Water-sensitive urban design

Increased peak flow also alters channel morphology and stability, further proliferating sedimentation and drastically reducing biotic richness.

Bioretention systems offer a smaller footprint than other similar measures (e.g. constructed wetlands) and are commonly used to filter and treat runoff prior to it reaching street drains.

The runoff water usually goes through a fine media filter and proceeds downward where it is collected via a perforated pipe leading to downstream waterways or storages.

Vegetation growing in the filter media can prevent erosion and, unlike infiltration systems, bioretention swales are suited for a wide range of soil conditions.

[7] In addition to the filtration and biological uptake functions of bioretention systems, basins also provide extended detention of stormwater to maximise runoff treatment during small to medium flow events.

Infiltration trenches are shallow excavated structures filled with permeable materials such as gravel or rock to create an underground reservoir.

Sand filters are very useful in treating runoff from confined hard surfaces such as car parks and from heavily urbanised and built-up areas.

The design process should consider the provision of detention storage to yield a high hydrologic effectiveness, and discharge control by proper sizing of the perforated underdrain and overflow path.

In flow events greater than their designed discharge, a secondary spillway directs water to a bypass channel or conveyance system, preventing the resuspension of sediments previously trapped in the basin.

These shallow, extensively vegetated water bodies use enhanced sedimentation, fine filtration, and biological uptake to remove these pollutants.

In addition to stormwater treatment, the design criteria for constructed wetlands also include enhanced aesthetic and recreational values, and habitat provision.

[10] The maintenance of constructed wetlands usually includes the removal of sediments and litter from the inlet zone, as well as weed control and occasional macrophyte harvesting to maintain a vigorous vegetation cover.

Ponds and lakes are artificial bodies of open water that are usually created by constructing a dam wall with a weir outlet structure.

[7] Similar to constructed wetlands, they can be used to treat runoff by providing extended detention and allowing sedimentation, absorption of nutrients, and UV disinfection to occur.

[1] Aquatic vegetation plays an important role for the water quality in artificial lakes and ponds in respect of maintaining and regulating the oxygen and nutrient levels.

[12] Bluegreen algae caused by poor water quality and high nutrient levels can be a major threat to the health of lakes.

To ensure the long-term sustainability of lakes and ponds, key issues that should be considered in their design include catchment hydrology and water level, and layout of the pond/lake (oriented to dominant winds to facilitate mixing.

[7] High costs of the planned pond/lake area and of vegetation establishment as well as frequent maintenance requirements can be deterrents to use of ponds and lakes as WSUD measures.

[13] Rain and stormwater from rooftops of buildings can be collected and accessed specifically for purposes such as toilet flushing, laundry, garden watering, and car washing.

[7] Potential water quality issues include atmospheric pollution, bird, and possum droppings, insects e.g. mosquito larvae, roofing material, paints, and detergents.

In Australia, due to the constitutional division of power between the Australian Commonwealth and the States, there is no national legislative requirement for urban water cycle management.

[1] At the state level, planning and environmental legislation broadly promotes ecologically sustainable development, but to varying degrees have only limited requirements for WSUD.

BASIX is an online program that allows users to enter data relating to a residential development, such as location, size, building materials etc.

The document presented an overview of stormwater harvesting and provided guidance on planning and design aspects of integrated landscape-scale strategy as well as technical WSUD practice implementation.

The Sydney Metropolitan Catchment Management Authority also provides tools and resources to support local council adoption of WSUD.

[32] These include Simplified modelling programs are provided by some jurisdictions to assess implementation of WSUD practices in compliance with local regulations.

The WSUD Roadway Retrofit Bioretention System is a small-scale project implemented by the Ku-ring-gai Council in NSW as part of an overall catchment incentive to reduce stormwater pollution.

It is a Greenfield residential development site that has focused its marketing for potential residents on innovative use of stormwater management technologies, following a pilot study by Melbourne Water.

[48] The project combines conventional drainage systems with WSUD measures at the streetscape and sub-catchment level, with the aim of attenuating and treating stormwater flows to protect receiving waters within the development.

Primary treatment of the stormwater is carried out by grass swales and an underground gravel trench system, which collects, infiltrates, and conveys road/roof runoff.