Saturday, December 30, 2006

Linchpin of the Lower Don

Quick question - what’s the most interesting construction project currently underway on the Lower Don - is it the restoration of the river mouth? Is it the creation of the Don River Park and the West Don Lands?

If you answered yes to either of these questions you'd be wrong. The most interesting project is the reconfiguration of the railway bridge just north of Lakeshore. Officially known as the "Kingston Overpass", this bridge has caused many problems for the Don River. Not to say that it has been the instigator, rather it has been against this intractable obstacle that problems with the river have been revealed.

It all started about 50 years ago when Hurricane Hazel roared through Toronto in its history making path of destruction. While the main loss of life was in the Humber River valley, Hazel dumped record amounts of rainfall in the Don River watershed. All this water rushed down the valley. Whereas water in the Humber emptied unimpeded into Lake Ontario, the Don flood came up against the railway underpass. The flow of water was over 400 times the daily flow so there was not enough space for all that water to flow underneath the bridge. The water had to go somewhere and it overflowed the banks as far east as Leslie Street and as far west as Bay Street.

Since then the impact of the flood has set the benchmark for all future development. The main reason why the West Don Lands has remained derelict is mainly because the Toronto Region Conservation Authority has a veto over any development. They insist that any new building be floodproofed against a reoccurrence of Hurricane Hazel, something that a majority of builders find too expensive. The naturalization of the mouth of the Don has also been delayed because no one knew how much water would flow south if the bridge were ever reconfigured.

Then along came the Waterfront Revitalization Task Force and they made the mouth of the Don and the West Don Lands redevelopment two of their priorities. In order to accomplish this, they had to fix the flooding problem. Much to everyone's surprise this is now well underway.

Basically, the idea is simple - in order to eliminate the flooding north of the bridge all you need to do is give the river more space to flow underneath the bridge. A simple idea but a complex implementation. Not only do you have to increase the span length you also have to do it while the bridge is still in use. The bridge contains four separate tracks that carry Go trains and other trains every day.

New construction creates two new underpasses

The construction procedure has been straightforward but meticulously slow. They divided the bridge into two sections. The northern half of the bridge (two tracks) were closed down and torn up. They excavated a new underpass on the west side of the river and built a new span over top. Concrete was poured and new track was laid. This process was also complicated by the fact that the space where they were excavating is also occupied by a high power electrical conduit. This had to be relocated as well. To date the northern half is finished and they are now working on the southern half.

Boring new pilings. Construction continues while a Go Train passes by.

Pouring the foundation for the Kingston underpass.

Tight deadlines necessitated work at all hours. Here a girder is installed on the Kingston span.

Pre-poured railbeds installed on top of new span.

Installing the new track.

A second smaller tunnel is also being created underneath the Don corridor that will eventually connect the trail to the new Don River Park and the West Don Lands.

The new tunnel to connect to the Don River Park.

Excavation the tunnel. The round posts on the right are the original pilings from when the railway was first constructed.

Top view of construction on Bala underpass

For anyone wanting a more detailed report, please view the Lower Don River West News on the project.

The path is scheduled to be reopened in May. When this happens we will have a new at grade pedestrian tunnel (no more dipping down then up again). Even more so, we will finally have a river whose flow is encumbered by one less manmade obstacle.

Note: Normally I would take my own photographs but due to construction site rules visitors are not permitted onsite. My thanks go to Ken Dion, TRCA project manager and Tony Angelo at Totten Sims Hubicki on behalf of TRCA and TWRC for providing these pictures.


Donwatcher said...

I received these comments on my post from Ken Dion, TRCA project manager.

1) The main flood protection feature that will prevent flooding into the West Don Lands and downtown Toronto up to the Hurricane Hazel sized event, will be the Flood Protection Landform that will underlie the future Don River Park. The Kingston Railway Bridge Extension is a critical mitigation feature that will provide sufficient hydraulic capacity underneath of the railway to compensate for the additional flood waters that will be pushed back into the Don River once the Landform is constructed. This will ensure that there is not an increase in flood levels upstream and to the east of the river, resulting from the construction of the Landform.

2) The level of flooding in the lower Don during the actual Hurricane Hazel event was significantly lower than the anticipated flood levels that are calculated by our computer generated hydraulic and hydrological models for the Don River because the actual Hurricane Hazel was centred over the Humber River. Our computer models calculate the level of flooding as if Hurricane Hazel was centred over the Don. As a result of the significantly lower levels during the actual hurricane in the Don as compared to the computer generated levels, the railwaybridge was not likely a significant contributor to the moderate level of flooding in the area that occurred in the 1950s storm. During a Hurricane Hazel sized event over the Don Watershed, the railway embankment will likely contribute to the extent of flooding in the area, however this sized event has not yet been observed in recorded history.

3) The Don Mouth Naturalization Project has not proceeded up to now not so much due to the uncertainty over the volume of water that will come south of the railway bridge, rather it was the sheer magnitude of costs to study and undertake the work, combined with the extensive infrastructure in the way, the extent of contaminated soils and uncertainty over the use of the Port Lands that has delayed progress. The naturalization is only possible in a highly coordinated process that examines and plans all these issues together, combined with the political will and financial commitment from all levels of government (through the TWRC) that makes this project possible. Even with this commitment, it has been a large undertaking to get all the complicating adjacent land issues moving at the same time - hence the resulting delays.

Donwatcher said...


Thanks for the very accurate and technical clarifications. I just want to add my own comments.

1) I realize the Flood Protection Landform or berm on the west side of the river is integral to the project. I see it as a separate yet parallel project to the bridge reconstruction. I didn't mention it because, a) it hasn't been started yet, and b) I felt that talking about both would make for a lengthy article. When the berm construction is started I will certainly blog about it.

2) I wasn't aware of the modelling aspect about the different rainfall amounts over the Don and the Humber being different. Nevertheless, I disagree with your assertion that the railway was not a significant contributing factor. Flooding north of the embankment was more serious than it was on the south side (at least to the west).

3) I am well aware of the complexities of the Don Mouth project. However, I don't believe that it can be done without first performing the flood protection work currently underway.