It’s hard to believe it’s already been over a year since the tragic floods that impacted Northeast Oregon and Southeast Washington. Heavy snow followed by heavy rain led to rapid rises on the Umatilla and Walla Walla rivers, which generated widespread flooding. The flooding caused the inundation of numerous homes and businesses, destroying or damaging several roads and bridges and damaging or overtopping levees.
Here we take a moment to review this record-breaking disaster.
The event, which began as a winter storm system, affected the Blue Mountains and adjacent foothills on Feb. 4 and Feb. 5, 2020, with some 12 to 18 inches of new snow falling atop an already above-normal mountain snowpack. Snow transitioned to moderate to heavy rain on Feb. 6, 2020, all the way up to 5,000 feet, bringing relatively warm rain over the deep snowpack.
This resulted in rapid snowmelt and erosion of the snowpack, as well as runoff from the heavy rains. With no way to penetrate the frozen or saturated ground, liquid from snowmelt and rainfall simply ran downhill into creeks and streams, finding its way into the Umatilla and Walla Walla rivers, resulting in rapid river rises and record flooding.
The Umatilla River at Pendleton and Gibbon, and the Walla Walla River near Touchet, Washington, all hit record levels and flow rates. Areas of Southeast Washington were also hard hit with the Touchet River, Coppei Creek and Mill Creek all setting new record stages and flows. While the scope of flooding was somewhat confined to Northeast Oregon and Southeast Washington, it was also quite severe.
Numerous homes and businesses were inundated and damaged, several roads were either damaged or washed away, and levees topped and/or breached, resulting in flooding in areas that rarely experience it. Multiple search and rescue missions were carried out to get to people cut off from civilization due to roads being washed out or underwater. Tragically, one fatality occurred near Bingham Springs.
These floods were especially dangerous because the waters rose so fast, leaving little time to gather important belongings and evacuate to safe shelter. While river flooding is commonly a gradual process occurring over one or two days, this event was much more acute. The rate at which water levels rose could be compared to a flash flood wave moving through a river basin. This is largely due to the complex terrain of the region, and the location of vulnerable watersheds and basins in the mountains. As heavy precipitation affects these regions, runoff is quite rapid and can quickly overwhelm rivers and streambeds downhill.
Floods of this kind are the result of what we call rain-on-snow events, and while they aren’t uncommon in the Pacific Northwest as we head into the warmer spring months, it’s highly unusual to see so much rainfall on top of so much snow all at once. It’s a timely reminder that as we continue to progress into the longer warmer days with mountain snowpack upstream in the mountains, flooding will remain a potential threat and it’s best to be prepared if you live in a flood-prone area.
If you live along or near a body of water, especially in a flood-prone area, make a plan now and know where you and your family will go if you must evacuate. Make sure you know where important documents and medications are so you can quickly grab them if needed. Oh, and don’t forget about your pets. They are part of the family, after all.
Let’s hope this year brings plentiful rain and snow, just not all at one time.