Water-loss investigations: Volume 1--Lake Hefner studies technical report

Abstract

STATEMENT OF PROBLEMDevelop an improved method or methods for the determination, and if possible the prediction from climatological and limnological data, of water losses by evaporation using mass-transfer and energy-budget theory. Develop improved techniques for converting evaporation-pan data to estimated lake evaporation. Test the proposed methods and techniques at Lake Hefner, Oklahoma, using evaporation computed from the water budget of the lake as the control. CONCLUSIONS1. The water-budget control met the requirement that errors in the water budget should not exceed 5 per cent of the monthly evaporation. In addition, 62 per cent of the determinations of daily evaporation were sufficiently accurate to provide a* check against estimates of daily evaporation by mass-transfer and energy-budget theories. 2. Only two (O. G. Button's and Sverdrup's 1937 form) of the many mass-transfer equations tested proved adequate for predicting daily evaporation with sufficient accuracy to be generally useful, employing equipment now available. 3. A simple empirical equation was developed from the water-budget data, using wind speeds and vapor-pressure differences measured at Lake Hefner. An operational version of this equation proved satisfactory for computing daily evaporation at Lake Hefner using standard meteorological observations from a nearby weather station, plus the surface-water temperature of the lake. 4. The energy-budget equation proved satisfactory for computing evaporation for periods of 7 days or longer provided the water budget can be approximated closely enough to estimate advected energy. The primary limitation on the accuracy of the method, for short periods of time, is the evaluation of change in energy storage. 5. The Cummings Radiation Integrator (CRI) promises to provide a satisfactory substitute for the expensive radiation-measuring equipment used at Lake Hefner, thus simplifying the computation of evaporation by the energy-budget method. 6. Study of evaporation from four types of evaporation pans confirmed previous studies in showing that pan evaporation is generally higher than lake evaporation and that pan-to-lake coefficients have a pronounced seasonal variation. Annual pan-to-lake coefficients are reasonably consistent with previous values, but further studies of such coefficients under different conditions of climate, lake area, and lake depth will be required for more accurate interpretation of available evaporation-pan records in terms iii CONTENTS pgge 1 INTRODUCTION t PERSONNEL l ACKNOWLEDGMENTS 9 GENERAL DESCRIPTION OF LAKE HEFNER by G. EgrI Hgrbeck, Jr. I Basis for Choice of Lake Hefner Physical and Climatological Characteristics References GEOLOGY AND GROUND-WATER HYDROLOGY OF THE LAKE HEFNER AREA by P. E. Dennis Scope of the Study Geology and Water-Bearing Properties of the Rocks Ground-Water Hydrology Conclusions on Geology and Hydrology References THE WATER-BUDGET CONTROL by G. EgrI Hgrbeck, Jr., and Frgnk W. Kennon Instrumentation and Methods 31 Results Conclusions on the Water Budget...