By Kevin Bunch, IJC
With winter here, annual efforts to manage ice flows in the St. Marys, Niagara, and St. Lawrence rivers are in full swing. Management efforts in these connecting channels of the Great Lakes aim to prevent ice jams that can cause winter floods and damage to hydroelectric turbines, while contending with difficult or unexpected winter conditions.
In cold seasons, ice typically forms along the Great Lakes and its connecting channels. Unregulated, this ice can take a while to form a solid layer due to currents, leading broken pieces of ice to jam up and cause flooding.
Control structures are in place for shipping and hydropower needs but hydropower dams and ice booms provide a way to influence how ice forms which in turn helps to prevent flooding and protect equipment.
The St. Lawrence River
Prior to dams being built on the St. Lawrence River, ice jams and winter floods were frequent in sections of the river from Ogdensburg, New York, to Montreal, Quebec, said Gail Faveri, co-secretary of the International Lake Ontario-St. Lawrence River Board. Construction of the Moses-Saunders Dam has allowed water managers on both sides of the St. Lawrence a way to control the amount of water flowing out of the river and thus influence how ice forms above and below the dam. By slowing down the velocity, Faveri said, a solid, stable ice cover forms more easily. As ice ages, it smooths out, allowing water flows to increase again without destabilizing the cover.
“When the ice is forming you can lower the flow and slow the velocity, allowing the ice to form (properly),” Faveri said. “Once it gets established, you can go and allow a higher outflow. It functions more like a pipe … and you can drive more water through.”
The gates at the Iroquois Dam at Iroquois, Ontario, also may be used to promote ice formation upstream.
Power companies also install ice booms around Nov. 20 each year between Prescott, Ontario, and Cardinal, New York, to help ice form upstream, Faveri said. Those are handled by Ontario Power Generation and the New York Power Authority, and the IJC is alerted when the booms are installed. Two main booms that stretch across the main channel of the river remain partially open until the Seaway closes to vessel traffic each winter.
Eastern Lake Erie
Now turning upstream, this season’s Lake Erie-Niagara River ice boom was installed on Dec. 16-17 by the New York Power Authority at the outlet of Lake Erie as it has been every ice season since 1964. The IJC issues approvals to the New York Power Authority and Ontario Power Generation to install the boom to accelerate the formation of a naturally occurring ice arch at the outlet of Lake Erie into the Niagara River, said Derrick Beach, secretary to the International Niagara Board of Control. Conditions for the operation of the ice boom are provided in the IJC’s approval to ensure that potential impacts, like flooding to surrounding residents and activities on the lake and river are minimized. The IJC has appointed the International Niagara Board of Control to oversee that the conditions of the ice boom’s approval are met.
“The ice boom reduces the amount of ice that goes down the Niagara River,” Beach said. “The ice naturally (accumulates) in that area on the lake creating an ice arch and the ice boom helps the formation of that natural ice arch that holds the ice back in Lake Erie.”
Once the ice arch forms, it naturally reduces the amount of ice entering the Niagara River and the potential of the ice jamming or damaging intakes in hydroelectric power plants along the way. As an added benefit, Beach said the ice boom helps prevent ice from jamming in the Niagara River and causing flooding and shoreline property damage along the river. However, as a floating boom, if high winds or thick ice cause a lot of ice to push against it, the boom will be pushed under water and allow some ice to pass, and then float to the surface again after the ice has passed, allowing some natural transport of ice to continue.
The Lake Erie-Niagara River boom consists of about 1.7 miles (2.7 kilometers) of floating pontoons cabled together, and is maintained by the New York Power Authority on behalf of the hydropower generating facilities on the US and Canadian sides of the Niagara River. Some of these conditions include that the boom cannot be installed each year until the water temperature of Lake Erie drops to 39 degrees Fahrenheit (4 degrees Celsius) or on Dec. 16, whichever comes first. As well, the boom’s approval requires that all floating sections be opened by April 1 unless there is more than 650 square kilometers (250 square miles) of ice remaining in the eastern part of Lake Erie. The latest the boom was taken out was May 3, 1971.
The St. Marys River and uncontrolled channels
Hydropower entities install ice booms in the St. Marys River connecting Lakes Superior and Huron to protect their operations, as does the US Army Corps of Engineers to protect a ferry operator, said John Allis, alternate regulation representative with the International Lake Superior Board of Control and Great Lakes Hydraulics and Hydrology office chief for the US Army Corps of Engineers (USACE) Detroit District. At the start of December, the focus of water managers – much as in the St. Lawrence region – is on reducing water flows using its compensating works flow control structure and hydropower operations so that a solid ice cover can form, allowing a consistent water flow the rest of the winter to reduce the chances of ice jams.
“Even if we could chip ice away from the compensating gates to be able to open them up during the winter, we don’t want to drastically change flows month to month, as you could begin to break up the ice cover and getting that ice flowing, causing ice jams,” Allis said.
The connecting channel between Lakes Huron and Erie has no control structures, Allis said, but the USACE and Canadian Hydrographic Service (CHS) monitors ice conditions along the St. Clair and Detroit rivers in the winter months in case of ice jams. The US National Oceanic and Atmospheric Administration and the CHS have gauges along the connecting channels, and when a jam is forming water levels can suddenly decline downstream and increase upstream as the water is backed up. When those instances occur, Allis said the Corps notifies the US Coast Guard so it can send an icebreaker to clear the jam before it can cause a flood event along the shoreline.
Kevin Bunch is a writer-communications specialist at the IJC’s US Section office in Washington, D.C.