Dam-age control: Lake Bella spillway undergoes emergency repairs
WORTHINGTON — The discovery of significant damage inside the Lake Bella dam’s spillway in early May may have averted a catastrophic draining of the man-made lake.
Worthington Public Utilities employees found a section of the concrete spillway’s floor completely eroded, exposing rebar and a six- to eight-inch hole in the soil underneath the spillway. The apparent cause of the damage was Sioux Quartzite rocks that were removed from the riprap along the lake’s shoreline and tossed into the dam structure by vandals over the years.
“The flowing water caused the rocks to bounce and spin, and they abraded through the concrete,” explained Dan Livdahl, Okabena-Ocheda Watershed district administrator, during a Tuesday afternoon watershed board meeting. The concrete floor of the spillway was 13 inches thick.
“The dam is 43 years old — it could have happened long ago,” Livdahl said, adding that some of the once jagged stones had become rounded after years of smacking against the interior floor and walls of the spillway.
“This is the only time in the 25 years I’ve been around that we’ve had a completely dry spillway, and you could see the problem and get in and fix the problem,” he said.
Steps were taken immediately to fix the structure, with the Minnesota Department of Natural Resources — the agency responsible for dam safety — rushing through a permit request and then contacting the Natural Resources Conservation Service, the agency that designed the dam and conducts annual inspections of it.
“Everybody agreed that the time was critical,” Livdahl said. With continued low water levels, it was an opportune time to make the repairs. “We may not see those same low water conditions in the future.”
The damage to the spillway stretched about four feet from the end wall, with abrading into both the end wall and side walls.
“It was critical to fix the dam,” Livdahl said. “If you have a hole in the spillway, you could have water coming from the lake and seeping into the hole. That could end up causing the lake to drain.
“The other thing is that water could come through the spillway, flow underneath the spillway conduit and cause it to fail,” he added. “How long that would take to happen — or if that would ever happen — Lake Bella is important enough to us that we wanted to make sure that would never happen.”
In addition to repairing the structure, workers created an angular slope to the concrete floor so that, in the future, the water flowing into the spillway would push the rocks out of the dam. The cost for the repairs is anticipated to be about $6,000.
The repair work was completed on May 24, and Livdahl said when he checked on the structure last week, vandals had already tossed more rock into the spillway — along with a bucket of bullheads that could not escape, died and had begun to decay there.
“There’s still an issue with people tossing rocks down the hole,” Livdahl said. “I don’t think there’s anything we can do about it. Human nature is to see a hole and try to fill it up.”
“You can’t fix stupid,” added OOWD Board Chairman Les Johnson.
Also on Tuesday, the watershed board received an update on the Lake Bella Park prairie burns and grass seeding projects, discussed cover crop plantings on the St. John property on the south edge of Worthington and heard a report on the watershed’s construction of a floating island, which is being tested on Lake Bella. The island cost about $400 — considerably cheaper than the $1,500 floating islands purchased earlier this year for the E.O. Olson Regional Stormwater Pond on the Minnesota West campus in Worthington.
Daily Globe Reporter Julie Buntjer may be reached at 376-7330.