488 ANNUAL KEPOET SMITHSONIAN INSTITUTION, 1908. 



a state of things occurs in successive years, the average level of the 

 vrater table in the valley will fall, and this also will act prejudicially. 

 History records that on more than one occasion the Nile at Cairo was 

 so low that it could be forded in the early summer, which was doubt- 

 less due to such a chain of causes as that above described, assisted by 

 such a distribution of sandbanks at Cairo as allowed the water to 

 spread over a wide bed without forming a definite channel ; for series 

 of low floods due to weakness of the Abyssinian rains are common, 

 but a diminution of the water of the river to such an extent has rarely 

 been recorded. 



It will be seen that, with such a reduction of the water supply in 

 the first half of the jenr, continuous cultivation of the arable land 

 was impossible until engineering works had been constructed to raise 

 the level of the water sufficiently for it to flow into the perennial 

 supply canals, and until reservoirs existed in which the surplus water 

 of the autumn could be stored for later use. Previously the flood 

 water was led on to the flood plains by canals, so that it might there 

 deposit the silt which it carried in suspension and soak the soil in 

 preparation for the crop which was to follow ; on this newly deposited 

 silt and the water-soaked land the seed was sown after the flood 

 water had drained off. Land in Egypt which was not watered by the 

 flood could not be cultivated for that year unless it was situated on 

 the bank of the river, or wells were sunk in the alluvial plain so that 

 the crops could be watered artificially. Hence the flood was all- 

 important; and one that did not reach the requisite level caused 

 scarcity, want, or even famine. Modern skill has greatly changed 

 these natural conditions until the whole of the delta, and a large part 

 of the valley north of Assiut, receive water throughout the year with 

 the aid of the regulating dams at Assiut, near Cairo, and at Zifta, 

 which enable the water to be turned into high-level canals; the Aswan 

 reservoir furnishes a supply at the season when the normal volume 

 of the river is insufficient for the demands made upon it by the pres- 

 ent amount of cultivation. Finally, the regulating dam which is now 

 being constructed at Esna, in Upper Egypt, Avill render it possible to 

 turn the flood waters on to the higher lands in the province of Qena 

 which are not watered by a low flood, and so insure their yearly 

 cultivation. 



Man has thus so altered the conditions of the Nile supply that in 

 future the flood will no longer have the same preeminent importance 

 that it has hitherto enjoyed. At the time of full flood there is always 

 more water than can be utilized, and now the Esna work will en- 

 able the high land to be flooded even in years of deficient supply. It 

 is the low-stage supply on which the cotton crop depends that is now 

 most anxiously studied. If the rainfall has been heavy and conse- 

 quently the flood has been large, the springs in Abyssinia provide 



