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.. - ; ,; -. , i Li: Ie;;:' 66 METROPOLITAN WATER DISTRICT expectancy at Lees Ferry of 11,000,000 acre-feet annually (called 10,500,000 acre-feet in 1948). This normal is defined as the 1920- 1944 adjusted average flow of the Colorado River at this gaging station, The mean historical flow for this 25-year period is only 7 per cent less than for the 1905-1949 period. The further reduction of 2,340,000 acre-feet is derived from a mathematical rainfall-runoff relationship. The U, S. Weather Bureau forecasted flow for 1948-49 was 11,500,000 acre-feet, or 104.5')'0, of the computed normal. Divid- ing the observed flow by this percentage gives 13,700,000 acre-feet, which is only 2 per cent less than the long-time mean derived directly from the recorded runoff without a rainfall-runoff adjust- ment. Forecasts for earlier years indicate that this close check is in some degree meTely coincidental. However the wide variation of 3,000,000 acre-feet in published values for the normal runoff expect- ancy on the Colorado River is extremely unsatisfactory, in view of the great importance of such estimates in connection with project planning in both the upper and lower Colorado River basins, It also adds a severe handicap to the already sufficiently hazardous sport or art of runoff forecasting. Including measured tributary side inflo\\' and also unmeasured gains, combiued with the observed flow of the Colorado Rivcr at the Grand Canyon gaging station (tentative and sub,;ect to further slight revisions), the total inflow to Lake Mead in 1948-49 was about 3 per cent above the estimated present normal inflow of 14.500,000 acre-feet annually. Lake Mead storage reached a maximum of 27.409,000 acre-feet (by the original capacity curve not corrected for silt deposits), including 3,207,000 acre-feet of dead storage, with a water surface elevation of 1196,61 feet on July 31, 1949. This was the highest level since 1944, though only 3,9 feet higher than the 1948 (July 7) maximum but 24 feet lower than the maximum of record in 1941 when the reservoir was first filled practically to the spillway gate crest. On April 16, 1949, before the start of the flood runoff, the minimum storage fo,' the season was 20,750,000 acre-feet with water level at elevation 1145,5 feet. or 9,0 feet below the 1948 minimum but 11 feet above the 1947 minimum. The latter is the 11-year record low water surface since the first filling of Lake Mead in 1938. Un figure 4 are ~:ott€d Lake !\1cad di~charge" ~nd ~torage COIl- tents with water surface elevation for the years 1934 to 1949, covering the period of operation of the reservoir, To supplement this historical water supply record, figure 5 shows the annual inflow i 'I I l ~