Stormwater Treatment: Why Is It Needed & Methods For Achieving Clear Water

Every time there is a storm, stormwater makes its way across the land, and as it travels, it picks up all sorts of chemicals and pollution – some of which can be harmful. In the absence of any stormwater treatment, this pollution ends up in our waterways, and our oceans.

Stormwater treatment is the process of removing those pollutants from stormwater before they discharge to our waterways and ocean. Here’s what you need to know.

What is stormwater?

A simple definition of stormwater is that it is rainwater – filled with whatever that water comes into contact with. If you’ve ever seen a flood, you’ll likely remember how dirty that water was – that’s stormwater and it’s filled with contaminants. This could include anything from oil the water has picked up on driveways before it’s made its way into the drains in your street, to exposed soil, chemicals, and more.

All of this water has to go somewhere … and it usually ends up in creeks and rivers, which lead to the ocean.

Why we need stormwater treatment?

As a business or property owner, if you don’t treat stormwater, you’re putting your health, your property, and your employees’ health, at risk. In addition, if local councils don’t treat stormwater, they’re putting communities, as well as ocean and river life, and natural habitats at risk.

The pollutants caused by stormwater are harmful and reducing those can enhance the health of not only people, but the planet in general.

Stormwater Treatment Methods

Stormwater must be effectively treated to adhere to government guidelines for Urban stormwater management and there are a few ways this can be done.

  • Retention is where stormwater runoff is stored to allow the contents to settle and lower the risk of flooding.
  • Separation is the use of hydrodynamic separators to separate materials from surface water runoff. This process uses a vortex to separate grit, sand, and silt from the stormwater, while catching nutrients, pollutants, or heavy metals attached to the solids.
  • Screening is where stormwater screens are used as physical barriers to prevent garbage, gross solids, and other large particles from entering a drainage network.
  • Infiltration systems replicate the soil’s natural impact, providing a surface for runoff to soak through, such as engineered soils to trap certain contaminants.
  • Filtration is the use of a filter to remove contaminants from surface water. The water goes through the filter, which catches any contaminants. These can be modified to target specific pollutants as well, including zinc, lead and copper.
Ocean Protect’s Stormwater Management StormFilter® is an example of filtration. It has been designed to clean stormwater through passive filtration. It removes pollutants, using rechargeable, self-cleaning, media-filled cartridges that absorb pollutants from stormwater runoff. This includes hydrocarbons, suspended solids, nutrients, soluble heavy metals, and more.

Stormwater Filtration Assets

Every time it rains, our waterways are at risk of flooding. And we’re not just talking about flooding of the water itself in the event of a substantial downpour, but flooding of contaminants. As the water then moves through our communities, it picks up pollutants in its path – from visible trash, oils and dirt to invisible heavy metals and microplastics. If these flow to our waterways and oceans, we risk the health of both marine life and humans.

That’s why stormwater treatment with stormwater filtration assets is essential – it removes the vast majority of those harmful pollutants to ensure the water that is making it’s way into rivers and oceans is as clean as possible. And thanks to Ocean Protect, there is a wide range of treatment solutions to assist. The following is a brief rundown:

A high-low biofiltration system, this is ideal for use in streetscapes and vegetated areas. Stormwater entering these systems percolates through the plant/ mulch/ soil environment and is treated through a variety of physical, chemical and biological processes before being discharged to downstream drainage systems and/ or waterways.

Using gravity, flow rotation and up-flow membrane filtration in an underground system, this filter can remove high levels of pollutants and has a high flow rate. The name comes from the ‘tentacles’ that catch and remove particles as small as 2 microns.

A gully pit insert (or basket) that catches pollution in stormwater drains, this is a stormwater filtration assets technology that can be adopted as a stand-alone technology or as part of a treatment train. It has a filtration bag, cage, and flow diverter working together to maximise the treated flow and the pollutants captured.

Designed to remove particles larger than 1mm, this is a high capacity trap that uses vortex separation and indirect screening to separate and trap rubbish, hydrocarbons and sediment.

Uses opposing vortices to enhance particle settling, allowing for greater sediment capture and retention. This stormwater filtration asset can treat high flow rates and is designed to remove trash, debris and hydrocarbons from stormwater runoff.

This system is a coalescing separator that removes free oil from contaminated runoff, ideally suited for sites where oil and grease need to be targeted. Can remove oil droplets as small as 10 microns and has a built-in shutoff valve to ensure capacity isn’t exceeded.

A high performance trap, this system is designed to remove sinking or floating debris, as well as fine sediment, oil and grease. It is designed for easy inspection and simple maintenance and is available in a range of models, all of which have been rigorously tested for efficiency.

An ideal option for large spaces, this system removes settleable solids and floating contaminants in an urban runoff system. It can connect to a range of pipe sizes and has an internal weir that bypasses excessive flows within the unit. It is housed inside a concrete manhole.

With an open bottom, plastic infiltration chamber system, this technology maximises available land space to provide economic storage or infiltration below-grade. It ensures space is reserved for green space or development space, and each chamber holds 1.3m³ of storage.

This is one of our most popular stormwater filtration assets.The StormFilter® uses a patented passive filtration system to remove pollutants. It is rechargeable, self-cleaning and absorbs and retains solids, hydrocarbons, nutrients, heavy metals and other pollutants. It is also available in multiple cartridge heights to meet site-specific hydraulic needs.

What Is Stormwater Management?

Stormwater management
is when stormwater runoff is managed for the purpose of quantity and quality
control. Any precipitation that falls from the sky such as rain, hail, or
melting snow that runs off hard surfaces is considered to be stormwater. When
it is absorbed into the soil and filtered, this stormwater will then continue
on until it ultimately replenishes aquifers or reaches a natural body of water such
as streams and rivers.

Whenever soil is
over saturated due to heavy rainfall or floods, the runoff remains on the
surface and flows across the soil. This causes erosion that carries untreated
pollutants such as nutrients, pesticides, and sediments depositing them into creeks,
rivers, wetlands, and larger water bodies such as the ocean.

When stormwater is
blocked from naturally soaking into the ground in developed urban areas by impermeable
surfaces such as sidewalks, roofs, streets, and driveways, it also leads to pollutant
runoff. However, stormwater management techniques such as green vegetated
infrastructure and design is utilised to capture stormwater then reuse to
maintain or restore natural absorption.

There’s always a
change in the natural patterns of runoff as more land is developed.
Construction of buildings, roadways, subdivisions, etc alters the velocity and volume
of natural runoff, meaning there a consistently significant necessity to
properly convey stormwater to where it needs to be.

When natural runoff
infiltration is interrupted, it results in increased runoff rates as well as
localized flooding. Impervious surface areas also often adds polluted water to creeks,
streams, rivers, and other large bodies of water. This increased runoff and decreased
infiltration creates the necessity for robust stormwater management designs which
provide significant benefit to public health and safety as well as environmental

Why Is
Stormwater Management So Important?

The primary
purpose of stormwater management is to reduce this runoff and detain as much as
possible, while removing pollutants to improve the quality of water, which are
both essential to support the function and resiliency of both community health
and the ecosystem.

Stormwater runoff
can include organic matter and bacteria from animal waste and trash, toxic
chemicals like pesticides, oil and grease from roads, and so much more. These
pollutants are ultimately carried by drainage structures and stormwater drains
into our creeks, and rivers into much larger bodies of water, and can be
extremely harmful to our environment.

Ocean Protect’s stormwater
management strategies encompass effective approaches and technologies that reduce
runoff volumes and capture harmful pollutants. Both vegetated and proprietary below
ground solutions are tested, proven and at the forefront of stormwater management

As we protect our
water resources and our ecosystems by instigating effective and robust stormwater
management techniques, we ultimately take care of our environment and invest in
our future. Contact Ocean Protect today to find out more.

What is MUSIC Modelling / Stormwater Modelling?

MUSIC, short for Model for Urban Stormwater Improvement Conceptualisation, is software designed to simulate rainfall and pollution generation which allows urban stormwater professionals to visualise a range of possible strategies for tackling the hydrology and pollution impacts of urban stormwater runoff. It also simulates flow reduction and pollution removal through rain harvesting, sediment basins, bioretention, wetlands, proprietary filtration devices and many other stormwater management systems.

MUSIC Software enables the evaluation of conceptual stormwater management designs to assess how appropriate they are likely to be if used in their proposed catchments. By simulating the proposed stormwater improvement measures, this software can also determine if the proposed systems will ultimately meet the specified water quality objectives. This software simulates water sensitive design, which allows for much easier design and assessment of WSUD in urban developments. 

As a reliable method of predicting the performance of stormwater systems, MUSIC can simulate any size catchment area including urban systems from a single dwelling regional and suburban and even entire towns and cities.

Many organisations from catchment management groups to local councils and governments have introduced aquatic environment protection initiatives within urban areas. While initially the main focus was on pollution sources, attention is now on reducing the amount of pollution in urban stormwater, which has been recognised as a major urban pollutant carrier.

The MUSIC software can simulate the use of a wide range of real-world treatment devices, such as:

Bioretention Systems

These vegetated stormwater filtration systems remove soluble contaminants and particulates via a sand or soil-based medium.

Infiltration Systems

These are unvegetated infiltration systems which have no underdrain that assist with removing contaminants.

Media Filtration Systems

Unvegetated stormwater filtration systems utilise fine granular material such as gravel or sand to remove contaminants.

Gross Pollutant Traps

These are mesh-like devices which are designed for the removal of suspended or floating rubbish or other types of debris that are above 5mm in size.

Buffer Strips

These roadside strips of vegetated land effectively remove medium-sized and coarse suspended particles.

Vegetated Swales

Vegetated swales are open channels which primarily utilise vegetation for the removal of suspended solids.

Ponds & Sedimentation Basins

Open water bodies such as ponds and basins act as temporary stores which will ultimately allow suspended solids to settle.

Rainwater Tanks

Domestic water storage which enables the roof runoff to be captured, stored, and used whenever needed, after contaminants have either been stopped before storage, settled inside the tank, or removed during use of the water.


Heavily vegetated water bodies like wetlands facilitate physical, biological, and chemical processes which ultimately remove soluble and insoluble contaminants as well as fine suspended sediment.

Proprietary Media Cartridge and Membrane Filters

Stormwater treatment systems often installed within Onsite Detention Tanks or standalone precast tanks and use rechargeable, self-cleaning, media-filled cartridges or membrane technology to absorb, physically trap and retain pollutants.  

Since the software was first developed in 2001, MUSIC has been successfully utilised by thousands of working professionals throughout Australia. Contact Ocean Protect today to find out more about the MUSIC stormwater modelling program.

Interested in our design service?

What are Stormwater Quality Improvement Devices (SQIDs) & how do they work?

When prevention of pollutants entering the stormwater drainage system is necessary, Stormwater Quality Improvement Devices or SQIDs are required to reduce the pollutant concentrations.

SQIDs are designed to remove a wide range of pollutants including sediments, metals, oils, nutrients, and gross pollutants from stormwater before it has a chance to join any natural bodies of water. SQIDs are used to implement best practice quality management of stormwater ensuringWater Quality Objectives are met as per the local requirements, protecting downstream rivers, creeks, and other water bodies.

Stormwater management strategies are an important component and will always be needed for the protection of downstream water bodies. If strategies are not employed or lack reasonable potency, things won’t change, and our waterway degradation will continue. Determining factors when it comes to SQIDs include geographic location, local annual precipitation and intensity, evolving waterway management strategies, and newly developed land.

Most SQIDs have been designed for management of pollutant loads during a developments operational phase. However, some regional or developing areas may require on-site stormwater treatment devices to be utilised during the construction phase as a sediment and litter trap. Because SQIDs are often associated with significant on-going maintenance and construction costs, alternative strategies such as source controls should always be considered and evaluated carefully.

Some Types of SQIDs

Constructed Artificial Wetlands

While they generally need to cover quite a large area to effectively remove pollutants, wetlands that have been constructed artificially can produce excellent results with stormwater treatment. It is essential that Artificial Wetlands are preceded by sediment basins which allow them to effectively remove small to large size sediment particles, as well as nutrients and toxicants such as heavy metals.

Gross Pollutant Trap and Trash Rack

Designed to trap coarse pollutants that can be carried by stormwater, a Gross Pollutant Trap or GPT is a device that is installed within the drainage system and typically end of line, or around an identified pollution hot spot as source control. Some are situated above the ground, while other GPTs are fitted below the ground and some with fine screens which trap smaller litter and sediment particles. GPTs help to reduce the amount of minor pollutants such as particulate phosphorus and nitrogen, as well as heavy metals that can often be carried by finer sediment particles.  

A trash rack is often a steel structure installed across an open channel and designed to collect larger items and pollutants or debris. This can include rubbish like glass bottles, containers, and aluminium cans, as well as green waste like leaves, branches, logs, and even dead or alive animals.

Stormwater Pit Inserts/Baskets

Usually installed inside stormwater pits on the roadside or throughout a development, these SQIDs are used to collect leaves, litter, sediment and other associated pollutants.

While SQIDs aren’t the only method of improving the quality of stormwater to protect receiving environments downstream, they certainly are one of the most effective. Other options include elements of Water Sensitive Urban Design including permeable paving, infiltration areas, and grass swales, as well as non-structural measures such as enforcement strategies and education. Contact Ocean Protect today to find out more about SQIDs.

What is Water-Sensitive Urban Design?

An important part of land planning and engineering, Water Sensitive Urban Design or WSUD integrates promotion of water cycle management into the design of urban environments. The coordinated development, management, and planning of resources using WSUD reduces the impact of urban development by allowing the water cycle to function much closer to how it would naturally.

When rain falls in natural environments, the stormwater is generally either absorbed into the ground, utilised by plants, or otherwise evaporated into the atmosphere. Alternatively, when it rains in urban areas, rainwater is stopped from being absorbed into the ground by hard surfaces such as roads, buildings, and impervious areas which ultimately creates stormwater runoff.

As a result of property development, industry practices, vehicles, public activity etc, high levels of pollutants are generated accumulating in urban environments. Stormwater runoff can therefore contain chemicals or other pollutants before it makes its way into the drains and ultimately ending up in our rivers, creeks, and oceans. There are many facets to WSUD with one of the main aims to make use of this valuable resource by improving the ability of capturing, treating, and utilising stormwater to reduce the harm these pollutants cause to waterways.

To reduce the volume of pollution in the stormwater entering waterways there are quite a few different WSUD techniques which can be utilised.

Constructed Wetlands

Commonly located near waterways, wetlands are an area that’s covered by water creating an aquatic ecosystem either at certain times or permanently all year round. Constructed wetland systems have multiple benefits, including providing a method for the stormwater cleansing, stormwater attenuation, while also improving urban amenity as well as biodiversity.

Green Roofs

Often constructed as architectural features in community spaces, a green roof is a vegetated landscape installed on the roof surface which has been built up from a series of layers. They capture and treat stormwater, insulate the building while also improving species diversity.

Infiltration Systems

An area excavated backfilled with a particular porous material compacted to a specific density, allowing collected stormwater runoff to filter into the natural surrounding ground. The water runoff is then soaked into surrounding soil which ultimately improves the groundwater levels.

Porous Pavements

Porous pavements or asphalt increases the permeability of urban surfaces which allows stormwater to pass through to ultimately infiltrate the soil below. Porous pavements also reduce the risk of flood by reducing stormwater volumes directed into stormwater drainage systems.


Also known as bioretention or biofiltration beds, Raingardens improve the health of our waterways by utilising media blends and certain plants to filter stormwater. Commonly situated at a low point on site, raingardens retain a volume of stormwater runoff temporarily, allowing for the removal of much of the pollutants through physical and chemical processes before these pollutants have a chance to wind up in our waterways.


Often used along roadside, centre medians, or nature strips, Swales are linear ground channels which are typically lined with grass or any another type of vegetation. Swales collect, transport, and slow down the flow of stormwater into drains, while also filtering sediment, nutrients, and pollution.

From the smallest of projects to regional scale developments, Water Sensitive Urban Design can be implemented at any scale. By adopting techniques that integrate both minor and major flow paths, WSUD can help areas achieve much greater water sustainability and amenity. Contact Ocean Project today to find out more.

See Also

Why Stormwater360 Australia rebranded to Ocean Protect

Ocean Protect have been leaders in the design, installation and maintenance of stormwater treatment assets and infrastructure for almost two decades. After realising the rapidly increasing urgency to reduce the amount of pollution entering our waterways, the company rebranded from Stormwater360 Australia to Ocean Protect in early 2019 to better reflect their purpose beyond profit – stopping the flow of pollution, including plastic and toxins, to our waterways.

Everytime it rains, an alarming amount of pollutants including tyre dust, heavy metals, nitrogen, cigarette butts and plastics are washed down our drains and swept into our oceans due to insufficient stormwater infrastructure and management. As part of the company’s rebrand, Ocean Protect are committed to lobbying local governments to implement a ‘Zero Litter to Ocean’ policy which will effectively reduce the amount of pollution entering our waterways.

Bringing about changes to legislation will have a real impact through actively raising public awareness and speaking with politicians to make maintenance of stormwater infrastructure and roads a legal and enforceable requirement by 2021. Ocean Protect estimate that this change in legislation will save 500 standard wheelie bins of pollution reaching the ocean per day.

As a result of this renewed focus, the company has already seen five councils including City of Sydney, Burwood Council, Noosa Council and Northern Beaches Council, commit to creating targets which involve the regular maintenance and implementation of local stormwater infrastructure.

Does your StormFilter system hold water permanently?

During a recent StormFilter design, the question came up about whether a StormFilter cartridge system will permanently hold water. The unique design and orifice discharge disc at the base of each cartridge allows the chamber where the cartridges are installed to drain dry between rain events.

The Engineer also asked whether a false floor is required as other systems don’t use a false floor. With the StormFilter system, regardless of the cartridge size or media type, a false floor is always used. The false floor allows us to fix the underdrain manifold in place, create a safe and trip hazard free floor and more importantly eliminates a permanent water pool which essentially can be considered an anaerobic zone.

It can be considered similar to the wet sump GPT situation and hence the limit on accepted nutrient reduction. Permanent water and particulate nutrient loads in time result in dissolved nutrient load (leachate) which can be a problem for receiving water courses. Obviously we want to steer clear of this if at all possible.

The real benefit of not holding water is recognised when leachate is assessed as part of the product performance evaluation. This has been demonstrated time and time again during the StormFilter field assessments both in Australia and the US and forms an integral component of field testing protocols used today.

Please call us on 1300 354 722 for more information.

See Also

Is it possible to locate cartridges in an OSD in a basement?

Ocean Protect has a number of cartridge options that can be located inside an OSD tank within the basement of your project. Unlike other cartridge based filters on the market which can weigh in excess of 250kg’s (when occluded) our StormFilter cartridges are manoeuvrable by hand, especially the lighter PhosphoSorb media cartridges.

Exhausted StormFilter media can be emptied inside the tank and removed with a vacuum truck or by hand if necessary. The empty StormFilter cartridges can then be stacked and lifted out very easily. Once the chamber has been cleaned it is simply a matter of lowering replenished StormFilter cartridges into the chamber and reattaching them to the underdrain manifold. In some cases side access is the only option so lighter and smaller cartridges would be the favourable solution. A simple tripod and hoist is also a good option to help assist in maintenance procedures and on smaller systems eliminates the need for a vacuum truck.

Since the StormFilter system can be located within your OSD it means that a separate precast chamber is not required and therefore the procedure is much simpler in terms of levels and space requirements. For many developments a single car space can represent tens of thousands of dollars in property value, so any additional space saving is desirable.

Please give us a call on 1300 354 722 to get more information. 

See Also