中文摘要：

以黄河下游不同河型河段为研究对象,选取下游河道处于相对冲淤平衡的4个时期（1967-1968年、1979-1980年、1989-1990年、1998-1999年）为研究时段。根据8年的水文资料及汛后实测断面地形资料,采用基于对数转换的几何平均与断面间距加权平均相结合的方法,计算了各时期游荡河段、过渡河段及弯曲河段的平均平滩流量及面积。通过分析平滩流量及面积与汛期水沙条件之间的关系,建立了准平衡状态下黄河下游各河段平滩流量及面积与相应来沙系数的经验关系式,用于预测不同水沙条件下各河段的平滩河槽特征,并估算黄河下游平滩流量维持在4 000m^3/s的水沙条件。

英文摘要：

Hydraulic geometry in an alluvial river under relative equilibrium or quasi-equilibrium usually represents the relationship between the bankfull channel dimensions and the incoming flow and sediment regime.An investigation to the processes of bankfull channel geometry under different quasi-equilibrium states is of great significance. Four different periods including 1967- 1968,1979- 1980. 1989- 1990,and 1998-1999 were selected for the Lower Yellow River（ LYR） under quasi-equilibrium state in this study. Based on observed hydrological data and sedimentation section profiles during these four periods,the reach-averaged bankfull discharge and bankfull area in the braided,transitional and meandering reaches were calculated by using an integrated method,which integrates a geometric mean based on the log-transformation with a weighted average based on the spacing between two consecutive sections. The relationships between bankfull discharge,bankfull area and incoming flow and sediment regime were investigated,with the corresponding empirical relations being developed,which can be used to predict the variation in the reach-scale bankfull channel geometry and to estimate the flow and sediment regime for maintaining the magnitude of bankfull discharge in the LYR at4 000m^3/ s.