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

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 activity 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 increasing 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.