Human impact on river planform within the context of multi-timescale river channel dynamics in a Himalayan river system
Human impact on river planform within the context of multi-timescale river channel dynamics in a Himalayan river system
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DOI：
10.1016/j.geomorph.2021.107659
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发表时间：
2021-02
期刊：
影响因子：
3.9
通讯作者：
K. Vercruysse;R. Grabowski
中科院分区：
文献类型：
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作者：
K. Vercruysse;R. Grabowski
河流是动态的景观特征，经常被人类活动所改变，这使得很难将人类对地貌变化的影响与自然河流动力学分开。这项研究评估了人类对河流平面形态变化的影响，在喜马拉雅山Sutlej和Beas河的短期和长期河道动态的背景下，（一）系统地评估河流平面形态变化百年，年度，季节和情节的时间尺度;（二）连接观察到的变化，人类环境的驱动因素;和（iii）概念化这些地貌变化的时间尺度依赖的演变轨迹（按，斜坡，脉冲）。Landsat图像被用来提取季风后活跃河道（1989-2018年）的组成部分，使用修改后的归一化差异水指数来确定潮湿的河流区域，并使用可见红色来确定活跃的砾石坝。调查结果进行了比较与历史地图，代表大坝前时期（1847-1850年）和数据的潜在驱动因素的变化（流量，气候和土地覆盖）。河流平面特征在所有时间尺度上发生了显着变化，表现出强烈的时空变化之间和两条河流内。大坝的建设可能导致河道变窄，并在百年尺度（新闻轨迹）拉直。在Sutlej，这一过程在过去30年中一直在持续，可能是由于水抽取和气候变化的累积效应（斜坡轨迹）。在Beas，河流平面形态指标的变化模式在同一时期不太明显，沿河流长度沿着变化更大，可能与不同的大坝运行有关，这些大坝运行保持了更高程度的流量变化和峰值流量（压力轨迹）。还观察到Sutlej的集料开采（间歇性）造成的局部侵蚀率很高（脉冲轨迹）。表达为进化轨迹，观察到的人类活动的反应证实了人类对河流系统的影响的遗产效应的重要性，并强调依赖于空间和时间尺度来确定变化的轨迹。多时间尺度的评估和概念化提供了对人类对河流平面变化影响的不同方面的见解，这对制定整体管理策略至关重要。
Rivers are dynamic landscape features which are often altered by human activity, making it difficult to disentangle human impact on geomorphic change from natural river dynamics. This study evaluated the human impact on river planform change within the context of short- and long-term river channel dynamics in the Himalayan Sutlej and Beas Rivers, by (i) systematically assessing river planform change over centennial, annual, seasonal and episodic timescales; (ii) connecting observed changes to human-environment drivers; and (iii) conceptualising these geomorphic changes in terms of timescale-dependent evolutionary trajectories (press, ramp, pulse). Landsat imagery was used to extract components of the post-monsoon active river channel (1989–2018), using the modified Normalized Differences Water Index to identify the wet river area, and visible red to determine active gravel bars. Findings were compared with a historical map to represent the pre-dam period (1847–1850) and with data on potential driving factors of change (discharge, climate and land cover). River planform characteristics changed significantly over all timescales, exhibiting strong spatiotemporal variation between and within both rivers. Dam construction likely caused channel narrowing and straightening at the centennial scale (press trajectory). In the Sutlej, this process has continued over the last 30 years, likely enforced by the cumulative effect of water abstraction and climatic changes (ramp trajectory). In the Beas, the pattern of change in river planform metrics was less pronounced over the same period and more variable along the length of the river, possibly linked to different dam operations that maintain a higher degree of flow variability and peak flows (press trajectory). High local erosion rates caused by aggregate mining (episodic) in the Sutlej were also observed (pulse trajectory). Expressed as evolutionary trajectories, the observed responses to human activity confirm the importance of legacy effects of human impact on river systems, and stress the dependency on spatial and temporal scales to determine trajectories of change. The multi-timescale assessment and conceptualisation provide insights into different dimensions of human impact on river planform change, which is pivotal to developing holistic management strategies.