Fish Passage Can Be Improved by Introducing Hydraulic Refuge: Can the Effects Be Quantified?

Design methods that account for the ability of fish to swim upstream through culverts are based on tests describing how fast and for how long different fish species can swim. These methods are based on an average water velocity but fail to recognize that fish can take advantage of resting places and non-uniform flow in culverts. Culverts that are designed using this average velocity are likely larger than is necessary. Current design methods could be greatly improved by accounting for the non-uniform velocity distributions in culverts, especially those with roughness elements. In order to better quantify the benefits associated with in-culvert hydraulic refuge, fish tests have been performed in a laboratory flume. This project has focused on one species of fish native to Utah—longnose dace—and the ability to ascend the flume with and without roughness elements—cylinders—in place. Results suggest that the cylinders did allow fish to navigate upstream more successfully than fish attempting to ascend the flume without cylinders at nearly identical average velocities. It is suggested that further testing be conducted by adapting this protocol to key variables affecting fish passage, producing probability distributions for fish performance applicable to culvert design.