In areas that experience very cold temperatures, like the northeast, it just makes good sense to take advantage of it. A national wildlife refuge located on the Canadian border of Vermont has successfully created and used an ice bridge to haul tons of rock over a frozen river to protect a Native American cultural site.
In early December 2013, U.S. Army Engineer Research and Development Center (ERDC) Cold Regions Research and Engineering Laboratory (CRREL) Research Civil Engineer Leonard Zabilansky was contacted by Missisquoi National Wildlife Refuge (NWR) Manager Ken Sturm, requesting support to provide ice thickness and conditions checks to ensure safe ice crossing prior to and during the project.
“This project began the winter of 2012,” said Zabilansky, “but because of the weather conditions and loss of ice, they had to suspend operations until just recently.”
In the winter of 2012, Zabilansky had worked with the refuge on a similar project, when 900 tons of rock were successfully transported across the ice. However, this time a total of 2,200 ton of rock needed hauling.
The Missisquoi NWR, established in 1943, provides habitat for migratory birds and other wildlife and spans 7,230 acres on the eastern shore of Lake Champlain. The refuge is also home to a cultural site where numerous artifacts – primarily fire-cracked rock and pottery shards – document Native Americans living in the area from roughly 500-1000 CE (Common Era).
The cultural site, located on the bank of the Missisquoi River, has been losing ground dramatically. In 2011, erosion along the river measured 6-7 meters (approximately 20-23 feet).
With this amount of erosion in just one year, “Clearly something had to be done,” said Sturm.
The refuge required large rock to build shore protection for the cultural site; however, the rock was across the river. In the summer, a barge is available to cross the river, but officials were weary of hauling using this method because of impact to the site’s marshy soil and time spent per round trip.
A refuge equipment operator came up with the idea to build an ice bridge.
In early January, the river’s ice cover was reported to be 15-17 inches thick. To increase the thickness of this natural cover, workers pumped water over the “bridge section” of the ice cover, increasing thickness to 21 inches, enough to support the loaded trucks.
The transport vehicle of choice was a Hydrema dump truck. The trucks are ideal, since they are equipped with large tires to reduce ground pressure, but in this case, to increase the footprint of the heavy payload on an ice cover.
Over five days, three trucks hauled the heavy rock, each weighing an average of 18 tons per load, resulting in a successful operation.
“They [NWR] were able to do more with the limited budget they had,” said Zabilansky. “Because they decided to use the ice bridge to haul the rock, they saved both time and money. They saved approximately 45 minutes per round trip. This was a really nice, successful project taking advantage of the cold temperatures we are having. So, they were able to do more with less.”
The final effort was to move the 28-ton excavator, used to load the rock into the trucks, across the river. They placed another call to Zabilansky for reassurance that the excavator would make the trip across the ice bridge successfully.
“There was 24 inches of ice!” said Zabilansky. “I told them to just drive it across.”
But not being one to deny himself a field trip, Zabilansky, along with CRREL Retiree Ginny Frankenstein, drove to the site to offer on-site assistance.
As the excavator crossed the ice bridge, Zabilansky monitored the deflection of the ice using the water level in a hole on the centerline of the bridge. With the excavator over the hole, the water level was flush with the ice surface; a clear indication the ice had more than enough bearing capacity for the load.
“Working with Leonard has been crucial to ensuring the safety of the operation,” said Sturm. “He has provided critical review of safety protocols and technical review of site conditions, which have allowed the refuge to move forward with planning the recent successful operation.”