Effectiveness Evaluation and Sustainability Study of River Regulation Project in the downstream of Dongjing River

This study aims to evaluate the effectiveness and sustainability of the first phase of the river regulation project targeting the restoration of the flood discharge capacity in the lower reaches of the Dongjing River.Based on the measured hydrological data during flood seasons before and after the project implementation, this study analyzed the water level reduction under the same flow discharge.The two-dimensional hydrodynamic numerical model was recalibrated and then used to re-verify the design conditions.By comparing changes in erosion and deposition over time at river cross-sections, based on the "sediment variation-sediment transport capacity response" dual-factor framework, a systematic evaluation of the regulation effectiveness and its sustainability was conducted.The results show that after the project implementation, at the regulation design flow (3000 m³/s), the water level at Yanglinwei Station was 0.06 m lower than the design value, achieving the expected objective.Under the condition that the 2023 flood peak flow increased by 16% compared to 2021, the water level at Yanglinwei Station decreased by 0.18 m instead, and the water levels along the course at equivalent flows significantly decreased, indicating a substantial improvement in the river channel's flood conveyance capacity.The actual siltation volume in the dredged areas was small, indicating good sustainability of the project.The approach of dredging floodplains demonstrated significant advantages in terms of farmland conservation and investment efficiency.This study, from the perspective of the synchronous variation in sediment concentration and sediment transport capacity factors, explored the intrinsic mechanisms of riverbed erosion and deposition changes after the implementation of the regulation project. It provides a novel research approach for predicting the development trend of erosion and deposition.And it offers key technical references for the subsequent management of the lower Dongjing River and regulation projects on other tributaries in the Yangtze River Basin.