WSP11356 - Laserfiche WebLink

Home Browse Search

further slight revisions), the total intlow to Lake Mead in 1951-52 of 18,500,000 acre-feet was about 32 per cent above the estimated present normal inflow. Lake Mead storage reached a maximum of 26,743,000 acre-feet, including 2,620,000 acre-feet of dead storage below the lowest outlet gate sill elevation. The corresponding max- imum water surface elevation was 1201.10 feet on Jul,' 16, 1952. This is 32.1 feet, or 4,360,000 acre-feet more than the 1951 maxi- mum and 19.3 feet, or 2,870,000 acre-feet (present revised capacity table) less than the maximum of record in 1941, when the reservoir was first filled practically to the spillway gate crest. On April 5, 1952, just before the start of the unusually early flood runoff, the minimum storage for the season was 18,230,000 acre-feet with water level at elevation 1133.24 feet, 8.0 feet below the 1951 mini- mum and a new record minimum since the first tilling of Lake Mead in 1938, though only 0.7 foot lower than the 1947 minimum water level. As of September 30, 1952, the Lake Mead water sur- face elevation was at 1190.00 feet with total contents of 25,163,000 acre-feet. This is 26.25 feet higher and 3,425,000 acre-feet more storage than on the same date one year ago. On figure 3 are plotted Lake Mead discharges and storage con- tents with water surface elevation for the years 1934 to 1952 covering the period of operation of the reservoir. To supplement this historical water wpply record, figure 4 shows the annual inl10w to Lake Mead since 1897, with years since 1921 measured and earlier data estimated from the best available upstream Or downstream gaging records. This inflow record is then replotted on the same plate in the form of a differential mass curve, in terms , of the average inflow for 1905-1951. This mass cUl'l'e shows the l-.---- -cumulanvnleviatiOl11'romtne meal\, tosinililate the operationcl- ,. such a reservoir as Lake Mead (but assllmed to be of unlimited capacity and with no allowance made for losses) if the same cycle of runoff now recurred under conditions of present upstream devel- opment and depletion and with full lower basin development or consumption approximated, the mean annual inflow being uniformly released from the reservoir. Each successive year's excess or deficiency is plotted upward or downward, re~pectively, gO that a sustained upward trend of the curve to the right, as from 1905 to 1930, indicates an abnormally wet period, while a gustained downward trend to the right shows a subnormally dry period of years. The steepness of the trend line, or of each segment of the curve, indicates the intensity or severity of the wet or dry period by its variation from the horizontal. The latter represents a year r , I I I I I ~ !. , ~ II t '''j ~(".O v....... HYDROGRAPHY 59