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<br />r~ INTRODUCTION <br />(n <br />C, The Upper Colorado River Basin upstream from the confluence of the <br />C) Colorado and Green Rivers produces about 7 million tons of salt annually <br />(Bentley and others, 1978). The salinity (as measured by dissolved-solids <br />concentration) of the Colorado River and numerous tributary streams is a major <br />concern to agricultural, industrial, and public water-supply users. The <br />average annual salinity of the Colorado River has almost doubled during this <br />century (Iorns and others, 1965). Although predictions are that salinity <br />concentrations may again double by the year 2000, some recent studies have <br />indicated a reduction in the increasing annual trend of the salinity <br />concentrations (Kircher and others, 1984). The salinity of the Colorado River <br />results in substantial economic damages to water users both in the United <br />States and Nexico. <br /> <br />The BLM (U.S. Bureau of Land Management) is responsible for regulating <br />all land and water use on Federal (public) lands under its jurisdiction and <br />for controlling the salinity of streamflow in the Colorado River basin. <br />Public lands administered by BLM comprise about 44 percent of the 62 million <br />aCres of land in the Upper Colorado River Basin within Colorado, Utah, and <br />Wyoming. BLM is conducting a study on the feasibility of salinity control in <br />the Upper Colorado River Basin. The objective of the BLM study is to identify <br />ambient salinity 'levels, to identify salt transport mechanisms on public <br />lands, and to formulate ways to control or reduce salt contribution. BLM <br />needs to be able to delineate 'surface- and ground-water salt contributions <br />from all SCUIces. <br /> <br />BLM entered into a cooperative agreement with the U.S. Geological Survey <br />to study the salt-load contribution from ground-water sources in the Upper <br />Colorado River Basin in Colorado and adjacent parts of Wyoming and Utah <br />upstream from the confluence of the Green and Colorado Rivers (fig. 1). The <br />area of intensive study is that part of western Colorado drained by the <br />Colorado, Gunnison, Oolores, White, Yampa, and Green Rivers. This study was <br />limited ,to ground water and other sources that are defined as those not <br />resulting from man's activities. Oata for this study were collected only <br />within Colorado. Salt-load contributions from ground water were' determined <br />from available data for the parts of the study area in Utah and Wyoming. <br /> <br />HYDROGEOLOGIC SYSTEM <br /> <br />Precipitation and Streamflow <br /> <br />The Upper Colorado River Basin consists of both low, arid watersheds that <br />yield little streamflow and of high, mountainous watersheds that contribute <br />large amounts of streamflow. Average annual precipitation ranges from less <br />than 8 in. in some of the low, arid areaS to more than 50 in. in the high, <br />mountainous areas. Most of the streams in low, arid watersheds are ephemeral <br />or intermittent. Runoff in these streams is generally derived from high <br />intensity spring and summer thunderstorms. Because of the meager <br />precipitation, little recharge reaches the water table in these areas and <br />little or no base flow discharges to these ephermeral streams. The high, <br /> <br />2 <br />