Heathcote River Draft Stormwater Management Plan

Water quality and ecological health

The quality and ecological health of waterways in the Ōpāwaho/Heathcote River catchment have declined greatly during 160 years of urban development. Metals in the stormwater runoff can harm many species of aquatic life, sediment can smother habitat, and E. coli poses a risk to human health during water activities such as wading or swimming.

Flood risk

River-side roads in the Ōpāwaho/Heathcote River catchment experience regular flooding and low-lying houses can be flooded in large events. Land sinking during the 2010/11 Canterbury earthquakes has increased the flooding risk for many properties, some of them distant from the river. Significant urban growth in the upper catchment will generate more and faster stormwater runoff that needs to be controlled.

What we know about copper

• Vehicle brake-pads are a major source of copper
• Copper in rainfall contributes
• Soils are a minor to moderate contributor
• Small changes in the number of copper roofs can affect copper concentrations in stormwater
• Products used to clean roofs and pathways may contribute.

What we know about sediment

• Rural erosion in the Port Hills has a major effect
• Cuttings and banks (road cuttings, old quarries, private sections) contribute
• Stormwater discharges to hillsides and hill waterways contribute to erosion
• Hillside earthworks have a major effect
• Construction has a major effect
• Deposits from the atmosphere contribute
• Road wear and vehicle tyres contribute
• Erosion of stream banks contributes to some extent.

What we know about zinc

• Roofs are the source of maybe 65 to 70%+
• Tyres are the source of maybe 25 to 30%
• Other zinc-coated steel items (fences, ventilation ducts, poles) may produce 1 to 5%
• House and garden products (e.g. moss control) contribute to some extent
• Soil contributes to a small extent.

Values

Water is a taonga (a treasured natural resource) and represents the lifeblood of the environment for tangata whenua. The maintenance of water quality and quantity is perhaps the greatest resource management issue for tangata whenua. All waterways are a major feature within the landscape and should remain as a feature. Culturally, all waterways are significant and come together as one. Waterways begin as rain drops and connect together as streams, lakes, estuaries, and wetlands, all leading to the sea.

Cultural health

The cultural health of the Ōpāwaho catchment is poor. Food-gathering sites contain high levels of pollution and are considered unsafe for food gathering and, in some cases, unsafe for swimming. The diversity of native plants and trees is very low, and coastal and estuarine sites typically hold only small amounts of native vegetation in the zones near waterways, which are often dominated by exotic species.

Our goals are:

1.1       To ensure the quality of stormwater from all new development sites or re-development sites is treated to best practice.

1.2       To have 100 per cent of stormwater treatment facilities built and operating to Waterways and Wetlands Design Guidelines standards.

1.3       To have less than 5 per cent of all consented construction activities on the flat reported non-compliant due to sediment discharges – by 2025.

1.4       To have less than 10 per cent of all consented construction activities on the Port Hills reported non-compliant due to sediment discharges – by 2025.

1.5       To investigate ways to reduce the environmental effects of sediment discharges – by 2022.

1.6       To look at options for carrying out street sweeping, sump cleaning, and send-to-wastewater trials – in 2020/21.

Recommended for the Surface Water Strategic Plan

1.7       Plant severely eroding natural areas of the Port Hills (approximately 600 hectares) from Ōpāwaho/Heathcote Valley to Hoon Hay Valley.

1.8       Work with farmers to control sediment from erosion sites on Port Hills farms, with subsidies as needed to speed up controls – by 2030.

1.9       Put in place best-practice sediment controls on Port Hills roads and tracks – by 2025.

1.10    Reduce road sediment by the best practicable option determined by the results of street sweeping, sump cleaning and trialing alternative treatments.

Our goals are:

2.1     To have 100 per cent of stormwater treatment facilities constructed and conforming to Waterways and Wetlands Design Guidelines standards.

2.2     To investigate zinc mitigation measures and carry out cost/benefit analyses toward identifying their effectiveness as best practicable options – by 2022.

2.3     To consult with key stakeholders and identify a long-term zinc strategy in line with current technologies – by 2025.

2.4     To collaborate with local and regional government in a joint submission to central government seeking national measures and industry standards to reduce the discharge of contaminants from buildings and vehicles.

Recommended for the Surface Water Strategic Plan

2.5     By 2025, install a large-scale facility (or an array of devices, such as rain gardens) in at least one urban sub-catchment, to treat runoff from busy roads. By 2029, install similar facilities/devices in at least three urban sub-catchments

2.6     Adopt a strategy to limit zinc, based on finding the best practicable options.

2.7     Research and trial ways of trapping roof-sourced zinc on-site.

Our goals are:

3.1     To consult with the Government, through the Ministry for the Environment, about legislation to limit the copper content in vehicle brake pads.

3.2     To not permit stormwater discharges into the network from unprotected copper building cladding, spouting or downpipes.

3.3        To investigate a District Plan rule to discourage the use of copper building claddings.

Our goals are:

4.1       To compile a database of industrial sites considered to be medium or high risk based on the best available information – by 2025

4.2       To audit high-risk industrial sites by the approved procedure under the Comprehensive Stormwater Network Discharge Consent.

Our goals are:

5.1       To work with community groups to educate participants about current stormwater practice and to enable the public to take action to stop contaminants at source – by 2025.

5.2       To engage regularly with the Ministry for the Environment to collaborate on initiatives to reduce contaminants – by 2025.

Our goals are:

6.1       To limit the quantity of stormwater from all new development sites to pre-development levels, and minimise stormwater increases from re-development sites through consent conditions.

6.2       To protect houses from flooding during and after development by having controls on new floor levels.