Kilombero River
The Ulanga River, also known as the Kilombero River, is a river that starts in the southwest of Tanzania on the eastern slope of the East African Rift that flows northeast into the Rufiji River then to the Indian Ocean.
The Ulanga Valley is an intact natural wetland ecosystem comprising myriad rivers, which make up the largest seasonally freshwater lowland floodplain in East Africa. The Ulanga River supplies ⅔ of the Rufiji waters.
The Ulanga river is formed by the convergence of major rivers coming the south, that flow north from the mountain ranges of the Mbeya and Iringa regions on the eastern slope of the East African Rift and south from the Udzungwa Mountains and Mahenge Mountains. From south the Ruhudji River winds eastward, losing height quite rapidly, to the head of the great floodplain of the Ulanga Valley. The floodplain occupies the flat floor of the Ulanga Valley at 210–250 m.a.s.l. The valley is oriented south-west north-east, between densely forested escarpments in the Udzungwa Mountains, which tower at 2,250 meters above the valley floor (7°47′0″S 36°36′0″E / 7.78333°S 36.60000°E), on the north-western side and the Mahenge Mountains on the southern side (8°45′0″S 36°39′0″E / 8.75000°S 36.65000°E). The Ruhudji receives several important tributaries and then divides on the floodplain into a number of channels, which produce a network in the central part of the floodplain. Other affluents draining the mountains on opposing sides of the valley join the network so that in the central part there are ten major channels flowing roughly in parallel. A zone of permanent swamps, 45 km long, extends up to 4 km away from the west bank of the Kihansi River. The Kihansi was dammed in its upstream ranges above the Kihansi Gorge in 1995. The southern central parts of the floodplain descend 40 meters over a distance of 210 km. At Ifakara the valley narrows in to be about 4 km wide and the rivers are united into the main stream of the Ulanga River. East of Ifakara the Ulanga flows through a delta of oxbow lakes and is joined on its left bank by the Msolwa River. This stream comes from the high escarpment of the Udzungwas and trverses the northern part of the floodplain, skirting another zone of permanent swampland to the west. From the point of confluence the Ulanga River swings sharply southeast and leaves the floodplain (and the Ramsar Site) on the border of the Selous Game Reserve. The Ulanga River then continuous for 65 km to confluence with the Luwegu where they merge at the Shuguli Falls to become the Rufiji River. The Rufiji then flows northeast through the Selous Game Reserve on its way to the Indian Ocean.
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