Advanced Studies of fish passage through culverts : 1-D and 3-D hydraulic modeling of velocity, fish energy expenditure, and a new barrier assessment method

Abstract

Fish passage through culverts is an important component of road and stream crossing design. Although no comprehensive inventory of the number of culverts on fishbearing streams in the United States is available, there is an estimated 1.4 million streamroad crossings. The most common physical characteristics that create barriers to fish passage include excessive water velocity, insufficient water depth and large outlet drop heights. Over the past decade, interest in the effect culvert barriers have on aquatic systems has grown; accordingly, various passage assessment techniques have been used to determine whether a structure is a barrier and to what degree (its "barrierity"). Recent research has shown that determining the barrierity of a culvert is not trivial, and that different methods are often not congruent in their classification of "barrierity". The purpose of this research was to investigate the effect of velocity on fish passage in great detail by: testing the use of computational fluid dynamics (CFD) for estimating the 3-D velocity field through a culvert; quantifying velocity diversity through culverts for a range of flows; characterizing the energy expenditure paths through a culvert and identifying the passageways Yellowstone cutthroat trout used to successfully negotiate passage; and developing and testing a new barrier assessment method. The research was done, in part, by studying fish passage through culverts in Mulherin Creek, an important spawning tributary for Yellowstone cutthrout trout migrating from the Yellowstone River. Comparisons between predicted and observed velocities show 86% and 82% of variation in the observed velocity data were explained by the CFD model, for flow rates of 1.44 m3/s and 0.87 m3/s, respectively. The diverse velocity field through the culvert barrel created a range of energy expenditure paths through the entire culvert length. Fish movement observations showed successful passage only for trout seeking and using the minimum energy path created, in part, by the skew between the upstream channel and the culvert. This research investigated a new hydraulic approach to assessing barriers that uses the 3-D velocity field. Comparisons between estimated passage and measured passage show the 3-D method most accurately indicated passability compared to a 1-D method.