Engineering Wonders of the World
Volume I

386 ENGINEERING WONDERS OF THE WORLD. CAIRO ' Sassiövt Fig- 1-—bird’s-eye view of the lower NILE, FROM THE ASSOUAN DAM DOWNWARDS. proper begins. With the exception of the At- bara (Black) River, which merges into it some 200 miles farther north, it receives no addi- tional water. At Assouan the Nile tumbles over the granite reefs known as the First Cat- aract, where the great dam is built, and so enters Egypt. Between this point and the embouchures at Damietta and Rosetta the river attains its greatest breadth—approximately 1,100 yards. The width of the Nile valley itself varies from 6 miles to 31 miles. The Blue Nile brings down from the Abys- sinian mountains the largest part of that fer- tilizing alluvium which is the wealth of agri- cultural Egypt. To the Blue Nile and the Atbara, fed by the mountain rainfalls and laden with silt, is due the annual inundation °f Egypt. The river begins its rise—at Cairo —in June, when the waters have a somewhat greenish colour. In July it swells rapidly, and continues rising till September. Then the waters, which are now of a reddish hue, will remain sometimes at one level for several days. Rising still further, about the middle of Octo- ber the river touches its highest level. At this stage its movements are somewhat irreg- ular. After receding a little, it may rise again ; but soon a steady decrease begins, and the waters continue to subside until in June again they reach their lowest level. To use the Nile waters to the greatest advan- tage throughout the year consti- tutes the art of irrigation. To enable the reader therefore to un- derstand clearly the various meth- ods employed by means of canals, barrages, reser- voirs, etc., to at- tain this object, it will be simplest to refer him at first to the ac- companying plan (Fig. 3), repre- senting an imag- inary tract of land on the left \fziftd Barrage De ItajBarrage sAss/out I Esnek ^Assouan Khärtounv L-No Sudd Lake Albert & L-Tsånå L.Vk tor/'d Fig. 2.—SKETCH MAP OF THE NILE, SHOWING RESPECTIVE POSITIONS OF THE DAM AND BARRAGES.