近期黄河下游游荡河段床面下切与横向展宽的定量关系

水库运用初期,坝下游河床通常会发生冲深下切及滩岸崩退过程,但是现有研究较少分析河床下切与横向展宽之间的定量关系。以1999-2015年游荡河段实测断面地形资料和水沙资料为基础,分析了近期游荡河段的河床调整过程,发现河床调整以床面下切为主,部分河段崩岸明显;建立了不同河段累计床面下切值与累计滩岸崩退宽度之间的经验关系,其相关系数均大于0.8;根据水沙控制方程推导了河床下切与展宽之间的定量关系,发现累计床面下切值与河宽变化率及初始水深有关,各河段的相关系数均大于0.8;预测了未来游荡河段河床形态的调整过程,发现当各河段持续下切至某一值时,两种方法计算下的河床展宽值较为接近,一定条件下可用来估算河床下切和横向展宽的实际情况。

Recent quantitative relationships between channel incision depth and bank retreat width in the braided reach of the Lower Yellow River

Downstream of a dam usually undergoes severe channel degradation and significant bank retreat processes due to the altered flow and sediment regime after the operation of a reservoir.In this study,the reach-scale bankfull channel dimensions in different subreaches of the braided reach were studied based on the observed cross-sectional profiles during the period from 1999 to 2015.Results indicate that the main adjustment in channel geometry was characterized by channel incision,with bank retreat being remarkable in local regions.Empirical relations were developed between the cumulative reach-scale bank retreat width and channel incision depth in different reaches,with the correlation coefficient above 0.8.Quantitative equations between channel incision depth and bank retreat width were derived in different reaches based on one-dimensional continuity equations of flow and sediment,and the channel incision depth is in close connection with the rate of bank erosion and the initial channel depth.In addition,the widths of cumulative bank retreat calculated by two methods were both in close agreement when the channel degradation approached a certain depth,which indicates the proposed two relationships can be used to estimate the tendency of fluvial processes in the braided reach of the Lower Yellow River.