Experimental study of bed structures evolution on natural mountain rivers

Bed structures which developed in many mountain rivers provide additional resistance to the flow. A field experiment was conducted on debris flow deposits in the valley of jiangjiagou ravine, a tributary of Yangtze river in southwestern China, to study the evolution and distribution of bed structures and their relationship with environmental conditions. Water and sediment from the jiangjiagou main stream were diverted into the experiment channel. Several hydrological schemes were adopted to scour the channel until equilibrium. And during this process the evolution of bed structures and channel configuration was investigated. The results indicated that stronger bed structures meant greater stream power consumption, larger resistance and steeper channel slope in a certain section when rivers are in dynamic equilibrium. Thus to some extent the channel longitudinal profiles could be determined by the distribution of bed structures. In natural cases, the strength and evolution of bed structures were under the influences of environmental conditions such as discharge and bedload transportation rate. That is, given the same conditions, the same bed structures distribution and longitudinal profile can be predicted.