Fish Passage through Culverts in Montana: A Preliminary Investigation

https://doi.org/10.21949/15182011996PDFTech ReportFHWA/MT-96/8117-28117-2CulvertsMigrationFish laddersEnvironmental impactsFishwaysMontanaMontana. Department of TransportationStein, OttoTillinger, Todd N.Montana State University--Bozeman. Civil Engineering Dept.Montana. Dept. of TransportationUnited States. Federal Highway AdministrationThe objective of this report is to combine, in one document, previously reported information on factors influencing fish passage through culverts, especially as it pertains to conditions indicative of Montana. First, the need for considering fish passage is discussed, followed by an investigation of biological, hydrologic and hydraulic criteria influencing fish passage. An integration of biological and hydraulic criteria is presented, as is a review of previous studies conducted in Montana. Recommendations for future research are also presented. The major biological criteria influencing fish passage are species and size of fish, jumping ability, and seasonal feeding and spawning migrations as related to the hydrologic regime of the stream requiring a culvert crossing. In general, salmonid species and healthy adult fish are the strongest swimmers and spawning is the major reason fish migrate. The main culvert features preventing fish passage include: a perched outlet, too great a velocity, too shallow a depth, or too long a distance between resting pools. The major hydraulic criteria influencing fish passage are: flow rates during fish migration periods; and type, roughness, length and slope of the culvert. In general, the optimum design for peak flow conveyance, a smooth pipe flowing full, will not meet fish passage criteria at any discharge. Fish size appears to have little influence on ability to negotiate a culvert despite its effect on swimming performance. One theory is that smaller fish utilize regions of low velocity near the culvert wall. Multiple possibilities for future research to better characterize fish passage are listed. Examples include better characterization of velocity gradients within culverts and evaluation of fish swimming performance for poorly characterized Montana species.88