Aging Lake Alvin spillway submerged by flood waters

East of Harrisburg, Lake Alvin has hit the point of bursting.

Significant rains, starting Thursday and continuing into late Friday night, filled the lake's spillway, a water control structure meant to control the release of water into Ninemile Creek, a tributary of the Big Sioux River.

When an Argus Leader reporter arrived 5 p.m. Thursday at the spillway's confluence with the creek along 480th Avenue in Lincoln County, the spillway was completely submerged with water. A nearby road leading to a fishing dock and vantage point by the lake was also under water.

Lakeside of the road, a visible whirlpool could be seen churning about 25 feet from the road, the reporter observed. Rushing water could be heard tumbling under the road and overflowing Ninemile Creek. Ditches along sections of the road were also partially flooded, but water had not risen above the street.

Gov. Kristi Noem addressed the situation during a 7 a.m. press conference Saturday as part of an overall update on flood conditions to the area. She said the spillway's "entire watershed is being impacted by that, and those flows will continue to increase."

"Unfortunately, I think that situation, the water will go even higher," Noem said.

She added the spillway "still looks to be in good shape, even with that kind of water pressure."

The spillway at Lake Alvin, a 105-acre reservoir owned by South Dakota Game, Fish and Parks, is slated for complete replacement after flooding in 2019 damaged the aging structural integrity of the dam system's infrastructure.

According to a 2001 report by the now-defunct state Department of Environmental and Natural Resources, the spillway was built in 1954, but portions of the structure deteriorated and collapsed in the early 1990s. The primary spillway was later repaired and renovated by 1994.

The state legislature approved a $5.6 million appropriation to support infrastructure improvements and repairs at Lake Alvin and Newell lake in 2022. More than $4.5 million has been set aside for the now-flooded spillway's replacement.

The spillway uses a concrete chute, but the new spillway plans will incorporate a stepped spillway design. State officials in the news conference said they wouldn't be able to check on the potential of overall damage to the infrastructure until waters lower and they can get a better look.

GFP closed Lake Alvin to swimmers Thursday after "unhealthy levels" of bacteria derived from rain runoff was detected in the waters.

More: Lake Alvin closed to swimmers after recent heavy rains

This article originally appeared on Sioux Falls Argus Leader: Aging Lake Alvin spillway submerged by flood waters