Tuesday, January 20, 2009

Don River Frozen (Barely)

Skaters and sledders using the Don for winter recreation in 1910 (Toronto archives).

100 years later. Only a thin sheet of ice covers the Don after a week long cold snap.

When I was younger, I used to hang at downtown Blues bars such as Grossman's Tavern. The Sunday evening open jam session was my favourite. One of the local musicians was Mike Macdonald. He never made it big but was well liked and was a mainstay of the Toronto club scene for many years. He mostly sang covers but he did compose a few songs including one that mentioned the Don River. I can't remember the entire song but the verse about the Don goes like this:
Why don't the Don River freeze?
Tell me, tell me, tell me if you please.
The weather here is freezin',
People are coughin' and sneezin',
So, why don't the Don River freeze?...
this was before I got heavily involved in the Don. Of course if I knew then what I know now, I could have answered him. The answer is that changing land uses in the Don watershed over the past 100 years have seriously impacted the Don River. At the beginning of the 20th century, the Don watershed was mostly rural. It still had large tracts of forests and wetlands. Nowadays, most of it has disappeared, replaced by urban land uses. At 80%, the Don watershed is one of the most heavily urbanized in the country.

When rain lands on forests, the trees and other vegetation absorb part of it and much of the remainder is absorbed into the ground. Slowly over time the water makes its way to the river and down to the lake. This water is relatively clean and cold. When water lands on rooftops and roads, it quickly drains away into storm sewers which often empty directly into our local rivers. This water is still fairly warm. One of the impacts has been to change the Don River from a cold water stream to a warm water stream. In cold water streams the water will be between 4-10 C year round. These days the Don can get as high as 23 C in the summer.

Since the water is so warm, this means that the river rarely freezes. It only happens when there is a deep freeze in January (such as the past week) and even then it is only thin surface ice. One result is that winter activities such as skating on the river (as can be seen from the archival photograph) are now no longer possible.

Unfortunately, I don't think that the Don River will ever return to a point where we can skate on it. The urban land uses are here to stay and that will have a permanent impact on the temperature of the river.


Anonymous said...

Thank you for your post, quite thought provoking. I've just recently discovered your site, and site. I appreciate your effort.

Anonymous said...

I had always thought it didn't freeze due to the salt water run off from the DVP and city storm sewers. I suppose its a combination.