A series of storms beginning before Christmas 2005 and ending after New Year's Day 2006 produced significant runoff over much of northern California. The storms resulted in an estimated $300 million in damages and Federal disaster declarations in 10 counties. Several precipitation stations in the Sierra Nevada had precipitation totals greater than 20 inches for the period December 24 through January 3, and several stations in the Coastal Range had precipitation totals greater than 18 inches. The peak stream discharges resulting from the storms in the north coast area generally had recurrence intervals in the 10- to 25-year range, although the recurrence interval for peak discharge at one station on Sonoma Creek near Agua Caliente was greater than 100 years. In the San Francisco Bay area, peak discharges also generally had recurrence intervals in the 10- to 25-year range. Further south along the central coast and in southern California, peak discharges had smaller recurrence intervals, in the 2- to 5-year range. Upper Sacramento River tributaries draining from the west had peak flows with recurrence intervals in the 2- to 5-year range, whereas upper tributaries draining from the east side had recurrence intervals in the 5- to 10-year range. Further south, Sacramento River tributaries such as the Yuba and American Rivers had peak discharges with recurrence intervals in the 10- to 25-year range. On the east side of the central Sierra around Lake Tahoe, peak discharges had recurrence intervals in the 10- to 25-year range. Further south in the Sierra, streams draining into the San Joaquin River Basin had flows with recurrence intervals ranging from 2 to 5 years.
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Storms and flooding in California in December 2005 and January 2006 - a preliminary assessment