Precipitation – not just a Middle English word whose origin goes back to 1425

Precipitation – not just a Middle English word whose origin goes back to 1425

It rained today. Edmonton is surprisingly dry compared to other major cities. All precipitation we get here seems to come in big dumps rather than spread out over a longer period. It’s kind of cool, I remember as a kid really being into the big storms. The ones that would circle, where you’d count (with Mississippis) the time between seeing the lightning illuminate the sky and the clap of floor-shaking thunder, to estimate the storm’s distance from your location. My siblings and I used to huddle together and watch the storms linger and eventually pass by, completely enthralled with the show. There was nothing like pelting rain against the windows set to booms of thunder, with lightning pyrotechnics providing the backdrop. What a bunch of fucking dorks. But would a dork do a post about low impact development in Edmonton?

When it rains, it pours

The old adage that ‘when it rains, it pours’ may not have been written for Edmonton specifically, but we take it literally. Today was one of those days, and I got to cross paths with a great example on a pedestrian experience we can find all over prairie cities that experience similar precipitation extremes:

flooded crosswalk without low impact development techniques

This was my view crossing the street on my way home. Large, ominous, and wet, this sort of thing happens everywhere. Lots of causes that if I even try to start explaining, engineers will appear and start correcting me, missing the point of this exercise. So I won’t go into detail, but what I think we can agree on is that the system that handles water runoff and drainage is overloaded. This one is particularly egregious both because of how big a disturbance this is to pedestrians, but also (hilariously) that it is right in the turning lane of Edmonton’s new bike lanes. This is phenomenal evidence that the city is designed primarily for cars. I think I’m getting off track.

flooded crosswalk at intersection

In this clearly professional zoom-in shot of the same location, you can kind of see a solution. The water is draining towards the curb, which is normal. However, the curbs are barriers from the water getting to the trees and grass – where they would be absorbed naturally. What you can’t see in this picture is that the city installed the bike lanes just last summer. At that time, they could have also installed an intervention that is being promoted in their policy documents. Hold on tight, this one may come out of left field and be a shock to you: rain gardens.

Low impact development = high impact

While you gasp in awe of my brilliance and get a slow clap going, let me explain. I’m going to take this next picture directly from the City of Edmonton’s webpage on bio-retention to highlight their commitment to low impact development.

picture of curb cut allowing water to enter rain garden

Can you see the intervention? I’ll wait while you spot it. Ignore the suburban context as well, if that helps. Instead, focus on the MASSIVE intervention – lowering the curb at certain points and having road drainage enter a landscaped area rather than the storm system. Pretty wild stuff.

Back to our example, here is an aerial shot highlights the new water feature:

aerial shot showing flooded intersection

I’ve drawn red lines along the boundary of the right-of-way on either side of the road. This is your typical 24m right-of-way, and north of the road and bike lane, the boulevard is 6m wide. Right now there is a 1.5m path right down the middle, leaving 2.25m strips of landscaping on either side. Symmetry is beautiful in theory and in plan view.

Personal Opinion

Here is a handy cross section to highlight what I’m talking about. If you haven’t heard of or tried, I highly recommend it when nerding out about road cross-sections.

before low impact development technique

By implementing the Low Impact Development Guidelines that the City of Edmonton has, we get this type of situation:

after low impact development technique

I put in a little rain garden there to highlight what I mean. Basically, when the city installed the bike lanes, they could have adhered to their own guidelines and revamped the boulevard to add rain gardens. This is much bigger project, obviously, but one that would lessen future drainage problems. Filtering water through a rain garden and letting the rest head into the storm system could prevent moats from forming. Everything is the same in terms of sizing. The only thing you’re changing is the sidewalk location and adding some planting.

I’m not saying this has to go everywhere. The boulevard is where snow is stored in the winter; but installing some close to the intersections where there are drainage issues could alleviate some of the problem. Practice what you preach, CoE. More importantly though, doing this would have taken away my opportunity to scoff and write about the topic smugly.


*A full 24 hours later and the problem has subsided but still exists…This is looking at it from the south side this time (before was from the east side)

24 hours later, intersection is still flooded


One Response

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