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<br />ti01334 <br /> <br />., <br /> <br />Deep artesian ground-water-ftow systems occur <br />in the Uncompahgre Project area (fig. 10) and in the <br />Grand Valley. Upward ground-water flow from these <br />artesian systems into the shallow systems is not <br />certain, except through wells that penetrate the deep <br />aquifers. Detailed descriptions of the deep ground- <br />water-flow systems are reported in Meeks (1950), <br />Lohman (1965), and Craig (1971). <br />Recharge to the shallow ground-water-ftow <br />system occurs through the seasonal application of <br />irrigation water, from snowmelt during spring, and <br />from infrequent thunderstonns during summer. <br />Water-level fluctuations in well143NO (located in the <br />Grand Valley, fig. 9) and the fluctuations of specific <br />conductance of ground water are shown in figure II. <br />Both respective traces of transducer and specific- <br />conductance data show the effects of irrigation on <br />ground-water recharge. Water-level altitude in <br />well 143NO increased during the irrigation season <br />(April-September 1992) (fig. II), and the water-level <br />altitude slowly declined during the winter of 1992-93. <br />The increase indicates storage of ground water in the <br />shallow aquifers of the irrigated area surrounding <br />we1l143NO. Specific conductance of ground water <br /> <br />in well143NO decreased during late summer and early <br />fall (August-October 1992) (fig. II) following the <br />irrigation season, indicating a delayed dilution of the <br />ground-water-quality constituents in response to <br />irrigation recharge. Irrigation recharge occurs through <br />leakage of unlined canals and irrigation ditches and <br />through flood-irrigation practices in the study area. <br />Calculations of recharge are difficult because <br />techniques frequently used for estimating recharge <br />(such as hydrograph separation) might not accurately <br />represent ground-water recharge in the irrigated area <br />where streams fluctuate greatly. However, a spring in <br />the Sweitzer Lake type area seemed to constantly <br />discharge about 0.25 gaIlmin. Assuming that the <br />discharge from the spring is constant throughout the <br />year, a rough estimate of recharge in the 160-acre <br />irrigated basin is about 0.03 in/yr. Snowmelt from <br />mesas and mountains adjacent to the Uncompahgre <br />Project area and the Grand Valley increases stream- <br />flows during early spring and recharges the natural <br />ground-water system near intermittent streams; <br />however, a determination of natural recharge to the <br />ground-water system from intermittent streams was <br />not made. <br /> <br />...J <br />UJ a: <br />> UJ <br />UJ 4,526 4,600 D- <br />...J <br />c( '\ WATER LEVEL en en <br />w / z=> <br />en 4,400 ~ en <br />w 4,525 I w...J <br />> -w <br />0 4,200 [g U <br />CD a: en <br />c( UW <br />I- O_w <br />w 4,524 4,00 ::;; a: <br />w zCl <br />u.. _w <br />~ 3,800 ui ~ <br />ui U", <br />Cl 4,523 zl- <br />=> 3,600 ~c( <br />l- I ua: <br />i= =>w <br />...J 3,400 ~ t;j <br />c( <br />...J 0::;; <br />w ui= <br />> SPECIFIC CONDUCTANCE 3,200 u z <br />w <br />...J -w <br />ci: !!:u <br /> U <br />w 4,521 J J A S 0 N D J F M 3,000 w <br />?- M A M D- <br />c( 1992 1993 en <br />== <br /> DATE, AT 1800 HOURS <br /> <br />Figure 11. Water-level altitude end specific conductance of water in well 143NO, Grand Valley, <br />March 1992-March 1993. <br /> <br />GROUND-WATER INVESTIGATIONS 27 <br />