Large roughness element effects on sand transport, Oceano Dunes, California

Gillies, John A.; Lancaster, Nicholas

doi:10.1002/esp.3317

Cited by 36 publications

(38 citation statements)

References 26 publications

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“…The Keeler Dunes datum fits very well with the data from other experiments. This further supports the observation of Gillies and Lancaster (2013) that sediment supply does not affect this relationship. It applies equally in both sediment rich (i.e., supply is essentially limitless as in dune and sand sheet settings) or in supply limited conditions such as those studied by Gillies et al (2006).…”

Section: Roughness Effect On Sand Fluxsupporting

confidence: 91%

“…The roughness array placed on the Keeler Dunes affects the sand transport system in two ways: (1) it increases the threshold wind speed and directly modulates the sand transport rate through shear stress partitioning effects that reduce the shear stress on the intervening surface (Gillies et al, 2007;Brown et al, 2008), and (2) by direct interaction of the saltating sand with the roughness elements (Gillies et al, 2006;Gillies and Lancaster, 2013). The TLS data revealed the plot scale changes in the surface elevation that indicate the erosion, re-distribution and deposition of sand in response to the multiple sand transport events from the north and the south.…”

Section: Discussionmentioning

confidence: 99%

“…To create a roughness configuration using this size bale and achieve the target sand reduction, the relationship between normalized sand flux (NSF) and roughness density (k) presented by Gillies and Lancaster (2013):…”

Section: Solid Element Roughness Array Characterizationmentioning

confidence: 99%

“…Previous research (Gillies et al, 2006;Gillies and Lancaster, 2013) also demonstrated that sand flux diminishes exponentially as a function of NDD (until reaching equilibrium) and the rate of that change is a function of k. For comparison purposes the exponent of the exponential relationship for the Keeler Dunes test site data (Fig. 11) is plotted along with the exponents from this relationship reported for two other test locations: the Jornada Experimental Range, NM (Gillies et al, 2006) and the Oceano Dunes in southern California (Gillies and Lancaster, 2013). The Keeler Dunes datum fits very well with the data from other experiments.…”

Section: Roughness Effect On Sand Fluxmentioning

confidence: 99%

“…Recent research has indicated that arrays of large roughness elements (height and width > 0.3 m) can be used effectively to increase threshold wind speeds that initiate wind erosion and modulate sand transport (and the associated dust emissions) on relatively flat topography (Gillies et al, 2006;Gillies and Lancaster, 2013). Prediction of the rate of sand flux reduction as a function of downwind distance upon entering an array of roughness elements, and the equilibrium flux reduction in the interior of the array is possible using the known geometric properties of the roughness elements, their number, and published relationships (e.g., Gillies et al, 2006;Gillies and Lancaster, 2013). For source areas that emit dust, due in large part to the ballistic impact of saltating particles, a reduction in sand flux results in reduction of the accompanying dust flux.…”

Section: Introductionmentioning

confidence: 99%

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Using solid element roughness to control sand movement: Keeler Dunes, Keeler, California

et al. 2015

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Section: Roughness Effect On Sand Fluxsupporting

confidence: 91%

Section: Discussionmentioning

confidence: 99%

Section: Solid Element Roughness Array Characterizationmentioning

confidence: 99%

Section: Roughness Effect On Sand Fluxmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Using solid element roughness to control sand movement: Keeler Dunes, Keeler, California

et al. 2015

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Estimating aerodynamic roughness over complex surface terrain

et al. 2013

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[1] Surface roughness plays a key role in determining aerodynamic roughness length (z o ) and shear velocity, both of which are fundamental for determining wind erosion threshold and potential. While z o can be quantified from wind measurements, large proportions of wind erosion prone surfaces remain too remote for this to be a viable approach. Alternative approaches therefore seek to relate z o to morphological roughness metrics. However, dust-emitting landscapes typically consist of complex small-scale surface roughness patterns and few metrics exist for these surfaces which can be used to predict z o for modeling wind erosion potential. In this study terrestrial laser scanning was used to characterize the roughness of typical dust-emitting surfaces (playa and sandar) where element protrusion heights ranged from 1 to 199 mm, over which vertical wind velocity profiles were collected to enable estimation of z o . Our data suggest that, although a reasonable relationship (R 2 > 0.79) is apparent between 3-D roughness density and z o , the spacing of morphological elements is far less powerful in explaining variations in z o than metrics based on surface roughness height (R 2 > 0.92). This finding is in juxtaposition to wind erosion models that assume the spacing of larger-scale isolated roughness elements is most important in determining z o . Rather, our data show that any metric based on element protrusion height has a higher likelihood of successfully predicting z o . This finding has important implications for the development of wind erosion and dust emission models that seek to predict the efficiency of aeolian processes in remote terrestrial and planetary environments.

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The effect of roughness elements on wind erosion: The importance of surface shear stress distribution

Webb¹,

Okin

Brown

2014

JGR Atmospheres

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Representation of surface roughness effects on aeolian sediment transport is a key source of uncertainty in wind erosion models. Drag partitioning schemes are used to account for roughness by scaling the soil entrainment threshold by the ratio of shear stress on roughness elements to that on the vegetated land surface. This approach does not explicitly account for the effects of roughness configuration, which may be important for sediment flux. Here we investigate the significance of roughness configuration for aeolian sediment transport, the ability of drag partitioning approaches to represent roughness configuration effects, and the implications for model accuracy. We use wind tunnel measurements of surface shear stress distributions to calculate sediment flux for a suite of roughness configurations, roughness densities, and wind velocities. Roughness configuration has a significant effect on sediment flux, influencing estimates by more than 1 order of magnitude. Measured and modeled drag partitioning approaches overestimate the predicted flux by 2 to 3 orders of magnitude. The drag partition is sensitive to roughness configuration, but current models cannot effectively represent this sensitivity. The effectiveness of drag partitioning approaches is also affected by estimates of the aerodynamic roughness height used to calculate wind shear velocity. Unless the roughness height is consistent with the drag partition, resulting fluxes can show physically implausible patterns. These results should make us question current assessments of the magnitude of vegetated dryland dust emissions. Representing roughness effects on surface shear stress distributions will reduce uncertainty in quantifying wind erosion, enabling better assessment of its impacts and management solutions.

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Large roughness element effects on sand transport, Oceano Dunes, California

Cited by 36 publications

References 26 publications

Using solid element roughness to control sand movement: Keeler Dunes, Keeler, California

Using solid element roughness to control sand movement: Keeler Dunes, Keeler, California

Estimating aerodynamic roughness over complex surface terrain

The effect of roughness elements on wind erosion: The importance of surface shear stress distribution

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