Solving Stormwater

To many eyes, plants look too simple to do anything but plants can remove most of our stormwater, lower council spending by 20% and store carbon, and everyone gets more real green-space too. But tradition and fear of the unknown mean few are rushing to do this. Also it is SO easy to dismiss planting designs as just aesthetics and those who design planting schemes as only gardeners – a loss to all of us.

Water drops on Lophomyrtus obcordata, a NZ native

This is where it all comes together – Sustainable Stormwater Systems*

*SuDS goes by lots of names: a word-war which weakens the original idea. SuDS suggests water – and the association is apt and useful. That said, these principles have broader application than just urban systems so I tend to use Sustainable urban Drainage Stormwater Systems (SSS) to encompass urban stormwater and rural run-off.

(L) Dentention basin and weir (M) Swale (R) Rain garden

Why do something different with stormwater? What’s wrong with pipes?

Water is a very strong solvent and stormwater is too. As rainfall turns into stormwater and then run-off, it dissolves and gradually erodes the surfaces it flows across and carries off loose particles. Some particles attract further particles and the whole flow ends up in a stream and then the sea. Due to our lack of thought this is a wasteful and destructive process that ignores natural cycles – we’re destroying the Earth.


A natural system (forest, grassland, wetland or even a river) conserves nutrients as they are scarce; it puts nutrients ‘in the bank’ all the time through plant uptake and growth. For instance nitrate – N, phosphate – P, and potassium – K are elements essential to plant growth, even water is held tightly.

Stream near Haast on the West Coast of New Zealand

But our technical society produces many complex chemicals that don’t break down and that accumulate in soils, groundwater, rivers, the sea and in us. We also mine some (e.g. phosphate) and make others (e.g. urea) and then use them wastefully where their levels far exceed natural systems’ ability to handle them (plants, soils, rivers). From this we get algal blooms, blue babies, and unswimmable rivers. With the complex chemicals (synthetics, plastic softeners, compounds with mercury, lead, cadmium, tin…) we experience chronic medical conditions and wildlife population crashes.

Our artificial surfaces shed water faster and in greater quantities than natural sites, with these volumes rising to such levels that no amount of engineering can reduce their impact.

Concrete lined river channels are a disaster and cause serious flooding. Los Angeles River

But bad habits have a habit of catching us unawares…

Currently approx. 30% of a city’s spending is stormwater-related. Climate change has resulted in a shift from stable seasonal weather to (for instance) flood events interspersed with droughts. Seasonal rains are a thing of the past for many regions – ask a farmer, ask yourself, ask the Earth, not the MSM.

At the same time we’re living in a new ‘now’ where the fuels that’ve enabled our society are now threatening both society and human life itself. As it takes many decades to introduce a new fuel we need to design systems that either self-maintain or that can be built and maintained manually.

What is SUDS?

The best way of solving stormwater (lowest-investment / real-results ratio) is to look at how forests, grasslands, wetlands and rivers handle storms and see where we can use their solutions to hold on to nutrients, destroy toxic agents and slow-and-reduce water flows … how far can we emulate nature and bring natural processes into the city?

SUDS in Otago (Wanaka)

SUDS can be very simple; it’s about doing three things repeatedly:

  • Intercept – stop and slow raindrops before they hit the ground
  • Detain – hold water so it evaporates (blue colour in image above)
  • Retain – keep some to give our plants the fuel they need, and

— let a tiny bit go to the river

… keep repeating from plants up to cities. We aim to create a multiply-redundant network. Redundant? yes, redundancy has been frowned upon but the natural world (and thoughtful engineering) have layers of fail-safes and apparent duplication. Redundancy means no part of the system is over-stressed and when it needs to work hard – in a storm or through a pandemic – it can and does, every time, with less input from us. You can easily see how the stormwater system works and problem-solve, fix and extend as needed – no digging (for buried pipes) required!

SUDS is open-source (like some software). Literally we need to see the water all the way from source – where it falls as rain and snow – to sea where it re-enters the water cycle.

SuDS chain pond scene at a research institute, Dunedin, New Zealand

By keeping the water above-ground we maximise water contact with air (and plants) to increase the rate of water loss to air. By doing this from single houses up to the whole town, severe storm run-off doesn’t occur and a piped network becomes unnecessary. This is where the monetary savings kick in big-time; for a single industrial site stormwater system savings of 20% to 50% are reasonable; for a subdivision or city, savings of 15%+ are normal.

Where conventional drainage is impossible this can make worthless land valuable.

Some SUDS – by least to most complex

– Lot parcelling to match with water flow (new developments)
– Rainwater barrels on downpipes, and rain chains
– The right plants … all plants have different abilities to transpire water
– Many small shallow water basins / rain gardens to detain the flow
– Rough surfaces
– Planted gravel drives (and parking lots) to detain and allow water to infiltrate
– Raintanks for car washing and non-drinking use
– Houses on piles not slabs … to protect existing natural water flow
– Porous concrete and asphalt (also provide much quieter roads)

Imagination is the only limit with SUDS

(L) water flows across rough surface to swale, detain/intercept (M) grass verge intercept (R) no kerb and rough surface to swale

Further Reading

Plants Really Work  by Nigel Cowburn April 14, 2020

What goes around comes around  by Nigel Cowburn April 21, 2020

Text/photos/graphics by Nigel Cowburn, editorial support, Liz; Growplan (2020)
Nigel is a NZ landscape architect: Growplan website | blog | twitter

3 thoughts on “Solving Stormwater

Add yours

  1. This is a wonderful explanation, Nigel. Nature-based solutions and permaculture are so underrated in a society that considers engineering solutions to be the best. Structures are more “impressive” and signify “development” (according to perceptions in the developing world, at least).

    Because engineering solutions are straightforward and give quick immediate results, rather than nature-based that are more complex to implement and given incremental savings over time.

    I also think that as a society, we are very poor at analyzing hidden costs, and thinking far into the future. If we considered this, nature-based solutions trump engineering ones by a considerable margin.

    It’s a by-product of a government system that runs for re-election every 5 years; anything over this timeframe is usually not of immediate priority.

    Are you working on such projects?

    1. Thank you Saurab, lovely simple graphics you are doing. Yes it is difficult to help people see that plants cost less; one barrier (I think) is that to design a planted stormwater system the design cost is twice to three times as much BUT the expenditure is at least 15% less. But they see the design fee first and choose the cheapest one, which the costs then hundreds of thousands more.

      Another thing people miss with plants is that they are getting more effective, more valuable with every day. Whereas that black box / shiny solution is depreciating and getting closer to the scrapyard from the day you put it in the ground.

      Yes we have government lag too – they are good in an emergency but slow otherwise; NZ is probably 40 years behind in the implementation of advanced planted/living stormwater as you would see in say Berlin, South London or Los Angeles.

      Hidden costs – yes. My continuing goal is to only use plants, soil and aggregates, then system energy remains close to natural and nothing non-biodegradable is used – I don’t always manage it but aim high – targets are much more valuable than limits!

      I have worked on a 60-lot subdivision where SUDS was done well, and I have some industrial sites in the works, as well as having just finished a wastewater site where I’ve managed to set some precedents. Look for my “plants-as-partners” post as a site I’ve been working on is the plan at the end of the page.

      I also have a series of upcoming posts on phytoremediation.

      1. “to design a planted stormwater system the design cost is twice to three times as much BUT the expenditure is at least 15% less.” This is probably the biggest factor. Most contracts are released based on design cost considerations, and not the maintenance costs over time.

        How are you convincing your clients to shift their perspective? If this shift is made, they will automatically become aware of the hidden costs…

        Looking forward to your phytoremediation series!

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