John Tatarko

COMPARISON OF THE WEIBULL MODEL WITH MEASURED WIND SPEED DISTRIBUTIONS FOR STOCHASTIC WIND GENERATION

Wind is the principal driver of the Wind Erosion Prediction System (WEPS), which is a processbased computer model for the simulation of windblown sediment loss from a field. WEPS generates wind using a stochastic wind generator. The objectives of this study were to improve the stochastic generation of wind speed and direction and to update the wind statistics used by the generator with statistics derived from more recent, qualitycontrolled data for the 48 contiguous states of the U.S. Erosive wind power density (WPD) was chosen to evaluate how well wind is generated, since it is proportional to sediment transport by wind. It is important that WPD calculated from stochastically generated data (WPDg) closely reproduces WPD calculated from the underlying measured data (WPDm). The commonly used twoparameter Weibull model did not fit wind speed distributions well enough for application in wind erosion models. WPDg deviated more than 20% from WPDm for 168 out of the 332 stations having WPDm > 5 W m �2 . Fitting the model to the high wind speeds only, with the expectation of a better curve fit, resulted in some generated wind speeds exceeding 100 m s �1 , which is unacceptable. A more direct method uses the wind speed distributions themselves instead of the Weibull model that describes them. Wind speeds are then generated directly from the distributions using linear interpolation between data points. With this more robust direct approach, there was only one station (down from 168 stations) where WPDg deviated more than 20% from WPDm. The direct method of wind speed generation reproduces wind speeds more accurately than the Weibull model, which is important for wind erosion prediction and may be important for other applications as well.

Enhancing Wind Erosion Monitoring and Assessment for U.S. Rangelands

On the Ground Wind erosion is a major resource concern for rangeland managers because it can impact soil health, ecosystem structure and function, hydrologic processes, agricultural production, and air quality. Despite its significance, little is known about which landscapes are eroding, by how much, and when. The National Wind Erosion Research Network was established in 2014 to develop tools for monitoring and assessing wind erosion and dust emissions across the United States. The Network, currently consisting of 13 sites, creates opportunities to enhance existing rangeland soil, vegetation, and air quality monitoring programs. Decision-support tools developed by the Network will improve the prediction and management of wind erosion across rangeland ecosystems.

EVALUATION OF BULK DENSITY AND VEGETATION AS AFFECTED BY MILITARY VEHICLE TRAFFIC AT FORT RILEY, KANSAS

Abstract. Studies were conducted using military vehicles to determine the influence of repeated traffic on soil compaction and vegetative losses. The resultant data will eventually be incorporated into models such as the Wind Erosion Prediction System (WEPS). A replicated field experiment was conducted in the fall of 2010 on two soils that dominate the military training grounds at Fort Riley, Kansas. Treatments consisted of two vehicle types and three levels of vehicle passes. We used an Abrams M1A1 tank and a High-Mobility Multipurpose Wheeled Vehicle (i.e., Humvee), representing tracked and wheeled military vehicles, respectively. Bulk density, aboveground standing biomass, and plant cover were measured before and after vehicular traffic in the fall of 2010 as well as in the spring and summer of 2011. Samples were taken from curved, straight, and cross-over sections of the vehicle tracks. A mixed-model analysis of variance of these data indicated that the overall mean bulk density under the M1A1 was significantly greater than under the Humvee (p ≤ 0.05). In general, as the number of passes increased, the bulk density under the M1A1 increased significantly (p ≤ 0.05), but the increases under the Humvee were not significant (p ≤ 0.05). Bulk densities were significantly greater in the curved part of the tracks than the straight part of the tracks. Reduction in standing biomass and vegetation cover was more severe on average under the M1A1 than under the Humvee (although not significant at p ≤ 0.05). For both vehicles, biomass and cover were affected more at the curved sections of the track than the straight sections (significant at p ≤ 0.05). Comparison of spring and fall bulk density data showed significant differences at the 0-5 cm and 5-10 cm depths, indicating that the winter freeze and thaw cycles loosened the top soil layers. Subsequent growth showed severe reduction in grass biomass growth in the curved sections of the tracked vehicle paths. Growth in forb species was not significantly affected.

Crop residue harvest impacts wind erodibility and simulated soil loss in the Central Great Plains

Crop residue removal can affect the susceptibility to soil wind erosion in climates such as those of the Central Great Plains, United States. Six on‐farm trials were conducted in Kansas from 2011 to 2013 to determine the effects of winter wheat (Triticum aestivum L.), corn (Zea mays L.), and grain sorghum (Sorghum bicolor (L.) Moench), residue removal at 0, 25, 50, 75, and 100% of initial height on soil wind erosion parameters. Those parameters include soil surface random roughness (RR), and wind erodible fraction (EF; aggregates <0.84 mm), geometric mean diameter (GMD) and geometric standard deviation (GSD), stability of dry aggregates (DAS). Complete (100%) residue removal decreased the surface RR, increased EF, and decreased GMD. Overwinter EF values increased for five of six sites from fall 2011 to spring of 2012, particularly for the uppermost removal height (≥75%). Measured EF, GMD, GSD, DAS, and RR were also input into the Single‐event Wind Erosion Evaluation Program (SWEEP) to determine the effect of these parameters on simulated soil loss. The SWEEP simulated the wind velocity needed to initiate wind erosion as well as soil loss under each residue removal height at a wind velocity of 13 m s−1 for three hours. Threshold wind velocity required to initiate wind erosion generally decreased with increasing crop residue removal height, particularly for >75% removal. Total estimated soil loss over the three‐hour event ranged from ≈2 to 25 Mg ha−1, depending on EF, GMD, GSD, RR, and percent crop residue cover. Removing 75% residue increased simulated wind erosion at three of six sites while removing 50% appears sustainable at all six study sites. Findings reinforce the need for site‐by‐site consideration of the potential amount of crop residue that may be harvested while mitigating wind erosion. Study results indicate the value of maintaining residue at >75% of original height.

Application of the WEPS and SWEEP models to non-agricultural disturbed lands

Wind erosion not only affects agricultural productivity but also soil, air, and water quality. Dust and specifically particulate matter ≤10 μm (PM-10) has adverse effects on respiratory health and also reduces visibility along roadways, resulting in auto accidents. The Wind Erosion Prediction System (WEPS) was developed by the USDA-Agricultural Research Service to simulate wind erosion and provide for conservation planning on cultivated agricultural lands. A companion product, known as the Single-Event Wind Erosion Evaluation Program (SWEEP), has also been developed which consists of the stand-alone WEPS erosion submodel combined with a graphical interface to simulate soil loss from single (i.e., daily) wind storm events. In addition to agricultural lands, wind driven dust emissions also occur from other anthropogenic sources such as construction sites, mined and reclaimed areas, landfills, and other disturbed lands. Although developed for agricultural fields, WEPS and SWEEP are useful tools for simulating erosion by wind for non-agricultural lands where typical agricultural practices are not employed. On disturbed lands, WEPS can be applied for simulating long-term (i.e., multi-year) erosion control strategies. SWEEP on the other hand was developed specifically for disturbed lands and can simulate potential soil loss for site- and date-specific planned surface conditions and control practices. This paper presents novel applications of WEPS and SWEEP for developing erosion control strategies on non-agricultural disturbed lands. Erosion control planning with WEPS and SWEEP using water and other dust suppressants, wind barriers, straw mulch, re-vegetation, and other management practices is demonstrated herein through the use of comparative simulation scenarios. The scenarios confirm the efficacy of the WEPS and SWEEP models as valuable tools for supporting the design of erosion control plans for disturbed lands that are not only cost-effective but also incorporate a science-based approach to risk assessment.

Evaluation of Bulk Density and Vegetation as Affected by Military Vehicle Traffic

There is a need for greater understanding of the relationship of dust emission levels to disturbances of soil and vegetation indices that occur during military vehicle activities in Department of Defense training areas. A replicated field experiment was conducted in the fall of 2010 on two soils that dominate the military training grounds at Fort Riley, Kansas. Treatments consisted of two vehicle types, and three levels of vehicle passes. An Abrams M1A1 tank, representing tracked vehicles, and a Humvee representing wheeled military vehicles were used. Bulk density, above ground standing biomass, and plant cover were among the parameters measured before and after vehicular traffic. Samples were taken from curved, straight, and cross-over sections of the vehicle tracks. A mixed-model analysis of variance of the data indicates that the overall mean bulk density under the M1A1 were significantly higher than under the Humvee (p=0.05). In general, as the number of passes increased the bulk density under the M1A1 increased significantly (p=0.05), but the increases under the Humvee were not significant (p=0.05). Bulk densities were significantly larger in the curved part of the tracks than the straight part of the track. Large differences in biomass and vegetation cover between different treatments were observed. Comparison of spring and fall bulk density data showed significant difference at the 0-5 cm depth; indicating that the winter freeze and thaw cycles loosened the top soil layer.

Applications of WEPS and SWEEP to Non-Agricultural Lands

Soil erosion by wind is a serious problem throughout the United States and the world. Dust from wind erosion obscures visibility and pollutes the air. It fills road ditches where it impacts water quality, causes automobile accidents, fouls machinery, and imperils animal and human health. Dust and specifically particulate matter less than 10 microns (PM10), is regulated by the US-EPA National Ambient Air Quality Standards. The Wind Erosion Prediction System (WEPS) model was developed by the USDA Agricultural Research Service, primarily for the USDA Natural Resources Conservation Service to simulate wind erosion and develop conservation plans on cultivated agricultural lands. WEPS is a process based, daily-time step model that simulates hydrology, plant growth and decomposition, land management, and soil surface erodibility to simulate soil wind erosion loss (total, saltation/creep, suspension, and PM10 sizes) as affected by stochastically simulated local weather. The WEPS erosion sub-model has been developed into a stand-alone companion product that is known as the Single-event Wind Erosion Evaluation Program (SWEEP). SWEEP consists of the stand-alone WEPS Erosion sub-model combined with a user-friendly graphical interface and simulates soil loss and dust emissions from single wind storm events (i.e., one day). In addition to cultivated agricultural lands, wind erosion results in sediment and dust emissions from construction sites, mined and reclaimed land, landfills, and other disturbed lands. Such disturbed lands are often regulated by government agencies. The US-EPA sets limits on pollution levels and establishes permits for pollution release. In addition, state agencies develop State Implementation Plans (SIP’s) and operate permit programs for release of fugitive dust. Although developed for agricultural situations, WEPS and SWEEP are useful tools for simulating erosion by wind for such lands where typical agricultural practices and control methods are not utilized. WEPS is suitable for simulating long term (multiple years) control strategies such as mulching, re-vegetation, and large roughness elements such as burms. SWEEP on the other hand can simulate the potential soil loss for site specific planned surface conditions and control practices for a given date. SWEEP also provides probabilities of dust events given the defined surface conditions for the specified location and date. This paper explores the use of WEPS and SWEEP for developing control strategies for fugitive dust on construction sites and other non-agricultural disturbed lands. Case studies and comparative scenarios with examples of modifying WEPS and SWEEP inputs and management files to simulate common erosion control strategies are presented. Control strategies discussed include the simulation of water and other dust suppressants, wind barriers such as silt and snow fencing and hay bales, anchored and crimped straw mulch, vertical mulches, erosion blankets, re-vegetation, gougers, basin blades, berms, and other roughening practices. For example, dust suppressants are simulated by creating a crusted soil with low loose erodible material on the surface. Example simulations will be demonstrated. The paper describes tools needed to design erosion control plans that are not only cost-effective but also demonstrate regulatory compliance by using a science-based approach to risk assessment.