Aspen Journalism is compiling a data dashboard highlighting metrics of local public interest, updated at least every Friday. Check back for updates as we add more features.

Air quality improving in Aspen

This past week, the air quality in Aspen improved compared to the week before, but it was still reported as “moderate” for three days. The air quality has been “good” since Aug. 22 with an AQI index for ozone down to 41 on Aug. 19 and 42 on Aug. 25. Poor air quality experienced in the region over the past few weeks was caused by smoke mostly from California and Pacific Northwest fires.

Air temperature getting lower than normal

Over the past week, maximum air temperature measured in Aspen was lower than normal, down to 58°F, or 18.5 degrees below normal, on Aug. 19. The minimum temperature was also lower than normal, down to 36°F on Aug. 20, which is about 10 degrees below normal.

Local streamflows back up

The USGS gauge located near the Utah state line measured the Colorado River flowing at 3,040 cfs, or 86% of average, on Aug. 25. The streamflow rate increased by 30% from Aug. 18 and 37% from Aug. 25, 2020.

Two weeks ago, upper Roaring Fork streamflow levels were lower than the minimum instream flow of 32 cfs established by a 1976 water rights decree. But the Cameo call — referring to senior water rights in the Grand Valley — on Aug. 13 led state authorities to cut flows into the Independence Pass transmountain diversion system that sends water collected from multiple creeks at the top of the Roaring Fork basin to Twin Lakes on the eastern slope. The diversion’s streamflow running through a tunnel under the Continental Divide dropped from 19.7 cfs on Aug. 13 to 1.6 cfs on Aug. 14. This has been helping the river meet the minimum instream flow.

The USGS gauge on the Roaring Fork near Aspen at Stillwater, located upstream of town and two major diversion ditches, measured streamflow at 41.4 cfs on Aug. 25, which represents 76.7% of average. Last week, the river was flowing at 47.8 cfs. On Aug. 25, 2020, the river ran at 32.9 cfs, or 60.9% of average. 

The ACES gauge, located near the Mill Street Bridge in central Aspen, measured the Roaring Fork at an average of 27.46 cfs on Aug. 25, down from 32.76 cfs on Aug. 18. The river ran at 11.73 cfs on that day last year.

The ACES gauge measures the river, which is already diminished by the diversion to the eastern slope, in an especially compromised stretch — below the Wheeler and Salvation ditches that divert water for upper valley users, and before the channel is replenished by Hunter, Castle and Maroon creeks.

The Crystal River above Avalanche Creek, near Redstone, flowed at 99 cfs, or 65.8% of average on Aug. 25. That was up 52% from last year, when the river ran at 65 cfs on Aug. 25, 2020. The Crystal River at the Dow Fish Hatchery bridge ran at 49 cfs on Aug. 25 after reaching up to 262 cfs on Aug. 20. The current streamflow remains below the minimum instream flow set at 100 cfs set by the 1979 water rights decree.

Lake Powell’s storage and elevation keep shrinking

Lake Powell‘s storage kept getting lower this past week, reaching its lowest level ever recorded on Aug. 25 when the reservoir was 31.26% of full.

Last week, on Aug. 18, the reservoir was 31.35% of full. The reservoir’s capacity has fallen significantly since last year, when on Aug. 25, 2020, the reservoir was 48.72% of full.

The surface elevation of Lake Powell is also in decline and hit record low on Aug. 25, 2021, when the reservoir’s elevation dropped to 3,550.3 feet, or 149.7 feet from full pool. The reservoir’s elevation has lost 0.3 feet since Aug. 18, when the elevation was at 149.4 feet from full pool. Last year, on Aug. 25, the reservoir reached 3,601.03 feet or 98.97 feet from full pool.

If the surface elevation of the reservoir on the Utah-Arizona state line, which stores Colorado River basin water, drops below 3.525.5 feet, it would trigger a host of consequences, including impacts to Glen Canyon Dam affecting hydropower production and potential litigation between the seven states that share water under the 1922 Colorado River Compact. The federal Bureau of Reclamation has begun releasing more water from reservoirs upstream in the basin to avoid this scenario.

Laurine Lassalle is Aspen Journalism’s data desk editor, where she works to catalogue and analyze local public data. She also heads our our “Tracking the Curve” project, documenting COVID-19 in Pitkin,...