Turbulent and advective momentum fluxes in streams

Noß, Christian; Salzmann, Thomas; Storchenegger, Isidor

doi:10.1029/2010wr009297

Cited by 13 publications

(17 citation statements)

References 45 publications

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“…() who evaluated Reynolds stress and associated sediment transport over a coastal foredune. Methods to derive τ using a modified TKE are used in fluvial geomorphology (Biron et al ., ; Pope et al ., ; Noss et al ., ) based on a linear relationship between TKE and τ (Soulsby and Dyer, ; Kim et al ., ). Research comparing TKE with τ _ LOW and τ _ REY has typically found that the TKE method is more suitable in complex flow conditions (Biron et al ., ; Bagherimiyab and Lemmin, ).…”

Section: Discussionmentioning

confidence: 99%

“…In part, the predictive deficiencies may be attributed to methodological or technological limitations in measuring shear stress in natural boundary layer environments (Heathershaw and Simpson, ; Biron et al ., ; Noss et al ., ; Lee and Baas, ). Across the Earth sciences, however, improvements in sensor technology have provided methods for determining shear stress directly from turbulence statistics measured within the flow.…”

Section: Introductionmentioning

confidence: 97%

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Variable and conflicting shear stress estimates inside a boundary layer with sediment transport

Lee

Baas

2015

Earth Surf Processes Landf

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This paper presents a comparison between two methods for estimating shear stress in an atmospheric internal boundary layer over a beach surface under optimum conditions, using wind velocities measured synchronously at 13 heights over a 1.7 m vertical array using ultrasonic anemometry. The Reynolds decomposition technique determines at-a-point shear stresses at each measurement height, while the Law-of-the-Wall yields a single boundary layer estimate based on fitting a logarithmic velocity profile through the array data.Analysis reveals significant inconsistencies between estimates derived from the two methods, on both a whole-event basis and as time-series. Despite a near-perfect fit of the Law-of-the-Wall, the point estimates of Reynolds shear stress vary greatly between heights, calling into question the assumed presence of a constant stress layer. A comparison with simultaneously measured sediment transport finds no relationship between transport activity and the discrepancies in shear stress estimates. Results do show, however, that Reynolds shear stress measured nearer the bed exhibits slightly better correlation with sand transport rate.The findings serve as a major cautionary message to the interpretation and application of single-height measurements of Reynolds shear stress and their equivalence to Law-of-the-Wall derived estimates, and these concerns apply widely to boundary layer flows in general.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Variable and conflicting shear stress estimates inside a boundary layer with sediment transport

Lee

Baas

2015

Earth Surf Processes Landf

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“…In low‐gradient small streams, Whiting [] and Noss et al . [] found that topographic forcing of the flow caused convective acceleration, which was the dominant component of the total momentum flux at lower stages, but was also not negligible at higher stages. Because depth and width are related to discharge and simultaneously provide the scale of the most effective roughness, the resistance strongly depends on the flow depth and on the riverbed topography at the corresponding length scales.…”

Section: Discussionmentioning

confidence: 99%

Roughness, resistance, and dispersion: Relationships in small streams

Noß

Lorke

2016

Water Resources Research

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Although relationships between roughness, flow, and transport processes in rivers and streams have been investigated for several decades, the prediction of flow resistance and longitudinal dispersion in small streams is still challenging. Major uncertainties in existing approaches for quantifying flow resistance and longitudinal dispersion at the reach scale arise from limitations in the characterization of riverbed roughness. In this study, we characterized the riverbed roughness in small moderate‐gradient streams (0.1–0.5% bed slope) and investigated its effects on flow resistance and dispersion. We analyzed high‐resolution transect‐based measurements of stream depth and width, which resolved the complete roughness spectrum with scales ranging from the micro to the reach scale. Independently measured flow resistance and dispersion coefficients were mainly affected by roughness at spatial scales between the median grain size and the stream width, i.e., by roughness between the micro‐ and the mesoscale. We also compared our flow resistance measurements with calculations using various flow resistance equations. Flow resistance in our study streams was well approximated by the equations that were developed for high gradient streams (>1%) and it was overestimated by approaches developed for sand‐bed streams with a smooth riverbed or ripple bed.

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“…Previous research quantified bed shear stress or the distribution of shear stress around the channel boundary (e.g. Wilcock, ; Biron et al ., ; Noss et al ., ; Nepf, ). Additional work modelled the distribution of boundary stress in prismatic channels with grain roughness as a function of channel cross‐sectional geometry, secondary flow structure, and friction at the channel boundary (e.g.…”

Section: Introductionmentioning

confidence: 99%

Comparison of Direct and Indirect Boundary Shear Stress Measurements along Vegetated Streambanks

Hopkinson

Wynn-Thompson

2016

River Research & Apps

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Estimates of boundary shear stress along vegetated streambanks are needed to predict streambank fluvial erosion. Because fluvial shear stress cannot be directly measured in the field, reliable estimation techniques using field instrumentation are needed. This study evaluated local bank shear stress estimation methods applicable to sloping, vegetated streambanks. Two reaches of a second order stream were modelled in a flume using a fixed-bed Froude-scale modelling technique. One reach was dominated by dense shrubs while the other reach was located in a mature forest. Direct measurements of local bank shear stress using a hot-film anemometer were compared to estimates based on velocity measurements (logarithmic method, Reynolds stresses, and turbulent kinetic energy). For channels with no or widely spaced vegetation, the velocitybased estimates underestimated the bank shear stress due to secondary flow contributions. For banks with dense vegetation, Reynolds stresses and turbulent kinetic energy estimates were statistically similar to direct measurements on average, but substantial error occurred when making point comparisons. Velocity-based estimates generally over predicted bank stress in areas of high shear at the vegetation edge and underpredicted stress within dense vegetation. Ultimately, results suggest that none of tested techniques can be broadly applied to streambanks, and flow structure is critical in selecting the appropriate estimation technique.

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Turbulent and advective momentum fluxes in streams

Cited by 13 publications

References 45 publications

Variable and conflicting shear stress estimates inside a boundary layer with sediment transport

Variable and conflicting shear stress estimates inside a boundary layer with sediment transport

Roughness, resistance, and dispersion: Relationships in small streams

Comparison of Direct and Indirect Boundary Shear Stress Measurements along Vegetated Streambanks

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