Sections 4.3.4 and 4.3.5 aim to provide designers with a clear understanding of the approach Auckland Council requires for the design of stormwater systems.
The council’s preferred approach is to minimise any impact upon the receiving environment. All development should, in the first instance, be in accordance with the Water Sensitive Design principles detailed in Section 4.3.3 above and in Auckland Council guideline document GD2015/004 (Water Sensitive Design for Stormwater). The information provided in the following two sections primarily focuses on the minimum standards required for the design of both primary and secondary systems.
The stormwater system shall be designed for the Maximum Probable Development (see Section 4.2.8) of the entire upstream catchment and in accordance with Auckland Regional Council technical publication TP108 (Guidelines for Stormwater Runoff Modelling in the Auckland Region) with allowances for climate change as described in Section 4.2.10 above. Effects on downstream systems shall be shown to be acceptable. The system shall be designed to collect surface water from all areas, including lots, roads, rights-of-way and reserves.
188.8.131.52. Primary Stormwater System
Primary stormwater systems include both open and closed conduits and shall be designed to cater for the flows generated by the event specified in the design standards in Section 184.108.40.206 below. The location of primary systems should be aligned with natural flow paths as far as possible.
220.127.116.11. Secondary Stormwater System
A secondary stormwater system consists of ponding areas and overland flow paths with sufficient capacity to transfer the flows generated by the event specified in the design standards in Section 18.104.22.168 below. The location of secondary systems should be aligned with natural flow paths as far as possible. The existing constructed or natural flow paths shall be retained as far as practical. Any alteration of the existing stormwater system shall result in no detrimental impacts to either upstream or downstream properties.
Secondary systems shall be located on public land where possible. However, creation of an overland flow path is not to be considered as justification for the land it passes through to be vested in the council. Overland flow paths on private property for flows in excess of 100L/s for the 1% Annual Exceedance Probability (AEP) event shall be protected by registered easements in favour of Auckland Council or by other encumbrances prohibiting earthworks, fences and other structures, as appropriate.