Birthe Zimmermann, Alssundgymnasiet Sønderborg

Too often basements were flooded because the precipitation pattern had changed to more rain in less time. To solve this problem you can either reduce or delay the runoff of water. Rather than leading the water down the drain, it was led into ponds and swamps in people's back yards, creating natural habitats where people live. The many flat or slightly sloped roofs were covered with vegetation mats consisting of Sedum-plants, and as plants absorb water in order to grow and also transpire water, the precipitation was simultaneously being reduced and delayed.
We visited Malmoe's "Roof-botanical garden", and the idea developed that we could solve a similar problem in our local area. On August 21st 2007 we had food for thought when in two hours 140 mm of rain created traffic chaos: The road between Sønderborg and Gråsten simply disappeared, and so did the dirt beneath the railroad tracks. On 20 August 2008 we were flooded again by 150 mm of "monster rain".
To actually measure delay and runoff reduction and find out the effects of a green roof we needed to establish one. Could a green roof really delay the runoff, or even reduce it by 60-70 %? Fortunately Dansk Naturvidenskabsformidling granted us enough money to get started in August 2009.

Ownership
In August we were suggested to go to Aarhus to get the vegetation mats ourselves, as Aarhus Festival Week had had a "green wall" exhibition, and the mats used were the ones we could have for our project. The idea was great! It made "form a11" take ownership of the project immediately. In groups they worked on methodology, discussing what they would measure, how they would monitor and calculate, whom they needed to establish contact to and make partnerships with. They also had to consider how to present their ideas to others - and the results were remarkable; they presented their work in flyers, posters, photo-stories, articles etc.
On 7 September we stopped at Handelsfagsskolen in Aarhus that with 5.600 m2 of green roofs won an environmental reward. Ladders enabled students to climb to the roof to actually see, feel, touch, photograph and sense what these Sedum-plants were like.
We also visited the green houses at Aarhus University's botanical garden to learn about succulent plants and why they so effectively store water.
Back at school the students had to work hard to actually establish the green roof, but with 30 committed students, great sunshine and a reporter and a photographers from the local newspaper, they changed the rather dull grey roof into a living green one in less than one hour!

Tell others about your work
Very close to our school a rain water basin has been constructed under ground to delay runoff rain water from the streets when heavy rain occurs. People from Sønderborg Forsyning came to our school and informed us that the municipality has constructed 35 of such underground storage tanks - each capable of storing 100 m3 of water (1 million liters of water!) in order to delay outlet into the pipes that carry the water directly into Sonderborg Bay.
Then we started monitoring the amount of rain and how much water the Sedum-vegetation mats could absorb. The results vary, but calculations show that from 8 - 14 mm of rain can be absorbed before the vegetation mats start dripping. With 20 m2 of green roof in the project, students calculated the amount of water that could be absorbed if the entire roof at school was covered, some students even calculated the amount if also the flat roofs at the hospital and other buildings in Sønderborg were green.

Next Step?
Monitoring the green roofs is not nearly as simple as the students thought when we started the project. They have begun reflecting on questions such as: What happens with the seasonal changes when the temperature, the amount of sunshine and the humidity differ? How will the plants grow and develop, and how will their growth influence upon our results? Can we measure the flow more accurately? And can we show that green roofs will also cool down houses in hot summers that will also be a local consequence of the climate change?

If time allows us, much more study work can easily be made, and we all look forward to a roof that does not always stay green. It will actually vary from green in some months with rain to red in rather dry periods and then change into various colours when in bloom.

So science and aesthetics work together to solve some of the local problems caused by our changing climate.

Projektet vandt DM i naturfag 2009. Se mere på www.formidling.dk