Water Sensitive Design for Stormwater: Treatment Device Design Guideline December 2019 Version 1.1 Water Sensitive Design for Stormwater: Treatment Device Design Guideline 1 Water Sensitive Design for Stormwater: Treatment Device Design Guideline Version No. Version Description Date 1.1 Minor update for corrections 18 December 2019 1.0 Initial published version 17 September 2019 Acknowledgements Authors: Stu Farrant, Francis Leniston, Emily Greenberg, Letticia Dodson, David Wilson, Sue Ira Editor: Francis Leniston Contributors: Tim Strang, Beverley Curley, Robyn Simcock Technical editorial panel: Stewart McKenzie, Gary Cullen, Ben Fountain, Emily Greenberg, Paul Gardiner, Amelia Seagrave, Kate Wynn, Matt Aitchison, Nadia Nitsche, Francis Leniston, and Ryan Rose Technical editor: Rosalie Chamberlain Graphic design: Helene Hall, Bianca Stables Cover image: Subsurface constructed wetland at Waitangi Park, Wellington. Constructed in 2005, Waitangi Park is a stormwater treatment system that is thoughtfully integrated into the Chaffers Wharf precinct. Waitangi Park is a good example of water sensitive design in the Wellington region Wellington Water or its client councils do not give warranty whatsoever, including without limitation, as to the availability, accuracy, completeness, currency or reliability of the information or data (including third party data) made available via this guideline and expressly disclaim (to the maximum extent permitted in law) all liability for any damage or loss resulting from your use of, reliance on the guideline or information and data provided via the guideline. The guideline, information, and data are provided on a “as is” basis. 2 Water Sensitive Design for Stormwater: Treatment Device Design Guideline HOW TO USE THIS GUIDELINE The diagram below shows the recommended design process and associated guidance for each step. Design Recommended process step guidance FULL GUIDANCE UNDER DEVELOPMENT In consultation with Land Development Project scoping Team at Wellington Water Sections A to D of Water Site assessment Sensitive Design for Stormwater (GD04) Section 2.1, District Define mitigation Plans, and the Natural requirements Resources Plan for the Wellington Region FULL GUIDANCE AVAILABLE Section 2.2 Concept Identify treatment design, 2.3 Treatment options options, and sections 3 to 6 Section 2.4 Technical Size treatment options design and sizing, and sections 3 to 6 Section 2.5 Life cycle Life cycle cost analysis costs Refine through design Section 2.6 Design development development Water Sensitive Design for Stormwater: Treatment Device Design Guideline 3 FRAMEWORK FOR IMPROVING WATER QUALITY The diagram below shows how this guideline fits into the national framework for improving water quality. National Policy Statement for Freshwater Management (NPS-FM) recognises te mana o te wai (the integrated and holistic well-being of water) and sets out objectives and policies that direct local government to manage water in an integrated and sustainable way, while providing for economic growth within set water quantity and quality limits. Regional councils must give effect to the national NPS-FM objectives set by the NPS-FM at a regional level Te mana o te wai in the Natural Resources Plan and integrate the recommendations made by community-led groups known as whaitua. In turn, district and city councils must set planning objectives and rules for new development and NRP and District associated three waters infrastructure that Plans support the Natural Resources Plan. Water sensitive design (WSD) is a best practice approach for the management of stormwater to Water sensitive reduce run-off volume and contamination design (WSD) WSD encompasses a wide range of activities, including but not limited to: • source control WSD for • urban design Stormwater: • water re-use Treatment Device • green infrastructure Design Guideline • run-off volume reduction. Water Sensitive Design for Stormwater: Treatment Device Design Guideline is a best practice guideline for the design of four types of stormwater treatment devices to reduce stormwater contamination. 4 Water Sensitive Design for Stormwater: Treatment Device Design Guideline CONTENTS Constructed wetland at Waitangi Park, Wellington. The functional design of Waitangi Park is focused on sustainability. Constructed wetlands are used to treat stormwater contamination and an open pond (out of picture) allows the re-use of the stormwater for irrigation of nearby greenspaces. Water Sensitive Design for Stormwater: Treatment Device Design Guideline 5 CONTENTS 1 GENERAL INFORMATION ........................................................................................................................................ 17 1.1 Purpose.....................................................................................................................................................................................18 1.2 Background..............................................................................................................................................................................18 1.3 Definition of water sensitive design .................................................................................................................................18 1.4 Scope .........................................................................................................................................................................................19 1.5 Other design guidance ..........................................................................................................................................................19 1.6 Subdivision requirements ....................................................................................................................................................19 1.7 Legislative requirements ....................................................................................................................................................20 1.8 Regulatory documents ........................................................................................................................................................20 1.9 Health and safety in design ................................................................................................................................................20 2 DESIGN PROCESS ....................................................................................................................................................21 2.1 Performance requirements ................................................................................................................................................ 22 2.2 Concept design ...................................................................................................................................................................... 22 2.2.1 Steps to support optimal WSD outcomes at concept design ................................................................................... 22 2.3 Treatment options ................................................................................................................................................................ 24 2.3.1 Device selection ..................................................................................................................................................................... 26 2.3.2 Stormwater treatment train .............................................................................................................................................. 26 2.4 Technical design and sizing ................................................................................................................................................ 27 2.4.1 Contributing catchment area ............................................................................................................................................. 27 2.4.2 Calculation of Water Quality Volume (WQV) .................................................................................................................28 2.4.3 Calculation of Water Quality Flowrate (WQF) ...............................................................................................................28 2.4.4 Design for stream protection, flood management and conveyance ...................................................................... 29 2.4.5 Continuous simulation modelling approach .................................................................................................................. 29 2.5 Lifecycle costs ........................................................................................................................................................................30 2.5.1 Life cycle cost analysis – Description ..............................................................................................................................30 2.5.2 Step-by-step guide to undertaking a life cycle costing ...............................................................................................31 2.5.3 Indicative NPV LCC estimates ............................................................................................................................................ 33 2.5.4 Optimising design to avoid common maintenance issues ......................................................................................... 33 2.6 Design development ...........................................................................................................................................................