Assessing River Habitat Impacts of Navigation Channel Regulation in Large Rivers

Abstract

Multi-scale habitat modelling is key for river management, yet meso-habitat metrics for navigable rivers remain scarce. This study presents a fish-swimming-capacity-based approach for delineating meso-habitat functional units in mountain rivers that can be directly embedded into hydraulic design. Environment DNA (eDNA) metabarcoding was employed to identify the dominant species in the study reach, from which one was selected as the target fish. Based on literature data regarding the relationship between fish body length and its critical swimming speed, a coefficient ? was introduced to obtain the relationship equation between the body length and the absolute critical swimming speed. The absolute critical swimming speed of the target fish was calculated to define the ecological indicators for fish habitat. Subsequently, a two-dimensional hydrodynamic model was employed to calculate the flow velocity distribution in the study reach during dry, normal, and flood periods. Combining the absolute critical swimming speed of fish with the hydrodynamic results yields a rule table for fish ecological functional habitat units. Case studies at Wanglongqi and Lianshitan regulation works showed that spur dikes significantly reduce migration-corridor area at low discharge, while medium and high discharge maintain connectivity. The method converts ecological thresholds into engineer-friendly spatial units, striking a balance between navigation development and ecological integrity.