Whitewater parks (WWPs) are increasingly popular recreational amenities, but the effects of WWPs on fish habitat and passage are poorly understood. This study investigated the use of a two‐dimensional (2‐D) model as compared with a three‐dimensional (3‐D) hydrodynamic model (flow‐3D®) for assessing effects of WWPs on fish habitat. The primary aims of this study were to (1) examine the utility of 3‐D modelling versus 2‐D modelling in a hydraulically complex WWP and (2) compare modelled habitat quality for resident fishes with actual fish abundance and biomass generated from field sampling surveys. Two reaches of a wadeable river in Colorado were modelled: a natural reach and a reach containing a WWP. A 2‐D habitat suitability analysis for juvenile and adult brown trout, juvenile and adult rainbow trout, longnose dace and longnose sucker predicted the same or higher habitat quality in the WWPs than the natural pools for all four species and for all modelled flow rates; however, results from fish sampling found significantly higher fish biomass for all four species in natural pools compared with WWP pools. All hydraulic metrics (depth, depth‐averaged velocity, turbulent kinetic energy, 2‐D and 3‐D vorticity) had higher magnitudes in WWP pools than in natural pools. In the WWP pools, 3‐D model results described the spatial distribution of flow characteristics or the magnitude of variables better than 2‐D results. This supports the use of 3‐D modelling for complex flows found in WWPs, but improved understanding of linkages between fish habitat quality and 3‐D hydraulic descriptors is needed. Copyright © 2015 John Wiley & Sons, Ltd.

EFFECTS OF WHITEWATER PARKS ON FISH PASSAGE:A SPATIALLY EXPLICIT HYDRAULIC ANALYSIS Whitewater parks (WWPs) provide a valuable recreational and economic resource that is rapidly growing in popularity throughout the United States. WWPs were originally thought to enhance aquatic habitat; however, recent studies have shown that the hydraulic conditions required to meet recreational needs can act as a partial barrier to upstream migrating trout and that WWP pools may contain lower densities of fish compared to natural pools. There is limited knowledge of the direct effects of WWPs on fish passage. Managers and policy makers are forced to review WWP designs and make permit decisions without sound scientific evidence. It is also difficult to make design recommendations for future WWPs and possibly retrofitting existing WWPs to allow for successful fish passage without improved understanding of the factors contributing to suppression of movement in WWPs. We describe novel approaches combining fish movement data and hydraulic results from a three-dimensional computational fluid dynamics model to examine the physical processes that limit upstream movement of trout in an actual WWP in Lyons, Colorado. These methods provide a continuous and spatially explicit description of velocity, depth, vorticity, and turbulent kinetic energy (TKE) along potential fish swimming paths in the flow field. Variation in the magnitude and distribution of velocity and depth relative to fish swimming ability is reflective of variation in passage success among WWP structures and size classes of fish. Logistic regression analyses indicate a significant influence of velocity and depth on limiting passage success and accurately predict > 86 percent observed fish movements. Relationships emerge at individual WWP structures that iii highlight unique hydraulic characteristics and their effect on passage success. The methods described in this study provide a powerful approach to quantify hydraulic conditions at a scale meaningful to a fish and mechanistically evaluate the effects of hydraulic structures on fish passage. The results of these analyses can be used for management and design guidance, have implications for fishes with lesser swimming abilities, and demonstrate the need to assess additional WWPs of various sizes.iv ACKNOWLEDGMENTS

Whitewater parks (WWPs) typically consist of instream structures that enhance recreational boating by constricting flow into a steep chute that generates a hydraulic jump in a downstream pool. Concerns have been raised that high velocities resulting from WWPs may be inhibiting fish movement during critical life stages. We evaluated the effects of WWPs on upstream fish passage by concurrently monitoring fish movement and hydraulic conditions at three WWP structures and three adjacent natural control (CR) sites in a wadeable river in northern Colorado. Fish movement was tracked with a network of Passive Integrated Transponder antennas over a 14-month period. Individual fishes (n = 1,639), including brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss), were tagged and released within WWP and CR sites. Detailed hydraulic conditions occurring during the study period were evaluated with a fully 3D model. Results reveal the WWPs monitored in this study are not a complete barrier to upstream salmonid movement, but differences in passage efficiency from release location range from 29 to 44% in WWP sites and 37 to 63% for CR sites and the suppression of movement is related to body length. Small numbers of monitored nonsalmonids were inadequate to directly observe effects on their movement; however, it is highly probable that movement of smaller native fishes is also suppressed. Hydraulic modeling helps in the design of WWP structures that protect fish passage.

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