Water Sensitive Urban Design (WSUD)

The rapid transformation of rural land into urban areas with hard surfaces means less rainwater is absorbed into the ground. During rain events, the increased volume of fast-moving urban runoff (stormwater) collects pollutants and flows into stormwater drains that eventually lead to our local waterways.

Water Sensitive Urban Design (WSUD) is the approach adopted by Council to manage stormwater and reduce the impact it has on waterways. WSUD is based on a scientific approach that is designed to integrate the urban water cycle with the built and natural landscape, keeping water in the landscape and providing environmental benefits.

With more than 26 kilometres of open drainage and 720 kilometres of stormwater pipes in the Camden Local Government Area that drain to the Nepean River and Wianamatta South Creek, it is important to understand what WSUD assets are and how they function.

Water Sensitive Urban Design (WSUD) Operational Guidelines

To better understand stormwater treatment measures and provide clarity for Council and the community on how these should be maintained, Council has developed the Water Sensitive Urban Design (WSUD) Operational Guidelines.

This document identifies the twelve main types of WSUD treatment assets and helps our teams responsible for Council’s parks, street sweeping and reserves to maintain these important assets.

The document will also help guide you on how to best operate any stormwater assets on your property, such as rainwater tanks or biofilters (raingardens).

WSUD Operational Guidelines

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Rainwater Tanks

A rainwater tank captures and stores roof water for reuse on-site. It may also function as local flood control.

The rainwater tank should fill and empty regularly to avoid health hazards associated with water being stored in tanks for extended periods of time.

Before installing a rainwater tank, read the State Environmental Planning Policy (Exempt and Complying Development Codes) 2008 for the latest information about exempt and complying development. You can also check site-specific regulations with Council.

To clean or maintain a rainwater tank, engage a licensed plumber or visit Rainwater Harvesting Australia for videos on rainwater tank maintenance.

Biofilters (Bioretention Systems or Raingardens)

Biofilters (also referred to as bioretention systems or raingardens) are engineered garden beds that filter stormwater runoff through a vegetated filter media.

Treatment of stormwater occurs as the water infiltrates/soaks down vertically through the system, where plant roots and microbes in the soil naturally remove pollutants. Biofilters can be constructed as basins (in raised beds, planter boxes or at ground level), swales or medians.

Biofilter Street Tree Pits

Biofilter street tree pits are small biofilter systems with filter media and underdrainage fitted into the street tree pit. The pits direct stormwater to the root zone of the street trees, providing the trees with an important water supply.

They are very similar to biofilters in design, operation and inspection and maintenance requirements.

Wetlands

A wetland is a vegetated wet basin (or series of wet basins) that filters and treats stormwater before it enters our waterways.

The plants in a wetland capture fine particles and absorb nutrients from stormwater by slowing and filtering the water and allowing sediment to settle.

Wetlands commonly have a gross pollutant and sediment trap upstream of them to capture coarse material, like litter, before stormwater enters the planted areas.

Floating Wetlands

Floating wetlands are buoyant rafts planted with wetland plants that assist in the removal of pollutants from stormwater. They are commonly retrofitted into ponds or wetlands that are experiencing water quality issues.

Floating wetland rafts remove common waterway pollutants and regulate the oxygen, temperature and erosion potential of water.

Vegetated Buffer Strips or Swales

Vegetated buffer strips and swales are simple stormwater transfer systems that treat runoff through filtration and sediment capture.

Buffer strips are vegetated surfaces (usually grassed) that allow runoff to flow towards a downstream outlet.

Swales generally form a sloped vegetated channel that conveys stormwater along a long path.

Both systems act to slow and filter stormwater as it flows through vegetation, capturing large sediments and absorbing stormwater runoff.

On-site Stormwater Detention

On-site Stormwater Detention (OSD) is the temporary storage and controlled release of stormwater generated on-site. OSD systems are designed to temporarily store and slow down the rate of stormwater runoff from a property, so it does not worsen flooding downstream.

OSD systems can be above or below ground and should remain empty except during periods of rainfall and shortly after the rainfall ceases. In most rain events, ponding of water should not last more than 2 hours.

In some cases, below ground OSD systems can also include filter cartridges that assist with the removal of pollutants.

Gross Pollutant Traps (GPTs)

Gross Pollutant Traps (GPTs) capture litter, sediment and debris that is washed into the stormwater system. Most GPTs are proprietary products that vary in exact form and function but are comprised of similar components. GPTs are required to be maintained regularly by removing and disposing of any captured material to ensure that they function well and continue to remove pollutants from our waterways.

Filter Cartridges

Filter cartridges include sand filters and proprietary products that are designed to filter finer pollutants such as fine solids, soluble heavy metals, oils and nutrients.

Filter cartridges may require a GPT upstream or include pre-treatment within the unit to prevent clogging from other gross pollutants. They are typically located offline as they are designed to treat limited flow rates. This means that during periods of high flow e.g. storm events, the flows will bypass the filter cartridges and not be treated.

Pit Inserts

These devices are fitted into stormwater drainage pits to capture litter, debris and other gross pollutants from urban runoff. They are often used as primary treatment of stormwater before it undergoes further treatment, for example in a wetland or biofilter.

Permeable Paving

Permeable paving allows water to infiltrate through the paving, reducing the volume of runoff from hard surfaces such as roads, car parks and footpaths. This reduces local flooding and surface ponding, and promotes infiltration into the soil.

Temporary Sediment Basins

Temporary sediment basins are installed during the construction stage of a development to help manage stormwater impacts during construction. These open water bodies treat stormwater by allowing coarse sediments and particles to settle.

Once construction in the catchment is completed, temporary sediment basins are converted into biofilters and on-site stormwater detention systems.