Natural cutoff is a sudden occurrence of meandering rivers evolvement,not only a terminal point of one meander dying out but also an origin of a new meander growth.Nevertheless,the law of types and geometrical critical form of cutoffs is not completely discovered.A large number of satellite images occurring to cutoff were unscrambled and analyzed.Based on the form and dynamics condition of cutoffs,types of natural cutoffs were classified as erosion ditch type,bank collapsing type and die cutting type.Form statistics of river bends indicated that the specific value of neck width and average river width from high to low follows as erosion ditch type,die cutting type and bank collapsing type,whereas the curvature following as bank collapsing type,die cutting type and erosion ditch type.By defining form parameters of river bend,parameters of 16 natural cutoffs images were measured.To the river bend happening to cutoffs,the curvature of channel central line was defined to limit curvature, which was regarded as a parameter of geometrical critical form.Generally,limit curvature of natural cutoffs was far lower than theoretical maximal curvature.Different types of cutoffs were correspondent with different limit curvatures. The critical form parameter of theoretical cutoff of sine-generated curve was the maximum angular amplitude of 121 degree.
