Fish Passage Through Road Culverts

Abstract

The North Carolina Department of Transportation (NCDOT) has regulations requiring road crossings to facilitate Aquatic Organism Passage (AOP). Due to a current inability to prove that AOP will not be inhibited, acquiring permits for the design and construction of culverts has become difficult. Often, bridges costing up to three times as much must be built in their place. To improve the design of culverts and the feasibility of obtaining a permit, this study determined the maximum swimming speed that can be sustained by a fish for a period of ten minutes. This speed, known as the critical velocity, is equivalent to traversing a 100m culvert. The critical velocities were determined for the following fish species native to the piedmont of North Carolina: Nocomis leptocephalus, Lepomis auritus, Etheostoma nigrum, Lepomis macrochirus, Noturus insignis, Notropisprocne. The fish were collected by electrofishing from local streams. After resting for 12 to 18 hours the fish were placed in a flume and allowed to accommodate at a resting velocity of 20cm⁄s. The velocity was then increased by 10cm⁄s every ten minutes, while returning to the resting velocity for five minutes between each step. The critical velocities for each species were 85.56cm⁄s, 43.89cm⁄s, 67.76cm⁄s, 37.05cm⁄s, 48.67cm⁄s, 61.42cm⁄s respectively. Based on the data collected in this experiment, it is recommended that the maximum velocity in a culvert be kept under 55cm⁄s for 90% of the fish migration period. A Microsoft Excel model was created based on the results. The model uses the critical velocities as guidelines for maximum flow rates in the hydrologic design of culverts. Using the model in addition to other hydrologic design models can aid in the design of culverts that do not impede fish passage.