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Traditional evapotranspiration calculations. Technical report 04-009. Project scenario document DWS-010 Final as-built Item Info

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. Calculation of net recharge from surface-water irrigation and calculation of net discharge from ground-water irrigation require estimates of crop evapotranspiration (ET). The details of the calculations proposed for the Eastern Snake Plain Aquifer Model Enhancement Project are discussed in Design Document DDW-002. The calculations involve diversion volumes that are large relative to the overall aquifer water budget. The proposed calculations are: (1) Field Delivery = Diversions - Canal Leakage - Return Flows (2) Net Recharge (surface)= (Field Delivery + Precipitation) - (ET x Adjustment Factor) (3) The calculation for net recharge from ground-water irrigation (typically a negative recharge, or net withdrawal) is: Net Recharge (ground) = Precipitation - (ET x Adjustment Factor). 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 former Snake Plain modeling efforts. The ET adjustment factor is an innovation added in this effort to accommodate differences between potential and actual crop conditions. ET adjustment factors are discussed in Design Document DDW-021. Calculation of recharge on irrigated lands will include a consideration of antecedent soil moisture and available irrigation diversions, to allow reduction of ET when water supplies are reduced. This helps avoid under-predicting recharge on surface-water irrigated lands, and avoids over-predicting extraction on ground-water irrigated lands. This paper describes the data sources and methods proposed for determining the basic ET rate for these calculations. Evapotranspiration is controlled by climate as well as crop and soil characteristics. Climate affects the evaporative power of the atmosphere, reflecting the capacity of air to accept evapotranspired water and the energy available to drive evapotranspiration. Soil and plant characteristics control the crop's ability to extract water from the soil, and biological characteristics of the crop that control the transpiration response to evaporative power. Soil texture, surface wetness and condition and shading by crop plants control the soil's evaporation response to evaporative power. Final as-built. Typographic error in title page: DWS-010 should be DDW-010.

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Title:
Traditional evapotranspiration calculations. Technical report 04-009. Project scenario document DWS-010 Final as-built
Authors:
Contor, Bryce A.
Date Created (ISO Standard):
2004-09-02
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. Calculation of net recharge from surface-water irrigation and calculation of net discharge from ground-water irrigation require estimates of crop evapotranspiration (ET). The details of the calculations proposed for the Eastern Snake Plain Aquifer Model Enhancement Project are discussed in Design Document DDW-002. The calculations involve diversion volumes that are large relative to the overall aquifer water budget. The proposed calculations are: (1) Field Delivery = Diversions - Canal Leakage - Return Flows (2) Net Recharge (surface)= (Field Delivery + Precipitation) - (ET x Adjustment Factor) (3) The calculation for net recharge from ground-water irrigation (typically a negative recharge, or net withdrawal) is: Net Recharge (ground) = Precipitation - (ET x Adjustment Factor). 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 former Snake Plain modeling efforts. The ET adjustment factor is an innovation added in this effort to accommodate differences between potential and actual crop conditions. ET adjustment factors are discussed in Design Document DDW-021. Calculation of recharge on irrigated lands will include a consideration of antecedent soil moisture and available irrigation diversions, to allow reduction of ET when water supplies are reduced. This helps avoid under-predicting recharge on surface-water irrigated lands, and avoids over-predicting extraction on ground-water irrigated lands. This paper describes the data sources and methods proposed for determining the basic ET rate for these calculations. Evapotranspiration is controlled by climate as well as crop and soil characteristics. Climate affects the evaporative power of the atmosphere, reflecting the capacity of air to accept evapotranspired water and the energy available to drive evapotranspiration. Soil and plant characteristics control the crop's ability to extract water from the soil, and biological characteristics of the crop that control the transpiration response to evaporative power. Soil texture, surface wetness and condition and shading by crop plants control the soil's evaporation response to evaporative power. Final as-built. Typographic error in title page: DWS-010 should be DDW-010.
Subjects:
Aquifers Computer models Evapotranspiration
Location:
Eastern Snake Plain Aquifer; Southern Idaho
Latitude:
42.52
Longitude:
-114.01
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:
"Traditional evapotranspiration calculations. Technical report 04-009. Project scenario document DWS-010 Final as-built", Idaho Waters Digital Library, University of Idaho Library Digital Collections, https://www.lib.uidaho.edu/digital/iwdl/items/iwdl-ddw-010_et_9_04.html
Rights
Rights:
Rights to the digital resource are held by the University of Idaho. http://www.uidaho.edu/
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