Water wise in Higgins

Getting started

When Helen and Ian decided in 2001 to redesign their garden and make it more water wise, the first thing they did was draw a plan of their block. They identified access routes and activity areas, as well as drainage lines. This initial planning proved crucial to developing an integrated house, garden and water system.

They then replaced thirsty lawns and exotic plants with ground covers (Myoporum, Grevillea and Correa) and low water, drought-tolerant shrubs (Westringia, Callistemon, Correa, Banksia, Acacia, Indigofera and Eremophila), and replaced their sprinklers with a water-efficient drip irrigation system. They also mulched extensively to conserve moisture in the soil and suppress weeds.

And finally, they looked at utilising rainwater, greywater and stormwater.

Rainwater

Rainwater from the house roof (180m²) is collected by all four downpipes and drains into three storage tanks with a total capacity of 5,500 litres.

When it rains, the first 30 litres of water from the roof is diverted away from the rainwater tanks and into a ‘first flush’ device, as it may contain decomposed insects, bird and animal droppings, tannic acid and other chemical pollutants.

Water collected in the tanks is pumped through the garden via the drip irrigation system and used on garden beds with plants sensitive to alkalinity. It is also used to top up the pond during long periods of dry weather.

Every month solids collected in the ‘first flush’ diverter pipes are removed, and every three months the rainwater tank inlet screens are cleaned.

Greywater

Greywater from the laundry passes through a mesh screen to filter lint before being held in a recycled 150-litre tank for 12 to 24 hours to allow any sediment to settle. The water is then pumped through a sand filter and stored in a second 150-litre tank from where it is pumped through an in-line filter to the garden drip irrigation system.

Non-phosphorus, low salt laundry detergent is used to protect plants with low nutrient tolerance. Many Australian native plants do not like phosphorous, and sodium from salts can affect plant metabolism and significantly reduce soil drainage capacity.

Twice a year the sand filter is backwashed and sediment is removed from the system. The in-line disc filter is cleaned once a week in summer and once every two to three weeks at other times.

Note: To minimise the potential to transmit disease or create environmental harm, greywater should not be distributed using a sprinkler or micro-spray, and should not be used to water the vegetable garden. It is best to drip it at the base of plants or set up a subsurface irrigation system.

For more information see Greywater Use: Guidelines for residential properties in Canberra (December 2004)

Stormwater

Aware that impervious areas (e.g. roofs, concrete surfaces) and stormwater pipes alter the natural flow of water, Helen and Ian decided to introduce surfaces and structures (swales*, pond) that would aid the absorption of stormwater into their block and slow the water’s entry into the stormwater system. They wanted to help reduce the peaks of stormwater flow and improve the quality of water entering downstream waterways.

They replaced their concrete driveway with open-jointed pavers and directed any overflow to gravel lined swales. These meander along the garden’s natural drainage lines and slow rainwater so there is a better chance of it being absorbed.

Helen and Ian disconnected the garage roof rainwater downpipe from the stormwater pipe. Water collected on this roof now flows into the swales, along with any overflow from the rainwater tanks. They also replaced concrete paths with porous, weathered granite pathways.

All the drainage from the block, including the rainwater tank overflows, is directed to the pond.

Note: A swale is a shallow, open channel of gravel, grass or other vegetation that conveys stormwater.

Pond

In the lower north-west corner of the block is a large 16m² pond which provides extended detention of stormwater as well as micro-habitats for a range of pond life (frogs, Dragonflies and Damsel flies).

The increased infiltration of stormwater via the swales and pavers, plus the detention of stormwater in the pond, has reduced peak discharge from the block by 90% for storm events with a return frequency of 1 in 3 years. Reducing flood peaks lessens the impact on habitats and biodiversity in downstream waterways.

The pond is fitted with a V notch spillway that connects to the public stormwater drain along the block boundary. This extends the time of storm discharge from a few minutes for the normal downpipe based system, to 6 to 9 hours. As the pond level rises with stored water, the rate of discharge increases, thereby protecting the pond bank from scouring during extreme storm events, and the neighbours from potential seepage!

Pond plants, including Schoenoplectus, Eleocharus, Juncus, Marsilea and Lythrum emergent and Myriophylum submergent plants, provide habitat for pond-life and help maintain well-oxygenated water that is low in suspended solids and nutrients.

Bird life

The garden sustains a great diversity of flowering plants and attracts Wattlebirds, Crimson and Eastern Parrots, Galahs, Cockatoos, Silver Eyes, Wrens, Thornbills, Magpies, Peewees, Crested Pigeons, Currawongs and Blackbirds.

The diverse range of birds bathing in the pond, as well as the evening frog chorus, is a continuous delight!