Water experts: Snowpack melting down, end of runoff in sight

Snowpack melting down, end in sight.

BOISE -- As of Thursday, the Boise River at Glenwood Bridge was flowing about 9,300 cubic feet per second, which is well above flood stage.

Water managers tell KTVB they intend on maintaining these levels at least through the end of next week. But the good news is, they say, we are nearing the end of the runoff season - which is a light at the end of the tunnel.

For the first time this year water experts are able to say this:

"We're finally seeing the signs that we're running out of snow," USDA Natural Resources Conservation Service hydrologist/water supply specialist Ron Abramovich said.

But they're not breathing a huge sigh of relief yet - they're taking it one week and one forecast at a time.

"Maybe in another week we'll have a better answer to say that most of the volume of water to come out of the hills is behind us," Abramovich added. "I wouldn't say that until we see what happens this weekend with these rain events."

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Hydrologists say mountain snowpacks are melting about two inches a day, so there's not enough to keep the stream flows as high as they have been.

"We still have a lot of snow above 8,000 feet, basically, it's the high sites that are still holding on to it. So that's what's feeding the streams now. The good news is we've lost a lot of the snowpack that's less than 7,000 or 7,500 feet."

But a wet winter and an abundant, well-above-normal mountain snowpack across the state means stream flows will stay high. Abramovich says in both the Payette and Boise Basin in the West Central Mountains, the remaining high-elevation snowpack is more than double normal for June 1.

In addition, the watersheds are primed and saturated. The Natural Resources Conservation Service states in their June 1 Idaho Water Supply Outlook Report that soil makes up part of the unsaturated zone, which is the space between the ground surface and water table, and this sometimes forgotten reservoir of water can temporarily store and release large quantities of water to aquifers, streams and lakes.

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The USDA report says the solid snowpack that still exists above 8,000 feet is in the central mountains and in most basins, the remaining high-elevation snowpack is more than twice normal. The report states residual streamflow forecasts call for average or greater June to July volumes across Idaho; some of the highest forecasts are 150 percent to 250 percent of average for streams with headwaters in Idaho's central mountains - being South Fork of the Payette, Boise, Middle Fork of the Salmon, Salmon, Big Wood, Little Wood and Big Lost. 

"It's the wet winter and fall rains that we had is going to keep streams high all the way through the summer. So just because we're running out of snow doesn't mean we're going to see below-normal stream flow, they'll still be above average for most of the year."

Hydrologists say water year-to-date precipitation in the West Central basins ranges from 130 percent to 155 percent of average, with the Boise River basin being the highest. 

KTVB Meteorologist Rick Lantz says an unseasonable cold front is coming in this weekend and is expected to bring moderate rain and even some snow in higher elevations.

"What that would actually do is stop the remaining snowpack from melting. It'll melt later on, which is good too," Abramovich added. "That might be better to have the moisture fall as snow rather than rain because rain flushes down the river so fast, that's when you get those spikes."

Cooler temps on the horizon will slow the current snowmelt down again, like it did off and on throughout the month of May, which is good news for water managers.

"We probably won't be able to cut back too much on the flows through town immediately," Bureau of Reclamation water manager, Brian Sauer, told KTVB.

But the Bureau of Reclamation says that slowdown should give them some breathing room and extra space in the Boise River reservoir system that, as of Thursday, was extremely full at 96 percent of capacity.

Sauer says they have no plans to either increase or decrease steadily high Boise River flows; they will work with the Army Corps of Engineers to drop them as soon as they deem it is safe to do so.

"Since we do still have a lot of snow there, we will be maintaining these flows for a little while longer just to make sure we don't have any rainstorms or anything like that that's going to cause any problems," Sauer added.

We might be out of the woods in the near future with high flows on the Boise River and with flooding issues near the river, but once the water recedes officials say there will be a lot of erosion and damage that will have to be assessed.

© 2017 KTVB-TV


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