Most northern reservoirs expected to fill with above average snowpack and runoff; southern basins, southeastern plains still under drought gun
By Bob Berwyn
FRISCO — Reservoirs in the northern and central Colorado high country will fill on schedule this year, water managers said Tuesday at the annual Summit County state of the river meeting, outlining their expectations for river flows and runoff volume in the Blue River Basin, a crucial water source area for both sides of the Continental Divide.
Most speakers focused was on these headwaters, but statewide maps also showed much of Colorado’s southern tier with below to well-below average snowpack — down to 50 percent in the Upper Rio Grande Basin, according to the Natural Resource Conservation Service’s Colorado snow survey program.
The dry conditions in parts of the eastern San Juans are part of regional Southwest drought footprint, which is increasing demand for this year’s runoff. Southeastern Colorado’s plains are still experiencing Dust Bowl conditions, along with parts of the adjacent south-central plains.
Troy Wineland, water commissioner for the Blue River Basin, said headwater streams in the Blue River Basin are flowing at twice their average volume for this time of year, with peak runoff yet to come. Generally, the Blue River and its tributaries reach peak flows some time in mid-June, though the exact timing is weather-dependent, Wineland said. The state of the river meetings continue the next few weeks with sessions up and down the Colorado River. Details here.
He concluded by pointing out that, even though Summit County saw above normal snowfall during much of the past year, the greater Colorado River Basin still faces long-term systemic issues that could add up to a 3.2 million acre foot gap by 2050. Careful stewardship of water should be hallmark of sustainable water management, not just a short-term reaction to drought, according to Wineland.
Denver Water is in good shape so far this water year, with above average snowpack in key river basins including the Upper Colorado and the South Platte. Starting with good storage gives Denver Water some room to juggle runoff flows to balance flood risks in Silverthorne with the over-arching mission of filling Dillon Reservoir, said Bob Steger, the utility’s manager of raw water supply.
Currently, the Roberts Tunnel, which conveys water from Dillon Reservoir to the South Platte system, is turned off and will stay off until sometime in July. Dillon Reservoir will fill sometime in the first half of July — earlier if the weather is dry the next few weeks, a bit later with persistent rain and snow.
For now, Denver Water is still passing water out of Dillon Reservoir downstream at the rate of about 1,000 cfs in the Lower Blue. The water level currently is about 18 feet below full, Steger said, adding that flows could remain at 1,000 cfs or higher for several more weeks, which means good conditions for rafters and kayakers.
Downstream, Green Mountain Reservoir should also fill by mid-July, said the Bureau of Reclamation’s Ron Thomasson, explaining the operations of the Colorado Big Thompson project and how Green Mountain Reservoir is a strategic link in storage chain that gives West Slope users some flexibility in using their allocations of Colorado River water.
State climatologist Nolan Doesken also offered up a few weather stats and facts, showing in one graphic how precipitation has been consistently above average for more than a year, leading to a 10-inch precipitation “surplus” going back to March 2013.
“This was a crazy winter we just lived through,” Doesken said, fingering the infamous polar vortex as a contributing factor in Summit County’s winter weather pattern. The polar vortex intensified the jet stream over Colorado, helping to squeeze out every potential drop of moisture, but leaving some upstream areas dry, he said.
Looking ahead, Doesken said a developing El Niño could be a factor in Colorado’s weather during the next six months. When El Niño forms, warmer than average sea surface temperatures in the eastern equatorial Pacific Ocean can nudge the winter storm track in a direction that favors Southern California and the Southwest, but the effects are less certain in the central and northern mountains.
An emerging El Niño in the spring and summer could help generate a wet monsoon season, and the NOAA Climate Prediction Center is now projecting better than even odds that Colorado will be wetter than average for the next six months.
But December, January and February can be rather dry in the mountains during El Niño winters, Doesken said. That doesn’t mean a big storm won’t roll through every now and then, but there can also be long winter dry spells under the influence of El Niño.