THE FERTILITY OF SOILS IN THE TROPICS 



377 



at Esna by means of which flood levels upstream of it 

 can be increased by 2 metres. In 1913, to save as much 

 land as possible, the irrigation authorities held up the 

 water to a higher head than the barrage was designed 

 for. The scour due to the increased head of water was 

 tremendous and great quantities of stone had to be 



DIAGRAM III. 

 AMOUNT OF WATER SUPPLIED TO EGYPT BY ASWAN RESERVOIR. 



JAMUAffV . FEBRUARY MAffCM APRIL 'MAY' 



- Water supplied by aid of Aswan Reservoir. 



Volume of water reaching Wadi Haifa, corrected for loss by 



evaporation and seepage between Wadi Haifa and Aswan. 

 _._._._ Water required to irrigate rice area. 



thrown into the holes which formed downstream of the 

 barrage. By the artificial increase of head obtained, irri- 

 gation was saved to hundreds of thousands of feddans 

 which otherwise would have gone waterless, and some 

 further land was flooded by means of the pumps at Nag 

 Hamadi* and Baliana, but even so there was a very large 

 area which the flood-waters did not reach. 



