Rain Gardens

The Bureau of Meteorology has called it; the summer of 2018/19 in Australia was thehottest on record! Headlines in major media outlets also informed us that the Town ofGawler is among nine local government areas in Australia most vulnerable to the impact ofextreme heat. Gardens are becoming increasingly stressed under these conditions; at thesame time it is important to cultivate green space in our urban and peri-urban areas to helpcool our communities. Drought adds the challenge of balancing water conservation withkeeping gardens alive in periods of low rainfall. In early 2019 Gawler Environment Centrepresented Climate Smart Communities North, a series of free workshops on water sensitivegardens and urban greening to help local gardeners maintain productive gardens and keeptheir homes cool in hot weather. A series of handouts, like this one, were developed for theworkshops and are available from the GEC office or on our website:www.gawlerenvironmentcentre.org.au

Why build a raingarden?

In our urban environments the naturalwater system is disrupted, rain falls onour roofs, pavements and roads, andinstead of soaking into the ground thewater is channeled away through stormwater drains. Instead of  replenishingthe water table and providing water forvegetation, stormwater flows into ourrivers and creeks, washing pollutantsfrom our hard surfaces into our localwaterways and out to sea, with heavyfalls potentially causing erosion andflooding. Raingardens are a simple way to helpretain more water in our gardens, whileimproving the health of our rivers,creeks and coastal waters.

What is a raingarden?

A raingarden is just like a regulargarden except that it is designed andsituated to receive and absorb rain andstormwater run-off from urban hardsurfaces such as roofs, driveways,walkways etc. A raingarden providesfiltration, improving the water qualityof the stormwater that reaches ournatural waterways and optimises thewatering of our gardens from our oftenlimited rainfall. Raingardens can be constructed in anumber of different ways, but generallyconsist of a porous soil layer on top of agravel based drainage layer (separatedby a "transition layer" to stop the finerparticles of soil clogging the drainagelayer), and are usually best planted witha combination of local native shrubsand grasses, but can also be adapted togrow vegetables. 

Rain GardensGawler Environment Centre / 43 High St, Gawler East, SA 5118

Ph: 8115 4620 Email: coordinator@gawlerenvironmentcentre.org.au

Gawler Environment Centre Climate Smart Communities North Project supported by ConservationSA and the Government of South Australia through the Sustainability Grants Program.

Building a raingarden is a simple way to help theenvironment and the health of our local waterways whileproviding a self-watering garden for your backyard.

Useful Information

There is a detailed "guide to raingardenplant selection and placement" that canbe found at: https://www.watersensitivesa.com/wsud-for-your-home-backyard/smart-water-solutions-for-your-home-backyard/raingardens-in-your-backyard/ Or ask a native nursery grower whatgrows best in your area.

Check out some public raingardensthat have been built in South Australia:www.epa.sa.gov.au/environmental_info/water_quality/programs/rain-garden-500 www.westtorrens.sa.gov.au/CWT/content/Environment/Water/Rain_garden_interpretive_trail

References

https://202020vision.com.au/media/162691/wsattg_combined-lr.pdf https://www.naturalresources.sa.gov.au/adelaidemtloftyranges/plants-and-animals/native-plants-animals-and-biodiversity/urban-biodiversity

A vegetable raingarden Image supplied by Melbourne Water

The layers of soil and gravel absorb thestormwater, trapping pollutants andsediments, and the roots of plantsimprove infiltration and permeabilityof the soil, as well as absorbing theexcess nutrients found in thestormwater such as nitrogen.Depending on the amount of waterentering the raingarden compared to itssize and capacity, the raingarden

Building your own raingarden.

There are many styles of raingarden,some examples include: Infiltration raingarden: A gravel filled trench designed to

can be the endpoint of drainage,however in our urban environmentdrainage of excess water during heavyrain events may require that the excessfiltered water is collected in pipes andflows into the stormwater system.

Inground raingarden: An excavated garden lined with a PVCliner to stop water infiltratingsurrounding soil. An inground raingarden is designed tocollect water from a disconnecteddownpipe, rainwater tank overflow orpavement runoff. It contains a slottedpipe connected to a storm water drainin the drainage layer and an overflowpipe on the surface to prevent flooding.

Which native plants to use?

A wide range of native species aresuitable for raingardens. The plantsthat are best suited to raingardens are:

Some native plants that are good atremoving excess nutrients fromstormwater include:

receive stormwater directly froma diverted downpipe or runoff fromsurrounding hard surfaces such as a driveway or paving. An infiltrationraingarden should not be built too closeto permanent structures (i.e. house,garage or shed) as the infiltration of water into the surrounding soils mayaffect building foundations.

Planter Box: An above ground version of an inground raingarden created in a planter box. A planter boxraingarden is positioned to collect waterfrom a diverted downpipe or rainwatertank overflow. Swales: A swale is much like an infiltrationraingarden, but is designed as a smallchannel that conveys water from onepoint to another, and can even be usedto transport stormwater to anotherraingarden elsewhere in your backyard. Vegetable raingarden: Unlike other typical raingardens thatreceive stormwater run-off at surfacelevel, a vegetable raingarden is subirrigated. The garden is created ina planter box, and a diverted downpipesupplies water to the base of theraingarden. This prevents vegetablesfrom being submerged after heavy rain,and supplies water to the vegetablesthrough wicking, in the same way as awicking bed works. A wide range ofvegetables can be grown in yourraingarden including tomatoes, beanslettuce, spinach, cucumber, beetroot,onions and leeks. Herbs such as basiland parsley should also grow well. For detailed instructions on buildingthese styles of raingarden visit:www.melbournewater.com.au/community-and-education/help-protect-environment/raingardens * * Some plants listed on the instruction sheetsfrom Melbourne water may not be ideal inSouth Australia.

Able to tolerate short periods ofinundation followed by longer dryperiods (The indigenous flora of theAdelaide Plains and Mount LoftyRanges are well adapted to wettingand drying cycles.)Are perennial rather than annualHave deep fibrous root systemsCan form understorey if grown withshrubs and trees overhead.

Everlastings (Chrysocephalumapiculatum, C. semipapposum,Helichrysum leucopsideum)Hop Goodenia (Goodenia ovata)Kidney Weed (Dichondra repens)Knobby Club-rush (Ficinia nodosa)Lemon Beauty-heads (Calocephaluscitreus)Rush grasses (Juncus flavidus, J.kraussii, J. pallidus, J. subsecundus)Sedges (Carex appressa, C. inversa)Small-fruit Fan-flower (Scaevolaalbida)

The most successful raingardens areplanted with a broad range of plantsand it is recommended that plants thatare effective at nitrogen removal (suchas those above) make up 50% of yourraingarden, with the other 50% selectedto add variety, biodiversity andresilience to the system.

Diverting water at home Rules and regulations around diverting water on your property can be veryconfusing and you should check with your council to see what theyrecommend. An engineer from the Town of Gawler has provided GEC withadvice relevant to its jurisdiction: There are no restrictions on diverting water from rainwater tanks in togarden beds, the water does not need to be filtered and overflow does notneed to be redirected to storm water. You may choose to manage overflowto further water savings and minimise impact on the rest of the garden. Diverting storm water pipes starts to get tricky as there is potential for crossconnection with SA Water pipes and engaging a certified plumber isrecommended. If you just have downpipes that discharge on to the groundyou can probably extend them to garden beds yourself.