A more environmentally-friendly approach to managing how and when stormwater can be discharged into Christchurch and Banks Peninsula’s waterways has been finalised.
The Environment Court has approved a settlement of Christchurch City Council’s appeal against some conditions in the Comprehensive Stormwater Network Discharge Consent that was granted by independent hearing commissioners appointed by Environment Canterbury in June 2019.
“The settlement of this appeal represents a major milestone in the management of stormwater in Christchurch and means all stormwater discharges will now be managed under a single consent,’’ says Christchurch City Council Head of Three Waters and Waste Helen Beaumont.
“This means there will be clear standards across the network for the management of stormwater, which should result in better environmental outcomes.’’
Environment Canterbury’s Chief Operating Officer Nadeine Dommisse says: “The consent supports the collaborative Canterbury Water Management Strategy approach between councils, Ngāi Tahu and the community to improve outcomes for water in Canterbury, and a similar approach is being taken for other stormwater network discharges throughout Canterbury.
"The consent supports leadership in behaviour change, technical innovation and community resources to achieve stormwater quality improvements in a systematic and cost-effective manner.”
Stormwater – any rainwater that falls on roads, paths and other hard surfaces – picks up pollution and flows via drains into local waterways. If the discharge is contaminated, this affects the health and water quality of local streams and rivers.
The comprehensive consent defines the conditions under which the Council may discharge stormwater into the territory’s water bodies, into land and to the coast. It includes a requirement for a reduction in contaminant loads in the discharges to improve the water quality in the receiving rivers.
The 25-year consent also covers how discharges from new developments are managed so they do not adversely affect flooding.
“We are investing millions of dollars into improving our management of stormwater so that we improve the quality of the water entering the waterways and reduce the risk of flooding,’’ Ms Beaumont says.
“In Wigram, for example, we have lowered a large area of the Canterbury Agricultural Park to create a flood storage basin with four hectares of wetland. In a one-in-100-year storm event, the basin will be able to store around 590 million litres of water – the equivalent of 236 Olympic-sized swimming pools – which means there’s less risk of properties flooding along the upper reaches of the Ōpāwaho/Heathcote River.
“The new wetland area provides a habitat for a number of threatened species and will also help to clean the water as it leaves the basin and flows into the Heathcote,’’ Ms Beaumont says.
Work is also under way in the Cashmere and Worsleys valleys to create storage basins that will reduce the flood risk to properties around the lower and mid-Ōpāwaho/Heathcote. ,
The basins will be contoured to allow as much sediment as possible to settle out prior to water leaving the valley, which will improve water quality in Cashmere Stream and the Ōpāwaho/Heathcote. Similar stormwater management systems are being installed the Ōtākaro/Avon and Pūharakekenui/Styx river catchments
“We are committed to working collaboratively with Environment Canterbury to improve the quality of our waterways,’’ Ms Beaumont says.