Evaluating fish passage at whitewater parks using a spatially explicit 2D hydraulic modeling approach
Date
2017
Authors
Hardee, Travis L., author
Nelson, Peter A., advisor
Bledsoe, Brian P., committee member
Myrick, Christopher A., committee member
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Abstract
In-stream whitewater parks (WWPs) are increasingly popular recreational amenities that typically create waves by constricting flow through a chute to increase velocities and form a hydraulic jump. However, the hydraulic conditions these structures create can limit longitudinal habitat connectivity and potentially inhibit upstream fish migration. Recent work has shown that three-dimensional (3D) hydraulic models of flow over WWP structures can be used to accurately predict fish passage rates. Here, I explore the extent to which these methods can be extended to two-dimensional (2D) hydraulic models, which are much simpler and less computationally expensive and data-intensive than 3D models. This study uses a 2D model to calculate flows across several different WWP structures on North St. Vrain Creek at Lyons, Colorado. Potential fish swimming paths are extracted from the model results and evaluated for depth and velocity criteria for fish passage, ultimately yielding for each WWP structure, the fraction of potential passable flow paths for a given discharge. These results are paired with fish movement observations, and logistic regression is used to determine hydraulic variables that significantly contribute to passage success. In general, the 2D model predicts smaller fractions of impassable fish swimming paths than the 3D model. However, the 2D model achieves prediction accuracies greater than 82% for all WWP structures combined, with prediction accuracies at individual WWP structures of 85 to 92%, which equal or exceed the accuracy of the 3D model. These results suggest that 2D flow modeling can be used to evaluate complex flow at WWPs at scales relevant to upstream fish movement. The 2D methods were also applied to new WWP structures to demonstrate the transferability of the methods and to analyze specific design features in terms of fish passage. The WWP structure design features included in this analysis are: chute slope, low flow fish channel, and sidewall terracing. Results showing the estimated fraction of passable flow paths and passable widths provided insight into the effects these design features have on fish passage. The results show that chute slope is an important factor in reducing the velocity barrier within the chute at low discharges. The inclusion of a low flow fish channel can potentially increase the number of upstream swimming paths available to a fish, especially at low discharges. Sidewall terracing can be used to alleviate the channelizing of flow and can be used to facilitate fish passage at larger discharges. Overall, these methods should be applicable to evaluating fish passage at other WWPs and other in-stream structures.
Description
Rights Access
Subject
2D hydraulic modeling
whitewater park
fish passage
2D CFD