Deciphering the role of riverbank collapse in the braided reach of the lower Yellow River: Helpful or harmful?

Riverbank collapse is a specific pattern of morphological adjustment and channel evolution in rivers. Here, the role of riverbank collapse in the braided reach of the lower Yellow River is examined through analysis of field-based results, cross-sectional profiles and water-sediment data. Results show that the braided reach with wide and shallow cross-sectional characteristics was prone to riverbank collapses, leading to lateral channel migration. The lateral erosion rate ( R 2 = 0.63) and the main channel migration distance ( R 2 = 0.58) increased with the rising cross-sectional geomorphic coefficient. Riverbank failure might trigger the reshaping of cross-sectional morphology. In 2018, the reach-scale bankfull width in the braided reach had widened to 153% of the dimensions in 2006, primarily due to riverbank collapses. However, the high lateral erosion rate hindered the growth of the reach-scale bankfull depth with increasing fluvial erosion intensity, indicating that collapses can inhibit riverbed undercutting. Furthermore, such failures can alleviate flood control pressures by removing river capacity limitations. Under the effect of riverbank collapses the reach-scale bankfull area increased by 184% over the past 12 years, resulting in a water level decrease of over 1.29 m at the main hydrological stations at a discharge of 3000 m 3 /s. Consequently, the role played by riverbank collapse may be thoroughly assessed in the braided reach of the lower Yellow River in order to enable the implementation of scientific planning and management.