Heavy, multi-day rain in early October sent the San Juan River through Pagosa Springs to its third highest level on record, the Western Water Assessment reported. The USGS gauge in Pagosa Springs recorded a peak gauge height of 12.82 feet and a peak flow of 8,570 cubic feet per second.
Watershed totals were extreme in the mountains, with 12.5 inches of precipitation measured at high-elevation stations over five days. Near Pagosa Springs the report says 4 to 5 inches fell during that period. The rains followed soils that had been wet from earlier storms, increasing runoff.
The flood unfolded in two peaks, according to WWA analysis. An initial surge crested on October 11 at about 12.66 feet and roughly 8,270 cfs. After a brief lull the river rose higher on October 14, driven by continued mountain rain tied to decaying tropical storms, the Colorado Climate Center noted in meteorological summaries cited by WWA.
Local authorities evacuated hundreds of residents. Archuleta County officials moved about 380 people from low lying areas in Pagosa Springs. North of Vallecito Reservoir in La Plata County, emergency crews evacuated roughly 383 residents. Vallecito Creek reached its second highest flow on record, and about 90 homes suffered damage, two of which were destroyed.
Impacts, Analysis and Recovery
Infrastructure damage included flooded streets, a hot springs resort inundated, and sewage system failures that released raw sewage to the river, as reported in the WWA assessment. A 28 mile stretch of Highway 160 closed because of erosion and boulders. Many rural bridges showed heavy damage.
The rains boosted reservoir storage across the region, offering hydrologic relief even as they caused damage. Vallecito Reservoir rose from 29,000 to 79,000 acre feet between October 9 and October 19. Navajo Reservoir and Lake Powell each increased by more than 100,000 acre feet, the report says.
WWA applied USGS Bulletin 17c flood frequency methods to evaluate probability. The team estimated the Pagosa Springs event has a return period of about 25 to 40 years, or a 2.5 to 4 percent annual chance. WWA cautioned that statistical analyses assume stationarity, an assumption that regional climate trends may challenge.
The assessment noted antecedent drought conditions across the Upper San Juan basin through much of the prior two decades, with soils near the lowest 20th percentile earlier in October before late season storms raised moisture. WWA said the sequence of storms that saturated soils was critical to producing extreme runoff.
Western Water Assessment offered continued scientific support to local planners and named Nels Bjarke and Seth Arens as contacts for communities seeking resilience guidance. The report emphasized that usable, locally tailored science can inform hazard planning as the region rebuilds.
