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a river in Orel and Lipetsk oblasts, RSFSR, a right tributary of the Don River. The Sosna is 296 km long and drains an area of 17,400 sq km. It flows through a wide valley and is fed primarily by snow. The mean flow rate 37 km from the mouth is 74cu m per sec. The Sosna usually freezes in November or December; sometimes it freezes in early January. The ice breaks up in late March or in April. The cities of Livny and Elets are situated on the Sosna.