The flooding of theNile (commonly referred to asthe Inundation) and itssiltdeposition was a natural cycle first attested inAncient Egypt. It was of singular importance in the history and culture of Egypt.[1] Governments and administrators of Egypt began constructinginfrastructure tocontrol the flooding in the 19th century, and these projects continued into the 20th. The annual flooding cycle in Egypt came to an end in 1970 with the completion of theAswan High Dam.[citation needed]
The river's predictability and annual deposits in theNile Valley andDelta[2] made for extraordinarily rich soil—classified today asalluvium on a bed ofentisol[3]— enabling the Egyptians to build anempire on the basis of its enormous agricultural wealth andsurpluses ofcereals which could be stored ortraded. Egyptians were one of thefirst groups of people to practice agriculture on a large scale. This in turn was only possible with their innovation ofsurface irrigation, also called "basin irrigation", which finally gave rise to the form ofAncient Egyptian agriculture that persisted into the 20th century. Their farming practices allowed them to grow surpluses of both cereals—especially thestaple cropswheat andbarley—andindustrial crops—such asflax for weaving intolinen andNile grass for manufacture intopapyrus. By the time ofRoman rule, Egypt was one of the most significant sources of wheat in the entire Roman Empire.[1][4][5]
Egyptians have celebrated the flooding since at least earlyantiquity. Today the annual flooding is commemorated by a two-week holiday calledWafaa El-Nil, beginning on August 15. It is also celebrated in theCoptic Church by ceremonially throwing amartyr'srelic into the river, giving it the name "The Martyr's Finger" (Coptic:ⲡⲓⲧⲏⲃ ⲛⲙⲁⲣⲧⲏⲣⲟⲥ,Arabic:Esba` al-shahīd).[citation needed]
The flooding of the Nile held a primary importance to the people of Ancient Egypt, reflected in theirfounding myths, theircalendar, and in their veryname fortheir land.[5] In theAncient Egyptian religion, the floodwaters wereIsis's tears of sorrow for the murderedOsiris, killed by hisown brotherSet. During inundation festivals, Egyptians planted mud figures of Osiris with barley.[6]
TheEgyptian calendar year was divided into three seasons:Akhet (Inundation);Peret (Growth); andShemu (Harvest). Akhet covered the Egyptian flood cycle. This cycle was so consistent that the Egyptians timed its onset using theheliacal rising ofSirius, the key event used to set their calendar.[7]
The Egyptians' name for the Nile wasAr orAur, meaning simply “black,” for the color of the sediments it carried and deposited asfertile black soils on thefloodplains of theNile Delta. The mud's black color is also the root of the AncientEgyptian name for the country:[5]𓆎𓅓𓏏𓊖 (km.t) (commonly vocalised asKemet; probably pronounced[kuːmat] in ancient Egyptian), literally: "black land."[8]Kemet, with its fertile black soil, stood apart from thedeshret (⟨dšṛt⟩), or "red land", of the surroundingEastern andWestern Deserts.[9][10]
Hapi was the god of the Nile and its annual flooding, which was also called theArrival of Hapi in addition to its proper seasonal name. Hapi, with thepharaoh, were said to control the flooding. His association with thefertilization of the soil also meant Hapisymbolised fertility itself.[11]
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The flooding of the Nile is an effect of the yearlymonsoon between May and August, which entails peakrainfall on theEthiopian Highlands, the summits of which reach heights of up to 4,550 m (14,930 ft). Most of thisrunoff flows into theBlue Nile and, by theAtbarah River, into the main Nile; a smaller amount flows through theSobat and theWhite Nile into the Nile. During this short period, the Atbarah and Sobatcontribute up to 90% of Nile's flow and most of itstransported sediment. After the monsoon season, they dwindle to minor rivers.
For Ancient Egyptians, the flooding as such was foreseeable, although its exact dates and levels could be forecast only on a short-term basis by transmitting theNilometer gauge readings atAswan inUpper Egypt to thelower parts of the kingdom where the readings had to be correlated with the local conditions.
The first indications of the rise of the river in Akhet could be seen at the first of thecataracts of the Nile at Aswan as early as the beginning of June according to themodern calendar, and a steady increase went on until the middle of July when the rate of increase usually peaked. The Nile continued to rise until the beginning of September, when the level remained constant for a period of about three weeks, sometimes fewer. In October, it often rose again and reached its highest level. From peak level, it began to subside and usually sank steadily until June, when it reached its lowest level again. Flooding reached Aswan about a week earlier than modernCairo, andLuxor five to six days earlier than Cairo. Typical heights of flood were 45 feet (14 metres) at Aswan, 38 feet (12 metres) at Luxor (andThebes) and 25 feet (7.6 metres) at Cairo.[12]
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Whilst the earliest Egyptians simply laboured those areas which were inundated by the floods, some 7000 years ago, they started to develop thebasin irrigation method. Agricultural land was divided into large fields surrounded bydams andlevees and equipped with intake and exitcanals. The basins were flooded and then closed for about 45 days to saturate the soil with moisture and allow thesilt to deposit. Then the water was discharged to lower fields or back into the Nile. Immediately thereafter,sowing started, andharvesting followed some three or four months later. In the dry season thereafter, farming was not possible. Thus, all crops had to fit into this tight scheme of irrigation and timing.
In case of a small flood, the upper basins could not be filled with water which could mean food shortages orfamine. If a flood was too large, it would damage villages, dykes and canals.
The basinirrigation method did not over-extract nutrients from the soils, and the soils' fertility was sustained by the annual silt deposit.Salinisation did not occur, since, in summer, thegroundwater level was well below the surface, and any salinity which might have accrued was washed away by the next flood.
It is estimated that by this method, in ancient Egypt, some 2 million up to a maximum of 12 million inhabitants could be nourished. By the end ofLate Antiquity, the methods and infrastructure slowly decayed, and the population diminished accordingly; by 1800, Egypt had some 2.5 million inhabitants.
Muhammad Ali Pasha,Khedive of Egypt (r. 1805–1848), attempted to modernize various aspects of Egypt. He endeavoured to extendarable land and achieve additionalrevenue by introducingcotton cultivation, a crop with a longer growing season and requiring sufficient water at all times. To this end, theDelta Barrages and wide systems of new canals were built, changing the irrigation system from the traditional basin irrigation to perennial irrigation whereby farmland could be irrigated throughout the year. Thereby, many crops could be harvested twice or even three times a year and agricultural output was increased dramatically.In 1873,Isma'il Pasha commissioned the construction of theIbrahimiya Canal, thereby greatly extending perennial irrigation.
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The British, during theirfirst period in Egypt, attempted to improve and expand the Egyptians' basin irrigation system, however the newinfrastructure was not sufficiently capacious to fully retain the annual flooding. To remedy this,William Willcocks, in his role as director general ofreservoirs for British Egypt, planned and supervised the construction of theAswan Low Dam, the first truestorage reservoir, and theAssiut Barrage, both completed in 1902. However, they were still not able to retain sufficient water to cope with the driest summers, despite the Aswan Low Dam being raised twice, in 1907–1912 and in 1929–1933.
During the 1920s, the British built theSennar Dam on the Blue Nile to supply water to the massiveGezira Scheme on a regular basis from its reservoir. It was the first dam on the Nile to retain large amounts of sedimentation (and to divert a large quantity of it into the irrigation canals) and, despite opening itssluice gates during flooding to flush its sediments, the reservoir is assumed to have lost about a third of its storage capacity.[13][page needed] In 1966, theRoseires Dam was added to help irrigating the Gezira Scheme. TheJebel Aulia Dam on the White Nile south ofKhartoum was completed in 1937 in order to compensate for the Blue Nile's low waters in winter, but it was still not possible to overcome a period of very low waters in the Nile and thus avoid occasionaldrought, which had plagued Egypt since ancient times.
To overcome these problems,Harold Edwin Hurst, a British hydrologist in theEgyptian Public Works, studied the fluctuations of the water levels in the Nile, and in 1946 submitted a complex "century storage" plan to cope with exceptionally dry seasons occurring statistically once in 100 years. His ideas of constructing new reservoirs usingLake Victoria,Lake Albert andLake Tana, and of reducing the evaporation in theSudd by digging theJonglei Canal, were opposed by the states concerned.
Eventually,Gamal Abdel Nasser,President of Egypt from 1956 to 1970, opted for the idea of theAswan High Dam atAswan in Egypt instead of attempting coordinate internationally with upriver states. The required size of the reservoir was calculated by Hurst's figures andmathematical methods. In 1970, with the completion of the Aswan High Dam and filling ofLake Nasser—which was able to contain even the highest of high water—the annual flooding cycle in Egypt came to an end.
