Stormwater design: embracing nature

Harrison Grierson's technical director, Scott King, discusses the importance of stormwater design and management when developing land in the wake of extreme weather events.

Integrating stormwater into a design solution as early as possible in a development project has never been more important.

In the wake of extreme weather events like the 2023 Auckland and Hawke’s Bay floods—and as storm warnings become common nationwide—stormwater management must be embedded at the very outset of project planning.

Leading developments are now incorporating nature-based solutions (“blue-green infrastructure”) that harness, rather than fight against, the natural landscape.

But it hasn’t always been this way.

Stormwater management in New Zealand has evolved in the 21 years I’ve been practising stormwater engineering.

I arrived here from the UK in 2004 at the back end of the collect-it-in-a-drain-and-pipe-it-to-the-nearest-stream era, and (following the 2003 update of ARC TP10) at the start of an increase in the use of stormwater detention ponds and wetlands across the country.

The change saw several councils outside of Auckland grappling with the choice between dry ponds, wet ponds or wetlands, and what design storms to stipulate.

During this period, councils focussed on flood protection, attenuating peak flows from large storm events. Unfortunately, the importance of managing changes to low flows was, at times, overlooked, resulting in bank erosion issues at the downstream reaches of urban streams. As a result, the importance and benefits of providing for extended detention became more widely known and recognised. For this reason and due to treatment benefits, the use of wetlands became and continue to be a favoured stormwater management solution.

The benefits of at-source treatment and treatment trains then also gained traction, with the previously obligatory roadside catchpit now being switched-out for raingardens and swales.

At-source treatment has since evolved into the importance of providing at-source retention, via soakage to ground (where possible) to recharge the groundwater, or via rain tank capture and reuse.

These measures are all aimed at trying to replicate the ‘greenfield’ hydrology as closely as possible and continue the evolution away from the historic, heavily engineered approach.

This evolution journey has had, and still has, several various labels (LID, SUDS, WSUD, blue-green infrastructure etc), but all centre around wanting to work with nature as opposed to against it! 

The implications of this evolution have seen stormwater management rise to prominence over the last 20 years, from being something to sort out at the back end of a design (once the roading had been solved - as roading requirements always took priority!) to being one of the most important elements to consider from the outset.

Nowadays, as a stormwater engineer, I have the pleasure of being involved at the very outset of a project, including the due diligence stage prior to land purchase, and get to work with the urban designers and master planners to help influence the overall look and feel of a development. Ideally, this involves working with the existing landform as much as possible and utilising what nature has already provided, with much less concrete needed and much more planting involved (hence the term blue green infrastructure)! 

A recent project at Harrison Grierson, the Rangiuru Business Park near Te Puke, is a best-practice example of where 148 hectares of previously rural land now features a 50-hectare integrated stormwater pond and wetland. That’s equivalent to 48 rugby fields devoted to sustainable water management, supporting both the business hub and the surrounding environment.

Constant advances in stormwater technology mean more efficient natural treatment systems are increasingly accessible. As a result, developers can achieve both regulatory compliance and environmental leadership with cost-effective, adaptable solutions.

Engaging stormwater specialists at the earliest stage pays off—both by future-proofing developments against climate-driven weather extremes and by realising ecological and commercial benefits.

With every project, our industry can lead by example, proving that development and nature can coexist for the benefit of communities and generations to come.

Scott King, Technical Director at Harrison Grierson, is a Chartered Professional Engineer, and brings 28 years’ experience in UK and NZ urban development, helping shape the future of New Zealand's land development with resilient, sustainable stormwater solutions.