During a press conference in Rapidan Dam Park, overlooking the west edge of the dam, Blue Earth County’s Public Works Director Ryan Thilges and Blue Earth Emergency Management Director Eric Weller clarified the dam had not collapsed, but there was a partial failure of the western abutment.

“The structure of the dam is still intact and in place,” Thilges said. “The water ran around the west edge of the dam and is now eroding soil to the west and the north.”

The Rapidan Dam was constructed in 1910. At the time of the construction it was built on a sandstone bedrock that has proven highly erodible.

“As we’ve seen there is already significant decaying of the sandstone outcropping coming off the left wing wall,” Thilges said.

Rapidan Dam Park has been cornered off by Blue Earth County following the partial failure of the dam’s western abutment on Monday. Tuesday morning Blue Earth officials held a press conference in the park addressing ongoing concerns about the dam’s potential failure.

The concern is the flow will continue to scour away the sandstone bedrock, but the full extent of the damage cannot be accessed at this time.

“With these flows we can’t get down there and evaluate how bad it is,” Thilges said.

Water flow through the dam peaked at 34,800 cubic feet per second (cfs) on Monday. As of Tuesday, the flow as down to 33,000 cfs. Thilges said this is still an extremely high flow. The discharge rate was under 10,000 cubic feet per second before June 21.

Historically, this is the second highest flood level to impact the Rapidan Dam after the flood of 1965. Maximum flow during the 1965 flow was measured at 43,100 cfs and flood water went over the top of the dam.

The partial failure of the western abutment on Monday was the combination of higher than normal flow and excess debris in the water.

Public Works Director Ryan Thilges (right) and Blue Earth Emergency Management Director Eric Weller (left) gave a press conference on the recent damage to Rapidan Dam. The dam experienced a partial failure to the western abutment, with water eroding soil to the west and north.

“We have had several dry years and had trees die along the river valley,” Thilges said.

Much of the debris that led to the partial failure is still collected at the dam. Work crews are unable to remove the debris due to safety concerns.

Though the discharge rate has decreased in the last 24-hours, Thilges could not say if it would continue to decrease over the next few days.

“We are still seeing a lot of standing water all over and drainage areas contributing,” Thilges said

Neither Thilges or Weller could say for certain if the dam could fail as a result of the current damage, but neither believed it posed a major threat to Mankato or North Mankato.

Water flow through the Rapidan Dam peaked at 34,800 cubic feet per second (cfs) on Monday resulting in water carving out the western abutment, carving a new channel around the dam. As of Tuesday, the flow is down to 33,000 cfs. Five days earlier on Friday, June 21 the discharge rate was under 10,000 cfs.

Weller said in the event of a total collapse there would be a surge in the river depth but downstream communities would not see a wall of water.

Thilges said based on data in the county’s emergency management plan, if the dam completely failed people two miles down river would see river levels rise two feet. By the time the water reached Mankato, 10 miles from the dam, the water rise would be three to four inches.

The white home belonging to the Dam Store owners still remains in place as of Tuesday. The house avoided being pulled into the river Monday. Officials were uncertain if the house could be saved. No assessment has been done on the building due to safety.

An Xcel substation was lost Monday morning during peak flows resulting in power outages to 600 electrical customers. Official confirmed power had been restored to all as of Tuesday morning.

The County Road 9 bridge running parallel to the Rapidan Dam is closed to traffic. The Minnesota Department of Transportation continues to closely monitor state highways in south central and the southwest corner of Minnesota due to recent flooding.

The home belonging to the Rapidan Dam Store owners remained standing on the west edge embankment Tuesday morning. Around 9:30 p.m. the house was lost to the river.

Tuesday, MnDOT closed Highway 169 from Le Sueur to Highway 22 (Dodd Road) in St. Peter this morning. Highway 169 from Highway 99 (south of St. Peter) to Mankato closed on June 24 and remains closed. Traffic from Le Sueur to Mankato is detoured County Roads 8, 20, 5, 40, Highway 99, County Road 13, to Highway 14.

With road conditions rapidly and continuously changing, motorists should continue to check www.511mn.org for current road information.