摘要
自然裁弯是冲积河湾演变的突变事件,它既是某个河湾走向消亡的终点,也是新的河湾发育的起点,但裁弯形式和几何临界形态的规律尚未得到完全揭示。通过解读众多河湾裁弯的卫星图像,依据河湾裁弯的平面形态和动力条件,将裁弯形式分为串沟型、崩岸型和冲切型。统计表明,河湾的颈口宽度与平均河宽比值从大到小依次是串沟型、冲切型和崩岸型,而河湾裁弯时弯曲率从高到低依次是崩岸型、冲切型和串沟型。通过定义河湾形态参数,测量了16个正裁弯的河湾形态,并确定河湾发生裁弯时河道中心线的弯曲率为极限弯曲率。极限弯曲率可作为自然裁弯的一个临界形态参数,河湾裁弯所能达到的极限弯曲率一般远小于理论最大弯曲率。不同的裁弯形式对应不同的极限弯曲率,这正好回答为何冲积河湾裁弯时的极限弯曲率并不是一个定值,而是处在某一个数值区间。正弦派生曲线裁弯的临界形态参数是最大偏角等于121°。Kinoshita派生曲线的裁弯临界形态参数是最大偏角等于121°、偏斜度系数0.16和丰盈度系数0.29,且只要其中一个参数达到临界值,河湾曲线便形成"8"字形,理论上发生自然裁弯。
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.
出处
《四川大学学报（工程科学版）》
EI
CAS
CSCD
北大核心
2012年第1期82-87,共6页
Journal of Sichuan University (Engineering Science Edition)
基金
清华大学自主科研计划资助项目(2009THZ02234)
国家国际科技合作计划资助项目(2011DFA20820)
