An analysis of soil crust strength in relation to potential abrasion by saltating particles

A standalone version of the Wind Erosion Prediction System (WEPS) erosion submodel, the Single-event Wind Erosion Evaluation Program (SWEEP), was released in 2007. A limited number of studies exist that have evaluated SWEEP in simulating soil loss subject to different tillage systems under high winds. The objective of this study was to test SWEEP under contrasting tillage systems employed during the summer fallow phase of a winter wheat-summer fallow rotation within eastern Washington. Soil and PM10 (particulate matter ≤10 μm in diameter) loss and soil and crop residue characteristics were measured in adjacent fields managed using conventional and undercutter tillage during summer fallow in 2005 and 2006. While differences in soil surface conditions resulted in measured differences in soil and PM10 loss between the tillage treatments, SWEEP failed to simulate any difference in soil or PM10 loss between conventional and undercutter tillage. In fact, the model simulated zero erosion for all high wind events observed over the two years. The reason for the lack of simulated erosion is complex owing to the number of parameters and interaction of these parameters on erosion processes. A possible reason might be overestimation of the threshold friction velocity in SWEEP since friction velocity must exceed the threshold to initiate erosion. Although many input parameters are involved in the estimation of threshold velocity, internal empirical coefficients and equations may affect the simulation. Calibration methods might be useful in adjusting the internal coefficients and empirical equations. Additionally, the lack of uncertainty analysis is an important gap in providing reliable output from this model. Published in

Section: Resultsmentioning

confidence: 99%

Evaluation of the SWEEP model during high winds on the Columbia Plateau

Feng

Sharratt

2009

“…These measurements were made to evaluate changes of the playa surface and its sediments at these few sites and were not intended for comprehensive description of playa sediment strength (see Sanglerat, 1972). The relations between sediment strength and eolian erosivity are not straightforward and are not assessed here (see Rice et al, 1997;Gillette et al, 2001;Langston and McKenna Neuman, 2005).…”

Section: Methodsmentioning

confidence: 99%

“…Gillette et al (1980Gillette et al ( , 1982 have documented the resistance of these kinds of crust to wind erosion using wind-tunnel experiments on natural surfaces. Many other laboratory studies have investigated the effects of salt-mineral content and (or) different kinds of crust on the threshold shear velocity (e.g., Nickling and Ecclestone, 1981;Nickling, 1984;Rice et al, 1996Rice et al, , 1997Argaman et al, 2006). We have observed that evaporite-mineral crusts commonly form a protective cover for a layer of unconsolidated and dry fine-grained sediment that may be relatively thick (of the order of 10 cm) compared to the crust (commonly <1 cm).…”

Section: Rapid Changes In Wet-playa Surfaces and Sedimentsmentioning

confidence: 97%

Dust emission from wet and dry playas in the Mojave Desert, USA

Reynolds¹,

Yount²,

Reheis³

et al. 2007

191

176

The interactions between playa hydrology and playa-surface sediments are important factors that control the type and amount of dust emitted from playas as a result of wind erosion. The production of evaporite minerals during evaporative loss of near-surface ground water results in both the creation and maintenance of several centimeters or more of loose sediment on and near the surfaces of wet playas. Observations that characterize the texture, mineralogic composition and hardness of playa surfaces at Franklin Lake, Soda Lake and West Cronese Lake playas in the Mojave Desert (California), along with imaging of dust emission using automated digital photography, indicate that these kinds of surface sediment are highly susceptible to dust emission. The surfaces of wet playas are dynamic -surface texture and sediment availability to wind erosion change rapidly, primarily in response to fluctuations in water-table depth, rainfall and rates of evaporation. In contrast, dry playas are characterized by ground water at depth. Consequently, dry playas commonly have hard surfaces that produce little or no dust if undisturbed except for transient silt and clay deposited on surfaces by wind and water. Although not the dominant type of global dust, salt-rich dusts from wet playas may be important with respect to radiative properties of dust plumes, atmospheric chemistry, windborne nutrients and human health. Lake playas) in the Mojave Desert are dynamic and at times are vulnerable to wind erosion and dust emission when sufficiently soft and (or) loose. Surface sediments at dry playas, on the other hand, are typically stable and hard and thus generally do not emit large amounts of dust when undisturbed by human activities. The emphasis of this report is on the hydrologic and sedimentologic interactions that may sustain dust production from wet playas. Wet and Dry Playas -Definitions and CharacteristicsPlayas vary greatly in their geologic and hydrologic settings, leading to several classification schemes that group playas by sedimentologic or hydrologic characteristics (summarized by Smoot and Lowenstein, 1991;Rosen, 1994;Gill, 1996). With respect to dust emission from playas, we find useful the distinction between 'wet ' and 'dry' playas (see Rosen, 1994). In a wet playa, ground water is near (typically <5 m) or at the playa surface, through which it is lost by evaporation or fluid outflow (Figure 1(a)). In a dry playa, ground water does not interact with the surface because the water table lies far below the surface (typically >5 m; Figure 1(b)). Both wet and dry playas may receive surface-water runoff.The different hydrological and hydrochemical processes operating at wet and dry playas produce very different surfaces and surficial sediments (see, e.g., Thompson

“…However, direct application of this technique for evaluating crust erodibility by saltating grains is questionable. Rice et al (1997) described the use of a flat-tipped 0·6 mm diameter penetrometer and a flat-ended cylindrical punch with inner and outer diameters of 5 and 6 mm, respectively, to estimate crust strength. They suggested that the small penetrometer gave results that can be used to characterize surface erodibility to saltating particles.…”

Section: Field Surface Conditionsmentioning

confidence: 99%

Measurement and data analysis methods for field‐scale wind erosion studies and model validation

Zobeck

Sterk

Funk

et al. 2003

178

107

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 nonerodible 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.