Browsing by Author "Thompson, Anita"

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    Antibiotic losses in runoff and drainage from manure-applied fields
    (2003) Gupta, Satish; Singh, Ashok; Kumar, Kuldip; Thompson, Anita; Thoma, David
    The objective of this research is to quantify the effects of liquid swine manure application on antibiotic and nutrient (N and P) losses via surface runoff and subsurface drainage under a conventional (moldboard plowing) and a conservation (chisel plowing) tillage system.
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    Characteristics of Erosion Control Measures and Their Impact on Erosion
    (2002-06-01) Singh, Udai; Thompson, Anita; Wilson, Bruce N.; Nguyen, Hung; Subramaniam, V K
    This project endeavored to expand experimental data on erosion control blankets and develop greater understanding of how blankets and erosion principles interact. Blankets that are effective in reducing raindrop impact may become ineffective in controlling soil detachment and runoff (rill erosion) on longer slopes. This field study of erosion control products under artificial rainfall conditions was conducted at the Highway 10 overpass in Coon Rapids, Minnesota. Examining long slope lengths (60 feet and 100 feet), bare soil erosion was compared to erosion under straw blankets, wood fiber blankets, straw mulch, and sprayed emulsion. Measurements of runoff, erosion, and biomass (vegetative growth) were made in spring and fall under wet and dry conditions. Sediment loads for bare soil were 8 times larger than other treatments. Sediment loads were substantially smaller for the fall runs than the spring runs, largely due to the substantially increased vegetative cover (biomass). Shear stress partitioning for erosion control blankets was evaluated using a laboratory flume and hot-film anemometry. Erosion control blankets partition shear stress into form shear (the portion that acts on the blanket) and particle shear (the portion that acts on the soil particles). Blanket type, flow conditions, and fastener impacts were considered. Shear partitioning was found to be an important process in design and erosion modeling. Attempts were made to correlate sediment load and vegetative density data gathered by Texas Department of Transportation (TxDOT) with manufacturer's information on blanket characteristics. However, the data from manufacturers was insufficient to determine patterns or predict performance. Keywords-erosion control products, vegetation establishment, soil erosion, slope hydrology
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    The Impact of Roughness Elements on Reducing the Shear Stress Acting on Soil Particles
    (2002-01-01) Thompson, Anita; Wilson, Bruce N.
    This report presents the results from a study on shear stress partitioning for vegetation. The project involved partitioning the shear stress from overland flow into one component that acts on the vegetation (form shear) and the remainder that acts on the intervening soil particles (particle shear). Particle shear is important for predicting soil erosion. The study used idealized shapes to represent vegetal elements. Researchers designed and constructed a unique laboratory hydraulic flume, which they used in conjunction with hot-film anemometry to measure particle shear. They also designed and constructed instrumentation to measure the form shear on individual rigid vegetal elements, taking detailed spatial and temporal shear stress measurements for three element densities. Form shear was measured on each element within the test array. The study investigated a total of 16 test scenarios. Particle shear accounted for 13 to 89 percent of the total shear. Shear partitioning theories developed for wind erosion adequately represent the observed data and can be used to determine an appropriate vegetation density for a threshold particle shear. Keywords-vegetation, overland flow, erosion, shear stress partition, hot-film anemometry