Water Sensitive Urban Design - the way forward

Water Sensitive Urban Design - the way forward

New Zealand has seen its fair share of extreme weather over recent months. These events, along with the 2018 Stormwater Conference in May, have prompted discussion from industry experts on smart stormwater solutions.

Mike Chapman, our Principal Engineer Lead – Water Resources says water sensitive urban design (WSUD) makes more sense than how we’ve managed stormwater in the past, and will continue to evolve.

“WSUD has to be the way forward, simply because it makes more sense. Instead of relying on traditional pipes and large-scale communal ponds, WSUD essentially mimics the natural drainage patterns pre-development.

“Only 20% of rainfall that hits the ground naturally runs off to the nearest watercourse. The rest returns to the atmosphere or infiltrates into the ground. When you create hard surfaces you interrupt the natural system and direct around 80% to the nearest watercourse.”

Mike says reducing water-resistant surfaces and factoring more green space into designs, not only reduces the risk of flooding, but also improves the quality of water entering our streams, rivers and ocean. “It’s a win-win.”

In Auckland, WSUD is becoming common practice due to growth and requirements from the Unitary Plan and Council guidelines. Mike says the uptake in WSUD in other regions will be an evolutionary process.

“More solid case studies and cost-benefit analysis of WSUD are needed to give authorities the confidence to adopt the approach fully in other regions. But I think it will become mainstream with time”

However WSUD has some challenges. WSUD devices take up much space, and can cause conflict between other design elements, such as road corridors and high density development.

Mike says Harrison Grierson, has found opportunities implementing WSUD in high density development with limited space on each lot. “We’ve had to work with our clients closely to overcome these obstacles and meet consent requirements”.

He says we need to move to a hybrid approach where WSUD is focused within public space and maintained by local authorities. “A series of smaller treatment basins or swales within central road medians will mean water treatment is still distributed, without needing it at each individual lot, but also not relying on a single end-of-pipe pond solution.”

After all, says Mike, it took a century or more to perfect the conventional approach to stormwater management, so we can expect it will take time to perfect WSUD. “But we will get there and be better for it.”

This thought leadership article by Mike Champan, Principal Engineer Lead - Water Resources, is intended to provide you with insights and relevant information on Water Sensitive Urban Design and its use in New Zealand.

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