#RioGrande basin: NCAR refining snowpack model for Conejos River watershed

Conejos River
Conejos River

From The Pueblo Chieftain (Matt Hildner):

The winter and spring snowpack that normally sits above this former mining town in the southeastern San Juan Mountains can be both a blessing and a curse.

It’s a blessing when there’s a lot of it — more runoff in the Conejos River basin in spring and summer is almost always a good thing.

But it can be a curse, especially for water managers trying to balance deliveries to local irrigators with the obligations of the Rio Grande Compact, because it’s difficult to measure, which, in turn, makes streamflows harder to forecast.

The Conejos Water Conservancy District, with the help of a host of federal and state agencies, has spent the last two years trying to change that.

The district is in the second year of a pilot project that’s prompted the installation of six new snow monitoring sites that can also measure soil moisture, humidity and temperature.

Another project component includes five new stream gauges in the upper reaches of the Conejos basin.

The project has also made use of a federal mobile radar and flights deploying a laser technology that precisely measured the watershed’s surface to get a better handle on the snowpack.

All of these steps result in data that are fed to scientists at the National Center for Atmospheric Research whom are refining a new forecasting model.

Nathan Coombs, manager of the Conejos district, knows a more accurate forecast model requires years of refinement but he’s encouraged by the project so far.

“We know we’re collecting better, usable data,” he said.

That’s a big improvement given that prior to the last two years, the 92-mile long Conejos had no snow gauges above its main stem and lacked stream flow gauges on many of its tributaries.

The lack of information can make it difficult for Colorado to predict its annual obligation under the Rio Grande Compact…

The Colorado Office of the State Engineer has traditionally used forecasts from the U.S. Natural Resources Conservation to project how big or small stream flows will be.

And the engineer’s office imposes curtailments on water users along both the Rio Grande and the Conejos to ensure delivery obligations are met.

Curtailments on the Conejos can often reach 30 percent and the timing of the restrictions can be exacerbated by an inaccurate forecast. “It’s headgates that are closed,” Coombs said. “It’s real, wet water that’s no longer available.”

Money for the project came from a wide range of funders.

The Colorado Water Conservation Board approved a $383,000 grant.

The U.S. Bureau of Reclamation and the National Oceanic and Atmospheric Administration also pitched in.

The Conejos district contributed $25,000, more than 10 percent of its annual budget.

But there are still some steps Coombs hopes to see happen that could further improve data collection for forecasting.

Right now the district’s highest snow gauge is at 10,500 feet in elevation, which excludes large swaths of the snowpack that run off in June.

“All of our late snow that throws our forecast completely out the window is above that,” Coombs said.

One solution to measuring that snowpack was a mobile radar unit stationed in Alamosa during the project’s first year that helped measure the intensity of late spring storms.

Coombs expects that unit to be back next year.

But a longer term solution may emerge from work with the U.S. Forest Service.

The district hopes to install snow gauges in the 161,000-acre South San Juan Wilderness, a move that would require forest service approval.

The wilderness area sits above the district’s gauges and is a monitoring blind spot.

It’s also home to a slew of important Conejos tributaries such as Elk Creek, and the South, Middle and Adams’ forks.

The end game of all the data collection and the work by federal scientists on the forecast model will give water managers a fuller picture of what’s coming downstream.

“Whether you have a compact or not, the priorities turn on and off because of what’s available,” Coombs said. “And if you know the why of what’s available, now you can start making management decisions.”

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