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Historical Floods

This section is intended to provide information about floods in California's past. Historical information regarding previous floods is essential in developing our understanding of current floods. Have earlier floods been larger or smaller? How big can floods get? We ask these questions in order to try and predict the size of floods and to give warnings about the potential flood risk. The goal is to protect life and property from flooding.
"The first flood reported in California occurred on the Los Angeles River in 1770."

H. B. Lynch
Rainfall and Stream Run-off in Southern California Since 1769
Metropolitan Water District of Southern California, August 1931, p. 2

Synopsis of California's Flood Measurements

Written accounts of floods began with the arrival of Spanish missionaries to Southern California in 1769. California's first rainfall measurements were recorded in 1847. James W. Marshall discovered gold in 1848 on the South Fork of the American River in northern California. The influx of people brought individuals and the U.S. Army, which in 1850 started measuring rainfall in San Diego. (Lynch, 1931, p. 5) Since 1850, rainfall measurements have been taken in Sacramento, San Francisco, and San Diego.

December 1861 and January 1862 Floods

The Sacramento Valley experienced four floods from December 1861 through January 1862. These floods are legendary in newspaper accounts from the time. The historic descriptions and pictures from these floods continue to hold fascination today. Can these floods happen again? This is the question covered in "Lake Sacramento" — Can It Happen Again? [PDF*, 8MB] by Leon Hunsaker with Claude Curran (2005).

The authors' approach to answering this question was to research the available historical data. After conducting field trips to libraries, newspaper offices, historical societies, and various public and private sources, Hunsaker and Curran concluded "… a realistic assessment of the runoff potential can be made for each December 1861-January 1862 flood event." (p. 2) Their publication describes their journey, what they found, how they used the data, and their conclusions.

Estimate of American River Peak Flow on January 10, 1862

In 2005 Leon Hunsaker and Claude Curran completed their book, "Lake Sacramento" — Can It Happen Again? They decided to continue their look into the historic 1862 flood.

"During the summer of 2006, we decided if our results were going to be conclusive we needed to demonstrate numerically that the flood peaks of January 1862 were greater than any that occurred in the 20th century. We chose the American River because of its early history of flooding the city of Sacramento. Then it was decided that a peak flow estimate would be made for January 10, 1862 at Folsom — the recognized date of the all-time record high flow on the American River at Folsom (Fair Oaks)."
They chronicle their reasoning behind estimating the American River peak flow on January 10, 1862 in Step by Step Development of Peak Flow Estimate on the American River @ Folsom for Record Flood: 1/10/1862 [PDF*, 273KB] (2011).

Rainfall and Stream Run-off (1769-1931)

Rainfall and stream run-off data from California's Spanish Mission period, beginning in May 1769, through 1930, the date this was written, are analyzed in Rainfall and Stream Run-off in Southern California Since 1769 [PDF*, 9.2MB] by H. B. Lynch (1931). The data apply to Southern California. Ten conclusions are reached (summarized and paraphrased here):
  1. There had been no material change in the mean climatic conditions for 162 years
  2. The 40 years from 1890-1930 had fewer fluctuations from average conditions than did earlier years
  3. A 28-year drought ending in 1810 was about as severe as, and more protracted than, the drought occurring when this paper was written
  4. Both 1810-21 and 1883-93 had rainfall surpluses more intense than 1890-1930
  5. Rainfall deficiency from about 1822 to 1832 was more severe than anything experienced up to 1930
  6. The longest rainfall deficiency occurred from 1842 to 1883, though it was not as acute as other periods
  7. The drought occurring when this paper was written (1930) could not be considered a major shortage
  8. Water yield of the areas under consideration closely approximates run-off from principal streams
  9. Run-off fluctuations generally track rainfall fluctuations, but are larger
  10. Useful water yield for Southern California has been 50% of average for a period of ten years, and 70% for a period of 28 years (within the dates studied)

This paper may be useful for students of historical water yield in California.

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