SUDD  , or

SADo (an Arabic word meaning "to dam" ), the name given to the vegetable obstruction which has at various dates closed the waters of the Upper Nile to navigation . It is composed of masses of papyrus and um suf (Vossia procera) and the earth adhering to the roots of those reeds . Mingled with the papyrus and urn suf (Arabic for " mother-of-wool") are small swimming plants and the light brittle ambach . The papyrus and um suf grow abundantly along the Nile banks and the connected lagoons between 70 N. and 13° N . Loosened by storms these reeds drift until they lodge on some obstruction and form a dam across the channel, converted by fresh arrivals into blocks that are sometimes 25 M. in length, and extend 15 to 20 ft. below the surface . These masses of decayed vegetation and earth, resembling peat in consistency, are so much compressed by the force of the current that men can walk over them every-where . In parts elephants could cross them without danger . The pressure of the water at length causes the formation of a side channel or the bursting of the sudd . (For sudd cutting see NILE.) In the Bahr-el-Ghazal the sudd, being chiefly composed of small swimming plants, is of less formidable nature than that of the main stream . Consult, O . Deuerling, Die Pflanzenbarren der afrikanischen Flusse (Munich, 1909), a valuable monograph; and the bibliography under NILE, especially Captain H . G .

Lyons, The Physiography of the Nile and its Basin (Cairo, 1906) .