Stormwater management for SEQ warehouses: GPTs, filtration, detention and why they're required
By Brenscot Builders | Last reviewed September 2026
Building a warehouse replaces grass and soil with roof, hardstand and car park. Rain that once soaked in now runs off quickly, carrying litter, sediment, oils and nutrients into drains and creeks and, across much of South East Queensland, on to Moreton Bay.
That is why councils and the State planning framework require stormwater management on industrial sites. It deals with two separate problems: water quality (what is in the runoff) and water quantity (how much leaves the site and how fast). They need different devices, and both have a large effect on site layout and levels, so the stormwater design has to be managed from the very start of a project.
The short answer
Most new warehouse developments in SEQ must treat stormwater to the State Planning Policy targets and control the rate at which it leaves the site. Treatment is done with a series of devices, typically a gross pollutant trap followed by either a bioretention basin or a proprietary filter. Flow is controlled with detention storage. Which devices you need depends on the council, the site and what infrastructure the estate already provides. The stormwater works themselves are usually built under an operational works approval, a separate development permit with its own assessment period.
Why stormwater works are required
Water quality
The State Planning Policy (July 2017) sets stormwater management design objectives. In South East Queensland, development must reduce the average annual pollutant load in runoff, compared with the same development untreated, by:
| Pollutant | Minimum reduction |
|---|---|
| Total suspended solids (sediment) | 80% |
| Total phosphorus | 60% |
| Total nitrogen | 45% |
| Gross pollutants larger than 5 mm | 90% |
These objectives apply to a material change of use for an urban purpose on a site of 2,500 m2 or more where the impervious area will exceed 25% of the net developable area. Almost every new warehouse meets that test. Councils apply the objectives through their planning schemes and may set additional requirements.
A new draft State Planning Policy was released for consultation in August 2026. The July 2017 policy remains in force until a new one takes effect.
Compliance is normally demonstrated by the civil engineer using MUSIC, a stormwater quality modelling program, following the Water by Design MUSIC Modelling Guidelines and the council's own parameters.
Water quantity
A large roof and hardstand shed water much faster than open ground. If that flow goes straight into the street drainage it can overload pipes and flood downstream properties. Councils therefore generally require the development to discharge to a lawful point of discharge and to show that it will not cause a legal nuisance (damage or interference a neighbour could take action over) or worsen flooding for others. This part of the design follows the Queensland Urban Drainage Manual (QUDM) and the council's drainage standards. Where the downstream system doesn't have capacity, on-site detention is needed.
During construction
Erosion and sediment control during construction is a separate, temporary obligation. The reference in SEQ is the International Erosion Control Association (Australasia) Best Practice Erosion and Sediment Control guideline (2008), and the Environmental Protection Act 1994 imposes a general environmental duty to take all reasonable and practicable measures to prevent or minimise environmental harm. Don't confuse the temporary construction-phase controls with the permanent devices that remain after handover.
Think "treatment train", not one device
No single device removes everything, so treatment is arranged in sequence:
- Rain falls on roof and hardstand
- Pits and pipes collect the flow
- A gross pollutant trap removes litter and coarse sediment
- Finer treatment follows, through a bioretention basin or a proprietary filter system
- Detention storage holds back the peak flow and releases it slowly
- Water leaves through the lawful point of discharge, such as the council drain or the estate's stormwater system
The order and combination vary. Clean roof water may bypass some treatment or go to rainwater tanks. Wash bays are a different matter: wash water is trade waste, not stormwater. It generally has to drain through an oil and solids separator to sewer under a trade waste approval from Urban Utilities or Unitywater, and the bay generally has to be roofed and bunded, or otherwise arranged, so stormwater cannot enter the sewer. Refuelling areas have their own containment and treatment requirements. Confirm these with the civil engineer and the water utility.
Gross pollutant traps (GPTs)
What it is: a device that physically traps litter, leaves, plastics and coarse sediment, generally material larger than 5 mm, before it travels further into the drainage system.
How it works: runoff enters a chamber or screened structure. Screens or baffles hold back the solids while water passes through. Types range from baskets fitted inside stormwater pits to large underground units on the main outlet pipe.
Why warehouse sites need them:
- Industrial yards shed pallet wrap, strapping, packaging, cigarette butts, leaves and sediment from tyres and pavement
- Finer treatment devices downstream, such as bioretention media and filter cartridges, clog and fail early if coarse material is not removed first
- Gross pollutants are one of the four targets in the State Planning Policy
What a GPT doesn't do: it is primary treatment only. It does not remove fine sediment or dissolved nutrients to any useful degree, and some councils, such as Moreton Bay, limit the removal that can be claimed for it in modelling. It is the first stage, not the whole solution.
Owner reality: GPTs need regular cleaning. A full trap stops working, lets rubbish through, can smell and breed mosquitoes, and can cause pits to block and the hardstand to flood. It is hard to overstate how important it is for the occupier to put a maintenance schedule in place and keep to it.
Bioretention basins
What it is: a shallow, planted basin with a layer of engineered sandy filter media over a drainage layer and slotted pipes. Stormwater ponds on the surface briefly, filters down through the media and plant roots, and drains away through the pipes. Large flows bypass through an overflow pit so the basin is not scoured out in a big storm.
Why it is used: bioretention is the workhorse of stormwater quality treatment in SEQ. It removes fine sediment and, through the plants and the media, a share of the nutrients. The Water by Design Bioretention Technical Design Guidelines are the standard reference. Typical features include filter media 500 to 1,000 mm deep, a ponding depth of no more than 300 mm, and, in many designs, a saturated zone at the base to keep the plants alive through dry spells. As a guide to size, the State Planning Policy notes a default bioretention area of 1.5% of the contributing catchment, although the actual size comes from modelling.
What it means for a warehouse site:
- It takes up land that would otherwise be hardstand or parking, and it usually has to sit at the low point of the site
- The site must be graded so runoff reaches it, which affects all the surface levels
- It needs pre-treatment (a GPT or sediment forebay) so it doesn't clog
- Construction and establishment are critical. It is not a matter of filling a hole with soil and planting it. The filter media has a specification, the plant species are specified, and the basin must be protected from construction sediment until the site is stabilised. A bare basin at handover is not a finished basin
Advantages: councils usually accept it as part of the landscaping, there are no cartridges to buy, and ongoing maintenance is generally cheaper than replacing proprietary filters.
Disadvantages: it takes usable site area, and the plants and media need ongoing care: weeding, replanting, removing sediment and eventually replacing the top layer of media.
Proprietary filtration systems
What they are: manufactured treatment devices such as cartridge filter systems, media vaults, hydrodynamic separators and oil-water separators. They are usually installed in underground concrete chambers with trafficable lids, so they can sit beneath the hardstand.
Why they are used:
- Tight industrial lots where there is no room for a bioretention basin
- Targeted treatment, such as hydrocarbons
- Retrofitting beneath existing pavement
- As one stage in a treatment train
Council acceptance varies. Councils need evidence that a device performs as claimed. Stormwater Australia runs an independent verification protocol called SQIDEP (Stormwater Quality Improvement Device Evaluation Protocol), and some SEQ councils, including Brisbane City Council, have moved to accepting only proprietary devices verified under it. Brisbane ran a transition period for devices already on its approved list, which ended on 10 December 2025. Some councils are also more willing to accept proprietary devices on private land than in assets they will own. Confirm the council's current position before designing around a particular product.
Advantages: compact, and they free up site area for hardstand and parking. They work very well on constrained sites.
Disadvantages: higher ongoing cost, because the cartridges or media must be replaced on the manufacturer's schedule, and the chambers must be accessible for maintenance vehicles. Lids and chambers must be rated for the trucks and forklifts that will drive over them.
Detention
What it is: storage that holds stormwater during a storm and releases it at a controlled rate through a restricted outlet. It can be an underground tank, oversized pipes, an above-ground tank, or an open basin. Some sites store water on the hardstand surface to a shallow depth in major storms.
Why warehouses often need it: a large impervious area produces a sharp peak flow. Detention protects the downstream drainage network and the neighbours. It is a drainage (QUDM) matter, separate from the water quality modelling.
Design considerations:
- Underground storage under trafficked areas must be designed for the full axle loads of trucks, forklifts, cranes and any other plant that will cross it
- The tank has to be high enough to drain by gravity to the point of discharge, which on a flat site can dictate the finished levels of the whole property
- Some industrial estates provide regional detention or treatment in the estate's own infrastructure, which reduces what each lot has to provide. Check the estate's approval before you design
Other components you may see
| Component | Typical role |
|---|---|
| Swales and buffer strips | Convey runoff and provide light treatment |
| Sediment basins | Capture coarse sediment, mainly during construction |
| Constructed wetlands | Vegetated treatment for larger catchments where space allows |
| Rainwater tanks | Capture roof water for reuse, which also helps the quality model |
| Oil-water separators | Treat hydrocarbon risk areas |
Not every site needs every item. The treatment train is matched to the pollutants, the area, the levels and the council's requirements.
Quality and quantity: keep them separate
| Goal | Typical tools | Reference |
|---|---|---|
| Cleaner runoff | GPT, then bioretention or proprietary filters | State Planning Policy targets, MUSIC modelling, Water by Design guidelines, council codes |
| Controlled peak flow | Detention tanks and basins, pipe design | QUDM and council drainage and flood codes |
Most warehouses need both. Confusing the two is how projects end up with the wrong devices.
Councils differ
Brisbane, Moreton Bay, Logan, Ipswich, the Gold Coast and the other SEQ councils each have their own planning scheme, design standards and approval conditions. What was approved next door is a useful clue, not a precedent you can rely on. The requirements for a site come from the current planning scheme, the council's infrastructure design policies, any estate-level approval, and the conditions of your own development approval.
Why this has to be resolved early
Stormwater sets the surface levels of the site. Moving a bioretention basin or adding a tank late in design shifts the building pad level, the dock heights, the hardstand falls and the retaining walls. It also sits on the critical path for approvals: the detailed stormwater design has to be finished and certified by an RPEQ before the operational works application can be lodged, and that application has its own assessment period before any earthworks can start. See how long a warehouse build takes. On Brenscot design and construct projects, the civil concept is developed with the building concept from the beginning of our process, so that the council's requirements are met while making the best use of the land. The same applies to new or extended hardstand on an existing site, where stormwater is often overlooked until the design has gone too far to change without rework.
Where we start
One of the first things we commission is a detailed identification and level survey, so that the boundaries, levels, easements, existing buildings and infrastructure are documented for the consultants from day one. Where there are existing underground services, we have them located and, where needed, inspected by CCTV to confirm where they run and whether they are serviceable. The stormwater design then starts from facts.
Frequently asked questions
Why does my warehouse need stormwater treatment?
Because the State Planning Policy and the council's planning scheme require new urban development on larger sites to reduce the pollutants carried in stormwater, and to manage the increased runoff so it doesn't cause problems downstream.
What is a gross pollutant trap?
A device that traps litter and coarse sediment, generally material larger than 5 mm, before stormwater passes to finer treatment or leaves the site. It needs regular cleaning to keep working.
Is bioretention or a proprietary filter better?
Bioretention generally costs less to maintain and is widely accepted by councils, but takes up site area. Proprietary filters save space but have higher ongoing costs and need council acceptance. The right choice depends on the site and the council.
Who maintains the stormwater devices after handover?
The property owner or occupier, or the body corporate in a multi-unit scheme. Development approvals commonly require the devices to be maintained for the life of the development, so the cost should be allowed for in outgoings.
Do I need on-site detention?
It depends on the council, the capacity of the downstream drainage and whether the estate already provides it. The civil engineer confirms this early in design.
Sources
- State Planning Policy (July 2017), water quality state interest and Appendix 2; State Planning Policy water quality guidance, planning.qld.gov.au
- Water by Design (Healthy Land and Water): Bioretention Technical Design Guidelines (version 1.1, 2014); MUSIC Modelling Guidelines; Maintaining Vegetated Stormwater Assets
- Queensland Urban Drainage Manual, fourth edition, Institute of Public Works Engineering Australasia Queensland
- Stormwater Australia, Stormwater Quality Improvement Device Evaluation Protocol (SQIDEP)
- City of Moreton Bay, Stormwater management plans information sheet
- Melbourne Water, Gross pollutant traps
- Environmental Protection Act 1994 (Qld), section 319
- Unitywater and Urban Utilities, trade waste requirements
General information only
This article is general information, current as at September 2026. It is not engineering design advice. Stormwater requirements are specific to each site and council and must be confirmed by your civil engineer against the current planning scheme and approval conditions.
Planning an industrial warehouse?
Talk to Brenscot about your site or your requirements. Call 0480 800 077, email enquiries@brenscot.com.au, or start an enquiry. You can also read how we work.