Water Sensitive Design
WATER SENSITIVE URBAN DESIGN
Water Sensitive Urban Design (WSUD) is a storage-orientated system that provides for temporary retention of stormwater on site. WSUD seeks to approximate the natural water balance on-site prior to the land being built on. It achieves this by slowing the water velocity of stormwater run-off, providing natural filtration, storage and infiltration.
The objective is to minimise impervious surfaces so that the least amount of water flows off-site into the stormwater system. At the scale of the individual housing lot, WSUD uses permeable paving, infiltration trenches, soakwells, lawn, garden areas and swales to detain the water and allow it to percolate into the soil. The slope of the block and the depth and type of soil determine the application of each of these practices.
THINGS TO CONSIDER
Water Sensitive Design is applicable on all sites but the degree of application will vary 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. When seeking to install sub surface units such as soakwells and infiltration trenches the following things should be considered.
SITE
- Soil Type - check the soil type. Sandy soils are excellent for infiltration but clay soils tend to become waterlogged. This will affect the efficiency of some of the water sensitive design solutions. For example, water sensitive design in heavy clay soils may need to be supplemented with traditional conveyancing methods.
- Soil Depth - ensure that you have sufficient soil 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 as severe slopes increase run-off velocities.
- Regulations - check with Council before employing water sensitive design solutions. Some components of WSUD may conflict with local government drainage regulations.
OTHER DESIGN SUGGESTIONS
- Ensure there are no illegal cross connections of sewer and stormwater drains.
- Prevent rain from washing sediment (e.g. sand, soil) into stormwater with a roof, tarpaulin or awning.
- Divert stormwater from driveways, paths and other impervious surfaces to vegetated areas to catch, filter and infiltrate water rather than directing water to the stormwater system.
MEASURES TO PROMOTE WATER CONSERVATION
* Appropriate landscaping [See: Outdoor Water Use; Sustainable Landscape]
* Water harvesting [See: Rainwater]
* Stormwater and greywater recycling. [See: Wastewater Re-use]
GARDEN DESIGN
Group plants with similar water needs together. Divide plants into high, medium and low water-use zones in your garden.
EXAMPLES OF PLANTS FOR WATER-USE ZONES
- High water-use: Lawns, vegetables, fruit trees, exotic shrubs like azaleas and camellias, flowering herbaceous annuals and many bulbs.
- Medium water-use: Hardy vegetables like pumpkins and potatoes, hardy fruit trees and vines like nut trees and grapes, many herbs, some exotic shrubs, most grey or hairy leafed (tomentous) plants, roses and daisies.
- Low water-use: Most Australian natives including banksias, grevilleas and eucalypts. Succulents and cacti, olive trees and some exotic ornamentals such as bougainvillea.
- Plant trees to create natural shade and windbreaks to reduce evaporation. High water-use plants are best located where they can be sheltered from drying winds and strong sunlight.
- Direct rainwater run off from downpipes towards high water-use areas.
SOIL IMPROVEMENT
SOIL TYPES AND WATER AVAILABILITY
- Soil types differ in their ability to retain water that can be used by plants. This is known as the water availability of a soil.
- Water holding capacity is determined by the texture of the soil. Finer soils have a greater capacity to hold water due to their greater particle surface area.
- There are three main soil types: sand, loam and clay. Sandy soils drain rapidly, clay soils hold water but make it difficult for many plants to grow. A soil with plenty of organic matter and a mixture of fine and coarse particles that form "peds" is ideal.
- Hardy, deep rooted plants can help break up poor soils and adding composted organic matter will encourage microbial activity and worms to improve soil condition and moisture retention.
- Organic treatments in various forms are available. Their benefits in encouraging microbial activity and soil remediation are well documented. Contact local permaculture, organic or biodynamic farming groups for more information.
SOIL TESTING
A simple test to identify soil type is to take a handful of soil from the garden and add just enough water to mould it into a ball. Test soil from various sites and from different depths in the garden.
- Sandy soils crumble and will not form a ball. They are light coloured, have little or no smell. Water drains away rapidly and they are low in nutrients.
- Loam soils will form a ball that is friable, usually brown with a pleasantly 'earthy' smell. Holds and drains water well and provides good levels of nutrients. Best for plants.
- Clay soils ball easily and range in colour from white to red or dark brown. Clay has fine, dense particles that do not allow water to soak in easily and which become hard and resist water when dry. They may be high in nutrients that are unavailable to most plants.
- Garden centres can usually provide advice on the soil type(s) in your local area.
IMPROVING SOIL
- Water and nutrient holding capacity of sand and clay soils can be improved by the addition of organic matter such as manure, leaf mould and compost. Dig in to a depth of 15 to 25 cm.
- Gypsum and sand added to clay soils help break the clay into clumps, improving air space and drainage. Add gypsum at the rate of 0.5 to 1.0 kg per square metre. A combination of gypsum, sand and composted organic matter will produce the best results in clay soils.
- Chemical additives often produce a "quick fix" but may have adverse environmental impacts in the medium or long term. Natural methods are better.
REDUCE LAWN AREA
- Lawns consume up to 90 percent of water and most of the energy used in most gardens. They also take the greatest amount of time and money to maintain. Lawns need mowing, weeding, edging & fertilizing, and equipment requires fuel and maintenance.
- Reducing lawn area is the easiest way to save water. Create garden beds, or mulch areas that are used infrequently or where grass grows poorly.
- Replace lawn areas with porous paving, pebbles or drought-tolerant ground covers such as prostrate grevilleas, snake vine (Hibbertia scandens), or myoporum. Seek advice at your local plant nursery.
WAYS TO REDUCE WATER USE ON LAWNS
- Different grass types have different watering needs. Select a turf that needs less water. Ask your local plant nursery for the most suitable low water species for your climate and soil type.
- Do not "scalp" the lawn. Set your mower to cut 4 cm or higher. This encourages a deeper root system and the longer grass blades shade the soil, reducing evaporation.
- Only water when the lawn is showing signs of stress. Long, slow soakings that allow water to penetrate to a depth of about 15 cm will encourage a deeper, more hardy root system.
- A lightly fertilised lawn uses up to 30 percent less water than an unfertilised lawn of the same grass type. A diluted spray of the liquid drained from your composting worm farm (or purchased from a commercial vermiculture operation) is ideal fertiliser. It returns your waste to the soil and plants.
- Drip irrigation is the most efficient system as it delivers water to the roots of individual plants and minimises evaporation and wind drift.
- Water-storing crystals can hold hundreds of times their weight in water. When mixed with water they form a soft gel and retain water that provides a reservoir of moisture for plant roots during dry periods. There are also products that can be sprayed on to plants' surfaces to reduce sunburn and water loss.
- Soil wetting agents allow water to penetrate deeply into soil.
BEYOND THE GARDEN
- Water is used outdoors for activities other than gardening and these also provide opportunities for savings.
- Wash your car, or boat at a car wash that recycles water and detergents. If washing the car (or dog) at home, washing it on the lawn prevents water and detergent flowing down the drain. Choose a different place on the lawn each time.
- Lawns have a limited ability to uptake the nutrients from detergents. If the lawn becomes water-logged or deteriorates, your car may be compacting the soil or the nutrient levels are too high. Aerate the lawn and switch to the car wash for a few months.
- Swimming pool covers significantly reduce evaporative losses and can save between 11 thousand and 30 thousand litres of water a year.
- Use a broom instead of a hose to clean paths and the outside of buildings.
The materials used to build our homes, can have significant health and environmental effects. these often extend far beyond the specific context of their end-use. Usually the impact of materials used is dictated by the processes adopted to extract, process and transport them to the site.