跌坎溯源冲刷的影响因素与两种发展模式  

Influence factors and two evolution patterns for retrogressive erosion of step

作　　者：杨飞 王远见[1,2] 江恩慧 YANG Fei;WANG YuanJian;&JIANG EnHui(Yellow River Institute of Hydraulic Research,Yellow River Conservancy Commission,Zhengzhou 450003,China;Key Laboratory of Lower Yellow River Channel and Estuary Regulation,Ministry of Water Resources,Zhengzhou 450003,China)

机构地区：[1]黄河水利委员会黄河水利科学研究院,郑州450003 [2]水利部黄河下游河道与河口治理重点实验室,郑州450003

出　　处：《中国科学：技术科学》2024年第7期1390-1398,共9页Scientia Sinica(Technologica)

基　　金：国家“十四五”重点研发计划项目(编号:2021YFC3200400);水利部重大科技项目(编号:SKR-2022021);国家自然科学基金项目(批准号:52179066);黄河水利科学研究院基本科研业务费专项(编号:HKY-JBYW-2022-12)和黄河水利科学研究院科技发展基金项目(编号:黄科发202111)资助。

摘　　要：水位降至水库淤积三角洲顶点高程以下时,顶点处形成的跌坎溯源冲刷是动态的河流裂点.本文采用水沙动力学模型模拟室内水槽试验和实际大型水库中的跌坎溯源冲刷过程.水槽试验模拟结果能够较好地反演非黏性沙跌坎的快速衰减过程和黏性沙跌坎的持续稳定溯源冲刷过程.非黏性沙跌坎冲刷后河床坡度较大且大于上游顶坡,跌坎快速衰减.黏性沙跌坎中水流切应力超过临界起动切应力的部分才能产生冲刷,最大冲刷位置靠近跌坎底部,使得跌坎能够持续稳定存在.对于小浪底水库的淤积三角洲,黏性沙跌坎在2020年汛期低水位运行时呈现逐渐衰减的溯源冲刷过程,模型较为准确地模拟了该跌坎的位置变化与冲刷塑造的淤积纵剖面.实际大尺度黏性沙跌坎与水槽试验中非黏性沙跌坎的溯源冲刷过程更为接近.结合数值模拟算例可以确定跌坎存在两种溯源发展模式:衰减型跌坎和增强型跌坎.两者塑造的地形差异明显,增强型跌坎下游河床坡度比上游要缓,而衰减型跌坎相反.非黏性沙跌坎属于衰减型跌坎.跌坎高度、跌坎顶坡坡度、泥沙粒径、单宽流量等控制变量均存在阈值,使得跌坎在衰减型和增强型之间变化.The stepped retrogressive erosion formed at the rollover point of the reservoir delta is a natural dynamic knickpoint when the water level drops below the rollover point elevation.This study presents a one-dimensional flow and sediment numerical model to simulate the stepped retrogressive erosion in laboratory flume experiments and a field large-scale reservoir.The rapid attenuation scouring process of the non-cohesive sediment step and the continuous and stable scouring process of the cohesive sediment step were well predicted.The formed downstream bed slope is larger than the top-slope and the step fast decays.Erosion occurs only at the part where the flow shear exceeds the critical bed shear stress in the cohesive sediment step.The maximum erosion is located at the bottom of the step,which enables stable existence of cohesive sediment step.For the fine-grained delta deposits in the Xiaolangdi Reservoir,the gradual and slow attenuation of the cohesive sediment step caused by lowering water level operation during the 2020 flood season has been observed.The simulated changes of the step location and the final longitudinal profile shaped by erosion match well with the observed features.The field large-scale cohesive sediment step in the reservoir is closer to that of non-cohesive sediment step in the flume.Combined with the numerical cases,it can be determined that there are two development types for the stepped retrogressive erosion:Attenuation type step and enhancement type step.The bed formed by the two types are significantly different,and the attenuation type step has a slower downstream slope than the upstream,while the attenuation type is the opposite.The control variables,such as the step height,upstream slope,sediment size,and unit discharge,all have thresholds,which cause the retrogressive erosion to transform between attenuation and enhancement types.

关 键 词：溯源冲刷 水库三角洲 衰减型跌坎 增强型跌坎 黏性沙 

分 类 号：TV145[水利工程—水力学及河流动力学]