Outlet and distributed approaches

The location of your treatment measures will determine how you maintain and operate your system. Decide whether you will adopt an outlet or a distributed approach to stormwater treatment.

Outlet approach

The traditional approach to stormwater quality treatment involves constructing a sediment pond and wetland at the bottom of a large catchment. 

Although this single-site approach can reduce travel time between maintenance activities, it does not reduce stormwater volumes enough to protect waterway ecosystems from erosion and unnatural disturbances.

The outlet approach is therefore more suited to reducing pollution loads to our bays, rather than protecting our rivers and creeks.

Distributed approach

The distributed approach involves installing a number of smaller and potentially different treatments throughout a catchment. In the case of managing urban hydrology, stormwater treatment measures are best implemented at every scale.


A distributed approach to stormwater pollution treatment has many advantages over the outlet approach. These include:

  • improved protection – more stormwater can be removed through evaporation, transpiration and infiltration, better protecting waterways immediately downstream
  • localised treatment – treatments can specifically target highly polluted sites
  • distributed risk – risk of overall system failure is lower, as the failure of any single treatment usually will not significantly impact total system performance
  • improved removal efficiencies – distributed treatments can remove pollutants from stormwater before it becomes more diluted
  • staged implementation – individual sites can be brought into operation in stages
  • urban greening – gardens and trees are already distributed throughout a catchment, and stormwater can be used to help them grow

Treatment train

A distributed treatment approach will typically incorporate a range of structural treatment types. To more efficiently remove pollutants, a treatment train approach should be considered during each step of the design process, particularly if pre-treatment may be needed.

Treatment train

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