On the east, the Msalala, the Wampuna, the Chambura, and the Mpanga which has its sources on the slopes of Ruenzori.
On the north, numerous glacier-fed torrents from the slopes of Ruenzori, the Nyamgasha and the Dibirra. The dry season discharges of all these rivers are small. The largest is under 10 cubic metres per second. The flood discharges are considerable.
12. Lake Albert Nyanza.
—Lake Albert has an area of 4500 square kilometres and lies about 680 metres above sea level. We have left the high lands of Uganda and are in the stifling heat of tropical Africa. There are considerable deposits of salt along the east shore of Lake Albert, as there are also around Lake Edward. According to Sir William Garstin, the waters of Lake Albert are brackish near the shores, but perfectly sweet and clear in the middle of the lake. It is due to the waters of Lake Victoria that those of Lake Albert are sweet. The catchment basin of the Albert Nile at its head where it leaves Lake Albert is about 379,000 square kilometres of which 244,000 square kilometres discharge into Lake Victoria. The rainfall over the additional 135,000 square kilometres may be considered as 1250 millimetres per annum, with seasons similar to those on Lake Victoria. The evaporation from Lake Albert must be greater than that from Lake Victoria, but if we exclude the joint areas of Lakes Victoria, Albert, Edward and Choga, and taking them as 70,000 square kilometres, consider that their rainfall is equalized by their evaporation, there remains from the 379,000 square kilometres of catchment basin about 309,000 square kilometres. An annual rainfall of 1250 millimetres means for 309,000 square kilometres a total rainfall of 380 cubic kilometres. The discharges of Lake Albert may be taken as varying from 500 cubic metres per second to 1100, with a mean of 800 cubic metres per second. This latter figure represents in one year 26 cubic kilometres or 1⁄15th the annual rainfall. We may compare with this the mean discharge of Lake Victoria of about 580 cubic metres per second and 1⁄12th of the annual rainfall of its catchment basin excluding the lake area.
A reference to [Plate V] will show how great is the regulating effect of Lake Albert on the Nile. Owing to the fact that an increase in the discharge of the Victoria Nile cannot pass down the Albert Nile before the whole area of Lake Albert has risen, the floods of the Victoria Nile are delayed nearly 5 months in their passage down the Albert Nile; a rise of 1 metre on Lake Albert meaning an increased cube of 4,500,000,000 cubic metres. If this takes place in one year, it represents an increased discharge of 150 cubic metres per second irrespective of what passes down the channel of Lake Albert.
If it were considered necessary to insure 1200 cubic metres per second as the discharge of the Albert Nile from the 15th January to the 15th May, it would mean adding 400 cubic metres per second to the mean discharge for 4 months, and deducting 200 cubic metres per second from the mean discharge for the remaining 8 months. By storing the surplus waters of good years by means of a weir capable of holding up 3 or 4 metres of water at the outlet of the lake, it would be possible to insure this discharge every year during the four months which decide the summer contingent of the White Nile to the Nile in Egypt during the months of April, May, June and July.
PLATE V.
GAUGE & DISCHARGE DIAGRAM of LAKES VICTORIA & ALBERT
Lith. Sur. Dep. Cairo.