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    Call number: AWI G4-22-94986
    Description / Table of Contents: Hydrological processes occurring within the vadose zone, especially in heterogeneous soils and tills typical of the Canadian shield, are not well understood. This research investigates the importance of the vadose zone in a small headwater basin (Harp 4-21) in the Canadian shield with respect to the generation of stream runoff quantity and quality during episodic rainfall and snowmelt events. The study focused specifically on: firstly the effect of variable antecedent moisture conditions on water-table and stream response, secondly, the significance of the stored vadose water in water extracted from a rising water-table, and thirdly the significance of preferential flowpathways in the vadose zone as a means of rapidly rotating, stored vadose water to the stream during runoff events. The instrumentation of the Harp 4-21 basin includes three v-notch weirs along the stream, numerous piezometers and wells, several soil lysimeters, and three tensiometer nests. Much of the data used in this study was obtained from five sites located along a hillslope transect. Soil water content at each of the hillslope sites was accurately determined using time domain reflectometry (TDR), whereas water table elevations were measured using both electronic water level tapes and calibrated rod floats. Preferential flowpath data was derived from flow gauging and chemical analyses of water samples. Results obtained from the near-stream and lower slope reaches of the hillslope transect indicated that soil water content in the vadose zone is maintained at a high level of saturation by shallow water-table depths. Further analysis of simultaneously measured soil water content and depth to water—table data clearly showed that the existence of a thick essentially saturated zone overlying the water table (capillary fringe) was responsible for the large and rapid water-table responses observed during many of the nine studied precipitation events. On a basin scale, the seasonal variability of the area in which the capillary fringe extended to the ground surface was largely responsible for the observed trend in basin yield (runoff volume/ rainfall volume) for the nine runoff events. Chemical tracing results using silica, pH and DOC showed that the large vadose water reservoir in the near-stream and lower slope areas was a dominant component in water extracted from a rising water-table during most precipitation events. Silica results from the near-stream vadose zone showed that only the massive groundwater recharge associated with spring snowmelt could completely replace the vadose water reservoir with shorter residence time snowmelt/rainfall water. The rapid routing of stored near-stream capillary fringe vadose water through preferential pathways (macropores, soil pipes) was a significant source of runoff to the stream during runoff events. The presence of soil pipes, along with the significant vadose water reservoir in near-stream and lower slope areas are sufficient to explain the large phreatic/vadose water component typically identified in two component flow separation models, and constitutes the basis of a physically-based conceptual runoff model for the Harp 4-21 basin.
    Type of Medium: Dissertations
    Pages: 172 Seiten , Illustrationen
    Language: English
    Note: Masterarbeit, Wilfrid Laurier University, Waterloo, 1992 , Table of Contents Abstract Acknowledgements List of Figures List of Tables Chapter 1 Introduction and Literature Review 1.1 introduction 1.2 Research objectives 1.3 Literature review 1.3.1 Overland flow 1.3.2 Overland flow from partial areas 1.3.3 Subsurface stormflow 1.3.4 The variable source area subsurface stormtlow concept 1.3.5 Groundwater and the capillary fringe effect 1.3.6 Preferential flow 1.3.6.1 Macropore flow 1.3.6.2 Unstable flow 1.4 Summary of uncertainties in the vadose zone Chapter 2 Methodology 2.1 Introduction 2.2 The Harp 4-21 basin: site description 2.2.1 Basin topography 2.2.2 Bedrock and surficial geology 2.2.3 Vegetation 2.2.4 General hydrology 2.3 Basin instrumentatio 2.3.1 Stream 2.3.2 Phreatic zone 2.3.3 Vadose zone 2.3.3.1 Soil moisture 2.3.3.2 Preferential flowpaths 2.4 Hillslope transect instrumentation 2.4.1 The hillslope transect 2.4.2 Time domain reflectometry 2.4.3 Vadose water extraction 2.5 Sampling techniques, frequency and chemical analyses 2.5.1 Precipitation 2.5.2 Stream 2.5.3 Phreatic zone 2.5.4 Vadose zone 2.5.4.1 Soil moisture measurement and analysis of the TDR trace 2.5.4.2 Vadose water sampling 2.5.5 Chemical analysis Chapter 3 Results and Discussion: Antecedent Moisture Conditions 3.1 Introduction 3.2 Runoff events ~ampled during the May 1990 - April 1991 field season 3.3 Assessment of antecedent moisture conditions in the Harp 4-21 basin 3.3.1 Seasonal basin yield 3.3.2 Seasonal depth to water-table 3.3.3 Tensiometric data 3.3.4 Soil moisture conditions in the hillslope transect (Time Domain Reflectometry) 3.3.4.1 Soil water content/depth to water-table relationship 3.3.4.2 Estimation of the capillary fringe thickness and the temporal variation of basin area in which it extends to the ground surface 3.4 Assessment of the origin of water in the vadose zone of near-stream and lower slope areas which experience significant water-table responses during runoff generating events 3.4.1 Introduction 3.4.2 Near-stream 07 piezometer nest 3.4.3 Lower slope TD4 mini-piezometer nest Chapter 4 Preferential flowpathways: Results and discussion 4.1. Discharge contributions to streamflow during runoff events 4.2. Assessment of the origin of water emmitted from the soil pipes during runoff events Chapter 5 Conclusions References Appendix I Appendix II Appendix Ill Appendix IV Appendix V , Englisch
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