000; and the bridge had taken 2 years to complete.The ratio of f42,OOO per engineer per annum was an interesting figure and might possibly l' hoc. Mr P. S. A. Berridge observed that the crescent shape of the arch was very pleasing to the eye, and he thought the bridge was a fine example of the export of one of Britain's greatest national assets, namely first-class engineering. A great deal of serious thought had clearly been given to the ingenious ways of simplifying the chord joints of the 805-ft arch and to the avoidance of secondary and deformation stresses in the connexions of the lateral bracings to the cross-girders.

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