The impact of channel sinuosity and hydrodynamics on fish-habitat suitability in high-gradient meandering rivers

Rivers that exhibit meandering characteristics are ubiquitous in both alluvial and confined geomorphic settings, yet the relationship between habitat suitability for fish species and channel sinuosity has not been well understood. In this paper, we look to tackle this issue by conducting a hydro-morphodynamic modeling of meandering structures with different sinuosity and assessing habitat suitability for two representative species, Schizothorax wangchiachii and Coreius guichenoti, living in high-gradient meandering rivers. We find that the increased discharge and sinuosity would maximize the range of flow velocity and channel depth, thereby exerting notable hydraulic influences on fish species. Specifically, meandering structures with greater sinuosity can typically produce greater suitable areas within the channel in the sense of the magnitude of suitability and the associated area due to increased channel area, especially the convex bank, as it is subject to less channel deformation when situated in highly sinuous channels. Over time, sediment at the concave bank and immediately downstream gets eroded and transported, tending to deposit in places toward the thalweg and the convex bank, which allows the convex bank to foster larger areas suitable for both fish species than concave bank. Among the three flow levels that we modeled, the medium flow generates the greatest habitat suitability. Beyond a specific region, this study provides a theoretical and practical basis for linking fluvial geomorphology with ecohydrology, stressing the necessity of ecological assessments for high-gradient meandering river restoration and hydraulic engineering projects.