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

52 WATER RESOURCES OF CALIFORNIA
been eliminated. However, this form of expression does not give a true
measure ofwinter floods from drainage basins subject to substantial snow
cover. Size of the area actually contributing to runoff will vary, depending
upon the extent and absorptive capacity of snow cover at the time
of flood. Only limited information on snow cover and its effect on rain
floods is available.
For streams with flow records of 20 years or longer, analyses have
been made and graphs prepared for 1-, 2-, 3-, 5- and 10000y floods in
drainage basins throughout California embracing areas in excess of 1,000
square miles, and for all except 10-day floods in basins of less than 1,000square
miles. Floods of various durations were determined on the basis
of the following criteria:
(1) One-day Peak Flow. This is defined as a daily flow that
was both preceded and followed by lower flows. However, if two or
more consecutive daily flows were equal, that flow was considered
the one-day peak flow if the series of equal daily flows was both
preceded and followed by lower flows.
(2) Multiple - day Peak Flow. (a) Moving totals of a
sequence of daily flows may be obtained by subtracting flows of the
first day from the summation of flows of "n" days, and adding flow
of the day succeeding the"nth" day. The largest total flow for "n"
days, over a given flood period determined by such moving totals,
was taken as the "n"-day peak flow of the flood.
(b) If consecutive flood periods occurred with one or more days
in common, only the larger flood was considered.
(c) If one or more days included in a peak flow fell beyond the
date arbitrarily set as the limit of the flood season, the flood was
considered if the sum of daily flows within the season was greater
than the sum of flows beyond the season.
Flood-frequency data on rainwater floods as developed in the current
investigation are presented on plates in succeeding chapters. Frequency
data on volume of snow runoff, for the period from April 1st to
July 31st, are presented only for the Central Valley and Lahontan Areas.
QUALITY OF WATER
Inorganic chemical analyses used in this bulletin for evaluating the
quality of water resources were obtained from files and publications of
the Division of Water Resources, the United States Department of Agriculture,
the United States Bureau of Reclamation, the United States
Geological Survey, and the University of California. Analyses of municipal
supplies were also obtained from the California State Department
of Public Health, from United States Department of Agriculture Technical
Bulletin 448, from the City and County of San Francisco, from
the City of San Diego and from the Department of Water and Power
of the City of Los Angeles.
Principal bases in mineral constituents of natural water solubles
are calcium, magnesium, and sodium. These occur almost entirely as
bicarbonates, sulphates, chlorides, and nitrates. Boron, usually present
in smaller amounts than the foregoing constituents, may be particularly