The Ultimate Guide to Stormwater Management and Maintenance
Expert Stormwater Management in Brisbane & Surrounds
Water sensitive urban design (WSUD) is taking fast hold across Australia. Bioretention basins, constructed wetlands and retention ponds are being implemented to support healthy ecosystems and waterways all over the country.
An effective WSUD plan relies on applying the best practice stormwater management techniques which requires specialist skills and resources that may be difficult to access. At Total Environmental Concepts, we offer a range of specialist services which can assist with the maintenance, protection and improvement of the health of our waterways.
For more information, read our in depth guide below or contact us if you have a project related to any of the following near Brisbane, Gold Coast or Sunshine Coast:
Structural stormwater treatment systems are commonly implemented to support the water sensitive urban design initiative introduced by many councils around Australia. Urbanisation has a very clear impact on the natural water cycle and water tables. This impact includes changes to both stormwater quantity and quality and actively contribute to environmental rehabilitation.
With urbanisation comes an increased number of areas through which water cannot pass. Areas that were once natural vegetated land, become roofs, roads, carpaks or other paved surfaces.
The impact of having a limited amount of areas through which water can flow results in:
- Increased amounts of stormwater runoff generated from urban catchments
- Hydrologic regime alterations
- Changes to geomorphology of groundwater movement
- Surface water flow leading to stream channel erosion
- Downstream sediment deposition and flooding
Add to this the levels of contaminants and pollutants that enter the waterways from residential, commercial and industrial land uses, the potential for irreversible environmental impacts is ripe.
That’s where storm water treatment solutions come in. They help to treat and filter pollutants from stormwater before they cause irreversible harm to local ecosystems.
Stormwater is water that originates during rainfall or other events with precipitation. Once stormwater reaches the ground, it has one of three courses of action:
- Soak into soil
- Be held on a surface and evaporate
- Runoff and end up in nearby streams, rivers or waterways
In natural environments and landscapes, such as forests, stormwater is absorbed by the soil and is held close to where it falls by plants.
In developed environments, stormwater that’s left unmanaged creates a host of issues as it generally becomes runoff. Flooding and contamination of waterways are two of the major concerns. Water treatment systems such as constructed wetlands, sediment basins and stormwater swales and drains, help to mitigate both of these risks.
Why Do We Need Stormwater Management?
In urban environments there is heightened risk of water being contaminated by a number of pollutants. These pollutants are often toxic or cause irreversible damage to ecological habitats and waterways as well as to human health.
Types of urban stormwater pollutants include:
Suspended solids usually originate from:
- land surface erosion,
- atmospheric deposition,
- pavement and vehicle wear,
- building construction and
These pollutants can be closely associated with other pollutants, such as nutrients, heavy metals and hydrocarbons. They can also be divided into two categories; suspended solids and dissolved solids.
Suspended solids are particles larger than 0.45 μm in the water while dissolved solids are smaller than 0.45 μm.
Nutrients are chemical compounds such as nitrogen, phosphorus, calcium, carbon, iron, manganese and potassium. From the perspective of water quality, nitrogen and phosphorus compounds play the most critical role in environmental degradation.
While nutrient compounds are essential for plant growth, excessive amounts in waterways can cause cascading damage to all forms of aquatic life.
Richness of nutrients in a body of water can promote the excessive growth of plants which in turn threaten the health of aquatic habitats. Excess plant life in water systems can reduce light penetration through the water and block the ability of some organisms to synthesise the nutrients they need from sunlight.
Excess plant growth can also decrease the amount of oxygen in the water thereby killing other organisms living in and depending on the aquatic environment.
Organic carbon originates from many sources directly and indirectly. Plant litter and soil erosion are two direct sources of organic carbon. Indirect sources include decaying vegetation, atmospheric deposition, waste materials and effluent (such as septic tank leaks, animal and bird faeces and spillage from vehicles transporting organic materials).
Biodegradation and chemical oxidation are the processes through which organic carbon is broken down and consumes oxygen. When organic carbon is mobilised by stormwater, it can lead to the depletion of dissolved oxygen in water systems and habitats, leading to the death of fish and other aquatic life which rely on oxygen for their respiration.
Due to their high levels of toxicity and potential of causing harmful effects, heavy metals are considered a critical pollutant. Not only are they a concern to human health, they also are concerning contaminants affecting our waterways and ecosystems.
Heavy metals include:
Exposure to these heavy metals can affect red blood cells, the nervous system and many organs very negatively. They can also be contributing causes of certain types of cancer, metabolic poisoning and damage to kidneys among other body systems.
As heavy metals can easily bioaccumulate in humans, plants and animals, they are a big threat to health and must be filtered out of our waterways.
Hydrocarbon compounds include oils, phenols and grease originating from natural, environmental and anthropogenic pollution. Human activity, especially commercial or industrial activity, commonly results in hydrocarbons and pollutants leading to emissions of sulphur dioxide.
Stormwater runoff from road surfaces has been reported to contain a greater hydrocarbon load than water from rooftops. Due to the heightened risk and ability to affect ecosystem health, hydrocarbons are a major concern in relation to stormwater runoff and must be filtered out as best as possible.
Water quality can be determined by the status of a number of factors. The acidity and alkalinity of the water are reliable indicators. Water with moderate amounts of acidity or alkalinity is fine for consumption without adverse effects.
High levels of acidity or alkalinity in water can indicate chemical pollutants are present and that the water is a risk to aquatic habitats and also the human body. Acidity and alkalinity of water can be determined by measuring the pH value, a very important water quality parameter.
Constructed wetlands are another type of treatment option to remove contaminants and pollutants from urban stormwater runoff. They are a series of shallow, constructed ponds that are vegetated extensively.
Ponds and wetlands work very well as a natural solution to treating and filtering water pollutants before stormwater runoff flows into nearby rivers, oceans and creeks.
Pollutants are removed by using enhanced sedimentation, fine filtration and biological uptake processes. They also provide habitats for local wildlife, passive recreation and temporary storage of treated water for reuse schemes.
Wetland Construction & Maintenance
Constructed wetlands offer a very similar filtration function to bioretention basins though also assist with filtering finer sediment. These are a series of constructed ponds that are quite shallow and with many plants. Ponds and wetlands work very well as a natural solution to treating and filtering water pollutants before the water flows into rivers, oceans and creeks.
The artificial wetlands we construct are water retention areas that are designed to achieve one or more of the below objectives:
- Control of stormwater including the reduction of peak flows and removal of nitrogen, suspended solids and heavy metals
- Surface water management
- Floodplain enhancement
- Habitat creation – for both native and migratory wildlife
- Enhancing the environment of the Wallum Frog, a species of ground-dwelling frog native to the east coast of Australia
Our team have both the skill and knowledge to construct wetlands for the above purposes, specific to local conditions and taking into consideration the pre-existing habitat. Read more about what we can do in our capability statement.
Constructed wetlands that are designed as a solution specifically for large systems can manage stormwater runoff from large catchments better than bioretention basins can. Not only can they cope with persistent base flows better, they are configured to slowly release flows, typically over two to three days.
As water levels rise during rainfall, constructed wetlands help manage stormwater runoff to avoid flooding until the water levels return to dry weather levels.
Constructed wetlands can help:
- Remove coarse sediments
- Filter fine particles
- Uptake soluble pollutants
- Protect against scour and vegetation damage
They consist of an inlet zone, macrophyte zone (a shallow yet heavily vegetated area) and a high flow bypass channel.
Such wetlands can remove pollutants including nutrients, heavy metals and sediment. The dense vegetation is critical for filtering stormwater before it flows through other treatment zones. Plants and biofilms capture pollutants as the water flows through.
Wetlands are a key component to managing local hydrology as they slow the rate of discharge of stormwater to the receiving environment and also reduce its volume through evapotranspiration.
It is important that careful planning, integration and collaborative design are adopted for wetland construction to provide this array of multiple benefits.
Weed control and management is important in constructed wetlands to make sure that invasive species do not limit the species planted for the particular design requirements. This may also apply to native species, especially some native grasses that can naturally appear in wetlands and out-compete more important planted species.
Healthy vegetation and adequate flow conditions are essential for a wetland to pass key maintenance considerations.
Our team are specialists with decades of experience maintaining the correct environment for constructed wetlands, and other stormwater treatment systems. We can assist with weeding, planting, mowing and removing debris. We advise against using herbicides or other chemicals as these can affect the quality of the water in the wetland.
In addition to maintaining the vegetation, constructed wetlands need to be protected from high volumes of sediment and debris. There is also an inlet zone which needs to be maintained in a similar way to sedimentation basins.
The most intensive period of maintenance is during the first couple of years, while plants are being established. Weed removal and replanting may be required at a more intensive rate during this time.
It is also during this period when large amounts of sediments could impact plant growth. This is especially applicable to building catchments with poor building controls.
Removing debris is an ongoing function of maintenance. If it’s not removed, debris can block inlets or outlets and can be unsightly if in a visible location. Debris removal and inspections should be completed frequently and regularly.
Bioswales & Rock-Lined Swales
All water management systems which collect, concentrate and move stormwater at the ground surface level are suited to the use of swales. Swales can be used to manage the flow of runoff both to and from underground stormwater management systems including constructed wetlands, sediment retention basins and bioretention basins.
There are two main types of swales used: vegetated swales (bioswales) and rock-lined swales. There is minimal benefit to the water quality with either swale design as the main function of both types is to move stormwater runoff rather than filter it.
Both bioswales and rock-lined swales can help decrease the velocity of water flow and facilitate some infiltration.
Bioretention Swale Treatment Processes
With these systems, the interaction between water flow and vegetation is what enables pollutants to settle and be retained by the vegetation. The type and height of the vegetation will influence the overall performance.
Low vegetation, such as mown grass, can achieve moderate sediment deposition rates if water flows are well distributed across the entire swale.
Swales with taller vegetation, like reeds, can offer better sediment retention by slowing down water flows more. They can also provide enhanced sedimentation for deeper flows. They do, however, have higher hydraulic roughness and require a much larger area compared to grass swales.
Bioswales and drains are shallow yet open vegetated channels. They are used mainly for moving water through a drainage pathway. They can also be designed to manage water quality through slowing down the speed of water flow compared to piped, concrete or bare soil systems.
Often combined with buffer strips, sediment basins and constructed wetlands, bioswales can remove coarse and medium sized sediments. The design of swales and drains should be such that they are well vegetated and move the required run-off volume effectively to allow for seasonal slashing.
Swales and drains work differently and the main difference is in how they hold water. Swales are in areas which can fully drain and are more dry whereas drains are located on flat or back-watered sections which result in them holding water.
Rock-lined swales are shallow trenches in a landscape that catch rainwater from roofs, driveways and other urban, hard surfaces. They are purposely designed to slow water down, spread it out and then let it sink into the ground during small storms.
A rock-lined swale is also considered to be like a dry creek bed. It uses rock instead of grass or other vegetation to safely infiltrate or manage runoff. Most rock-lined swales are designed with rounded rock on the surface to facilitate an aesthetically pleasing landscape feature.
These types of swales are very versatile and can be formed to fit almost all site conditions and interests from landowners. Depending on the space and landscape, swales can either be straight lined or they can meander.
The advantage of a meandering design is that it maxmises the amount of time water spends in the swale and thus aids infiltration by trapping sediments and pollutants.
Advantages and Disadvantages of Swales
- Swales may be a less expensive option to install.
- Swales assist with the prevention of stormwater runoff discharge from the site.
- Aesthetics of a property may be enhanced with vegetated swales.
- Compared to other options that have no contact with the underlying soil, swales have a number of advantages for how they manage the flow of stormwater runoff.
- Swales can convert sheet flow into channel flow, which can potentially increase flow velocity and erosive energy.
- Concentrates the volume of runoff.
- Bioswales are not practical on steeper slopes or when runoff velocities are high.
Information for Developers
If you are a developer or working with a developer, it is likely you are largely affected by local compliance laws related to water sensitive urban design (WSUD) guidelines.
As experts in our industry, we have all the specialist tools and knowledge required to help developers receive their bond back faster post-construction. Our on the ground specialists have worked with many developers to ensure the state of the bioretention basins and other stormwater management systems are left in tip top shape prior to being handed over to council.
Read the knowledge we’ve shared below or contact our team if you’re a developer looking for ways to secure your bond return faster. Check out our section on bioretention basins for more specific information on construction, installation, design, maintenance and costs.
To ensure compliance with all WSUD guidelines, developers must pay a bond calculated at 150% of the cost to reconstruct the WSUD asset if it were to be damaged by sediment. This is a hefty amount to pay and it is in your best interest to have that returned as soon as possible once construction is over.
Until the asset handover between you, the developer, and the Council is complete, you are responsible for ongoing clean outs and maintenance of the asset. Once the asset has been handed over, that responsibility is either taken on by the Council, or in the case or private property, the owner of the property.
In either case, it can take up to 12 months until off maintenance is reached and the bond is returned. Chat with our team about how to go from construction to off maintenance as soon as possible.
Here’s everything you need to know about WSUD asset handover and how to avoid sediment damage occurring.
WSUD asset handover is an essential process of development. It refers to how stormwater treatment systems, like bioretention basins, constructed wetlands and sedimentation ponds are constructed, maintained and ultimately, handed over to Council.
Such assets are a form of green infrastructure and require a different handover process to traditional stormwater assets, though this may vary across different councils.
As traditional stormwater infrastructure assets do not require as many of the same requirements, it is far too often that we see WSUD assets irreparably damaged due to sedimentation before handover to the Council simply because developers weren’t aware of the differences.
WSUD asset handover is a more streamlined, and cost-effective method for the construction, maintenance and handover of WSUD assets to the Council, without sediment damage occurring.
The two WSUD asset handover paths generally available to developers are below. You may choose the process that best suits your needs on a site-by-site basis.
No matter whether you choose a normal or early asset handover, a majority of the process will be similar.
The core elements of the process according to the Logan City Council are here. Make sure to check the process your nearest council requires you to go through as there could be variations.
- Lodge the operational works application. Make sure to address both the civil and planted (or landscaped) aspects of the WSUD asset(s). This application can be combined with operational works for other civil construction or it can be lodged on it’s own.
- Begin construction of the bioretention basin, constructed wetland, sedimentation pond or other WSUD assets. Make sure to follow the methods outlined in the relevant guidelines the council follows. In South East Queensland, Water by Design’s Construction and Establishment Guidelines cover a number of appropriate methods of construction. Once a method is chosen, document it in your development’s Site Based Stormwater Management Plan that is submitted with the operational works application.
- Arrange an inspection with the council during the installation of the bioretention underdrainage.
- Before plan sealing, a WSUD bond must be lodged with the council and retained until off maintenance.
- With both a normal or early asset handover, a 12 month maintenance period will take place with the bond returned once the WSUD asset is accepted off maintenance.
The key elements of the WSUD asset handover process will vary depending on the local council laws that govern the development zone.
In general, with a normal asset handover, the developer is responsible for completing construction of the WSUD asset. The bioretention basin, constructed wetland or other asset will be partially completed before plan sealing.
Functional completion with a normal handover includes final construction and planting and will take place after 90% of onsite construction is complete or 3 years after plan sealing (whichever happens earliest).
Once the asset has been completed, including planting, an on-maintenance inspection needs to be arranged with council. This is followed by the 12 month maintenance period at the end of which the bond is returned if the asset is accepted off maintenance and vegetation is suitably established.
The biggest difference between a normal and early WSUD asset handover is the responsibility of completing the asset construction. With a normal handover, the responsibility to complete the construction and planting is with the developer.
With an early handover, developers have the option to handover the asset before it has been completed and allow their local council to complete the construction and planting.
To choose this option, you will need to make a separate financial contribution to the council in addition to the bond. This contribution covers the fees of having the council complete the work and will not be returned.
With an early handover, there is still a 12 month maintenance period though the WSUD asset will be accepted for off maintenance and bond returned based on the suitable performance of the asset in its semi-constructed state.