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<br />66 <br /> <br />METROPOLIT,IN WATER DISTRICT' <br /> <br />. ,... ," -, <br />'. 0" I <br /> <br /> <br />Pi,r;. 6. CIIlfo"ado Hi,:c/' bosiJ/ <br /> <br />Colomdo R/:vel' water quaz.ity <br />The regulated outflow from Lake Mead, which furnished the <br />water supply for Lake Havasu and the Metropolitan Water Dis- <br />trict aqueduct, as well as numerous other diversions, showed <br />increased salinity and hardness during the fiscal year 1951-52. This <br />trend had in fact persisted since December 1949, when diversions <br />at the aqueduct intake above Parker Dam were of the best quality <br />available since December 1936, after which date Lake Mead stor- <br />age became effective in mixing the relatively pure May-Ju]y flood <br />inflows with the low runoff of other months. This recent increase <br />in hardness, etc., of the Lake Mead discharge was a result primarily <br />of the subnormal runoffs of 1950 and 1951, as records shice 1925 <br />show proportionately poorer water quality with be]ow-normal Co]o- <br />rado River discharges. A secondary factor was that near the end <br />of December 1949, discharge was begun from the Hoover Dam <br />lower gates at elevation 900 feet instead of the upper gates at <br />elevation 1050 feet, ('hanging the outflow to a mixture of the res- <br />ervoir contents instead of the less saline stratified s\Il'fa('e storage. <br />