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.

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  1. How does it look complex or give the appearance of not scaling? Planting trees scales from a single tree to a forest, same principle applies here.

  2. There is a lot of standing water in the photos. Is anything done to prevent mosquito breeding. Other ponds are allowed to drain & dry out.

      1. It’s run off so I assume it’s fresh water – putting frogs in there would probably deal with the mosquitos, but I wonder what they do.

        1. I would guess small fish would help as well. Really you could create a whole eco-system with these. With the loss of so many wetlands to farming this could be important to keep many wetland endangered species alive. Plus the motorway could act as a barrier disrupting predators.

        2. The ponds have v-shaped weirs at each end. Although it’s not clear from the photos how deep they are thy should ensure there is always at least some flow through the system. It looks like they are designed to be suitably for natural springfed streams as well as conventional swale/ditch runoff systems.

        3. Dragonfly larvae are great predators, particularly fond of mosquitoes’ larvae. They’re used in Europe to try keeping the mozzies numbers down without using other pollutants.
          But I guess who designed this thing knows it.

  3. The major impact of road use is the production of carbon dioxide. Half of carbon dioxide emitted from any source (including cars) is in the air 100 years from now, 10 percent 1000 years away, and the climate impacts will still be being felt 100,000 years away. This effort is commendable. But it is akin to lowering the tar in a cigarette and pretending it’s ‘healthy’. Unless we see a rapid adoption of low/zero emissions road transport, roads will continue to be an environmental disaster. Unfortunately current policy settings, technology development, and consumer choices preclude such a shift within the next 10-15 years.

    As a thought experiment, does anyone want to look at what things would be like if we put _all_ new roads spending into cycling and walking for a period of about 3 years? I’m assuming that would be about $5 billion. We could see some huge shifts with such an investment. It might be time for the Greens to call for a moratorium on all non-safety related road spending, with such a diversion.

    1. Based on the last Budget, it’d be more like $7-8b. We could surely throw a couple of bil at some of Auckland’s pressing rail needs, too?

  4. Developments like this also have potential to be applied to controlling pollution from dairy farming.

    CO2 impacts from road use are widespread and long term. But at the very least, controlling the discharge of heavy metals and toxins in to the environment is a short term, and localized improvement. Even gathering concrete data on just how dirty these roads are are might help to discourage the current national obsession with morotways being The One and Only form of personal transport.

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