Sudan 73 AndredorEgyptian ] SOBAT , PIBOR, BLUE NILE (Gila ), which also rises in the Abyssinian highlands, and has a total length of about 200 miles. Steamers have reached the Gog rapids on the Gillo, about 130 miles from its confluence with the Pibor . As the Pibor and its tributaries derive their water chiefly from the swamps, they do not begin to rise until the middle of June.

- At Khartum , or more precisely opposite Omdurman, is the confluence of the White and Blue Niles . The Blue Nile, which rises in the mountains of Abyssinia, where it is known as the Abbai , enters the Anglo Egyptian Sudan at Famaka, whereafter it is called by the natives the Bahr el- Azrak (the blue river), on account of the clearness of its waters when not in flood.

Fifty -five miles below the spot at which it enters the Sudan is Roseires ( right bank ), where it first becomes .navigable by river steamers . Between Roseires and Khartum, a distance of about 400 miles, the river has a fall of 218 ft . The next place of importance down stream is Singa (left bank ), 120 miles distant, before reaching which the river falls 97 ft . At Sennar (left bank ) , about 50 miles below Singa, the Khartum Sennar railway leaves the Blue Nile to run west to Kosti on the White Nile .

Fifty-five miles below Sennar , on the right bank, is the confluence of the Dinder, a large tributary rising in the Abyssinian hills, which is navigable during flood time by steamers for about 130 miles , and by small boats for a much greater distance. Some thirty seven miles lower is Wad Medani, and on the right bank , 5 miles farther down-stream, is the confluenceof the Rahad , the second great affluent of the Blue Nile .

The Rahad rises in the Abyssinian highlands west of Lake Tsana, has a total length of about 400 miles , and is navigable by small steamers during flood time over practically the whole distance. Near the confluence of the Rahad is the post of Abu Haraz,some 70 miles below which is Kamlin (left bank ) . Sixty -five miles farther down -stream is Khartum . Here there used to be a steam ferry, now replaced by an iron railway bridge