Video 2 C3: Where does stormwater go? Flashcards
urban stormwater management (17 cards)
what is one of the biggest challenges for cities when it comes to stormwater management?
the proportions of all these different paths the water can take. Since the streets/buildings/parking lots cover the grounds with impervious surfaces, the water doesn’t infiltrate- it runs off toward creeks and rivers. But this can lead to swelling those areas faster, higher, and polluting them.
one of the biggest impacts on the environment of building anything is…
its effect on how water moves above and below the ground during storms
urban watersheds act less as a sponge to absorb rainwater as it falls, and more as…
funnels, gathering and concentrating rainwater runoff
why do most cities have rules to manage runoff/flooding when new buildings or neighbourhoods get built?
because its easy to make bad drainage decisions and turn it into someone else’s problem downhill.
what is the term that we still use today (as we try to give that runoff somewhere to go)?
drainage
most cities are organized so the streets serve as…
the first path of flow for rainfall
How are cities designed so that streets become the first route for water to flow during rainfall?
individual lots (like houses) are graded with a slope toward the street so that water flows away from buildings, then the standard city street has a crown in the center with gutters on either side for water to flow
How does the crown in the middle of a street help manage stormwater?
It helps keep the road mostly dry and safe for vehicles by directing water toward the edges instead of allowing it to pool in the center.
Why is it no longer common to send street runoff directly into the sewage system? what do most cities do instead?
- At the end of each sanitary sewer system lies a wastewater treatment plant, which aren’t designed to handle both sewage and stormwater. So sending street runoff into the sewer can overload the system.
- now most cities used Municipal Separate Storm Sewer Systems (aka MS4s)
what is included in MS4s? what are they dedicated to do?
A system of ditches, curbs, gutters, sewer pipes, and outfalls designed specifically to carry runoff from across the city to nearby natural waterways.
what is a floodplain?
the area most likely to be inundated during a major flood
why do cities use straight, concrete-lined pathways to move water?
because the smooth material moves water faster compared to if there were vegetation.
why do cities try to avoid these long, straight, concrete-lined channels?
- ugly
- worsens the flooding downstream for the next guy
retention and detention ponds act like…
mini sponges to absorb rain from urban surfaces and slowly release it back into waterways. EX: Costco has a retention pond behind it to manage excess runoff from its site
why are retention/detention ponds helpful?
- They help lower the peak runoff, trying to match or improve pre-development conditions by slowing and storing excess water.
- They also help reduce pollution by slowing down the water so suspended particles can settle out.
what is the best way to manage storm water? why?
watershed delineation.
- naturally clean runoff with vegetation
- slows down water at the source rather than letting it quickly wash away
- allows water to infiltrate the ground and recharge aquifers
What does low-impact development include?
rain gardens, vegetated rooftops, rain barrels, permeable pavement, etc.
