Date of Award

1995

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Civil and Environmental Engineering

First Advisor

Sklash, Michael,

Keywords

Hydrology.

Rights

CC BY-NC-ND 4.0

Abstract

The main objective of this study was to assess old and subsurface water contributions to storm runoff generation in flat, fractured, clayey terrain with integrated tracer studies and field measurements. This study was conducted at Agriculture Canada's Whelan Experimental Farm near Woodslee, Ontario between June 1992 and August 1993. The study area (0.64 km$\sp2)$ is flat and the soil is clayey and fractured. Surface water contamination by herbicides and nitrates from cropping practices has increased in the Great Lakes basin including this study area. By investigating surface and subsurface runoff generation processes and amount generated during individual storm events, this study was aimed to provide a better understanding of transport processes in the study area. Eleven storm events were investigated during this study. Water samples were collected from the drainage ditch, groundwater monitoring wells, subsurface collection pits, tile drains and surface runoff collecting systems. Isotopic (oxygen-18 "$\sp{18}O'')$ and chemical (electrical conductivity "EC", chloride "Cl$\sp-''$ and dissolved silica "SiO$\sb2'')$ parameters were utilized in a two-component mixing model or the trial-error separating method developed in this study to determine relative contributions of old and new water, or subsurface and surface water during individual storm events. The magnitude of these contributions were compared to the physical flow measurements from two experimental plots. Chemical hydrograph separation results indicate that the subsurface water contributions were between 16-72% of the peak discharge and between 35-95% of the total runoff volume. Isotopic hydrograph separation results indicate that the old water contributions were up to 65% of the peak discharge and between 19-76% of the total runoff volume. These separation results are generally consistent with the physical flow measurements from two experimental plots (subsurface water contributions between 11-58% of the peak discharge and between 36-97% of the total runoff volume). The overall conclusion of this study is that subsurface/old water is an important contributor to storm runoff generation in this study area characterized by flat, fractured clayey terrain. compared with the separation results reported in the literature, the subsurface/old water contributions in this study area, however, are relatively small. This is due to the geologic and topographic differences existed between this study area and the study areas reported in the literature (hilly terrains with permeable soils). The degree of contribution of subsurface/old water in this study area largely depends on the integrated effect of antecedent moisture condition, rainfall amount and intensity, and tile drainage system. The natural tracers used in this study are effective. However, non-conservative behaviour of SiO$\sb2$ and wash-off effect for EC and Cl$\sp-$ were observed. The $\sp{18}$O content of new water varied significantly during individual storm events. Direct use of bulk rainfall $\sp{18}$O content as new water input would result in incorrect interpretations of old/new water contribution to storm runoff (old water contribution being $$100%). The trial-error separating method was developed in this study to consider the significant variation in isotopic inputs and successfully separated hydrographs for events in which the two-component mixing model failed.Dept. of Civil and Environmental Engineering. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1994 .H820. Source: Dissertation Abstracts International, Volume: 56-11, Section: B, page: 6004. Co-Advisers: Michael Sklash; Nihar Biswas. Thesis (Ph.D.)--University of Windsor (Canada), 1995.

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