Instead of a 'canal' what you really need to think about is the concept of a 'sponge' city.
These can be natural like ponds or soccer fields. The whole field can be used to hold water during a storm event. The flow out is controlled by the size of the outlet pipe.
Similarly they can be made out of plastic. It provides structural support while also allowing areas like parking lots or fields to retain water.
Here's a good video.
Some screenshots from the video. You also have buildings in Japan where the ground floor is designed to be able to hold water and not be damaged.
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This is the right idea.........which to be clear, we are going the opposite direction of generally.
We continue to experience more sprawl upstream, and more density {which includes toilet flows, showers flows, dishwashing flows etc.) not only without more sponge, but with less.
It's not just a simple matter of more greenspace, thought that's convenient shorthand.
It's a variety of things.......
But aside from just increasing infrastructure elevation (which will be the solution in some cases).............
Here's what I would like to see:
1) More total green area, this is everything from greened boulevards, to fewer driveways, to green roofs and yes, parks etc. Toronto is nowhere near the percentage of green space it could be.
2) Where you can't do green, increase infiltration.........permeable paving of laneways and low volume side streets. Same for all parking lots, if allowed at all.
3) Maximum feasible green roofs..........Anything not absorbed must come off the building or it's in your unit..........where's it going?
4) High quality tree canopy...........you need things that drink excess water and can store it for future use.
5) We need to talk about one problem w/towers, even w/o lots of parking........deep foundations mean less absorption capability of soil and strand the water table. If you build down to bedrock.........where is the water supposed to go?