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Design documents are a series of technical papers addressing specific design topics on the eastern Snake River Plain Aquifer Model upgrade. Each design document will contain the following information: topic of the design document, how that topic fits into the whole project, which design alternatives were considered and which design alternative is proposed. In draft form, design documents are used to present proposed designs to reviewers. Reviewers are encouraged to submit suggested alternatives and comments to the design document. Reviewers include all members of the Eastern Snake Hydrologic Modeling (ESHM) Committee as well as selected experts outside of the committee. The design document author will consider all suggestions from reviewers, update the draft design document, and submit the design document to the SRPAM Model Upgrade Program Manager. The Program Manager will make a final decision regarding the technical design of the described component. The author will modify the design document and publish the document in its final form in .pdf format on the SRPAM Model Upgrade web site. Final model documentation will include all of the design documents, edited to ensure that the "as-built" condition is appropriately represented. In the Eastern Snake Plain Model Enhancement Project, the basic equation for calculating net recharge from irrigated agriculture is: (1) Net Recharge = (Field Delivery + Precipitation) – Evapotranspiration (ET) (2) Where Field Delivery = (Surface Water Diversions – Returns – Canal Leakage). The base ET in equation (1) will be calculated as described in Design Document DDW-010. When the water source is ground water, surface water diversions are zero and the calculated net recharge is negative (net withdrawal). These are commonly used and accepted methods (Burt 1999) and are the methods used by the US Geological Survey (Garabedian 1992) and Idaho Department of Water Resources (1997) in previous Snake Plain modeling efforts. In the recharge tools of the model enhancement project, ET is expressed first as a depth, then multiplied by irrigated area within each model cell to obtain a volume of ET. Various conditions have the potential to alter the actual field ET depth from the wellwatered- disease-free condition represented by typical planning ET calculations and tables. The actual consumptive use depth may also be different than calculated ET if there are consumptive fates for diverted water other than those contemplated by equations (1) and (2). Finally, the actual volume of ET calculated can be affected by bias in the data used for irrigated area within each model cell. If these differences can be identified and quantified, an ET adjustment factor may be applied to correct the calculation of net recharge: (3) Net Recharge = (Field Delivery + Precipitation) – (ET x Adjustment). The recharge tools allow for two ET adjustment factors per ground-water entity or surfacewater polygon, one for sprinkler application and one for gravity application. These potentially could be adjusted by the PEST software during parameter estimation. This Design Document explores the conceptual basis for ET adjustment factors and describes the proposed approach to calculate these factors.

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Title:
Evapotranspiration adjustment factors. Draft. Design document number DDW-021
Authors:
Contor, Bryce A.
Date Created (ISO Standard):
2003-05-19
Description:
Design documents are a series of technical papers addressing specific design topics on the eastern Snake River Plain Aquifer Model upgrade. Each design document will contain the following information: topic of the design document, how that topic fits into the whole project, which design alternatives were considered and which design alternative is proposed. In draft form, design documents are used to present proposed designs to reviewers. Reviewers are encouraged to submit suggested alternatives and comments to the design document. Reviewers include all members of the Eastern Snake Hydrologic Modeling (ESHM) Committee as well as selected experts outside of the committee. The design document author will consider all suggestions from reviewers, update the draft design document, and submit the design document to the SRPAM Model Upgrade Program Manager. The Program Manager will make a final decision regarding the technical design of the described component. The author will modify the design document and publish the document in its final form in .pdf format on the SRPAM Model Upgrade web site. Final model documentation will include all of the design documents, edited to ensure that the "as-built" condition is appropriately represented. In the Eastern Snake Plain Model Enhancement Project, the basic equation for calculating net recharge from irrigated agriculture is: (1) Net Recharge = (Field Delivery + Precipitation) – Evapotranspiration (ET) (2) Where Field Delivery = (Surface Water Diversions – Returns – Canal Leakage). The base ET in equation (1) will be calculated as described in Design Document DDW-010. When the water source is ground water, surface water diversions are zero and the calculated net recharge is negative (net withdrawal). These are commonly used and accepted methods (Burt 1999) and are the methods used by the US Geological Survey (Garabedian 1992) and Idaho Department of Water Resources (1997) in previous Snake Plain modeling efforts. In the recharge tools of the model enhancement project, ET is expressed first as a depth, then multiplied by irrigated area within each model cell to obtain a volume of ET. Various conditions have the potential to alter the actual field ET depth from the wellwatered- disease-free condition represented by typical planning ET calculations and tables. The actual consumptive use depth may also be different than calculated ET if there are consumptive fates for diverted water other than those contemplated by equations (1) and (2). Finally, the actual volume of ET calculated can be affected by bias in the data used for irrigated area within each model cell. If these differences can be identified and quantified, an ET adjustment factor may be applied to correct the calculation of net recharge: (3) Net Recharge = (Field Delivery + Precipitation) – (ET x Adjustment). The recharge tools allow for two ET adjustment factors per ground-water entity or surfacewater polygon, one for sprinkler application and one for gravity application. These potentially could be adjusted by the PEST software during parameter estimation. This Design Document explores the conceptual basis for ET adjustment factors and describes the proposed approach to calculate these factors.
Subjects:
Aquifers Computer models Evapotranspiration
Location:
Eastern Snake Plain Aquifer; Southern Idaho
Latitude:
42.96
Longitude:
-115.13
Collection:
Boise Basin
Series:
ESPAM
Rights:
Rights to the digital resource are held by the University of Idaho. http://www.uidaho.edu/
Publisher:
Idaho Water Resources Research Institute; University of Idaho
Contributing Institution:
University of Idaho
Type:
Text
Format:
application/pdf
Cataloger:
KIT

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Preferred Citation:
"Evapotranspiration adjustment factors. Draft. Design document number DDW-021", Idaho Waters Digital Library, University of Idaho Library Digital Collections, https://www.lib.uidaho.edu/digital/iwdl/items/iwdl-ddw021_etadj-1.html
Rights
Rights:
Rights to the digital resource are held by the University of Idaho. http://www.uidaho.edu/
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