Flood in Ketchikan Channels, Alaska

There was 5 days of heavy rain with very high rainfall totals from December 10-14. The Ketchikan airport received thirteen point forty six inches for a five day total with a daily record of five point zero four inches on the 11. It was the wettest five day total in December for the period of record going back to 1902. Other notable five day rainfall total from around the area was ten point twenty three inches at Ketchikan Powerhouse, twenty three point twenty three inches at Sivlis powerhouse. The excessive rainfall event produces enough runoff that area power generation reservoirs rose significantly. There was a fourteen foot rise at Upper Silvis lake and over five feet at Swan Lake. Ketchikan Lake rose over seven feet and triggered the first level of the emergency action plan as the lake level was two feet over the emergency spillway. This overflow from the reservoirs caused very high water levels down stream and produced minor to moderate flooding within the city of Ketchikan. The highest flow from the reservoirs coincided with high tide on December 14th and exacerbate the flooding situation.

A strong, moist and slow moving weather front moved across the Southeast Alaska through the second week of December. The weather front had connection to tropical moisture and satellite imagery showed a well established atmospheric river pointed at the southern half of the Alaska panhandle. The front produced very heavy rainfall for multiple days to produce significant runoff into local hydroelectric dams which rose the water level above the emergency spillway for a few dam in the Ketchikan area. The uncontrollable flow from the dams and heavy precipitation rates produced very high water level in streams and river which produced some minor to moderate flooding.