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<br />minor shortfalls in the ditch supply for the decreed acreage, were assumed to
<br />have been supplied by the irrigation wells. This conceptual separation of the two
<br />water sources is possible because each source is adequate for the supply of the
<br />respective acreages, and because the development of the irrigation wells in the
<br />mid-1950's aM 1960's did not diminish the reliance on ditch diversions for irrigation.
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<br />Support for these assumptions can be demonstrated through an examination
<br />of water commissioner records of irrigated acreage and annual diversions for
<br />the periods prior to and following 1954, when the first well was installed. These
<br />records are included in Table II.
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<br />For years prior to 1945, the ditch was used to irrigate an average of
<br />approximately 1400 acres, and in some years a much greater acreage. Beginning
<br />in 1945, the irrigated acreage increased dramatically and averaged more than
<br />2000 acres through 1955. The reasons for this increase are not clear and may
<br />involve a combination of factors such as changes in crop types, more efficient
<br />irrigation usage, and anticipated benefits in water supply - resulting from the
<br />construction of John Martin Reservoir. This pattern does however, suggest the
<br />adequacy of the ditch water rights in supplying, at a minimum, the decreed 1400
<br />acres. Since 1956, the total irrigated acreage has averaged approximately 1900
<br />acres and remained consistent from year to year. This consistency probably reflects
<br />an optimum area for irrigation under the current ditch distribution system, crop
<br />mixture and land ownership, combined with the reliable supplemental water supply
<br />afforded by the development of the irrigation wells.
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<br />An examination of diversion records indicates an average annual diversion
<br />for the Keesee Ditch of about 4,250 acre-feet for the period 1911 to 1953 prior
<br />to development of the irrigation wells. The average annual diversion for the period
<br />1954 to 1983, after well construction, is nearly 4,700 acre-feet. This increase
<br />in ditch diversions indicates a continued reliance on surface water for irrigation
<br />and is probably due to the benefits of John Martin Reservoir operations.
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<br />By separating the ditch operations from the use of the irrigation wells and
<br />by limiting the analysis to the decreed 1,4jl0 acres, a conservative and practical
<br />determination of historical stream depletions associated with the Keesee Ditch
<br />water rights can be made. As a supplement to the surface water rights analysis,
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