Then river width increased and the intensity of deep point lowing and bed material coarsening decreased and water level lowed continuously . so the bed form changed toward to u type . the bed regulation is realized through sediment silting in different parts in cross section during silting period and the deformation of bed form changed from broad u type channel to narrow and deep v type channel 研究表明，河道在持续冲刷前期深泓点及水位下降与河床粗化同步发展，河床向v型发展；冲刷后期深泓点下降、河床粗化减弱，河道展宽增大，水位继续下降，河床向u型发展；在以淤积为主时期的调整，是通过断面不同部位的淤积来实现的，但都是由u型较大河槽向v型窄深小槽发展。
