Author(s): Mirko Musa; Michele Guala; Marco Redolfi
Linked Author(s):
Keywords: River bars; Sediment transport; Shallow water flows; Water power; Anthropogenic stressors
Abstract: While testing the geomorphic effects of fluvial in-stream hydrokinetic turbines, Musa et al. (2019) observed experimentally that asymmetric deployment of these devices could induce persistent alternate bathymetric distortions, resembling bar-like features. River bars are meso-scale bedforms that emerge spontaneously from riverbed instabilities (Seminara, 2010) or can be forced by localized geometric variations such as channel curvature, bifurcations, or in-stream obstacles, including turbines. Linear stability theories (e.g., Zolezzi & Seminara, 2001) suggest that the spatial extent of bars is primarily governed by channel characteristics—specifically, the width-to-depth ratio (b), the Shields stress, and relative roughness—rather than the nature of the forcing itself. However, the experimental findings by Musa et al. (2019) suggest that characteristics of the external forcing may also play an active role in shaping bed morphology. This raised two key questions: (1) Is the observed bathymetric distortion indeed a bar-type phenomenon? (2) How do the characteristics of the external forcing (in this case, turbines) affect the resulting bed deformation? To address these questions, this study develops a new analytical model based on a linear perturbation approach, hypothesizing that bar formation is driven by the asymmetric distribution of the drag force exerted by the turbines. Model predictions are validated through a new set of experiments and compared to prior observations (Musa et al., 2019). The full study, including theoretical developments, experimental validation, and detailed analyses, is presented in Redolfi et al. (2021).
Year: 2025