Wind Erosion

ABSTRACTStokes surfaces in aeolian deposits are caused by wind scour of unconsolidated material to a roughly planar horizon controlled by near-surface water-tables (Stokes, 1968). A water-table forms a downward limit of scour through the cohesion of damp or wet sand near water-table, and through early cementation by evaporites precipitated in the sediments as water evaporates near the sand-air interface. Study of modern analogues reveals that Stokes surfaces exist in a variety of depositional settings, including a coastal offshore prograding sand sea (Jafurah, Saudi Arabia); a coastal onshore prograding sand sea (Guerrero Negro, Mexico) and a continental sand sea (White Sands, New Mexico, USA). These modern analogues indicate that our concept of Stokes surfaces must be broadened to include the following: (i) modern analogues for Stokes surfaces described here cover areas on the order of 25 km2. These may be as representative of similar surfaces in ancient rocks as hypothesized plains of deflation requiring removal of entire sand seas; (ii) Stokes surfaces occupy a continuum in scale from local to extensive, and erosional surfaces of different magnitude may be stacked closely in the sediments; (iii) Stokes surfaces, although erosional in nature, are commonly associated with deposits both above and below the Stokes bounding surface which plainly reveal the influence of a near-surface groundwater control on wind sedimentation. Moreover, the erosional relief of the bounding surface itself (as well as other features) reveals the influence of a groundwater-table; (iv) Stokes surfaces may be diachronous, representing the lateral shift of a zone of scour within a sand sea rather than simultaneous removal of all dunes from the area encompassed by the erosional surface; (v) Stokes surfaces and associated deposits are often laterally transitional to surfaces and deposits of adjacent depositional environments, including interdunes, tidal flats, lagoons, beaches, lakes and non-aeolian sabkhas. Finally, modern examples from different depositional settings suggest that while most Stokes surfaces have many features in common (such as erosional ridges due to early cementation), there are some features which may, with further study, be revealed to be distinctive of an individual depositional setting.

Accurate and reliable methods of measuring windblown sediment are needed to confirm, validate, and improve erosion models, assess the intensity of aeolian processes and related damage, determine the source of pollutants, and for other applications. This paper outlines important principles to consider in conducting field-scale wind erosion studies and proposes strategies of field data collection for use in model validation and development. Detailed discussions include consideration of field characteristics, sediment sampling, and meteorological stations. The field shape used in field-scale wind erosion research is generally a matter of preference and in many studies may not have practical significance. Maintaining a clear non-erodible boundary is necessary to accurately determine erosion fetch distance. A field length of about 300 m may be needed in many situations to approach transport capacity for saltation flux in bare agricultural fields. Field surface conditions affect the wind profile and other processes such as sediment emission, transport, and deposition and soil erodibility. Knowledge of the temporal variation in surface conditions is necessary to understand aeolian processes. Temporal soil properties that impact aeolian processes include surface roughness, dry aggregate size distribution, dry aggregate stability, and crust characteristics. Use of a portable 2 tall anemometer tower should be considered to quantify variability of friction velocity and aerodynamic roughness caused by surface conditions in field-scale studies. The types of samplers used for sampling aeolian sediment will vary depending upon the type of sediment to be measured. The Big Spring Number Eight (BSNE) and Modified Wilson and Cooke (MWAC) samplers appear to be the most popular for field studies of saltation. Suspension flux may be measured with commercially available instruments after modifications are made to ensure isokinetic conditions at high wind speeds. Meteorological measurements should include wind speed and direction, air temperature, solar radiation, relative humidity, rain amount, soil temperature and moisture. Careful consideration of the climatic, sediment, and soil surface characteristics observed in future field-scale wind erosion studies will ensure maximum use of the data collected. Copyright © 2003 John Wiley & Sons, Ltd.

Resource condition targets have been specified for river salinity, biodiversity conservation, and wind erosion mitigation in the South Australian Murray-Darling Basin (SA MDB). The revegetation of cleared, privately owned agricultural land with deep rooted perennials has been widely promoted as one approach to satisfy the resource condition targets. Current estimates indicate the scale of revegetation necessary to meet the targets

ABSTRACT The effect of several wind characteristics on sand transport was studied in three experiments in north Burkina Faso, West Africa. The first experiment is used to analyse the relation between wind speed and shear stress fluctuations across height. The second experiment is used to study the relation of these wind characteristics with saltation transport for fourteen convective storms, registered during the rainy seasons of 2002 and 2003. The effect of sampling time is studied for two of these convective storms. The third experiment relates the turbulent structures of four convective storms to saltation transport. Wind speed measurements were undertaken with two sonic anemometers and sediment transport was measured by two saltiphones. The sampling frequency was either 8 or 16 Hz. The sonic frame of reference was rotated according to a triple rotation. Horizontal fluctuations showed a (fairly) good correlation with height because the wind speed at both sensors was affected by the same vortices. The correlation coefficients ranged from 0.42 (when the distance between the sensors was 1.75 m) to 0.92 (when the distance was 0.25 m). The instantaneous Reynolds' stress had the weakest correlation (correlation coefficient of 0.05 at 1.75 m between the sensors and 0.56 at 0.25 m between the sensors), because the momentum at 2 m above the soil surface is transported by different eddies than those close to the ground. This also explains the fairly good correlation coefficients between the horizontal components of the wind and saltation compared to the poor correlations between instantaneous Reynolds' stress and saltation. An increase in sampling time did not have much impact on these correlation coefficients up to sampling periods of about 30 s. However, this sampling interval would be too coarse to describe the vertical wind component adequately. The classification of the moments of shear stress into the turbulent structures, sweeps, ejections, inward and outward interactions, showed that the mean saltation flux is higher at sweeps and outward interactions than at ejections and inward interactions. Also, saltation occurred more often during sweeps and outward interactions than during ejections and inward interactions.

In the Sahel, with average annual precipitation in the order of 500mmyr− 1, wind erosion occurs mainly on cultivated millet fields whose surfaces are only partially covered by crop residues. The impact of these residues on wind erosion was not clearly established. The ...

Proceeding from the percentage of natural stable situation, 13 generalized taxa were distinguished on the map of soil vulnerability and degradation. Most Histosol and Gleysol expanses as well as large forested areas on different soil complexes are natural stable. Neglected drainage systems have often led to continuation of gleying and restoration of waterlogging of formerly drained areas. This kind of physical degradation is actual, even on neighboring forested and arable lands. Owing to privatization of land and changes in the types of machinery used today, decrease in soil compaction and consequent surface reductomorphic processes are evident. As the majority of Estonian territory is plain and soil texture is loamy, water and wind erosion do not present a natural hazard. Changes in land use have resulted in the decline of erosion even on the endmorainic hills of South-Eastern Estonia. Acidification has occurred in some sandy Podzols; alkalinization and contamination with heavy met...

In the last decades, many countries have been characterized by soil conservation concerns since agricultural land management local practices led to soil impoverishment and destructuration. Argentina, recently, has been hardly hit by these phenomena of soil degradation that, depending on the specific region concerned, show up in different forms of soil erosion. The research tries to give an answer to the questioning concerning the relationship between agricultural land management and wind erosion occurrence in one specific area placed within the province of Còrdoba. The research results from an ample review of the literature and a period of field study in the relevant area, where interviews with local farmers and experts were carried out.
The research revealed an agricultural system, which in the last 20 years has fully joined the no-tillage farming practices focused on soil conservation. Whether on one hand, no-tillage actually reduced erosion, on the other hand it brought to a widespread use of genetically modified soybean (and to a lesser extent maize) which require increasing levels of herbicides also due to the spread of resistant weeds, which is mostly caused by the common practice of sharing harvesters and other machineries. Despite this diffusion of soil conservation methods, the research reveals how soil erosion still represents a threat for the province of Cordoba. However, the study also discovered that erosion occurs differently within the province (in some places mainly as water erosion, in others as wind erosion) depending on human factors, concerning land management, and natural ones. Among the human factors, an unbalanced crop rotation, but especially the peanuts cultivation (due to the particular tasks required for cultivating this crop) have been identified as the main causes of wind erosion.
It has been noticed, however, as the underlying problem lies both in the absence of legal constraints aimed at reducing the risk of wind erosion occurrence with peanuts and in the presence of higher taxes and limitations for the export of certain agricultural products.

Quantitative estimation of the material transported by the wind under field conditions is essential for the study and control of wind erosion. A critical step of this calculation is the integration of the curve that relates the variation of the amount of the material carried by the wind with height. Several mathematical procedures have been proposed for this calculation, but results are scarce and controversial. One objective of this study was to assess the efficiency of three mathematical models (a rational, an exponential, and a simplified Gaussian function) for the calculation of the mass transport, as compared to the linear spline interpolation. Another objective of this study was to compare the mass transport calculated from field measurements obtained from a minimum of three discrete sampling heights with measurements of nine sampling heights. With this purpose, wind erosion was measured under low surface roughness conditions on an Entic Haplustoll during 25 events. The rational function was found to be mathematically limited for the estimation of wind eroded sediment mass flux. The simplified Gaussian model did not fit to the vertical mass flux profile data. Linear spline interpolation generally produced higher mass transport estimates than the exponential equation, and it proved to be a very flexible and robust method. Using different sampling arrangements and different mass flux models can produce differences of more than 45% in mass transport estimates, even under similar field conditions. Under the conditions of this study, at least three points between the soil surface and 1·5 m high, including one point as closest as possible to the surface, should be sampled in order to obtain accurate mass transport estimates. Additionally, the linear spline interpolation and the non-linear regression using an exponential model, proved to be mathematically reliable methods for calculating the mass transport. Copyright © 2010 John Wiley & Sons, Ltd.

The objectives of this study were to explore the effects of long-term and continued application of fertilizers and manures on microbial biomass, soil biological activity and their seasonal variations in surface and subsurface soils in relation to soil fertility. For this, soils were sampled in spring, summer and autumn from Shenyang Long-term Experimental Station, northeastern China. The results showed that soil total nitrogen (N), organic carbon (C), basal respiration, microbial biomass and enzymatic activity increased in manure-amended surface soils, but decreased with soil depth. Long-term application of inorganic fertilizers significantly decreased soil pH value, sucrase activity and microbial biomass C, but increased soil metabolic quotient (qCO2). However, no significant effect of inorganic fertilizers on soil total N, urease activity and microbial biomass N was observed in comparison with CK0 (neither tillage nor fertilization) and CK (no fertilizers). There was no significant difference between CK0 and CK in soil total N, organic C and microbial activity in surface soil layer (0–20 cm), but these parameters in subsurface soil layer (20–40 cm) were higher in CK than in CK0. Moreover, seasonal changes were observed in terms of soil nutrient contents, enzymatic activity, microbial biomass and soil respiration. There were significant correlations between soil microbial biomass C and N, between organic C and sucrase activity and between total N and urease activity, respectively. It is recommended that combined use of organic manure with inorganic fertilizers should be considered to maintain higher microbial biomass, soil biological activity and soil fertility. Considering considerably high nutrients reserve and microbial activity in subsurface layers of soil and wind-erosion-caused nutrient loss in spring in north China, we also propose that low tillage should be considered to make use of nutrients in soils.

A simple low-cost sand catcher has been developed for use in wind-tunnel experiments. It is 500 mm high with a 300 mm by 20 mm inlet opening, and is designed to measure total mass transport directly. The length is 280 mm and its walls slowly expand at an angle of 5·6°. The top view is similar to that of the widely used BSNE sampler. Each sidewall is vented with three ventilation screens. Two sets of experiments were conducted on dune sand and at different wind velocities to investigate to what degree the catcher samples isokinetically, efficiently and non-selectively. The results indicate that the catcher measures sufficiently isokinetically (inlet wind velocity over outside wind velocity >0·9). Catch efficiency was around 0·75 and the degree of non-selectivity was >0·80 for 95 per cent of the particle sizes of the test material. It was also observed that the influence of wind velocity on the tested sampler characteristics was of minor importance so that no specific corrections need to be made for different wind velocities. Copyright © 2003 John Wiley & Sons, Ltd.

‘Wind erosion’ is somewhat of a misnomer, since the formation of wind-eroded landforms takes place not as the result of the wind itself, but because of the blasting effects of mineral grains (and in some cases ice crystals) that the wind is transporting. Nevertheless, this chapter uses the term wind erosion to describe how landforms are shaped by wind-blown particles. The wind can erode both hard bedrock or sediment surfaces, and loose surface materials, although the preservation potential of wind-eroded features developed in loose materials, for example blow-outs in sand dunes, is relatively low. The entrainment of loose surface sediments is discussed in other chapters in this book. Here, we discuss the effects of wind erosion on bedrock or loose boulder-covered surfaces. Discussion of these wind-eroded landforms is grounded in the historical context of research by such workers as Charles Keyes (Goudie, 2012) and Ralph Bagnold (Thorne and Soar, 1996). Definitions of terms used in this chapter are provided in Table 3.1.