ST. GEORGE — When a 4.5 magnitude earthquake rumbled through southwest Utah last month, employees of the Washington County Water Conservancy District immediately fanned out across the county to check on the dams that store one of the area’s most precious resources.
“With an earthquake of that size, it was enough of a concern that we sent myself and three other employees out to check all the dams in the district all the way from Quail Creek to Kolob,” David Jessop, the water district’s operations manager said as he stood outside with Quail Creek Reservoir’s southern dam in the background.
“Within two hours of the earthquake, we were able to get all of the dams checked and ensure their integrity,” he said.
The July 28 earthquake occurred 15 miles south of Brian Head at 11:29 p.m. and was felt region-wide, as previously reported by St. George News. According to the United States Geological Survey, a 4.0 quake can cause moderate damage.
The tremor felt from the quake was enough to wake Jessop who said he received phone texts from his boss to check on the condition of the district’s dams as a precautionary measure.
Jessop and others quickly checked the dams at the Kolob, Sand Hollow, Quail Creek, Ivins and Gunlock reservoirs for any potential problems.
“What we do is check the tops of the dams, we check the downstream toes of the dams, we check for any cracking and any wet spots,” Jessop said. “We check the outlet works…and just get a good visual.”
Inspection of the dams determined the late-night rumble hadn’t impacted them in any significant way.
While not caused by an earthquake, the 1989 failure of the Quail Creek dam was in the back of the minds of those inspecting the dams following the quake, Jessop said.
At the time, flooding from the dam’s failure created a 40-foot-high wall of water that ultimately damaged up to 60 homes and 100 apartments and displaced 1,500 people. Farms, roads and bridges in the path of the flood were damaged or destroyed. The event also caused more than $12 million ($30 million today) in damages. Fortunately, no lives were lost.
In addition to avoiding a potential flooding event if a dam is damaged, making sure the dams at Quail Creek and Sand Hollow were intact and unaffected was considered particularly important as they supply drinking water to 60% of Washington County, Jessop said.
“We don’t want to have any sort of failure, any issues,” he said. “If there are issues, we’ll want to be ahead of them enough before they become a big problem … The water district takes dam safety very seriously.”
The seismic construction and overall condition of the water district’s dams are checked on a regular basis and is one district employee’s sole focus, Jessop said. When the reservoirs are at 90% capacity or higher, the dams are checked weekly by that individual. The water district also works closely with engineers and the state’s own dam safety program, he said.
“Our dam safety program is such that we, a lot of the time, go above and beyond our standard operating procedures and the state requirements, just as a precaution,” Jessop said.
Over 800 dams in Utah are monitored and inspected by the Division of Water Rights’ Dam Safety Section while the 50 federal dams in the state are overseen by the Bureau of Reclamation.
Both the state and federal agencies have standards for dam construction that include taking seismic, or earthquake, potential into account. This includes an analysis of earthquake history and seismic-related activity in the area where a dam is proposed to be built, to building dam in accordance with specific design standards and operating it in line with the many regulations and requirements attached to such infrastructure.
Zach Renstorm, the general manager of the county water district, praised the swift response of Jessop and others who made sure the dams weren’t affected by the earthquake.
“It just goes to show how seriously we take our jobs,” he said. “Even though it was a small earthquake, we wanted to make sure everything was safe and the district employees were willing to jump in the middle of the night and go and check everything out.”
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