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POPULAR SCIENCE MONTHLY 



area of about 300,000 acres under such irrigation, by throwing more 

 water at a higher level into the great Ibrahimiyah Canal, whose intake 

 is immediately above the Barrage (Fig. 2). 



The piers and arches are founded upon a platform of masonry 

 87 feet wide and 10 feet thick, protected up and down by a continuous 

 and impermeable line of cast-iron grooved and tongued sheet piling, 

 with cemented joints. This piling extends into the sand bed of the 

 river to a depth of 23 feet below the upper surface of the floor, and 

 thus cuts off the water and prevents the undermining action which 

 caused so much trouble and expense in the case of the old barrage. The 

 height of the roadway above the floor is 41 feet, and the length of the 

 piers up and down stream 51 feet. The river bed is protected against 

 erosion for a width of 67 feet up stream by stone pitching, with clay 



Fig. ?,. Asyut Lock. 



puddle underneath to check infiltration, and down stream for a similar 

 width by stone pitching, with an inverted filter-bed underneath, so 

 that any springs which may arise from the head of water above the 

 sluices shall not carry sand with them from underneath the pitching. 



It is easy enough to construct dams and barrages on paper, but 

 wherever water is concerned the real difficulty and interest is in the 

 practical execution of the works, for water never sleeps, but clay and 

 night is stealthily seeking to defeat your plans. On the Nile the con- 

 ditions are very special, and in some respects advantageous. There is 

 only one flood in the year, and within small limits the time of its occur- 

 rence can be foretold, and arrangements made accordingly. It would 

 have been impossible to have carried out the Nile works on the system 

 adopted had the river been subject to frequent floods. The working 

 season for below- water work on the Nile lies practically between Novem- 



