Explaining the difference between stormwater and flooding...

Australia has seen unprecedented flooding in the last 12 months. The 2022 Eastern Australia floods were one of the nation’s worst recorded flood disasters.

Most people are aware that engineers carry out design for stormwater, but is there a difference between ‘Stormwater’ and ‘Flooding’?

When talking about stormwater, we are typically referring to the management of rainfall and runoff that occurs within the development site itself. The water that falls on your property is generally conveyed off-site via stormwater drainage, e.g. a stormwater pit and pipe system. Federal, State and Local Government have design standards with regards to managing this and each locality has a different historical rainfall pattern that dictates the design of a stormwater drainage system. For example, coastal areas with higher rainfall will required a larger stormwater pipe compared to the same catchment area of an inland areas with lower rainfall.

Flooding, on the other hand, relates to water coming from an external catchment. The source of flooding can be from neighbours’ properties, rivers, creeks, or infrastructure upstream. The characteristics of flooding on your site can be quite complex, but if your land is flood affected, it doesn’t necessarily mean it is void of development potential.

At the most basic level, Council’s typically have available flood mapping in your region that has been derived from large scale flood investigations. This information is usually very accessible, and some Councils have this resource available on their website.

With regards to development of your flood affected site, there is likely to be restrictions or constraints that need to be considered, in this regard - the sooner the better. Working with an experienced engineer will ensure it’s at the forefront of your planning considerations and incorporated into your design. Your development must facilitate the use of the land in a flood scenario, and at the same time, development works such as earthworks and structures shall not ‘worsen’ the existing flooding conditions on adjacent properties. Your engineering team will therefore analyse surrounding properties and ensure the design does not worsen the impact on your neighbours.

Flood affected development sites are becoming more common due to the lack of available land. These sites can create the most technical and intricate earthworks design requirements – and for that reason, gets our design engineers salivating.

Interestingly, State Government guidelines have begun to include provisions for climate change and the impact of worsening natural disasters. Nonetheless, finding an experienced engineer is key to ensuring your development has lasting value for your buyers and homeowners in the future.