The binding of the Nile and the new Soudan

by Sidney Cornwallis Peel

Meantime heavy rains have been falling about Lado and on the Sobat. Towards April 15 the river begins to rise, the effect of which is felt at Khartoum about May 20, and at Assouan about June 10. A most curious phenomenon accompanies this preliminary increase—the appearance of the ‘green’ water. It used to be thought that this ‘green’ water proceeded from the sudd region. During the previous months the swamps in that country have been lying isolated and stagnant under the burning tropical sun; their waters have become polluted with decaying vegetable matter. When once more the rising river overtops its banks, this fœtid water was supposed to be swept out into the stream, and finally make its appearance in Egypt. But a closer examination of the facts, which has only been possible since the Soudan was re-opened, has caused this view to be abandoned.

The ‘green water’ is caused by the presence of an innumerable number of microscopic algæ, which give it a very offensive taste and smell. So far as can be ascertained, their origin is in the tributaries of the Sobat above Nasser. The rains in April carry them out into the White Nile, and thence they pass down to Nubia and Egypt. Under a hot sun and in clear water they increase with amazing rapidity, and sometimes they form a column 250 to 500 miles long. These weeds go on growing, drying, and decaying, until the arrival of the turbid flood-water, which at once puts an end to the whole process, as they cannot survive except in clear water.

Horrible as the ‘green’ water is, its appearance is hailed with delight by the Egyptian, for he knows that it is the forerunner of the rushing waters of the real flood-time, and the first sign of the coming close of the water-famine. By September 1 the Nile at Lado has reached its maximum of 1,600 cubic metres. In the valley of the Sobat the rains last till November, with the result that by September 15 or 20 the White Nile at Khartoum has attained its maximum discharge of 4,500 cubic metres per second.

Meanwhile great things have been happening on the Blue Nile and the Atbara. About July 5 the Blue Nile begins to rise, and the flood comes down with considerable rapidity till it reaches its maximum of 5,500 cubic metres per second on August 25. The famous ‘red’ water reaches Assouan on July 15, and is seen ten days later at Cairo. The flood on the Atbara would begin at nearly the same time as on the Blue Nile, but for the fact that it spends a month in saturating its own dry bed and the adjoining country. Once it begins, however, about July 5, it comes very rapidly, and about August 20 reaches its maximum, which is usually some 3,400 cubic metres per second, but occasionally amounts to as much as 4,900.

If these three contributors, the White Nile, the Blue Nile, and the Atbara, all reached their maximum at the same time, the result in an ordinary year would be a discharge at Assouan of some 13,000 to 14,000 cubic metres per second, and in occasional years a very great deal more. But this is not the case. In an ordinary year the Nile is at its lowest at Assouan at the end of May, discharging no more than 410 cubic metres per second. After the arrival of the ‘green’ water it rises slowly till July 20. By that time the ‘red’ water is fairly on the move, and the rise goes on with increased rapidity till the maximum is reached, on September 5, of 10,000 cubic metres. But both date and amount are liable to variation. If the White Nile flood is a weak one, and the Atbara early, the maximum may be reached a day or two earlier; but if the White Nile is very strong it will not be attained until September 20. A late maximum, in other words, means a good supply of water in the White Nile, and as the White Nile is the principal source of supply after the flood is over, this fact is of inestimable importance to Egypt. But occasionally, as in 1878, this is carried to excess. In that year the White Nile flood was very late and very high. The maximum was not reached till September 30, when 13,200 cubic metres per second were passing Assouan, with very disastrous results in Egypt. All through the following summer the supply was very good, and at its lowest, in May, was more than three times as great as the average.[3]

Curiously enough, the preceding year offered a startling contrast. It was the lowest Nile on record. The maximum was reached on August 20, and was some 3,500 cubic metres below the average, and in the following May the discharge at Assouan fell to 230 cubic metres per second, as against the average 410.

By the end of October the Atbara has usually disappeared altogether, and the Blue Nile falls very quickly after the middle of September. The White Nile, however, owing to the regulating effect of its natural reservoirs and the slackness of its current, is very much more deliberate in its fall, and the results at Assouan are as follows in a normal year: By the end of September the discharge has fallen to 8,000 cubic metres per second; end of October to 5,000; end of November to 3,000; end of December to 2,000; end of January to 1,500; end of March to 650; and end of May to 410.

In other countries the year is divided into seasons, reckoned according to the position of the sun and the temperature, or according to the rainfall. In Egypt the state of the all-important river is the principal factor in determining the seasons. These are, first, the months of the inundation, or Nili, August to November; second, the winter, or Shitwi, December to March; and, third, the summer, or Sefi, April to July, when the river is at its lowest. Nowhere else do the actual seasons correspond with the nominal in a manner so regular and unfailing. But, of course, within these limits there is a great variation in the amounts of both the maximum and the minimum of the volume of the Nile, and the dates at which they occur from year to year. During the twenty-six years 1873-1898 the maximum flood at Assouan varied from the exceptional height of 9·15 metres above zero on the gauge to the equally exceptional 6·40 metres. And the dates on which these maxima were attained varied from October 1 in the first case to August 20 in the other. The dates on which the volume of water passing through reached its minimum varied from May 8 to June 24; while the worst lowest on record was ·71 metre below zero, and the best was 1·88 metres above it. (Zero, it should be explained, is the lowest level which the river would touch in an average year.)

These figures are the result of the free and unimpeded flow of the Nile. To us, with our wider field of observation, with our knowledge of the sources of the Nile, and preciser information as to the conditions prevailing in those distant countries, the behaviour of the river seems, after all, but the resultant of many natural causes, and capable of prediction, and even regulation. But to those who, living in a country where rain was practically unknown, knew nothing of the tropical lakes or the rain-shrouded hills of Abyssinia, and who merely saw the great river issuing from the burning deserts of the south in flood at the very time when other rivers were parched and dried, how marvellous it must have seemed, and how inexplicable must have appeared those occasional variations, threatening destruction, on the one hand by excessive inundation, and on the other by famine and drought! Few floods in the history of Egypt can have been higher than that of 1878, and few lower than that of 1877, when 1,000,000 acres were left without water. But several great famines have been recorded in the past. Perhaps the worst of these began in A.D. 1064. A succession of low Niles took place, lasting for seven years, like the seven lean kine of Pharaoh’s dream. Terrible results followed. Even human flesh was eaten, and the Caliph’s family had to flee to Syria. Similar disasters occurred in A.D. 1199.

Such extraordinary catastrophes are rare, but their possibility is always present to the minds of those responsible for the government and welfare of Egypt. We shall see what steps have been taken to guard against them, and first we shall examine the different systems of irrigation which have prevailed, and the nature of the services which the water, whose variations we have described, is made to perform before it finally reaches the sea.