Streambank erosion and bank stability, an overview

Fabian Friedl, Volker Weitbrecht, Robert Michael Boes

Tuesday 30 june 2015

16:00 - 16:15h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 7A. Sediment - Erosion

Predicting and quantifying streambank erosion plays an important role in loss prevention and risk management, for understanding the morphodynamics of rivers and river restoration strategies. The triggering mechanisms for bank erosion, namely hydraulic-fluvial processes and geotechnical mass failures, are influenced by a wide range of factors. In the past decade serious progress has been made in understanding the influence of the level of the groundwater table, positive and negative pore water pressures, the seepage forces and the effect of riparian vegetation, and root reinforcement on bank stability. Furthermore, different numerical models for the prediction of the changes of the channel due to bank erosion were developed. Two-dimensional numerical flow and sediment transport models were combined with geotechnical failure models for bank erosion, which were successfully tested. Few studies have been conducted concerning the fluvial erosion, however, because of the difficulty to determine the shear stress distributions. To improve the prediction of the erosion directly by the flow, methods to estimate more accurate near-bank shear stresses have to be developed. A challenge in understanding the bank stability of non-cohesive material is not only the occurrence of apparent cohesion. Furthermore no specific measurement technique or model exists to determine the coefficients describing the erodibility of coarse-grained sediments. So far this is done by calibration of the limited available models. The deposition of bank material at the bank toe and the re-erosion, especially in relation with the transport capacity have to be understand to get an idea of the overall impact of streambank erosion on river systems. An overview on the topic of streambank erosion and bank stability in gravel-bed rivers is presented in this paper. The most important concepts of describing bank erosion processes in cohesive and non-cohesive material are discussed. Furthermore a summary of the state-of-the-art in numerical modelling is given and the corresponding field data and physical laboratory experiments in the lab are described.