So we’ve managed to get the overhead wires underground – what’s the next step in our green street refurbishment? There are a few options but it’s good practice to work from underground upwards, so let’s sort out our stormwater situation.
A few facts before we go on;
- Rainwater = generally defined as ‘rain’ that has fallen but contains little or no dissolved matter or soil – so it’s generally what we can catch on roofs;
- Stormwater = essentially rainwater that is running off over land, and the main source of downstream water pollution;
- Sewage = from toilets and the like. In Australia the sewer and stormwater mains are required to be physically separated.
A typical residential neighbourhood will see around 55% of all of its rainfall leaving as stormwater runoff. In more built up urban areas it reaches up to 95%. This runoff picks up contaminants along the way, sending everything to the nearest waterways. Two major problems here; loss of a valuable resource, and the downstream pollution (which can’t be fixed downstream).
Reducing our stormwater runoff to 10% (and you can aim even lower) requires a series of interventions, all of which add some value for homeowners (and I’ve chosen some dowdy images simply to demonstrate how easy some of the interventions can be);
Rainwater Harvesting – Adding a rainwater tank pulls out a certain amount of the total water flow – plumbing this back into landscape irrigation or toilet flushing saves you some water costs and adds value to your landscape (worth up to 10% of your home’s value). There are so many tank types around now that you could fit one almost anywhere. Keep using the water! This effectively increases the tank’s capacity.
Rain Gardens and Swales – rather than sending your excess rainwater off-site (and usually into the street gutters), slow it down and let it soak into the ground (more landscape benefits). Rain-gardens alone can strip out the majority of the stormwater runoff, and will take most of the pollutants out as well. When approached with design intent these gardens can become great additions to a landscape scheme – you might need help with ensuring that you don’t set up local flooding instead! (inlet-outlet invert levels etc.). Think of a ‘rain garden’ as a planted pond that only fills up during rain, and a ‘swale’ as a planted open spoon drain.
Street Rain Gardens – a great way to re-vegetate the public space and treat almost all of the stormwater. Check these out; rain garden retrofit and green streets for a cleaner harbour.
Soft Kerbs – ever watched all that stormwater running down the street in the gutters and wondering if there’s a better way? Soft kerbs can be suitable as part of the street rain garden retrofit, allowing stormwater an easier path into soft ground. This one requires considerations around traffic & safety and is typically only suited to local low-traffic streets, but streets with soft kerbs often have that something ‘special’ about them.
These first two Blitz steps go hand-in-hand – removing the overhead wires allows us to get some serious planting into the street, and the stormwater bounty supports a much richer landscape.
Our next instalments will cover street trees and traffic calming.
Do you know which is the cleanest part of Sydney Harbour? I’m fortunate enough to get out onto the Harbour in a sea kayak on a regular basis. I know the clean parts and the dirty ones. I know where I can see the fish through the water, and where I can’t.
The correlation between the catchment area and the water quality is obvious and well documented – the more ‘nature’ there is in the catchment, the more the runoff is filtered before it reaches the Harbour.
I regularly post on ‘green streets’, and here’s another terrific source of case studies from the US, via the Montreal Urban Ecology Centre’s site. The main case study is Seattle’s Street Edge Alternatives project (SEA) where one neighbourhood street has been refurbished with bioswales, soil engineering and extensive landscaping. The aim of the project was to test ways in which runoff water quality could be improved so that local Salmon stocks could be protected.
photo: City of Seattle photo archives
The results speak for themselves. The streetscape is beautiful, full of vegetation and shade [reduced heat island effect], and 99% of the stormwater runoff now stays on site – pretty much as would have been the case pre-development. The water that does leave the site is clean.
The Urban Ecology site also provides a Google street map interactive so you can take a walk down the street and check out the detail. Apparently well loved by the residents and locals.
The price tag for this pilot project was some $850k US, which seems to be approximately $40k per dwelling. Assuming that this cost could be halved through improvements in the process and building from lessons learned, I’d be fascinated to understand what the payback for this might be. I’ve posted thoughts around this before so I won’t repeat here. Might make a good Masters for someone ; )
And the cleanest part of Sydney Harbour? The upper half of Middle Harbour wins hands down, and most of it is surrounded by State parks.
I’ve wished for years that I could do this out the front of my house, and after researching this post I think I now have enough ammo to get started.
One thing that typifies our neighbourhoods is expanses of lawn between footpath and road, with extruded concrete kerb-and-gutter supported by some significant storm water piping. I’ve posted about rain gardens before in a strictly built up urban context [NYC Bioswales], so this post has more of the suburban emphasis.
Adams Street Rain Garden Project, Madison, Wisconsin US
Rain gardens are landscaped storm water soakage swales or ponds, often constructed alongside roads, car parks and pavements but also in front and rear lawns.
A study conducted around 10 years ago in the US compared a ‘rain garden street’ with a control street around the corner. The rain garden street installed a number of rain gardens within the existing lawn kerbs, at an approximate cost of $7,500 per household. The results, after several years of gathering data, showed that the rain garden street had reduced its total storm water run-off by 90% (!).
Something I love about this rain garden concept is that it is completely adaptable, stage-able and scale-able, it can form part of a new residential street layout or it can be retrofitted into an existing one.
Rain gardens are an investment with multiple benefits;
- significant reduction in storm water management costs – for new developments this could significantly reduce the cost of storm water infrastructure;
- increase in groundwater re-charge, making more water available for street trees;
- increase in street planting, reducing heat island effect and improving local microclimate, habitat and street pavement life;
- uplift in real estate value – personally I think this is the big one… presentation is everything and a street full of landscape and healthy trees is always going to have increased value, regardless of what’s inside the houses. People pay for good places and streetscapes;
- community building – typically the retrofit rain garden projects are initiated and delivered by local residents groups, so the investment is in their community as much as it is in the green infrastructure.
I suspect a lot of us are already tinkering with this concept under the heading of Water Sensitive Urban Design [WSUD], but a quick trawl for ‘rain garden’ images online reveals that there’s a lot more to this than just managing water. It’s at the same time an environmental bonus and, when done well, a real estate booster.
Next step for me is giving my local Council a call to see what they think. If you don’t ask you don’t get.
I’ve often felt sorry for the poor street trees that are surrounded by asphalt and concrete, and I’ve wondered how they get enough to drink with so much impermeable paving around them.
A while ago I posted about the value of street trees in our cities [no brainer really], now along comes this cool design solution out of NYC that shines even more value on the idea. It’s the result of collaboration between design professionals, planning / governing authorities, and residents, and is one outcome of the USD$1.6billion that has been pledged by New York City to the Green Infrastructure Plan [check out the site – it’s a treasure trove of cool initiatives around water management]. This bioswale is a street retrofit solution that;
- increases groundwater re-charge & reduces stormwater volume;
- cleans stormwater and reduces waterway pollution;
- increases vegetation, habitat and nature outlook;
- creates local shade and cooling [reduces heat island effect];
- filters out dust & buffers wind;
- increases real estate value.
Image from Nature of Cities article by Adrian Benepe, Senior Vice President, Director of City Park Development, The Trust for Public Land, NYC
It might sound trivial, but the inlet and outlet integrated with the existing gutter is just cleverness – it allows volumes of stormwater to take a significant detour into the bioswale, which is effectively a deep soakage pit filled with gravel and lined with geotextile… so it’s a great retrofit idea. The example above is cut into the existing footpath, but the same applies when cutting into the roadway instead.
There are many variations on this theme too – soft kerbs, swales instead of extruded gutters… there is an effective solution for each type of street.
Next time you take a walk [or drive] through your own city, imagine where such bioswales could be added, and think about how you might build the justification to have some installed. And be sure to spend some time browsing NYC’s Green Infrastructure Plan web site – they’re really getting on with things.
Personally I really think I need to get to NYC to do some ground-truthing.