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

WATER RESOURCES OF CALIFORNIA 41
areas. It occurs principally in the desert regions, especially in the
Lahontan and Colorado Desert Areas and in adjacent portions of the
Central Valley and South Coastal Areas. Analyses of floods caused by
cloudbursts are not included in this bulletin, since sufficient data with
reference to areal extent and frequency of occurrence are not available.
Those rainstorms in California which produce floods not associated
with cloudbursts are general and cover large areas. In nearly all cases
they occur during winter and early spring, and may last several days,
although periods of intense rainfall are comparatively short. While
general storms are common during the rainy season, destructive floods
are only infrequently produced. To cause a major flood the storm must
either be of long duration, or must occur while watersheds are saturated
and little channel storage space is available. The combination of a
saturated watershed and such a storm is rare.
Estimated magnitudes of mean daily flows of rainwater floods with
probable frequencies of once in 100 years and once in 250 years on seven
representative streams in the State are given in Table 5. This table also
shows maximum instantaneous recorded flows on these streams, including
preliminary estimates for the floods of November, 1950, where applicable.
No estimates are given for streams in the Colorado Desert Area, as :floods
in this Area are mainly of the cloudburst type.
Snowfloods
Floods resulting from melting snow occur in streams that drain the
higher mountains of the State, and characteristically have longer duration
and lower peak :flows than rainwater floods. Data relating to daily
flow for one, two, three, five or even ten days have little significance in
these floods. In the present investigation snow-melt season from April
to July, inclusive, has been considered as one :flood period, and total
volume of flow has been computed for these four months. Volumes of
BIlOW melt were determined for those 13 streams of the Sierra Nevada on
which have occurred the greatest snow-melt :floods experienced in the ­
State. Nine of the streams are in San Joaquin Valley in the Central Valley
Area, and four are in the Lahontan Area. Estimates of volumes of snow
floods with probable frequencies of once in 100 years and once in 250
years are shown in Table 5, for two of the representative streams of
California.
QUAUTY OF WATER
Most fresh waters in California are of excellent quality and well
suited to irrigation and other beneficial uses. This is especially true of
drainage from the North Coastal Area and from the eastern side of the
Central Valley Area, both of which Areas have large watersheds with
high water yield. Analyses show that their surface and underground
waters possess remarkably slight concentrations of salts, low percent
sodium, and relatively small amounts of elemental boron. These waters
are of the bicarbonate type, and calcium is the predominating base. Surface
waters of comparatively high salinity are found in streams on the
west Bide of the San Joaquin Valley, in Cache Creek in the Sacramento
Valley, in basins on the west slope of the Diablo Range that separates
the Central Coastal and Central Valley Areas, in Cuyama and Santa
Maria Rivers in the Central Coastal Area, and in Piru and Sespe Creeks