Abstract: Motion characteristics of water flow and sediment in bend reach are different from that in straight stream by ocurring transverse velocities and transverse sediment transportation.Considering the effects of transverse flow in river bend,a formula for starting velocity of sediment in river bend is derived and rational analysis performed.It is regarded that,under the condition of same longitudinal velocities,the values of particle size of the started particles and their transporting speed on the concave bank are all larger than those in straight river section.In the meanwhile,the evolution regularity of bend river is represented in combination with the motion characteristics of water flow and sediment in bend reaches.

Key words: bend river reach, starting velocity, transverse velocity, bending river evolution