374 



THE FERTILITY OF SOILS IN THE TROPICS 



January 



February 



March 



April 



May 



June 



July 



August 



September 



October 



November 



December 



1912 

 January 



White 



Nile 



71 



77 

 76 



77 

 72 



73 

 27 



2 



6 



32 

 39 

 52 



63 



Blue 

 Nile 



29 

 23 

 24 

 2 3 

 28 

 27 



73 

 98 



94 



68 

 61 

 48 



37 



This shows clearly that the White Nile is the more 

 important river in low stage, and the Blue Nile in flood. 



The waters of the Blue and White Niles meet at 

 Khartoum, and thereafter the only tributary joining the 

 main river is the Atbara, which is entirely dry from 

 October to May, but in July, August and September has 

 a high flood discharge, supplementing the flood waters of 

 the Blue Nile. 



Having thus described the origin of the water which 

 makes agriculture in Egypt possible, we are in a position 

 to consider the abnormal character of the last twelve 

 months, but before doing so it will perhaps be well to 

 describe briefly the methods of water supply. 



Putting aside minor details, the cultivated area of 

 Egypt may be divided into two great classes : land which 

 receives perennial irrigation, and basin land which re- 

 ceives one watering a year only, at time of flood. 



I will describe briefly the former system first. For the 

 greater part of the year the river is flowing several 

 metres below land level, and to give continual irrigation 

 it is necessary either to pump the water from the river 

 to high level canals running through the fields, or to 

 construct barrages across the river to raise the water 

 level artificially to the neighbourhood of land-level. A 

 typical case of the former is the Kom Ombo estate, which 

 depends entirely on pumps for its water supply, whilst 

 the perennially irrigated area of Upper Egypt is de- 

 pendent 'for its regular supply at low stage on the Assiut 

 Barrage. This barrage holds up the water-levels by a 

 maximum of about 2 metres, and enables the Ibrahimia 

 Canal to receive a proper supply of water during the 



