#Snowpack #Runoff news: Dust on snow will affect runoff

Westwide SNOTEL map May 22, 2016 via the NRCS.
Westwide SNOTEL map May 22, 2016 via the NRCS.

From the Valley Courier (Ruth Heide):

Thanks to spring snowfalls and cooler temperatures keeping the snow in the mountains a bit longer, the Rio Grande Basin’s snowpack is now above normal.

In fact in the northern part of the basin the threat of flooding conditions now exists, Colorado Division of Water Resources Division 3 Assistant Division Engineer James Heath told water leaders at the Rio Grande Roundtable on Tuesday afternoon in Alamosa.

He said as of [May 16], the basin snowpack was 104 percent of normal.

“We exceeded last year’s peak, which is good,” he said. “We are looking at a pretty good runoff. The northern part of the Valley is looking at flooding conditions already.”

He said La Garita and Carnero Creeks are already running at about 100 cubic feet per second (cfs). They typically peak at 50-60 cfs.

“They will get higher over the next week,” he said.

He said Saguache Creek is running at 175 cfs and is steadily climbing.

Heath said the Division of Water Resources is reviewing three forecasts to help determine what the annual flow of the Rio Grande and Conejos River systems will be this year, but the three forecasts vary quite a bit. Traditionally the water office has relied on the Natural Resources Conservation Service (NRCS) but is also now reviewing forecasts from the National Weather Service and WRF-Hydro, a modeling system developed by the National Center for Atmospheric Research.

On the Rio Grande, the National Weather Service has the highest forecast of 659,000 acre feet for the April-September time period , WRF-Hydro the next highest at 542,100 acre feet with NRCS at 445,000 acre feet for April-September . Division Engineer Craig Cotten decided to use a figure of 540,000 acre feet for the April-September time period and 660,000 acre feet for the calendar year.

“That’s above average on the Rio Grande system,” Heath said.

Thanks to return flows, the water division is going to maintain curtailment levels at 13 percent on the Rio Grande.

Curtailments on the Conejos River system have gone up, however, Heath explained. Curtailments were at 22 percent when the irrigation season started and now are at 26 percent.

The total anticipated flow of the Conejos River system this year is 300,000 acre feet, which is about average, Heath said, with 267,500 acre feet anticipated April-September. The forecasts between NRCS, the National Weather Service and WRF-Hydro were not as disparate on the Conejos system, with NRCS estimating 208,500 acre feet April-September, the National Weather Service predicting 327,000 acre feet and WRF-Hydro anticipating 297,700 acre feet.

From the Valley Courier (Ruth Heide):

Dust on snow is more than unsightly.

It also causes the snowpack to melt sooner, which affects runoff into the San Luis Valley’s rivers, creeks and irrigation ditches.

The only place in Colorado to do so, the Center for Snow & Avalanche Studies (CSAS) monitors and measures dust-on-snow events at 11 mountainous locations including two affecting the San Luis Valley, Wolf Creek Pass and Spring Creek Pass.

CSAS Director Jeff Derry talked about the center’s work and made a preview presentation for financial support to the Rio Grande Roundtable on [May 17] in Alamosa. The water group will consider the formal request during its next meeting.

Derry said the data the dust-onsnow studies provide helps improve snowmelt forecasts.

“We collect a lot of data that SNOTEL does not,” he said.

The monitoring sites are at higher elevations than most SNOTEL measurement sites, he said.

Colorado’s recently completed water plan acknowledges dust on snow as a problem, Derry said. Simply put, when the snow is dirty, it melts faster because it does not reflect off the sun as well, Derry explained.

He said there could be several dust-on-snow events through a winter, which create layers of dust between snowfall layers in the snowpack, and in the spring when the snow begins to melt off the mountain, when the snowpack reaches those dust layers, it melts at a higher rate. This can explain erratic peaks in runoff, he said.

“Dust can be a major error in forecasting because they don’t know where dust might be in the snowpack so they can’t account for it,” Derry said. He said the biggest source of dust is from the Southern Colorado Plateau. The only way to know how many layers of dust there are in the snowpack is to dig snow pits, Derry said. “There’s just no substitute for going out and digging a snow pit.” He said this year on average there were about six dust events, with most of those being moderate events. Last winter there were three. “We usually see about eight events a year,” Derry said. There have been as many as 12-13 dust events in a year, however.

Rio Grande Roundtable Chairman Nathan Coombs said this type of information could be valuable for water management in the basin.

“This is a very big decision-making tool,” he said.

“Any kind of forecasting tool is very important to us,” added Roundtable member Travis Smith.

Derry will be asking for financial assistance from each of the basin roundtables . His first request was to the Rio Grande Basin roundtable.

He is asking for $25,000, but that could be split over more than one year, he said.

Dust on snow in the San Juans
Dust on snow in the San Juans

From The Mountain Mail [May 9, 2016] (Paul Goetz):

Colorado snowpack reached 104 percent of median by May 1, the Natural Resources Conservation Service reported Friday in a news release.

Conditions have shown the first improvement over the previous month since Jan. 1.

Mountain precipitation across the state during April was the best in 2016 at 110 percent of normal. Water year-to-date is at 100 percent of normal.

Colorado’s current snowpack and precipitation levels are right where they should be this time of year, Brian Domonkos, Colorado snow survey supervisor, said.

Elsewhere in the West seasonal snowpack has succumbed to early spring warming and has not recovered as Colorado did from recent storms, he said.

“In the Pacific Northwest, low precipitation and high temperatures led to a dramatic reduction in snowpack,” said NRCS hydrologist Cara McCarthy. “In this area, peak streamflow is arriving weeks earlier than normal this year.”

Not all areas have low snowpack. “Parts of Wyoming and Colorado have seen much above-average precipitation in recent weeks, causing concerns about potential flooding in the North Platte,” said McCarthy.

Snowpack for the North Platte River basin is 114 of median, 177 percent of last year.

The South Platte River basin is 114 percent of median, 117 percent of last year.

The seven major mountain watersheds in Colorado all received 90 percent of normal April precipitation or better. Special mention is warranted in the Arkansas, Upper Rio Grande and combined Yampa, White and North Platte basins because these areas received 120 percent of normal or better precipitation.

Rio Grande River Basin snowpack reached 77 percent of median and 269 percent of last year’s snowpack.

Yampa/White river basins are sitting at 106 percent of median, 224 percent of last year’s snowpack.

The seven major watersheds also have 90 percent of normal or better water year-to-date precipitation.

Arkansas River Basin snowpack reached 110 percent of median, 122 percent of last year’s snowpack.

Snowpack metrics indicate that the North and South Platte river basins have the best snowpack in the state at 114 percent of normal.

The Arkansas River saw the greatest improvement in April, while the Upper Rio Grande and combined San Miguel, Dolores, Animas and San Juan basins saw little change. Snowpack there is now 77 and 85 percent of normal, respectively.

Although not reflected in snowpack values, the NRCS noted it is also fortunate that rain was abundant most particularly in the Upper Rio Grande, which added to the greater water budget.

Statewide reservoir totals increased 1 percent since April 1, ending the month at 112 percent of normal, with declines occurring in the Rio Grande, Arkansas and combined Yampa, White and North Platte watersheds.

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