Scientific Investigations Report 2006–5205
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5205
To provide a necessary framework to assess ground water availability in the Yakima River Basin, ground-water pumpage was estimated for eight categories of water use for 1960-2000. Information was presented and described concerning (1) water wells in the basin; (2) ground-water rights and water uses; (3) relations between rights and a drillers’ logs; (4) relation between primary and standby/reserve rights; (5) methods used to estimate ground-water pumpage for 1960-2000 (annual and (or) 5-year values) for eight categories pumpage; (6) estimates of pumpage for each category and a summary of these estimates; (7) delineation of the reliability of estimates for each category of pumpage; and (8) comparison of estimated and appropriated quantities for six categories of pumpage.
Ground-water is the principal source of drinking water in the basin and supplies about 330,000 people in the three-county area or about 80 percent of the population. At least 45,000 wells in the basin withdraw water for various uses. Drinking-water use accounts for most wells. However, irrigation of croplands is the largest use of ground water, although less than 2,300 irrigation wells are in the basin. Agriculture and its related industries and infrastructure is the dominant economic driver in the basin.
To provide a better understanding of ground-water availability, the ground-water rights were associated, to the extent possible, to drillers’ logs. This association allowed for an assessment of the spatial withdrawals, by depth of ground water. Of the 2,874 active rights identified in the Water Rights Tracking System, all but 220 were associated with a log. It is acknowledged that all associations may not be correct. Associations include temporal changes in the points of withdrawal to account for such aspects as well deepening, reconditioning, abandoning and replacing with a new well or wells, and constructing additional wells. As part of this analysis of rights, an estimate was made of which irrigation wells held primary rights and which wells held rights that are, in almost all cases, supplemental to junior surface-water rights. About 560 ground-water rights with allowable acreage for irrigation were estimated to be standby/reserve and 21 rights with the sole purpose of frost protection were also estimated to be standby/reserve.
Pumpage estimates varied widely, both temporally and spatially, and within and between the pumpage categories. If the estimate of standby/reserve pumpage is included, about 395,096 acre-ft of pumpage occurred in 2000. Without standby/reserve pumpage, the total annual value in 2000 was 312,284 acre-ft, which was an increase of about 200,000 acre-ft since 1960. In 2000, the largest amount of withdrawals is for irrigation use at about 271,042 acre-ft. The standby/reserve part of the total irrigation pumpage was estimated to potentially be 82,812 acre-ft in a year with extreme prorating; the standby/reserve pumpage would occur only in years of prorating of junior surface-water rights. Pumpage in a prorating year would be some percentage of the estimated value and the percentage is a function of the amount of prorating for the year. For 2000, a year without prorating, the total irrigation pumpage was about 188,230 acre-ft. The standby/reserve estimates are important for understanding the effects on ground-water availability from potential additional pumpage in prorating years.
The next largest category of pumpage was for PWS at 46,385 acre-ft, followed by ground-water claims at 34,310 acre-ft. Pumpage for claims (mostly for irrigation) were the most difficult to estimate, but the estimate is considered reasonable. Exempt well pumpage was 20,036 acre-ft, which, excluding the standby/reserve pumpage is about 5 percent of the total pumpage. Together, the remaining categories of livestock, commercial and industrial, and fish and wildlife propagation account for about 23,323 acre-ft or about 6 percent of the pumpage.
The reliability of the pumpage estimates for 2000 was estimated for each category by estimating a lower and upper bound. Based on these ranges, the total 2000 pumpage estimate can be as small as 249,570 acre-ft or as large as 463,534 acre-ft. Excluding the standby/reserve pumpage, this potential range is reduced to from 249,570 to 380,723 acre-ft. Estimates with the largest potential ranges were for primary and standby/reserve irrigation values. The PWS, and fish and wildlife propagation categories had the smallest percentage error (5 percent) because estimates were principally based on provided data.
Excluding standby/reserve pumpage, the total annual pumpage for 2000 was estimated to be about 11 percent of the appropriated quantity of the surface water diverted for irrigation and PWS and about 56 percent of appropriated ground water. Total pumpage in 2000 without standby/reserve pumpage was about 430 ft3/s (0.31 million acre-ft) compared to mean annual precipitation of about 12,000 ft3/s (8.7 million acre-ft), unregulated streamflow of about 5,600 ft3/s (4.1 million acre-ft), regulated streamflow of about 3,600 ft3/s (2.6 million acre-ft), and the above diversions of about 3,900 ft3/s (2.8 million acre-ft). The maximum pumpage occurs during July and August and is on the order of 100 ft3/s. Potential pumpage was estimated to be about 185 ft3/s for the outstanding applications.
U.S.
Department of the Interior | U.S. Geological
Survey
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