The dangerous high waters on the San Juan River and Upper Rio Grande are beginning to recede following the surge from heavy rains that created historic autumn peak streamflows on the San Luis Valley’s river system.
The high flows also came at the end of irrigation season for Valley farmers and the Colorado Division of Water Resources, which will now account for the extra water in its management of the Rio Grande Compact.
The Rio Grande itself peaked at 7,000 cfs from the bounty of rain that came through the southwest region here in mid-October. The Colorado Division of Water Resources is estimating that the out-of-character weather event added 20,000 to 25,000 acre-feet of water to the Rio Grande system itself and around 10,000 to 15,000 acre-feet that was diverted into the Valley’s canal system, according to staff engineer Pat McDermott.
That measuring of the water and accounting for how it fits into this year’s obligations under the Rio Grande Compact is underway. The irrigation season ends Nov. 1.
McDermott, in a report Tuesday to Rio Grande Basin Roundtable members, said not all of the water will be of beneficial use to the Valley and the Upper Rio Grande Basin. The middle Rio Grande could see about 5,000 acre-feet flow downstream, but with a largely dry riverbed in Albuquerque, benefits from the October storms likely won’t extend as far south as Elephant Butte.
“This is not a significant event in New Mexico,” McDermott said.
For the reservoirs on the western and southern end of the Valley, it has been. Rio Grande Reservoir, Platoro Reservoir and Terrace Reservoir all will increase storage, with the reservoirs all in priority during the irrigation season for the first time since 2019.
Rio Grande Reservoir will have somewhere between 2,000 and 4,000 acre-feet of storage, Platoro Reservoir has increased its storage and Terrace Reservoir has gone up about 2,000 acre-feet, McDermott said.
“This is kind of unusual to have this big a flow event,” McDermott said. “It doesn’t happen.”
McDermott noted the importance and effectiveness of the Valley’s canal ditch riders, who worked to push water into their ditches to help with the surges of streamflow.
The Empire Canal, Monte Vista, the Rio Grande Canal, the Farmers Union, San Luis Valley Canal all opened their ditches to take in water, McDermott said.
“We here have very, very cooperative owners that have opened up their ditches after several months of non-use. We want to thank all those ditch operators for getting out there and taking some of this available flow. It is a wonderful thing.
“This is a really good thing for our basin,” said McDermott. “It’s going to give us an opportunity to get some water back out into the ditches late in the season, which we don’t see very often.”
Much of Valley will now go into its offseason with moist soils. But as McDermott noted, areas like the critical Saguache Creek, Carnero Creek, and the east side of the Valley down south through Trinchera didn’t receive much benefit from the rains.
The next best thing would be a normal to above-normal snow season in the San Juan Mountains and Sangre de Cristo range.
La Niña is still looking weak. But as October has shown, weather can happen.