Impact Assessment of River Evolution in the Yellow River Using Ecohydraulic Model

The construction and operation of the Xiaolangdi Reservoir and the cascade reservoirs have significantly altered the flow and sediment dynamics in the lower reaches of the Yellow River, impacting riverbed evolution and fish habitat. However, few studies have assessed the impact of river shapes and river evolutions on fish habitat suitability in the Yellow River. In this study, we investigated the impact of the shape of river reach on fish habitat suitability level based on the model system incorporating hydrodynamics, sediment transport and fish habitat suitability parameters. The habitat and ecological situation regarding HSI, WUA and OSI were evaluated for both goldfish (Carassius auratus) and bronze gudgeon (Coreius heterodon) in braided river and meandering river reaches in the lower Yellow River. Additionally, long-term changes in riverbed physical conditions and fish habitat suitability were examined to better understand the effects of river reach and river evolution. Modelled results indicate that fish habitat suitability in both upstream braided and downstream meandering sections enhances with the increasing of flow discharge. Goldfish shows higher habitat suitability in the braided river, whereas bronze gudgeon is more suitable in the meandering river. Over time, however, significant riverbed deformation degrades fish habitat suitability. Habitat suitability decreases progressively, and after the 10th year, neither the upstream braided river nor the downstream meandering river remains suitable for goldfish or bronze gudgeon. Overall, coupling hydrodynamic models with fish habitat models improves our understanding of how river shape and long-term river evolution affect fish habitat suitability, providing valuable insights for future ecological management and conservation efforts.