Abstract:

Fluvial erosion of bedrock channels plays a crucial role in controlling denudation rates in orogenic belts. Dynamic adjustment of bedrock channels in response to perturbations such as tectonic and climatic events controls the mechanisms and pace of regional geomorphic evolution. Fluvial systems generally evolve toward a steady state, adjusting their channel geometry to maintain a stable erosion rate. However, variations in tectonic activity, channel substrate strength, and sediment cover can cause fluvial systems to deviate from this equilibrium state. In response to those disturbances, fluvial systems modify their stream power by altering their geometry. Thus, channel morphology is vital for revealing the processes of geomorphic evolution and their control mechanisms. Stream power incision model is the base for quantitative studies of how fluvial systems adapt to tectonic, climatic, and lithological changes. Channel slope and channel width are the two most commonly used parameters to determine the state of channel stream power. Channel slope influences the rate of stream power dissipation along the downstream direction, while river width dictates the distribution of stream power across the channel bed. A reduction in channel width can concentrate stream energy, thereby promoting downcutting. Previous studies that have used fluvial geomorphology to infer tectonic and climatic information have largely focused on changes of channel slope, often overlooking the critical role of channel width. And the controlling factors and geomorphic indications of channel width, another important parameter of the hydraulic system, have not been fully revealed. Bedrock channel width is a key parameter for revealing the tectonic-erosional interaction and the geomorphologic evolution process, and has gradually become a hot spot in geomorphologic research in recent years. This paper addresses this gap by exploring how variations in channel width in response to external perturbations contribute to geomorphological evolution. In this paper, we provide a systematic review of hydraulic geometry modelling, erosion dynamics theory and global case studies, focusing on the factors controlling the width of bedrock channels(bed erodibility, tectonic deformation, sediment effects, and climate change, etc.). The synthesis of existing studies reveals that: 1)Bed erodibility is the core intrinsic factor controlling channel width, and rock mass strength and joint density regulate channel morphology by influencing the erosion mechanism(abrasion/abrasion): channel in high erosion-resistant bedrock zones tend to have narrower width, and higher steepness; on the other hand, weak or fractured rock layers promote lateral erosion and the formation of wide, shallow river valleys. 2)Tectonic deformation drives channel morphology through changes in uplift rate: rivers in high uplift rate areas concentrate shear forces by contracting width, accelerating downcutting to balance uplift, while rivers in low uplift areas weaken erosive capacity by widening the channel. 3) The dual effect of sediment supply significantly influences the response to width: adequate sediment cover of the streambed inhibits downcutting but enhances lateral erosion, whereas low sediment supply concentrates the energy on basement erosion, creating narrower and deeper channels. 4)Extreme climatic events trigger short-term adjustments in channel width through drastic changes in flood flow and sediment pulse inputs, and in the long term influence morphological evolution through changes in erosion datum. Thus, the current study still has the problems of an unknown multi-factor coupling mechanism and insufficient universality of the quantitative model. In the future, we need to combine high-resolution remote sensing, numerical simulation and chronological data to deepen the application of the width parameter in the geomorphological evolution model, so as to provide a new perspective for the study of tectonic-climatic interactions in orogenic zones.

Key words: channel width, stream power erosion, transient geomorphology, fluvial landform

摘要：

活动造山带地貌演化是构造抬升与侵蚀作用竞争的结果, 河流作为关键营力, 其形态调整可反映区域构造活动与气候变化信息。传统研究聚焦于河流坡度对构造扰动的响应, 而河道宽度作为水力系统的另一重要参数, 其控制因素及地貌指示意义尚未充分揭示。基岩河道宽度是揭示构造-侵蚀相互作用与地貌演化过程的关键参数, 近年来逐渐成为地貌学研究的热点。文中系统地综述了水力几何模型、侵蚀动力学理论与全球典型案例研究, 重点讨论了基岩河道宽度的控制因素(河床可蚀性、构造变形、沉积物效应及气候变化等)。综合现有研究可以发现: 1)河床可蚀性是控制宽度的核心内在因素, 岩体强度与节理密度通过影响侵蚀机制(磨蚀或拔蚀)调控河道形态: 高抗侵蚀性基岩区河流收缩变窄, 陡峭度增加; 软弱或破碎岩层则促进侧蚀, 形成宽浅河谷。2)构造变形通过隆升速率变化驱动河道形态调整: 在高隆升速率区, 河流通过收缩宽度集中水流剪切力, 加速下切以平衡抬升; 而在低隆升区则以拓宽河道削弱侵蚀能力。3)沉积物供给的双重效应显著影响宽度响应: 具有充足沉积物覆盖的河床抑制下切但增强侧蚀, 而低沉积物供给则使能量集中于基底侵蚀, 形成窄深河道。4)极端气候事件通过洪水流量剧变和沉积物脉冲输入, 触发河道宽度短期调整, 长期则通过侵蚀基准面变化影响形态演化。由此可见, 当前研究仍存在多因素耦合机制不明、定量模型普适性不足等问题, 未来需结合高分辨率遥感、数值模拟与年代学数据, 深化宽度参数在地貌演化模型中的应用, 为造山带构造-气候相互作用研究提供新视角。

关键词: 河道宽度, 水力侵蚀模型, 瞬态地貌, 河流地貌