Stout, Olin B.

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 The Knowledge Bank at The Ohio State University Ohio State Engineer   Title:  Egyptian Irrigation Works Creators:  Stout, Olin B. Issue Date:  May-1924 Publisher:  Ohio State University, College of Engineering Citation:  Ohio State Engineer, vol. 7, no. 4 (May, 1924), 9-10, 15, 28. URI:  http://hdl.handle.net/1811/33635  Appears in Collections: Ohio State Engineer: Volume 7, no. 4 (May, 1924)     OHIO STATE ENGINEEREGYPTIAN IRRIGATION WORKS0. B. STOUT, C. E., '24OUR earliest conception of Egypt (see any-elementary treatise on Geography) is aland of intense heat and dry, shifting sandswhose awful monotone is relieved here andthere by an occasional oasis sheltering a caravanof nomadic traders. The more modern versionseems to be a land much overrun with "sheiks"and speckled with sepulchres whose contentswould make Solomon (were he alive) green withenvy. The Egypt with which this article dealsis like neither. It embraces the Nile Valley fromThe Great Assuan Damthe mouth to the second cataract, a distance ofabout a thousand miles. This area, a total of sixand a quarter million acres of arable land, fur-nishes food to about twenty millions of people,or about twice the combined population of NewYork and Chicago. The need of an efficient irri-gation system has been keenly felt in Egypt formany years. For centuries the Egyptians livedin fear of dreadful famines. The story of Josephand Pharaoh's dream will be recalled, how hestored the grain of the seven fat years againstthe seven lean years which were to follow.Our familiarity with the great engineeringprojects in the United States, the Panama Canal(1914), the New York Water Supply, just recent-ly completed, and the proposed Great Lakes-St.Lawrence Waterway, is apt to give us the im-pression that all the big things in engineering aredone in the Western hemisphere. Some widerreading and a consequently broader outlook willsoon disprove this popular misconception. TheAssuan Dam of Egypt, though from a construc-tion standpoint it may not compare favorablywith similar structures in other parts of theworld, from the standpoint of service to themasses (by which all engineering success shouldbe measured) deserves a place at the top. Theconstruction of this project was started in 1898and was finished in 1903. W. G. Bligh, in "Damsand Weirs," says, concerning this project, "Nosingle irrigation of modern times has been moreuseful or far reaching in beneficial results uponthe industrial welfare of the people than thisdam."Previous to the construction of Assuan Dam,the inhabitants depended upon the more or lessmakeshift method of "basin" irrigation. Theannual overflow from the Nile at flood, whichoccurs from August to November, was turnedinto basins or natural depressions in the ground.The water in these basins was controlled bymeans of crude gates and in some cases by mereearthen dams of sand and silt. After a basinwas filled, the water was allowed to stand for atime and was then turned into another depressionat a lower elevation. By these means the landwas saturated with water and the rich alluvialdeposit so necessary to the cultivation of cropswas allowed to settle upon the land. The grainwas then planted and a fair degree of successwas attained. The chief objection to this methodother than its lack of efficiency has been theabsence of any organization or control of theavailable supply of water. In particularly dryyears, the lands of the upper regions were natu-rally more favored. When there was a plentifulsupply no one suffered, but no water was storedfor the dry season.A system of perennial irrigation in conjunctionwith the basin method was tried in parts ofEgypt. This method consists of storing the waterin flood season for use during dry weather. Thesuccess of this method depends upon some per-manent means of storage and control of water.The Dam from BelowLack of a responsible head and an efficient meansof execution caused the failure of this system.In very wet years when there was some flow theentire year the perennial system was satisfac-tory, but if the season of dry weather persistedthe supply was soon exhausted. As a rule, theNile is almost dry nine months of the year and isa raging torrent for the remainder.Some consideration of the economic and indus-910 OHIO STATE E N G I N E E Rtrial conditions of Egypt will give a clearer un-derstanding of the importance of this project asa great work of humanity, as well as a betterconception of some of the difficulties encounteredby the engineers of the Daira Land Companywhen they went in there to investigate the irri-gation possibilities in 1894. The very nature ofthe inhabitants increased the difficulty of prose-cuting the work. The source of the Nile was notdiscovered until the middle of the nineteenthcentury. By the common people this historicstream was looked upon as a mysterious god. Ourearliest records show them making sacrifices offirst-born children to this all-powerful and de-stroying deity. Yet they revered it as a greatsource of food supply. Without it and the annualdeposit of rich earth they knew that starvationwould result. In a nation which is by naturesubdued and superstitious, it is difficult to carryout any work of a progressive nature for whichthere exists no precedent.Too much credit cannot be given to Sir WilliamWillcocks and his corps of English engineers,who were responsible for the conception andexecution of this great project. The preliminarywork was carried on under odds. No assurancethat the project was to be the success it hasproved to be was to be had at the outset. Verylittle co-oy.eration was to be had from the verypeople who were to be benefited the most. Theexecution of a work of this kind under the aboveconditions is a good example of engineeringfaith which is so necessary in a work of thismagnitude. But the greatest wonder is that anundertaking which has had such a stupendouseffect upon the industrial welfare was not con-ceived earlier.The engineering difficulties, though different incharacter from the political and social, were nomore easily overcome. After an extended inves-tigation and consideration from all angles, threepossible methods of storing the surplus water ofthe flood season for use throughout the year weresuggested.The first method suggested was by storing thewater in depressions outside the Nile Valley. Longexperience with the basin method previously out-lined had proved inefficient and unsatisfactory.The loss, upon long storage, due to evaporationand percolation, was too great to make that sys-tem practical.The second method proposed storing the excesswater in waste lands of the Delta. If this methodwere adopted, only a small portion of! the landwould be benefited. The Delta comprises onlyabout one-fifth of the total arable land.The last method, the one finally adopted, con-sisted of storing the water in a reservoir in thevalley itself. This final method necessitated theconstruction of some type of barrier to impoundthe water. The consideration and selection of asuitable structure called forth more serious study.Again three possible solutions presented them-selves; first, by building solid submergible damsover which the floods may discharge; second,by building solid insubmergible dams and turningthe Nile through waste weirs; and third, bybuilding insubmergible dams provided with un-dersluices which are capable of discharging thefloods through the dams.Building solid submergible dams would provesatisfactory where the floods were infrequent andof short duration. Since the Nile floods occurannually and as a rule last for three months, themaximum height of such a structure would beabout forty feet with safety. Here the conditionsrequired a much higher dam, so this solution wasdiscarded.Insubmergible dams provided with waste weirsare suitable for streams with very little sedimentor where the slope of the stream is great enoughto provide a velocity to keep the silt scoured outof the reservoir. The Nile drops only one footin about two and a half miles and, consequently,has a very sluggish current. This means a largedeposition of alluvium. It was computed by theengineers that about two billion cubic feet of siltpass Assuan annually, or enough earth to coverthe entire University lands to a depth of aboutforty feet. With the reservoir filling this amounteach year, a great loss of capacity would resultand consequently the entire basin would be filled.It was cited that the Puentes Dam in Spain siltedup about fifty feet in just a few years. As aconsequence, this method had to be abandoned.Insubmergible dams with undersluices for dis-charging the flood through the dam was the onlyalternative. During the flood season the ports orsluices at the bottom of the dam could be openedto allow the water bearing the silt to pass andthen when the water was clear the openings couldbe closed to impound the surplus water. Thistype of structure was finally adopted and is in useat the present time.It remained to design such a dam. A consider-ation of the geologic formation underlying Egyptwill give some conception of the difficulties inbuilding such a structure. Possibly the firstrequisite of any engineering structure is the foun-dation. Unless the base is founded upon safeprinciples the whole structure may fail. Thehistory of masonry dams shows that the largermajority of failures of dams is due to foundationfailures. To be absolutely safe the foundation ofa dam should be upon solid rock. This require-ment, then, was one of the prime factors govern-ing the location of Assuan Dam. It is commonlyknown that the Nile Valley is of deltaic origin,that is, it has been produced by the constant depo-sition of sediment at the mouth which continuallymoves farther out into the body of water intowhich the stream discharges. Under conditionssuch as this, the possibility of finding solid rockfor foundation is v6ry remote without going tosuch depth as to make the construction econom-ically impossible. This condition fixed the loca-tion at one of the cataracts where the rock out-crops. Another condition affecting the locationwas the number of people served. In consideringthis condition, the greater the distance from themouth the more irrigable the land.A location a few miles below Assuan, nearSilsila, was suggested, but a test of the NubianSandstone at that location showed it unfit formasonry. The site at Assuan was finally chosenon account of the rock outcrop for foundation,the fine granite for the masonry, and the greatwidth of the stream at that point, which reducedthe necessary height appreciably. The onormous(Continued on Page l,r>)OHIO STATE E N G I N E E R 15EGYPTIAN IRRIGATION WORKS(Continued from Page 10)volume of water impounded made this latter pre-caution necessary. This type of dam is in directcontrast to those usually built in the UnitedStates, where the site is usually chosen wherethe valley narrows down to a gorge. The extremewidth of the Nile at this point necessitated theuse of a dam more than a mile and a quarterin length, or about six times as long as theO'Shaughnessy Dam now under construction forthe Columbus Water Supply. Owing to the irreg-ularities of the stream bed, the height variesfrom a few feet to one hundred and twenty-five.It is twenty-three feet wide on top and abouteighty-one at the widest point at the bottom.Lying just above Assuan in the middle of theNile is the Island of Philae, upon which is situ-ated the famous Temple of Philae. The designof the original dam was of such height as to com-pletely submerge this temple. The engineerssuggested that the temple be removed and recon-structed at another site. This suggestion metwith much disfavor among archaeologists all overthe world. The officials were beset with petitionsbeseeching them to spare the temple. As a resultthe design was changed and a dam about twenty-five feet lower was finally adopted. This proced-ure was a mistake, and it was realized before thedam was in operation a year. The people weresoon crying for more water. A few years laterthe dam was raised to the original elevation andthe previous proposal to remove the temple wascarried out.General sanitation offered another objection tothe construction of this work. The committee onsanitation held that the impounding of the waterwould lead to stagnation and a consequent injuryto health, due to the penetration of the stale waterto the drinking supply. Investigation showed thatunder the proposed system conditions could be noworse than those already existing.The construction of this project occupied aboutfive years. The work was done by contract. JohnAird and Son, of London, were the contractorson the original work and they also raised thestructure about 1910. The original structure wasfinished in 1903.The bulk of the masonry is local granite. Theexposed surfaces are, with the exception of thesluices, of course, rockfaced ashlar, which isroughly rectangular stone blocks laid with thinjoints. The sluices are all lined with finely dressedstone, with the exception of thirty, which arelined with cast iron. The interior masonry ishandlaid rubble or irregular stone blocks laid inPortland cement mortar, of which forty percentis mortar.The total cost of the project was about twelvemillions of dollars. The direct computed benefitto the land is, in round numbers, twenty millionsof dollars. This figure is, however, but an infini-tesimal part of the great benefit to the peoples ofEgypt.At present this is the largest masonry dam inthe world. It will be exceeded, however, as anengineering structure by the Wilson Dam atMuscle Shoals, Alabama, which is now underconstruction.(Cont inued on Page 28)28 OHIO STATE E N G I N E E REGYPTIAN IRRIGATION WORKS(Continued from Page 15)The writer wishes to acknowledge his indebt-edness for much of the information containedherein to Sir William Willcocks, whose book,"Egyptian Irrigation," is highly recommended toany who are further interested. Acknowledg-ment is also made to Engineering News-Record.

Egyptian Irrigation Works

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Egyptian Irrigation Works

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