Modelling riverbank retreat by combining reach-scale hydraulic models with bank-scale erosion and stability analyses

In recent years many progresses have been made in understanding and modelling bank ero- sion processes, but an accurate quantification of shear stresses exerted by the flow on the bank area, and consequently of the fluvial erosion rate continues to be a challenging issue. The objective of the present research is to test different methods to evaluate the rate of riverbank retreat. The first step of the research consisted in data collection, which included field surveys along a study reach of the Cecina River. Differ- ent hydraulic models have been selected in order to calculate the flow parameters involved in the quanti- fication of erosion rates, with an attempt to test new methods for the estimation of near-bank shear stresses, and subsequently to link them to bank erosion models. Specifically, we have employed a method recently developed by Kean & Smith (2006) to determine the form drag exerted on small-scale topog- raphic bank features and thus to quantify the near-bank flow field. Mass failure analyses have been car- ried out applying the Bank Stability and Toe Erosion Model (BSTEM) on the eroded profiles obtained from the fluvial erosion analysis. Results and comparisons of the different methods are discussed.