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<br /> <br />D. Description and Definition of Water Salvage <br /> <br />Water salvage generally connotes a scheme where irrigation water use is reduced by <br />using more efficient delivery and application methods. . Salvage measures usually involve <br />recovery, transfer, and use elsewhere of the water made available by the reduced irrigation <br />use. Recent salvage bills provided that the original irrigator would retain the legal rights, <br />including the priority date, for some portion of the recovered water, and allowed sale of it <br />as an incentive to make the improvements to his delivery system. <br /> <br />Much of the debate over water salvage indicates that imprecise use of terminology <br />creates needless confusion and often obscures the real policy considerations. A better <br />evaluation of the role of salvage will be fostered by the use of consistent language and an <br />understanding of irrigation water use. An irrigation water budget which identifies and <br />quantifies water in the various stages as it passes through the hydrologic cycle is a useful <br />tool to illustrate the terminology and physical processes related to irrigation water use. <br /> <br />A Irrigation Water Budget <br /> <br />Examples of water use from a typical unimproved and improved irrigation system are <br />shown in Appendix B. Water in its various locations can be quantified and tracked on a <br />daily, weekly, monthly, or annual basis. A tabular quantification of the annual water <br />budgets for the illustrated systems is shown in the accompanying table. A water budget <br />becomes more complex if done on a short term basis because water moves through different <br />parts of the system at different rates. Generally, water is stored in the soil and groundwater <br />systems while stream diversions are taking place, and then returns to the stream from <br />ground storage much later in the season. In a very large system diversions can occur several <br />days prior to farm deliveries due to of the transit time required to move water through the <br />canal and ditch system. With sufficient information about the ditch, soil, and groundwater <br />systems these storage and time lag effects can be accurately computed. On an annual basis <br />they tend to average out and can be ignored, unless precise timing of competing needs is <br />important. <br /> <br />A review of the water budget indicates that after the initial headgate diversion losses <br />of water from the delivery system begin to occur. These losses reduce the amount of water <br />arriving at, and available for use by, the irrigated crop. Losses decrease the overall <br />irrigation efficiency, measured as the ratio of crop use to headgate diversions. When losses <br />occur between the headgate and the farm they are called conveyance or transit losses. After <br />turnout to a particular farm field losses are referred to as field or on-farm losses. <br /> <br />Some of these losses are consumptive, meaning the water is permanently lost from the <br />system and can not be recovered elsewhere in the basin. When water is consumed it is no <br />longer available for other uses and the water supply is depleted or reduced by the actual <br />consumptive use. Consumptive losses include: evaporation from water surfaces in ditches, <br />ponds, and puddles on the farm, seepage which percolates into geologic zones not <br /> <br />3 <br />