Quantifying hydrodynamic changes associated with bioengineered stabilization measures using numerical modelling

Abstract

River bank stabilization is a common practise and can be observed on most rivers around the world, often using hard-engineering riprap. Increasingly, bioengineered approaches using vegetation-based constructive materials is promoted to alleviate some of the negative ecological stresses of bank stabilization. Because these stabilization projects use a variety of techniques to create a site-specific design, they can have unexpected morphological implications and variable ecological benefits which can be anticipated using numerical modelling. Bioengineered bank stabilization creates roughness elements on both micro and macro scales, where only macro-roughness can be captured by bathymetric adjustments. The definition of micro- and macro-roughness depends on the spatial resolution of the model domain, and may be considered analogous to skin and form friction when characterizing natural alluvial bed environments. The objectives of this research are to assess the hydrodynamic impact of the added micro- and macro-roughness associated with a bioengineering pilot project planned in Quebec, Canada and to use this case study to propose new techniques for integrating increased roughness due to bank stabilization into numerical models. The roughness of the stabilization project is assessed by adjusting bathymetry to simulate macro-roughness features, and roughness coefficients to simulate micro-roughness features. Results show a significant dampening interaction term that reduced the cumulative effect on resistance to flow when both roughness types were applied.