Engineering Commons^™

Assessing Intra-Event Phosphorus Dynamics In Drainage Water Using Phosphate Stable Oxygen Isotopes, William Ford Iii, Mark R. Williams, Megan B. Young, Kevin W. King, Eric Fischer

Biosystems and Agricultural Engineering Faculty Publications

Quantifying fluxes and pathways of dissolved reactive phosphorus (DRP) in tile-drained landscapes has been hampered by a lack of measurements that are sensitive to P fate and transport processes. One potential tool to help understand these dynamics is the oxygen isotope signature of phosphate (δ¹⁸O_PO4); however, its potential benefits and limitations are not well understood for intra-event dynamics at the field scale. The objectives of this study were to quantify intra-event variability of δ¹⁸O_PO4 signatures in tile drainage water and assess the efficacy of δ¹⁸O_PO4 to elucidate mechanisms and flow …

Statistical Procedures For Evaluating Daily And Monthly Hydrologic Model Predictions, Marilyn E. Coffey, Stephen R. Workman, Joseph L. Taraba, Alex W. Fogle

Biosystems and Agricultural Engineering Faculty Publications

The overall study objective was to evaluate the applicability of different qualitative and quantitative methods for comparing daily and monthly SWAT computer model hydrologic streamflow predictions to observed data, and to recommend statistical methods for use in future model evaluations. Statistical methods were tested using daily streamflows and monthly equivalent runoff depths. The statistical techniques included linear regression, Nash-Sutcliffe efficiency, nonparametric tests, t-test, objective functions, autocorrelation, and cross-correlation. None of the methods specifically applied to the non-normal distribution and dependence between data points for the daily predicted and observed data. Of the tested methods, median objective functions, sign test, autocorrelation, …

The Development Of Relationships Between Constituent Concentrations And Generic Hydrological Variables, Carmen T. Agouridis, Dwayne R. Edwards

Biosystems and Agricultural Engineering Faculty Publications

The collection and analysis of samples from storm events constitutes a large portion of the effort associated with water quality research. Estimating concentrations or loads from these events is often difficult. The equipment necessary to analyze the samples and the required laboratory resources are typically significant expenses incurred by the researcher. One potential method to reduce these costs is through the development of generic relationships between concentrations and easily measured variables such as dimensionless flow rate or time. The benefits recognized from such an effort include a reduction in the number of required samples, resulting in a reduction in cost. …

Effect Of Parameter Distributions On Uncertainty Analysis Of Hydrologic Models, C. Thomas Haan, Daniel E. Storm, T. Al-Issa, Sandeep Prabhu, George J. Sabbagh, Dwayne R. Edwards

Biosystems and Agricultural Engineering Faculty Publications

Increasing concern about the accuracy of hydrologic and water quality models has prompted interest in procedures for evaluating the uncertainty associated with these models. If a Monte Carlo simulation is used in an uncertainty analysis, assumptions must be made relative to the probability distributions to assign to the model input parameters. Some have indicated that since these parameters can not be readily determined, uncertainty analysis is of limited value. In this article we have evaluated the impact of parameter distribution assumptions on estimates of model output uncertainty. We conclude that good estimates of the means and variances of the input …

Comparison Of Daily Water Table Depth Prediction By Four Simulation Models, Eric D. Desmond, Andrew D. Ward, Norman R. Fausey, Stephen R. Workman

Biosystems and Agricultural Engineering Faculty Publications

The Agricultural Drainage And Pesticide Transport (ADAPT) model was compared to the water management simulation models DRAINMOD, SWATREN, and PREFLO. SWATREN and PREFLO are one-dimensional finite-difference models while ADAPT and DRAINMOD are one-dimensional mass balance models. ADAPT, an extension of the computer model GLEAMS, also provides chemical transport information. All four models were tested against field data from Aurora, North Carolina. Observed water table depth data were collected during 1973 through 1977 from a water table management field experiment with three subsurface drain spacing treatments of 7.5, 15, and 30 m.

Both the standard error of estimate and the average …