Message:

The Winter of 2025 has had some long periods of cold weather that haven’t been seen in the last few years. For the upper Thames River watershed, this has produced some significant depths of snowpack, while in the lower Thames River watershed this has produced a significant thickness of ice on the Thames River.

The above freezing temperatures seen in the last week of February have begun the thawing process in the lower Thames River watershed. Most of the snow has already melted away in in Essex and Chatham-Kent, with a significant amount of melting having happened in other areas of the lower watershed as well. Some of the smaller watercourses have already lost their ice cover. However, there is still a significant thickness of ice on the Thames River itself. Over the next few weeks, the thawing will continue to progress.

The Upper Thames River Conservation Authority (UTRCA) conducts snow surveys to measure the snow depth and how much water it holds. The last survey was conducted on February 14, just before another winter storm hit the area. This data is supplemented with precipitation gauges that weigh the snow as it falls. Based on this data, they estimate that the UTRCA watershed snowpack currently has around 100 mm of stored water on average. This amount of water is about 50% greater than the long-term average for this time of year.

The Lower Thames Valley Conservation Authority (LTVCA) measured the thickness of the ice on the Thames River at several locations from Chatham down to Lighthouse Cove on February 25. On average, 23 cm of ice was measured. This amount of ice is slightly thicker than what was present when the 2019 ice jam occurred, and slightly less than the thicknesses that were producing ice jams in the late 1970s and early 1980s.

The amount of water stored in the snowpack in the upper watershed means that there is the possibility of significant flooding along the entire Thames River when the snow in upper watershed melts. However, the amount of flooding that will occur still depends on day-to-day weather conditions that will determine how fast the snow melts, such as daily high and nighttime low temperatures, as well as any rainfall amounts and patterns. Temperatures that stay below double digits during the day and return to below freezing overnight, with no significant rain, will result in a more gradual melt and less flooding.

The possibility of high flows on the Thames River, combined with the current thickness of ice on the river, means there is also an increased risk of ice jams this year. Ice jams occur when the ice cover on the river is lifted up by high flows, the ice breaks into smaller chunks, and then those chucks jam up upon themselves. This can restrict flows in the river and cause water to spill out of the river channel causing flooding. While smaller ice jams can occur anywhere along the Thames River, they tend to have less impact upstream of Chatham. Ice jams at the mouth of the Thames River can impact the community of Lighthouse Cove. Historically, ice jams have also occurred between Prairie Siding and Big Creek, where they have caused significant flooding if they overtop or breach the flood protection dikes in this area. Ice jams in these downstream areas can also back up the water in the river all the way into Chatham and produce flooding in the city. With the right weather conditions, enough of the ice on the river could melt away before river flows get high enough to break up the ice and potentially cause an ice jam. Again, the best weather situation would be where temperatures stay below double digits during the day and return to below freezing overnight, with no significant rain.

As the thawing continues in the Thames River watershed, residents should pay attention to local conditions and be prepared for potential flooding.

Personal safety around watercourses is extremely important at this time of the year. People should take extra caution around the Thames River, as well as ditches, creeks and streams. Any ice remaining on the region’s watercourses should be considered unsafe and should be avoided. The banks of watercourses can be slippery, and the cold water and fast-moving water can be dangerous. Even standing water can present its own unseen hazards. Children, pets, and livestock should be kept away from the water.

Officials will continue to monitor the situation and update this advisory as necessary.

This message will be in effect until April 1st.

Contact: Jason Wintermute ([email protected])