No abstract

Floods and subsequent bank erosion are recurring hazards that pose threats to people and can cause damage to buildings and infrastructure. While numerous approaches exist on modeling bank erosion, very few consider the stabilizing effects of vegetation (i.e., roots) for hydraulic bank erosion at catchment scale. Taking root reinforcement into account enables the assessment of the efficiency of vegetation to decrease hydraulic bank erosion rates and thus improve risk management strategies along forested channels. A new framework (BankforNET) was developed to model hydraulic bank erosion that considers the mechanical effects of roots and randomness in the Shields entrainment parameter to calculate probabilistic scenario-based erosion events. The one-dimensional, probabilistic model uses the empirical excess shear stress equation where bank erodibility parameters are randomly updated from an empirical distribution based on data found in the literature. The mechanical effects of roots are implemented by considering the root area ratio (RAR) affecting the material dependent critical shear stress. The framework was validated for the Selwyn/Waikirikiri River catchment in New Zealand, the Thur River catchment and the Sulzigraben catchment, both in Switzerland. Modeled bank erosion deviates from the observed bank erosion between 7% and 19%. A sensitivity analysis based on data of vertically stable river reaches also suggests that the mechanical effects of roots can reduce hydraulic bank erosion up to 100% for channels with widths < 15.00 m, longitudinal slopes < 0.05 m m −1 and a RAR of 1% to 2%. The results show that hydraulic bank erosion can be significantly decreased by the presence of roots under certain conditions and its contribution can be quantified considering different conditions of channel geometry, forest structure and discharge scenarios.

Passive earth resistance plays an important role in slope stability analyses for predicting shallow landslide susceptibility. Three‐dimensional models estimate the contribution of this factor to slope stability using geotechnical theories designed for retaining structures and add it to the resistive forces. Systematic investigations have not been conducted to quantify this resistance in soils experiencing compression during the triggering of shallow landslides. This study presents field‐scale experimental data of passive earth force for cohesive and frictional clayey gravel evaluated at different combinations of soil depths and slopes. The experimental setup included a specialized device composed of a steel structure and a stiff plate that moved toward a mass of soil. In both dynamic and quasi‐static states, force‐displacement curves and maximum compression resistance were determined for several water content conditions induced by a rainfall simulator. The maximum dynamic force ranged from 8.49 to 31.67 kN for soil depths ranging between 0.36 and 0.50 m, whereas the quasi‐static force corresponded to 60% of the dynamic force. Furthermore, rainfall generated an additional decrease of compression resistance compared to that measured in the field. A comparison of measured data with theoretical models of passive earth force indicated that Rankine's solution provided the best estimate, whereas the logarithmic spiral approach significantly overestimated passive earth force by up to 70%. Therefore, the correct choice of geotechnical formulation or the direct use of field measurements to estimate passive earth force may significantly improve the accuracy of 3‐D limit equilibrium models for assessing slope stability over natural landscapes.