In the first of a two-part series, Dr Tom Young, STRI technology manager and green roof consultant, discusses how green infrastructure can be used to help store stormwater on sites and how that can be linked to sports turf surfaces.
Here’s a transcript of the video.
Hi, I’m Dr Tom Young, technology manager for STRI, and today we’re going to explain how green infrastructure can be used to help store stormwater on sites and how that can be linked to sports turf surfaces.
To start off with we’ll look at what is the normal hydrological cycle for most buildings and sites. So, what we’ve got here is a normal roof that is very common on most buildings and this represents most buildings and sites in terms of the drainage plan. We have an artificial rain event provided by Aaron, you’ll see the water is taken off the surface into a guttering or drainage system and it’s taken away from the site as quickly as possible into the main drainage system.
Now that’s worked very well for the last 200 years, but what’s started to happen now is that the pipes that this water is drained into are now full and water companies are telling people you can no longer attach into our drainage system. So civil engineers have looked for alternative ways of solving this problem and we’re going to go through a few of these now. So, the first type of solution you can have is called a blue roof, you store the water that falls on a roof or a site in situ.
So, we have another rainfall event now. Essentially all we’re doing is trapping the water on site and then slowly releasing that back into the system when it’s appropriate. A lot of these systems don’t actually have manual taps, they just have simple overflow systems, but the whole concept is you can see that we’re very slowly releasing that water back into the whole drainage system. It’s much slower, it’s not as violent as the water that all fell in one go.
So that works well, it’s very efficient to maintain all that water on site and physically holding it. Obviously, that’s not appropriate for all roofs due to weight restrictions, but you can have these systems below car parks for example where weight is less of an issue. But what we can do to make things a bit prettier is use vegetation on roofs and these are called green roofs.
This can go from a very basic system like you see here where we’re using plants called succulents, which are very drought tolerant and they can survive changes in water very quickly as well. These can survive basically anything so perfect for putting on shallow layers of substrates and sticking on roofs where maybe the weight loading isn’t as great.
You can also use much bigger plants, but the substrate depth has to increase and obviously that increases the weight loading. We have another rain event here. You’ll see that this probably isn’t as efficient as the blue roof for holding the water, but what it does do is slow down that flow. The water has to go through that substrate and come out the bottom and you’ll see here that it will slowly leach out and have the same effect as the blue roof at slowing the flow down.
What you also get from green roof is additional benefit, so green roofs in cities are very good at cooling the local environment which helps prevent heat related deaths. It also makes the environment much more pleasant for people to live in, aesthetically, they also look very nice and can be used to help buildings get planning permission and also improve the value of certain properties.
So, we’ve had a blue roof and a green roof, but what we can actually do is combine these two together into a system called blue green roof, and we’ve demonstrated that with this final system over here. You can see the planting design has changed slightly and we’ve got more herbs and perennial species here, but as Aaron irrigates this roof you’ll see that the water goes into the substrate, but what we do have below is a tank which holds onto the water.
So, what you’re having is a double whammy, you’ve got the green roof holding the water and then you’ve also got the tank holding on to the water as well. Then what you will find is that the water can then be reused by the plant as irrigation water so it’s reusing it in a continuous cycle. Barely any water will come out of this tap even if it’s left open and the whole point of this is that it almost becomes a circular cycle. You can actually direct water from other parts of the site to this system or roof.