Use of Numerical Hydraulic Modeling to Improve Fish Passage at Perched Culverts

Perched culverts are a ubiquitous threat to the aquatic habitat connectivity of streams and small waterways. In response, the hydraulic characteristics of a light weight and readily installed fish ladder were investigated by means of computational fluid dynamics. The baffle consists of a lower main passageway, to accommodate fish passage at low flow rates, and a higher secondary passageway as an auxiliary option for fish and debris passage during spate conditions. The elevated center arch of the baffle develops pool depths, thus reducing volumetric dissipative power at high flow rates. At the flow rates studied, passageway velocities were found to respect critical swim speeds for a wide range of fish species of socioeconomic importance. Turbulent kinetic energy distributions within the 3D dimensional flow structure of the pool were also discussed. Investigation of the large scale flow structure identified a large hydraulic refuge zone near the upstream section of the pool showing promise for staging jumping attempts. Subsequent prototype field verification is envisioned in the near future to establish the relevance of the proposed design for widescale use.