The Cashmere catchment has been a focus for the Christchurch West Melton Water Zone Committee and its sub-committee, the Cashmere and Port Hills Working Group, over the winter months.

As part of an education campaign to raise awareness of sediment and erosion issues in the Cashmere Stream and the Heathcote/Ōpāwaho River, posters have been placed around the Cashmere and Mount Pleasant areas encouraging people who see sediment to report it.

Education first: understanding sediment

The Port Hills are covered in a very fine sediment called “loess”.

Where this becomes exposed, it can easily be washed out with rain.

Key sources of sediment coming from the Port Hills include:

• exposed soils from forestry and inadequate forestry riparian buffers
• poorly constructed and maintained recreation tracks
• unfenced waterways resulting in loss of vegetation
• loss of vegetation due to fire
• exposed soils during subdivision development, and
• poorly performing and managed sediment and erosion control strategies.

Sediment that leaves properties in the Cashmere and Port Hills areas ends up on footpaths, in gutters, and on roads. When it rains it washes into the Cashmere Stream, which feeds into the Heathcote/Ōpāwaho River.

Sediment smothers the habitat for fish and insects, making it harder for fish to see their food. It makes the river look dirty and makes it more likely to flood.

Chair of the Christchurch West Melton Water Zone Committee, Kevin Brown, said the aim is to get people thinking about what the source of dirty water might be when it rains, but equally, where dirt ends up once it’s made its way onto roads, footpaths, and into gutters.

“Residents may have seen the posters encouraging people to report sediment issues to Environment Canterbury and Christchurch City Council (CCC), through the 0800 765 588 incident response number,” Brown said.

Schools and community groups have also been encouraged to share the message with their students, parents, members, and others.

Industry informed of sediment control practices

In previous years, the Committee and Environment Canterbury have organised well-attended seminars for developers and construction workers on methods to control sediment run-off.

As part of our educational approach, several hundred industry and building sites were visited by our staff over the winter, to assess sediment and erosion control methods and provide information on how to manage sediment and erosion issues in the Cashmere catchment.

A significant number of sites were well informed when it came to the risk and mitigation of sediment and erosion on building sites, so the campaign’s scope was widened to other areas of Christchurch.

The campaign will be repeated in other areas of Canterbury facing similar sediment issues.

Working Group working hard to advocate

At its August meeting, the Cashmere and Port Hills Working Group received a presentation from Environment Canterbury and CCC staff.

The Group is now working on priority areas for sediment and erosion control in Cashmere and Port Hills areas. These include themes such as:

• collaboration, specialisation, planning, efficiency
• celebrating those being proactive
• communication and engagement with both industry and community
• defining guidelines in the sediment and erosion toolbox, and
• prioritising sediment and erosion control.

Staff, committee and working groups members will also be completing a ‘rainy day inventory’ to identify and locate some of the worst offending locations in the Cashmere and wider Port Hills.

This will be carried out following the next heavy rain, with the information gathered used to help staff target their efforts for future education and information.

Seen some sediment? Report it

If you see sediment or erosion issues during heavy rains or surrounding building/construction sites, call our incident response hotline on 0800 765 588. Once we know, we can investigate.

Find out more

For our online toolbox containing guidelines for land and waterway disturbing activities that can cause sediment and dust discharge to water and air, see ESC Canterbury.

Learn more about sediment in waterways, by watching this video with EOS Ecology Principal Scientist, Shelley McMurtrie.

Other resources and information sources:

• View the latest information on Cashmere and Port Hills catchment
• Christchurch City Council – Healthy Ōpāwaho Project
• Cashmere Stream Care Group – Facebook
• Ōpāwaho/Heathcote River Network – News and updates
• Christchurch West Melton Water Zone – News and events
• Environment Canterbury sediment and erosion control campaign – Winter 2020