- Stormwater is water from rain or storm events that flows off a house or building site.
- Stormwater can cause problems downstream when peak events cause flooding. It can also be a source of pollution when litter, sediment, nutrients and chemicals are washed into waterways.
- But stormwater can be a valuable resource. Managing stormwater on your site can reduce your use of potable water and your water bills, and improve environmental outcomes.
- Minimising hard surfaces on your site, along with careful landscaping, can help to slow the movement of stormwater and keep it on your site, for example, to water gardens.
- Harvesting rainwater for use in your home also reduces stormwater runoff.
- Paying attention to the use of chemicals in your home and to site management during construction can reduce the contamination of stormwater.
Stormwater is the water that drains off a house site from the rain that falls on the building roof and land, and everything that the water carries with it. This can include soil, organic matter, litter, fertilisers from gardens and oil residues from driveways, which can pollute downstream waterways. Rainwater refers only to the rain that falls on the roof, which is usually cleaner.
Poorly managed stormwater can cause problems on and off site through erosion and the transportation of pollutants to downstream waterways. In Australia, the stormwater system is separate from the sewer system. Unlike sewage, stormwater is generally not treated before being discharged to waterways and the sea.
But stormwater can be a valuable resource. Well-managed stormwater can replace imported water for household uses where high-quality water is not required, such as garden watering. An expanded garden improves habitat for native wildlife and can make the area surrounding the house cooler in summer. Using stormwater can save potable water and decrease water bills. It can also have broader environmental benefits, including:
- reduced flooding
- cleaner rivers, lakes and beaches that are safer for swimming
- a healthier environment for plants and animals.
Subject to local government regulations, a homeowner can take simple steps to manage stormwater and reduce their environmental impact.
Photo: Edwina Robinson
The traditional approach
The traditional stormwater management response relied on conveyancing. Water was conveyed by a pipe or channel from a collection area (for example, house and street) to a discharge point (for example, the nearest ocean, creek, river, or lake). The conveyancing system sought to remove the most water (high quantity) from a site in the shortest time possible (high velocity).
The traditional system of conveyancing is highly effective in reducing stormwater nuisance and flooding on site, unless the pipes get blocked. But it merely transfers the problem to the other end of the pipe and ultimately upsets local water balance. Stormwater is carried rapidly with its suspended litter, oil, sediment and nutrients, and dumped into a receiving waterbody that then becomes flooded and temporarily polluted because all the stormwater arrives at one time.
Water-sensitive urban design
Water-sensitive urban design (WSUD) seeks to imitate the natural water balance on site before the land was built on. WSUD slows stormwater runoff so that it can be used and filtered on site. The water eventually reaches the river, lake or ocean, but has been cleaned and filtered by the soil and used by plants before it gets there.
With WSUD, the extent of hard surfaces is minimised so that the least water flows off site into the stormwater system. For the individual household, options such as permeable paving on driveways and footpaths, garden beds designed for infiltration (raingardens), lawns and vegetation, swales and soakwells can detain stormwater and increase percolation into the soil.
In some cases, it may be advisable to place perforated pipes beneath infiltration areas to direct excess stormwater to the stormwater system (refer to References and additional reading).
Photo: Edwina Robinson
Things to consider
WSUD is applicable on all sites, but the degree of application varies according to the site’s opportunities and constraints. All sites should be able to maximise permeable surfaces such as garden beds, lawns, porous paving and paths.
Before installing subsurface units such as soakwells and infiltration trenches, consider the following matters for your site:
- Regulations — Check with your local government before employing WSUD solutions. Some aspects of WSUD may conflict with local government drainage regulations.
- Soil type — Check the soil type, which affects the efficiency of some WSUD solutions. Sandy soils are excellent for infiltration, but clay soils tend to become waterlogged. For example, water sensitive design in heavy clay soils may need to be supplemented with traditional conveyancing methods.
- Soil depth — Ensure that the soil has sufficient depth. Areas with shallow soil underlain by impervious rock such as granite, shale or limestone may impede infiltration and may require some stormwater pipes to remove water for discharge off-site.
- Groundwater — Determine the depth to groundwater. A high groundwater table may reduce the effectiveness of infiltration methods during storms.
- Slope — Ensure that the stormwater design accounts for the terrain. Severe slopes increase runoff velocities.
To conserve and retain water on your site:
- Retain vegetation, particularly deep-rooted trees. They lower the water table, bind the soil, filter nutrients, decrease runoff velocities, capture sediment and reduce the potential for dryland salinity.
- Minimise the area of impervious surfaces, such as paved areas, roofs, and concrete driveways.
- Include permeable paving, pebble paths, infiltration trenches, soakwells, lawns, garden areas, and swales in your landscaping.
- Grade impervious surfaces, such as driveways, during construction to drain to vegetated areas.
- Divert excess overflow from hard surfaces such as driveways, patios and roofs through downpipes to a raingarden to filter water before it enters local waterways through the stormwater system.
- Harvest and store roof water for use (refer to Rainwater for further information).
To reduce the chance of flooding:
- Do not build on floodplains, as the land may be periodically subject to inundation and may have a high water table. Local government can advise on the 1-in-100-year flood level.
- Include on-site detention facilities to capture stormwater runoff. The facilities, usually large concrete basins built beneath driveways, are designed to capture stormwater runoff from a residential lot and hold it a little longer to reduce the impact of downstream flooding. The stored water drains slowly through a small opening near the base of the tank to the stormwater system. When many properties in flood prone areas have these detention systems, the downstream flood ‘peak’ during large storms is reduced and flood damage minimised. Local government sets regulations for on-site detention systems; check with your local government to find out if your new home needs one.
Reducing water contaminants
To reduce contamination of the stormwater leaving your site:
- Avoid cut and fill on your block when preparing the building foundations. Try to maintain the existing topography and drainage pattern.
- Reduce erosion potential during building works. Use sediment traps and divert ‘clean’ stormwater around the disturbed site.
- Take care with the substances used on your land as they can end up in the stormwater. Do not overuse fertilisers, herbicides and pesticides; follow the manufacturer’s instructions on the amount and frequency of application. Look for organic alternatives.
- Avoid using solvent-based paints. Plant-based or water-based paints are the most environmentally benign. After using water-based paints, clean brushes and equipment on a lawn area to trap contaminants before they reach waterways.
- Ensure there are no illegal cross-connections of sewer and stormwater drains. This can cause sewage overflows on your property during heavy rain.
- Visit a car wash that recycles wash water. If this is not an option wash your car on the lawn or on an area that drains to lawn. The nutrients (mostly phosphates and nitrates) in the detergent fertilise the lawn instead of degrading waterways. Note that many native plants do not tolerate detergents.
These recent examples of neighbourhood and subdivision scale water-sensitive designs show that the principles of WSUD can be applied at any scale.
- Christie Walk, an ‘eco-city’ development in inner-city Adelaide, has 27 dwellings with a mixture of townhouses, apartments, and strawbale cottages. All stormwater from roofs, balconies and impervious surfaces is collected in 2 underground tanks below car parking areas, and reused for toilet flushing, and irrigation after filtration and disinfection.
- Mawson Lakes, a growing suburb in outer Adelaide, has about 4500 dwellings and retail, commercial, education and recreation facilities. Stormwater runoff is treated in natural wetlands and used to fill lakes within the development. Wastewater and stormwater is collected, treated, and supplied to all houses, industries and open spaces by dual reticulation for outdoor water use and toilet flushing. Non-potable water supplies are seasonally balanced by using aquifers to store surplus stormwater and treated wastewater for retrieval during summer and dry seasons.
- Baltusrol Crescent (pictured), off a suburban street in south-eastern Melbourne, comprises household lots each with a bioretention system. Gravel beds and vegetated areas drain and filter the stormwater that lands on each property before it slowly passes into conventional stormwater drainage beneath the road.
Photo: Melbourne Water
References and additional reading
- Argue J (ed) (2009). Water sensitive urban design: basic procedures for ’source control’ of stormwater: a handbook for Australian practice, Urban Water Resources Centre, University of South Australia, Adelaide.
- Build, Stormwater systems.
- Hatt B, Deletic A and Fletcher T (2004). Integrated stormwater treatment and re-use systems: inventory of Australian practice. Technical report 04/1, CRC for Catchment Hydrology, Monash University, Clayton, Victoria.
- Lloyd S, Wong T and Chesterfield C (2002). Water sensitive urban design: a stormwater management perspective. Industry report, 02/10, CRC for Catchment Hydrology, Monash University, Clayton, Victoria.
- McQuire S (2008). Water not down the drain: a guide to using rainwater and greywater at home. Alternative Technology Association, Melbourne.
- Melbourne Water, Raingardens.
- Melbourne Water, Stormwater management.
- Mobbs M (1998). Sustainable house: living for our future, Choice Books, Marrickville, NSW.
- Renew, Put your stormwater to use.
- New South Wales Government (2010). State of the catchments (SOC): river ecosystems Sydney metropolitan systems [PDF].
- Upper Parramatta River Catchment Trust (2003). What is on-site stormwater detention? Parramatta, New South Wales.
- Witheridge G (2020). A public guide to managing stormwater drainage on residential properties [PDF], Catchments & Creeks Pty Ltd, Brisbane, Queensland.
- Review Rainwater to discover how you can capture and use this resource in your home.
- Explore Landscaping and garden design for ideas on water sensitive gardens.
- Visit Sediment control for tips on managing stormwater during construction.
Original author: Scott Woodcock
Contributing authors: Steve Shackel
Updated: Monique Retamal 2013