黄河上游干支流交汇区沙坝淤堵形成条件

On conditions of sandbar clogging at confluences in the Upper Yellow River

针对黄河上游干、支流交汇区形成的沙坝淤堵事件,利用野外观测资料,分析了支流高含沙洪水特性及交汇区沙坝淤堵特点,探讨了汇流比(支流流量与干流流量之比)、支流洪水水量、支流洪水沙量等因素对沙坝淤堵形成的影响;根据动量原理建立了交汇区形成沙坝淤堵的判别关系,结合黄河上游干、支流洪水输移特性,得出了基于汇流比与支流洪水水量关系及支流洪水沙量与支流洪水水量关系的沙坝淤堵判别条件。由此,可根据汇流比、支流洪水水量及沙量判断交汇区能否形成沙坝淤堵,可为暴雨洪水期黄河上游交汇区形成沙坝淤堵灾害的预报及防治提供参考。

Sandbar clogging occurred frequently at the confluence between hyper-concentrated flood flows from tributaries and the main stream in the Upper Yellow River,with consequence of severe flooding disasters.The properties of hyper-concentrated flood flow in tributaries and the characteristics of sandbar clogging at the confluences between tributary and main stream were analyzed based on field data for sandbar clogging events in the Upper Yellow River.Effects of key factors,such as discharge ratio（tributary discharge to that of main stream） and water amount and sediment load of hyper-concentrated floods,on the sandbar clogging were investigated.A general discriminant formulation for sandbar clogging at confluences was proposed based on the momentum principle.By taking account into the characteristics of flood and sediment transport in the main stream and tributaries,two criteria for sandbar clogging were further derived from the general discriminant formulation,one expressed by relationship between discharge ratio and water amount of tributary flood and another expressed by water amount and sediment load of tributary flood.Therefore,the occurrence of sandbar clogging can be predicted using discharge ratio,water amount and sediment load of tributary flood.This is of critical importance for preventing disasters caused by sandbar clogging at confluences that is associated with hyper-concentrated flood flows during rainstorm events in the Upper Yellow River.