What are our options to mitigate this. Could a giant cistern be built below ground to collect excess rainwater?
As part of the City's Wet Weather Flow Master Plan, a large tunnel will begin construction this year from roughly Don Mills/DVP following the valley to around Queen/Lake Shore then shunting east to Ashbridges.
This will hold stormwater for that area (east of the Don, south of Taylor-Massey Creek and should be finished in the early 2020's.
Thereafter, another tunnel will be built along Taylor Creek to roughly Warden Avenue for a similar purpose.
The most recently discussed options for downtown, envision enhanced storm water collection in the Lake Shore/Queen's Quay area, before shunting east.
Even when built, however, this will only address portions of the issue.
Areas like the Simcoe underpass will require pumping solutions in all likelihood, as will some other low points where surface water accumulation alone can pose a serious risk of flooding.
Lower levels of parking/foundations, particularly where set below the water table are always at risk. Pumping is the most likely answer.
A more comprehensive set of options is also available, ranging from hideously expensive universal sewer separation, to green roof(s), grey water systems, building-level cisterns, to open water retention.
The latter is hard to do right downtown, but there are excellent nearby spaces which could still relieve the issue nearer the core.
But none are cheap, or without controversy
(ie. you could use the 'bowl' area at Trinity Belwoods to retain storm water, but that would eliminate other uses of that space. )
This project could be undertaken w/digging out the original ravine shape and buried bridge, but that would eliminate much needed table parkland. Replacing that space would be quite expensive, and if done adjacent to Trinity would also potentially impact heritage structures and/or homes.
Likewise the low-point in Bedford Park is also part of the former Garrison Creek corridor and offers similar opportunities and challenges; as does the baseball diamond at Riverdale Park West.
But replacing that space is no easy task.
All in all lots of trade-offs and lots of $$$ however you choose to tackle it.
There is one major opportunity in the budget now....which is the Yonge Street re-do. If it incorporated large, open-style trench tree planters at select locations, that would help (albeit in a small way).
That above project is, however, illustrative that we can, should and must incorporate solutions to this sort of thing (along w/urban heat island issues) into every project of significance the City under takes, if remotely practical.
