534 THE NILE RESERVOIR DAM AT ASSUAN. 



iron, but the greater number are lined witli dressed granite blocks of 

 large size. 



Around the western end of the dam a ship canal 32 feet wide, with 

 four locks, has been completed. This canal added very materiall}' to 

 the total cost of the dam. The gates in the canal are said to be con- 

 structed on plans drawn for lock gates on the proposed Nicaraguan 

 Canal. 



The sluice gates in the dam are opened during the tirst part of the 

 flood season. In this time the muddiest part of the flood pu.sses 

 through the dam. As the river commences to fall — and fortunately 

 the water carries much less sediment at that time — the gates are 

 gradually lowered. As the flood subsides, a portion of the water is 

 thus held up, and when the season of low water arrives, with its con- 

 sequent scarcity in the perennial canals lower down the river, the 

 reservoir is full. Then the gates are slowly opened, and as the river 

 continues to fall the reservoir supply is drawn upon and the flow 

 downstream from the dam maintained sufficiently to irrigate the 

 d(\sired acreage of land. The flow out of the dam is arranged so that 

 the reservoir will be empty and the gates of the sluices open when the 

 flood again comes tlown the river. There are no canals of large size 

 taken from the river near the dam, so the water which is stc)r(>d is 

 turned into the river and taken out again farther down the stream. 



By this system of managing the gates in the sluices, it is hoped to 

 allow the greater part of the nuuldy water to go below the dam and 

 to store the clearer waters of the later part of the flood. These later 

 waters are known to be much clearer and to carr}' a sediment which 

 will r(Mnain in suspension for a long time; yet the ])roblem of silt in 

 this reser\oir is a serious one and the results which are ohtaininl from 

 this t3'pe of dam will be watched with interest by American irrigation 

 experts. 



The reservoir as now completed has a capacity of SOU, 000 acre-feet, 

 or, according to Mr. Willcocks, enough water to irrigate »)00,000 acres 

 of cotton and sugar cane. As has Ixhmi stated, this water is not to be 

 used for tln^ extcMision of the irrigated area in Egypt, but is intended 

 to he used in extending the area of perennially iri'igated land at the 

 expense of the area under basin irrigation. 



The cost of the dam can not l>e stated accurately. The oi'iginal 

 estimate was $S, 750,000, but this sum was exceeded. The total cost 

 to date is Ix^tween the at)ove sum and $10,000,000, making the cost 

 about i|^12..50 per acre-foot. The \'alue of this water to EgN'pt is said 

 to h(^ $100,000,000, or ten times th(» actual cost. 



'i'lie Assuan dam is but one of a lai'gc luunherof engineering works 

 planned for the complete sulijugation and conti'ol of th(> Nile. It is 

 hoped to build weirs and controlli^ig works on the Nileata luunherof 

 points ah<)\-e Assuan for t\\o irrigation of desert land in th.e Sudan and 



