THE FERTILITY OF SOILS IN THE TROPICS 



Thus it will be seen that the period of deficiency in a 

 normal year is practically confined to April and May. 

 Seepage from the banks, the amount of which is at 

 present rather uncertain, helps to reduce the deficiency 

 and a certain amount of water is obtained from wells 

 driven into the subsoil, but the main portion of the 

 deficiency is made good by the storage water of the 

 Aswan dam. In normal years, and years of good low 

 supply, the natural river is nearly and sometimes quite 

 sufficient for the present area of cultivation, but when the 

 river is below normal the cotton crop depends on the 

 additional supplies from the reservoir, which in extreme 

 years like the present is indeed of insufficient capacity. 



Turning now to the last eighteen months, the flood 

 of 1912 was low, but thanks to the increased height of 

 the Aswan dam the quantity of water during the early 

 summer was not worse than in previous years. Early 

 in April, the river at Roseires began to rise rapidly and 

 it was thought by many that the flood was to be an early 

 one. But on May 10 the Blue Nile began to fall 

 rapidly, and at the end of June the river was almost at 

 its lowest for the year, with the result that the real rise 

 did not 'begin to reach Haifa until July 20. In conse- 

 quence, until late into July the natural supplies had to 

 be supplemented by water from the reservoir. The false 

 or spring rise which in some years anticipates the true 

 flood is meteorologically independent of the latter, and 

 we may have years in which good spring rains are fol- 

 lowed by low flood rains, or vice versa. In 1913, whilst 

 the spring rise was above normal, the flood was the worst 

 for more than a century. The actual volume of the flood 

 was less than half that of an average year. But what 

 is the more correct way of looking at it is the river level 

 at Aswan did not rise above 90 metres and fell away very 

 rapidly. The result was that in many cases it was im- 

 possible to fill the basins, and in others water was only 

 kept on for a much shorter time than usual. In all, 

 about 400,000 feddans either were without water entirely, 

 or received a very inadequate supply. 



Owing to the difficulty of irrigating Kena Province 

 in low floods, a barrage was constructed some years ago 



