Summer Streamflow and Precipitation Summary
Updated: Apr 26, 2020
As the summer sizzled, the monsoon fizzled, and the
streamflow dwindled. The tubing opportunities decreased and now the all the trout are deceased.
After a strong start to the monsoon season in early July, high pressure dominated and diverted moisture around the Southern San Juans throughout August, which is typically our rainiest month.
Since mountain precipitation generally switches over to snow in fall, and that snow usually doesn't melt until the spring of the next year, hydrologic records are tracked over the water year (October 1st through September 30th). That means there's one more month before we finish out the dismal 2018 water year, which is nearly 25 inches of precipitation below normal.
The lack of precipitation combined with water depletion by the Park Ditch have nearly squeezed the San Juan River to the historical low, which occurred during the summer of 2002. During that summer, the river dropped to an astonishing 7.5 cfs on 8/16/02.
The United States Geolgical Survey (USGS) maintains a stream gauge in downtown Pagosa Springs, and the river is a few inches from being too low to measure with their automated sensor. The USGS is currently reporting 31 cfs for the daily mean, but this value is preliminary and in my opinion is too high. I'd guess there's about 15 cfs flowing through downtown Pagosa Springs, which makes the stream nearly jump-able and certainly un-tube-able. Fortunately, deep pools can be found below each white water structure.
Sadly, while swimming with the kids in July, the river smelled strongly of dead fish. Trout are stressed at 70 degree Fahrenheit and I measured the river at 76 degrees last week at Yamaguchi Park.
In addition, the low flow has exposed sections of the riverbed that I've never seen before. I assumed that the riverbed of the San Juan was like many mountain streams, consisting of rounded cobble and gravel. What I didn't realize until this year is how much of the riverbed through town consists of smooth Mancos shale.
The rarely seen shale shelves that are now exposed in the streambed became more significant after I read a recent article about "hunger stones" in the Elbe River of the Czech Republic. The article explains how exceptional drought has recently depleted the Elbe River exposing large stones that are carved with dates commemorating the hardship that accompanied past drought. One stone dates to 1417! Another stone warns, "If you see me, weep"!
Since the flow is so low, collectively crying into the river might actually help! But don't forget that our biggest flow events on record have happened in the fall so hold your tears until then!