ALAMOSA — Major streams in the San Luis Valley will be running with less than half their average flows, and some spots will dry up this season.
Colorado Division of Water Resources Division 3 Engineer Craig Cotten delivered the bad news on Tuesday during the Rio Grande Roundtable’s April meeting.
Cotten had been predicting a dryer than normal water year for some time. However, the forecasts are now firmer for the irrigation season, which began early this year so farmers could utilize what little water there will be this year.
“We don’t have to deliver any water during the irrigation season to meet the obligation to the compact. We can take all the water that we have,” Cotten said, “which isn’t going to be very much.”
He added, “We are going to have low stream flows in both the Conejos and Rio Grande. I am sure we are going to dry up the Conejos and potentially the Rio Grande in some spots.”
Cotten’s current forecasted annual index flow for the Rio Grande is 300,000 acre feet, which is 46 percent of the long-term average, and the forecasted flow for the Conejos River system is 140,000 acre feet or 44 percent of the long-term average. The obligations to downstream states to meet the Rio Grande Compact can easily be met with wintertime flows, Cotten explained, so curtailments during the irrigation season will be zero. He said the obligation on a flow of 300,000 acre feet for the Rio Grande would be 75,000 acre feet and the obligation on the Conejos would be 16,000 acre feet. The Conejos has already delivered 12,000 acre feet to downstream states during January, February and March, Cotten explained, and he expected the Conejos system would deliver about 6,000 acre feet more in November and December, so “we will be over-delivered at least on the Conejos if the 140,000 turns out to be accurate.”
He added that the final flow could vary depending on factors such as future rainfall. He said the National Weather Service is predicting below-average precipitation through June but “equal chances” of average precipitation from July through September.
Snowpack as of Tuesday put the Rio Grande Basin second from the bottom in the state. The San Juan Basin sat at 41 percent and the Rio Grande Basin at 42 percent of average while some basins in the state such as the South Platte were at 100 percent. “As you get farther south, it gets less and less,” Cotten explained.
Even within the basin, there are areas that are in worse shape than others, he added. For example, the Alamosa/Trinchera sub-basin, which runs from Alamosa to Trinchera Creek, is at 31 percent of average and the Sangre de Cristo’s at 26 percent.
“It’s not real good anywhere,” Cotten said.
The Natural Resources Conservation Services (NRCS) forecasts for the rivers in the basin range from 50-51 percent at best for some of the rivers in the basin to 15 percent for Sangre de Cristo Creek, “the worst of all as far as the forecast,” and Cotten believes most of the NRCS forecasts are too high.
“They are just not going to have much flow at all, unfortunately,” he said.
It could be worse, however, Cotten added. “We are above 2002 for the basin but not very much on our forecasts.”
Although this year’s forecast for the Rio Grande is 300,000 acre feet or 46 percent of the long-term average, that’s still twice as much as the flow in 2002, which only saw 150,000 acre feet on the Rio Grande during that drought year.
In a separate presentation on Tuesday, Jeff Derry, executive director of the Center for Snow & Avalanche Studies shared similar news from a different perspective and showed data illustrating a trend of warmer, dryer years with earlier runoff peaks over time.
“I think you are all aware what’s going on and how abysmal everything is this year,” he said.
He shared snow course data at various elevations on April 1 that proved his point. For example, the snow course data for Pool Table Mountain, elevation 9,840 feet, is the worst year on record since 1950, and snow course data at La Veta Pas, elevation 9,440 feet, is the lowest since the 1960’s.
Derry showed trend lines for various areas from the 1930s forward that indicated snowpack was less and less over the years. He said in the Rio Grande Basin, areas that used to routinely have 15 inches snow water equivalent now experience around 10.
He added that data is also showing that the snow is melting and streams peaking earlier than in the past. In 2002 the Rio Grande’s high flow occurred about a month earlier than it typically had. He said he did not know if this year would be comparable.
In addition, Derry shared analyses reflecting warmer minimum temperatures and less precipitation during the winter in recent years than historically.
Caption: Forecasts for the Rio Grande this season are less than half the long-term average./Courier photo by Ruth Heide