WSP07375

• File Number: 8210.140.20
• Description: Colorado River Basin Organizations and Entities - Colorado River Basin States Forum - California
• State: CA
• Basin: Western Slope
• Date: 7/2/2003
• Author: Robert W Johnson
• Title: Part 417 Determinations and Recommendations Imperial Irrigation District Calendar Year 2003
• Water Supply Pro - Doc Type: Report/Study

3:)82

losses of337,300 acre-feet are reasonable for 2003. These losses are expected to
continue to decrease in the future as other improvements, such as the All-American Canal
(AAC) lining project, are completed,

FACTOH 12. OPEHATlNG EFFICIENCIES
Introduction and Background

P3I1 417.3 identifies operating efticiencies as a factor to be analyzed. Operating
efficiencies are mathematical computations expressed as a ratio and based upon data
relating to a combination of the following components: water loss in the delivery system,
water use for crop evapotranspiration (ETc), water usc for leaching salts !Tom the soil,
and some fraction of tailwater. Operating efliciency calculations are sometimes used as a
comparative measurement indicating the amount of water consumed in OIl- fann uses
versus the amount of water delivered,

Questions concerning lID's CUlTent and past levels of water use for irrigating crops, and
whether that use is in excess of its needs, are most effectively answered with appropriate
on- farm water measurement data. Consistent and timely farm-level data on water use
within the lID are not available, since lID has not implemented means to capture these
data (See discussions in the Record of Water Orders - Factor 9 and General Operating
Practices - Factor 10). Many irrigation districts in the western United States do measure
the distribution and use of water and thus have actual data to support assessments of
operating efficiencies.

In the absence of appropriate measurement and reporting of on- farm water uses within
the District, IID, CVWD, and MWD have each prepared estimates of historical water use
for water needed by the crops (crop evapotranspiration, or ET" water needed to leach
salts from the soil (leaching is the removal of soluble material by the passage ofwaler
through the crop root zone), and tail water runoff (tailwater is irrigation water that flows
off the end of a field). In addition to considering the estimates submitted, Reclamation
prepared its own analysis of these issues.

Various consultants and expet1s have perfonned highly-detailed studies of liD,
mathematical modeling of f1ows, and analysis and interpretation of thelt results. They
have formed opinions about what the various levels of on-farnl water use are, what
effects this water use has on the crops, and whether there is any water being delivered in
excess of the amount reasonably required for beneficial use within lID for 2003. The
submittals relating to on- farm uses of water within IID were rigorously reviewed by
Reclamation in this technical review.

As part of these submittals, the various experts performed calculations of efficiency using
the components of water use (ET" leaching, and some fraction of tail water), as a
percentage of diversions (some with adjustments for conveyance losses; some without).

July 2, 2003

31

Determinations and Recommendation;
For lID - Calendar Year 2003