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Aquatic weeding to prevent flooding

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15 April 2020

Aquatic weed removal crews in Christchurch have received lots of compliments from the public as they’ve walked by during their exercise breaks in the COVID-19 lockdown.


“The teams are really proud of the work they do and getting recognition from the public has reinforced they actually do a great job,” Citycare Water Wastewater and Land Drainage Supervisor Mel Cameron said.


Residents sometimes query if the weeding is ‘essential’ work at the moment.


“When the team members explain that it stops flooding, people can still be confused,” Mel said.


Murray McLaren from the Heathcote River team has a good explanation.


“Imagine you are running a bath. When you hop into this, what happens? The water level rises, and the same thing happens with the river. Removing the weed removes potential for overflowing when tides are higher or rain events happen,” he said.   


The weeding in the Avon and Heathcote Rivers for the Christchurch City Council is a seasonal job, taking place from 1 November to 30 April.


When the teams are out of the water, they leave the rivers to the fish - the inanga (whitebait), salmon and trout - for spawning.


The teams’ uniform is special neoprene waders as the water isn’t warm or shallow – they’re often in the river up to their chests, Mel said.


Both rivers are spilt into sections and the teams work on section by section in a continuous circuit.


“It’s a very physical job. The aquatic weed grows quickly. One person is usually cutting the weed and it floats down to gates set up to trap it. Then others are hoeing the weed from the gates to the riverside,” Mel said.


Once the weed is heaped on the riverside, a Hiab crane truck from Citycare Civil or Citycare Water collects it and buckets it up for delivery to a composting facility, where it is drained, dried out and composted.


The waterway teams in Christchurch are split into two – one for the Avon and one for the Heathcote – and each team has six people. In the off-season, they undertake other maintenance and reactive work on Christchurch’s stormwater systems.

Weed Heathcote

Shannon Winiata, Cameron Gledhill, Daniel Rush, and Murray McLaren are weeding in the Heathcote River.