It's not just property, but people's lives are at risk because of these structures. —Utah Dam Safety Director David Marble
FAIRVIEW, Sanpete County — Dams can provide drinking water, hydroelectric power, flood control and recreation. But when a dam is breached, it can put people and homes downstream in harm’s way.
Utah has about 1,800 dams, and it’s Utah Dam Safety Director David Marble’s job to make sure they are safe.
"When everything is going right, nobody knows what we're doing," Marble said. "It's when something goes wrong that it becomes an issue."
With time, dams age, deteriorate or malfunction. Marble and a handful of inspectors on his staff check every dam in Utah and make sure they're working properly. They look for possible structural, mechanical or hydraulic failures.
"It's not just property, but people's lives are at risk because of these structures," he said.
Embankment dams are the most common type of dam in use today, according to the Federal Emergency Management Agency. Soil, rock or waste material obtained from mining or milling operations can be used to make the dam.
Of the nearly 1,800 dams in the state, 400 are considered high-risk, 400 are moderate, and roughly 1,000 are low risk. High-risk dams are inspected every year. Moderate dams are inspected every two years and low-risk dams every five years. The risk is based on consequences of a failure, not the condition of the dam itself.
There will never be zero risk with a dam, Marble said. No matter what it's made out of, there will always be some risk. He said it’s his job to get to as close to zero as possible.
"There's an element of risk, and it's hard to eliminate that risk," Marble said, "but we work every day to minimize that risk."
Dam failure floods are almost always more sudden and violent than normal stream, river or coastal floods, according to FEMA.
Last September, a breach in the Santa Clara dam near St. George sent water and debris into homes and businesses below. The dam was built in 1919. It was considered a high-risk dam. The earthen dam was evaluated April 25, 2012. The report 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. While fixing leaks and potential problems is something engineers can do, there’s little they can do to stop Mother Nature.
A huge rainstorm was just too much for the dam. The average rainfall in the area is only 0.56 inches, with an annual average of 8.25 inches. In September of 2012, 3.24 inches — or three months’ worth of rain — came down on the neighboring city of Ivins in a single day.
The Fairview Dam in Sanpete County is a high-risk dam. It was put on the list of about 40 dams in Utah that need to be rehabilitated because it was leaking about 400 gallons a minute.
"The whole goal is to minimize the seepage, because with a dam, you can't stop seepage," said Eric Dixon with Franson Civil Engineering. "Water finds a way through anything, even a concrete dam. It finds its way through joints and cracks."
Many people who live in a dam inundation zone are not aware of the potential danger upstream, according to FEMA. Information on dams in Utah can be found at www.waterrights.utah.gov under dam safety.
Contributing: Viviane Vo-Duc