Human regulations are involved in the hydrogeomorphic processes of silt-laden rivers with unprecedented intensity, and further, affect the structures and functions of the riverine social-ecosystem. The braided reach (BR) of the lower Yellow River is one of the world's most sediment-rich and dynamic rivers. In the recent twenty years, the Xiaolangdi Reservoir constructed upstream and the growing river training works have deeply changed the conditions of the BR, however, the behaviors of the fluvial system under multiple human influences and their mechanisms remain unexplored. Here we systematically analyze the changes in the BR in the past four decades from the view of a coupled human and natural system. We find that compared with the pre-dam period, the channel of the BR in the post-dam period is 60 % narrower and 122 % deeper. Meanwhile, the lateral erosion rate and lateral accretion rate have decreased by 164 m yr-1 and 236 m yr-1, and the flood transport capacity has increased by nearly 79 %. These changes were mainly caused by anthropic flow regime changes and boundary modifications, whose relative contributions were 71 ± 10 % and 29 ± 10 %, respectively. The interactions among channel morphology change, regional flood risk and human activities underpinned the evolution of the fluvial system by shifting the human-river relationship. Reach-scale stabilization of a silt-laden river needs the effective management of erosion and deposition processes, which calls for integrated management of soil conservation, dam regulation, and floodplain governance at a basin scale. Lessons from the lower Yellow River have important implications for other rivers faced with siltation problems, especially in the Global South.
Keywords: Braided River; Channel morphology; Coupled human and natural system; Flood risk; Hydrogeomorphology; Lower Yellow River; River management.
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