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Late-Season Flood Makes History in Oregon's Willamette Valley

A hydrologist for the National Weather Service in Portland said the weather service has no record of a flood event in the southern Willamette Valley occurring this late in the rainy season.

(TNS) — No, it hasn't been flooding like 1996.

But the moderate flooding that forced the evacuation of about 500 people along the Coast Fork of the Willamette River and Row River between Dorena and Mount Pisgah on Sunday night and into Monday is notable in one sense.

Andy Bryant, hydrologist for the National Weather Service in Portland, said the weather service has no record of a flood event in the southern Willamette Valley occurring this late in the rainy season.

"The time of the year, just in my mind, makes it historically significant, that we're having a flood like this a week into April," he said.

Bryant added: "It's very unusual to have this kind of heavy rain in April. What we've had is more of a November through February kind of weather event."

The monitoring station at the Eugene Airport recorded more than 4.3 inches of rain had fallen since Thursday. It recorded 2.34 inches of rain on Sunday alone. That's the most precipitation that's fallen there in a single calendar day in more than seven years and breaks the mark for the wettest April day on record.

"Lane County really bore the brunt of the heavy rain," Bryant said.

But those are rookie numbers compared to the 1996 floods when more than 9.1 inches fell over four days in early February of that year, including 3.69 inches on Feb. 7, among the rainiest days in Eugene's recorded history.

Adding to the woes in 1996 was the presence of low-elevation snow and a rapid warmup, Bryant said. The melting snowpack contributed only somewhat to the recent flooding, the hydrologist said.

The 1996 flooding, the biggest event in three decades at the time, was regional, while the recent flooding has been largely confined to the central and south Willamette Valley.

"There was really high river levels right in downtown Portland," Bryant said of the flooding 23 years ago. "Especially from Albany northward, (for) most of the rivers ... the flow of record was from that February 1996 event."

But the lateness of last weekend's heavy rains created a unique challenge not present more than two decades ago.

Now is the time the Army Corp of Engineers is refilling its reservoirs behind flood-control dams both for the summer recreation season and to mete out water during the dry season to maintain flows for fish.

"Even as recently as last week we were trying to get up to the level ... where we like to be at this time of year," said Sarah Bennett, a spokeswoman for the federal agency. "Then this atmospheric river came through and gave us all this water."

The deluge meant the corps is spilling more water than it would typically. Lane County reported Sunday night that the corps notified its emergency manager that water flow from Dorena Dam, which creates the reservoir on the Row River, exceeded the rate during the 1996 flood to avoid an uncontrolled release of water.

The corps said in a news release Monday that the higher-than-normal releases would keep river levels in the Willamette Valley at flood stage — meaning water inundating areas not normally covered — through the middle of the week at several gauges, including at Goshen.

"We are managing flows in a way to protect the downstream public from flood to the extent we are able, and to maintain space in the reservoirs to avoid uncontrollable releases," Ross Hiner, the corp's Portland district dam safety manager, said in a news release.

He added: "However, inflows are so high that we are having to increase our releases to minimize the overall flooding risk."

Bennett said there's been no reports of damage to the flood-control dams. The corps has dispatched dam safety teams to keep an eye on the structures due to the high water.

Eugene Water & Electric Board shut off power generation at its hydroelectric dams along the McKenzie River as a precaution to avoid damage to its turbines and generators due to the atypical water flows.

EWEB spokesman Joe Harwood said there's been no damage to its hydroelectric dams due to heavy water flow. There's been a lot of debris floating downstream. The utility posted on its Facebook page video of what it said was a 75-foot tree trunk passing through a Leaburg Dam roll gate.

"It's roaring out there," Harwood said Monday afternoon.

Follow Christian Hill on Twitter @RGchill. Email christian.hill@registerguard.com.

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