Source: Environment Canterbury Regional Council
Bare soil and loose material from the Port Hills can be swept along by heavy winter rains to become run-off. When this reaches stormwater drains, it flows straight into local streams.
We’re counting on Christchurch builders and residents to help us clean up Cashmere Stream and Ōpāwaho/Heathcote River.
Port Hills loess soil prone to erosion
A soil type found in the Port Hills – fine clay-sized loess particles – is particularly problematic. When it ends up in our waterways, it can damage ecosystems by poisoning land or water, removing plants and trees or killing the fish, insects, birds and animals that live there.
Loess is prone to erosion due to chemical and physical properties that cause dispersion of soil particles when wet. When vegetation and protective topsoil is removed from loess deposits, the underlying loess subsoil is subject to erosion.
Once these soil particles are washed into streams, chemical forces prevent settling, which ultimately leads to water quality problems. These particles are a key source of problematic sedimentation in the Cashmere Stream which flows into the Ōpāwaho/Heathcote River.
Learn more in this video with Shelley McMurtrie, Principal Scientist at EOS Ecology.
Improving Cashmere Stream water quality
We are taking an integrated approach to improve the water quality and clarity of Cashmere Stream and the Ōpāwaho/Heathcote River, by working with local rūnanga, community groups and local councils in addition to managing compliance with regional rules and resource consents.
Of particular importance is the relationship between Environment Canterbury and Ngāi Tahu of shared understandings and values with both having a kaitiakitanga (guardianship) role to play. Water is a significant cultural resource that connects Ngāi Tahu to the landscape, and the culture and traditions of the tūpuna (ancestors).
Water is the life-giver of all things and is central to Māori life. The mauri (the life force) of a waterway is degraded if it no longer has the capacity to support traditional uses and values such as food gathering (mahinga kai).
Fundamental to mana whenua perspectives on freshwater is that water is taonga (a precious treasure), and water management and land use should reflect this importance.
Decline in stream life
The Cashmere Stream Care Group is a community group working with us to contribute to the health of the Cashmere Stream.
Chair Ken Rouse, who moved to live in Cashmere with the Cashmere Stream at the bottom of his garden eight years ago, said he was concerned by the sediment loads the stream was regularly subjected to.
“The sediment appears to have impacted on fauna that had been living in the stream as I have not seen koura at the bottom of the garden for some five years now. In 2016 Salmon spawned at the road bridge site 150 metres downstream but not since then. Sediment coats all surfaces and smothers the stream life.”
Rouse backed up his concerns citing the recently published report, ‘Water Clarity of Cashmere Stream Catchment‘.
“Data shows (a) four percent year-on-year decline in water clarity for the past seven years…which is completely unacceptable. Keeping loess soil sediment stabilised on the Port Hills is the priority.”
Rouse is advocating the installation of a public access path from Sutherlands Road to the Confluence of Milns Waterway. He notes that along this stretch the stream runs very clear as most of the water flow is provided by a network of springs in the Halswell area. “If the community could see the Cashmere Stream in such pristine condition they would challenge practices that result in the sediment-laden water as observed at its confluence with the Ōpāwaho. We should not accept the status quo!”
On-site reviews of erosion and sediment control practices
Construction is a key source of sediment depositing into the Cashmere Stream.
Over the winter, we are conducting on-site reviews of erosion and sediment control practices at building sites in Cashmere and the Port Hills.
Regional leader Resource Management Act investigations Valyn Barrett said, we must ensure that run-off from construction sites is not going into our waterways, having a negative effect on biodiversity and water quality.
“In recent years we have spent a lot of time working with the construction industry to make sure they know their obligations to manage on-site erosion and sediment control. We’re happy to help if that’s what is needed, but we want people to know that on-the-spot fines may be issued in order to get the improved environmental outcomes we want,” Barrett said.
Builders are required to apply the best practicable options for erosion and sediment control in each situation within each building project, and to make sure that all site activities comply with regional rules or Resource Consents.
Penalties for non-compliance
Whether or not you are the holder of the Resource Consent; all builders and sub-contractors are required to comply with its conditions while undertaking activity on site. Under the Resource Management Act, failure to comply with the conditions can result in the site being shut down, fines and/or court action.
Need a sediment and erosion plan?
We can assist builders and contractors in the development of an effective Erosion and Sediment Control Plan. Our comprehensive toolkit at www.esccanterbury.co.nz is a great online resource, and we welcome a phone call with any questions. We’re here to help find the right solution for a site, but we’re letting industry know that on-the-spot fines may be issued for sites that are not compliant.
Help identify sources of erosion and sediment
If you see footpaths, gutters or roads covered in sediment (soil) phone 0800 765 588 or use the Snap Send Solve App to notify us and The Christchurch City Council.
To get some advice about an Erosion and Sediment Control Plan give us a call on 0800 324 636 or visit the online toolkit at www.esccanterbury.co.nz.
Learn more about The Cashmere Stream Care Group.
You can also get involved by attending a meeting for your local water zone committee. The Christchurch West Melton Water Zone Committee will next meet on 30 July at Environment Canterbury, Council Chamber, Ground Floor, 200 Tuam Street, Christchurch Central City, Christchurch 8011.
Lead photo: Cashmere Stream, Worsleys Reserve, Cracroft.