Proposed stormwater systems shall cater for stormwater runoff from within the land being developed together with any runoff received from upstream catchments.
The upstream catchment shall be considered for the Maximum Probable Development (MPD) scenario, meaning that it allows for development within a catchment that takes into account the maximum impervious surface limits of the current zone or, if the land is zoned Future Urban in the Proposed Auckland Unitary Plan, the probable level of development arising from zone changes. If the upstream catchment includes areas outside the Rural Urban Boundary then the MPD shall be agreed with the council. In order for a system to be considered for vesting in council ownership, or for stormwater discharges to be authorised under the council’s Network Discharge Consent (see Section 220.127.116.11), the system must be designed to cater for the MPD scenario as defined in this section.
For a proposed land development (including projects involving changes in land use or coverage) the design of the stormwater system shall include the evaluation of the effects on both upstream and downstream properties. This evaluation will be required at the resource consent stage and may be linked to a requirement to achieve alteration of the hydrological regime to the benefit of the wider catchment.
The council will endeavour to provide guidance at an early stage in the resource consent application process as to whether a catchment-wide solution will be required.
Downstream effects could include (but are not limited to) changes in peak flows and patterns, flood water levels, contamination levels and erosion or silting effects, and effects on the existing stormwater system. Developers shall allow for any specific mitigation requirements for the area being developed. If the proposed development area is not covered by a specific catchment management plan, and the proposed development includes effects that are assessed by the council as being more than minor, mitigation measures such as peak flow attenuation and volume control will be required. Where a proposal details effects that are assessed by the council as being less than minor, the developer may or may not be required to implement mitigation measures as directed by the council, in particular where the cumulative effects of similar development within the catchment are considered.
Where modification of a watercourse is required, fish passage shall be maintained. Refer to relevant consent requirements and Auckland Council technical publication TP131 (Fish Passage Guidelines for the Auckland Region) for further detail. Auckland Council will look for opportunities to enable fish passages in watercourses where these have been obstructed by ‘man-made’ structures. In circumstances where the developer can demonstrate that fish passage would provide no nett benefit, the above criteria may be exempted at the council’s discretion.