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<br />o l) ,1f.j.z' .. <br /> <br />When the efficiency of water used for any purpose is improved there are resulting <br />changes to stream flows, depletions, and return flows. Changes potentially effect both the <br />quantity and timing of water in the stream system. When a water right is transferred the <br />same changes can occur, but the "no-injury" rule has a counter balancing tendency to <br />preserve stream conditions, at least to the extent otber appropriators can demonstrate <br />reliance on those conditions. Changes in the stream system result in a variety of related <br />environmental impacts. <br /> <br />A. Water Supply Impacts <br /> <br />In an efficiency improvement project some combination of incidental consumptive uses <br />and return flows will change in response to the typical mix of activities. The following <br />discussion considers those changes separately to illustrate discrete impacts. <br /> <br />When consumptive use (either productive or incidental) is reduced by efficiency <br />improvements tbe reduced depletion produces a gain, or accretion to the net available water <br />supply in the basin. How that increased supply gets used depends on the hydrology of the <br />particular basin, the location in tbe basin where the efficiency. improves, demands for water, <br />tbe distribution of water rights in the basin, and interpretations of water law. The increased <br />supply may be picked up by the original diverter to meet new or existing needs, by other <br />appropriators above or below the location of the improvements, or may flow downstream <br />if there is no current demand for this new supply. While it is not possible to identify in <br />generic terms the final fate of a particular accretion to the basin supply, it is clear that any <br />reduction in depletions by one user leaves more water in the stream for other users. <br /> <br />When an efficiency improvement reduces return flows the effect on the stream system, <br />in absolute terms, is less clear. Return flows can be reduced by increased consumptive use <br />(if allowed) or by lower water diversions made possible by reduction of conveyance and on- <br />farm losses. If consumptive uses (either productive or incidental) are not reduced there will <br />be no change in depletions and no gain to the basin water supply. In a basin which already <br /> <br />25 <br />