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543agreed upon by the interested countries, is the working of the Equatorial Nile project, of which the h t component, the Lake Victoria Reservoir, has been constructed, fo which later must be added the Lake Kioga Regulator, the Lake Albert Reservoir, and the Jonglei Diversion Canal project. These involve protection against both drought and flood, and are more complicated than the cases considered in the present Paper. ACKNOWLEDGEMENTS Throughout the work described in this Paper, which haa extended over several years, the Author has had valuable advice and assistance from his colleagues in the Egyptian Ministry of Public Works: Mr R. P. Black, M.C., M.A., B.Sc., now scientific Consultant, Ministry of Public Works; and Mr Yusef Simaika, B.Sc., InspectorGeneral, Nile Control, later Under-Secretary of State, and now Technical Consultant.W Naguib Boulos, the Author's personal assistant for more than 30 years, haa done a great deal of work on the details of the Paper, assisted by the staff of Nile Control. To all of these the Author offers his thanks.The Paper, which was received on 17 June, 1955, is accompanied by twenty sheets of diagrams, from which the Figures in the text have been prepared. DiscussionM r W. N. Allan (Irrigation Consultant to the Sudan Government) said it was a notable achievement to have developed statistical equations in forms which fitted such varied types of phenomena, so that the consideration of a single case could be based on knowledge of the characteristics of a much larger sample. The Author had pointed out, in the conclusion, that each individual case must be treated separately, using as data the practical conditions by which it was governed. It was on that aspect of the subject, the practical consideration of individual cases, that Mr M a n commented, with particular reference to the effects and implications of the losses which in varying degrees were necessarily incurred in long-term storage.In the Author's statistical investigations such losses had been ignored, for reasons which were obvious. There was no absolute relation between a phenomenon itself and the losses, which would vary with the conditions of storage and the methods of regulation adopted. But in the practical consideration of any individual case, the losses could not be disregarded, since they affected the amount of storage capacity which was hydrologically desirable, the net usable draft which could be maintained, and the methods of regulation which were most likely to be suitable.To illustrate those points Mr Allan used the example of Aswan, not only because that was one of the cases which the Author had found to be difficult in regulation, but also because the rate of evaporation was high, and the losses were thus significant in relation to the total annual flows, so that their effects showed up clearly. For that site as a reservoir data were already available up to a capacity of about 130 milliards of cubic metres; from those Mr M a n had prepared a Table of annual losses extended to cover a much larger range, on th...

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ON D 5A 5A A 4 x 7~7~1 1 = 2 , 1 5 6~4~ 2 X 13 X 34A --A 11 X 7 X 99 X 11 X 49-4,648 Hemet = L(l +~+~a + z~ Y Y2 Y 3 +W,+. Y4 . . where y = -. y E = 4/28 .) . . . . . (7) 28 P that the hydrostatic uplift ranges from a maximum at the upstream face to zero at the B. Allowance for hydrostatic pressure, as for a pervious dam. If it be assumed downstream face, the effect is almost the same as taking the weight of the dam in water. This assumption is correct for a purely triangular dam and is a reasonable approximation in this case. Therefore it is necessary only to write ( 8 -1) instead of 8 in formula (7). which gives C = & ( l + Y + Y + -+ -+ 1/2(8 -1) 7 49.5 2 431 y3 4,648 y4. . .) DiscussionThe Authors introduced the Paper with aid of a film. Mr C. A. Risbridger observed that the present very valuable Paper, dealing with the development of the Claerwen gathering ground, when added to the classic Paper presented in 1912 by the Mansergh brothers,l dealing with the development of the Elan gathering ground, would almost complete the thrilling story of the development of those gathering grounds. He said " almost " because the story might be rounded off in due course by information based upon the very careful records of rainfall, run-off, losses, and so on, which had been maintained on those gathering grounds during the past 50 years. Although the present Paper dealt mainly with constructional matters, it would probably not be out of place to make very brief reference to the total storage which now existed in terms of the yield expected to be obtainable from the gathering ground. The number of days was in fact slightly more than 200, on the basis of a yield of 104 million gallons per day. That figure of 200 might be compared with a figure of 180, which Mansergh had intended to provide in his original project, and with 150 days, which would be obtained by applying the old Hawksley formula of y = 500 divided by the cube root of the average annual yield of the three driest consecutive years. It was a great tribute to Mansergh that with the information provided by only one long-standing rain-gauge on the gathering ground 60 years ago, supplemented by two or three very short-term gauges, he had See footnote 1, p. 249. Downloaded by [] on [12/09/16].

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