水沙条件对黄河下游河道输沙功能的影响

提出河道输沙功能指标F_s为进入某一河道的泥沙总量(干流与支流输入沙量之和)与输出这一河道的泥沙量之比。河道输沙功能与来水量和来沙量有密切关系,若来水减少,来沙增多,则河道输沙功能减弱。来沙中大于0.05 mm粗泥沙含量百分比与河道输沙功能指标成负相关。来沙系数、特别是粗泥沙的来沙系数,是决定黄河下游输沙功能的重要因子;来沙系数越大,则河道输沙功能指标越低。场次洪水的输沙功能指标随场次洪水最大含沙量的增大而降低,历年河道输沙功能指标随各年中高含沙水流频率的增高而降低。小浪底水库修建后,为我们通过调水调沙提高河道输沙功能提供可能。研究表明,场次洪水平均含沙量35 kg/m³,或场次洪水平均来沙系数为(0.015 kg·s)/m⁶,是在调水调沙中实现河道输沙功能优化的最优含沙量和最优来沙系数,平滩流量则是实现河道输沙功能最大化的最优流量级。

Sediment Transferring Function of the Lower Yellow Riveras Influenced by Discharge and Sediment Load Conditions

The sediment transferring function of the lower Yellow River has been studied in this paper by using a geomorphological approach. An index for sediment transferring function (F_s) of a river has been proposed, which is defined as the output of sediment load from a given river reach divided by the input of sediment load to this river reach. The F_s index was found to be closely related with discharge and sediment load conditions. When water discharge decreased and sediment load increased, F_s decreased. The >0.05mm percentage in suspended load was negatively correlated with F_s. The index C/Q, especially the index C_>0.05/Q, where C is suspended sediment concentration, C_>0.05 is the concentration of the >0.05mm sediment, and Q is water discharge, is a major factor determining sediment transferring function of the lower Yellow River. The higher the C/Q and C_>0.05/Q are, the lower the F_s will be. The event-based F_s decreased with both the increasing event maximum suspended concentration and the increasing frequency of hyperconcentrated flows. The construction of Xiaolangdi Reservoir provides some possibility for enhancing the sediment transferring function of the lower Yellow River by means of water discharge and sediment load regulation. This study shows that the event-averaged suspended sediment concentration C=35 kg/m³ and the event-averaged index C/Q=(0.015 kg·s)/m⁶ are the optimal values for the optimization of F_s, and so is the bankfull water discharge.