DiscussionThe Author introduced the Paper with the aid of a series of lantern slides. J. A. Banks said that the Author had presented information ofgreat value to all engineers who were concerned with the design of pressure tunnels and similar works. The Paper was particularly welcome a t the present time, because it was only in very recent years that the construction of underground generating stations had been undertaken in Great Britain. The Author had referred to the Clachan station in Argyllshire and, whilst others had been constructed since or were in hand, it might be relevant to give some particulars of the Clachan works which formed part of the North of Scotland Hydro-Electric Board's Glen Shira project.Clachan generating station, with an inclined pressure shaft (the general arrangement of which was shown in Pigs 30,31, and 32) housed one verticalFrancis turbine of 54,000 horse-power operating under a head of 960 feet.As stated in the Paper, the station had been excavated by the cut-and-cover method. The concrete walls below main floor level had been poured hard against the rock and the reinforced concrete columns and mane girders, which carried a 150-ton overhead travelling crane had been anchored into the rock both longitudinally and transversely. There was an inner lining of brickwork and a suspended ceiling, the main roof having been formed by a reinforced concrete arch springing from skewbacks cut into the rock, and with that internal lining and ceiling there was a complete clearance
DISCUSSION ON DAER WATER SUPPLY SOHEME since a too-rapid or too-slow rate would cause cavitation in the joint either from entrapped air not escaping, or the bitumen reaching too low a temperature and so not flowing properly.in the joint would vapourize in contact with hot bitumen and cause blow holes in the 186. The dryness of the gap for bitumen filling was also important, since any moisture completed joint.187. "Turbine-blade" effect in the completed joint was found to be caused by insdiciently cleaning old limewash, to prevent bitumen adherence, from the rubber backing-strips.London) said that B difflculty encountered in the design of the Daer dam and reservoir had been the lack of reliable information from which to estimate the average rainfall over the catchment area. The rain-gauge records in existence prior to the Water Order of 1948 had been very sparse and quite insufficient for the purpose; consequently, reliance had had to be placed on an isohyetal map supplied by the Scottish Meteorological Office. From the information given on that map it had been calculated that the average annual rainfall was 65 in. over the 11,700 acres of the Deer drainage area, but all those who had been connected with the project in any way realized that that was not 8 reliable estimate.190. There were three vitally important factors in the design of a water-supply scheme which depended on the amount of rainfall: (i) the yield of the scheme; (ii) the amount of compensation water; and (iii) the required storage capacity deduced from the amount of rainfall run-off and therefore the top water level of the reservoir.191. The difficulty about the amount of compensation water, so far as the Water Order was concerned, had been overcome by fixing the amount at one-sixth of the yield estimated from the rainfall of 65 in. and by including certain clauses in the Water Order. The gist of the first, Clause 5(4), was that: "Subject to the provisions of the next succeeding section the County Council shall . . . discharge into the Daer Water" not less than 4& m.g.d.192. The next clause read: "6(l). The County Council shall, as soon as practicable after this Order comes into operation, install rainfall gauges in the catchment area of the reservoir in such positions and of such type as may be approved by the Director of the Meteorological Office, Air Ministry, and shall furnish to him copies of the records made by the said gauges, and the County Council shall, when such records have been furnished to the Director of the Meteorological Office in respect of seven complete calendar years, request him to assess in inches the average annual rainfall on the said catchment area for the period from the year 1881 to the year 1955 inclusive, and the assessment so made shall be final and conclusive and binding on the County Council and the British Electricity Authority for the purposes of this Order.(2) If 80 per cent of the average annual rainfall assessed in accordance with the provisions of the last preceding subsection less 14 inches exceeds 38 inches ...
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