At Lado, 381 kilometres, the range is 2·30 metres, and the discharge in summer averages from 600 to 700 metres cube per second. The maximum (generally attained in September) varies between 1,000 metres cube per second in a low flood, and 2,000 metres cube per second in a high one. This increase in the flood supply is due to the rainfall throughout the river valley, and to the volume added by the many important tributaries, such as the Asua, the Kit, etc., which feed the Bahr El Jebel between Wadelai and Lado. At Bor, 559 kilometres, the loss of water in flood is some 50 per cent. of the amount passing Lado, and the discharge here can rarely, if ever, exceed 1,000 metres cube per second. This loss is due to the filling up of the entire river valley, which thus forms an immense basin or reservoir, and reduces the discharge passing to the north. This reservoir extends from Lado to the head of the Bahr El Zeraf, a distance of some 378 kilometres. As the river falls the water of this basin, with the exception of the large amount lost by evaporation, slowly filters back through the marshes into the river during the winter months, and thus maintains the constancy of supply. Throughout the “Sudd” region the loss of water in the Bahr El Jebel, both in summer and in flood, is very considerable. By the time that Lake No (1,156 kilometres from Lake Albert, and 749 kilometres from Lado) is reached, 85 per cent. of the discharge at Lado has been lost in a high flood, and 70 per cent. in a low one. During the summer months the loss at this point varies between 50 and 60 per cent. Lastly, the discharge which enters the White Nile from the Bahr El Jebel is nearly constant at all seasons of the year, and never even in the highest flood exceeds 300 or 320 metres cube per second. The regulating effect of the great marshes is thus very apparent. 3. THE BAHR EL GHAZAL. The discharge of this river, as a feeder of the White Nile, may be neglected entirely. Its summer volume entering Lake No varies from 20 to 30 metres cube per second, while its flood discharge is even less, equalling from 12 to 20 metres cube per second. None of this water enters the White Nile, merely increasing the flooded area of Lake No. It, however, helps to augment the reservoir area of the main stream. 4. THE BAHR EL ZERAF. This branch of the Bahr El Jebel adds to the volume of the White Nile by an amount varying from 30 to 60 metres cube per second in summer, and from 80 to 160 metres cube per second when in flood. If, however, the Bahr El Jebel is closed by “Sudd” then the discharge of the Bahr El Zaraf increases, possibly to from 300 to 400 metres cube per second during the flood season. 5. THE SOBAT.