We built and tested our own miniature rain garden using plastic bottles.
We prepared a bottle with just clay to act as our control for the investigation. The clay represented the concrete / tarmacked / roofs of buildings in our environment which show that when it rains all the water runs off as they do not allow the water to soak in. They are impervious surfaces.
Miniature Rain Gardens
We then prepared a second plastic bottle as our miniature rain garden. We put clay in the closed end to represent the pavement and then filled the remainder of the bottle with soil ( our rain garden).
Setting up our investigation
We set up our plastic bottles with a collection cup ready for us to add our polluted water to see the difference between the run off from the two bottles.
Bottle 1 - clay only and bottle 2 - clay and soil.
Homemade runoff - Polluted water
We made some polluted water using the following recipe:
3/4 cup of water
2 teaspoons of oil to represent oil leaking from cars
A few drops of green food colouring to represent pollution that is too small to see with the naked eye, such as plant fertilizer
A few pieces of food that floats on water, some cereal to represent rubbish.
We then mixed it well.
Performing our test
To test our rain garden, we poured a cup of homemade runoff on the pavement of each container. This was like a rainstorm. Then we measured how much runoff was collected in the runoff collection cup. This was like measuring how much runoff reaches a storm drain after a storm. We also looked to see if the collected runoff was as polluted as the poured runoff. This would help us to understand if rain gardens filter out pollutants.
We found that there was a smaller volume of run off when we had a 'rain garden'
(soil) than when we just had the concrete (clay). We also found that there was less pollution thus proving that rain gardens are a successful way of fighting flooding and pollution after heavy rain.