The damp days of October bring with them fallen leaves, foggy mornings, and puddles on the sidewalks. October 1 is also the start of the new water year, as rainy days become more frequent and our river and streams begin to flow more strongly.
While a calendar year ends a couple of months into the wet season, a water year follows the flow of the season. During the 2021-2022 water year — which ended September 30 — the Tualatin River Watershed received 37.7 inches of rain, as recorded at the Hillsboro Airport. That’s greater than the average annual rainfall of 35.9 inches, and significantly more than has fallen each of the last few years. The majority of rain occurred last fall and this spring. That wet spring was immensely helpful for stream flows after a dry and hot summer in 2021, meaning Clean Water Services did not initiate stored water releases until the end of June — much later than in recent years.
The Tualatin River is an essential resource for Washington County, with high demands on its water for agricultural, industrial, and urban use. To keep up with those demands and ensure the small and slow river flows throughout the drier summer months, CWS and our Tualatin River Flow Management Committee partners — Joint Water Commission, Tualatin Valley Irrigation District, and Lake Oswego Corporation —release water from Hagg Lake and Barney Reservoir
. CWS closely monitors releases to ensure healthy water quality and also discharges clean water from our water resource recovery facilities all year. That combination of released and discharged water makes up about 80% of the flow in the Tualatin River in the summer.
Forecasters with the National Oceanic and Atmospheric Administration (NOAA) and the National Weather Service predict another La Niña winter, which typically means cooler and wetter weather and could again bode well for stream flows in the Tualatin River Watershed.
“We are heading into a third La Niña water year,” says CWS Water Resource Analyst Jamie Hughes, “but overall climate change cyclical patterns are still something to keep in mind. We may get a few really wet years like this one, but the drought years are coming.”