May 28, 2012

Steel a saviour for Winnipeg Beach

PETER KENTER

correspondent

The 11th largest freshwater lake in the world, Lake Winnipeg, packs a wallop during stormy weather — so much so that Manitoba is turning to corrugated steel to protect the shoreline near the town of Winnipeg Beach from erosion damage.

The current project involves replacing 140 metres of the kilometre-long concrete seawall with sheet steel.

“The existing seawall was built of concrete during the 1950s and it’s reaching the end of its design life,” says project manager Tony Merkl, a regional park specialist with Manitoba Conservation and Water Stewardship.

Merkl notes that the lake is notorious for vicious October and November storms, which can last for days, battering the shoreline and causing severe erosion.

“It can be a mean lake,” he says.

“Portions of the lake can rise from five to six feet during a storm and even after the rain stops, the winds persist, with 10-foot rollers crashing into shore. During spring storms, the waves pound huge chunks of ice into the seawall.

“The lake levels have been quite high recently and there’s a lot of concern about the damage the waters could do to the town of Winnipeg Beach if the seawall collapsed. The lakefront is full of businesses and accommodations and if the wall collapsed, the lake would easily eat through the clay and dirt dike and flood the community, causing millions of dollars of damage.”

A similar steel project was carried out in 2005 to replace a section of concrete seawall that was in danger of collapse.

The current project was designed by engineering firm KGS Group of Winnipeg and was installed by contractor OSC Western of Riverton, Man.

The contractor has developed considerable expertise in installing steel seawalls, having completed similar projects in the province’s Gulf Harbour and Grand Beach.

“The sheet steel we’re using is 3/8-thick and sold in 60-foot sections, that are then cut down to sections of 20-foot depth for our use,” says Merkl.

“Standing up, each sheet of steel is about six feet wide and interlocks into the sheet beside it.”

OSC Western project manager Kyle Bacon says that the set-up on each steel pile takes longer than driving it into the ground using a hydraulic pneumatic vibration system purchased specifically to bid on such projects.

“Once we set up the driving frame, the unit grips the sheet pile and sets it into the tongue and groove retaining system,” says Bacon.

“It vibrates it into the ground while it’s driven from above, much faster than if you were using a diesel hammer. The speed of installation depends on the soil underneath, but at Grand Beach we were driving 35-foot sheets into sandy clay in six-and-half minutes.”

Merkl says that the Winnipeg Beach piles took anywhere from a half-hour to 40 minutes to install from set-up to finish.

The metal was driven from 14 to 16 feet into the ground to hard, compacted aggregate or solid rock below, with about five to six feet of metal remaining above ground.

“OSC Western did an excellent job,” says Merkl.

“What’s really nice is that you can even do this work during the busy tourist season because the equipment makes no noise other than the sound of the diesel motors.”

Every third or fourth pile was backed up by a Y-shaped steel beam that reinforced the pile from behind. The area behind the sheeting was then filled with riprap and aggregate. A concrete apron will be placed on top of the aggregate, providing the community with a boardwalk and bike path.

“The other parts of the seawall that are not directly hit by the worst storm surges are not in bad shape,” says Merkl.

“The sheet steel work is expensive, so we’ll continue to replace portions of the seawall that are deemed immediate issues, doing the worst sections first.”

Print | Comment