Council explained the purpose of the planned wetland is to create an environmentally friendly stormwater treatment wetland. The wetland is expected to cost about $400,000 of which about $250,000 is Council’s contribution.

What value in water quality improvement is achieved from this wetland?

To find out what water improvement could be achieved, one of our members used Dial Before You Dig to get the drainage plans and created a map that shows there are 3 catchments that provide stormwater into Koolunga Reserve. Anyone can get the stormwater plans from Dial Before You Dig: https://www.1100.com.au/.

The drainage plans indicated three catchments as shown in the drawing. (Thanks to Google maps!)

The large black area from Marie Street /Boronia Road /Forest Road outlets water into Blind Creek at the west end of the park. This is the drain that runs from Westmere Drive between houses and then along the west end of the park. You can see the inspection pits in the park near the Golden Elm. This catchment area is about twice as large as the pink area.

The small pink area from Sassafras Court/ Forest Road /Harnett Street/ Anderson Street is the catchment area for the wetland. It’s the smallest catchment in the area. The wetland plan includes taking a small amount of water from this already small catchment. Most of the water from the pink area will still be in the underground drain.

The large blue area is more than twice the size of the pink area and outlets water into Blind Creek at the Forest Road end of the park. This is the area that feeds the creek we see in the park. There appears to be no natural creek feeding this drainage line – all the water comes from roads and house rooves when it rains.

You can see the Pink catchment area that would supply the wetland, appears to be about 20% of the catchment area for the Creek. And the wetland only takes a part of this stormwater. This appears to mean the wetland will treat less than 20% of the stormwater in the reserve. It appears any water quality improvement by the wetland is swamped by the quality of stormwater from the remaining catchments.

There seems very little value in water quality improvement from this wetland compared to the amount of untreated stormwater.

Part of the discussion about the wetland proposal should be about balancing the value of treating stormwater and the loss of community green space. The wetland can treat only a small amount of stormwater and costs the community the entire large green space. This imbalance seems to be not good value.