Now an expenditure of between £400,000 and £1,000,000, say £800,000, could secure a regulator for Lake Albert at any point between the outlet and Dufilé. Such a regulator would insure 1200 cubic metres per second every year to the Albert Nile at Gondokoro between the 15th January and the 15th May. With this supply insured, the training works in the Sudd region would soon begin to affect the discharge at the north end of this region where the White Nile begins.
The way in which this work of training should be carried out has been admirably laid down in page 174 of Sir William Garstin’s Report. “Alter the flood conditions of the Albert Nile (Bahr-el-Gebel) as little as possible, let the excess flood water escape on both sides, but keep the summer supply in its channel.” This is, to my view, the soundest statement from an engineering point of view in the whole report. Hitherto we have always assumed a vast expenditure for keeping the flood supply in one channel; but with our attention devoted to the summer channel, we should have before us all the advantages of summer training works without any fear of inundations. The very wildness of the regions would be in our favour. To be able to train a river in summer without any nervousness about floods, is given to few engineers. I had never thought that any good thing could come out of the sudd region, but looked at from this point of view, we can, even in this inhospitable waste of waters, confirm Shakespeare’s saying that “there is some soul of goodness in things evil.”
The Lake Albert reservoir could easily insure 1200 cubic metres per second every year between the 15th January and the 15th May. To pass through the Sudd regions as much as possible of the 1200 cubic metres per second received at Gondokoro, the following works would be necessary:—
The first work to be done would be the removal of sudd block No. 15 which for 37 kilometres south of Hillet-el-Nuer has turned the Albert Nile out of its course. The importance of this is strongly insisted on by Sir William Garstin on page 55 of Appendix VI of his Report, which is the very last thing he wrote. With this block removed, the Albert Nile would be given a good opportunity of working out its own salvation.
The next point is one to which I attach the greatest importance. Indeed, I look upon it as the key of the whole region. The Albert Nile enters the south-east corner of Lake No and almost immediately afterwards leaves its east corner. Now Lake No is the final evaporating basin of the Bahr-el-Gazelle, probably the most unsatisfactory river in the whole world; and it is open to doubt whether in a year of deficient rainfall on its own catchment basin and a year of good supply down the Albert Nile, it does not evaporate a considerable quantity of the water of the Albert Nile. If the discharge of the Albert Nile north of Hillet Nuer was brought to 450 cubic metres per second in April, this lake might waste much of it. Such being the case, a cut of a maximum length of some 5 kilometres should be dredged south of the south-east corner of the lake, and the waters of the Albert Nile separated from those of the Gazelle. A cheap wooden lock and regulator would allow boats to pass, and take in any water from the Gazelle river when it had it to give. The maximum water we have to deal with is zero in summer and 40 cubic metres per second in flood. If the Albert Nile were separated from the Gazelle, it might be found that the waters of the Gazelle river found their way into the Albert Nile through that mysterious and unsatisfactory river the Lolle. Some use might even be found for it. I have, since I wrote this, been informed by Capt. Lyons that Marno in 1881 proposed this cut round the south-east corner of Lake No. (Pet. Mitheil, 1881, page 425 and plate 20).
The Albert Nile to-day at Hillet-el-Nuer is capable of carrying 450 cubic metres per second. North of Hillet-el-Nuer, the Albert Nile has a mean width of 75 metres, but owing to want of training and papyrus swamps, the discharge dwindles down to 320 cubic metres per second. The Albert Nile has in this reach a very good section indeed and by beginning with the west bank and dredging round corners and closing spills by dredged earth, an improvement of section and slope, backed up by a permanent discharge of 450 cubic metres per second at Hillet-el-Nuer, might speedily result in this very discharge of 450 cubic metres per second being obtained south of Lake No. We are here in such swamped land that percolation would be practically zero. There are only 200 kilometres of channel with all its curves, or 160 kilometres of trained channel to work at, in which 75 per cent of the work is to hand; and we have to confine our attention to the low supply without worrying over the flood supplies.
Now the Bahr-el-Zeraf could be made capable of carrying 150 cubic metres per second by an improvement of the inlet at Baker’s channel and by dredging north of Ghaba Shambe, as will be seen by examining the measured discharges of the Bahr. With the Bahr-el-Zeraf carrying 150 cubic metres per second and the Albert Nile carrying 450 cubic metres per second, we should have ensured 600 cubic metres per second. As time went on, improvements in the channels would make themselves felt, as they are even doing to-day, and we might even have 700 and 800 cubic metres per second at the head of the White Nile below the Sobat mouth. We must always remember that it is assumed that the lake Albert reservoir dam has been constructed and a supply of 1,200 cubic metres per second assured at Gondokoro from January to May. If the Sobat river were capable of regulation downstream of the Pibor marshes, we might get an increase from that direction as well. The possibility of a good site for a reservoir upstream of Nasser is very great. The Nasser gauge rises and falls so slowly that there must be very great natural accumulations of water upstream of it, which might be improved. The question of quality needs study.
The discharge of 435 cubic metres per second, which the rivers in their present state, aided by the Lake Albert reservoir, could deliver into the White Nile, would thus see itself gradually increased to 500, 550, and 600 cubic metres per second and even more, and would enter the White Nile past the Sobat mouth in February, March, April and May. During these months the whole of the supply would pass down the White Nile without throwing backwater on the rivers. Later on, when the Sobat river came down in flood and filled up the channel of the White Nile, the Albert Nile would have its waters reduced at the Albert regulator, and the waters of Lake Albert would again be stored for the day when the Sobat floods had fallen and the White Nile channel was free and ready to take in the waters of the Albert Nile.
While I had contemplated the training of the flood waters of the Albert Nile through the Sudd regions I had estimated the cost at £100,000 per annum, for 25 years, or at £2,500,000. Now, however, that Sir William Garstin has shown how we need only attend to the summer supplies, the sum may be reduced to half the former figure or to £1,200,000, and be more than ample. With £2,000,000 devoted to the Lake Albert reservoir and the training works in the Sudd region, the summer supply of Egypt and the northern Sudan would be put on a firm base.
Dr. Schweinfurth, the eminent African traveller and savant, was the first to call the attention of the Egyptian Government to the necessity of closing the spills from the White Nile to the north of Gondokoro, and so beginning the training of the river. He very rightly said:—“Many years would elapse before the desired result would be obtained by the strengthening of the banks, but the works would be increasingly felt every year in Egypt as the works progressed.”