Abstract
Reliable estimation of evapotranspiration is important for many hydrological applications, including agriculture, climatology, and assessment of stormwater control measures. An automated chamber system was constructed to measure field evapotranspiration. The system consists of six chambers, sampled consecutively by means of a dynamic closed-chamber design, and is fully automated to allow replicable long-term measurements. However, the use of such a system is subject to measurement errors due to vapor adsorption along the sampling tubes and inappropriate internal ventilation. Because these issues are rarely addressed in the literature on flux chambers, a laboratory calibration was performed to estimate errors in evapotranspiration rates measured by the system. The effects of the sampling tube length and air mixing were investigated. A correction factor for evapotranspiration rates relative to the tube length was established. Appropriate air mixing induced by small fans ensured that the measured rates were representative of the internal conditions of the chambers. With appropriate internal ventilation and correction factors, the relative error of measurements was less than 5% for high evapotranspiration rates.
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Acknowledgments
We thank the technical staff of the Civil Engineering department, Frank Winston, Richard Williamson, and Anthony Brosinsky, for their help in building and testing the chamber system. This project was in part funded by the Cities as Water Supply Catchments Program under the CRC for Water Sensitive Cities, with Hamel supported by a scholarship from this program. Fletcher and Beringer are both supported by ARC Future Fellowships (FT100100144 and FT110100602, respectively).
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Published In
Journal of Hydrologic Engineering
Volume 20 • Issue 2 • February 2015
Copyright
© 2014 American Society of Civil Engineers.
History
Received: Aug 30, 2013
Accepted: Apr 2, 2014
Published online: Apr 3, 2014
Discussion open until: Dec 22, 2014
Published in print: Feb 1, 2015
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