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<br />. <br /> <br />PART VI <br /> <br />EVALUATION OF' EXISTING SALINITY CONDITIONS <br /> <br />.... <br />CJl <br />I\;, <br />/'.:. <br /> <br />be decrt!Bsing th~ salinity of the Colorado River. However, several <br />factors complicate the analysis of the decline and leveling off Df <br />salinity concentrations. The most significant of these are the natural <br />variations in concentrations stemming from variations in runoff and the <br />effects of initial filling and oper.nieo of the mainstem reservoirs. <br />These and other factors, loIhich may cause shifts in sal ioity, are dis- <br />cussed in the fa llowing sect ions. <br /> <br />I. Hydrologic Conditions <br /> <br />The sal inity conceoleal ion In rivers generally decreases with <br />increased flow on an annual basis. Years of lower flows art" charactPr- <br />ized by higher TDS C<.lncentrat ions than years of higher flo....s. Combining <br />this characteristic with the lag time in the reservoir system because of <br />storage suggests the decline of TDS concentrations may have been in part <br />caused by the transition from a relatively drier period (1955 to 1965) <br />with an annual virgin (undepleted) flow of 13.23 ~F at Lees Ferry, to a <br />relatively wetter period (1965 to 1975) with an annual virgin flow of <br />14.76 MAF. This is an incrt"asE' in the ftow of approximately to percent <br />and may be responsible fvr atl or part of the 9 percent decrease in TDS <br />concentration observed at Imperial Dam. <br /> <br />2. Reservoir Effects <br /> <br />. <br /> <br />The period of 1963-80 represents the most significant period of <br />reservoir storage in the history of water development on the Colorado <br />River. The storage in Flaming Gorge Reservoir, Lake Powell, and Lake <br />Mead increased from ll?sS than 20 MAF in 1963 to over 50 ~F by 1980 <br />(Figure VI-)). The spill of Glen Canyon Dam in 1980 ended the initial <br />filling of the major reservoirs on the Colorado RiVer. <br /> <br />During <br />(calcium sulfate) <br />voirs(15) and at <br />Reudi Reservuir <br />salt leaching at <br />constituency and <br /> <br />the initial filling, significant leaching of gypsum <br />was documented at Flaming Gorge[ 14j and Reudi Reser- <br />Lake Mead, [ 16] but gypsum leach ing at Lakf' Mead and <br />has diminished. Final documentation of the long-term <br />Flaming Gorge and Lake Po....ell is part of the ongoing ion <br />reservoir studies described in Part IX. <br /> <br />The reservoir system, having completed its initial filling, is <br />approaching a dynamic hydrologic equilibrium but chemical equilibrium has <br />yet to be documented. The long-term implications of this dynamic equi- <br />librium will require a very detailed analysis of reservoir ....ater quality <br />conditions for at least the 1975 to 1985 period. <br /> <br />. <br /> <br />In additi.on to salt leaching, the reserVOirs may play an <br />imp.Htant part in other major factors which influence TDS. There is <br />strong evidence that Flaming Gorge and Lake Powell have stored higher <br />TDS water and routed the lower TDS spring runoff downstream from 1965 <br />through 1980. There is a question as to whether this situation will con- <br />tinue after the reservoirs reach a more stable or equilibrium condition. <br />Flaming Gorge is present ly und~rgoin~ significant chemical changes as <br /> <br />27 <br />