Water-resources appraisal of the upper Arkansas River basin from Leadville to Pueblo, Colorado

Abstract

The upper Arkansas River basin from Leadville to Pueblo, Colo., is a high altitude, intermountain, agricultural and ranching community that consists of several structurally formed, alluvial-filled subbasins joined by the Arkansas River. The purpose of the study was to provide a reconnaissance investigation of the quantity, quality, and availability of groundand surface-water resources of the area. Most water supplies in the basin are presently (1982) diverted by canals from surface-water sources. During droughts, the exercise of senior water rights in the lower Arkansas River in Colorado can substantially reduce upstream diversions. The recently completed Fryingpan-Arkansas River project has changed the flow regime of the Arkansas River by increasing reservoir storage and by importing 69,200 acre-feet per year of water from the Colorado River drainage. The volume of hydrologically recoverable ground water in the upper 200 feet of unconsolidated saturated materials in the Leadville and Buena Vista-Salida basins and the Wet Mountain Valley is estimated to be 10.2 million acre-feet. Ground water also is available in the Dakota-Purgatoire aquifer, with well yields reportedly as much as 300 gallons per minute. Gain-loss studies indicate hydraulic connection between the Arkansas River and the ground-water system with ground water contributing to streamflow in the study area. The quality of ground and surface water is acceptable for most uses with hardness, iron, manganese, pH, and sulfate exceeding recommended drinkingwater criteria during low flow in the river. Dissolved solids increase downstream because of increased water use and decreased precipitation and groundwater inflow. Acid mine drainage has seriously degraded water supplies in the Leadville area. Water in the Dakota-Purgatoire aquifer has concentrations of radiochemical constituents that exceeded drinking-water criteria. INTRODUCTION The upper Arkansas River basin is an agricultural and ranching community that relies extensively on water locally available in the Arkansas River and its tributaries. At present (1982), ground water is used mostly for domestic purposes, stock watering, and some municipal supplies. The upper Arkansas River basin is the headwaters of the Arkansas River and the source area for a large percentage of the surface water used in southeastern Colorado. Colorado water law stipulates that the volume and frequency of diversions from the river be administered according to the priorappropriation doctrine by the Colorado Division of Water Resources, Office of the State Engineer. That doctrine establishes a priority system based on in-use, first in-right. During extended low flows or drought, senior water rights in the lower Arkansas River basin in Colorado can stop or substantially reduce upstream diversions. The objectives of this study were to determine on a reconnaissance level (1) the quantity, quality, and availability of both surface and ground water; and if possible (2) the potential for development of the ground-water system. The scope of this investigation included a review of data and reports previously written about the basin, an evaluation of streamflow and reservoirs, a determination of the quality of available water, the expected yields from properly constructed wells completed in various aquifers, the volume of water available in ground-water storage, and a definition of the potentiometric surface in the confined and unconfined aquifers. Gain-loss evaluations were made on several main-stem reaches of the Arkansas River and its tributaries to determine surfaceand ground-water relationships. Location and General Features of Study Area The upper Arkansas River basin (fig. 1) is a high-altitude, semiarid basin that extends from Leadville to Pueblo, Colo., a straightsline distance of approximately 120 mi. The total study area is about 5,200 mi and includes all of Lake, Chaffee, Fremont, and Custer Counties; and parts of Saguache, Park, Teller, El Paso, and Pueblo Counties. National forests cover about onethird of the area. Altitudes in the basin range from about 4,670 ft at Pueblo to 14,433 ft at Mount Elbert in Lake County the highest peak in Colorado. Most of the population and related activities are located along the broad, gently sloping terrain of the Arkansas River. The principal towns in the study area are Pueblo, Canon City, Salida, Buena Vista, Leadville, and Westcliffe. According to the 1970 census (U.S. Bureau of Census, 1971), the population of the upper Arkansas River basin, excluding the city of Pueblo, was 48,200. This represents an increase of about 2,000 people since 1960.