Posted: February 11, 2016

Frazil Ice and High Water Levels

What's up with the water levels on the Ottawa River this winter? Learn about the impacts of frazil ice.

Many people have noticed the unusually high water levels for this time of year between Ottawa/Gatineau and the Carillon Dam. High water levels and fluctuations along this section have contributed to thinner ice in the main channel for ice fishing and shoreline flooding. The National Capital Region (NCC) has put out a flood warning urging people to stay away from certain pathways along the shoreline that have been flooded as a result of these high water levels. The upper Gatineau River has also experienced similar low-level flooding this winter.

So why are the water levels so high?

Many factors have come together to cause the unusually high water levels for this time of year. Rain coupled with periods of melting has contributed to near historic flows. As a result of the high flows and recent weather, the main stem of the river above Carillon Dam didn’t develop its typical ice cover. High flows and rapidly cooling conditions have caused frazil ice to form instead. Frazil ice looks a lot like slush and is a collection of ice crystals suspended in the water column.  The combination of high flows and frazil ice has caused water levels to rise along this section.

How does frazil ice impact water levels?

Unlike the ice layer that typically forms over the surface of the river this time of year, these suspended ice particles that make up frazil ice are very sticky and can adhere to almost any surface including ice sheets and other structures in the river. This makes for a rougher channel that slows water flow and creates partial obstructions. Additionally, the slush ice is also more viscous and resistant to flow (think of honey which has a greater viscosity than water). By making the river channel more rough and making the water more viscous, frazil ice can thus slow down the flow of water in the river, causing water to build up and water levels to rise upstream of these areas. These factors coupled with the higher than normal flows this year, have caused the higher water levels. Current flows and levels are expected to slowly decrease but remain above normal for the next few weeks.

Photo: Wikipedia

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