弯道推移质横向输沙规律与床面平衡机理

弯道推移质运动直接影响弯道输沙特性、床面形态和河湾演变。弯道推移质输移有4个典型规律,即同岸输移远大于异岸输移、推移质成带性、形成横向底坡和床沙横向分选。归纳了5家推移质横向输沙强度公式,并选择Parker公式分析了推移质横向输沙强度与横向底坡的关系。结果表明,随着横向底坡变大,从凹岸向凸岸的输沙强度将变小,当横向底坡变大到某个临界值时,输沙强度为零;当横向底坡继续变大,推移质输移的方向发生改变,推移质将从凸岸指向凹岸的输移,输沙强度随底坡的变大而变大。弯道床面的凹岸陡坡和凸岸缓坡横向平衡机理各不相同,凹岸陡坡受泥沙水下休止角、横向环流、床沙粒径、床沙分选的制约,而凸岸缓坡主要受上游来沙、横向环流、床沙粒径、床沙分选的影响。弯道床面横向平衡机理关键在于推移质颗粒静力平衡或力矩平衡,横向床沙分选机制使得底坡必须经历反复的动态调整过程,床沙分选总是朝着减小横向底坡方向进行。

Bedload transverse transport and bed equilibrium mechanism in river bends

In river bends,sediment transport characteristics,bed topography and bend evolution are directly influenced by bedload movement,such as four typical laws of bedload transport,much more bedload transport from convex reach to convex reach than from concave reach to convex reach,banding transport of bedload,formation of transverse bed slope,and transverse sorting of bedload.This paper sums up five formulas of bedload transverse transport intensity and analyzes its relationship with transverse bed slope using Parker’s formula.The analysis indicates that the concave-to-convex transport intensity is decreased as the bed slope increases.When the slope reaches a certain value,the intensity will become zero.A further increase of the slope beyond this value will cause a direction change into convex-to-concave transport.The equilibrium mechanism of transverse transport on a steep slope of concave reach generally is different from that on a gentle slope of convex reach.This steep slope often depends on grain submerge weight,transverse circulation,bed particle size and bedload sorting,while the gentle slope depends on upstream incoming sediment,transverse circulation,bed particle size and bedload sorting.Static balancing or moment equilibrium of bedload particles is a key factor that determines equilibrium mechanism.Under the transverse sorting mechanism the bed slope has to adjust itself through a dynamic reiterative process,while bedload sorting always develops to favor reduction of transverse bed slope.