The amount of snow on the ground might be low, but the chances of a flood this spring are still high, according to a report released this week by the Grand River Conservation Authority.
Much of the ground across the watershed is frozen solid, which creates potential for high runoff from melting snow and spring rains. Most winters, a covering of snow insulates the ground. In the spring, the snow can soak up some rainfall, slowing the amount of water making its way to a water course. In addition, if the ground is unfrozen, water can soak into the ground rather than run off.
This year, the amount of snow on the ground is only a quarter to half of normal for February. The ground is saturated from rain in January and there is a consistent frost cover.
“Given the saturated ground conditions in some areas of the watershed, the potential for a major flood is higher than normal if heavy spring rains occur along with a rapid spring snow melt,” Gus Rungis, senior water resources engineer with the GRCA told municipal and emergency services personnel meeting at the GRCA head office in Cambridge. About 100 people attended the annual flood warning emergency planning meeting on Feb 17.
The ideal conditions to avoid flooding would be a spring characterized by “maple syrup weather” – warm days and cool nights that allow for a gradual snow melt and ice breakup.
Rungis said the chance of flooding as a result of ice jams is also high this year. Most of the Grand River and its tributaries are covered with sheet ice because of the steady cold temperatures this winter. There is a risk that, as the ice breaks up in the spring, chunks could become lodged in the river creating an ice jam that causes water to back up behind it.
“Whether a major flood occurs is dependent on how the spring thaw unfolds,” said Rungis. “Fifty millimeters (two inches) of rain, in combination with a quick spring thaw or heavy rain on frozen or saturated ground would see the conditions needed for a major flood.
The GRCA operates seven reservoirs to reduce flooding. The reservoirs currently are about two-thirds to three-quarters empty and are ready to receive water from the spring melt.
GRCA staff are doing regular tours of the watershed to look for potential trouble spots such as ice jams. Twice a month, GRCA workers measure snow depth in 12 locations throughout the watershed in order to calculate potential flows during the spring melt. In addition, water levels are monitored through more than 50 stream gauges, which automatically send data back to the head office 24 hours a day. That information is available in the River Data section of the website at www.grandriver.ca.
Real time flood messages
The GRCA has set up a Twitter feed to distribute flood messages throughout the watershed.
The new feed is called grca_flood_msg. Whenever a flood message is issued to the public, a tweet will be sent out announcing the message and linking back to the full text of the flood message on the GRCA website.
Emergency services and News outlets in the watershed are being invited to become followers of the GRCA’s Twitter feed and to retweet flood messages to their followers. More information and a link to the feed is available on the GRCA web site.
The Twitter service is one of two ways that watershed residents can get direct notice of GRCA flood messages.
They can also sign up for the GRCA News release service which sends out e-mails of GRCA News releases at the same time as they are distributed to the media.
Instructions on how to sign up are available in the Newsroom section of the GRCA website.
