Modeling forced pool–riffle hydraulics in a boulder-bed stream, southern California

Harrison, Lee R.; Keller, Edward A.

doi:10.1016/j.geomorph.2006.02.024

Cited by 78 publications

(43 citation statements)

References 42 publications

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“…Obstacles create wakes with shedding of quasi-periodic vortex structures that fixed the location of scour and deposition (Clifford, 1993;Thompson, 2007). Vortices along the shear layer represent intense turbulence capable of removing smaller particles from the bed of the pool (Kieffer, 1985;Harrison and Keller, 2007;MacVicar and Roy, 2007a;Thompson, 2007). Downstream of the constriction, lateral flow divergence, upwelling and boil formation along the pool-exit slope encourage deposition at the tail of the pool and head of the riffle (Petit, 1987;Sear, 1996;Thompson et al, 1996;Milan et al, 2001;Thompson and Wohl, 2009).…”

Section: Hydraulics and Turbulent Patterns In Forced Poolsmentioning

confidence: 99%

A flume experiment on the effect of constriction shape on the formation of forced pools

Thompson

McCarrick²

2010

Hydrol. Earth Syst. Sci.

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Abstract.A series of 18 flume runs were conducted in a 6-m long, 0.5-m wide recirculating flume with a bed gradient of 0.8% to determine the influence of obstruction shape on the formation and characteristics of forced pools. Six differentshaped obstructions were added to the flume with the maximum width of the obstruction held constant at 20 cm, which equaled a 40% constriction of flow. The obstruction shapes used included a square, a rectangle, a right triangle with the hypotenuse-facing upstream, a right triangle with the hypotenuse-facing downstream, a combination of a square and triangle with the hypotenuse-facing upstream, and a rectangle and semi-circle shape. Three flume runs were conducted with each obstruction shape. A profile of the flume bed was taken after each experiment and a grid measurement of bed elevations for the last run were conducted to create topographic maps of the flume bed to compare pool-riffle morphologies. ANOVA results indicate pool depth, pool location, and the distance between the pool center and the riffle crest all vary with the obstruction shape. Obstructions with a more blunt upstream face created deeper pools, more total scour and longer pool-riffle sequence lengths than pools formed by obstructions with a more gradual narrowing of flow. The increased volume of scour associated with obstructions that rapidly narrow flow also creates larger volume riffles that cover a greater extent of the channel bed.

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Section: Hydraulics and Turbulent Patterns In Forced Poolsmentioning

confidence: 99%

A flume experiment on the effect of constriction shape on the formation of forced pools

Thompson

McCarrick²

2010

Hydrol. Earth Syst. Sci.

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“…Water-surface and energy gradients over riffles are typically steeper than over pools at low flows and generally converge as stage increases and relative roughness decreases (Leopold et al, 1964;Keller, 1971;Richards, 1976;Wohl et al, 1993). Similarly, mean velocity and shear stress are greater over riffles than pools at lows flows, but the reverse may occur at high flows where channel conditions promote that phenomenon (Keller, 1971;Carling, 1991;Clifford and Richard, 1992;Wilkinson et al, 2004;MacWilliams et al, 2006;Harrison and Keller, 2007). Variations in depth, velocity and water surface gradients between riffles and pools at low flows lead to distinct sediment sorting patterns that may even persist at high flows and affect channel hydraulics (Keller, 1971;Lisle, 1979).…”

Section: Riffle-pool Unitsmentioning

confidence: 99%

Comparison of methods for analysing salmon habitat rehabilitation designs for regulated rivers

Brown¹,

Pasternack²

2008

River Research & Apps

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River restoration practices aiming to sustain wild salmonid populations have received considerable attention in the Unites States and abroad, as cumulative anthropogenic impacts have caused fish population declines. An accurate representation of local depth and velocity in designs of spatially complex riffle-pool units is paramount for evaluating such practices, because these two variables constitute key instream habitat requirements and they can be used to predict channel stability. In this study, three models for predicting channel hydraulics-1D analytical, 1D numerical and 2D numerical-were compared for two theoretical spawning habitat rehabilitation (SHR) designs at two discharges to constrain the utility of these models for use in river restoration design evaluation. Hydraulic predictions from each method were used in the same physical habitat quality and sediment transport regime equations to determine how deviations propagated through those highly nonlinear functions to influence site assessments. The results showed that riffle-pool hydraulics, sediment transport regime and physical habitat quality were very poorly estimated using the 1D analytical method. The 1D and 2D numerical models did capture characteristic longitudinal profiles in cross-sectionally averaged variables. The deviation of both 1D approaches from the spatially distributed 2D model was found to be greatest at the low discharge for an oblique riffle crest with converging cross-stream flow vectors. As decision making for river rehabilitation is dependent on methods used to evaluate designs, this analysis provides managers with an awareness of the limitations used in developing designs and recommendations using the tested methods.

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“…Although the interaction of flow and sediment is capable of producing spatial patterns of habitat favorable for various life stages (Trush et al, 2000), this interaction alone tends to create smooth, stream-lined forms without the strong depth and velocity gradients that supply the recommended flow complexity . Exceptions to this generalization occur at the sub-meter scale such as near the beds of boulder-rich streams and at bedrock outcrops (Crowder and Diplas, 2000;Harrison and Keller, 2007). However, the most widespread and effective agent forcing morphological and hydraulic complexity on channel flows in lowland, alluvial rivers is large woody debris http://dx.doi.org/10.1016/j.ecolmodel.2014.04.015 0304-3800/© 2014 Elsevier B.V. All rights reserved.…”

Section: Introductionmentioning

confidence: 99%

Quantifying the role of woody debris in providing bioenergetically favorable habitat for juvenile salmon

Hafs

Harrison

Utz

et al. 2014

Ecological Modelling

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a b s t r a c tThe habitat complexity of a riverine ecosystem influences the bioenergetics of drift feeding fish. We coupled hydrodynamic and bioenergetic models to assess the influence of habitat complexity generated by large woody debris (LWD) on the growth potential of juvenile Chinook salmon (Oncorhynchus tshawytscha) in a river that lacked large wood. Simulations indicated how LWD diversified the flow field, creating pronounced velocity gradients, which enhanced fish feeding and resting activities at the sub-meter scale. Fluid drag created by individual wood structures increased under higher wood loading amounts, leading to a 5-19% reduction in the reach-averaged velocity. The reach-scale growth potential was asymptotically related to wood loading, suggesting that the river became saturated with LWD and additional loading would produce minimal benefit for the configurations we simulated. In the scenario we analyzed for illustration, LWD additions could quadruple the potential growth area available before that limit was reached for the configurations selected for demonstration. Wood depletion in the world's rivers has been documented extensively, leading to widespread attempts by river managers to reverse this trend by adding wood to simplified aquatic habitats. However, systematic prediction of the effects of wood on fish growth has not been previously accomplished. We offer a quantitative approach for assessing the influence of wood on habitat potential for fish growth at the microhabitat and reach-scales.

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Modeling forced pool–riffle hydraulics in a boulder-bed stream, southern California

Cited by 78 publications

References 42 publications

A flume experiment on the effect of constriction shape on the formation of forced pools

A flume experiment on the effect of constriction shape on the formation of forced pools

Comparison of methods for analysing salmon habitat rehabilitation designs for regulated rivers

Quantifying the role of woody debris in providing bioenergetically favorable habitat for juvenile salmon

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