An accurate determination of evaporative fluxes is critical for efficient water management in semi-arid climates such as in the Canadian Prairies. The main achievements of this research are the design and operation of a bench-scale atmosphere simulator, performance evaluation using selected weather scenarios pertaining to regional atmospheric conditions, validation using established empirical correlations, and estimation of evaporation rates and the amount for a typical local water body. Results indicate that the measured data achieved the target values for the various parameters and the data were found to be stable during the 3-h test duration. The vapour flux was found to have large variation during summer (0.120 g∙s−1∙m−2 during the day and 0.047 g∙s−1∙m−2 at night), low variation during spring (0.116 g∙s−1∙m−2 during the day and 0.062 g∙s−1∙m−2 at night), and negligible change during fall (0.100 g∙s−1∙m−2 during the day and 0.076 g∙s−1∙m−2 at night). The measured vapour flux was generally within one standard deviation of the equality line when compared with that predicted by both the mass-transfer equations and the combination equations. The average evaporation ranged from 4 mm∙d−1 to 8 mm∙d−1 during the day and decreased to 1 mm∙d−1 to 3 mm∙d−1 at night. The 24-h evaporation was found to be 8 ± 1 mm∙d−1 from late April through late October. Likewise, the cumulative annual evaporation was found to be 1781 mm, of which 82% occurs during the day and 18% at night.
An assessment of evaporation losses from soils is critical for sustainable agriculture in semi-arid regions. The purpose of this research was to determine the effect of desaturation and shrinkage on evaporative flux from representative soils. Results indicated that the surface area did not change for silty sand (6% volume reduction) and substantially increased for lean clay (17% volume reduction). The evaporative flux for silty sand decreased from 31 to 25 mg/m2∙s in Stage II, remained constant during Stage III, and decreased to 11 mg/m2∙s in Stage IV. In contrast, the lean clay showed a longer Stage II (34 to 14 mg/m2∙s), a near constant Stage III, albeit a similar Stage IV (13 to 3 mg/m2∙s). The air entry and residual suction values were 1 kPa and 100 kPa for silty sand and 5 kPa and 1400 kPa for lean clay. In both soils, the total suction merged with the matric suction at Stage II–Stage III boundary. Furthermore, the shrinkage curve was J-shaped for silty sand with the only void ratio decrease in Stage II, whereas that for the lean clay showed a significant void ratio decrease in Stage II, marginal decrease in Stage III, and no decrease in Stage IV. Under high demand, the silty sand exhibited Stage III and Stage IV evaporation, whereas the lean clay also showed significant flux during Stage II. For the investigated range of water content, the total water loss under high demand was found to be 7 times that under low demand.
Evaporation from fresh water and saline water is critical for the estimation of water budget in the Canadian Prairies. Predictive models using empirical field-based data are subject to significant errors and uncertainty. Therefore, highly controlled test conditions and accurately measured experimental data are required to understand the relationship between atmospheric variables at water surfaces. This paper provides a comprehensive dataset generated for the determination of evaporative flux from distilled water and saturated brine using the bench-scale atmospheric simulator (BAS) and the subsequently improved design (BAS2). Analyses of the weather scenarios from atmospheric parameters and evaporative flux from the experimental data are provided.
Saline conditions govern soil behavior during evaporation, thereby affecting the water budget in semi-arid regions. This research examined the effects of saline pore fluid on soil behavior during evaporation. The results indicated volumetric reductions of about 5% for silty sand and about 15% for lean clay. The evaporative flux for silty sand decreased from 26 mg/m2∙s to 22 mg/m2∙s in StageII, remained at a constant flux in StageIII, and decreased to 13 mg/m2∙s in StageIV. The air entry and residual suction values were found to be 5 kPa and 100 kPa, respectively, and the total suction of about 5000 kPa merged with matric suction near the Stage II/Stage III boundary. The swell–shrink curve (SSC) was J-shaped with the only void ratio decrease in Stage II. In contrast, the evaporative flux for lean clay decreased from 30 mg/m2∙s to 15 mg/m2∙s in StageII, to 10 mg/m2∙s in StageIII, and then to 5 mg/m2∙s in StageIV. The air entry and residual suction values were 5 kPa and 2000 kPa, respectively, and the total suction during Stage II and Stage III ranged from 1000 kPa to 6000 kPa, with an average value of 3500 kPa. The SSC showed a major void ratio decrease in Stage II, marginal decrease in Stage III, and no decrease in Stage IV. Under high demand, the evaporative flux for silty sand was constant at 180 mg/m2∙s in StageIII and decreased to 50 mg/m2∙s in Stage IV, whereas it decreased for the lean clay from 230 mg/m2∙s to 145 mg/m2∙s in StageII, to 95 mg/m2∙s in StageIII, and then to 25 mg/m2∙s in StageIV. For both soils, the total water loss was found to be six times higher than that under low demand.
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