人类活动影响下的干旱区河流地貌演变——以塔里木河为例

Human impacts on fluvial processes in a very arid environment:case of Tarim River in China

全球范围内干旱区河流正日益受到高强度人类活动的扰动,但较少研究报道这种扰动对河流地貌过程的影响。采用历史文献、水文数据和遥感影像相结合的方式,详细分析了人类活动影响下中国最大内陆河塔里木河(简称塔河)的河流地貌变化过程。结果表明:塔河流域人类活动的规模和强度日趋上升,对河流水沙过程和地貌形态等影响显著。近50年来,塔河干流低流量过程发生频率呈显著上升趋势,而中、高流量过程则呈降低趋势,河道径流和输沙量减少显著。塔河干流上游现为游荡河道,冲淤变化剧烈且总体处于淤积抬升状态,但河道平均河宽呈减小趋势,可能是因为塔河两岸冲积平原的开垦和河岸加固。塔河中游弯曲河道蜿蜒系数在近几十年呈缓慢上升趋势,但明显低于废弃古河道。

Dryland rivers have long been subject to the influences of various human interventions in many parts of the world, however, little attention has been paid on how the fluvial processes of these rivers have responded to. Here we report a case study of the Tarim River, the largest inland river in China. By analyzing historical literature, gauged hydrological data and satellite images, this study performed a detailed examination on how the fluvial process of the river has changed under ever-increasing human influences in recent decades. The results demonstrate that human ac- tivity in the river basin have exerted significant impacts on the Tarim River, causing major changes in runoff, sediment transport and river morphology. Hydrological data observed over the past five decades shows an obvious reduction in both runoff and sediment load in the Tarim River, even though the runoff from source tributaries exhibits a gently in- creasing trend. The annual occurrence of low-flow events shows a significantly increasing trend, while the occurrences of both moderate-and high-flow events take a decreasing trend. The upper reach of the Tarim River is dominated with a wandering channel pattern, which is in aggradation and yet in a strong fluctuation form. The mean width of the wandering channel has been in a gently decreasing trend, perhaps due to the reclamation of river floodplains into farmlands and river embankments. The middle reach of the Tarim River takes a typical meandering channel pattern, the sinuosity index of which is distinctively lower than those of the old （abandoned） channels, even though it shows a gentle increasing trend in recent decades probably due to the increased occurrence of low-flow events.