PROJECT ALERT NOTICE (OR) Responding to our first WY24 Atmospheric River Event

Date: Tue, 05 Dec 2023 23:10:34 EST

Summary: Moderate to heavy rainfall causing flooding and sediment transport in western Oregon tributary rivers in the Coast Range and Willamette Valley.

Several rounds of moderate to heavy rain are forecast through Thursday of this week, combined with mountain snowmelt, which will increase the chance of flooding in western Oregon, especially in tributary rivers. Significant amounts of precipitation are occurring in watersheds recently affected by wildfires in 2020 and 2023.

On Tuesday a landslide event occurred near Cougar Reservoir in the South Fork Mackenzie watershed. Oregon Water Science Center is not responding to the landslide event, but we are situationally aware. Watersheds draining the western Coast Range, including the Siletz, Trask, and Wilson Rivers, and emptying into the Willamette system east of the Coast Range including Luckimute, Tualatin, and Pudding Rivers are forecast to exceed flood stage in the coming days.

Monday through Thursday, multiple crews from Portland, Eugene, and Central Point offices will measure and sample (WQ and Sediment), and one crew is mobilizing for bed load measurements. One station went down due to vandalism, and repair was completed Tuesday.

Several Willamette Basin reservoirs are in deep drawdown to manage for juvenile fish passage, and staff are working with the U.S. Army Corps of Engineers staff to monitor the reservoir water level and outflow conditions including streamflow, dissolved oxygen, and turbidity.