558 



NATURE 



[December 30, 1920 



and much criticism has been directed against the 

 tables of discharge which the Public Works 

 Ministry has published; but there are no valid 

 grounds whatever for doubting their correctness, 

 and the accounts given of the rating of current- 

 meters in this report, the accuracy of the discharges 

 measured with them, and the method of measur- 

 ing the volume discharged through the sluices of 

 the Aswan Dam, show that the greatest care has 

 been taken to obtain as high an accuracy as 

 possible. The report of the Nile Projects Com- 

 mission, which has just been issued, affords a 

 complete vindication of the accuracy of these 

 measurements. 



In the early days of the British occupation of 

 Egypt the reorganisation of the irrigation of the 

 country was recognised as being of the first im- 

 portance, and every improvement that was 

 achieved produced large returns in the shape of 

 increased economic prosperity. But as the margin 

 of possible improvement grew narrower with each 

 advance, greater precision of measurement be- 

 came necessary, and for some years a special 

 branch of the Public Works Ministry has been 

 engaged upon the scientific investigation of all 

 the problems of Nile hydrography. The necessity 

 for this was clearly shown in the exceptionally low 

 flood of 191 3, and in the consequent deficiency in 

 the supply in the following spring and summer. 

 The volume discharged by the river in this ex- 

 ceptional year 'was only 41,000 million cubic 

 metres, whereas the total requirements of Egypt 

 and the Sudan by 1955 are estimated to reach 

 56,000 million, so that additional works must 

 be constructed, even though such an extra- 

 ordinarily low flood occurs but rarely. The Blue 

 and White Niles, from which this additional 

 supply must be obtained, differ fundamentally in 

 their hydrographic character. The Blue Nile, 

 with a comparatively short course of approxi- 

 mately 1500 kilometres and a fall of 1400 metres, 

 carries a heavily silt-laden flood past Khartum 

 which may reach and even exceed 9000 cubic 

 metres a second. The White Nile, on the other 

 hand, has deposited most of its load in the marsh 

 region of its upper reaches, or on the plains of 

 the Sobat River, so that its waters are clear and 

 can be stored in a reservoir; also the shallow 

 valley of the White Nile, with its exceedingly low 

 slope, allows a very large volume to be held up 

 by a work of moderate height. 



The present scheme provides both for a dam 



across the White Nile valley at a short distance 



upstream of Khartoum, and for a dam on the 



Blue Nile near Sennar. The site selected for the 



NO. 2670, VOL. 106] 



White Nile dam is at Gebel Aulia, 45 kilometres 

 upstream of Khartoum, where the valley is wide 

 and shallow. A continuous masonry dam 5 kilo- 

 metres long and further extended by i^ kilometres 

 of an earthen dam with a masonry core wall will 

 hold up the waters of the White Nile to a height 

 of 8 metres above summer river level, and to 

 95 metres in years of high flood ; it will thus 

 provide an additional 4000 million cubic metres 

 of water for the development of Egyptian agri- 

 culture and for the reclamation of the northern 

 shore of the Delta ; it will also act as a protection 

 work in high floods by holding up water until 

 the crest of the Blue Nile flood has passed and 

 the White Nile water can be released without 

 danger. Evaporation over the surface of the 

 reservoir which will be formed by the dam will 

 be large, for the maximum area is 540 square 

 kilometres, and observations show that it will 

 amount to 11 mm. per day in April, and to 24 mm. 

 in the rainy season when allowance has been 

 made for the rainfall. The loss by absorption over 

 the area of the reservoir must also be considerable, 

 and I cubic metre of water per square metre of 

 surface has been allowed for this. 



For meeting the requirements of the Sudan, a 

 dam is proposed on the Blue Nile near Sennar, 

 and the one which has been designed will be a 

 solid masonry structure of granite, with sluices 

 and spillways sufficient to discharge 15,000 cubic 

 metres per second. By the control which this 

 dam will afford, such water as is needed for use 

 in the Gezira can be withdrawn from the Blue 

 Nile from July 15 to January 18, after which the 

 reservoir upstream of the dam will supply the 

 further requirements of the Sudan in order that 

 the water flowing in the Blue Nile may pass on to 

 Egypt without diminution. 



The data relating to both these schemes are 

 set out fully in the report, from which the amount 

 of water which is required for the agricultural 

 development of different regions at each season 

 can be seen, and the provision for meeting these 

 requirements by means of the storage and con- 

 trol provided by the dams at Aswan, Gebel 

 Aulia, and Sennar can be readily examined. 



Some subsidiary works will be needed, and one 

 of these is a barrage at Naga Hamadi, in Upper 

 Egypt. One effect of filling the new storage 

 reservoir by means of the White Nile dam will 

 be to lower slightly the maximum of the flood at 

 Aswan, and, consequently, to make the watering 

 of the higher lands of Upper Egypt more diffi- 

 cult. The conversion of land in this part of 



