The Coon Rapids Dam on the Mississippi River has a new failure in its concrete apron -- a problem that is not yet a safety concern but could cost millions to repair, a Three Rivers Park District inspection shows.

Repairing the cracked area with steel pilings could cost $1.5 million to $2 million, and reinforcing the entire apron could cost $6 million or more, Bill Holman of Stanley Consultants advised the park board.

Three Rivers officials are scheduled to discuss the problem with the Department of Natural Resources on Jan. 6 and with park board members later in the month.

The apron, an underwater layer of concrete, takes the pounding of the river water spilling over the dam and prevents scouring that could undermine the dam structure. Scuba divers inspecting the dam found a section of apron had broken up "and large pieces were lying on the bottom," Holman said.

A similar failure was found in 2004 and repaired with steel piling at a cost of $1.2 million in 2005. Two failures in five years raise the odds that more of the apron will fail and other repairs will be needed, Holman said. Sonar soundings already indicate another area of concern, he said.

The dam was built in 1913 and rehabbed in 1998.

Once used to generate electricity, the dam now serves primarily a recreational purpose: It backs up the flow of Mississippi River water to create a six-mile lake for boating and fishing.

The park district accepted the dam as a gift from Northern States Power in 1969 along with 225 acres of park land on the Mississippi. Now the park district is a responsible but reluctant dam owner, and since the mid-1990s it has been looking for another entity to take it over, said Margie Walz, associate superintendent for Three Rivers. "It's not in the interest of the park district to run a dam. It's becoming very expensive."

The district tries not to have dam costs paid entirely by suburban Hennepin County residents whose property taxes support the Park District. When the district made the $1.2 million repair in 2005, the state dam repair fund paid $250,000 of the cost.

Since 1974, the dam has undergone $11 million in major repairs, and Three Rivers has paid $4 million, with the balance coming from the state and a Metropolitan Council agency, Walz has said.

Operating the dam is "threatening our ability to do other things," Walz said. The board learned of the apron cracks on the same night it considered whether to replace the Eastman Nature Center at Elm Creek Park Reserve in Dayton and whether to improve the chalet and parking at the Hyland Ski and Snow board areas in Bloomington.

Whether its recreational function merits continuing repair of the dam is a question the park district is looking to the DNR to address, Walz said. "This is a lake on one of their major rivers. It is probably beyond the call of the suburban Three Rivers Park District."

DNR regional hydrologist Dale Homuth said, "We have no position on it. There are obviously hundreds of people who have lakeshore now and wouldn't have lakeshore if the dam were removed. It becomes political."

Asked why Three Rivers is having such a hard time finding a new owner for the dam, Homuth said, "The term 'white elephant' comes to mind."

The state could not take it over without special legislation, and the DNR, with an already tight budget, would not favor that, Homuth said.

In general, said DNR hydrologist Judy Boudreau, "I don't know that we necessarily as a department or a division see a lot of value" in maintaining a dam for recreational purposes. "If you were to talk to our ecological resources, stream habitat people, they are tending toward dam removals. They love to see structure that helps promote spawning, but that dam does not allow for fish passage."

The dam does, however, act as a barrier to invasive species along the Mississippi and would stop Asian carp if the species ever got that far, Homuth said.

Laurie Blake • 612-673-1711