Coon Rapids dam project aims to keep the Asian carp out

  • Article by: JIM ADAMS , Star Tribune
  • Updated: March 31, 2013 - 5:56 PM

A $16 million construction project beginning this spring was designed to make the structure a better barrier to block invasive Asian carp from moving up the Mississippi River.

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Five new steel gates will be installed this summer on the Coon Rapids side of the dam over the Mississippi River, and another four next summer on the other side.

Photo: DAVID JOLES , djoles@startribune.com

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Efforts to stymie the Asian carp will ramp up this spring with the start of a $16 million project to make the Coon Rapids dam a stronger barrier to the invasive species moving up the Mississippi River.

Five new steel gates — each 8 feet tall, up to 97 feet long and weighing up to 90,000 pounds — will be installed this summer on the Coon Rapids side of the dam, part of a two-year project. Another four gates will go in next year on the Brooklyn Park side, said Jason Boyle, a dam safety engineer for the state Department of Natural Resources (DNR), which is overseeing the state-funded project.

This month, the state awarded a $10.8 million contract to a Edward Kraemer & Sons of Burnsville to install the gates, made in Pennsylvania at a cost of about $3.5 million, Boyle said. The work is expected to begin by the end of May.

Kraemer & Sons also will replace the pocked 50-by-430-foot concrete apron below the century-old dam with a deep concrete stilling basin. The basin will dissipate erosive energy from the churning water pouring down before it hits the river bed.

Boyle said the closest to the dam that an Asian carp has been netted in the Mississippi in Minnesota was near Hastings in March 2012. A month later, a leaping silver carp, a variety of which can jump 10 feet, was caught near Winona.

However, silver carp DNA was found in three of 19 water samples taken from the Mississippi above the Coon Rapids dam in September 2011 and in 16 of 29 samples taken below it. The sensitive tests are designed to detect DNA from carp excrement or mucous in the river water.

Department of Natural Resources leaders have expressed alarm about the DNA findings, although none of the carp was found in tested areas. The agency has urged quicker action, such as the dam makeover, to block the Asian carp.

DNR spokeswoman Julie Forster said Thursday that another round of DNA river tests has been done but that results aren’t yet available.

Massive gates

The new steel gates will replace rubber tube gates currently used to raise or lower the water level in the recreational pool above the dam.

The DNR’s Boyle said the new gates will be more effective as a fish barrier because they are lowered gradually from the top, unlike the tube gates, one or more of which must be deflated entirely to reduce the water level.

Boyle noted that the 97-foot gates will arrive in two parts and must be bolted together on site.

During work on the dam, the walkway across it will be closed. So will some trails and the boat launch near the Anoka County Parks Visitors Center.

A temporary coffer dam will be built above the work area to divert water.

With normal maintenance, the rehabilitated dam is expected to last 50 years, Boyle said.

Pool will stay high

To help ensure that any large, leaping carp stay below the dam during and after the upgrade, the pool above it will be kept indefinitely at its high, summer level, Boyle said.

For about 40 years until this winter, the 6-mile-long pool had been lowered 5 or 6 feet during the winter and raised again after the spring runoff.

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