|
<br />16
<br />
<br />period of 6 consecutive years when the trend indicated the average flow was con-
<br />
<br />sistently low.
<br />
<br />The information given in table 12 and figure 7 is that the drought of the
<br />
<br />1950's was severe, and that records for 1942-64 tend to dominate the records for
<br />
<br />the longer period, 1900-64, so far as low disCharges are concerned. Information
<br />
<br />also is given that a drought of 6 years duration when irrigation water supply will
<br />
<br />be deficient, may be anticipated.
<br />
<br />The drought of the 1950's was unusually severe and, while records to evaluate
<br />
<br />its possible recurrence do not exist in long enough time for reliable computations,
<br />
<br />there is some justification for assuming that its recurrence is not likely to be
<br />
<br />repeated in the near future. However, a more severe drought could occur at any
<br />
<br />time.
<br />
<br />Table 12.-Minimum flow for consecutive years, 1900-64.
<br />
<br />Minimum Average Calendar Mininrum Average Calendar
<br />Consecutive annual flow Years Consecutive annual flow Years
<br />Years (acre-feet) Years (acre-feet)
<br />-
<br />1 444,000 1952 11 1,223,000 1943-53
<br />2 520,000 1952-53 12 1,306,000 1942-53
<br />3 626,000 1951-53 13 1,271,000 1951-6.3
<br />4 741,000 1950-53 14 1,257,000 1950-63
<br />5 1,038,000 1949-53 15 1,290,000 1950-64
<br />6 1,161,000 1948-53 16 1,349,000 1949-64
<br />7 1,158,000 1947-53 17 1,338,000 1947-63
<br />8 1,194,000 1946-53 18 1,344,000 1946-63
<br />9 1,193,000 1945-53 19 1,336,000 1945-63
<br />10 1,224,000 1944-53 20 1,340,000 1944-63
<br />
<br />Rainfall An additional source of water is the rainfall. For the period
<br />
<br />1922-63, annual rainfalls over the U. S. side of the Valley from Falcon Dam to
<br />
<br />the Gulf of Mexico varied from 12.35 inches in 1956 to 38.84 inches in 1941, and
<br />
<br />averaged 24.26 inChes, according to published records of I. B. & W. C. There is
<br />
<br />also a variation from the upper to the lower end of the Valley, annual rainfalls
<br />
<br />~veraging from about 17 to 27 inches from one place to the other. (See table 13 p.22.)
<br />
<br />.~\ ~ "", (' .' ,
<br />'I... '.
<br />IJV..........\.,.Iw
<br />
|