With their dense populations and extensive development, urban areas are particularly vulnerable to rising global temperatures, changes in rainfall patterns, and more extreme weather events.
As population grows and land development continues, cities are facing increased risks of flash flooding due to a lack of natural drainage and an increasing number of impervious surfaces. This means stormwater runoff and its return to the water table becomes more difficult, eventually leading to water overflow, habitat loss and erosion.
The problem of diminishing levels of natural drainage is further compounded by the heat island effect associated with dense urban areas, where higher temperatures lead to increased precipitation.
To achieve and maintain appropriate drainage that can service severe weather events, it is important to adopt solutions that can closely mimic the natural systems that existed pre-development.
There are many systems and practices that are able to fulfil this approach, such as permeable paving and concrete, infiltration trenches, roof reservoirs and detention reservoirs.
To determine which system is suitable for any given area, there are a number of factors to take into consideration, including urban factors, social, economic and environmental issues; including the drainage area, the infiltration capacity of the soil, groundwater level, land slope, and the presence of sediments.
Permeable paving is recognised as an integral part of water sensitive urban design (WSUD), and is increasingly being employed as a vital method in complying with requirements for permeability, tree protection, and WSUD compliance.
Permeable paving allows rainwater to seep through the surface and into the ground, effectively disconnecting the runoff from the traditional municipal drainage system by minimising the amount of water that needs to be channelled through storm drains.
The water quality is profoundly contested when it comes to drainage systems, as stormwater could be one of the biggest sources of pollution of waterways. However, permeable paving can have a positive impact as it contributes to sedimentation, filtration, adsorption, biodegradation and can remove sludge, heavy metals and hydrocarbons from stormwater.
Nevertheless, to ensure permeable paving performs optimally, it is important to consider the entire permeable surface, including ensuring the surface material, subgrade and subsoil all have proper infiltration rates.
While permeable paving is used widely in commercial settings, there are elements of its composition that are still undergoing research to improve performance and design life aspects, and to ensure its continued effectiveness as an urban drainage system and in the removal of pollutants.
Permeable paving can be made from a variety of materials, but is predominantly made of concrete, however, the industry is exploring a range of nontraditional materials that can increase the performance and reduce the use of virgin resources. As an example, researchers at the University of Melbourne have studied the effects of introducing recycled tyres in the manufacture of permeable pavement.
The researchers developed the product in a lab, which was later installed in Victorian urban areas, predominantly around tree protection zones, footpaths and bicycle paths.
With around three old tyres used per square metre of paving, the completion of one single project equated to more than 1000 tyres removed from landfill.
The study showed the pavement required less maintenance, offered superior performance for traffic loading, was more cost efficient compared to other existing technologies and had higher levels of water infiltration compared to other products.