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  • Writer's pictureJosh Kurz

Predicting the Peak: Spring Runoff 2023

As I enter my 25th year of living in the Southern San Juans, I’ve witnessed events this spring that I’ve never seen before!

The San Juan River on 5/2/23 at 2400 cfs

For example, the spring runoff forced the closure of Highway 151 near Chimney Rock on April 11th. The culvert below Stephens Lake washed out. In multiple locations, snowmelt overwhelmed culverts sending water across North Pagosa Boulevard during the week of April 9th. And the Piedra River topped 4110 cfs on April 14th, breaking the all-time flow record for early April.

In addition, all of the signs of spring that I've been tracking for the last 14 years were 3 weeks late (the first chorus frog chirps, Lake Hatcher's ice-free date, and the first daffodil sprouts in my yard). These delayed phenological observations combined with early season flooding indicate that the San Juan River's peak spring runoff might break into the top 10!

In Colorado, the snow water equivalent (SWE), or water in the snowpack, is measured primarily at accessible, high-elevation sites such as Wolf Creek Pass. Unfortunately, there is little information on our remote low-elevation snowpack, which makes up most of the San Juan River’s 284-square-mile drainage area. Our high-elevation snowpack at the Upper San Juan Snotel site is 162 percent of normal, but the events I described above suggest that the remaining low-elevation snowpack is substantially higher than normal as well.

Although the 2019 snowpack was impressive, the winter of 2022-2023 delivered more water. In 2019, the Upper San Juan Snotel site peaked at 40.5 inches of SWE, which produced a peak streamflow of 4340 cfs on June 9th. May 2019, however, was cold and wet, which put the breaks on the snowmelt and replenished the snowpack. During May 2019, the site received an additional 3.7 inches of SWE and temperatures only climbed above 60 degrees Fahrenheit five times.

So far, daily temperatures at the Upper San Juan Snotel site have already climbed above 60 degrees six times this year shinking the SWE peak from 47 to 35 inches of water. As of today, we have the same SWE at the Upper San Juan site as we did in 2019. However, unlike 2019, the current snowpack is covered with an above-average dust layer that was deposited during several dust-on-snow events this spring. The dust will accelerate the melt rate (Read A Little Dirt Never Hurt, Right?), but that will be partially counteracted by cooler temperatures and a few glancing storms. However, it's unlikely that we will receive as much late-season snow as we did in 2019.

Already, the San Juan River reached 3080 cfs on May 2nd driven by 3 consecutive 60-degree days on Wolf Creek Pass. Normally, the San Juan River peaks around 2500 cfs on May 25th. Runoff has slowed in concert with cooler temperatures, but the river is still running over 2 times higher than normal.

Even though the river has eclipsed 3000 cfs, the snowfields indicate that the mountains have more water to deliver. The cutthroat and geese have yet to reveal themselves on the Eastern Range like they did last year in early May (Read Signs in the Snow).

Last winter, a major dust-on-snow event in February caused our snowpack to disappear a month early (compare Pagosa Peak in 2022 and 2023). The river peaked at 1970 cfs on May 8th, two days after the above picture was taken.

My snow-flow model is predicting the peak flow of 3900 cfs on June 2nd. However, there is quite a bit of uncertainty because the data represents only one location and doesn't consider temperature, dust, wind, and soil moisture. Regardless, the model is still a good starting point. I’m going to adjust the model's peak flow prediction up to 4400 cfs and move the date up to May 30th. In the meantime, enjoy the high flows!

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