中文摘要：

以1950—1985年间274次洪水的资料为基础，对黄河下游洪水的输沙效率进行了研究，查明了场次洪水排沙比随流量变化的3个临界点。同时还发现，当场次洪水平均含沙量小于34．02kg／m^3时或当来沙系数小于0．01kg·s，/m^6时，下游河道可以不淤。黄河下游游荡段排沙比最小，过渡段次之，限制性弯曲段最大，可见窄深河段的输沙效率要高于宽浅段。上述3个河段处不冲不淤状态时的临界含沙量依次增大，证明窄深河段可以在含沙量较大时保持临界不冲不淤状况。

英文摘要：

Based on data from 274 flood events in the lower Yellow River, a study has been made for the sediment transport efficiency of floods in relation with water-sediment combination and channel geometry. Three thresholds have been identified in the variation of channel sediment delivery ratio （SDR） with event-average water discharge. It has been found that when event average suspended sediment concentration Cmean, was higher than 34.02kg/m^3 , or the index Cmean /Qmean was smaller than 0.01kg· s/m^6, no deposition occurred. The SDR for the braided reach was the smallest, that for transitional reach the second, and that for the confined meandering reach the largest. In this order, the threshold Cmean for no-fill and no-scour state increased. It indicated that a narrower and deeper channel can better remain no-fill and no-scour state at higher Cmean. values than a wider and shallower channel can.