Roads are dirty places, they pick up all sorts of contaminants as part of regular use, things like oils, zinc, chromium and copper as well as the residue of tires and brakes. When it rains these materials wash off then wash off the road and can pollute local waterways. More recent motorway developments have seen storm water ponds built to capture and help treat that run off but it is pleasing to see that the NZTA is hoping to take this a step further. They are taking part in an international trial using a system called a Floating Vegetated Island. This is effectively a floating mat on which plants can grow and their roots will dangle into the water below and act as a filter and plants have been selected that have thick and extensive root masses to help capture the pollutants.
It is currently being trialled in a pond beside SH1 near Silverdale and if successful will be rolled out to ponds in other parts of the city. The trial will last for two years and is also involving the University of Auckland as well as the council. The pond itself has been split in two with one side getting the treatment and the other side left as it is so the scientists can see exactly how effective the system is.
Here are some images of what these floating islands look like and you can read the full press release here
The NZTA often gets a bad reputation from some on this site but I do think it is important that we commend them when they work to reduce the impacts of the roading system.