5.3.5 Surface water quality - discharges from roading and hard surfaces.
5.3.5.1 Desired environmental outcomes
Stormwater discharges from roading and hard surfaces do not degrade surface water quality.
5.3.5.2 Regional council methods
Roading: Regional plans may contain rules regulating discharges to waterways and the coastal marine area from roads. These discharges of stormwater can contain contaminants including fuel and oil from vehicles. This could relate to rural subdivision where new roads are built to access the subdivision.
A regional plan could regulate discharges of contaminants from roads by incorporating performance standards which the road design is required to meet in order for the discharge to be a permitted activity. These performance standards could require, for example, treatment of stormwater runoff to a particular standard before discharge or that the best practicable option be adopted to minimise discharge of contaminants.
Such controls may be justifiable in areas where roads are immediately adjacent to sensitive aquatic ecosystems.
Guidelines could be incorporated or referred to in a regional plan, which illustrate the types of treatment devices which may be appropriate. For example:
- design of road edges to incorporate swales. These must be kept vegetated and are generally not appropriate for slopes steeper than 4%. [ Auckland Regional Council Technical Publication 10, Design Guideline Manual for Stormwater Treatment Devices] . The treatment efficiency is highly variable and depends on the quality of vegetation, permeability of soils and residence time in the swale. Maintenance may be required e.g. replanting or weed removal.
- maintenance of stormwater ponds to collect and treat road runoff (this is more an issue for larger roads such as State Highways and motorways in ecologically sensitive areas. It is unlikely to be relevant for roads required as a result of rural subdivision).
Other hard surfaces: In areas where runoff may contain contaminants from hard surfaces, rules could be applied to land use activities on hard surfaces. Rule in a regional plan could regulate the way in which contaminants such as chemicals, fertilisers, fuel and other hazardous substances are stored and handled, requiring storage on impervious surfaces and bunding or other methods to prevent runoff to land (also see above for discussion on contamination of groundwater by pesticides and hazardous substances).
Water management classes: Section 69 of the RMA provides that regional councils may include in a regional plan rules which require that certain waters be managed for the different purposes set out in the Third Schedule to the RMA. These purposes include waters managed for aquatic ecosystems, contact recreation, water supply, cultural and irrigation.
A regional plan would identify by way of planning maps or schedules, the different classes applied to the waterways of the region. Standards (either numeric or qualitative) are then stated for each class. Activities which discharge water or contaminants to waterways would then be assessed against the standards specified for the particular water management class.
This method, if adopted, may be used to control the effects of all types of discharges.
5.3.5.3 District council methods
District plans focus more on the land use rather than the discharge.
Contaminants from roading could be addressed in the subdivision and roading design standards, at the stage of subdivision consent. Assessment of the effects of a subdivision could include the potential for contaminants in road runoff to enter waterways, and conditions could be imposed requiring the use of methods such as those discussed above for the regional council, such as swales.
Control of runoff of contaminants from hard surfaces by district councils could be achieved in the following ways:
- district plans may require resource consents for storage or use of hazardous substances above a certain threshold, determined in accordance with a risk assessment process or calculation. This risk assessment may be designed to assess risk to human health and property as well as the environment. This method could perhaps be relevant to rural subdivision where intensive horticulture was being carried out requiring the storage and use of large quantities of chemicals;
- rules in a district plan could restrict activities such as washing cars on hard surfaces where the runoff may get into the stormwater system. However this is more relevant for an urban environment and is not likely to be an issue for rural subdivision;
- ponds could be used within a rural subdivision to remove sediment and treat stormwater runoff from hard surfaces, whilst also acting as an amenity feature and providing habitat. A permanent pond may not be able to be maintained with very permeable soils unless a liner is used. However it is unlikely that a pond would be necessary for stormwater/runoff treatment purposes from a rural residential subdivision unless the development density was relatively high and/or the receiving environment was very sensitive. A pond may also be appropriate as part of a non-residential development in the rural area, such as a tourist accommodation complex, or educational institution. A pond could be required as part of the consent to subdivide, or as part of a resource consent for the activity that would be located on the subdivided allotment;
- vegetated riparian strips along the edges of lakes or streams may assist in the removal of sediment and other contaminants from stormwater flow. Retention or enhancement of buffer strips could be achieved by esplanade reserves or strips being taken or required upon subdivision (where appropriate), consent conditions requiring fencing and/or planting and maintenance, or protection covenants as part of a "conservation lot" type of subdivision.
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