Fish passage through culverts in Montana: A preliminary investigation

Publication Date



culverts, fish passage, hydraulic criteria, future research, spawning, migration, adult, swimming, resting pools, pool, flow rates, flow rate, slope, design, swimming performance, Gradient

Report number


Publication place

Helena, MT


Montana Department of Transportation


The objective of this report is to combine, in one document, previously reportedinformation on factors influencing fish passage through culverts, especially as it pertains toconditions indicative of Montana. First, the need for considering fish passage is discussed,followed by an investigation of biological, hydrologic and hydraulic criteria influencing fishpassage. An integration of biological and hydraulic criteria is presented, as is a review ofprevious studies conducted in Montana. Recommendations for future research are alsopresented.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 streamrequiring a culvert crossing. In general, salmonid species and healthy adult fish are the strongestswimming 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 adistance 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 peakflow 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 effects onswimming performance. One theory is that smaller fish utilize regions of low velocity near theculvert wall.Multiple possibilities for future research to better characterize fish passage are listed. Examplesinclude better characterization of velocity gradients within culverts and evaluation of fishswimming performance for poorly characterized Montana species.

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