Arizona Dam Overtopped Amid Heavy Runoff
• Watson Lake Dam, a century-old concrete arch dam near Prescott, Arizona, was overtopped on Sunday, November 1, despite preemptive measures to manage water levels. The city had opened a 36-inch release valve and a crosscut channel to neighboring Willow Lake ahead of the storm, but runoff at two to three times normal levels overwhelmed the reservoir. Peak inflow reached over 4,000 cubic feet per second (cfs), equivalent to nearly 30,000 gallons per second. The dam is rated to handle water flowing up to 10 feet over its crest, and city staff are continuously monitoring for structural concerns. The Arizona Department of Water Resources inspects city-owned dams annually, with Watson Lake Dam receiving concrete repairs in
• Heavy rains across the region caused significant flooding, prompting a state of emergency declaration in Prescott.
Impact & Risks
The overtopping of Watson Lake Dam posed risks to downstream areas, though no structural concerns have been reported. Prescott experienced widespread flooding, with low-water crossings closed, traffic signals disrupted, and emergency shelters opened. Nearby areas faced more severe impacts, including over 100 homes flooded in Camp Verde and two fatalities in Flagstaff. Oak Creek reached 20,000 cfs, far exceeding its typical flow of 200 cfs. While Watson Lake Dam is designed to withstand overtopping, the event highlights the vulnerability of infrastructure during extreme weather conditions.
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