Thesis (M.S.)--Ohio University, August, 1994. / Title from PDF t.p.

Thesis (Ph. D.)--Auburn University, 2009. / Abstract. Vita. Includes bibliographical references (p. 107-120).

Thesis (M.S. in civil engineering)--Washington State University, May 2009. / Title from PDF title page (viewed on July 27, 2009). "Department of Civil and Environmental Engineering." Includes bibliographical references (p. 82-84).

Thesis (Ph. D.)--University of Washington, 1995. / Vita. Includes bibliographical references (leaves [256]-272).

Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2006. / Dr. Spyros Pavlostathis, Committee Member ; Dr. Mustafa M. Aral, Committee Chair ; Dr. Turgay Uzer, Committee Member ; Dr. Ching-Hua Huang, Committee Member ; Dr. Sotira Yiacoumi, Committee Member. Vita. Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 38-40). Also available on the World Wide Web.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves [135]-139). Also available on the Internet.

No description available.

Water table control by subsurface drainage has been shown to affect leaching losses of nitrate-nitrogen: a concern both for economic use of fertilizer, and for maintenance of water quality. The effect of water table height on leaching of NO₃⁻-N was investigated in this study in nineteen 15cm x 100cm undisturbed cores of silty clay loam. The experiment simulated fertilization followed by rainfall, then rapid water table rise and fall, under conditions similiar to those experienced in the early spring in the Lower Fraser Valley. In the first part of the experiment, a concentrated solution of KNO₃ and KG (equivalent to 35 kg/ha of N and 22 kg/ha of Cl) was applied to the columns, followed by intermittent leaching with distilled water. Leachate from two depths in each column was collected before and after a period of static water table, and analyzed for NO₃⁻, No₂⁻, NH₄⁺, and Cl⁻. This procedure was repeated without nutrient addition in the second part of the experiment. Chloride was used an inert tracer to follow anion movement and retention within the columns. There was no significant difference in the leachate NO₃⁻ concentration or leachate N/CI ratio from any of the four water table heights tested (15, 35, 55, and 75 cm above drain depth). The NO₃⁻ concentrations and N/CI ratios decreased with depth in the soil columns, indicating removal of N from the percolating soil solution, either by denitrification or immobilization. The variability in leachate concentrations among all columns was very high (eg. for a typical sample time, NO₃⁻-N ranged from 0.01 to 15.72 mg/L, and Cl⁻ ranged from 4.8 to 14.5 mg/L), as was the variability in constant head satiated hydraulic conductivities (range: 1 to 1468 cm/day; CV = 181%), and drainable porosity (range: 2.7 to 10.4%; CV = 39%). Cross sections of columns leached with 1% methylene blue solution did not reveal differences in patterns of water transmission between low and high conductivity columns. Indications were that penetration of dye was greater in columns with higher conductivities, and that preferential flow occurred in all columns examined. Leachate concentrations and N/CI ratios correlated significantly with hydraulic conductivity: Spearman's correlation coefficients were always > 0.8 for samples obtained from the bottom of the columns. However, even when the conductivity was included as a covariate in an analysis of covariance, there was no significant effect of water table height on nitrate leaching. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Literature on subsurface drainage theories, determination of drainage parameters, and analysis approaches of uncertainty was reviewed. Sensitivity analysis was carried out on drain spacing equations for steady state and nonsteady state, in homogeneous soils and in layered soils. It was found that drain spacing is very sensitive to the hydraulic conductivity, the drainage coefficient, and the design midspan water table height. Spacing is not sensitive to the depth of the impermeable layer and the drain radius. In transient state, spacing is extremely sensitive to the midspan water table heights if the water table fall is relatively small. In that case steady state theory will yield more reliable results and its use is recommended. Drain spacing is usually more sensitive to the hydraulic conductivity of the soil below the drains than to that of the soil above the drains. Therefore, it is desirable to take samples from deeper soil when measuring hydraulic conductivity. A new spacing formula was developed for two-layered soils and a special case of three-layered soils with drains at the interface of the top two layers. This equation was compared with the Kirkham equation. The new formula yields spacings close to the Kirkham equation if the hydraulic conductivity of the soil above the drains is relatively small; otherwise, it tends to give more accurate results. First and second order analysis methods were employed to analyze parameter uncertainty in subsurface drainage design. It was found that conventional design methods based on a deterministic framework may result in inadequate spacing due to the uncertainty involved. Uncertainty may be incorporated into practical design by using the simple equations and graphs presented in this research; the procedure was illustrated through an example. Conclusions were drawn from the present study and recommendations were made for future research. / Applied Science, Faculty of / Graduate