UCD Drag Plate Lysimeter—Momentum and Mass Transfers

by W. O. Pruitt, Univ of California, Davis, United States,
F. J. Lourence, Univ of California, Davis, United States,
C. B. Tanner, Univ of California, Davis, United States,
P. Lal, Univ of California, Davis, United States,

Document Type: Proceeding Paper

Part of: Lysimeters for Evapotranspiration and Environmental Measurements


The second large (6.1 m dia., 0.97 m deep) lysimeter built at the University of California, Davis (UCD) was largely the brainchild of Dr. F.A. Brooks, the initial Project leader of a U.S. Army sponsored 10-year study of energy and mass transfers above vegetative surfaces. This unit in the 1960's was unique in the world. Although a number of earlier studies had employed surface drag plates, all had involved very small sample sizes, e.g., less than 1 square meter in area, and none had more than a few inches of soil, precluding any chance of obtaining truly field-representative evapotranspiration (ET), or even surface drag (TAU) for anything other than bare soil or short grass. Covered in this paper are descriptions of design, operation and calibration for this 45 metric ton floating drag-plate lysimeter for measurement of both ET, and TAU. Also covered are analyses of data collected by research groups of the UCD and of the University of Wisconsin (UW) during a major Army-sponsored Cooperative Field Study at Davis. Presented are comparisons of (TAU) and heat transfer (H) measurements of the two groups. The (UW) data were from three pressure sphere and fast thermometer systems (P.S.A.T.). Measurements of TAU were in good agreement except for some periods of very light wind and when widely varying wind directions were involved. Agreement was marginal for the P.S.A.T. data for H and the (UCD) values of H based on the Bowen ratio method. Both (UCD) and (UW) data including (UCD) wind, temperature and humidity profiles, are then used to develop Monin-Obukhov φm data for comparing with φm(z/L) and φm(Ri) published relationships. The analogous functions for water vapor and heat transfer were also investigated. Although the results will be reported on at the meeting if time permits, they will have to be included in a later paper.

Subject Headings: Measuring instruments | Mass transfer | Evapotranspiration | Plates | Case studies | Heat transfer | Wind engineering | Water resources

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