Debris Flow — Juneau Borough, Alaska

2019-10-06 · near Douglas, Juneau Borough, Alaska

Event narrative

Most of the damage from the erosion when culverts were overwhelmed or blocked and debris flows that blocked roadways in Douglas were reported by trained weather spotters or emergency management right after midnight on October 6th. There was multiple calls from the public located on St. Anns Ave about minor street flooding in Douglas along with a debris flow on David and John Street washing out portions of the street. Police started to evacuate people out of harms way with the Red Cross helping people displaced from the damage. Just before sunrise more reports came in that Thane Road was blocked by a debris flow just before Mt.Roberts street. There was also other reports in the morning of the 6th that there was a debris flows in Cope Park in downtown Juneau along with major damage to the Alaska Electric Light and Power's flume system as a debris took out a section of the flume. One report came in that a person's oil tank became dislodged from erosion and was spilling heating fuel into the ground and street.

Wider weather episode

On the night of October 5th through the morning of the 6th, two weather systems merged over the Northeast Gulf of Alaska producing a strong and moist weather front. This front moved through Southeast Alaska causing strong winds and heavy rain. Complex (mountainous) terrain and strong winds as the front moved over the Juneau area resulted in enhanced rainfall in the early morning hours of October 6th.

Localized flooding on small creeks and debris flows occurred around the downtown Juneau area, Douglas and along Thane Road during the overnight hours. John Street, on Douglas Island, saw massive erosion when culverts were overwhelmed or blocked by debris from the rainfall runoff. This event produced highly variable 24 hour precipitation totals ranging from just over one inch at the Juneau airport to more than seven inches in Douglas with most rainfall falling in 6 to 12 hours. This was a very anomalous event with return periods ranging from a 200-500 year event in Douglas to a 10-25 year event in downtown Juneau for 12 and 24 hours time frame.

View location on OpenStreetMap → (58.2697, -134.3840)

Source: NOAA Storm Events Database, event_id 863218. Narrative written by the NWS forecast office that issued the report.