Eden Prairie looks to keep storm runoff out of river

Eden Prairie also seeks ways to curb the erosion of a bluff that holds houses overlooking the Minnesota River.

By LAURIE BLAKE, Star Tribune

Last update: October 7, 2009 - 11:14 PM

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Eden Prairie, grappling with storm water runoff from a bluff overlooking the Minnesota River, will repair two catch ponds at the base of the bluff to reduce pollution going into the river.

The City Council voted this week to spend $35,500 developing plans to repair the ponds about 1 1/2 miles west of Hwy. 169. But the city is still under pressure from the state to build a new pond -- and under orders to report back to the Minnesota Pollution Control Agency by February on all its storm water ponds across the city. The city has told the MPCA that it has about 800 ponds, and the agency wants to see a maintenance schedule for them.

The Lower Minnesota River Watershed District has also commissioned an engineering study on how storm water, groundwater and river water are interacting to erode the north bank of the river below the bluff, where Riverview Drive is located.

The river has cut 100 feet into the north bank just below the bluff over the past 20 years. Concerned about the long-term stability of the bluff, where houses are located, Eden Prairie hired consultants to size up the problem in 2008. In September, the city asked the U.S. Army Corps of Engineers for advice on how best to address the riverbank erosion.

After visiting the site, the corps concluded that the problem would not qualify for its funding, corps community planner Mike Wyatt said Wednesday. Groundwater and storm water figure into the erosion, and the corps focuses strictly on river issues, Wyatt said.

By December, the Lower Minnesota Valley Watershed District hopes to have completed a study that will suggest options for curbing the riverbank erosion, said District Administrator Terry Schwalbe. The study will determine how groundwater, storm water and water leaking from a closed landfill on top of the bluff may be combining to cause the erosion.

Consultants also will place a measuring device on the bluff slope above the river erosion for a year, to determine if the slope is eroding from underneath, Schwalbe said.

In the meantime, the city plans to repair the two retention ponds at the base of the bluff over the winter, said Leslie Stovring, environmental coordinator for Eden Prairie.

The two ponds were designed to catch water and let sediments and pollution settle out before the water reaches the river. The smaller basin was for seeping groundwater. It now overflows into a ravine that leads to Purgatory Creek. The larger pond was built in 1987 in the Minnesota River floodplain to receive storm water piped down from streets on the bluff above. It is now missing a wall, which was washed away by the changing course of the river, and allows storm water to flow directly into the river.

Repairing the ponds would temporarily satisfy the MPCA, which has taken enforcement action against the city to require it to better manage storm water coming from the top of the bluff, said Dale Thompson, supervisor of the MPCA's municipal storm water unit. But within about a year, the MPCA wants Eden Prairie to present plans for permanently replacing the larger pond with a new one, Thompson said.

Lacking a place to locate a new pond, the city would like to wait until Riverview Road is rebuilt -- that's scheduled to occur between 2014 and 2019 -- "to determine how the drainage can be managed in a more effective way," Stovring said in a memorandum to the council.

But the MPCA considers that too long to wait, Thompson said. "We asked them to come up with a plan in a shorter time period than that."

Laurie Blake • 612-673-1711

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