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<br />Temnorary mr......WJll <br /> <br />0' <br /> <br />'r, <br />....'- <br /> <br />The plan of implementation as set forth in this Review is designed to remove or control <br />enough salt from the river system to maintain salinity levels at or below the 1972 levels as far <br />as it may be determined that development and/or human activity have impacted the salinity <br />levels. The program is not, however, intended to offset the salinity fluctuations that are a result <br />of the highly variable annual flows (natural variations in the hydrologic cycle). The plan of <br />implementation for this Review is based on the use of the long-term mean water supply, as were <br />the 1975 Report and all subsequent Reviews. <br /> <br />C''J <br />i-" <br /> <br />It should be recognized that the river system is subject to highly variable annual flow. <br />The frequency, duration, and availability of carryover storage greatly affect the salinity of the <br />lower main stem. Therefore, it is probable that salinity levels will exceed the numeric criteria <br />in some years and be well below the criteria in others. Given the above assumptions, the flow- <br />weighted average annual salinity will be maintained at all times at or below 1972 levels. <br /> <br />Periodic increases in salinity above the criteria as a result of reservoir conditions or <br />periods of below long-term average annual river flow will also be in compliance with the <br />standards. With satisfactory reservoir conditions, and when river flows return to at or above <br />the long-term average annual flow, concentrations are expected to be at or below the numeric <br />criteria. <br /> <br />As shown in Figure 2.2 of Chapter 2 (page 2-5), the flow-weighted average annual <br />salinity concentrations can fluctuate greatly. Recent analyses have shown that the impact of <br />natural variations in the hydrologic cycle can have a significant impact on salinity. These <br />natural variations in runoff can cause a fluctuation in average annual salinity concentrations of <br />about 450 mg/L IDS at Imperial Dam. The plan of implementation, as set forth in this Review, <br />will, by the year 2015, prevent a salinity concentration increase of approximately 140 mg/L at <br />Imperial Dam. <br /> <br />The federal regulations provide for temporary increases above the 1972 levels if control <br />measures are included in the plan. Should water development projects be completed before <br />control measures are identified or brought on line, temporary increases above the numeric <br />criteria could result. However, these increases will be deemed in conformance with the <br />standards if appropriate salinity control measures are included in the plan. <br /> <br />PLAN OF IMPLEMENTATION <br /> <br />The plan of implementation has been reviewed and modified as a result of this Review. <br />The changes that have been made in the plan of implementation since the last triennial review <br />are described more fully in Chapters 4 and 5. The plan of implementation is designed to <br />maintain the salinity concentration of the river at or below the numeric criteria, principally by <br />reducing the salt contribution to the river from existing sources and minimizing future increases <br />in salt load caused by human activities. The control measures are selected on the basis of cost- <br /> <br />3-3 <br />