^6 SCIENCE IN AFRICA 



should certainly be started when funds become available, as well 

 as the study of subterranean reservoirs. 



Even for the Nile Valley there are certain important gaps in 

 our knowledge, especially concerning part of the Lake Plateau 

 basin, the Upper Blue Nile, and the valleys of the Sobat and 

 Bahr-el-Ghazal. But a mass of data has been accumulated since 

 scientific irrigation was introduced and has been made available 

 by Drs. H. E. Hurst and P. Phillips (193 1-3). 



Knowledge of hydrology for irrigation purposes demands data 

 on altitudes of an order of precision which can only be attained 

 by precise levelling. This branch of survey has been applied in 

 Africa in a few parts of the major river valleys only, and in connec- 

 tion with railway construction. Elsewhere heights have in many 

 cases been fixed by vertical angles, and are therefore subject to 

 considerable error. For the Nile Basin the extent of levelling is 

 shown by Hurst and Phillips (1933, vol.3, plate i): lines of level- 

 ling of first order precision have been carried out from Alexandria 

 upstream to Wadi Haifa, and again from Khartoum up the White 

 Nile to the Murchison Falls above Lake Albert and up the Blue 

 Nile as far as Roseires. The intermediate stretch between Wadi 

 Haifa and Khartoum, including the main series of cataracts, has 

 been levelled with less precision, and so has a line from the Mur- 

 chison Falls to Entebbe on Lake Victoria. In connection with the 

 proposed scheme for a barrage below Lake Albert and an artificial 

 water-course to shortcut the sudd area, another line of first order 

 levelling has been carried from Malakal on the White Nile, up the 

 Sobat River and thence across country to rejoin the White Nile 

 above the sudd area. 



In territories where development has reached an advanced 

 stage, special irrigation departments have been found necessary. 

 This is the case in the Union of South Africa, Southern Rhodesia, 

 and the Anglo-Egyptian Sudan. In most of the colonial territories 

 water-supplies are supervised by the geological departments, and 

 prospecting for water absorbs a considerable part of their resources. 

 In some territories the sinking of wells or bore-holes is undertaken 

 extensively by the geological departments, while in others these 

 activities are carried out by the public works engineers. In several 

 of the colonial territories it is felt that greater knowledge and con- 



