WSP10371

• File Number: 8111.805
• Description: Arkansas River Compact Administration - Keesee Ditch
• Basin: Arkansas
• Date: 1/1/1986
• Author: HRS Engineering
• Title: Keesee Ditch Change of Water Rights Vol 1 - Historical Operation of Kessee Ditch
• Water Supply Pro - Doc Type: Publication

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Irrigation Water Requirements

The irrigiltion water requirement, or the potential consumptive use of irrigation
water, is the' amount of irrigation water potentially consumed or lost from the
river system; through evapotranspiration based on a full water supply. It is
calculated as' the difference between potential evapotranspiration and effective
precipitation.

Potential evapotranspiration is the total amount of water used by a growing
crop through transpiration and evaporation from adjacent soils under full water
supply conditions. The rate of potential evapotranspiration is influenced by
climatalogical factors such as temperature, humidity, wind movement and solar
radiation, and by factors specific to individual crops such as length of growing
season, growth rate stages, crop density and crop rooting characteristics.

The method selected for calculating potential evapotranspiration was the
Modified Blaney-Criddle Method, a practical procedure developed by the U.S.
Soil Conservation Service and published in Technical Release No. 21 (U.S. Soil
Conservation Serice, 1970). This method is well established and used commonly
throughout the western United States when a limited selection of climatic
parameters (usually temperature and precipitation) are available, as is the case
in southeastern Colorado. The Modified Blaney-Criddle Method incorporates mean
monthly temperature data and generalized rates of solar radiation for estimating
potential evapotranspiration. Appendix B includes monthly temperature data
for Lamar, Colorado which were used in the analysis.

In additiQn to climate data, the Modified Blaney-Criddle Method requires
a series of monthly crop growth stage coefficients which relate evapotranspiration
rates to the variations in growing season and growth stages of the individual crops.
These crop coefficients were determined based on planting and harvesting dates
specific to the Lamar area. The Modified Blaney-Criddle Method was used to
calculate potential evapotranspiration for the four crop types irrigated under
the Keesee Ditch:. alfalfa, grain corn, grain sorghum (milo), and winter grains
(wheat and barley). Appendix C lists estimates of potential evapotranspiration
for each of the crops for the study period.

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