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Lysimeters: Data Acquisition and Analysis

by Randy R. Kirkham, Pacific Northwest Lab, Richland, United States,
Mark L. Rockhold, Pacific Northwest Lab, Richland, United States,
Glendon W. Gee, Pacific Northwest Lab, Richland, United States,
Mike J. Fayer, Pacific Northwest Lab, Richland, United States,
Melvin D. Campbell, Pacific Northwest Lab, Richland, United States,
Leo J. Fritschen, Pacific Northwest Lab, Richland, United States,



Document Type: Proceeding Paper

Part of: Grouting in Geotechnical Engineering

Abstract:

Lysimeters provide the most direct method for measuring evapotranspiration (ET). For ten years we have used weighing lysimeters capable of a resolution equivalent to 0.02 mm of water. However, in semi-arid climates where sparse canopies exist, representing the natural system using lysimeters is difficult. Lysimeter construction and materials may change the micro-environment and disturb the surrounding environment. In addition, long-term data collection is susceptible to 1) failures of data acquisition systems and 2) errant data caused by mechanical binding or freezing, and surface effects such as erosion, animal trespass, and external measurements (e.g., neutron probe). To remedy these problems data acquisition and management have been automated using commercially available software; graphic summary reports and simple rule-based programs are used to notify staff of errant data. Automation of data analysis to near real-time allows researchers to operate several lysimeter facilities on a minimal maintenance schedule without significant loss in data integrity. Data analysis programs compare each hour's measurement with pre- or post- measurement hours, with replicates, and with similar treatments. Examples of rule-based equations useful for checking lysimeter measurements are presented. A simple equation predicting ET independently of lysimetry is needed for comparison in data analysis programs. An example of an aerodynamic calculation of sensible heat flux coupled with the energy budget equation for estimating ET is presented.

Subject Headings: Measuring instruments | Data collection | Data analysis | Hydrologic data | Evapotranspiration | Arid lands | Water resources

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