New York City’s Simple, and Green, Flood Prevention

New York, like other large cities, has a lot of impermeable services which means that when it rains there is little to contain the water. By using green infrastructure of soil, broken stone, shrubs, trees, etc. the bioswales can capture a lot of water. This green infrastructure is good for water management and obviously benefits the local environments through cleaner air and more pleasant views.

The Big Apple’s pretty new bioswales, built into city sidewalks much like standard tree pits and more modest in size than their suburban brethren, will join about 250 of these aesthetically pleasing drainage ditches that have already popped up around the city as part of the city’s stormwater management-focused Green Infrastructure Program. The price tag attached to this aggressive — and much needed — onslaught of vegetated swales is $46 million.
While that might seem like a hefty wad of cash for the city to dedicate to curbside rain gardens, it’s nothing compared to the costs associated with upgrading New York’s aging combined sewage system (a system that handles both storm runoff and domestic sewage) and cleaning up after perfectly foul combined sewage overflow (CSO) events that strike following heavy rainstorms (and, of course, hurricanes).

Read more.

Thanks to Shealyn!

London Starts Planting Green Walls for Flood Prevention

Earlier this year, Toronto suffered some severe flooding and city planner Jennifer Keesmat composed this great tweet:

One of those programs she is referring to is the tower renewal program which helped energy conservation, local ecologies, and improve housing conditions. Toronto’s mayor ensures these programs don’t get funding.

Here in Toronto where we have a druggy mayor who hates the environment who also sat in an idling SUV during the flooding (idling is illegal in the city). The mayor has gone out of his way to ensure that Toronto treats the local environment worse than it did the year before. I mention this as a contrast to what is happening in England’s biggest city.

In London, they have a mayor who actually knows that climate change is happening and the city is doing something about it. London is no stranger to threat of flooding, indeed the Thames barrier’s lifetime has been reduced due to the increased pace of climate change. With most usable space already consumed, what is the city to do?

London has turned to constructing green walls! The walls absorb water that would otherwise contribute to flooding within the city by soaking up rainwater.

The wall captures rainwater from the roof of the hotel in dedicated storage tanks; the rainwater is then channeled slowly through the wall to nourish plants, simultaneously reducing surface water on the streets below. “The plants themselves will take up rain too, so the rain doesn’t fall on the street below,” says Beamont.

During the design process, Grant picked out native ferns, English ivy, geraniums, strawberry and primroses for the living wall, using the Royal Horticultural Society’s pollinators list as a guide. “My approach is to use native species in natural associations, however sometimes it’s not practicable because of problems with availability or a lack of visual interest or late flowering,” he says. “It’s still necessary to choose plants that are known to thrive in living walls, or are likely to thrive in living walls, and are suited to the aspect and microclimate.”

Read more at Co.Exist.

Green Roofs Assist in Flood Prevention

Yesterday Toronto got more rain in two hours than it normally does in a month which meant some serious flooding happened. This got me thinking of a program that Toronto (alleged crackhead) Mayor (busted for DUI) Rob (loves pollution) Ford (reads while driving) cancelled. The cancelled program promoted green roofs to help with flood control while lessening wear on existing infrastructure.

So the ineptitude of the current Toronto mayor got me thinking of how things could have been different with forethought of climate change. It’s worth noting that Rob Ford spent the flood idling in his SUV:

I gathered some example of other cities and areas that are using green roofs (and similar) to curb their flooding problems.

In Singapore they have combined recreation with flood prevention:

The barrage is part of a comprehensive system of flood control to decrease flooding in the low-lying areas in the busy quarters of the city. During the heavy rains, a series of nine crest gates activate to release excess storm water into the sea when the tide is low. When high tide comes in, giant pumps drain excess storm water at at a rate of one Olympic-size swimming pool per minute.

In New York they are looking into a variety of solutions, which we looked at before.

In Rotterdam, the city’s green roof initiative has proven to be effective in flood alleviation.

Although large areas of green roofs have many benefits for cities, such as reducing air pollution and helping to combat the heat island effect, Rotterdam’s priority was for water retention, since the city has a shortage of areas where water can be stored following heavy rainfall. Water management has always been a major concern in the Netherlands, since approximately 60% of the country lies below sea level. The analysis of the potential of green roofs in Rotterdam that preceded the introduction of the subsidies focused heavily on their capacity for water storage in order to reduce peak water discharge following a rain storm and help prevent flooding.

Over in the UK, the Green Roof Centre has quite a lot of information on how green roofs can help flood management:

Once established a green roof can significantly reduce both peak flow rates and total runoff volume of rainwater from the roof compared to a conventional roof. Green roofs store rainwater in the plants and substrate and release water back into the atmosphere through evapotranspiration.

The amount of water that is stored on a green roof, and then evapotranspired into the atmosphere, is dependent on the depth and type of growing medium, type of drainage layer, vegetation used and regional weather. The FLL Guidelines should be followed to ensure that actual runoff will be in accordance with calculated runoff.

A green roof can easily be designed to prevent runoff from all rainfall events of up to 5 mm and as part of a SuDS strategy, should reduce the volume of surface or underground attenuation required at the site boundary. In summer, green roofs can retain 70–80% of rainfall and in winter they retain 10–35% depending on their build-up (Green roofs benefits and cost implications, Livingroofs.org In association with ecologyconsultancy, March 2004). The difference is due to a combination of more winter rainfall and less evapotranspiration by the plants because growth is not as vigorous during the winter months.

Edit:
I like this tweet from Toronto’s chief planner Jennifer Keesmat as a good conclusion to this post:

Good Designs to Protect Against Flooding

The damage of Hurricane Sandy is still being fully realized and we won’t know the full cost of the damage for a little while. What we can do for know is to look into ways to lessen the damage the next time an anthropogenically influenced storm hits the city. The Atlantic has put together some previously thought-out plans for preparing New York City for flooding from ideas that are used elsewhere in the world.

As ocean levels rise this will be a more pressing issue for New Yorkers and other cities on coasts.

Here’s what I think will be the easiest for NYC to implement, but I haven’t been there for years so I could be way off.

2. Elevated infrastructure. There are very few buildings in the entire state of New York built at grade at elevations below sea level. But New York City has constructed one massive piece of infrastructure below that threshold: the subway system. As we saw this week, flooding can devastate an underground network of tunnels, train platforms and corridors. So how do you keep more of that water out? For one thing, elevating subway entrances would help. Bangkok, another low-lying city susceptible to rising tides, has built precisely these kinds of subway entrances. They’re raised a meter off the ground and include built-in floodgates.

See the rest of the ideas here.

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