Dundas suffered aggressive rainfall, flooding, mudslides and streets like rapids Thursday. And it's no wonder, Environment Canada says β€” a full month of rain dumped on the area in one day.

'It was a pretty dramatic scene.' - Dan McKinnon, general manager of public works

The gauge at the Royal Botanical Gardens (RBG) site adjacent to Dundas, registered 72.4 mm, said Peter Kimbell, an Environment Canada warning preparedness meteorologist.

That's the most rain that's ever fallen on an April day since at least as far back as the records go, which is 1866. 

In fact, Hamilton usually gets about 73 mm of rain in April, Kimbell said. So "at the RBG site, there was a full month of rain in one day."

The agency expected other areas of Ontario to get pummeled too, he said. But Hamilton got it the worst.

​There was flooding in nearly every ward of the city Thursday, particularly below the escarpment, said Dan McKinnon, general manager of public works. But Dundas was hit hardest.

Dundas flood cleanup

Cleanup after floods in Dundas was underway Friday. This shows the scale of debris that blocked a culvert and caused a stream to overflow and flood a plaza and nearby streets. (Dave Beatty/CBC)

There were numerous flooded basements, flooded roadways and mud slides, he said. The worst happened when Sydenham Creek washed limbs and tree trunks down to pool in front of the King Street Tim Hortons, and blocked storm drains. On Watson's Lane, water flowed like rapids, and one homeowner set up boards to try to redirect the water.

"It was a pretty dramatic scene," McKinnon said.

Calls about the flooding began around 7:40 p.m. as flooding cut off the main thoroughfare between Dundas and Highway 6. Rising water also cut off the CP rail line. 

Hamilton Conservation Authority's flood warning remains until Monday. Most of the flooding has subsided, the city says, but some areas were still underwater Friday morning.

There were other issues too. On the Red Hill Valley Parkway, a shoulder between Stone Church and Greenhill washed away. That portion of the highway temporarily closed overnight. Crews are repairing it.

The storm also strained the Woodward wastewater treatment plant, McKinnon said. Storm water may have overflowed and backed into the sewer system, McKinnon said. That can cause basement flooding, although "it's difficult to know with certainty."

Roads crews and Hamilton Water staff worked overtime overnight to handle the flood, which was worst across the lower city from the west end to Stoney Creek, McKinnon said. They'll work the rest of the day, and over the weekend if necessary.

Hamilton's Waterfront Trail flood

Heavy rains have caused Cootes Paradise to overflow onto Hamilton's Waterfront Trail. The trail is closed until the water recedes. ( (Jessica Palumbo/CBC))

The Waterfront Trail is closed and underwater between Princess Point and the Desjardins Canal. The city will reopen the trail once the water has subsided.

Mayor Fred Eisenberger issued a statement Friday morning thanking residents and staff who fought against the flood.

"I appreciate the community's patience and cooperation as we continue to clean up from the storm."

As for why Dundas was pummeled so hard, McKinnon said that's simply how the rain fell.

"It's just where the worst of the weather pattern formed," he said.

"That's the one thing that's difficult about predicting and dealing with storms. They're not uniform when they come through. For whatever reason, this one seemed to hover over Dundas."

samantha.craggs@cbc.ca | @SamCraggsCBC