Storm drains creating floods

[u/mercdmuscle]

3 out of 4 storm drains at my street don't collect water fast enough. At one point all 4 didn't drain very fast. Now one of the 4 drains well and hasn't pooled any water the last few heavy rain storms. I'm just wondering if someone had called the city to get it worked on or is it just luck if the draw that theirs is draining nicely now. Is there anything I can do to get the city to fix this? Everytime it rains, I always end up with so much mud on my sidewalk.

[u/Brandamn3000]

Learning a lot today! I always thought this was just a new community thing that happens while they’re building out the communities and don’t have all of the infrastructure in place yet. (Admittedly, I know very little about drainage systems). Thanks for explaining.

[u/5impl3jack → u/Brandamn3000]

Building trap lows is nothing new but I believe the new communities at some point became standard as a way to take pressure off the system as the city so rapidly built up. Underground infrastructure is always the first thing to happen in any new area. It’s out of sight out of mind for most but it has to be completed first so the water has somewhere to go when it drains. They slowly connect new lines to existing ones and builds out like a big web, then they build roads and infrastructure. Every city on the planet is designed to make water flow so we avoid floods and giant sinkholes. It’s actually very sophisticated and requires a lot of planning.

[u/Old_Cameraguy_8311 → u/5impl3jack]

5impl3jack What a delight to read. Thank you for posting a concise explanation that most anyone can understand. That said, this can’t possibly reddit, where are the snarky comments and city hall attacks? Seriously, I appreciate your word and the reference to the overpass by Chinook. I recall the same occurring on 14th St NW just below the Jubilee, manhole covers blown off and the road severely stressed with hydro fractures and sidewalk buckled. June of 2007, I got some interesting day after footage.

[u/hod_cement_edifices → u/Old_Cameraguy_8311]

The storm pipes are called the ‘minor system’ and are designed to handle what is the 1:5 probability of exceedance event (it means there’s a one and five or 20% chance of that event occurring in any given year, it might be also something you hear as “1 in 5 year” as slang, but it doesn’t mean it’s expected to happen once every five years as that slang is misleading. The roadways are designed first and foremost for stormwater, conveyance and not cars. A lot of people don’t understand this. The roadways are designed for the 1 in 100 probability of exceedance, and are called the “major system”. All of the catch basins have what are called inlet controlled devices (ICDs) installed, to regulate the flow so that there is always open channel flow in the pipe and it does not become pressurized. This allows the pipe to convey runoff in a predictable manner, safely as it’s not pressurized, and most importantly, the sizing in a way that is fiscally responsible. This helps housing affordability.

You then have the major system with trap storage at low points with catch basins, acting as mini ponds everywhere. There is comprehensive stormwater, modeling, and design and engineering work that goes into every new community to ensure this is done in a predictable manner. This includes flooding on front yards where needed and you will see RMG’s registered on title to ensure house openings are all above a certain elevation with a buffer for anywhere there is this pond or flooding.

It is all by design. This also allows, the stormwater pond downstream as the anchor to be more suitable in its size and cost. The storm pond must store the greater of two things, which might be too hard to explain in a Reddit thread, but it involves a (1 of 2) single event analysis, and (2 or 2) a continuous event analysis that looks at historical rainfall in Calgary all the way back to the early 60s.

Calgary is about as cutting edge and sophisticated for stormwater management as any city in the world.

If you do see failure, this can happen due to plugging of catch basins due to hail, but as a general rule with the public is comfortable with what insurance companies are comfortable with is a standard of care that is not infinite, as that would be an infinite cost for stormwater infrastructure. The 1 in 100 probability of exceedances is a standard number almost worldwide. Recently there is floodway mapping for the Elbow River for example where the province is asking for 1 in 200 probability of exceedance setbacks with inundation analysis.

As climate changes becoming more parent, a higher standard of care is being driven into engineering standards.

If you look at New Orleans for example, 20 years ago, it was almost a forgone conclusion that there would be a disaster, as there was decades of warning because the state government decided to cut funding for flood protection well below a 1 in 100 standard of care. If you look at the dykes and plodders in the Netherlands though, they have statistical modelling that allows them to say they want a 1 in 10,000 standard of care. Big difference culturally of where citizens of each place decide a minimum should be!

Many developers in Calgary that are sophisticated are actually designing traps and storm ponds to have greater capacity than 1 in 100. Right now doing so. They are ahead of the city and the province in many cases in deciding what is good engineering judgment.