The position of power axis of flow is determined by main channel when runoff is small, while the change law conforms with the law of rectangular section when runoff is large.
当小流量时水流动力轴线的位置取决于主槽的位置，当大流量时水流动力轴线的变化规律接近矩形断面的情形。
2
And so, we partition the small watershed to the both of slope and channel first time, and, we can research runoff and sediment transportation laws of channel by using small watershed normal model.