|
<br />2826
<br />
<br />Pipeline project was completed in June 1985. Water is
<br />released through the Bessemer Ditch outlet during
<br />the spring. summer, and fall. During the winter,
<br />S!. Charles Mesa obtains its surface water by diverting
<br />Arkansas River water downstream from the dam.
<br />
<br />In general, at least since 1985, a volume of water
<br />comparable to the amount of annual inflow has been
<br />released annually from the reservoir outlet works,
<br />However, a net increase in storage occurs from Novem-
<br />ber to April of each year because of the Winter Water
<br />Storage Program. Because of Pueblo Reservoir opera-
<br />tion practices, the reservoir has a short residence time,
<br />From 1985 through 1989, an average of 12 percent of
<br />the reservoir contents was released each month during
<br />November to April (the period of the Winter Water
<br />Storage Program); an average of 52 percent of the res-
<br />ervoir contents was released each month during May
<br />and June (the major snowmelt-runoff period); an aver-
<br />age of 47 percent of the reservoir contents was released
<br />each month during July and August (the upper-basin
<br />reservoir-release period and rainfall-runoff period);
<br />and an average of 15 percent of the reservoir contents
<br />was released each month during September and
<br />October.
<br />
<br />Water Quality of the Upper Arkansas River
<br />Basin
<br />
<br />A discussion of the physical and chemical condi-
<br />tions of the Arkansas River upstream from Pueblo Res-
<br />ervoir is necessary to fully understand the physical and
<br />chemical characteristics of the reservoir, because the
<br />Arkansas River has a dominant effect on the reservoir.
<br />The chemical quality of the upper Arkansas River
<br />Basin has been studied by the Federal Water Pollution
<br />Control Administration (1968), Moran and Wentz
<br />(1974), Wentz (1974), La Bounty and others (\975),
<br />Miles (\ 977), Roline and Boehmke (1981), Crouch and
<br />others (\ 984), Cain (1987), and Kimball and others
<br />(1988). The reader is referred to these reports for a
<br />detailed description of the historical water quality in
<br />the upper Arkansas River Basin, The following discus-
<br />sion is intended to provide an overview of the quality
<br />of water in the upper basin and to provide a description
<br />of the quality of water entering the reservoir.
<br />
<br />The chemical quality of surface water in the
<br />Arkansas River Basin is affected by runoff from snow-
<br />melt and rainfall, lransmountain diversions, mine
<br />drainage, wastewater-treatment-plant effluents, ground
<br />water, and land and water use within the basin. Water
<br />entering the basin near the headwaters of the Arkansas
<br />River and its tributaries is derived mostly from snow-
<br />
<br />melt and generally is suitable for most uses (Federal
<br />Water Pollution Control Administration, 1968).
<br />Dissolved-solids concentrations in the upper
<br />reaches of the Arkansas River have been increased
<br />by acid mine drainage in the basin headwaters
<br />(Cain, 1987), Dilution by tributary inflows results in
<br />decreasing dissolved-solids concentrations and specific
<br />conductance between Leadville and Buena Vista. Dis-
<br />solved solids and specific conductance increase down-
<br />stream from Buena Vista because of: (I) dissolution of
<br />sedimentary rock minerals, (2) irrigation return flows
<br />and saline ground-water inflow, and (3) discharges
<br />from wastewater-treatment plants. Dissolved solids
<br />and specific conductance increased only slightly
<br />between Buena Vista and Canon City (fig. 1), but dis-
<br />solved solids increase substantially and specific
<br />conductance almost doubles in the 20-mi reach down-
<br />stream from Canon City, primarily as a result of saline
<br />ground-water inflows and irrigation return flows
<br />(Cain, 1987),
<br />The limited amount of nutrient data available for
<br />the upper Arkansas River Basin indicates that nitrogen
<br />and phosphorus concentrations increase downstream
<br />(Edelmann and others, 1991). Concentrations of total
<br />nitrogen generally are less than I mgIL, and total-
<br />phosphorus concentrations generally are less than
<br />0.2 mgIL.
<br />Acid mine drainage has resulted in relatively
<br />large concentrations of cadmium, iron, lead, manga-
<br />nese, nickel, and zinc in the upper Arkansas River and
<br />is a major source of these constituents to Pueblo Reser-
<br />voir (A.J. Medine, Water Science, Boulder, Colorado,
<br />written commun., 1991), Weathering of sedimentary
<br />rocks in the lower half of the basin seems to be another
<br />major source of iron and manganese to the river and
<br />reservoir. Chemical precipitation; sorption to iron and
<br />aluminum oxides, organics, and clay minerals; sedi-
<br />mentation; and dilution contribute to downstream
<br />decreases in most dissolved-metal concentrations in the
<br />upper Arkansas River.
<br />The chemical quality of water entering Pueblo
<br />Reservoir can be summarized by using data collected at
<br />station 07097000, Arkansas River at Portland (table I).
<br />The U.S. Geological Survey has been analyzing water-
<br />quality samples collected at this station since 1977.
<br />Daily measurements of water temperature and specific
<br />conductance have been made since 1979. A summary
<br />and discussion of water-quality data collected at this
<br />station from 1977 through 1985 are provided in Edel-
<br />mann (\ 988).
<br />Strong seasonal variations in water temperature,
<br />specific conductance, and dissolved-solids concentra-
<br />tions occur in the Arkansas River. Mean daily water
<br />temperature of the Arkansas River at Portland ranged
<br />
<br />INTRODUCTION 7
<br />
|