A small leak leads to a massive hillside clean-up

Innovative thinking by the Citycare Water maintenance team was needed recently to solve the difficult problem of a hillside washout caused by a small water leak at Taylor’s Mistake, Christchurch.

Fixing the mains valve leak at a Taylor’s Mistake property was simple for the Citycare Water team, which manages Christchurch City Council’s water, wastewater and stormwater.

However, water infiltration caused so much damage to the surrounding area that the hillside collapsed onto the sections below and more than 20 tonnes of clay then had to be removed over a four-week period.

“What a mess to clean up! With the steepness of the hill there was no way any machinery was getting up the hill,” Citycare Water Christchurch Maintenance Supervisor Craig Allsopp says.

“There was only one way to clean it up. For the bottom half of the clean-up, the team had to dig into buckets and carry them down the steps and tip them over a concrete wall on to a truck each day for a week – that was about 10 tonnes of clay.”

The top half of the site was even more difficult to clear because it was steeper.

“Due to lack of access and the steep angle at which our crew had to work, we had to think outside the square,” Citycare Water Health and Safety Advisor Alf Cosgrove says.

“The weather did not help either – as soon as it rained the hillside became a problem.”

“It turned into a large-scale project with Christchurch City Council crane permits, road closures and skips being lifted into the section over power and telecoms lines to get the job completed, along with some innovative ideas on how to move the dirt as quickly and safely as possible,” Alf says.

After brainstorming and a discussion with Titan Cranes, it was decided to lift a skip 30 metres up onto a hand-dug flat surface on the site.

Once Level 3 began, the maintenance team reassembled at the site and the skip was lifted into place by a crane.

Three tonnes at a time, the skip was removed by the crane and replaced empty to be refilled over the following days. Around 11 tonnes of soil were lifted out over a week.

“It was a great job of teamwork!” Craig says.

The description of the original problem was simple, but the ramifications of the leak were not.

“A small water leak in a valve assembly had over time softened the earth around the pipe manifold and the pipeline eventually failed and the volume of water escaping washed the side of the hill down into the sections below,” Alf says.