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Ellerslie Flower Show Gold-award Raingarden
The Ellerslie designers set out to create a contemporary outdoor space that incorporates features that reduces the impact of stormwater runoff on urban waterways by capturing and slowing down runoff. This outdoor space has three features that reduce the impact of runoff from this urban space:
- Water is collected from the roof into a central storage tank.
- Excess water spills from the water tank via a water feature into raingardens
- Permeable decking – let rain wash unto the underlying soils.
More information on the design philosophy
The Designers 
Designers Jamie Douglas, Kirsten Sach and Zoe Carafice in their award-winning garden
Email: raingardendesign@gmail.co.nz
Plants
The raingardens are densely planted with species selected for their foliage colours and textures to complement the contemporary garden design. Most of the plants are native rushes, sedges and reeds edged with rare native groundcovers, with a sprinkling of exotic plants that provide colour (e.g., blue flowered Iris sibirica) or contrasting texture provided by the broad leaves of taro (Alcoasia gageana) and spikey seed heads of miniature papyrus (Cyperus haspan). These exotic plants were chosen to minimise risk of spreading outside the garden. All the plants are adapted to fluctuating wet and dry conditions, and are generally found on the edges of wetlands.
Key native plants in the raingarden:
- Sedges – Baumea complanta, Baumea rubigimosa include strappy leaves
- Wiwi – Juncus pallidis and Juncus sarophorus common in wasteland and poor pastures have narrow leaves
- Pepe - Machaerina sinclarii – large strappy leaves and impressive seed heads
- Leptinella tenella – a groundcover that is critically endangered
Key raingarden features
Excess rainwater overflows from the raintank as a water feature, falling onto rocks which reduce the energy and force of the water flow.
The overflow spreads into channels which transport the water to each rain garden. Each inflow falls onto a gravel mulch which protects the soil surface from erosion.
Dense planting increases filtering and uptake of water and contaminants, suppresses weeds, and maintains infiltration rates.
Note:
- Unlike most road runoff, roof runoff is clear – this means short groundcover plants can be used as their leaves won’t be covered with sediment
- These raingardens have very rapid drainage and minimal ponding – often a raingarden would be set about 100 to 150 mm lower to allow deeper (temporary) ponding.
Water brings the garden to life as it flows down the face of the water tank, down a channel, and into the gravel of the densely-planted raingardens (left and central photos). Right photo: Tall, slender rushes and broad-leafed taro feature in the raingarden along the walls of the courtyard.
Links and further reading
Choosing plants:
- The Ellerslie Flower Show raingarden brochure
- ARC Factsheet 8b
- ARC Technical Publication 10: Design guidelines for stormwater treatment devices. Look at chapters 1 (introduction), 7 (sand filters and raingardens) and 14 (Landscaping guidance for stormwater treatment devices).
Get children involved! A Link to US site on teaching children to ponder puddles and track what happens to stormwater.
Information on stormwater in general and other ways of reducing and treating stormwater, and reducing water use, also known as Water Sensitive Urban Design:
- Auckland Regional Council Stormwater website
- Landcare Research LIUDD website (this web site)
- Water sensitive urban design (Melbourne)
An inspirational book on garden design using stormwater
- Nigel Dunnet and Andy Claydon – Raingardens. Managing water sustainably in the garden and designed landscape. 2007. Timber Press. Note: Some of the plants listed as useful for landscaping are weeds in NZ. To find out if a plant may be a weed go to Ecological traits of New Zealand flora (both introduced and exotic).
