Managing On-Site Water

About this pattern

Water Sensitive Urban Design (WSUD) is a form of water management for on-site storm water and runoff. It involves capturing and storing stormwater, reducing water consumption and impact on local water systems, and improving water quality. This is achieved using grassed or landscaped swales, infiltration trenches and bio-retention systems, gross pollutant traps, wetlands, sediment ponds, rainwater tanks for storm water harvesting and as cooling devices, rain gardens, rooftop greening and urban forests, porous pavements, aquifer recharge and reuse.

Rain gardens and bioswales are vegetated depressions located on gradients. Their main function is the retention and infiltration of stormwater. Acting as a filter for runoff from permeable surfaces, they reduce pollutants which enter storm systems. They are a way to manage bioretention areas by capturing and holding roof and road runoff but will not maintain optimal drainage rates if soils become compacted, it is therefore important to minimize foot traffic in this area, except walking for maintenance. Regular applications of mulch maximize the swale’s ability to capture and break down contaminants. Rain garden plantings should not be fertilized to prevent excess nutrients run-off.

Structural soils are an engineered soil mix designed to allow three functions: reduce pavement heaving and breakage; improve stormwater infiltration; and improve tree growth.  Structural soils can also improve stormwater infiltration if covered with a porous paving material (see Seattle Green Factor (2008 p.4) for more information). Stormwater planters are containers designed to capture and either retain or filtrate stormwater, based on their design. The amount and frequency of water captured depends on storm events, so they should be populated with a variety of plants adapted to both wet and dry conditions. Visually, they can be striking landscape features providing a high functional value.

Properly designed soil conditions are required to achieve stormwater infiltration and increased plant growth. Deep soil is considered to be that which is penetrating to base rock and water table. In planters, soil depth should be a minimum of 600mm for shrubs and ground covers and minimum of one metre for small trees.

For improving water efficiency: rain sensors fitted to irrigation systems can reduce water use; amalgamated planter beds will improve efficiency of irrigation systems and mulch in garden beds reduces water evaporation from soils.

Permeable Paving

Permeable paving allows sites to infiltrate stormwater in a way similar to natural systems. Permeable pavements also restrict non-point source pollution from entering surface water bodies, which helps keep creeks and streams clean. Permeable pavements also contribute towards healthier plantings because root systems are aerated. Permeable asphalt can be used in some cases to replace traditional asphalt and allow for infiltration of stormwater.

Permeable concrete can be used in place of impervious concrete in many non-driving situations. Its use in parking lots can help reduce the amount of stormwater runoff and non-point source pollution.

Instead of pavers, the top layer can be either 150mm of Permeable Asphalt or 150mm of Permeable Concrete, layered over 150mm of Open Graded Aggregate, layered over Geotextile on the existing subgrade.

Irrigation

An integrated irrigation system must suit site the condition and the requirements of the landscape. Efficient irrigation systems include: rainwater storage tanks; appropriate species selection; soil depth and soil quality to help minimise watering requirements and use of recycled water. TANKLESS® Underground Rainwater Storage* is one means to collect quality surface rainwater.

Using Storm Water for Wetlands and Water Features

On-site storm water management can ideally finish in wetlands and water features.

• Wetlands contribute important wildlife habitats and pleasant recreation areas. 
• Water features can add interest to paved public spaces. Their wide range of design styles and possible functional attributes can make them useful elements for cooling and aesthetics. Water features can also be engineered to clean & aerate water as well as recycle it.

Sustainable Sydney 2030 targets include 10% of the City’s water to come from recycled sources and a 50% reduction in the pollution being discharged into waterways. Within landscaped areas, Water Sensitive Urban Design (WSUD) provides the means to achieve these targets.

Pattern Conditions

Enablers:

• Local & State Government legislative requirements regarding on-site water management, such as Local Environment Plans requiring on-site roof water storage for irrigation, and State Environment Plans requiring site by site water pollution controls for river catchments.

Constraints:

• Any water feature should use roof runoff or on-site stormwater for at least 50% of its annual flow.
• Urban water features will require child safety considerations.

Commoning Concerns

Access: Controlled in private developments; general access in public space.

Use: Water storage, irrigation, amenity, wildlife habitat.

Benefit: Reduced water pollution, flooding, cooling public space.

Care: Individual property owners, Local Government, community.

Responsibility: Individual property owners, Local Government, Body Corporate.

Ownership: Individual property owners, Body Corporate of estate.