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.

July highway traffic in Aspen nears 2019 levels — but was still the second lowest in the last 22 years

While July 2021 hit summer occupancy records in Aspen and Snowmass Village, the car counts recorded by the city of Aspen at the intersection of Highway 82 and Cemetery Lane, located at the entrance of town, remain low compared to averages over the last 20 years.

On average, the city counted 25,844 cars each day passing through the intersection, up to 28,188 on July 2. That is just 0.9% below July 2019’s daily average 26,083. July 2021’s count is the second lowest over the past 20 years, with July 2020 hitting a record-low daily average of 23,766. This year’s mark is nearly even with July 2011, which saw 25,849 cars on average each day. In the last 10 years, the highest July average car count was set in 2015 at 28,825 while the three highest marks since 1999 came in 2003 (29,258), 2004 (29,278) and 2005 (29,544).

Local streamflows below minimum instream flow — again

Three 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. This helped the river meet the minimum instream flow for about two weeks. The Cameo Call is still on, but over the past week, streamflow levels on the upper Roaring Fork have gone down and are no longer meeting 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 29.9 cfs on Sept. 1, which represents 59.8% of average. Last week, the river was flowing at 41.4 cfs. On Sept. 1, 2020, the river ran at 59.6 cfs. 

The ACES gauge, located near the Mill Street Bridge in central Aspen, measured the Roaring Fork at an average of 14.26 cfs on Sept. 1, down from 27.46 cfs on Aug. 25. The river ran at 38.01 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 81 cfs, or 63.5% of average on Sept. 1. That was down 2.5% from last year, when the river ran at 83 cfs on Sept. 1, 2020. The Crystal River at the Dow Fish Hatchery bridge ran at 27.5 cfs on Sept. 1. The current streamflow remains below the minimum instream flow set at 100 cfs set by the 1979 water rights decree.

The Roaring Fork Conservancy monitors water temperature on the Roaring Fork and Crystal rivers. According to the conservancy’s findings published in the nonprofit’s September River Notes newsletter, the average daily water temperature fluctuation on the lower Roaring Fork River during this drought-impacted summer has been 10°F. The most significant cooling effect came during cool rainy days. The Crystal River in Carbondale and the Roaring Fork River at the Westbank Boat Ramp both exceeded 68°F — the threshold above which fish exhibit significant levels of stress — several times in July and August.

This week’s air quality still “moderate”

This past week, the air quality in Aspen was reported as “moderate” for four days, from Aug. 29 to Sept. 1. The AQI index reached 65 for PM2.5 on Aug. 30. The air quality was”good” between Aug. 26 and 29 with an AQI index for ozone down to 42 on Aug. 26. 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 back up

Over the past week, air temperature measured in Aspen is back up, reaching 83°F on Aug. 28, or 8.5 degrees above normal. The minimum temperature was also higher than normal, up to 49°F on Aug. 26, which is about 4 degrees above normal.

Lake Powell keeps shrinking

Lake Powell‘s storage kept getting lower this past week, reaching its lowest level recorded since it began filling in the 1960s and ’70s on Sept. 1, when the reservoir was 30.93% of full.

Last week, on Aug. 25, the reservoir was 31.26% of full. The reservoir’s capacity has fallen significantly since last year, when on Sept. 1, 2020, the reservoir was 48.14% of full.

The surface elevation of Lake Powell is also in decline and hit a record low on Sept. 1, 2021, when the reservoir’s elevation dropped to 3549.1 feet, or 150.9 feet from full pool. The reservoir’s elevation has lost more than one foot since Aug. 25, when the elevation was at 149.7 feet from full pool. Last year, on Sept. 1, the reservoir reached 3599.56 feet or 100.44 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 (a surface elevation below 3,490 would mean no hydropower could be generated) 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,...