Aspen Journalism is compiling a data dashboard highlighting metrics of local public interest, updated weekly on Tuesdays.

Local streamflows close to average

While streamflows in the Roaring Fork basin in fall are generally dropping, river levels came up between Sept. 11 and 18 as precipitation re-emerged in the weather pattern following an 11-day-long dry spell in Aspen.

Below Maroon Creek, the USGS gauge measured streamflow at 128 cfs on Sept. 18, or 103.2% of average. That’s up from Sept. 11, when the river was flowing at 123 cfs at 87.2% of average.

At Emma, below the confluence with the dam-controlled Fryingpan, the Sept. 18 streamflow of 450 cfs represented about 97.2% of average. That’s up from 419 cfs, and 89.3% of average, on Sept. 11.

At Stillwater, located upstream of Aspen, the Fork on Sept. 18 ran at 41.2 cfs or 85.8% of average, up from 36.3 cfs and from 75.6% of average, on Sept. 11. That put the river above the decreed minimum instream flow for the stretch of 35 cfs.

The transbasin diversion that sends Roaring Fork basin headwaters to Front Range cities was flowing at 1.4 cfs on Sept. 18, which was unchanged from Sept. 11.

Meanwhile, the Crystal River above Avalanche Creek, which is not impacted by dams or transbasin diversions, flowed at 90 cfs, or 78.5% of average, on Sept. 18. Last week, the river ran at 77 cfs, or 62.4% of average.

Lake Powell’s water level keeps dropping

Lake Powell‘s storage remains at one of its lowest levels recorded since it began filling in the 1960s. On Sept. 18, the reservoir was 23.87% full (with a total capacity based on a 1986 sedimentation survey) or 24.9% full (based on 2017-18 sedimentation data), down from Sept. 11, when it was 24.03% full (1986 data) or 25.06% (2017-18 data).

On July 1, the Bureau of Reclamation revised its data on the amount of water stored in Lake Powell, with a new, lower tally taking into account a 4% drop in the reservoir’s total available capacity between 1986 and 2018 due to sedimentation.

“After inputting the new data on July 1, 2022, storage values at the current elevation were updated, resulting in a decrease of 443,000 acre-feet,“ bureau officials wrote in an email. 

Aspen Journalism published a story explaining the recent drop in storage due to sedimentation.

The reservoir’s capacity has fallen since last year, when on Sept. 18, 2021, it was 30.37% full (1986 data).

On Sept. 18, Lake Powell’s elevation reached 3,529.5 feet, or 170.6 feet from full pool, down from 3,530.3 feet on Sept. 11. That puts the water level just five feet above the target elevation of 3,525. Powell’s surface elevation this year peaked at 3,539.84 feet on July 3, after it dipped to its lowest level since filling of 3,522.24 on April 22. Last year, on Sept. 18, the reservoir reached 3,547.2 feet, or 152.8 feet from full pool.

The “minimum power pool” for turbines generating hydropower at the Glen Canyon Dam is 3,490 feet, and 3,525 feet has been set as a buffer to ensure that the reservoir and the turbines can continue to function properly.

Air temperatures get closer to normal

High air temperatures at the Aspen airport are dropping as they went from 88°F on Sept.7 to 75°F on Sept. 10, which was still about five degrees above normal. Maximum air temperatures went back up to 79°F on Sept. 12 before going down to 65°F on Sept. 14, which is four degrees below normal. Meanwhile, low temperatures went from 48°F on Sept. 9 to 35°F on Sept. 11. On Sept. 14, minimum temperature was hovering around 43°F, or about four degrees above normal.

Air quality in Aspen was cleaner last week

The air quality in Aspen improved last week after air quality was impacted by out-of-state wildfires. Only Sept. 12 recorded “moderate” air quality last week. The AQI index reached 53 for PM2.5 on that day. For the remainder of the week, the air quality was “good” with an AQI index ranging from 13 for PM2.5 on Sept. 18 and 40 for ozone on Sept. 13.

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,...