Rockville vacated, Zion Park closed as dam appears at risk

ST. GEORGE — The potential of a dam failure caused the evacuation of a southern Utah community and put others on high alert, though by late Tuesday it appeared the worst case scenario would not occur.

Engineers confirmed Tuesday that there were small breaks in the privately owned Trees Ranch Dam, also known as the South Creek Dam, on the east fork of the Virgin River near the south end of Springdale.

Washington County Commissioner Jim Eardley signed a declaration of disaster around 2:45 p.m. during a news conference where officials said they were preparing for the worst and hoping for the best.

Shortly after 1 p.m., the National Weather Service reported the failure of the Trees Ranch Dam was "imminent," but later amended its website to say a failure was "possible." County officials said at a 5:30 p.m. news conference that they were "cautiously optimistic" a dam failure was no longer imminent.

"We're not out of the woods yet on this," Eardley said.

Some of the dam's saturated soil was sloughing off, but it remained structurally sound. And water flowing through its drains was clear, indicating there was no internal erosion, officials said.

The worst-case scenario was that the dam would fail entirely and the water released "could double the depth of the river," Eardley said. But by 5:30 p.m., he said the county was "in pretty good shape." The Virgin River had receded 3 feet since 2 p.m.

The first town to be impacted by a dam failure would be Rockville. The town of about 300 residents was evacuated. Select residents in nearby communities were also evacuated and residents who live along the river were told to start gathering their "irreplaceables."

If the leaking dam were to break, "I think it would impact every community downstream, including (the) Mesquite and Beaver Dam," said St. George City Manager Marc Mortensen. "Our primary concerns would be those communities closest to the reservoir, which would be Rockville, Virgin, possible areas of La Verkin down by Pah Tempe hot springs, as well as Washington, subdivisions near the Virgin River, and of course areas of St. George."

The warning by the National Weather Service said in a worst case scenario, with a catastrophic failure of the dam, water would spill in excess of 50,000 cubic feet per second, reaching Rockville in 35 to 40 minutes.

It would take several hours for the surging water to reach larger communities such as St. George, authorities said. The dam holds about 1,900 acre feet of water.

While there has been severe flooding in the area in the past decade, officials said Tuesday's circumstances are more complicated.