Colorado water managers are saying good riddance to water year 2018. It enters the history books alongside 2002 and 1977 as one of the driest on record for the Upper Colorado River Basin.
According to preliminary numbers from the Bureau of Reclamation, water year 2018, which ended Sept. 30, had the third-lowest unregulated inflow into Lake Powell at 4.62 million acre-feet. That’s just 43 percent of average.
Only 1977 and 2002 saw less water flow into Lake Powell from the upper basin, at 3.53 million acre-feet and 2.64 million acre-feet, respectively.
The average yearly inflow is 10.8 million acre-feet.
The months of August and September 2018 were the third- and fourth-worst months for unregulated inflows into Lake Powell behind only July and August of 2002.
The unregulated flow in August was just 2 percent of average. Lake Powell is currently 46 percent full.
“We know if we have another drought, the risk of draining Lake Powell is real,” said Jim Pokrandt, director of community affairs for the Colorado River Water Conservation District and chairman of the Colorado Basin Roundtable. “If we have another year as bad as this one, you’re going to see lots of discussions about who’s going to take reductions. We really need three, four, several years of average or above-average snow years to get us out of this pickle.”
Roaring Fork conditions
Locally, the Roaring Fork watershed was extremely dry this water year. The region was plagued by record-low snowpack — the lowest snow-water equivalent ever recorded for some dates at the McClure Pass and Independence Pass SNOTEL sites — sparse runoff, record-low streamflows and a hot, dry summer.
Low flows were prevalent across Colorado during the last two weeks of the water year, which runs from October through September. According to the National Oceanic and Atmospheric Administration’s drought information system, 30 percent of U.S. Geological Survey stream gauges in the intermountain West reported record-low seven-day-average stream flows for the last two weeks of September, including some in the Roaring Fork watershed.
On Sunday, the last day of the water year, the USGS river gauge on the Roaring Fork at Stillwater Road just east of Aspen showed the river flowing at 19 cubic feet per second, beating the previous minimum flow of 21 cfs in 1977.
Flows on the Crystal River were similarly low. Above Avalanche Creek and above a series of diversion structures, the river was running at nearly 46 cfs, lower than the previous record low of 48 cfs in 1977.
At the river gauge near the state fish hatchery and downstream from several diversion structures just outside of Carbondale, flows dribbled down at just under 7 cfs Sunday.
Colorado Department of Water Resources Engineer for Division 5 Alan Martellaro said the summer’s weak monsoons exacerbated conditions caused by little snowfall.
“We had a bad snowpack,” Martellaro said. “It was not the worst, but then we have had an incredibly dry summer, a total lack of rain. I think when we start analyzing it, we are going to find the flows in late summer are unprecedented. We have done some things we have never done before.”
Martellaro is referring to curtailment on the lower Crystal in late July. Amid rapidly dropping flows, the district 38 water commissioner turned down the headgate of the Lowline Ditch, which he determined was diverting too much water. The ditch diversion did not exceed its legally decreed amount; the problem was that it was violating new state guidelines regarding wasting water.
According to data from the Natural Resources Conservation Service, many sites around western Colorado rank as the driest since recording began for water-year precipitation, including McClure Pass, Schofield Pass and Independence Pass.
Statewide, the water year precipitation average at all SNOTEL sites measured just 21.4 inches, which is 64 percent of average — the second-lowest on record behind only 2002.
“It was pretty consistently dry throughout the entire year,” said Karl Wetlaufer, a hydrologist with the NRCS Colorado Snow Survey. “February may have been the only month where we had near-normal precipitation across the state.”
In some instances, reservoir releases have come to the rescue of downstream anglers, fish and ecosystems.
Releases from Ruedi Reservoir will continue through October to bolster flows for endangered fish in what’s known as the 15-mile reach, a notoriously dry section of the Colorado River between the Palisade area and the confluence with the Gunnison River in Grand Junction.
As of Sunday, Ruedi Reservoir was discharging roughly 300 cfs and the Colorado River below Glenwood Springs was running at 1,360 cfs, meaning Ruedi releases accounted for just over 20 percent of the volume in the Colorado at that location.
Periodic releases from Green Mountain Reservoir near Kremmling also boosted summer flows in the Colorado River. But that water will need to be replaced this winter by snowfall, Martellaro said. Ruedi Reservoir is currently 63 percent full while Green Mountain Reservoir is nearly 46 percent full.
“Where we have large reservoirs that can supplement the flows, yeah, we’ve gotten by,” Martellaro said. “But even that is coming to an end. We are running out. It remains to be seen what the snowpack is like to refill these large holes we’ve put in these reservoirs.”