Functional degradation of the water-sediment regulation scheme in the lower Yellow River: Spatial and temporal analyses.

Heavy sedimentation has led to the phenomenon of a secondary perched river in the lower reaches of the Yellow River. The water-sediment regulation scheme (WSRS) using the Xiaolangdi Reservoir was first implemented in 2002 to try to solve this problem. In this study, we analyzed the spatial and temporal effects of the current WSRS (2005-2013) on the lower Yellow River. Our results suggest that the current WSRS is exhibiting a tendency towards functional degradation, meaning that the scheme is no longer as effective as it was initially for the lower Yellow River. Although the main river channel has been fully scoured in the lower reaches since the implementation of the WSRS, we found that the degree of erosion declined gradually in a top-down fashion from the braided reach, through the transitional reach, to the meandering reach. Of the total eroded sediment, 69.64% came from the braided reach and only 6.61% came from the meandering reach. In addition, the reduction in riverbed elevation-a key function of the WSRS-has clearly slowed since 2005. We discuss the mechanisms underlying this functional degradation of the current WSRS and future challenges for the management of the lower Yellow River. Insights gained from this study will likely be of use to those weighing up options for future implementations of the WSRS.