Cutting The Keys For Flood Prevention

"First thing they do is they take these large saws out on the river, and they cut ... long slots in the direction of flow in the ice. These slots are like parallel lines running under bridges and over some utility crossings, whether it's telecommunications cables or sewer lines or water lines that run under the river."
"They use the amphibex to loosen up the ice on the Ottawa River below the Rideau Falls, and then they move it up onto the river. Usually this happens in early March where they start at the downstream end of the Rideau and work their way progressively upstream."
"[City crews] know enough now about the process that it takes a certain amount of natural runoff or flow in the river just to move things out onto the Ottawa River, otherwise the ice just sits there and slows their progress. So it's about watching the weather, watching the river conditions, and moving when things seem appropriate."
"When you look into the old newspaper accounts -- even as far back as the early 1900s -- there would be ice jams on the river when spring comes, and the snow melts, and the river flows rise. So, in the early days it was done just in reaction to flooding ... In the midst of ice jams, they'd be sending men and equipment out to try and break up the broken ice and alleviate the flooding that had already occurred."
Bruce Reid, director of watershed engineering and science, Rideau Valley Conservation Authority

City of Ottawa crews get started on the annual ice breaking operations on the Rideau River.    Photograph by: Chris Mikula, Ottawa Citizen

 

Residents of the City of Ottawa breathed a sigh of relief in the past when word arrived that work crews were cutting 'keys' in the ice immobilizing the Rideau River that runs through the city. That surely meant, to winter-depressed people living in the country's capital, that icy cold, ferocious winter winds and incessant snowfalls would shortly be on the wane. And spring wouldn't be far behind.

Powerful saws make quick work of the ice as a work crew cuts slots or ‘keys’ in the Rideau River.   Photograph by: Wayne Cuddington, Ottawa Citizen

 

Once those keys were cut and a week or so had passed, people might drive over to the Rideau Falls in expectation of witnessing an impressive exhibition. If the river was in good flow, it would be bringing great, thick ice pans downriver, to slide down beside the Rideau Falls, with a tremendous blast into the icy water, the weight of the ice pans taking them initially down deep into the water, until they bobbed back up and continued their journey downstream.

This year, in Ottawa, municipal and Conservation Valley crews appear to be starting the key-cutting earlier than usual. And no doubt the blasting will follow, although explosives are used far less frequently now, since the introduction of mechanical means of cutting the ice through the use of am amphibious excavator, called the "amphibex". It looks like a giant crab, clambering atop the thick ice layered on the river. Before it can be used, the snow that has accumulated over top the ice must be removed.

The amphibex can crawl up on the ice surface and break it apart using its weight alone. If that doesn’t work, the hydraulic arm can finish the job.   Photograph by: Chris Mikula, The Ottawa Citizen

 

You'd have to know there's a river down there. It looks like a placid snow-covered valley, until it's disturbed.The icebreaking program follows a route that experiences backups historically as a result of flooding from the Rideau River flood plain. Jason Stanforth, manager of core roads for the city, said about 900 structures exist along the 3,800-square kilometre watershed, risking damage if the city neglected this program.

The amphibex uses various attachments breaking up the ice. "It's sort of like a hydraulic excavating machine that's mounted on pods that enable it to float on the water and allow it to climb around", explained Mr. Reid.  Mr. Stanforth explains the use of the amphibex further: "That comes in and breaks up around the base of the falls around the Ottawa River, and then we take it out of the water and bring it up onto the Rideau River itself, and that does the majority of the ice breaking now."

The program is not cheap, but it is a proactive requirement for the city. Prevention of property damage and the critical issue of public safety are at play. The amphibex machine in combination with key-cutting has resulted in fewer explosives having to be used. "Really, the blasting that's done is at the falls right between the Sussex bridge and the dam, and then leading back to the next set of bridges, and essentially it's just because there's no way to put the boat into the water, the amphibex machine into the water to break up the ice."

Blasting is used as a last resort to clear especially stubborn ice jams.    Photograph by: PAT McGRATH, THE OTTAWA CITIZEN

 

The yearly cost in this operation is about one-half million in total with the provincial Ministry of Natural Resources picking up $100,000 of the associated cost. A mid-1990s independent review of the ice-breaking procedure commissioned by the conservation authority concluded that the program was required to prevent public safety problems and property damage. It also stressed the utility of the amphibious excavator, and less frequent use of explosive for environmental reasons.

The catastrophic flooding experienced last June in Calgary, Alberta had been foretold by a state-of-the-art weather computer system located in the United Kingdom, in Reading. Their program uses leading-edge weather forecasts capable of 'seeing' weather events approaching weeks before they occur. It is a pilot project of the European Centre for Medium-Range Weather Forecasts.

And although the program was able to determine that the Bow River was almost certain to surge to levels higher than any previously seen, even during the 2005 floods, the information hadn't been passed along to the Province of Alberta.

Whether that heads-up might have been useful in the event, is a matter of conjecture.