The Free Press, Mankato, MN

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  • The Minnesota River is lapping at the walkway as city employees Don Nies (left) and Steve Radzak walk along the floodwall near the Veterans Memorial Bridge Friday. John Cross

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March 19, 2010

Flood wall gets twice-daily inspections

Patrols looking for 'sand boils' behind the barrier

By Brian Ojanpa Free Press Staff Writer

MANKATO —  More or less, Mike McCarty drove his Chevy to the levee, but the levee was dry.

Which is what he and his city co-workers want as they go through their daily paces along Mankato’s flood-control walls.

With the Minnesota River approaching flood stage, three-person inspection teams are making twice-daily foot patrols along the city’s five-mile levee and flood-wall system.

Object: To make sure any actual or potential breaches are dealt with before encroaching waters can hold sway.

The daily dike look-see regimen may appear to be perfunctory monotony, but hoofing it along the asphalt river-walk trail is good exercise, McCarty said.

Not to mention an opportunity to visit with onlookers apparently enthralled by swollen waters.

“There were quite a few people out observing in Sibley Park and Riverfront Park,” McCarty said. “A lot of them were wondering what we were doing walking around the river with life jackets on. That’s kind of a sight in itself.”

The wall patrols are federally mandated during flood conditions. City Engineer Jeff Johnson said crews walk the walls on a rotating basis with two walkers inspecting on foot and a third in a truck to shuttle the pair past gaps in the foot trail.

The city’s earthen berm levee system is designed to withstand a 300-year flood, loosely defined as an event of such magnitude that it likely would occur only every 300 years. 

The likelihood of 30-foot floodwaters rising over Mankato’s 18-inch-thick concrete flood walls — construction was completed in 1987 — is virtually nil this spring.

Johnson said of more pertinent concern is potential fissures in the levee

system.

“We’re looking for ‘sand boils’ — water coming up behind the dikes. In that case, you just take sand bags and build a mass of bags over the soil to push the sandy soil back down.”

Johnson said that’s yet to happen. Meantime, flood patrollers will continue their daily morning and afternoon three-to-five-hour treks, south  from Land of Memories Park and north to Happy Chef restaurant.

Johnson said the inspections likely will continue into early next week, ceasing when the river’s Mankato water level in feet recedes to the prescribed mark:

When it falls below 21, they’re done.

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