Ice jams on Thames pose flood threat to Chatham
Not a year after it was menaced by early spring flooding, low-lying Chatham is again in the crosshairs of dangerously high water levels.
But this time the culprit is an ice jam in the Thames River, not just the massive Southwestern Ontario snow melt coursing down the river, unlocked by the region’s springlike weather and heavy rainfall a week after a deep freeze.
While officials say they don’t expect a replay of last February’s brush with what might have been a record disaster, they took no chances Thursday, issuing a flood warning for Chatham and zeroing in on the ice jam now lodged around the Prairie Siding bridge, about 12 kilometres southwest of Chatham.
That jam — huge floating chunks of ice and debris, which formed Wednesday night — has caused the river to rise, backing up into Chatham and making basement flooding in its downtown riverside business district unavoidable. Late Thursday, officials said the ice jam had begun to move but cautioned such jams are unpredictable and can easily form again downstream.
“We’ve had people out there three or four times today,” Jason Wintermute, an official with the Lower Thames Valley Conservation Authority, said earlier in the day.
The low-lying Chatham area is vulnerable to flooding from ice jams downriver and at the mouth of the Thames where it empties into Lake St. Clair.
But because traditional ways to break that ice — blowing it up, or calling in tug boats to clear it — can be ineffective and dangerous, the conservation authority is instead turning to other flood defences. It’s now operating its Sixth Street dam and pumping station in Chatham, which is expected to protect the south end of the city along McGregor Creek from flooding. The situation — it can take a while for water flowing through the Thames to reach Chatham from the river’s upper reaches — is “dynamic and changing,” said Chatham-Kent fire Chief Bob Crawford.
“There’s no disaster. There’s no state of emergency,” he said after a Thursday afternoon meeting with municipal officials at ChathamKent’s civic centre. “The mayor decided that he would prefer to be prepared. We’re monitoring and we’re preparing, and we’re planning to see how we’re going to respond.” Firefighters and economic development personnel went door to door Thursday, checking in on downtown businesses and providing updates.
The river level was 4.15 metres above normal Thursday, and expected to peak at 4.65 metres Friday, still shy of the 5.25 metres above normal to which it rose late last February, causing flooding that triggered a state of emergency in the city and evacuations of affected areas. Chatham-Kent Mayor Darrin Canniff said safety is the priority. “We want to emphasize, stay away from the river,” he said. “It’s a common-sense thing. There’s heavy flows moving there and you just never know. The banks might be weak. We don’t want anybody falling in.”
Officials expect the river to top out “a couple of feet lower than what we had last year,” said Wintermute, the conservation authority’s water management supervisor. The last time ice jammed at Prairie Siding with similar flows in the river, water levels in Chatham rose an additional 0.7 metres from where they were early Thursday, the conservation authority said. If that happens, the fallout would be levels similar to those seen in floods of 2008-09 and 1985. But the authority also noted ice thickness was significantly greater in the 1985 ice-jam flood. If conditions change to bring water levels of that era, there could be expansive flooding near Chatham’s downtown and other effects downstream in the Raleigh and Dover areas and into the town of Lakeshore. Chatham-Kent is working closely with the conservation authority and will determine next steps based on all variables, including river flows and weather, said Thomas Kelly, its general manager of infrastructure and engineering. Last year’s flooding was far more widespread than what appears to be in the cards, causing hardships. But it also provided valuable experience for emergency crews, Crawford said.
“We learned an awful lot about how to respond, how to communicate, how to collaborate between our departments,” he said. “This is a co-ordinated team approach and it’s a group of highly skilled professionals.
“We’re very hopeful this is going to be a non-event, (that) the jam will move downstream, the rain doesn’t come, and the waters recede.
“We do prepare for the worst and hope for the best.”