from Khartum to Assuan, a distance of 1124 mill4. 11 is a region. of cataracts, there be ing 351 miles of rapids. with a total fall of 1156 ond 773 miles of novimtion. with a fall of 312 feet. The cataracts, in their order as the river is descended, may be briefly described: The Sixth Cataract, beginning 52 miles below Khartum, is a little over one mile long, and the drop in the river is 20 feet. The Fifth Cataract begin, 26 miles north of Berber, is 100 miles long, has three principal rapids, and the descent is over 200 feet. Abu named is a little below the foot of this cataract. The Fourth Cataract is between Abu Hauled and Dongola, and drops 160 feet in 68 miles. The very fertile region of Dongola is between the Fourth and the Third cataracts. The Third Cataract. with two rapids, is 45 miles long and the fall in the river bed is 36 feet. The Second Cataract is 73 miles farther down the river, is 124 miles long, with four rapids, and it falls 216 feet. The town of Wadi Haifa lies at its foot. The First Cataract is 214 miles farther down the Nile, is three miles long, drops 16 feet, and Assuan lies at its foot. The fact that below Assuan lies the great region of irrigation, fertility, and dense population, and that this portion of the Nile is hemmed in by high bills. marked Assuan as the best place to build a great dam across the river to keep back at flood time much of the water which hitherto had gone to waste, so that it might be utilized in the dry season and give Egypt perennial irriga tion.
The third section of the river is the Lower Nile, extending from Assuan to the bead of the Delta, au open waterway: navigable by large vessel,. with Cairo near its foot. The current is slow during the river in than two feet a second. The velocity in flood i5 from to feet per second. Along the lower part of this section a divergent channel known the Canal) extends paral lel to the Nile on the west side, finally ing its waters in the depressed area of the Faymn (q.v.). The fourth section of the river is the Delta or 'Garden of It is pierced in all directions by irrigation canals and navigable When the Nile is in flood, its tendency is to increase the height of its banks by deposits of loam and sand. These banks are artificially strengthened and the river thus kept to a definite course. The river reaches the sea through the Rosetta and Damietta mouths, and the canals that cove• the Delta like a network carry their surplus waters into n chain of lakes that tends lac•Bind the sandy shore. As a drainage let, a navigable highway. and a source of power the Nile is surpassed by many other Its unique distinction is that it has turned Egypt front a desert into one of Om richest agricult oral lands, supporting a population of about GOO to the square mile. There are periods of exceptional flood and low water: but the extraordinary regu larity with which, as a ride, the river rises and falls contributes to the security of farming.
The heavy rains in the basin of the White Nile during April drive the waters of that marshy region down upon Egypt, where they appear at Cairo about dune 15th. A fortnight later the
real (hood begins, for the :May rains in Abyssinia till the litho Nile with the richest muddy water. The rise is sometimes as rapid as three feet a day. the llood being heightened by the large vol ume brought down by the Alban. The maxi mum finod readies Assuan ahout September 1st, it would be at Cairo a few days later were it not that the water is diverted to the land and the whole Nile Valley i• a great lake. For this reason the maximum flood at Cairo appears only about October 1st, The rains cease in Abyssinia about the middle of Septemher, the floods of the Blue Nile and the Atliara disappear, and then the great lakes and marshes of Central Africa are the main supply of the river until the following June. This routine of the waters is marked by marvelous regularity. The time between an early and a late Hood is not more than that weeks. The height of the flood at Assuan is usually about 25 feet above the minimum supply. If the Water rises 29 feet above the minimum, the crops of Egypt are in danger. if it rises only 2)) feet above the minimum, large areas cannot be flooded. The mean flood discharge at Cairo is about 250,000 cubic feet per second (about equal to the average flow of the Niagara liver), the maximum about 400.000 feet. The genoTal slope of the valley on each side is away front the river. Along each edge of the river is an earthen em bankment too high to he topped by the floods. Along the valley is a series of embankments. one end of which is at the river edge and the other on the sides of the hills that wall in the valley. The whole country is thus divided into a series of oblongs surrounded by artificial embankments on three sides and by the slope of the desert hills on the fourth. There are 1•30 of these oblongs, varying in extent from 60,000 to about 3000 acres. It is easy to cut short. deep canals in the banks which fill as the flood rises and carry the mud-charged water into these basins of irriga tion. There the water remains for a month or more, ,three to four feet cheep, depositing its mud. At the end of the flood the water is passed off through sluices from one basin to another and ultimately back into the river. in November seed is sown, and so saturated is the soil that the grain sprouts and thrives and the harvest is gathered in April or Slay without a drop of rain or any fresh irrigation. After the crop is reaped the fields remain dry and cracked in the fierce summer heat until the next flood conies on. A little below Cairo is a great dam or barrage across the river, by means of which all available wate• in the Nile before it begins to rise in June is diverted into canals that carry it to the cotton fields of the Delta. This Imrrage makes it possible to irrigate Delta crops in the dry sea son, so that to a large extent two erops a year are raised there. The water in the Delta would not be sufficient if a strict system of control were not maintained by which each cultivator is sup plied in turn every fifteen o• twenty days.