WATER SUPPLY. 29 



The oasis of Nefta is supplied with water by a large number of 

 springs that arise in the " Corbeille," or "basket" (p. 15). Their 

 combined flow, amounting to about 292 gallons (1,100 liters) per sec- 

 ond, gives rise to the stream which waters the southern part of the 

 oasis. This quantity of water is estimated by Rolland to be sufficient 

 for irrigating the entire oasis at the rate of about 2 acre-feet per acre 

 annually. 



Taking as the number of date palms existing at Nefta the mean of 

 the two estimates given on page 15, we should have 282,500 trees. If 

 the total supply furnished by the springs were divided equally among 

 them, each would receive about 0.24 quart per minute, or about 86 

 gallons per day. As it has been calculated by Holland that to give 

 the best results each date palm should be allotted at the source of sup- 

 ply 0.53 quart (0.5 liter) per minute (hence about 190 gallons per 

 day) 6 it is evident that the supply available is not sufficient for the 

 perfect irrigation of more than one-half of the date palms of the 

 oasis. 



The 140 springs that supply the oasis of Tozer with irrigating 

 water give rise to a stream that delivers about 278 gallons (1^050 

 liters) per second; hence about 3,200,000 cubic feet daily. This 

 quantity is estimated to suffice for irrigating the oasis at the rate of 

 about 1.5 acre- feet per acre annually. Assuming that there are 

 385,500 palms (the mean of the two estimates given on page 16) in 

 this oasis, and making the calculation upon the same basis as for 

 Nefta, the share of water at the source of supply available for each 

 tree would be only 0.17 quart per minute, or 62.4 gallons per day, 

 which is less than one-third the amount (0.53 quart per minute) esti- 

 mated by Holland as the optimum. It should be noted, however, that 

 the distribution of water among the different parts of the oasis is very 



de la Tunisie, Assoc. Frang. Avancem. Sciences, 1884, p. 72) regards the infil- 

 tration water drained through the sands of the adjacent region as sufficient to 

 supply these springs. He does not consider the water sheet to be of artesian 

 character. 



a Holland, assuming that there were 201,100 palms at Nefta, calculated that 

 there should be available for each, at the source of supply, 0.33 liter (0.35 quart) 

 per minute. In his, as in the writer's calculation, no deduction is made for 

 the amount of water lost to the palms through seepage and evaporation from the 

 ditches, growing of other crops, and use by the inhabitants and their domestic 

 animals. 



& See Bui. 53, Bureau of Plant Industry, p. 45. 



c A much lower estimate has been made by M. Minangoin, inspector of agri- 

 culture at Tunis, of the amount of water theoretically available for each date 

 palm in the oasis of Tozer. He states that the combined flow of the 140 springs 

 is only 1,700,000 (instead of 3,200,000) cubic feet daily; and assuming that there 

 are 300,000 trees in the oasis, he arrives at the figure of 42 gallons (160 liters) 

 as representing the amount available at the source of supply for each palm daily. 

 92 



