THE FERTILITY OF SOILS IN THE TROPICS 



373 



a comparatively small area about its upper reaches. The 

 dotted lines in Diagram II show the height and volume 

 of the discharge during an average year. It will be seen 

 that, unlike the White Nile, the Blue Nile has an enor- 

 mous range, the discharge varying in a normal year from 

 about 8,000 to 100 cubic metres per second, whilst in 

 abnormal years the discharge in flood may reach 12,000 



DIAGRAM II. 



VOLUME OF WATER PASSING KHARTOUM AND MALAKAL. 

 JAN. FEB. MAR. APR. MAY JUNE JUlV /AUS . SER OCT. HOM PEC 



cubic metres per second, and may drop at the time of 

 minimum supply in the early summer to as little as 50 cubic 

 metres per second. 



As an example of the relative volumes of the river 

 at different times in the year we may take the figures 

 for 1911 as fairly representative of a normal year. The 

 following table gives the percentage contributions of the 

 two rivers to the main Nile at Khartoum. 



