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<br />TemporaQ' Increases <br /> <br />.::. <br />~.... <br />o <br />N <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 as <br />it may be determined that development and/or human activity have impacted the salinity levels. <br />The program is not, however, intended to offset the salinity fluctuations that are a result of the <br />River's 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 />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 mainstem, therefore it is probable that salinity levels will exceed the numeric criteria in <br />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 periods <br />of below long-term average annual river flow will also be in compliance with the standards. With <br />satisfactory reservoir conditions, and when river flows return to at or above the long-term average <br />annual flow, concentrations are expected to be at or below the numeric criteria. <br /> <br />Recent analyses have shown that the impact of natural variations in the hydrologic cycle <br />can have a significant impact on salinity. These natural variations in runoff can cause a <br />fluctuation in average annual salinity concentrations of about 450 mg/L TDS at 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 additional water development projects beyond those <br />anticipated to occur be completed before control measures are identified or brought on line, <br />temporary increases above the numeric criteria could result. However, these increases will be <br />deemed to conform with the standards if appropriate salinity control measures are included in the <br />plan. <br /> <br />Plan of Implementation <br /> <br />The Forum believes it should assess whether implementation of the salinity control <br />program maintains salinity at some interim point in time at or below the numeric criteria as <br />provided for in the standards. For this report, the Forum has decided to look ahead about 20 <br />years to the year 2015. The Plan of Implementation has been designed to maintain the salinities <br />of the Colorado River at or below the numeric criteria below Hoover Dam. As described in <br />Chapter 2, the plan of implementation must remove 1,476,600 tons of salt to meet this goal. This <br />will principally be accomplished by reducing the salt contributions to the River from existing <br />sources and minimizing future increases in salt load caused by human activities. <br /> <br />3-3 <br /> <br />:.Ii: <br />