What is stormwater and how do we manage it?
Stormwater is rainwater that is not absorbed into the ground, and instead travels over the land into drains, pipes, and creeks or via hard surfaces including driveways, roofs, and paths.
Throughout this process, the water picks up pollutants such as litter, sediment and organic pollution before eventually being discharged into natural waterways. These pollutants can significantly impact the water quality and consequently the health of the diverse ecosystems in our waterways.
In comparison to sewerage, stormwater is not treated before it enters waterways, and therefore establishing ways to manage stormwater run-off is crucial in helping to create healthy waterways and ecosystems.
Stormwater management is the process of controlling the quantity and quality of stormwater before it enters a waterway. The process involves civil engineering design and is based on environmental and hydraulic parameters.
Two common acronyms used when discussing stormwater management are WSUD (Water Sensitive Urban Design) and OSD (On Site Detention).
Water-sensitive urban design (WSUD) is a land planning and engineering design approach which integrates the water cycle into urban design to minimise environmental degradation and improve aesthetic and recreational appeal.
On-site detention (OSD) is the capturing and storing of stormwater generated on site and releasing it at a controlled rate.
Why is stormwater management important?
Put simply, effective stormwater management is important to maintain healthy waterways and help build more liveable cities.
Research has demonstrated that stormwater run-off is the most predominant source of degradation in urban waterways and poses significant ecological risks, including changes to the number of species present, release of toxic compounds and nutrient cycling.
In Sydney alone, more than 80% of the city’s catchment is covered by concrete, significantly increasing the amount of stormwater run-off and reducing the time it takes to reach its discharge point.
It has been estimated that over two-thirds of the pollutants entering the Sydney Harbour waterway do so via stormwater drains, creating pollution hotspots with concentrations 20 times higher than natural levels.
Effective stormwater management is evidently important in protecting our waterways by ensuring that both the volume of pollutants entering the ecosystem is limited and that the rate at which the water reaches its discharge point is controlled.
What are the most effective solutions to managing stormwater?
Stormwater can be managed in several ways, including the following:
- Bioretention swales provide both stormwater treatment and conveyance functions. The design of the swale provides stormwater pre-treatment by filtering stormwater runoff to remove coarse to medium sediments, and the bioretention system removes finer particulates and contaminants at the base.
- Bioretention basins or raingardens are above ground areas that collect and treat stormwater. Low flow stormwater is directed to an area where it ponds slightly and is absorbed into a special ‘filter media’ typed soil material. The filter media combined with the vegetation growing in the soil collects nutrients as the water is absorbed, resulting in the water collected under the filter media to have significantly less pollutants. This clean water can be either collected in a series of pipes and discharged off site or the water can seep into the surrounding ground.
- Proprietary stormwater quality improvement devices (SQIDs) are proprietary products designed to remove certain pollutants including sediment, metals, oils and nutrients from stormwater. They are typically installed in pits or large tanks that site stormwater is directed to, and filter stormwater before it is released from a site. The products range from trash racks, to filter cartridges to gross pollutant traps and are available through a number of Australian and overseas providers. Many Councils have a list of proprietary products that they accept as stormwater management products for developments in their LGA.
- Detention tanks and basins are storage areas provided above or below ground that capture stormwater and collect or ‘detain’ it and control the rate of release (quantity) of this water by means of a control structure. The control structure could be an orifice plate, a weir, a pipe or any combination of these. By controlling the rate of release of the water we ensure that stormwater infrastructure and the downstream waterways are not exposed to increased flow rates that may cause flooding or scour and erosion of the waterway banks.
How can Barker Ryan Stewart assist?
Stormwater management is required on most, if not all, developments subject to Council requirements and Barker Ryan Stewart can provide effective design of these measures based on industry accepted software modelling and many years’ experience doing just that.
Our team have provided stormwater management solutions for all development types and sizes working with many Councils across NSW and South-East QLD. Our highly qualified civil engineering team would be happy to assist in offering their expertise for the design of the stormwater management aspects of your next project.