Sediment Mobilisation by the Wind

Wiggs, Giles F.S.

doi:10.1002/9780470710777.ch18

Cited by 20 publications

(10 citation statements)

References 195 publications

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“…The amount of sediment entrained from a horizontal sand surface depends primarily on incident windspeed and the grain size of the material. Here, the various physical processes involved in entrainment and transport (for in‐depth discussion see Durán et al ., ; Wiggs, ) are not explicitly modelled and the sand flux (in units kg/m/s) is calculated, as a function of windspeed, using the semi‐empirical relationship given in Equation (reformulated from Dong et al ., ):

q (u) = {((), c_{1} + ((), c_{2} d true/ D))}^{- 1} {((), 1 - ((), v_{T} true/ u))}^{2} (u^{3} ρ / g)

where c 1 = 475.24 and c 2 = 93.62 are fitted constants; d is grain size (here d = 200 µm) and D is a reference grain size ( D = 250 µm), u is windspeed (m/s), g is acceleration due to gravity (g = 9.81 m/s 2 ) and ρ is the density of air ( ρ = 1.25 kg.m ‐3 ). The threshold velocity for entrainment ( v T ) is interpolated from the data of Dong et al .…”

Section: Aim and Model Descriptionmentioning

confidence: 99%

A quantitative approach to understanding dated dune stratigraphies

Bailey

Thomas

2013

Earth Surf Processes Landf

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Attempts to reconstruct past changes in climate-related forcing of dryland landscapes are hampered by the lack of an adequate quantitative framework for understanding the production and interpretation of dated sedimentary records. In drylands, as in other environments, information on past forcing conditions is progressively modified, degraded and removed from the available stratigraphic record by a series of 'filters' involving changes in the primary forcing factors themselves, geomorphological processes and the sampling/dating procedures. In this paper we describe a quantitative model that includes these effects, and use the model to examine the nature of preserved dryland sedimentary records and their relationships to primary forcing conditions: thicker preserved sedimentary records reflect periods of more intense aeolian activity; localized switching between erosion and deposition results in discontinuous and highly variable stratigraphic sequences; a preservation bias towards younger deposits is observed, potentially leading to a continuum of accumulation that decays approximately in proportion to 1= ffiffiffiffiffiffiffi ffi age p . Time periods not represented by deposition can in some cases be interpreted as periods of higher precipitation and/or lower wind energy. An asymmetry exists between the efficiency with which past 'drier' and 'wetter' episodes can be identified, which relates to the timeseparation of depositional periods and the correct distinction between hiatuses due to forcing conditions and those due to undersampling. Relevant to this is the effect of random dating errors (statistical uncertainty), which (increasingly with age) filter-out higher frequency events from the record. A new data treatment method (termed Accumulation Rate Variability) provides an efficient proxy for accumulation rates, and therefore the intensity of aeolian activity, with significant improvements over existing date-frequency methods. The filtering problem discussed applies to all attempts at understanding the timing and nature of past events, independent of the proxies and dating methods employed. Further explicit analysis of these issues would be beneficial.

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q (u) = {((), c_{1} + ((), c_{2} d true/ D))}^{- 1} {((), 1 - ((), v_{T} true/ u))}^{2} (u^{3} ρ / g)

Section: Aim and Model Descriptionmentioning

confidence: 99%

A quantitative approach to understanding dated dune stratigraphies

Bailey

Thomas

2013

Earth Surf Processes Landf

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“…The presence of silt and coarse (pebbly and sandy) units in the fine silt deposits exposed in the SE (Ravi basin) of the Jammu area do suggest fluctuations in water budget that could be attributed to seasonality in the hydrological regimes of the area. The dominance of silt deposits in Jammu foothills, both in SE (Ravi basin) and NW (Chenab basin), suggest the deposition of silt, transported by saltation process (Wiggs 1997), in the channel/bank of rivers under reduced flow conditions. The fluctuation in the water budget due to seasonality acts as a factor in sporadic high sediment load in rivers.…”

Section: Discussionmentioning

confidence: 99%

Late Quaternary fine silt deposits of Jammu, NW Himalaya: Genesis and climatic significance

Ganjoo

Kumar

2012

J Earth Syst Sci

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The fine silt deposits of Jammu (J & K State, India) stretch all along the Siwalik foothills from Jammu to the Potwar Plateau in Pakistan. The post-Siwalik deposits, first discussed by de Terra and Paterson (1939), are attributed to wind action. The deposits termed as 'Potwar loessic silt' comprising sandy silt are essentially of late Quaternary age (75-18 ka) and are re-looked herein from the point of view of genesis and climatic significance. The sorting, skewness and kurtosis parameters of fine silts of Jammu suggest fluvial environment of the deposits wherein the water budget fluctuated. The weak pedogenesis of fine silts at certain intervals corroborate to periods of less or no sedimentation. The bivariant plot studies further suggest fluvial environment of deposition for the fine silt at Jammu, with regular fluctuations in the budget of river water that was perhaps in consonance with oscillations in the climate of the region.

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“…A wind rose for Bloemfontein (South African Weather Service, ) is presented in Figure . The conditions affecting erodibility (susceptibility of soil to erosion) and erosivity (power of the wind to erode; see Wiggs, ) evident in the region are therefore currently potentially highly conducive to wind erosion. Localised dust storms, with dust plumes emanating from pan surfaces and agricultural land, are observed in late winter and spring (Holmes et al ., ) when soils are usually at their driest and have the least vegetation cover.…”

Section: Geographical Contextmentioning

confidence: 99%

Evidence for Land Degradation From Aeolian Sediment in the West‐central Free State Province, South Africa

et al. 2012

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Evidence for historical and recent/contemporary aeolian activity in the west‐central Free State Province, South Africa, is here reviewed, synthesised and supplemented by new data. The evidence is derived from three sources, namely lunette dunes and their capping sediments, fence‐line dunes and buried fences, and contemporary dust entrainment. Prior to settlement by farmers of European origin during the 18th and 19th centuries, this grassland biome supported significant populations of native herbivores and carnivores. Human impact was limited to grazing of cattle and small stock by indigenous inhabitants of the region, with limited subsistence agriculture. The first Europeans to inhabit these grasslands were itinerant trekboers, who hunted game and drove cattle. Subsequent to permanent settlement by farmers in the 19th century, the area was surveyed, title was acquired and commercial agriculture was introduced, further impacting on the environment. There is currently evidence in the landscape that this human impact may have led to enhanced aeolian activity. This paper reviews such evidence. Numerous pans (playas) occur in the area, with sand/clay lunette dunes typically occurring on their downwind margins. At most sites, the lunettes are unconformably capped by sand. Optically stimulated luminescence dates from dunes at five localities reveal a suite of ages between 580 and 60 years, suggesting renewed aeolian sediment mobility in historic times. Further evidence for sediment mobility, which suggests dune building post ca. 1880, was derived from buried barbed‐wire fences and recent fence‐line dunes, which border land currently under the plough. Finally, there is evidence of mobile dust derived from dust traps used to monitor aeolian sediment mobility on agricultural land, as well as at a pan site. It is proposed that historic and current land‐use practices have contributed to sediment mobility and, by implication, may promote land degradation in the area. Copyright © 2012 John Wiley & Sons, Ltd.

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Sediment Mobilisation by the Wind

Cited by 20 publications

References 195 publications

A quantitative approach to understanding dated dune stratigraphies

A quantitative approach to understanding dated dune stratigraphies

Late Quaternary fine silt deposits of Jammu, NW Himalaya: Genesis and climatic significance

Evidence for Land Degradation From Aeolian Sediment in the West‐central Free State Province, South Africa

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