Evaporation of Water With Emphasis on Applications and Measurements

Frank E. Jones

• Publisher: CRC Press
• Year: 2018
• Print ISBN: 9781315892863
• eBook ISBN: 9781351088862
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Environmental Science
• Index: Biological Sciences

The loss of water from lakes, rivers, oceans, vegetation, and the earth, as well as man-made structures such as reservoirs and irrigation conduits, is a major concern of hydrologists and irrigation specialists. This loss, compounded by the lack of usable water in some areas, indicates a need for field and laboratory research that will contribute to the understanding of the processes and parameters that comprise and contribute to evaporation.This book emphasizes the process of the air-water interface and discusses such important topics as evaporation and condensation coefficients of water, heat and mass transfer, surface temperature, interfacial tension, convection, diffusion, thermal gradients, wind-generated waves, and the roles that these processes play in evaporation. The book also discusses subjects such as methods for suppressing evaporation using films, water vapor distribution, wind tunnel investigations, evaporation from water drops, preparation of pure water, molecular diffusion, the eddy-correlation method, and evaporation estimation methods. The book will be of considerable value to hydrologists, irrigation specialists, meteorologists, civil engineers, chemical engineers, hydraulic engineers, water resources specialists, water conservation specialists, geophysicists, environmental engineers, and anyone interested in understanding the evaporation of water and its consequences.

CHAPTER 1

Introduction

Water is the most abundant¹ and one of the most complex of known compounds on the surface of the earth.

The volume of the oceans is 1.32 × 10¹⁸ m³, 3.49 × 10²⁰ gal, or 1.07 × 10¹⁵ ac-ft (1 m³ = 264.2 gal, 1 ac-ft = 3.259 × 10⁵ gal = 1234 m³).² The volume of the freshwater lakes is 1.25 × 10¹⁴ m³, 3.30 × 10¹⁶ gal, or 1.01 × 10¹¹ ac-ft. The volume of the saline lakes and inland seas in 1.04 × 10¹⁴ m³, 2.75 × 10¹⁶ gal, or 8.43 × 10¹⁰ ac-ft. The volume of the rivers (average instantaneous volume) is 1.25 × 10¹² m³, 3.30 × 10¹⁴ gal, or 1.01 × 10⁹ ac-ft. The volume of the soil moisture and vadose zone is 6.7 × 10¹³ m³, 1.77 × 10¹⁶ gal, or 5.43 × 10¹⁰ ac-ft. The vadose zone is the unsaturated zone above the water table.

The annual precipitation on the ocean and land areas of the earth is 4.20 × 10¹⁴ m³, 1.11 × 10¹⁷ gal, or 3.40 × 10¹¹ ac-ft. The annual evaporation from ocean and land areas is the same as the annual precipitation.

Evaporation of water is a major factor in hydrologic systems. In general, an understanding of hydrologic systems requires an understanding of evaporation. There are many examples of the need for such understanding; several of these are mentioned here.

Less than 0.027% of the total amount of water distributed over the earth is fresh and immediately available.³ The steadily increasing need for water requires an adequate knowledge of water management and the water balance. An important term in this balance is the evaporative loss of water from a free-water surface, from soil surfaces, or by evapotranspiration of crops.⁴ Evapotranspiration can be defined as the loss of water from soil and plant surfaces.⁵ The word evapotranspiration is often used when it is not possible to separate evaporation and plant transpiration. Consistent measurement of evaporation is crucial to utilization of evaporation data for water management.⁶ A knowledge of the magnitude and variation of evaporative losses is required for the design and management of many hydrologic systems.⁷

The most economical means of providing additional usable water supplies is the conservation of water contained in existing storage facilities.⁸ Evaporative losses from such storage facilities can be relatively great. For example, measurements have shown that 15.6 million ac-ft of water is lost from storage impoundments in the 17 western states of the United States each year.⁹ This loss is equivalent to the disappearance of all the usable stored water in California (in 1965).

Since much of the available supply of water is stored in reservoirs, emphasis has been placed on preserving this water for future use. One approach to attempting to conserve water stored in reservoirs has been the application of a monolayer to the water surface to reduce evaporation.¹⁰

Evaporation is important in determining the water balance of watersheds, allowing prediction and estimation of runoff and groundwater recharge. Evaporation from soils is an important factor in managing both irrigated and dryland farming operations.¹¹

Agricultural irrigation is the largest consumptive use of water in the United States. The total withdrawal of water for irrigation in the United States in 1980 was 170 million ac-ft, of which 40% was groundwater. This was 81% of all the withdrawn water used consumptively.¹² There are about 60 million irrigated acres in the United States and about 500 million irrigated acres in the rest of the world.¹³ In Arizona and California, about 85% of the total water use is for crop irrigation. Most of the irrigation systems are surface or gravity systems, which typically have efficiencies of 60 to 70%.¹⁴ Measurement of evapotranspiration is necessary to obtain engineering data on the time pattern of water use by crops and for irrigation criteria.¹⁵ Estimates of evapotranspiration are used extensively in assessing the irrigation water-management efficiency of existing projects.¹⁶ The meteorological variables which characterize the different seasons of the year produce large changes in the rate of evaporation from exposed surfaces after irrigation.¹⁷

A weighing lysimeter has been used as a feedback irrigation controller to measure crop evapotranspiration and simultaneously schedule irrigations for the lysimeter and three drip irrigation systems in a surrounding experimental field.¹⁸ Pan evaporation measurements are useful in water use projections, such as forecasts of irrigation water demand for crops, estimates of losses from percolation ponds used for groundwater recharge, and the design of ponds for concentrating brines and effluents from waste disposal facilities.¹⁹

Quantitative forecasting (both hydrologic and meteorologic), the radar measurement of rainfall, the planning of water supplies for sprinkler irrigation, and many other related problems may require a knowledge of water lost by evaporation of water drops. These drops may be falling raindrops, spray from sprinklers or breaking waves, and raindrops falling on vegetation.²⁰ A model for accurate prediction and separation of the losses due to evaporation and wind drift under varying climatic conditions would be of considerable value to designers of sprinkler systems.²¹

Attempts have been made to stabilize aqueous fogs and atmospheric mists using monolayers.^22,23 Retardation of water fog evaporation could be used in diverse applications including blanketing of frost-threatened crops with a radiative barrier and military optical screening.²⁴

The possibility of evaporating water at lower temperatures to reduce scaling and corrosion problems has been explored.²⁵ In problems of practical importance, such as liquid film cooling, drying of solids, and evaporation of water from large reservoirs, simultaneous heat and mass transfer between gas-liquid phases is present.²⁶ Heat exchange at the air-water interface is of increasing importance in the abatement of thermal pollution, design of cooling ponds, and in modeling temperature as an important element of water quality.²⁷

Studies of the effect of salinity and ionic composition on evaporation can be applied in many engineering applications including water balance calculations for saline lakes, salt production ponds, and evaporation ponds used for disposal of saline effluents.²⁸

The evaporation of water from vegetated surfaces is one of the less understood aspects of the hydrologic cycle.²⁹

References

1. Eisenberg, D., and W. Kauzmann. The Structure and Properties of Water (New York: Oxford University Press, 1969), p. v.

2. van der Leeden, F., F. L. Troise, and D. K. Todd. The Water Encyclopedia (Chelsea, MI: Lewis Publishers, Inc., 1990), 2nd ed., p. 58 (Source: Mace, U. S. Geological Survey, 1967).

3. Franks, F., Ed. Water, A Comprehensive Treatise, Vol. 1, (New York: Plenum Publishing Corporation, 1972), p. 2.

4. Bloeman, G. W. “A High-Accuracy Recording Pan-Evaporimeter and Some of its Possibilities,” J. Hydrology 39:159–173 (1978).

5. Jackson, R. D., “Evaluating Evapotranspiration at Local and Regional Scales,” Proc. IEEE 73:1086–1096 (1985).

6. Gunderson, L. H. “Accounting for Discrepancies in Pan Evaporation Calculations,” Water Resour. Bull. 25:573–579 (1989).

7. Warnaka, K., and L. Pochop. “Analyses of Equations for Free Water Evaporation Estimates,” J. Geophys. Res. 93:979–984 (1988).

8. Cooley, K. R. “Evaporation Suppression for Conserving Water Supplies,” in Proceedings of the Water Harvesting Symposium, U.S. Department of Agriculture, Agricultural Research Service, February 1975, 192–200.

9. La Mer, V. K., and T. W. Healy. “Evaporation of Water: Its Retardation by Monolayers,” Science 148:36–42 (1965).

10. Bartholic, J. F., J. R. Runkles, and Ε. B. Stenmark. “Effects of a Monolayer on Reservoir Temperature and Evaporation,” Water Resour. Res. 3:173–179 (1967).

11. Idso, S. B., R. D. Jackson, and R. J. Reginato. “Estimating Evaporation: A Technique Adaptable to Remote Sensing,” Science 189:991–992 (1975).

12. Bouwer, H. “Water Conservation in Agricultural and Natural Systems,” in Proceedings of the Conference on Water for the 21st Century (Southern Methodist University), 7:414–423 (1984).

13. Bouwer, H. “Effect of Irrigated Agriculture on Groundwater,” J. Irrig. Drain. Eng. 113:...

Table of contents

• Cover
• Title Page
• Copyright Page
• Dedication
• Preface
• The Author
• Table of Contents
• Chapter 1 Introduction
• Chapter 2 Transport of Water Across the Interracial Region
• Chapter 3 Evaporation and Condensation Coefficients
• Chapter 4 Evaporation from Water Drops
• Chapter 5 Surface Tension, Convection, and Interfacial Waves
• Chapter 6 Surface Temperature, Temperature Differences between Surface and Bulk, Temperature Gradients, and Humidity Gradients above a Water Surface
• Chapter 7 Wind Tunnel Investigations of Evaporation
• Chapter 8 Monomolecular Films
• Chapter 9 Equations Used to Calculate Evaporation Rate and Evapotranspiration
• Chapter 10 Evaporation Pans
• Chapter 11 Lysimetry
• Chapter 12 Evaporation Reduction by Various Means
• Index