Even with the development of the electric car and greener fuels, no one can deny that car travel is fundamentally bad for the environment.

However, Australia is a large country that is dependent on motor vehicles, particularly in non-metropolitan centres.

This form of transport directly correlates to not only the need for large roads but for large areas of car parking. Shopping centres and commercial zones, as well as education, health, transport and aged care facilities are surrounded by swathes of car parking. Is there an opportunity here to offset, at least to some degree, the impact of the motor vehicle?

Historically, car parks were designed simply to provide drivers and their passengers with somewhere to park as close as possible to the area they are trying to access. This was originally achieved through large single-level car parks.

The first known multi-level car park was built in Washington in 1918 at an early time in the evolution of the motor car. Even from this point in time, it was evident that the large space required to construct car parks would be an issue.

One benefit Australia has in this regard is space, the availability of which saw the construction of thousands of single level car parks around the country.

Since the 1960s, with increasing land values and densities in our cities, the push has been toward multi-level car parks. This design evolution has continued, begetting the inner city apartment and office tower parking solutions we see today. These often include vertical stacking systems that make multi-level car park space more efficient in areas where space is at a premium and deep multi-storey basement construction is cost prohibitive.

However, there is still a substantial number of large single level parking areas, and these too have evolved.

Their appeal lies in their cost but they often lack convenience, with long walking distances the norm. This has seen a shift toward the concept of ‘placemaking.’ Large bitumen areas have been transformed to include Water Sensitive Urban Design (WSUD), landscaped environments and, in some cases, sculpture and art.

But it is not just the convenience that is an issue. Single level parking also suffers from the following:

• Low to no shade protection for vehicles
• Weather affected on rainy days
• Substantial stormwater runoff from large impervious areas

In an effort to solve these additional challenges, savvy carpark owners and managers are now seeing the potential of their car parks as an untapped resource for energy generation and stormwater harvesting.

Figure 1, Sustainable carpark canopy.
Images: Meinhardt

The Australian sun is harsh on vehicles, causing paint fade and shortening the lifespan of vehicle components such as plastic bumpers and mirrors.

It is particularly preferable to provide shade for vehicles in long-term parking areas such as airports and train stations and in staff parking areas where vehicles are regularly parked in full sun. Shade structures and canopies have been provided in car parks for some time across the country. They can result in customers staying longer as their concern for a hot car is mitigated.

They make business and operational sense, and they can also make environmental sense.

Solar generation in Australia has traditionally been through roof mounted panels or large solar ‘farms.’ Shade canopies that incorporate solar generation in car parks are becoming more prevalent across the country with car park owners seeing the benefit of using large open spaces for off-structure solar generation that can offset daytime electricity use.

Solar typically meets up to 35 per cent of a space’s total power requirements and can typically save up to 15 per cent in energy costs. These ‘sustainable car parks’ also have short pay back periods (five to eight years) and offer multiple benefits by providing both shade and electricity.

If self-funding is not possible, Solar Power Purchase Agreements (PPA) can cover the upfront capital cost of the system with a fixed term contract to supply the solar at a heavily discounted price when compared to grid power. They also provide the added benefit of covering all maintenance costs of the system.

Developments in the solar industry are also trending toward the development of ‘solar pavements’ or ground mounted solar panels, although these are still not commercially viable.

Stormwater Treatment and Harvesting

Single level car parks generally feature substantial areas of impervious pavement, meaning all rainfall runs off the surface without infiltrating the soil.

Traditional pit and pipe drainage systems are designed to convey flows away from the parking surface to the underground drainage network as quickly as possible.

The introduction of a requirement for new carparks to meet minimum stormwater treatment objectives (Best Practice Environmental Management Guidelines – Stormwater CSIRO 2006) has driven the implementation of WSUD elements such as rain gardens, vegetated swales, permeable pavements and stormwater harvesting to be included in car parks.

These WSUD measures can be used as a treatment train to increase the water quality of stormwater runoff to allow stormwater to be harvested for non-potable water uses such as irrigation, toilet flushing and cleaning. Stormwater runoff from carpark pavements can contain higher levels of sediment and hydrocarbons which need to be removed prior to harvesting and reuse. Many cost effective proprietary systems exist that can achieve this treatment.

A smarter solution is to incorporate stormwater harvesting into shade and solar sustainable car park canopies. Clean roof catchments from the canopies remove the need to treat for sediment and hydrocarbons and can include a first flush device.

Stormwater harvested from sustainable canopies is fit for purpose with minimal treatment. Modular underground storage tanks can be linked together to create large storage volumes that are then pumped into retrofitted plumbing reticulation.

Rainwater storage can be optimised with water balance modelling to meet 75 to 85 per cent demand reliability of the potable water needed for irrigation, toilet usage and other non-potable uses.

Figure 2 – Factors to consider when ensuring maximum stormwater harvesting reliability.

A 16-bay carpark canopy module Meinhardt has been developing could provide up to 100,000 litres of harvested stormwater in Melbourne per year. When these modules and tanks are linked together, the potable water offset is only limited by the carpark total area.

The potable water usage that is reduced will also offset upfront  construction costs over a period of time.

The construction of multi-functional canopies that provide shade, renewable energy and non-potable water, combined with WSUD surface stormwater treatment, will see car parks become truly sustainable features of our cities and towns.

By: Scott Carne, Meinhardt