THE AVAILABILITY OF UNDERGROUND WATER IN HOT DESERTS 



Professor F.W.Shotton. 

 (Birmingham) 



This paper claims to be nothing more than a general survey of the problems and 

 possibilities of obtaining water from underground in the really dry and hot parts of the 

 earth's surface where, without it, human existence would be impossible. If its con- 

 clusions are rather pessimistic, their recording may nevertheless be desirable as a 

 counter to the optimism which is often expressed, usually in broad generalisations, 

 and which so frequently proves to be based on experience in semi-deserts where rain- 

 fall is by no means unimportant. 



In full desert, vegetation is either non-existent or scanty and specialised. Often 

 such plants that exist spring into a short-lived period of abundance after the rare 

 event of rain following perhaps years of quiescence. It is obvious that to convert 

 such regions into productive areas on any useful scale, a regular supply of water must 

 be ensured. This is true even if special drought resistant crops are developed, for 

 these can only be expected to grow when they are being supplied with water. It is not 

 my intention to discuss here those cases such as the valleys of the Nile and the Eu- 

 phrates or that peculiar accident, the Fayum depression, which though truly desert in 

 climate, can draw irrigation water from large rivers. Situations of this sort are usually 

 fully developed and, even where this is not the case, the controlling factors of topo- 

 graphy and volume of the river's flow can clearly be assessed. Over most desert areas, 

 no gift of a large river is there for the taking, and any hope of increased productivity — 

 of productivity at all — lies in the development of underground water. 



Water obtained by means of wells and pumps must, apart from any question of eco- 

 nomics, satisfy two conditions:- 



(a) It must be produced in sufficient quantity and 



(b) It must have a quality, judged by its dissolved constituents, acceptable to man 

 for his own drinking, for watering hig stock, and for the irrigation of his crops. 



The second factor may be discussed first. Much information on this point has 

 been summarized by Dixey(^) and it is quite clear that the limits of quality for differ- 

 ent purposes may be broadly lain down, even if there is no general agreement on exact 

 figures for these limits. 



The salts which are commonly found in important amounts in water are common 

 salt (sodium chloride), the carbonates and bicarbonates of calcium, magnesium and 

 sodium and the sulphates of the same elements. Not all can occur together, for some 

 are incompatible; and the carbonates and bicarbonates of calcium and magnesium, and 

 calcium sulphate, though important in producing 'hardness', are of such low solubility 

 that they do not in themselves affect the limits of potability. Sodium chloride is often 

 the dominant constituent and may conveniently be taken as the basis for assessing the 

 quality of a desert water — remembering always that the sulphates of sodium and mag- 



(1) Dixey, F. 1950, A Practical Handbook of Water Supply, 2nd Ed., London : Murby. 



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