In addition to the specific flood data, this section provides a description of the hydroclimatology and a summary of significant floods for each State or territory in the United States. The summary of significant floods includes those with loss of life or excessive damage during the period 1970 through 1989. The floods that were in the top 5 percent of each streamflow-gaging station's record during this period are tabulated, and an estimated recurrence interval is provided along with other pertinent data. A map of each State or territory is supplied to locate the streamflow-gaging stations.

California

Hydroclimatology

California is located on the West Coast of the United States. It borders about 800 mi of the Pacific Ocean and makes up nearly two-thirds of the coastline between Canada and Mexico. Precipitation in California is caused primarily by moisture-laden marine air moving in from the Pacific Ocean. A semipermanent high-pressure system located off the coast tends to regulate the movement of Pacific storms and is a key feature of the atmospheric-circulation patterns that determine California's climate (Paulson and others, 1991). Most of California's precipitation is received between November and March. California's mountain ranges induce precipitation and create "rain shadows" in the leeward valleys and plains. The combined effects of topography and atmospheric-circulation patterns result in mean annual precipitation that ranges from about 3 in. in the desert areas of southern California to 120 in. in the coastal mountains near the Oregon border (Paulson and others, 1991).

Flooding is limited generally to the winter storm season, except in the southern deserts, where summer thunderstorms occasionally produce localized flash floods. On the basis of regionalization procedures that relate flood characteristics to watershed and climatic characteristics, the magnitude of maximum discharges for streams in California is dependent on drainage area of the basin, mean annual precipitation, and an elevation index, which is the mean of elevations (in thousands of feet) at points along the main channel at 10 and 85 percent of the distances from the site to the divide (Jennings and others, 1994).

Significant Floods

The flood of February 1986 was the most extensive in California during 1970-89. Twenty-three percent of the streamflow-gaging stations in the State recorded significant discharges. The flood was caused by a storm that produced substantial rainfall and excessive runoff in the northern one-half of the State (California Department of Water Resources, 1988). A series of storms embedded in a flow of moist air from the southwest moved across the State. Rain continued for 12 consecutive days in many areas of northern California. The largest total rainfall was 49.6 in., recorded at Bucks Lake in the Feather River Basin (Paulson and others, 1991). Storm totals of 20 to 30 in. were common for many locations. Maximum discharges of record were measured on the Russian River at Guerneville (station 11467000, fig. 27a, 27b and 27c) and the Napa River near Napa (station 11458000, fig. 27a, 27b and 27c)

California also had significant floods in 1980 and 1983. During the 1980 flood, 13 percent of the streamflow-gaging stations in the State recorded significant discharges, and 17 percent had significant discharges during the 1983 flood. The 1980 flood was most severe in central and southern coastal California.

The location of streamflow-gaging stations in California that had significant floods for 1970-89 is shown in figure 27a, 27b and 27c by station number. The specific data for each significant flood are listed in table 6. A significant flood is one that ranks in the top 5 percent of all annual maximum discharges for that station's period of record.

References

California Department of Water Resources, 1988, California highwater 1985-86: California Department of Water Resources Bulletin 69-86, 107 p.
Jennings, M.E., Thomas, W.O., Jr., and Riggs, H.C., 1994, Nationwide summary of U.S. Geological Survey regional regression equations for estimating magnitude and frequency of floods for ungaged sites: U.S. Geological Survey Water-Resources Investigations Report 94-4002, 196 p.
Paulson, R.W., Chase, E.B., Roberts, R.S., and Moody, D.W., compilers, 1991, National water summary, 1988-89-Hydrologic events and floods and droughts: U.S. Geological Survey Water-Supply Paper 2375, 591 p.

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