In Chapter 1, a numerical computer technique is developed to determine radiation view factors between planar surfaces whose geometry is sufficiently regular so as to be defined by algebraic equations. This technique does not require spherical, cylindrical or rectangular symmetry, although such symmetries may be exploited when they exist. Once the essential geometric problem is formulated, enough generality can be built into the solutions so that certain "new" configurations, derived from translations or rotations of one surface relative to the other, can be solved as a matter of course. In Chapter 2, a model of bare soil evaporation is tested against measured flux from lysimeters obtained in the Peace River region of British Columbia and Alberta. Hydraulic diffusivity characteristics, measured from separate, adjacent field samples, were used in the model. Certain procedural difficulties in the measurement of hydraulic diffusivity are examined in detail, and recommendations for improvement are made. The degree to which evaporation simulation agrees with measured flux is discussed. / Land and Food Systems, Faculty of / Graduate

A new experimental approach to determine the hydraulic characteristics of unsaturated soils using a centrifuge permeameter was developed in this study. Specifically, the centrifuge permeameter is used to determine the water retention curve (WRC), which quantifies the energy required to retain water in the soil pores during wetting and drying, and the hydraulic conductivity function (K-function), which quantifies the soil's change in impedance to water flow as it becomes unsaturated. An aim of this study is the promotion of using experimentally-derived hydraulic characteristics in engineering practice. Accordingly, the goals behind development of the centrifuge permeameter were a reasonable testing time, measurement of all variables relevant to water flow in unsaturated soils, and a methodology allowing straightforward interpretation of experimental data to determine the hydraulic characteristics. Development of the centrifuge permeameter was guided by lessons learned from an evaluation of previous characterization approaches. Specifically, issues such as the use of steady-state or transient water flow, boundary condition effects, and the use of instrumentation were evaluated in conventional tests to better develop the centrifuge permeameter. Steady-state infiltration of water through a soil specimen instrumented with tensiometers to measure matric suction and time domain reflectometry to infer moisture content was found to be the most reliable means of characterization. Steady-state water flow permits straightforward, repeatable interpretation of instrumentation results, boundary conditions, and flow data to determine the hydraulic characteristics. Centrifugation is employed to decrease the time required to reach steady-state water flow through a soil specimen by imposing a centripetal acceleration on the infiltrating water. The water infiltration rate and centripetal acceleration can be independently controlled in the centrifuge permeameter in order to reach different target hydraulic conductivity values. Continuous, in-flight measurement of the variables relevant to hydraulic characterization is possible through an on-board data acquisition system. The experimental component of this study is focused on validation of the centrifuge permeameter and verification of the hydraulic characteristics obtained using this approach. Simultaneous determination of the WRC and K-function for a clay of low plasticity was found to be possible in less than a week using the centrifuge permeameter, whereas several months were required in conventional tests. Consistent measurements of hydraulic conductivity were obtained using this approach, and little hysteresis was observed in the hydraulic characteristics. Additional experiments were performed to evaluate the validity of different assumptions required to interpret the experimental data and different issues in centrifuge testing. Two major assumptions required in previous centrifuge permeameter approaches were evaluated using the instrumentation available in the centrifuge permeameter. During steady-state water flow in the centrifuge, the suction and moisture content were found to be relatively uniform along the longitudinal axis of the permeameter, and the outflow boundary was found to have a negligible influence on the suction profile. Settlement under the increased body forces in the centrifuge were found to be negligible for the soil investigated in this study. The hydraulic characteristics were found to be sensitive to the calibration of the transducers and sensors used to infer the water pressure and moisture content during centrifugation. Overall, the expeditious, direct determination of the hydraulic characteristics of unsaturated soils was successfully achieved using centrifuge technology. Accordingly, the centrifuge permeameter approach helps promote the use hydraulic characteristics of unsaturated soils in geotechnical engineering design.

The recent development of the peltier-type thermocouple psychrometer has made possible the measurement of soil moisture potentials to values as low as -80 bars. The applicability of this type of psychrometer to "in situ" measurements of moisture potential at a Sonoran desert field site is investigated. An evaluation is made of the effect of variations in soil temperature, moisture content, and solute concentrations on the psychrometric measurements. Moisture potential measurements with the psychrometer are shown to be limited to a moisture content range composing approximately 50 per cent of the total variation in soil moisture observed during the study. A significant quantity of moisture is transferred across the soilatmosphere interface at moisture contents both above and below the measurement range of the psychrometer. Psychrometric measurements cannot be used to determine the total moisture flux into or out of the soil horizon. The temperature component of the total soil moisture potential is not measurable with the thermocouple psychrometer. Under conditions occurring frequently within the study period, this component is shown to be of equivalent or greater magnitude than the components measured with psychrometric techniques. Laboratory measurements of the sorption-desorption isotherms for the field soils were made using thermocouple psychrometers. The isotherms vary significantly among samples, as a function of soil composition. This variation prevents the determination of absolute values of soil moisture content from measurements of soil moisture potential. However, for the soils at the field site, the slope of the moisture isotherms at a given potential does not vary significantly among samples. Psychrometric measurements can be used to determine moisture content changes at the study site, within the measurement range of the psychrometers. The variation in moisture isotherms, the significance of temperature induced moisture flux, and the limited moisture range of psychrometric measurements prevents the construction of a quantitative model of soil moisture movement from potential measurements made with thermocouple psychrometers. The effect of Celtis pallida (desert hackberry), a native plant species, on the soil moisture regime is described. Moisture uptake by the plant, and precipitation input to the soil near the plant are described in terms of the potential variations they produce. The particular hackberry plant studied is shown to be removing moisture from the soil at potential values as low as -30 atmospheres. Moisture potentials in the root zone were within the measurement range of the psychrometers throughout most of the year. The measurement of soil moisture potentials with the thermocouple psychrometer is shown to be an effective means of studying moisture content variations in the root zone of desert plant species.

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The application of the widely used Penrnan-Monteith evapotranspiration equation to hybrid poplar trees is impossible without a valid surface resistance. The increase in applications of drip-irrigated hybrid poplar trees for wood chip stock and veneer production, as well as bioremediation, constitutes a need for estimating the evapotranspiration of these trees. To the author's knowledge, there are no published estimates of surface resistance for poplar trees. Six years of weekly soil moisture content for drip-irrigated, hybrid poplar trees were used in a water balance to compute evapotranspiration. The weekly data were adjusted with reference evapotranspiration data to compute a daily evapotranspiration. Only data that represent fully leaved hybrid poplars are used in this study and the data were screened for the effects of drainage. Additional parameters applied in this study include solar radiation, temperature, wind speed and relative humidity taken at a nearby AGRIMET Weather Station. The results of this study indicate that surface resistance values cannot be described as a function of meteorological data within the constraints of the current experiment design. The graph of poplar evapotranspiration versus surface resistance shows that for a given evapotranspiration there can be multiple rs values. This scatter is the influence of parameters other than rs within the Penman-Monteith model. The use of an instrument to directly measure the surface resistance is recommended in further studies. / Graduation date: 2000

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Typescript (photocopy). / Digitized by Kansas Correctional Industries