Bulletin 1.pdf - California Department of Water Resources - State of ...

114 WATER RESOPRCES OF CALIFORXIA
RUNOFF
Estimated mean seasonal natural runoff of the San Francisco Bay
Area for the 53-year period from 1894-95 to 1946-4i is 1,245,000 acre-feet.
or 1.8 percent of total surface runoff from mountain and foothill lands
in the State. The minimum seasonal total of 93.000 acre-feet occurred in
1923-24, and the maximum, amounting to 3,130,000 acre-feet. in 1906-07.
The lO-year period from 1923-24 to 1932-33 was the driest of record in the
Area. During each season of that period, except 1926·27, runoff was less
than the 53-:rear mean, and the average was only 49.1 percent of this
long-time mean.
Runoff from the Area is derived principally from rain, since snow
falls on only a small portion. Approximately half the total runoff occurs
between October 1st and February 15th, and about 30 percent during
the following 90 days. )[onthly runoff varies from approximately 1.5
percent of the seasonal total during the period from July to !\ovember
inclusive, to 28 percent in the maximum month, usually in the spring.
As of September 30,1947, the United States Geological Survey was
maintaining 14 stream gaging stations in the San Francisco Bay Area,
principal stations being Coyote Creek near :Madrone with a drainage area
of 192 square miles, Alameda Creek near !\iles with a drainage area of
634 square miles. and Xapa River near St. Helena with a drainage area
of 85 square miles. The only long-time records are those for Alameda and
Coyote Creeks.
Stream gaging stations of the Area are listed in Table 24, together
with average, maximum, and minimum seasonal runoff for stations with
records of ten years or more. The 14 gaging stations maintained by the
Geological Survey measure runoff from 1,216 of the 3.967 square miles
of land area in the San Francisco Bay Area. These stations are supplemented
by several, maintained by other agencies, which measure runoff
from minor basins, each of less than 50 square miles.
Estimated mean seasonal natural runoff from the Area by basins.
subbasins, and stream groups for the 53-year period from 1894-95 to
1946-47 is shown in Table 25. Of total mean seasonal natural runoff.
approximately 614,000 acre-feet was estimated by the empirical formula
described in Chapter III. Estimates of seasonal natural runoff of m8in
stream and tributary basins for which there are partial records are given
in Table 26.
A record of flow of Lagunitas Creek at Alpine Dam was obtained
from the :Marin County Municipal Water District. This record was begun
in 1914-15 and covers 27 of the past 33 )·ears. Runoff for missing seasons,
and for seasons prior to commencement of the record was estimated by
comparison with runoff of San Leandro Creek. Among records used in
computing and estimating natural flows in the Area secured from