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.