496 



FORESTRY AND IRRIGATION. 



December, 



These later waters are known to be 

 much clearer and to carry a sediment 

 which will remain in suspension for a 

 long time ; 3^et the problem of silt in 

 this reservoir is a serious one, and the 

 results which are obtained from this tj^pe 

 of dam will be watched with interest by 

 American irrigation experts. 



The reservoir as now completed has a 

 capacity of 800,000 acre feet, or, accord- 

 ing to Mr. Willcocks, enough water to 

 irrigate 600,000 acres of cotton and 

 :sugar cane. As has been stated, this 

 water is not to be used for the extension 

 of the irrigated area in Egypt, but is 

 intended to be used in extending the 

 area of perennially irrigated land at the 



for the irrigation of desert land in the 

 Sudan and Central Africa. Below As- 

 suan a weir has already been built at 

 Assiut and one is under construction at 

 Zifta. These weirs are designed to raise 

 the level of the Nile at low water to fill 

 the irrigating canals already in opera- 

 tion or to be constructed. As a safety 

 valve, to let the highest and destructive 

 floods escape, a plan is under considera- 

 tion to construct a canal to Wady Ray an, 

 a depression in the Sahara to the west 

 of the Nile Valley, and drain into it the 

 excess of water which would otherwise 

 damage Middle and Lower Egypt. 



To again quote from Mr. Willcocks : 

 ' ' The Assuan dam is a work of a t3^pe 



Photo by Thos. H. Means. 

 UPSTREAM SIDE OF DAM. THIS VIEW SHOWS THE MINIMUM HEIGHT OF WATER. 



expense of the area under basin irriga- 

 tion. 



The cost of the dam cannot be stated 

 accuratel}-. The original estimate was 

 $8,750,000, but this sum was exceeded. 

 The total cost to date is between the 

 above sum and ;^i 0,000, 000, making the 

 cost about $12.50 per acre foot. The 

 value of this water to Egypt is said to 

 be $100,000,000, or ten times the actual 

 cost. 



The Assuan dam is but one of a large 

 number of engineering works planned 

 for the complete subjugation and con- 

 trol of the Nile. It is hoped to build 

 weirs and controlling works on the Nile 

 at a number of points above Assuan for 



the conservation of the flood waters and 

 which is new in the world. If success- 

 ful it will mark an epoch in dam-build- 

 ing. There must be sites on the tor- 

 rential rivers of the arid and semi-arid 

 regions of South Africa, Australia, and 

 North America, where dams of the type 

 of the one at Assuan will supply a want 

 which has long been recognized. 



"A reservoir dam, which will allow 

 the earlier floods laden with deposits a 

 free and unimpeded passage and which 

 will afterwards captivate the compara- 

 tively clear waters of the terminal inun- 

 dations and early percolations and store 

 them for subsequent use, ought to put 

 new life into man}- abandoned projects 



