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Reference tool estimates water required for irrigated agriculture


May 2, 2016
By Ground Water Canada

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The American Society of Civil Engineers’ second edition of Evaporation, Evapotranspiration, and Irrigation Requirements: Manuals and Reports on Engineering Practice No. 70, provides a tool for accurately estimating the water quantities needed for crop irrigation based upon the physics of evaporation and evapotranspiration.


This edition, provides engineers and scientists working on water issues with improved and standardized methods to estimate evaporation and ET and to apply and evaluate calculations, the association said in a press release. 

The beginning of MOP 70 covers basic concepts and physical principles, such as evaporation and evapotranspiration (ET) processes, soil-water-plant systems, energy balance, surface energy–air mass interactions, and evaporation from water surfaces.

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The second part on ET from land surfaces explains components of measurement and details on estimation; reference crop ET; evaporation from soil; the crop coefficient method; the Penman-Monteith and energy-balance equations; and regional estimates. The final section discusses estimation of irrigation water requirements (IWR) and streamflow depletions. Thirteen appendixes provide tables of mean and basal crop coefficients and background information on concepts and equations used throughout the manual.

www.asce.org/pubs