Little is known of the state of the sudd during the years of the Mahdi and the Khalifa; but in 1898 Lord Kitchener found the Bahr el Gebel blocked by sudd immediately above Lake No; and about the same time Colonel Martyr, coming from Uganda, was unable to penetrate more than 20 miles north of Shambe for the same reason. As soon as the Khalifa had been finally crushed, operations to clear the channel were immediately undertaken. In the first three months a length of 80 miles of river had been cleared, including 5 miles of actual sudd in eleven blocks, besides three more blocks which broke away of themselves. The blocks that came away of themselves represented a very large amount of sudd. After one of them had burst, the floating weed took thirty-six hours to pass a given point. The effect produced by the sudd in damming up the river is illustrated by the fact that when the third block, which was nearly 20 feet thick, was removed, the upstream level fell 5 feet in four days, and all the swamps and lagoons began to drain into the river.
The amount of labour was prodigious. At one place, owing to the enormous masses of um soof and papyrus that kept pressing into the river, no less than eleven clearances had to be made in one year. Five gunboats and 800 dervish prisoners, besides officers and guards, were employed. Sir W. Garstin gives an interesting description of the methods by which the sudd was removed:
‘In the first place, the papyrus and reeds on its surface were burnt (curious to relate, these green reeds burn readily when the marsh is dry), and in a few hours’ time the surface of the sudd was an expanse of blackened stalks and ashes. As soon as the fire had died down, gangs of men were landed from the steamer and employed in cutting trenches on the surface of the sudd. These trenches averaged from 0·60 to 0·80 metre in width, and from 1 to 1·25 metres in depth—i.e., as deep as the men could work. The surface was thus divided into a number of rectangular blocks some 3 metres by 4 metres. To these blocks were attached, one by one, steel hawsers and chains. This done, the steamer downstream went full speed astern. It invariably took several pulls to detach a block, and in some instances as many as nine were necessary. Both hawsers and chains kept constantly breaking, although the former were calculated to stand a strain of 35 tons per square inch, and the latter as much as 60 tons. As soon as a block was detached from the mass, it was allowed to float downstream. It was curious to see the green reeds and papyrus which had been confined beneath it reappear on the surface of the water. A horrible stench prevailed from the rotting vegetation.’
In 1900-1901 four more blocks were removed. An experiment was made to break up one of the blocks by means of explosives, but it was found that the sudd, though very solid, was too elastic, and the only effect was to make large holes in it and no more. The old method had to be once more resorted to. By the end of 1901 only 23 miles of the channel remained uncleared, but this proved to be the most difficult of all. One block was actually 7 miles in length. Portions of the sudd had rotted, and, sinking to the bottom, completely filled up the channel, so that there was no stream at all, and it was impossible to tow pieces away and float them downstream by the usual process. To get up the river it is still necessary to go round by a series of lagoons, in which navigation is difficult, and operations have been suspended for the present.
The sudd in the Bahr el Ghazal was much easier to remove, and great progress has been made, so that now the whole of that river is free, and boats can even ascend the Jur River to Wau.
It is very difficult to ascertain the precise effect of the removal of the sudd on the water-level in Egypt. But it is certain that as each block was removed a quantity of water drained off the marshes and helped to diminish the fall of the river in summers of very small supply. Most of this water, spread out over a large surface, must otherwise have been evaporated and lost altogether. There can be no doubt that the improvement of the channel has been a permanent gain to Egypt of a very substantial kind, to say nothing of the advantage to the Soudan from the opening up of such an important line of communication. Those who laboured at the task deserve the highest praise. The river was so low that all communication with Khartoum was cut off for several months, and transport of supplies was always difficult. Besides this, the climate is always unhealthy, and the mosquitoes at night are almost beyond endurance.
Under present conditions it will require constant care and watchfulness, especially in years of high flood, to prevent the sudd from frequently obstructing the river. But if the danger is to be permanently removed, the main channel must be so much improved by widening and deepening it that it will carry a greater volume. This will at the same time prevent the water from being dissipated in the marshes, and diminish the chances of any obstruction. The necessity for some work of this kind, if there is to be a reservoir at Lake Albert or Lake Victoria, has already been referred to. The clearing of the sudd is only the essential preliminary to the greater scheme.
One point remains to be noticed. Under the old basin system in Egypt there could hardly be too high a flood, nor did a low summer Nile create any extraordinary difficulties when there was so little summer cultivation. But with perennial irrigation a high flood becomes a matter of supreme anxiety, and the preservation of its dykes is the anxious care of every village. On the other hand, all the schemes for reservoirs aim at increasing the summer supply. If the Bahr el Gebel was trained so as to bring down more water in summer, it would also bring down more in flood, though the swamps would still act as an escape for the waters beyond a certain rise. It might therefore become a matter of great importance to Egypt to actually diminish the supply during the flood, especially as year by year more of the basin land is converted to perennial irrigation. Regulators at Lakes Victoria and Albert would serve in some degree for flood protection as well as for storage against summer use. It is calculated that the complete closing of the outlet of Lake Victoria at the Ripon Falls would only raise the surface of the lake 20 inches in a year. But it would be far more effective if some of the flood-waters of the rivers—e.g., the Blue Nile and the Atbara—which are fed by the rains of Abyssinia could be intercepted before they reached Egypt. A large irrigation during the flood and early winter along the Blue Nile might indeed actually lengthen out the flood in Egypt, whilst depriving it of danger through excess at any one period.