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...." "" '~.......J HYDROGRAPHY 75 'J Havasu water. The latter averaged 60 colder for 1949 than in previous more normal years, and as much as 100 colder in the midwinter months, evidently as a result of the severely cold winter. Air temperatures at Boulder City, Needles. and Gene camp averaged 11 0 below normal for January 1949 and 60 below normal for November 1948 to March 1949, inclusive. As a result, Lake Mead stored waters became much colder than in recent previOUfi years and these lower temperatures still continue at the deeper leve]s where, as of September 30, 1949. the uniform deep temperature is 490 compared with 53' one year earlier. In line with the mentioned improvement of the water quality at the aqueduct intake during 1949, a similar improvement was finally evident in the aqueduct water reaching the La Verne softening plant, as was anticipated and forecllst in the Tenth Annual Report, page 67. The average for the fiscal year 1948-49, compared with the previous year's average, shows a reduction of 27 parts pel' million total dissolved solids, 10 p.p.m. total hardness, 7 p.p.m. non- carbonate hardness. 11 p.p.m. oulfate, etc. This improvement has continued during the summer of 1949, so that October 1949 com- pared with the year 1948-49 shows similar further reductions of 36 p.p.m. total dissolved solids, 20 p.p.m. total hardness, 1:3 ]l.p.m. noncarbonate hardness and 16 p.p.m. sulfate. As the Colorado River water presently diverted contains about 90 p.p.m. less total dissolved solids than the aqueduct flow reaching La Verne. after storage in Lake Mathews, there is still a large margin and the quality of the delivered water should therefore continue to show substantial im- provement (softer and less dissolved solids, etc.) for the next year or more, regardless of subsequent runoff conditions on the Colorado River water6hed. In Lake Mead. at a long-used sampling point just upstream from Hoover Dam, a dozen water samples at 50-foot depth intervals gave the following average analyses for September 1949 and for the comparable dates for previous years. For comparison there is listed also the most saline analysis on record for the reservoir, as of March 31, 1941. These representative averages are weighted in proportion to the storage volume corresponding to each sample, as the reservoir is sharply stmtified in summer after the inflow of re]atively pure flood runoff, and the top 50 feet of storage, for example, though only about 10 per cent of the water depth, includes 24 per cent of the present total storage and 28 per cent of the active storage contents of the reservoir. \ I 1\