AUTHORS' REPLIES

Mr A. Bleasdale, Mr A. Gerard Boulton, Dr J. Ineson and Mr F.

Law (Joint Authors of Paper 10) thanked Mr Kennard for his contribution to the discussion but wished to point out that the important words in his argument were 'critical drought'. In former days this had been taken as 80% of the average rainfall falling in 'three dry years', but Mr Kennard had mentioned in § d3 that in 1952 he had asked whether the 'critical drought' should have a return frequency of 10, 20, 30 or 50 years, and had invited comments thereon. The lack of response to this request surely showed that the concept was not fully appreciated by engineers. d152. Mr Kennard had said that he was puzzled by § 89, and wondered if supplies were to be restricted in drier years. It seemed he had overlooked the words 'if augmented by other resources, such as boreholes, which can be drawn upon in drier summers'. d153. The Authors could not emphasise too strongly the advantages to be gained by running several major resources in combination, but to do this there had to be surplus carrying-capacity and ample treatment plant. Mr Risbridger had shown in Paper 9 that exploitation of Birmingham's Elan Works was restricted by the carrying-capacity of the aqueduct, and it was quite easy to find many similar examples. The difficulty was, of course, akin to that mentioned in § d5—that of the heavy burden of interest charges in the early years of a scheme.