WSP12980

• File Number: 8210.140.20.C
• Description: Imperial Irrigation District ‎(IID)‎
• State: CA
• Basin: Colorado Mainstem
• Date: 1/9/1996
• Author: Imperial Irrigation District
• Title: Water Requirements and Availability Sutdy ‎(draft)‎
• Water Supply Pro - Doc Type: Publication

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IV.B On Farm
The importance of irrigation water management to the amount of conserved water obtained from
the proposed on-farm projects cannot be over emphasized. All of the savings estimated for the
various on-farm projects assume "good" on-farm irrigation water management. The estimated
savings could increase or decrease significantly depending upon the level of management
applied. Researchers (Influences on the Efficiency of Irri(:ation Water Use, ILRI publication 51,
Wolters, 1993; and Conversion to Drip Irrigation: Water Savin(:s. Fact or Fallacy - Lessons from
the Jordan Valley, DAI, Wolf, et. aI., 1995.) have shown that a drip irrigation system can have a
lower irrigation efficiency than a surface system if poorly maintained and managed. Thus, a
means of ensuring that these systems are well maintained and managed is needed for the
estimated savings to be achieved.

Tailwater is the pnmary target of on-farm water conservation. Deep percolation is not
considered in this analysis. The reasons for excluding deep percolation are clearly stated in a
report prepared for lID.

The majority of the Imperial Valley is characterized as having heavy soils and a
shallow water table. The majority of fields are irrigated with row or flat irrigation
methods with field lengths between 1/4 and 1/2 mile. Available flow rates are
high and allow for large volumes of water to be directed down each furrow or
border strip. The combination of cracking clay soils and high flow rates allows
for irrigations with high DUs (Distribution Uniformities). DU values averaged 90
percent in evaluations done by lID and the SCS in the 1980s. However, in order
to achieve high DUs with row and flat irrigations, surface water (tailwater) must
occur. Without tailwater, the DUs would be lower. (On-Farm Irrigation
FJjicienc;y, Boyle Engineering, August 1993, page 23.)

Therefore, in the District, conservation opportunities are due to tail water and not deep
percolation beyond the leaching requirement. Care must be taken that DUs remain high if and
when alternative practices are introduced. The guiding question in reviewing possible on-farm

Draft: Subject To Revision 12/21/95

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