5IO 



NATURE 



[SeptExMBer 24, 1903 



managing director of Messrs. Ransomes and Rapier, of 

 Ipswich, who undertook the manufacture and erection of 

 the sluices and lock-gates. 



The Nile reservoir has been constructed for the purpose 

 of impounding the water of the River Nile during the winter 

 months, and discharging it in the months of May, June, 

 and July, so as to supplement the ordinary flow of the river, 

 and thus enable land to be irrigated which would otherwise 

 receive either no water, or an insufficient supply. The 

 situation chosen for the dam was the head of the Assuan 

 cataract. There were various reasons for the choice : there 

 was a wide section of the river, the waterway being about 

 seven-eighths of a mile, thus permitting the construction of 

 sufficient sluices at different levels to discharge the whole 

 volume of the Nile in flood without weakening the dam by 

 placing them too close together ; the height of the dam 

 would be moderate ; the site chosen seemed to promise good 

 rock foundation throughout, and there were several natural 

 channels when the water was low, each of which could be 

 dealt with separately if desired. 



Arrangements had to be made to house and feed a 

 population of 15,000; offices, workshops, a hospital, and 

 other temporary buildings had to be erected, and a line of 

 railway about 3 miles in length had to be constructed to 

 connect the railway from Luxor to Assuan with the works 

 at the dam. This preliminary work was carried out in 

 1898, and on February 12, 1899, H.R.H. the Duke of 

 Connaught laid the foundation-stone of the dam. 



To- enclose the site of the permanent masonry dam, and 

 to render it dry for the purpose of excavation and laying 

 the masonry, temporary dams, known in Egypt as " sudds,'' 

 had to be formed both above and below the site of the 

 permanent dam. At low Nile the river at the Assuan 

 cataract divides itself into five channels, and this work was 

 done in five sections. The down stream " sudds " were first 

 made, and consisted t)f stones. After the rush of water 

 had been thus stopped, the up-stream " sudds " were formed 

 of bags of sand. 



It was found that the rock on the site of the dam was 

 decomposed. The importance of a solid rock foundation 

 was paramount^ and to obtain it the excavation had to be 

 carried down to a considerable depth, necessitating the re- 

 m.oval of double the amount of material which had been 

 contracted for, and the construction of nearly one and a 

 half times the quantity of masonry that had been antici- 

 pated. The masonry, consisting of local granite set in 

 Portland cement mortar, was commenced in May, 1900, 

 was carried on vigorously during two working seasons in 

 which the Nile was abnormally low, and was finished in 

 June, 1902, less than 3^ years after the first stone was laid, 

 and one year before the expiration of the contract time. 

 The dam is nearly i^ miles in length, and the difference 

 between the surface of the water on the up-stream side and 

 that on down-stream side is 655 feet when the reservoir 

 is full. The masonry is pierced by 180 sluices, of which 

 140 are 23 feet high by 6 feet 6f inches wide and 40 are 

 II feet 6 inches high by 6 feet b\ inches wide. 



The construction of the dam having closed the river to 

 navigation, provision for the passage of vessels was made 

 by means of a canal formed on the west bank of the Nile 

 and having a succession of four locks. 



The capacity of the Nile reservoir when filled to the top 

 water height of 348 feet above mean sea level is about 

 37,600 million cubic feet, a quantity which might have been 

 greatly increased had not the desire to preserve the Temple 

 of Phil?E prevented the raising of the water to the level 

 originally proposed. Even now many portions of the temple 

 or its adjacent buildings are partially submerged. 



It is anticipated that by allowing" the whole volume of 

 the Nile to pass through the sluices when most laden with 

 mud during floods, the silting up of the reservoir to anv 

 considerable extent will be prevented. The cost of the 

 works was nearly 2,450,000/. or about loZ. per million 

 gallons of water impounded. 



The original surveys and designs for the works were pre- 

 pared by Mr. Willcocks (now Sir William Willcocks, 

 K.C.M.G.), under the instructions of Lord Cromer and Sir 

 William Garstin, Sir Benjamin Baker, K.C.B., K.C.M.G., 

 F.R.S., Past President Inst.C.E., being the consulting 

 engineer. On the retirement of Mr. Fitzmaurice, he was 

 succeeded by Mr. C. R. May, M. Inst.C.E., as engineer in 

 charge. The work was carried out by Messrs. John Aird 



NO. 1769, VOL. 68] 



and Co., as contractors, Mr. John A. C. Blue, 

 Assoc. M. Inst.C.E., acting as their agent. 



All concerned in the inception and execution of this great 

 undertaking are to be congratulated on its successful and 

 speedy completion, in the face of the many difficulties which 

 were encountered and overcome. 



Water Supply. 



To everyone a plentiful supply of good water is not only 

 a luxury, but almost a necessity of existence, yet how few 

 even amongst the more intelligent of the millions who are 

 accustomed to find such a supply ready to hand at the 

 nearest tap have more than a very imperfect notion of the 

 works that have to be constructed" to obtain it, or the daily 

 care and attention given to secure and maintain its purity, 

 to ensure its efficient distribution, and to prevent its waste 

 by careless, ignorant, or reckless consumers. It may there- 

 fore not be out of place that when the chair of this Section 

 of the British Association happens, as now, to be occupied 

 by one whose professional life has been largely associated 

 with waterworks undertakings, he should address you on 

 that subject, and endeavour briefly to direct attention to 

 some of the main features of waterworks construction and 

 management. In following that course I shall, however, 

 necessarily have to describe what is already well known to 

 at least a portion of my audience, on whose indulgence I 

 must therefore rely. 



Water supplies may be divided into two main classes, 

 namely, " Gravitation " and " Pumping." In some in- 

 stances a combination of gravitaiton and pumping is re- 

 sorted to, especially in those cases in which the more 

 elevated portions of the district to be supplied are situate 

 above the gravitation level. In selecting a suitable source of 

 supply the main points for consideration are the quantity 

 and the quality of the water. The quantity should be such 

 as will not only suffice to meet the requirements throughout 

 the most protracted periods of drought and frost of the 

 existing population to be served, but should provide for the 

 probable growth of that population during a reasonable 

 number of years to come. The quality of the water selected 

 should be the best that can be obtained, having due regard 

 to considerations of expense. The question of the altitude 

 being sufficient to permit of a supply by gravitation is of 

 far less moment than those of quantity and quality, because 

 the difference in cost between water derived by gravitation 

 and that obtained by pumping is, in the United Kingdom, 

 less than is generally supposed ; indeed, contrary to popular 

 belief, gravitation water is frequently more costly than 

 pumped water, owing to the much greater capital outlay 

 usually incurred in the construction of the works for storing 

 and conveying it. 



Gravitation works may be divided into three classes, 

 namely, those in which water is taken directly from a spring 

 or stream without storage, those in which it is taken from 

 a natural lake, in which case the surface level of the water 

 is usually raised so as to increase the capacity of the lake 

 as at Thirlmere, and those more numerous cases in which 

 the water of a spring is impounded in an artificial reservoir 

 generally formed by the construction of an earthen or 

 masonry dam across the valley along which flows the 

 stream to be taken. 



In the more populated portions of England it is becoming 

 more and more difficult to find an unappropriated gathering 

 ground available as a source of water supply. The gather- 

 ing ground, or drainage area as it is frequently termed, 

 should either be free from human habitations and other 

 sources of possible pollution, or any pollution arising there- 

 from should be capable of being efficiently disposed of by 

 removal from the area of the gathering ground or other- 

 wise. 



The gathering ground must also possess a site suitable 

 for the formation of an impounding reservoir. When this 

 has been selected it next becomes necessary to ascertain the 

 amount of the available rainfall, as tecorded by rain-gauges 

 situate in the drainage area or its immediate vicinity, or 

 where these are not available, as deduced from the returns 

 obtained from more distant rain-gauges, care being always 

 taken that some at least of the gauges have been observed 

 for a sufficient number of years to enable the true average 

 rainfall to be determined. To store the whole of the water 

 flowing from a gathering ground during a cycle of wet 

 years in order to utilise it during a cycle of dry years would 



