Above: Ice on the Athabasca River near Fort McMurray, Alberta, on Monday, April 27, 2020. (Chris Schwarz/Government of Alberta)
They seem to come out of nowhere. In a matter of minutes, water levels can rise several feet on waterways from little creeks to larger streams and even the biggest rivers across parts of the world that experience sustained winter seasons. They are called ice-jam floods, and the last few days brought a dramatic example to Fort McMurray, Alberta (see photo above and discussion below).
An ice jam occurs when chunks of ice in a waterway pile up as they move downstream. The ice is typically carried within the flow of a stream or river. However, the ice can begin to pile up and accumulate if it encounters an obstruction to the flow, including sharp bends on a river or objects such as a bridge that lies close to the river’s elevation. Ice jams can also occur at the mouth of a tributary, or even an area where the river’s slope decreases enough to slow the current and allow for the buildup of ice. All of that ice can very quickly back up the flow of water and cause a flood.
Whereas excessive rainfall and runoff typically produce river flooding on the order of days, ice jam flooding can occur on a time scale of hours, more like a flash flood. Once an ice jam occurs, it can quickly break up, and the wall of rushing water will flood downstream locations, especially if the ice hits another impediment and jams again.
There are a number of meteorological factors that can increase the likelihood of ice jams, and when they all come together at the wrong place and wrong time, the results can be catastrophic. Ice builds up on waterways as a result of an extended period of cold weather. The colder it gets, the thicker the ice gets. If nature cooperates, the ice is held fast in the river until a spring thaw begins to melt the ice. The key to this process is a gradual, controlled ice melt.
However, that’s not always how nature works. A thick ice cover can rapidly break up under certain conditions, including a period of very warm temperatures and the addition of rainwater and/or snowmelt into the waterway. Warm temperatures will not only melt ice, but in most northern regions, if there is a significant snow cover, that warmth will melt the snow and result in a lot of meltwater to enter the stream. The meltwater will raise the level of the stream and increase its flow, causing ice breakup. Higher water levels also swell the stream and that pressure promotes ice breakup.
Below are video clips of ice moving under a bridge in St. Marie-de-Kent, New Brunswick, in 2014, and a massive ice jam moving through the Aroostook River in Maine.
In addition to an increase in water levels from meltwater, the same weather patterns that provide abnormally warm weather often produce significant rainfall. Of course, the rain will also swell the rivers and that will result in increased flow and the breakup of ice cover. The rain itself will also help to melt or weaken the ice cover. The “perfect storm” scenario is an extended period of cold weather with significant snow cover followed by a rapid warm-up and rainfall.
Back in February 2019, an ice jam produced significant flooding in the suburbs of South Buffalo and its adjacent suburb of West Seneca in New York. A midwinter thaw, accompanied by a rapid meltdown of nearly two feet of snow cover, led to the ice-jam flood.
The gauge that monitors the height of Buffalo Creek tells the story of just how fast the water levels can rise behind an ice jam, as shown below. In fact, the water level rose from 9 feet to over 14 feet in a little less than two hours that day, giving residents precious little time to react and protect the lives and property. The gauge readings were unavailable for a brief period during this flood event as a result of the ice buildup.
In late April 2020, the city of Fort McMurray, in northern Alberta, Canada was hit by a major ice jam flood on the Athabasca River. You may remember Fort McMurray if you follow the news and weather. The city is a boomtown for the oil sands industry that thrives in parts of northern Canada. Back on May 1, 2016—almost four years to the day of the 2020 flood—a major wildfire developed to the southwest of the city. Before the fire was eventually brought under control in early July, it ravaged nearly 1.5 million acres across the region and led to an evacuation of the entire city of close to 80,000 residents, plus thousands more in nearby areas. With direct and indirect damage estimated at more than $9 billion (USD 2016), it was the costliest disaster in Canadian history.
After a very cold winter of 2019-20 in the province of Alberta, Canada, the Athabasca—one of the major rivers of western Canada—developed a thick ice cover. This river covers a length of over 700 miles, much of that flowing northward and eastward from its origins in the Canadian Rockies toward the Prairies. Ice jams can be a particular threat for north-flowing rivers such as the Athabasca, or the Red River of the North in the United States. This is due to the fact that the headwaters of these waterways are typically in warmer climate zones, where the spring warm-up occurs earlier than in downstream locales farther north. So all of that meltwater can encounter still frozen waterways as it moves downstream.
As spring evolved across the Canadian Prairies, mid-April took a rapid turn toward milder conditions. Temperatures at Fort McMurray approached the 60°F mark for several days before the ice jam developed. The warm weather melted the snowpack, and there was even a little rain.
As the Athabasca approaches Fort McMurray, the topography becomes flatter and the river widens. Both of these features combine to slow the current, leading to the potential for ice floes to slow down and pile up. Another waterway, the Clearwater River, feeds into the Athabasca from the east in the city, and can contribute to slowing the flow of the river. All of these conditions led to a massive ice jam, reported to be over 15 miles long, developing in and near Fort McMurray. Up to 15,000 people were notified to evacuate.
Unfortunately, the ice-jam flood came at the peak of the COVID pandemic, making matters even worse for residents, first responders, and government officials alike. As often seen with other rivers, the jam caused the level of the river to rise very quickly over a short period of time. At a gauge just upstream of Fort McMurray, on the Clearwater River, the water level rose over 12 feet in the course of a day. On the Athabasca, just downriver from Fort McMurray, the gauge reading was as dramatic, rising over 18 feet in two periods, on April 24 and again on the 26th before the data became unavailable.
What we can do about ice jams
So, what alternatives are available to manage something of this size? There have been suggestions to dynamite the jams. In fact, this has been attempted before, both on the ground and even from the air. However, those types of mitigation efforts are typically successful for only the smaller-sized jams. For something of this size, the efforts would have very little impact and could even worsen the jams as re-distributed ice may compact even further. About the only way an ice jam of this size is reduced is the natural process of warmer conditions which eventually will melt it all.
There have been many local efforts to predict ice jam formation. In the National Weather Service office where I worked in Buffalo —an area prone to annual ice jams on many of the smaller creeks—we used a simple method of finding the number of hours where the temperature consistently went above 32°F, and summing the number of degrees above 32°F for each of those hours. Known as melting-degree hours, the method proved relatively successful in helping us raise awareness that the potential for ice jams could occur.
Those local forecast methods, however, do not take into account the many variables that are different from one location to the next, including the size and shape of the body of water, the input of flow from other waterways, etc. Recently, I spoke with Dr. Karl-Erich Lindenschmidt, an associate professor at the University of Saskatchewan’s Global Institute for Water Security. Lindenschmidt and his colleagues have been working on a sophisticated ice jam flood forecasting system, known as RIVICE. They have tested it on the Athabasca River and also on the Red River, the same northward-flowing river that transits Fargo and Grand Forks, North Dakota, and has a history of producing major ice-jam flooding through southern Saskatchewan including the city of Winnipeg.
Lindenschmidt is working to expand the RIVICE model worldwide with testing on the St. John River between Maine and New Brunswick, and the Oder River between Germany and Poland. The goal is to use the model to provide forecasts of ice jam flood potential around the world based on weather forecast models. According to a paper published in Advances in Water Resources, “The model shows promising results in predicting the timing of ice cover breakups with an average error of about 5 days, demonstrating its usefulness in real-time operational forecasting.”
Ice-jam flooding is significant. A recent report estimated that ice-jam flooding in North America causes an average of $300 million per year in damage (USD 2017). The rapid rise in water levels associated with these types of events makes them very dangerous. For that reason, it is imperative for those who live in areas prone to ice jam flooding to maintain a vigil when favorable conditions exist and stay tuned to your local National Weather Service office and local emergency management for updates.
