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<br />activities can influence the rate of natural salt movement from rock fonuations and soils to the river
<br />system and include; livestock grazing, wildlife management, logging, mining, oil exploration, road
<br />building, recreation and urbanization,
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<br />.
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<br />Approximately 53 percent of the salinity concentration in the water arriving at Hoover Dam,
<br />as identified by EPA, results from various human activities, EPA estimated that out.of-Basin
<br />exports account for about 3 percent of the salt concentration at Hoover Dam, with irrigation
<br />accounting for 37 percent, reservoir evaporation and phreatophyte use accounting for about 12
<br />percent, and about 1 percent attributed to municipal and industrial uses, Much of the salt load
<br />contribution from irrigated agriculture is from federally-developed irrigation projects,
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<br />Salinity control activities necessarily include a water quality monitoring and analysis
<br />component that provides basinwide infonuation 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 for evaluating the effectiveness of salinity control
<br />measures,
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<br />Continuing evaluations of the salinity ofthe Colorado River are made by Reclamation, the
<br />U.S, Geological Survey (USGS) and the Bureau of Land Management (BLM), The results of several
<br />studies were published by the agencies during the period of this Review (1996-1999), To evaluate
<br />changes in salinity, water quality and streamflow data are obtained on a daily, weekly, monthly,
<br />and/or quarterly basis at various points on streams throughout the Basin by the USGS in cooperation
<br />(through financial and/or direct services) with private entities, the states and other federal agencies,
<br />Gaging stations in the Colorado River Basin which are of significance to the programs and for which
<br />streamflow and water quality records are available are shown on Figure 2-1,
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<br />Salinity data are based on total dissolved solids (TDS) as the sum of constituents, whenever
<br />possible, The sum of constituents values are defined to include calcium, magnesium, sodium,
<br />chloride, sulfate, a measure of the carbonate equivalent of alkalinity and, if measured, silica and
<br />potassium, If a sum of constituents value could not be computed, TDS as residue on evaporation
<br />(at 180 degrees Celsius) is substituted, Further, some reported salinity values are based on
<br />correlation with specific conductance measurements, In this Review, the tenus "salinity," "TDS"
<br />and "concentration" in mgIL are used interchangeably,
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<br />Average annual salinity concentrations and salt loads are detenuined on the basis of a flow-
<br />weighted average annual salinity concentration, The flow-weighted average annual salinity is simply
<br />the concentration detenuined from dividing the annual total salt load passing a measuring station by
<br />the total annual volume of water passing the same point during a calendar year, The flow-weighted
<br />average annual salinity is calculated by first multiplying the daily concentration values by the daily
<br />flow rates, These values are then summed over a calendar year and then divided by the sum of the
<br />daily flow rates,
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<br />2-2
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