Impact of an artificial chute cutoff on the river morphology and flow structure in Sipaikou area of the Upper Yellow River

Artificial chute cutoff can fundamentally eliminate the threat of flood caused by the meandering river, but it significantly changes its morphodynamic characteristics. Channel adjustments after cutoff are rapid, which makes it difficult to study the interaction between river morphology and flow structure only through field measurement. However, numerical simulations can provide insights into the hydrodynamic characteristics after artificial chute cutoffs. In this study, both field measurement and numerical simulation are employed to investigate the flow structure and bed morphology caused by an artificial chute cutoff in Sipaikou area of the Upper Yellow River in 2018. The measured hydrological data provide boundary conditions and initial values for the numerical model. The field measurement results reveal that the concave bank of the study area is severely scoured up to 270 m after the artificial cutoff, and a 20 m deep scour hole and a 2.26 km long pool are formed at the entrance and near the left bank of the chute channel. The numerical simulation results of velocity at typical cross-sections are in good agreement with the measurement results. Flow separation and stagnation zones are observed near the right bank during the low flow conditions (discharge of at least 902 m³/s), but this phenomenon is not seen during larger flow conditions (discharge exceeds 2000 m³/s). Interestingly, flow recirculation zones are also found near the left and right banks of the scour hole. Further, a long flux belt is formed at the scour hole and the pool. Consequently, the impact of the bed topography on the hydrodynamic characteristics is relatively prominent when the discharge is small, while the impact on the river banks and river bed is more noticeable when the water discharge is large. In addition, high shear stress is observed near the left bank at the downstream of the studied area, which indicates that the left bank at the downstream is still being scoured. These results suggest that bank protection measures along the left bank are required to maintain the effectiveness of the artificial chute cutoff.