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<br />I'\:) <br />o <br />(0 <br />l\.) <br /> <br />Salinity has long been a water-quality issue in the Colorado River basin. <br />(As used here, salinity is synonymous with dissolved-solids concentration as a <br />measure of the inorganic-solute concentration in water.) The Colorado River <br />Basin Water-Quality Control Project was established in 1960 by the U,S. Public <br />Health Service to evaluate the most critical pollution problems in the basin. <br />By 1963, ".. .salinity was ~dentified as a pressing problem..." (U.S. Environ- <br />mental Protection Agency, 1971, p. 2) and detailed studies were initiated. <br />During 1972, concerned with increasing dissolved-solids concentrations, the <br />seven basin States adopted a nondegradation policy for the Lower Colorado <br />River, The Colorado River Basin Salinity Control Program was proposed to <br />offset salinity increases that were expected to occur because of planned <br />water-resources development in the Upper Colorado River Basin. The Colorado <br />River Basin Salinity Control Act of 1974 gave primary responsibility for the <br />Salinity Control Program to the U,S. Bureau of Reclamation. <br /> <br />At that time, the U.S. Bureau of Reclamation was developing a compre- <br />hensive river-basin model for studying the operation of reservoirs on the <br />Colorado River system. To evaluate Salinity Control Program options, <br />dissolved-solids routing was incorporated into the model. The model consists <br />of a package of computer programs and data bases known as the Colorado River <br />Simulation System (CRSS). It operates on a monthly time-step using the hydro- <br />logic record from 1906 through 1983 adjusted to natural conditions (U.S. <br />Bureau of Reclamation, 1985), Mass-balance estimates of dissolved-solids <br />discharge are computed by subtracting the dissolved-solids discharge diverted <br />and adding the discharge contributed by water-resources-development projects <br />to the discharge that would have been present under natural conditions. This <br />computation requires estimates of natural dissolved-solids discharge for all <br />the river reaches used in the model. Dissolved-solids discharge, as used in <br />this report, is defined as the load, or mass, of inorganic solutes flowing <br />past a specific site during a unit of time. Natural dissolved-solids <br />discharge is the discharge that would have existed at the site if there had <br />been no water-resources development upstream. <br /> <br />Purpose and Scope <br /> <br />The present study was conducted to provide the U.S. Bureau of Reclamation <br />with consistent, realistic estimates of natural dissolved-solids discharge for <br />use in the CRSS model. The purpose of this report is to: <br /> <br />1. Describe a method for estimating the natural dissolved-solids discharge <br />at a site, using the historical streamflow and dissolved-solids data for <br />the site and the data for water-resources development upstream from the <br />site. <br />2. Present estimates of monthly natural dissolved-solids discharge for 16 <br />sites in the Upper Colorado River Basin. <br /> <br />The sites selected for analysis and the corresponding periods of record <br />are listed in table 1, and the location of each site is shown in figure 1. <br />Headwater sites are defined as the most upstream on the respective rivers; all <br />other sites are classified as downstream sites. <br /> <br />3 <br /> <br /> <br />,. <br /> <br />