Flood profiles on the Cedar River, King County, Wash., were developed from 21.1 to 33.65 miles upstream from the mouth for the flood of December 3-4, 1975, and for a 100-year flood. Estimated water-surface elevations during a 100-year flood indicate virtually all the flow would be contained in the river channel. Since 1914, Cedar River flows have been affected by impoundment and release of storage from Chester Morse Lake at river mile 35.6, and since 1901 by diversion for water supply at river mile 21.6. Flood-frequency analysis, based on 62 years of regulated flows (period 1915-76), indicate the 100-year flood would have a discharge of 8,600 cubic feet per second at river mile 23.4 and 6,870 cubic feet per second at river mile 33.2. The highest flood since regulation began occurred December 3 and 4, 1975, and was 7,930 cubic feet per second at river mile 23.4 and 6,860 cubic feet per second at river mile 33.2. Recurrence interval of this flood is about 70 years at river mile 23.4 and about 100 years at mile 33.2 under present conditions of storage and regulation.
