CONCLUSIONS

Since the operation of the XLD reservoir began in 2000, the objective of mitigating riverbed elevation increases in the LYR has been achieved. With the proposal of the new goals for environmental protection and high-quality development of the Yellow River Basin, the environmental management and rehabilitation of floodplains have received increasing attention from people in all walks of life. Our research investigated the changes in the sediment budget and morphology of the braided reach between HYK and GC in the LYR, and the main findings are as follows:
During the operation of the XLD reservoir from 2000 to 2017, the total eroded volume of the braided reach (between HYK and GC) was approximately 11.47×108 m3, of which approximately 8.38×108 m3 occurred along the main channel and 3.09×108m3 in the floodplains. The main channel was fully scoured, with an average erosion rate of 14.16 cm/yr, leading to increases in channel depth and bank-full discharge. The floodplains gradually changed from a sedimentation pattern to an erosion pattern, with an average erosion rate of 1.30 cm/yr, due to the implementation of the WSRS, continual construction and reinforcement of control works along the channel and other human activities.
Sediment is the primary source of a sustainable agro-ecosystem in the lower Yellow River, which influences morphological development and may counteract floodplain subsidence and soil erosion. The shortage of sediment resources is unfavourable to the environmental management of floodplains. We propose a new management mode for the floodplains in the LYR. Some floodplains in local reaches are rebuilt into high floodplain, second floodplain and new floodplain areas, with some mechanical measures such as pipeline sediment transport and floodplain filling. This mode could eliminate the unfavourable form of a secondary suspended river and optimize the allocation of sediment resources downstream, which lays a good foundation for the environmental management of the lower Yellow River and the economic development of the floodplain region.