黄河下游洪水冲淤相对平衡的分组含沙量阈值探讨

Study on threshold of grouping sediment concentration about floods scouring and silting relative balance in the lower Yellow River

河床冲淤相对平衡下的洪水分组含沙量阈值是多泥沙河流水沙调控的重要参数。基于河床演变学的原理,根据黄河下游200余场次洪水实测资料,探讨了洪水分组含沙量阈值和分组来沙系数阈值。研究表明,黄河下游洪水过程中,在一定的分组含沙量及来沙系数条件下,可以使得河床冲淤达到相对平衡。对于悬沙以细泥沙为主的洪水,其河槽冲淤临界含沙量与主槽单宽流量、最大日均流量、花园口以下河段最小平滩流量、床沙中值粒径大于0.05 mm的沙重百分数有关;对于悬沙以中粗泥沙为主的临界含沙量则与粒径大于0.05 mm的沙重百分数无关;对于悬沙以粗泥沙为主的临界含沙量除与细泥沙临界含沙量的因素有关外,还与悬沙中值粒径小于0.025 mm、大于0.05 mm的沙重百分数有关。对于含沙量级相近的洪水,若流量级不同,同样可以产生不同的冲淤结果,即存在着分组来沙系数临界值。

The important parameter of water-sediment regulation is the threshold of grouping sediment concentration about floods scouring and silting relative balance in hyperconcentration river. The study on the threshold of flood grouping sediment content and incoming sediment coefficient is based on the more 200 flood data measured in the lower Yellow River. The data shows that the riverbed scouring and silting can obtain relative balance when the floods have determinate grouping sediment content and incoming sediment coefficient. For the floods with the suspended sediment consisting of thin silt, the critical sediment content of watercourse scouring and silting are influenced by unit discharge of main riverbed, the average maximal daily discharge, the least bankful discharge in the lower Yellow River beginning from Huayuankou and the weight percentage of riverbed sediment whose median diameter d50 is bigger than 0.05 mm; For those vdth the suspended sediment consisting of the middle-coarse silt, the critical sediment content of watercourse scouring and silting is irrelative to the weight percentage of riverbed sediment whose median diameter d50 is bigger than 0.05 mm; For those with the suspended sediment formed by the coarse silt, the critical sediment content of watercourse scouring and silting are influenced by the unit maximal daily discharge , the least flat beach discharge in the lower Yellow River beginning discharge , the average from Huayuankou and the weight percentage of riverbed sediment whose median diameter d50 is less than 0.025 mm and bigger than 0.05 mm. The similar sediment content floods have the critical grouping incoming sediment coefficient, which means that different discharge can bring forth different scouring and silting outcome. The result can provide evidence for water-sediment regulation of Xiaolangdi reservoir on the Yellow River, and enrich the river dynamics research.