Questions over muddy waters

An east Auckland community is frustrated with its silty reserve.

After a six year hiatus Auckland Council cleaned out Waiatarua Reserve, once in October and again in January, but that’s not enough for some.

Orakei Protection Group’s Lynley Olsen said residents had noticed water coming into Orakei basin was much dirtier than it should have been.

She said it was having a negative effect on the area.

‘‘The water coming in is damaging, it’s starting to smell, and the wetland is choking up with weeds,’’ Olsen said.

‘‘You’ve got to remember this is a water treatment facility, that’s what it is, that’s what it was built for.’’

The $5.9 million 40ha reserve is the largest urban constructed wetland in New Zealand and took 16 years to complete.

While popular for dog walking, the reserve is actually a stormwater treatment plant filled with drains and sediment traps.

It was designed to stop 130 tonnes of sediment that previously washed into the Orakei Basin every year.

The issue was raised at a Meadowbank and St John’s Residents meeting several weeks ago, where residents were shocked that the silt hadn’t been removed for such a long period of time.

Healthy Waters central team manager Frank Tian said it removed 128 million cubic metres of sediment in the most recent clean earlier this year.

Tian said that six years between cleans was normal and it would have no long term effect on the reserve.

However the silt might have had an effect further down stream.

Auckland Council’s senior marine scientist for research and evaluation Megan Carbines said Auckland’s harbours and estuaries were already very muddy.

‘‘Fine sediment and associated stormwater contaminants are affecting the ecology of Auckland’s harbours and estuaries,’’ Carbines said.

She said most sites near older urban centres had locations with unhealthy ecology, particularly within the Waitemata Harbour and Tamaki Estuary.

A 2012 report on the wetland said weed invasion and high sediment loadings were a concern to the wetland and it recommended regular monitoring.