Inspectors unsure why Santa Clara dam failed

SANTA CLARA, Washington County — State inspectors were working Wednesday to determine why the dam that had been pronounced sound less than five months ago suddenly gave way following a downpour Tuesday.

Dave Marble, the assistant state engineer who evaluated the earthen dam on April 25, stood at the base of the breach Wednesday and estimated it was at least 80 feet wide — and even wider at the crest.

The dam is categorized as a high hazard dam because of its proximity to homes and is inspected once every two years. It had successfully protected the area for decades, and upon initial inspection, Marble is unsure what went wrong. 

"The dam was built in 1919. It's been here 93 years," he said. "There is a substantial history of the dam being successful … over that period of time."  

In his April report, Marble indicated that no immediate repairs were necessary but that the city needed to inspect and possibly back fill active rodent burrows that could be seen along the banks and crest of the dam. 

Santa Clara Mayor Rick Rosenberg said the burrows were a recurring problem. Crews already had been out spreading poison for the rodents and filling in the holes, he said.

The huge rainfall, Rosenberg said, likely was just too much for the dam. 

"There was no settlement, no differential cracking, nothing like that to indicate we had any problem," he said. "My gut is telling me it's just the magnitude of the event."

KSL meteorologist Kevin Eubank reported that average rainfall in the area is only .56 inches, with an annual average of 8.25 inches. On Tuesday, 3.24 inches — or three months' worth of rain — came down on the neighboring city of Ivins in a single day.

It is still uncertain just how much water escaped the retention basin, but Marble estimates that if it was full to the crest, as much as 50 acre-feet may have come down on Santa Clara.

Residents and officials in Santa Clara are beginning to evaluate the damage that was done by the flood of water that came tearing through the heart of the southern Utah town.

At least 31 homes were damaged by the flooding, some of them suffering severe structural damage, while others filled with mud, water and debris. A dozen businesses met the same fate.

Santa Clara city manager Edward Dickie has estimated the damage at $3 million. That estimate reflects only damage done to the dike itself and city infrastructure, not private or commercial properties.

Dickie took to the streets Wednesday, along with the City Council and hundreds of volunteers, to help clean mud and water out of residents' homes and businesses. The Santa Clara Flood Relief Fund 2012 has been set up through State Bank of Southern Utah to collect donations for flood victims.

The breached dam still poses a potential hazard for the area, Marble said. City officials have begun working with the state's water division in order to secure the breach and prevent remaining sediment and debris from coming down on the town in future rainstorms.

Until the dam is replaced, there will be nothing to deter any flood waters that may come down, Rosenberg said. The city is preparing a plan to divert runoff to storm drains or, if that doesn't work, to run the water down city streets the way Salt Lake City did during the 1983 floods.

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