CORVALLIS, Ore. – The relentless storm battering western Oregon is creating havoc and threatening records – and more rain appears on the horizon.
The Mary’s River already is a record stage, according to Kathie Dello of the Oregon Climate Service at Oregon State University. It reached 21.41 feet Thursday morning, breaking the old record of 20.9 feet, and causing flooding in Corvallis and Philomath.
“Many streams in western Oregon are now classified as ‘high,’ or above the 90th percentile,” Dello said. “What makes this so unusual is that a few days ago, most of these same streams – especially in southwest Oregon – were near record low levels.
“We needed the rain,” she added, “but not all at once.”
The Mary’s River data goes back 72 years for the gauge, according to Gordon Grant, a research hydrologist with the Pacific Northwest Research Station of the U.S. Forest Service. When it floods, he says, it usually creates problems.
“Once the Mary’s gets out of its banks, even a small increase in the flood stage represents a huge volume of water because the floodplain is so flat,” said Grant, who is a courtesy professor of geosciences and forestry at OSU. “The crest of the flood is largely driven by when the precipitation starts to taper off. The rain is projected to begin tapering off this afternoon, but we are still projected to get another 1-2 inches.
“So expect to see the Mary’s continue to rise through much of today,” he added. “Once the rains diminish, we can expect the floodwaters to stick around for a while – a day or more – because the valley and floodplains are quite flat and do not drain quickly.”
The rainfall has been significant. On Wednesday, 4.02 inches of rain fell at Hyslop Farm outside of Corvallis – the third highest 24-hour total in the station’s 101-year history. The only other days with more than four inches of rain occurred on Nov. 19, 1996 – when massive flooding hit Oregon – with 4.45 inches; and on Jan. 28, 1965, with 4.28 inches.
The Coast Range has been especially hard hit with five to seven inches of rain common in many areas. This is causing flooding of the rivers draining those hills, including the Siuslaw, Mary’s and Luckiamute rivers.
“We’re getting what is called an ‘atmospheric river’ or ‘pineapple express’ event, with warm, wet weather coming from the southwesterly direction,” Dello said. “These tend to be big rain events here in Oregon, though it is still cold enough at higher elevations to snow in the mountains, which was desperately needed.”