摘要:
建立反映河床调整幅度的体幅指标K,分析2003～2008年三峡水库下游宜昌—昌门溪河段河床调整幅度的沿程变化。研究发现该河段K与河段净冲刷强度不成正相关,而是与河道宽深比成正相关,当床沙中值粒径小于0.5 mm时,K与床沙中值粒径成负相关。初步分析认为:三峡下游粗颗粒泥沙容易达到输送饱和状态,当水流挟沙力减小时出现落淤,使得宽浅河段局部出现较大淤积,净冲刷强度较小,调整幅度较大;当床沙中值粒径小于0.5 mm时,该河段河床冲刷以悬移质输沙为主,河床组成越细,被冲刷的量越大,河床调整幅度也就越大。结合建库前后不同粒径组悬移质输沙量的沿程变化,对水库下游河床粗化方式进行了讨论。
Abstract:
An index K,which stands for the extent of riverbed evolution,is proposed and used to analyze the riverbed evolution in the reach of Yichang to Changmenxi.The study finds that K is inconsistent with the net scour intensity,while positively correlated to the ratio of width to depth and negatively correlated to the median diameter of bed material when the diameter is less than 0.5mm.Preliminary analysis shows that:it is easy to reach the state of transport saturation for coarse sediments downstream of the Three Gorges Reservoir.And the coarse sediments deposit when transport capacity decreases,causing great local deposition on wide-shallow river channels and the net scour intensity decreases,and riverbed evolution strengthens.When the median diameter is less than 0.5mm,the suspend loads is dominant in the downstream scouring amount,resulting that:the finer the bed material is,the greater the scouring a-mount and the riverbed evolution is.Considering the changes of capacity of sediment transport along the river reach after dam construction,two ways of coarsening the river bed are discussed.
下载:
