The Influences of Riparian Vegetation on Bank Failures of a Small Meadow-Type Meandering River

The outer banks of meadow-type meandering river bends in the source zone of the Yellow River are especially vulnerable to bank failure. This study aims to understand how vegetation affects bank stability and the mechanism of bank failure, especially via a prediction of the width of a collapsed block of small rivers through a proposed bank stability equilibrium as well as field sampling. Soil and vegetation properties were surveyed at four sites near the riverbank in 2013–2016. It was found that the failed blocks had, on average, a dimension of 0.865 m (width) by 0.817 m (thickness) by 2.228 m (length). The variability in the size of all the failed blocks was attributed predominantly to the roots of plants. Block thickness could be logarithmically predicted by root length at R2 ≥ 0.76. The block width predicted from the proposed equilibrium equation deviated from in situ measurements by approximately 22.1%, a discrepancy highly subject to the overestimation of root reinforcement using Wu’s model. By reducing the coefficient of Wu’s model from 1.2 to 0.85, the proposed equilibrium equation was reliable to predict the width of bank collapse. However, its applicability to other study areas needs to be verified in further studies.