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Unsaturated flow and chemical transport from an unlined feedlot runoff storage pond
Abstract
Research was performed to investigate seepage from a 22-year-old feedlot runoff storage pond located in silt loam soils 30 m above the groundwater. Soil and water samples collected from 14 borings indicated that moisture content and chemical concentrations were elevated near the pond, and were greatest near the base of the sidewalls. Chemical concentrations indicated that the plume had traveled further than the 6.1 m maximum depth explored. Nitrate-N was not found beneath the pond bottom, but was found beneath the pond sidewalls. A mathematical water balance model was developed to predict daily inflow due to runoff and rainfall, and outflows due to evaporation and seepage. The seepage component was estimated using a finite element saturated/unsaturated flow model, while feedlot runoff was estimated using the Natural Resources Conservation Service (NRCS) runoff method. Modeling was performed at sludge depths of 0, 6.8, 34, and 150 cm, which corresponded to sludge accumulation periods of 0, 1, 5, and 22 years, respectively. An analysis consisting of more than 8,500 annual simulations was performed to evaluate the effects of sludge accumulation, starting stage, and annual precipitation. Predicted seepage rates and volumes decreased with increasing sludge thickness. Seepage volumes from the sidewalls of the pond ranged from 49 percent (0-year sludge period) to 73 percent (22-year sludge period) of total pond seepage. At the 22-year sludge period, the average infiltration rate from the sidewalls was eight times greater than the infiltration rate from the pond bottom. Seepage losses were 1.5 to 3.2 times as great as evaporation losses. Of the log Pearson, lognormal, normal and Gumbel probability distributions, the log Pearson and normal distributions gave the best fit to the simulated seepage data. A method was developed for sampling soft, near-saturated sediments using a freezing technique. Physical and hydraulic conditions of the sludge varied with depth and spatially throughout the pond.
Subject Area
Agricultural engineering|Environmental engineering|Civil engineering
Recommended Citation
Parker, David Bruce, "Unsaturated flow and chemical transport from an unlined feedlot runoff storage pond" (1996). ETD collection for University of Nebraska-Lincoln. AAI9637076.
https://digitalcommons.unl.edu/dissertations/AAI9637076