0336
<br />Purpose and Scope
<br />This report lists the types of water - quality data
<br />collected, describes methods of data- collection, analy-
<br />sis, and quality- assurance procedures and presents a
<br />compilation of selected water - quality data. Data were
<br />collected from April 1990 through March 1993 at
<br />59 surface -water stations in the Arkansas River Basin
<br />of Colorado (pl. 1) that included 19 Arkansas River
<br />stations, 31 tributary stations, 2 mine - drainage stations,
<br />and 7 transmountain diversion stations. Water - quality
<br />data presented in this report include onsite measure-
<br />ments of instantaneous discharge, specific conduc-
<br />tance, pH, water temperature, and dissolved oxygen,
<br />bacteriological analyses; chemical analyses of selected
<br />inorganic constituents, pesticides, and radiochemicals;
<br />analyses of suspended - sediment concentration; and
<br />analytical quality- assurance data for selected water -
<br />quality constituents.
<br />Acknowledgments
<br />The authors gratefully acknowledge the assis-
<br />tance of many government and local agencies that
<br />cooperated with the U.S. Geological Survey to develop
<br />a basinwide water - quality study. Appreciation is
<br />extended to the many landowners along the Arkansas
<br />River corridor who permitted access to their property
<br />to measure discharge and to collect water samples. The
<br />authors thank State hydrographers Frank Kipple and
<br />Tony Gutierrez, Colorado Department of Natural
<br />Resources, Division II of Water Resources, Office
<br />of the State Engineer, for their timely assistance
<br />with streamflow determination. Special thanks are
<br />extended to Jeffrey West, Charles (Chuck) Moore, and
<br />Matthew Kurchinski of the U.S. Geological Survey for
<br />the collection and compilation of water - quality data.
<br />DESCRIPTION OF THE STUDY AREA
<br />The study area includes the entire Arkansas
<br />River Basin of Colorado and consists of approximately
<br />the southeast one - quarter of the State (fig. 1). Eleva-
<br />tions in the basin range from 3,350 ft above sea level at
<br />the Colorado -Kansas State line to 14,433 ft at the high-
<br />est mountain peak in Colorado. Mean annual precipi-
<br />tation in the basin ranges from more than 40 in. in the
<br />mountains to less than 10 in. in areas of the eastern
<br />plains (Colorado Climate Center, 1984).
<br />Streamflow in the Arkansas River primarily is
<br />from melting of snow that accumulates in the moun-
<br />tains from October through May each year. At lower
<br />elevations, runoff from summer thunderstorms can
<br />contribute substantial quantities of streamflow for short
<br />periods of time. Much of the streamflow that occurs
<br />east of La Junta (fig. 1) can be irrigation -return flow
<br />during parts of most years (Cain, 1985). Mean annual
<br />runoff decreases from more than 30 in. in the moun-
<br />tains to less than 0.1 in. downstream from Pueblo
<br />(Abbott, 1985). For the interested reader, a more com-
<br />prehensive description of the historical water resources
<br />of the Arkansas River Basin of Colorado is reported in
<br />Crouch and others (1984), Abbott (1985), Burns
<br />(1985), Cain (1985), and Kuzmiak and Strickland
<br />(1994).
<br />Land use in the study area predominantly is
<br />agricultural, consisting of rangeland and cropland
<br />areas throughout the drainage basin. National forests
<br />are located upstream from Canon City and cover about
<br />one -third of the upper Arkansas River Basin. The
<br />upper basin extends downstream to about Pueblo.
<br />Historically, substantial mining of precious metals
<br />occurred in the basin upstream from Canon City,
<br />but most of the mines are abandoned and ranching
<br />presently (1994) is a principal land use in the upper
<br />basin. Irrigation water use constitutes the largest
<br />withdrawals of surface water in the Arkansas River
<br />Basin. It was estimated that irrigation used about
<br />1,730 Mgal/d of water during 1985, with 88 percent
<br />of the total irrigation withdrawal from surface -
<br />water sources (Litke and Appel, 1989). More than
<br />411,000 acres of alluvial lands in the basin are irri-
<br />gated, including about 56,000 irrigated acres located
<br />in the upper basin. Mainly alfalfa, hay, and pasture
<br />grass are irrigated in the upper basin, although fruits
<br />and some grain crops are grown on irrigated land in
<br />the foothills located around Canon City. Truck - crops,
<br />alfalfa, and grain -crops are grown on irrigated land in
<br />the lower basin downstream from Pueblo. Most of the
<br />nonirrigated agricultural lands in the basin are used for
<br />rangeland or dryland wheat production.
<br />Population in the study area was determined by
<br />the 1990 census (U.S. Bureau of the Census, 1991) to
<br />be 641,700, about 19 percent of the total population of
<br />Colorado. Most of the population is located near the
<br />cities of Colorado Springs and Pueblo or concentrated
<br />in small towns and rural areas along the Arkansas River
<br />corridor.
<br />DESCRIPTION OF THE STUDY AREA
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