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<br />0'. ,". - ") , <br />..) ~=; ~ ...J '. <br /> <br />these storage and time lag effects can be accurately computed. On an annual basis they <br />tend to average out and can be ignored. <br /> <br />A review of the water budget indicates that after the initial headgate diversion water <br />losses from 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 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. Consumptive losses include: <br />evaporation from water surfaces in the ditch and on the farm, seepage through ditch <br />bottoms with deep percolation into geologic zones not hydraulically connected to the surface <br />stream, and transpiration by non-agricultural vegetation along ditches and on the perimeter <br />of cropped areas. These types of losses are called "incidental" or "nonproductive <br />consumptive use" in this analysis because they are unintended results which produce no <br />economic gain for the irrigator. While these losses are not intentional, neither are they <br />completely avoidable under practical irrigation techniques. Since part of this consumption <br />of water occurs during the necessary process of moving water from the stream to the point <br />of use,it probably can not be considered a non-beneficial use, In fact, the tiser benefits from <br />these losses in that diversion of an equivalent amount of water allows for a practical method <br />of delivering his crop water needs. <br /> <br />A second category of losses illustrated in the water budget result in water returning <br />to the stream from which it was diverted. These losses include deep percolation from <br />ditches and fields into tributary aquifers, intentional or accidental water spills from the <br />distribution system, and tailwater or unused irrigation water which runs off of the irrigated <br />acreage. These losses collectively result in "return flows" to tbe stream system. Since these <br />losses can frequently be observed and can be as high as 50% of the amount diverted they <br /> <br />4 <br />