Damaged Mina spillway needs repairs, would cost $1.8M to replace

Three months after damage was discovered at the Mina Lake spillway, South Dakota Department of Game Fish and Parks officials have determined it is significant and repairs are needed.

That comes after an inspection of the structure. The extent of repairs is yet to be determined.

Initial damage was found March 31 when a piece of the spillway was spotted at its base. With the high volume of water running across the spillway at the time, officials weren’t certain where the piece came from.

Water from Mina Lake goes over the spillway into Snake Creek at the southeast corner of the lake, which is about 10 miles west of Aberdeen.

GFP Program Administrator Al Nedved said Banner Engineering recently evaluated the spillway and noted considerable damage.

Nedved said when heavy flows of water entered a lower section of the spillway, it lifted and moved a piece of concrete.

The dam has been in place since 1934. According to a Brown County history book published in 1980, Richmond and Mina lakes were both created in the 1930s. Nedved said the structures are considered Category 2 dams, which means they are significant hazard dams.

“The recommendation is to do a substantial section replacement or replace the structure,” Nedved said.

“As of right now, there are no signs that a dam failure is imminent,” he said. “There’s no indication that the dam is leaking or that the structure itself was compromised.”

While the damage can’t be ignored, Nedved said, GFP hasn’t determined the next step.

Brown County Emergency Management Director Scott Meints said under normal circumstances Snake Creek can handle the water from the spillway, but not if the structure fails. The creek doesn’t have that capacity, he said, and water would go everywhere.

That could mean along U.S. Highway 12 and into Aberdeen, Meints said.

“We’re talking walls of water. In a catastrophic incident, if the dam were to cut loose completely, there would be fatalities,” he said.

Nedved said GFP plans to visit with Banner Engineering about short- and long-term solutions, including ways to temporarily shore up the structure until more extensive repairs can be done.

Before work can begin, he said additional evaluation of the structure is needed, including evaluation of parts of the dam that can’t be seen.

“We have to do a new hydrological analysis to determine if this spillway site is still considered adequate,” Nedved said. “These dams were built when they had a snapshot in time. Now we understand what some of the extremes can be.”

The preliminary cost estimate to replace the dam is $1.8 million, Nedved said, and that’s to rebuild the structure as it is today.

Nedved said the Mina spillway is one of three in South Dakota that have seen significant damage this year due to high waters.

The other dams are on Lake Alvin in Lincoln County and Newell Lake Butte County. A fourth dam on Jones Lake in Hand County has potential damage, he said.

The dam has been in place since 1934. According to a Brown County history book published in 1980, Richmond and Mina lakes were both created in the 1930s. Nedved said the structures are considered Category 2 dams, which means they are significant hazard dams.