The Nile in 1904

by Sir William Willcocks

The Sobat river gave as a minimum a discharge of 40 cubic metres per second in April, and then rose to a maximum in November of 1,080 cubic metres per second.

At its tail, the Albert Nile gave a mean discharge for the year of 390 cubic metres per second and the Sobat of 550.

The White Nile at its head was at its lowest in April with 400 cubic metres per second and at its highest in December with 1,460 cubic metres per second, with a mean discharge of 940 cubic metres per second. At its tail near Khartoum the White Nile was at its lowest in May with 420 cubic metres per second and at its highest in October with about 1,700 cubic metres per second. As this latter figure was about 400 cubic metres per second more than it was receiving at its head, the additional water represented Blue Nile water which had run up the valley of the White Nile, been stored there while the Blue Nile was high and then been discharged into the Main Nile when the Blue Nile had fallen. The mean discharge at the tail of the White Nile was 830 cubic metres per second. This figure was much below that at the head and was due to the fact that in July, August and September the Blue Nile water was flowing up the White Nile.

The Blue Nile was at its lowest in April when it was discharging 120 cubic metres per second. During its maximum in August and September it was discharging 8,200 cubic metres per second. Of the discharge of the Blue Nile in July, August and September, a considerable part flowed up the White Nile which here has a slope of ¹⁄₁₀₀₀₀₀ and a bed from 3,000 to 1,500 metres wide. It is for these reasons that the Blue Nile water does not hurry on to Assuân in its full strength. The mean discharge of the Blue Nile for the year was 2,350 cubic metres per second. Gauges and discharge tables at Kamlin on the Blue Nile, and north of Omdurman on the Main Nile, would be very much better than the Khartoum or Duem gauges of to-day which are both in back waters.

The Atbara river was dry from January to May, in June the discharge was 200 cubic metres per second, rising to 2,300 cubic metres per second in August. In October, November and December it was dry. The mean discharge for the year was 380 cubic metres per second. When the Atbara river rises in flood it cannot flow down the Nile to Egypt in its strength until it has filled up the trough of the Nile as far as the 6th Cataract. Gauges up and down stream of the 6th Cataract and at Shendy would be interesting when compared with Berber.

The minimum combined discharges of the White Nile, Blue Nile and Atbara river were 540 cubic metres per second in April. The maximum combined discharges of 10,900 cubic metres per second were in August. The mean combined discharges for the year were 3,560 cubic metres per second.

The minimum discharge of the main Nile above Assuân was 440 cubic metres per second in May and the maximum of 8,600 cubic metres per second was in September. The mean discharge for the year was 2,650 cubic metres per second.

[Table 25] gives the actual daily minimum and maximum discharges during 1902 and 1903 for each stream, with their dates. For the Blue Nile in 1903 they were 100 and 9,600 cubic metres per second; for the White Nile 380 and 1,470; for the Atbara 0 and 3,100; and for the Nile above Assuân 420 and 9,000 cubic metres per second.

[Table 26] compares the discharges for a maximum year like 1878, a minimum year like 1877, and a mean year, at Khartoum, Assuân and Cairo. The maximum discharges in 1877 were 5,300, 5,900 and 4,400 cubic metres per second, at Khartoum, Assuân and Cairo. In 1878 they were 12,500, 12,100 and 10,300 cubic metres per second respectively, while for a mean year they are 8,500, 9,200 and 7,200 cubic metres per second.

The modulus of the river at Assuân is 3,040 cubic metres per second, and at Cairo 2,640. After the very high flood of 1878, the lowest discharge in May 1879 at Assuân was 1,500 cubic metres per second.