清水作用下全动床复式河槽河床演变特性

通过水槽试验,探讨了清水作用下由非均匀沙构筑而成的全动床复式河槽的演变特性,包括河床完全粗化后河道稳定宽度及滩岸侵蚀的沿程变化.复式河槽断面构筑而成后,实施倒灌,然后恢复地形,最后用全站仪施测初始河道地形,在试验结束后,相应断面再做精细床面形态测量.复式河槽流量由槽首的矩形堰量测,水位由自动水位仪量测.试验结果表明,随着泥沙淤积量的增大,主槽水深变浅;而河道水深变浅,又将会使床面泥沙起动的作用力减小,河道水深将变得更浅.清水作用下的全动床复式河槽达到稳定时,河道稳定宽度将沿程变化;河道完全粗化后,主槽宽度增大,滩岸侵蚀速率在空间上变化趋势表现为越往下游,滩岸侵蚀速度越小;在清水作用下,河道滩岸发生侵蚀,其侵蚀面积有沿程减小的趋势,这与流速沿程的变化相一致.

Evolution characteristics of compound fluvial channels with totally movable-bed under clear water

The evolution characteristics of compound fluvial channels with totally movable-bed that was made of non-uniform sediment were studied experimentally under clear water. They include the variations of stabilized width and bank erosion along the channel after the riverbed is roughened completely.Before the experiments,the compaction of sand was finished by slowly flowing water. After the whole self-formed channel was submerged for some time,the water was discharged slowly; then,the movable-bed channel was restored. The original and eroded bed surface levels were probed by using a total station and the discharge and water levels were measured by a triangular weir and automatic water level meter,respectively. The results show that with increasing deposition of sediment,the flow depth in the main channel becomes shallow,leading to the force under which sediment particles start to move is decreased. When the channel becomes stabilized,the channel width varies along the channel. After the riverbed is roughened totally,the width of the main channel is increased and the retreat rate of river bank becomes small along the channel. Under the action of clear water,the floodplain and bank of the main channel are eroded and the eroded area decreases along the channel. This is consistent with decrease in the cross-section averaged velocity along the channel.