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<br />. Lowland wells near the Arkansas River have rela-
<br />tively flat hydrographs compared to the three
<br />upland wells.
<br />
<br />. In general, the three upland wells have hydro graphs
<br />that are similar to each other.
<br />
<br />. Water levels in upland wells may be as little as about
<br />10 feet to as much as about 40 feet from the land
<br />surface.
<br />
<br />. Periods of water-level declines exist in the
<br />records for upland wells but are absent or less
<br />pronounced in records for wells near the Arkan-
<br />sas River.
<br />
<br />Historical water levels for 141 wells also indi-
<br />cated that the average range in ground-water levels at
<br />individual wells was about 6 feet and that the largest
<br />fluctuations occurred in upland wells. Although there
<br />are some wells in which water levels have been
<br />measured as frequently as once a I week, the historical
<br />water-level data, in general, do not describe short-term
<br />changes. Also, even though a few places where short-
<br />term reversals in water-level gradients between the
<br />river and the aquifer can be identified, the historical
<br />water-level data generally are not sufficient to deter-
<br />mine short -term gradient changes.
<br />
<br />Several hydrologic factors that affect water
<br />levels are flow in the Fort Lyon Canal, flow in the
<br />Arkansas River, surface-water applications for irriga-
<br />tion, ground-water withdrawals, and changes in the
<br />river-bed elevation. All of these factors had temporal
<br />changes in the study area. The Fort Lyon Canal and the
<br />Arkansas River generally conveyed larger amounts of
<br />water after about 1980 and during most of the 1980's
<br />than before that time. Ground-water withdrawals and
<br />surface-water applications have generally decreased
<br />although surface-water applications, much like
<br />surface-water conveyances, did increase noticeably in
<br />the 1980's.
<br />
<br />Some simple interrelations, mostly on the basis
<br />of coincidence of change, between hydrologic factors
<br />can be described:
<br />
<br />. The combined effects of flow in the Fort Lyon
<br />Canal, surface-water applications, and ground-
<br />water withdrawals can be associated with both
<br />increases in the 1980's and decreases in the
<br />1970's in ground-water levels.
<br />
<br />.
<br />
<br />Steady, long-term increases in ground-water levels
<br />in a well near the Arkansas River are similar to
<br />changes in the river-bed elevation.
<br />
<br />.
<br />
<br />Short-term increases for water levels in the
<br />Arkansas River are associated with short-term
<br />high ground-water levels observed in a well near
<br />the river.
<br />
<br />.
<br />
<br />The high river-bed elevation combined with rela-
<br />tively low amounts of ground-water withdrawals
<br />are likely related to increases in ground-water
<br />levels observed in a well near the river during the
<br />1990's.
<br />
<br />.
<br />
<br />Sustained levels of relatively high flows in the
<br />Arkansas River also can be associated with a
<br />step-like increase in ground-water levels
<br />observed in a well near the river in about 1980.
<br />
<br />REFERENCES CITED
<br />
<br />Abbott, P.O., 1985, Descriptions of water-systems
<br />operations in the Arkansas River Basin, Colorado:
<br />U.S. Geological Survey Water-Resources Investiga-
<br />tions Report 85-4092, 67 p.
<br />
<br />Boyle Engineering Corp. 1990, Arkansas River Basin
<br />Study: Estimates of groundwater pumping in the
<br />Arkansas RIver Basin, Pueblo Dam to Stateline:
<br />Prepared for the Office of the State Engineer, Division
<br />of Water Resources, Lakewood Colorado: Boyle
<br />Engineering.
<br />
<br />Cleveland, W.S. and others 1979, Robust locally weighted
<br />regression and smoothing scatterplots: Journal of
<br />American Statistical Association, v. 74, p. 829-836.
<br />
<br />Dash, RG., 1995, Irrigation water use for the Fort Lyon
<br />Canal, southeastern Colorado, 1989-90: U.S.
<br />Geological Survey Water-Resources Investigations
<br />Report 94-4051, 47 p.
<br />
<br />Goff, Karin, Lewis, M.E., Person, M.A., and Konikow, L.F.,
<br />1998, Simulated effects of irrigation in the Arkansas
<br />River Valley in Colorado: Ground Water, v. 36, no. I,
<br />p. 76-86.
<br />
<br />Hutchinson, M.F., 1989, A new procedure for gridding
<br />elevation and stream line data with automatic
<br />removal of spurious pits: Journal of Hydrology, v. 106,
<br />p.211-232.
<br />
<br />Konikow, L.F., and Bredehoeft, J.D, 1974, Modeling flow
<br />and chemical quality changes in an irrigated stream-
<br />aquifer system: Water Resources Research, v. 10,
<br />no. 3, p. 546-562.
<br />
<br />REFERENCES CITEI) 25
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