弯曲河流斜槽裁弯模式与发育过程

结合遥感影像、野外调查和形态统计,深入分析斜槽裁弯现象,将其划分为切滩冲刷、串沟冲刷和主流顶冲3种模式。切滩模式发生于洪水期间主流水流动力轴线偏向凸滩后,形成漫流水流冲刷,极可能在边滩形成新的斜槽。切滩裁弯的形态统计表明,弯道曲率半径与平均河宽之比约2.92,分流角约54.8°。串沟模式是前期洪水漫过河湾内侧洪泛平原,漫滩水流冲刷形成若干串沟,后续洪水沿串沟继续冲刷,串沟逐步横向展宽和向下游侵蚀,直至形成新的河槽。主流顶冲模式是水流顶冲河湾内侧河岸,形成湾状缺口,后续洪水持续顶冲湾状缺口,直至上下游水流贯通,形成斜槽裁弯。

Development processes of chute cutoffs on meandering rivers

Chute cutoff is one form of natural cutoffs on meandering rivers.This paper studies the patterns and development processes of chute cutoffs through field investigations and statistical analyses using remote sensing images.The natural chute cutoffs are divided into shoal-cutting pattern, ditch-scouring pattern and embayment-eroding pattern.The shoal-cutting pattern is caused by the direction of main flow turning to the shoal of convex bank during flood, which results in overbank flow on the shoal and a new chute on shoal.Such a cutoff is found on 67 meanders among the examined rivers.The average ratio of the bend curvature radius is about 3 times of the average stream width and the average angle of dividing flow is about 55. The ditch-scouring pattern is the result of pre-flood overflows forming several ditches, and one of the ditches is scoured, enlarged and deepened, and finally formed the cutoff.In the embayment-eroding pattern, the mainstream flow erodes the inside bank of river bends and forms an embayment, and then the flood erosion results in the downstream extension of the embayment until cutoff the meander.