Data dashboard: Wastewater flows follow unusual trends of 2020


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

What local wastewater data tells us about the number of people in the city

Wastewater flows reported by the Aspen Consolidated Sanitation District, located near the Aspen-Pitkin County Airport, provide a benchmark that corresponds to the volume of people in town at any given time.

According to ACSD data, the volume of wastewater passing through the treatment plant dropped 35% in seven days in mid-March 2020 – that’s when the ski lifts closed due to COVID-19. 2020 flows remained below 2019 levels for most of the summer season until mid-August, when numbers started to catch up. During the fall season, flows exceeded 2019 figures, up to a 3.5% increase for October 2020.

The volume of wastewater totaled 97.73 million gallons from September to November 2011. In the fall of 2020, this volume increased to 102.939 million gallons. This is the highest volume for those fall months in the past decade, while the total volume for 2020 was the lowest, at 439 million gallons.

This spike last fall may reflect the influx of newcomers and part-time residents to Aspen who have decided to spend more time in the valley than usual with the rise of remote work and online learning. line that accompanied the COVID-19 pandemic.

As the winter season approached and COVID cases increased again, the volume of wastewater passing through the facility was reduced from the previous year, down to a 15.8% drop in January. 2021 compared to January 2020.

With the recent reopening of the county and city as the number of cases in Pitkin County declined, flows began to increase and reached 2019 levels on June 1, 2021.

Local stream flows remain low

The gauge operated by the Center for Environmental Studies in Aspen near the Mill Street Bridge is the only gauge showing the steam flow from Roaring Fork as the river passes through central Aspen. This is an important reading, separate from the US Geological Survey gauge upstream at Stillwater, since the ACES gauge measures the river downstream of the diversions of the Salvation and Wheeler ditches. It therefore shows the Roaring Fork at its most threatened level, reduced both by diversions of the transbasin to the Front Range from the springs near Independence Pass and by local water users – and before the canal. is replenished by the flows of Hunter, Castle and Maroon creeks.

The ACES gauge shows that on June 28, the river flowed at 84 cfs on average, against 426 cfs on the same day in 2019 and 101 cfs on June 28, 2020.

City ACES gauge data shows that the Roaring Fork River’s daily average in 2020 was 53.9 cfs, up from 142.2 cfs in 2019. 2018 was another year of low flow for the river, with a average of 38.8 cfs. With a more persistent snowpack in 2019, less than 1% of the state was unusually dry, while in June 2020, 72% of Colorado was unusually dry, according to the US Drought Monitor. The US Drought Monitor’s weekly report released on July 1, 2021 showed that about 45% of the state was abnormally dry last week.

On June 28, the USGS gauge located in Stillwater, just outside of town, recorded the flow of the Roaring Fork River at 110 cfs, which is 26 cfs higher than the ACES gauge. As of June 30, this flow was 112 cfs, 33% of the average. Last year, the same day, the river flowed at 126 cfs.

After a slight peak for local watersheds thanks to rainfall around June 25-27, flows have been declining since. The Colorado River downstream from Glenwood Springs peaked on June 25 at 3,090 cfs. On June 30, it sank at 2,490 cfs, or about 29% of the average.

Low water levels for Lake Powell in June

Lake Powell’s water elevation was particularly low in June, ending the month with an elevation of 3,560 feet, or about 140 feet from the full pool. On June 30, the reservoir was 34.2% full.

Last year on the same day, the reservoir was 52% full and 53% full in 2019, while the water elevation was around 89 feet from the full pool in 2020 and 88 feet in 2019.

If the reservoir’s surface elevation on the Utah-Arizona border, which stores water from the Colorado River, drops below 3,525.5 feet, it will have a host of consequences, including changes in Glen Canyon Dam operations affecting hydroelectric generation, discharges from upstream reservoirs to support Lake Powell, and potential litigation between the seven states that share water under the 1926 Colorado River Compact.

Drop in air temperature

After a heat wave that saw temperatures approach all-time highs in Aspen, air temperatures at Aspen-Pitkin County Airport began to drop between June 22 and 23, rising from 87 ° F on June 22 to 77 ° F the next day. day for maximum temperature. The maximum air temperature dropped to 65 ° F on June 26, 12.7 ° F below normal. Minimum temperatures hit their lowest on June 27 with 39 ° F, nearly 5 ° F below normal.


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