下切性河流的床沙响应与纵剖面调整机制

Riverbed sediment response and longitudinal profile adjustment in incised river channels

天然河流中一些下切性河流具有独特的河床演变规律,如不规则形式的纵剖面等。通过现场调查、资料统计和GIS分析等方式,探讨了河道自然下切过程中河床演变相关机理及其对河流纵剖面的影响,揭示了其中蕴含的定量规律。分析结果表明,下切性河流系统存在床沙的响应与补偿机制,是河流系统由下切转为平衡的重要动力因素之一。响应调整后深切河段的床沙能消耗更多侵蚀能量,从而维持高比降的陡坡河道。因此,下切深度的沿程分布与一些特殊的纵剖面形态有关。经统计发现,流量与床沙(下垫面条件)是最重要的纵剖面控制性因素,引入量纲一参数可与比降建立良好的线性关系。

Some of the natural incised river channels have unique features in fluvial morphology and longitudinal pro- files. In this study, the relevant mechanisms of fluvial morphology during incision and their influence on longitudinal profiles are investigated through field surveys, and the use of data analysis and geographic information system （GIS） techniques. Results show that there exists a loss and compensatory mechanism of sediment transport in response to ri- verbed incision, which is an important factor driving this type of river systems towards a state of equilibrium. After deepening, riverbed sediments consume more erosive energy and sustain high gradient channels, leading to special longitudinal profiles. River discharge and riverbed sediment are the dominant elements controlling the formation of lon- gitudinal profiles. After introducing a dimensionless parameter derived from river discharge and riverbed sediment, the channel gradient and the new dimensionless parameter shows a good linear relationship.