Literature review and empirical analysis of bend scour formulas.

Bank erosion is essential for the proper functioning of rivers and the preservation of their freedom space. However, when the assets are at risk, it is sometimes necessary to implement protective structures along the banks. Unlike civil engineering, soil and water bioengineering techniques offer the advantage of addressing various ecosystem services, thereby contributing to environmental preservation while protecting against erosion. Despite these advantages, the development of such techniques is hampered by a lack of understanding regarding their failure modes. Scour was identify as a factor of failure for 45% of cases of mechanical destruction on bioengineering structure. This is why accurate prediction of scour depths is a predominant factor for a successful design. In order to reduce the scope of the study, this work focuses on bend scour, where stresses on the outer bank are often significant. A review of existing literature was conducted to gain a deeper understanding of available methods for estimating this depth. Twelve empirical formulas for bend scour predication were identified and their domain of validity gathered. All these formulas were developed between 1930 and 2006 and some links between them were highlighted. Depending on the country in which they were developed, the news ones were often inspired from the old ones and used a part of the same dataset. Fifty natural bend were visited on ten lowland or piedmont rivers. Topographical and granulometric measurements were performed to compare the scour depths derived from literature formulas with field values. Some formulas appear to stand out due to their general tendency to overestimate depths or their precision under specific application conditions. Despite the limitations of the study, these results provide an initial overview of the trends for each formula, making it easier to understand the most appropriate conditions of application for each of them.