WSP06975

• File Number: 8273.100
• Description: Colorado River Basin Salinity Control - Federal Agencies - Bureau of Reclamation
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1979
• Author: BOR
• Title: Colorado River Basin Salinity Control Project - Background Plan and Status Report
• Water Supply Pro - Doc Type: Report/Study

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It was estimated that irrigation efficiencies could be improved by improved
water 'management, that is, applying the necessary amount of water tosati sfy
crop qonsumptive use and the leaching requirement. A further increas.e in
irrigl!tion efficiency could be attained by improvement of the onfarmirriga-
tion ~ystems. Four program levels were developed to evaluate the cost of
onfam improvements and thei r effect on reducing return flows.

The p~ogram levels considered and their irrigation efficiency and estimated
return flow associated with each are presented in the following tabulation.

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PROGRAM LEVELS II

1
2
3
4

Efficiency
( Percent)

64
69
72
82

Return Flow
(1.000 AF per year)

167
147
136
94

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Level

'.1

It was concluded that the highest level capable of achievement prior to the
desal~ing plant startup is a desirable goal. This is identified as ~rogram
Level ,3. The calculated return flow for Program Level 3 of 136,000 acre~feet
per year is a reasonable objective. Irrigation efficiencies of 64 percent
on th~ mesa lands and 74 percent on the valley lands are projected. The
average District-wiqe irrigation efficiency is 72 percent.

If measures under Program Level 3 are fully implemented and if the effective-
ness of these improvements increase irrigation efficiencies as projected in
these 'studi es, rlltut'n flows shoul d eventua 11y reduce to 136,000 acre-'feet
per year. However, there are uncertainties in reaching this objective.
They are (1) imprecision in the calculations of return flow quantities,
(2) r~set'vations that not all projected onfarm improvements will be fully
implemented prior to the plant startup date or that the measures will be
as effective in increasing irrigation efficiencies as estimated, and
(3) ctianges in cropping patterns. The Advisory Committee is highly confi-
dent ~hat return flows due to drainage requirements will be reduced to
l75,0~0 acre-feet per year and considers it reasonable to expect that return
flows iwill be reduced to 150,000 acre-feet per year.

In la~er work for the 1977 Sizing Study by the Bureau of Reclamation.
Program Levell and Program Level 3 irrigation efficiencies were reevaluated.
The ortiginal Program Levels 1 and 3 irrigation efficiencies were deri~ed
from 1:970-1972 crop data and efficiencies based on 11 percent canal loss.
Later~ changes were made for the 1970-1972 historic data to identify more
crops. use better estimates of consumptive use values, and reflect effi-
cienciles based on 8 percent canal loss. More recent and reliable data
obtairiedfrom ,theWMI&DD indicate that canal losses are closer to 8 percent.

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Z! Based on 75,000 acres within the District.
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