The 1996 Floods: How the JWC Kept Water Flowing During Oregon’s Worst Floods

This month marks 30 years since Oregon’s largest flood event.
That winter, an unusual confluence of weather events made the floods particularly severe. Abnormally high rainfall and relatively low snowfall saturated ground soil and raised river levels.

In late January, a heavy snowstorm was followed by a deep freeze that lasted for six to ten days. That new layer of snow was quickly melted by a warm subtropical rainstorm in the first week of February. The combination of the additional rain, the saturated ground, and the melting snowpacks flooded dozens of streams and tributaries.
The region’s major rivers reached historic levels. The Tualatin River rose five feet above the flood stage, reaching 125.2 feet.

The floods had a major impact on the Joint Water Commission (JWC)’s Water Treatment Plant. Water treatment processes were significantly slowed due to the levels of debris and sediment in the water. The raw water turbidimeter at the plant, which measures the number of suspended particles in water pumped from the river (not yet treated), peaked at 1,248 NTU. Under normal winter conditions, untreated water NTU usually ranges from about 12-80 NTU. The JWC plant regularly produces finished drinking water with 0.03 NTU.

Despite the challenging conditions, the plant continued treating water throughout the flood. Three operators were stranded at the plant for three days before the National Guard was able to evacuate them. The operators worked around the clock to successfully treat the highly turbid water to normal levels before it left the facility.

The JWC Water Treatment Plant’s continued operations during those three days ensured that the cities of Hillsboro, Forest Grove, Beaverton and Cornelius, as well as the Tualatin Valley Water District had access to clean drinking water, even as the flood disrupted nearly every other aspect of daily life.