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<br />INTRODUCTION
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<br />Because of ~he detrimental effects of mineral salts on agricultural, munici-
<br />l\) pal', and' in:dustrial water use in the Colorado River Basin, the U.S. EPA
<br />~ (En'vi ronmen!ta 1 Protecti on Agency), i n1972, mandated the estab 1 i shment of
<br />~ salinity st~ndards for various gaging stations along the river.
<br />(0
<br />On December 18, 1974, the Colorado River Basin States, through amendments to
<br />40 CFR, Part 120, Colorado River Water System, adopted the 1972 levels of
<br />salinity a~ three lower main stem stations (Hoover Dam, Parker Dam, and
<br />Imperial Dam) as the salinity standards; in essence, a no degradation stand-
<br />ard. In ortler to meet these standards, the USBR (Bureau of Reclamation)
<br />is implemen~ing the Colorado River Salinity Control Program to reduce the
<br />rate of sallt; loading to river, The USBR has 'al so developed mathematical
<br />models for ~stimating the effects of past water development projects on the
<br />salinity an~ streamflow of rivers in the Colorado River Basin and for pre-
<br />dicting the! effects of future developments.
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<br />Since 1972, salinity levels at Imperial Dam have fallen steadily, from
<br />879 mg/L in, 1972 to 810 mg/L in 1981, in contrast to USBR, EPA, and CRSCF
<br />(Colorado River Salinity Control Forum) projections, Unpublished USBR and
<br />CRSCF studih have indicated that starting in the mid-1960's, the salt
<br />load from s~me areas in the Upper Basin began to decrease. Projections of
<br />future salipity are based upon historical salt-flow relationships, under the
<br />assumption that these relationships are relatively constant over the period
<br />of record. ;If, however, the declining salt loads result from a physical
<br />~hange to t~e system, rather than a short-term aberation, prediction of
<br />future salinity will be inaccurate. A systematic change may manifest itself
<br />in a shift in the individual solute concentration-streamflow relationships
<br />or in the values of solute loads or mass fractions.
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<br />In order tO'evaluate the possibility of such a systematic change, this study
<br />will addresS the following questions:
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<br />1. What'is the most accurate model for describing the relationship
<br />between $olute concentrations and streamflow? What are the estimated
<br />values of parameters for individual ions?
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<br />2. ,Do significant long-term trends exist in the recorded values of
<br />streamflQw, solute loads or concentrations, or relative composition of
<br />total di$solved solids, or in the estimated parameter values of the
<br />concentr4tion-streamflow relationship?
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<br />3. What are the causes of any identified trends?
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<br />In addition, this study will develop a data base containing monthly values
<br />from as early as 1926 for streamflow and concentrations of 7 ions at 16 major
<br />locations. .Documentation for updating the data base will be provided for use
<br />in future statistical analyses.
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