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<br />O~1..,tH' <br />lJ l t... to' 0 <br /> <br />evaporation, evapotranspiration, or deep percolation to non-tributary aquifers. Likewise, <br />the term "saved water" will be used to describe the larger increment of water produced by <br />changes to historical diversion rates made possible with efficiency improvements. <br /> <br />C. Methods of Improving Irrigation Efficiency <br /> <br />An accepted measure of overall irrigation efficiency is the ratio of crop consumptive use <br />to gross headgate diversions. This efficiency can be improved by either reducing diversions <br />or increasing crop consumptive use (or by a combination of both). Generally, the expanded <br />use doctrine limits adding new consumptive uses to a decreed Colorado water right. In <br />some circumstances, such as when an irrigator who historically has never had enough water <br />to satisfy his crop needs becomes able to get more water to his existing acreage, increased <br />consumptive use is allowed. Efficiency changes considered herein will focus on the more <br />common means of increasing irrigation efficiency - reducing losses thereby reducing the <br />diversion side of the efficiency ratio. <br /> <br />Often, an increase in efficiency is endorsed as a reduction in "waste" without an attempt <br />to define the term "waste". As already shown, non-consumptive losses generate return flows <br />which are used by others and such water is not necessarily wasted. While frequently an <br />increase in irrigation efficiency is promoted as conserving water supplies and in the public <br />interest, such generalities fail to recognize the intricate movement of water within an <br />irrigated region. Further, it is tempting to classify conveyance losses as non-beneficial uses <br />of water, but, in fact, such water actually serves the necessary and beneficial purpose of <br />moving the remaining water to its place of need. It is only when the method of conveyance <br />is llil! "reasonable and appropriate under reasonably efficient practices" that these losses <br />should be characterized as "non-beneficia1." Section 37-92-193(4), c.R.S. <br /> <br />What "reasonably efficient practices" means is central to statements about the efficiency <br />and waSte involved in irrigation water use. A common understanding is that beneficial use <br />is a flexible concept which tolerates whatever degree of "inefficiency" is present in the <br />prevailing irrigation methods of an area. Courts will likely be reluctant to require <br />innovations with private investment that force any advance beyond those prevailing methods. <br />Likewise, the State Engineer can probably not require state-of-the-art irrigation systems in <br />an effort to reduce irrigation water diversions. However, the legislature, as the best arbiter <br />of public perceptions and desires, may be in better position to balance policy questions and <br />decide to move water users towards more efficient practices. It can do so by providing <br />incentives (funding or creating a marketable right as proposed in the salvage bills) or by <br />regulating (Le., by declaring which "reasonably efficient practices" are necessary or otherwise <br />tightening the definition of beneficial use). Similar approaches have already been applied <br />to municipal users, Le., financial and technical assistance on the one hand and mandatory <br />plumbing code revisions containing maximum fixture demands on the other. <br /> <br />Absent regulation, current conditions give some incentives for irrigators to make <br />improvements to their systems. Some of the reasons cited by irrigators who have made <br /> <br />6 <br />