21 



its suppl}^ from the heaA^y raius in the equatorial re<,aons where it has 

 its source. The high-water season of both the Blue Nile and the Atbara 

 begins with Jul,v and end« with September. These two streams fur- 

 nish nearl}^ all of the sediment which has built up the valley of the 

 river in Egypt and maintained the fertility of the soil. The effect of 

 the hiffh water from all sources is felt at Cairo soon after the 1st of 

 August, but owing to the demand for water in upper Egypt during 

 the late summer and early fall month:, extreme high water does not 

 reach Cairo until toward the end of September, when the basins have 

 discharged into the river. 



While the Nile varies each year in discharge it is a singularly steady 

 stream, and in this respect is ludike the rivers with which we are 

 familiar. It has but one high- water season each year, and this begins 

 and ends so regularly that irrigators know when to prepare for the 

 flood. Although the stream is remarkable in this respect, its varia- 

 tions in discharge in different years affect agriculture greatly. During 

 years of low Nile large areas go unirrigated. In average years the 

 Nile furnishes sufficient water to bring prosperity to Egypt. Once 

 in fffteen or twenty years it is unusually high, when large areas are 

 devastated by floods. If a sudden rise should occur in the Nile, as so 

 often happens in many of our Western streams, it would be a great 

 curiosity to the natives. 



The accompanying chart (fig. 1) makes a comparison between the 

 discharge of the Nile at Assuan and of the Mississippi at St. Louis. 

 It will be seen that the discharge of the Mississippi is very irregular. 

 High water may appear at St. Louis at any time between April and 

 June, and this maximum discharge may range from 250,000 to nearly 

 1,000,000 cubic feet per second. The maximum discharge of the Nile 

 varies from 300,000 to 420,000 cubic feet per second. If the Nile 

 varied as the Mississippi does at St. Louis, agricultural Egypt 

 would soon cease to exist, unless the great volumes of water which 

 would descend at flood times could be stored and the flow of the river 

 equalized. 



Fig. 2 shows the relation between the discharge of the Nile at 

 Assuan and of the Missouri at Kansas City for the four years begin- 

 ning with 1897, giving the maximum, minimum, and uican yearly 

 discharges for these four years. Both streams flow through arid 

 countries. The Nile rises in a region of tropical rains, although a 

 considerable portion of its supply comes from the Abyssinian Moun- 

 tains and the ranges of central Africa. The Missouri has its source 

 in the snow-covered Rockies. It will be noticed that the high-water 

 period of the ]VIissouri ma}' occur at almost an}- time between the 

 middle of April and the 1st of July, while the Nile reaches its maxi- 

 mum near the 1st of September. The discharge of the two streams 

 is about the same during January and February and during the first 



