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Drones, hydraulics, and climate change: Inferring barriers to steelhead spawning migrations

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Abstract Global climate models suggest dramatic changes in the timing and form of future precipitation in the Pacific Northwest, United States. By some estimates, in the Columbia River drainage, basin‐wide snow‐water equivalencies could decrease by more than 50% before the end of the century, with locally more extreme variation. In the South Fork Clearwater River, Idaho, where hydraulic barriers are currently thought to partially limit ESA‐listed steelhead migrations, changes in precipitation that could exacerbate the intensity and timing of hydraulic barriers presents an obvious conservation concern. Evidence indicates that the strongest steelhead swimmers are capable of sustaining burst speeds for up to 20 s, with maximum speed being a function of fish size (length). Understanding hydraulic dynamics that have implications for migrating fish requires integration of high‐resolution hydraulic models with sufficient resolution to characterize the hydraulic experience of the fish. Unmanned aerial vehicles (drones) have recently emerged as useful platforms for measuring river ecosystems with high precision. Results from habitat surveys and hydraulic modeling can identify locations where intense hydraulic energy may preclude fish passage during critical migration periods. The current as well as future range of discharges can be evaluated with a spatially explicit hydraulic model to quantify when, where, and how long barriers to migration exist. Further, this approach provides a powerful tool for manipulating the digital physical channel form and presents a heuristic opportunity to test hydraulic scenarios to improve migration success. This article is categorized under:   Water and Life > Nature of Freshwater Ecosystems   Water and Life > Stresses and Pressures on Ecosystems   Water and Life > Methods
Percent reduction (compared to baseline conditions) in the spatial extent of all potential barriers across the study reach, under Alternatives 1 and 2, as a function of increasing discharge, expressed in terms of m3/s
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Spatial extent of all potential (i.e., 5, 10, and 20 s steelhead burst speed) hydraulic barriers, in the “Bird House to Snagging Hole Reach,” at 28 m3/s, under baseline (brown), modeled “Alternative 1” (light tan), and modeled “Alternative 2” (green) conditions. Wetted channel area inferred to be passible under these conditions are shown in blue
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Oriented minimum bounding box (MBB) used to approximate length of homogeneous hydraulic patches in the study reach
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Conceptual diagram coupling a fish's upstream burst speed capability (VB) with the downstream flow velocity (VW) to determine forward (upstream) velocity (VF)
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Orthogonalized photo from drone survey showing large boulder‐dominated channel conditions (top), and modeled flow depth (middle) and continuous velocity grid (bottom) at approximately 1.7 cubic meters per second (m3/s) discharge
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Location of South Fork Clearwater River case study (black filled circle). Inset map shows project location within the Columbia River Basin (green polygon)
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Percent reduction (compared to baseline conditions) in the spatial extent of 5 s burst speed barriers across the study reach, under Alternatives 1 and 2, as a function of increasing discharge, expressed in terms of m3/s. Below 28 m3/s, no such barriers are present under baseline conditions
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Water and Life > Methods
Water and Life > Stresses and Pressures on Ecosystems
Water and Life > Nature of Freshwater Ecosystems

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