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Experts marvel at precipitation totals

Monday was the first day of spring, yet there's a lot more winter weather on the way.

From the Crater Lake rim to Mount Ashland and ridges above the region's waterways, it's been a wet year. Snowpack numbers range from 120 inches at Crater Lake to 175 inches at Mount Ashland, while precipitation figures are well above norms.

The spring equinox touched the Northern Hemisphere at 3:28 a.m. Monday. Yet, for the time being, there isn't a visible difference in Southern Oregon.

The National Weather Service has measured 21.5 inches of precipitation at the Medford airport since Oct. 1, when the water year began.

That's 8.33 inches above the normal 13.17 inches of rainfall. Since Jan. 1, NWS has recorded 9.81 inches of rain, 5.53 inches above normal. March has been a little slower, but 0.4 inches is expected Tuesday, and more rain — and snow at higher elevations — is anticipated during the next week.

The winter of 2016-17 isn't destined to be remembered for any catastrophic moments, but its sustained drenchings have been noteworthy.

"Things stand out when there's an extreme storm," said Chris Park, a forest hydrologist at the Rogue River-Siskiyou National Forest in Grants Pass. "But I can't honestly remember in recent history anything like we're seeing right now. We're, on average, 150 percent of normal. When the ground gets supersaturated, groundwater levels keep raising."

"I don't see a flood threat unless we have rapid and intense warming with unseasonable warmth or long duration of heavy rain," said Spencer Higginson, an NWS hydrologist.

As snowpack melts, moisture sinks into the soil, recharging the groundwater. But once the moisture level is maxed out, what doesn't refreeze into the snowpack heads downhill.

"If you think of it like a sponge, you can pour water on it and it absorbs to a point and then the water just runs off," Higginson said. "What you lose into the ground takes the burden off the streams, creeks and rivers. Once there's no more capacity, there's a greater chance of being overwhelmed."

Usually, slides and other road upheavals are associated with large-scale storms, but this year has been different.

"We haven't seen any big storm events, just a long duration of rain across the forests," Park said. "When roads are cut into hillsides and the bank cut gets saturated, that's when you see failures and slides onto the road. We keep getting fluctuating weather with the ground supersaturated. The snow level drops, warm fronts follow, and that keeps the cycle going."

High flows are normal for this time of year, said Mark Schuster, a hydrologist with the U.S Geological Survey Oregon Water Science Center. As runoff pours down soggy hillsides and squeezes into creek beds, packing narrow channels, the flow gnaws off chunks of rock and soil; sometimes taking trees with it.

"With the high flows, water blows through, changing the channel configuration," Schuster said. "When material sloughs into the river, it forms new controls that slow how fast the water goes down the river."

Continual precipitation presents its own problems. 

It's much easier to obtain federal funds to repair damage from a single storm than from a slow, steady drip.

The flooding in the winter of 1964-65 was considered a 100-year event, Park said. The 1997 flood was a 50-year event.

"They were triggered by heavy rain on snow, kicking streams up and causing bank failures," Park said. "When roads fail like that, we can get federal highway support."

Persistent rainfall and melting snow don't fit the criteria.

"They come to me when there are road failures, and I can't show a 25-year event," Park said. "We have records back to the 1800s. You see very wet and very dry years, it's all part of the big cycle."

Surging torrents, fed by fluctuating snow levels and rain, have rearranged channels here and there.

"With the snow melting, along with rain, the flows kick way up," Park said. "That's when we see bank failures. Wood gets into streams and can clog on bridges, which is what happened below Union Creek last year."

 — Reach reporter Greg Stiles at 541-776-4463 or business@mailtribune.com. Follow him on Twitter at www.twitter.com/GregMTBusiness, on Facebook at www.facebook.com/greg.stiles.31.

High water roars through the Rogue River Gorge Sunday. High water will be a common sight throughout the region this spring after a steadily wet winter. [Mail Tribune / Greg Stiles]