The spatial distribution of local evaporation from ground-based sources behind solid and porous windbreaks was studied in laboratory models for steady state and intermittent flows. Field observations of wind and turbulence characteristics (turbulence intensity, power spectra and integral length scale L) over surfaces whose zero displacement (d) and roughness length (z$ sb0$) had also been determined, were used to scale the laboratory simulations. Scaling parameters were z/z$ sb0$, $ sigma$/U, L/z$ sb0$ and Uz$ sb{0}$/K, where z, U, $ sigma$ and K are height, wind speed, standard deviation of velocity fluctuations and turbulent diffusivity, respectively. The 50% porosity barrier was found to be the most effective single-barrier set-up for the reduction of moisture loss. / Conditional sampling of fluctuations w' and q' of the wind and moisture, respectively, with sonic anemometer and fast-response Krypton hygrometer behind solid and porous windbreaks in the field, revealed frequency of occurrence, duration and intensity of those turbulent structures primarily responsible for moisture transfer.

The purpose of this work was to investigate the evaporation rates of various brines and to compare them to the evaporation rates of pure water under the same environmental conditions in the laboratory. NaCl, MgCl 2 and KCl were the salts used in the experiments, at three densities. Mixtures of the salts were also used. One set of experiments was conducted under free convection while the other was conducted under forced convection, both over pans. Temperature was relatively constant for the experiments but relative humidity was not controlled. Wind profiles were measured during the forced convection experiments and an aerodynamic equation used to calculate evaporation for comparison with the observed evaporation rates. Surface temperatures were also measured. Water activities of all the brine and brine mixtures were also measured and compared to predictions by Raoult's law. In general, it was found the evaporation rate of brines was lower than that of pure water and that the water activities and evaporation rates were density-dependent to a certain extent. More precisely, they were dependent on the actual constituents in the brine due to the different molecular weights, and the number of ions dissolving from a given weight of salt or salt mixture. Evaporation rates can better be estimated on this basis than on the basis of density alone, as one would expect from Raoult's Law.

Thesis (Ph. D - Soil, Water abd Environmental Science) - University of Arizona. / Includes bibliographical references.

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Three goals of this research were: 1) to develop a field-scale research facility that could be used for conducting a variety of soil water experiments in both deep (greater than 2 meters) and near-surface soils where the soil water balance could be accurately determined; 2) to develop a transient experimental technique for calibrating time domain reflectometry (TDR) probes; and 3) to study the use of vertically-installed TDR probes for measuring near-surface soil water movement in a field setting, and to compare these measurements with those made by the weighing lysimeter. The weighing lysimeter facility consists of two lysimeter tanks, 4.0 m deep and 2.5 m in diameter, which rest atop a scale with a resolution of ±200 g, equivalent to ±0.04 mm of water on the surface. Data collection is completely automated with a data logger and personal computer. Both lysimeters are instrumented with TDR probes, tensiometers, and pore water solution samplers; thermocouples are installed in one lysimeter for measuring temperature. The TDR probes were calibrated using a transient method known as upward infiltration. The method is rapid, allows the soil to remain unchanged during the experiment, and provides many data points. The upward infiltration method was tested using two different length probes in soils of three textures. Results show that the upward infiltration method is stable, repeatable, and provides accurate dielectric constants and calibration curves. Four, vertically-installed TDR probes of different lengths (200, 400, 600, and 800 mm) were placed in the lysimeter at ground surface to measure water added and water lost during a one-month period in the presence of daily irrigated turfgrass. The purpose of this study was to compare changes in soil water storage as measured by the TDR system, against measurements made using the weighing lysimeter. The TDR probes detected diurnal changes in water content due to irrigation and evapotranspiration, even when these amounts changed slightly from day to day. The TDR probes underestimated the measurements of both water added and water loss, as confirmed using measurements from the weighing lysimeter. The presence of a 47-mm thick biomass above the TDR waveguides retained water that otherwise would have percolated the soil surface into the measurement domain of the probes. Addition and loss of water in the biomass were recorded by the lysimeter, but not by the TDR probes, thus explaining the underestimation. Modeling of near-surface water movement with the HYDRUS model showed very similar water movement behavior as measured by the TDR probes. This confirms our hypothesis that TDR would a useful tool for measuring diurnal changes in water content for irrigation scheduling.

Research Project Technical Completion Report (A-109-Ariz.) For: United States Department of the Interior, Project Dates: 1981-1983, September 1, 1983. / The Research on which this project is based was financed in part by the U.S. Department of the Interior, as authorized by the Water Research and Development Act of 1978 (P.L. 95-467) / A liquid level interferometer has been built to measure changes in water level to an accuracy of /8. A novel magnetic suspension is used to position the floating retroreflector of a laser interferometer. Direction sensing is achieved by dual optical channels phased near quadrature by means of an absorbing beamsplitter. The interferometer (laser) has been used to measure very accurately the drop in water level of a lined reservoir. The drop in water level thus provides a precise method of measuring evaporation. It was found that this drop in water level essentially ceased when the relative humidity approached very closely or equaled 100 percent during early morning calm periods. This provides a method of determination of seepage loss. In an unlined reservoir during calm periods when the relative humidity is 100 percent any remaining drop in water level is due to seepage. The laser can measure this rate.

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