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COLUMN: NVCA measures snow to forecast flood risk

Specialists measure depth and density of snow twice a month from November to April

While many of us would agree winter has not been ‘normal,’ we’ve certainly seen snow accumulate and then disappear during a warm spell.

Where does the snow go when it melts? Is there a way to measure that? The answer is yes.

Twice each month, from November to April, flood specialists from across Ontario head out to conservation areas to measure and report on the depth and density of the snow. They do this with weigh scales and metal tubes called snow survey tubes.

The Nottawasaga Valley Conservation Authority (NVCA) sends its own specialists out to drive their snow survey tubes into the snowpack and weigh the results. The information helps NVCA’s flood forecasting and warning team estimate how much snowmelt we’ll get, how much of it will flow into the rivers and streams, and whether people who live in low-lying areas and flood plains will be impacted by overflowing water courses.

There is a specific process in recording data for snow surveys. Samples are taken as close to at the same time as possible, which means the flood specialists from across the province co-ordinate to take samples on the same days. NVCA’s specialists collect samples from nine properties. At each property, they take 10 samples from marked areas to ensure the data is consistent. Each sample area is exactly 30 metres away from the last.

The snow samples collected are measured and weighed, and calculations are done to find out how much water is held inside the snow. Other conditions, like whether the ground is frozen or if there is an icy crust on the snow, are noted as well, since they contribute to the area’s ability to mitigate flooding. The reports are submitted to the Ministry of Natural Resources and Forestry.

Each day, NVCA’s flood forecasting and warning team completes an assessment of the potential for flooding in the Nottawasaga watershed. Snow surveys are one of many methods the team uses to determine potential for flooding. They also monitor weather forecasts, rainfall, and lake and stream water levels across the watershed.

If the potential of flooding is high, a flood message will be sent to organizations such as municipalities, schools, first responders, media and residents to take the appropriate action.

There are three flood messages that can be issued. Watershed conditions statements are issued when weather conditions can pose a risk to personal safety or have the potential to lead to flooding. Flood watches and flood warnings are issued when there is a possibility of flooding.

In 2023, NVCA issued five water safety messages and one flood outlook message. In January 2024, one water safety statement and one flood outlook were issued.

Learn more about NVCA’s flood statements at

Taryn Arsenault is a flood specialist with the Nottawasaga Valley Conservation Authority.