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<br />The salinity control activities include a water quality monitoring and analysis component <br />that provides information on a basin-wide basis for program evaluation. The monitoring and <br />analysis component provides an essential database for future studies, supports state and regional <br />planning activities, and provides an objective basis in evaluating the effectiveness of salinity <br />control measures. <br /> <br /> <br />Of the land within the Colorado River Basin, about 75 percent is owned and administered <br />W by the Federal Government or held in trust for Indian tribes. By far the greatest portion of the <br />~ naturally occurring salt load originates on these federally owned and administered lands. <br />w <br />Human-caused increases in salinity concentration, as identified by EPA, result from a <br />number of human activities. EP A estimated that out-of-basin exports account for about 3 percent <br />of increased salinity concentrations, irrigation accounts for about 37 percent, reservoir <br />evaporation and phreatophyte use accounts for about 12 percent, and municipal and industrial <br />uses account for about 1 percent. Much of the irrigated agriculture contribution is from <br />federally develOped irrigation projects. <br /> <br />Evaluations of the salinity of the Colorado River have been made by Reclamation, the <br />U.S. Geological Survey (USGS) and the Bureau of Land Management (BLM). They were <br />published by the agencies during the period of this Review (1990-1993). In order to evaluate <br />changes in salinity, water quality and streamflow data are obtained on a daily, weekly, monthly, <br />or quarterly basis at various points on streams throughout the basin by the USGS in cooperation <br />with the states and other federal agencies. Average annual salinity concentrations and salt loads <br />are determined on a flow-weighted basis using the most accurate data available2. Gaging <br />stations in the basin which are of significance to this report, and for which streamflow and water <br />quality records are available, are shown on Figure 2.1. <br /> <br />Data collection at these stations include: streamflow, specific conductance, and periodic <br />sampling for dissolved solids concentration. In addition to those stations shown in Figure 2.1, <br />the USGS maintains monitoring stations whose data can, in part, be used to analyze the <br />effectiveness of the salinity control program. <br /> <br />Some of the Basin states also maintain monitoring networks. As an example, the Utah <br />Division of Water Quality maintains approximately 25 stations in the Utah portion of the <br />Colorado River Basin. Water from these sites is sampled bimonthly and analyzed for chemical <br />constituents, nutrients, 5-day biochemical oxygen demand, suspended solids, dissolved solids, <br /> <br />2To compute the flow-weighted average annual salinity concentration, the average flow of <br />the river in acre-feet per day at a measuring point and the average concentration of salts in the <br />water in mg/L are determined on a daily basis. Concentration of salt may be measured directly <br />by chemical analysis of dissolved constituents (TDS) or indirectly as specific conductance and <br />correlated to IDS. Daily flows are multiplied by daily salinity concentrations and then summed <br />to produce an annual mass number. The annual mass number is then divided by the total flow <br />for the year at the measuring point (sum of the daily average flows) to yield the flow-weighted <br />average annual salinity for the station. <br /> <br />2-2 <br />