Pond dredging targets midges

A new means of controlling the midge population at the Bromley oxidation ponds will be trialled over the coming months.

Christchurch City Council is going to try disturbing the bottom of the ponds where the midge lay their larvae by mechanically dragging chains across the pond floor.

The chains will be dragged by a boat that will travel across the ponds at a steady walking pace.

It is a control method that has delivered promising results at the Mangere oxidation ponds in south Auckland, which has also historically been plagued by midge problems.

“At the moment the Bromley oxidation ponds are the perfect breeding ground for midges, so in order to control their numbers, we need to make the ponds more inhospitable. We believe that mechanically disturbing the floor of the ponds is a quick, cost-effective way we can do that,’’ says Council Three Waters and Waste Operations Manager Adam Twose.

“We will need to use the boat on the ponds every 10 days for about five hours. The result from Mangere suggest that it should lead to a reduction in the midge population this summer.’’

Mr Twose says longer term there are plans to change the engineering of the ponds so that the inflow of treated wastewater can be altered to create a less hospitable environment for the midges.

The Council is also doing more planting around the ponds to reduce the light from nearby homes so that midges, which, like moths, are naturally attracted to light, are not drawn towards them.

“It is going to take a while for the plants to grow up to the point where they make an effective screen but in the meantime we’re hoping we can provide nearby residents with some relief from the midges this summer through the mechanical disturbance work we’re doing,’’ Mr Twose says.

Find out more about what's being done to control the midge population.