Preventing new development on flood-prone sites

Approving development on sites that are highly vulnerable to river flooding, creek flooding and coastal inundation ultimately leads to more challenges and higher costs for governments and future residents.

Most of Brisbane's land area is located on higher ground, well above creek and river flood levels, but due to pressure from private developers, Brisbane City Council is still approving new residential and commercial developments on land that is severely flood-affected. Developers take their profits and run, leaving residents and body corporates to deal with rising insurance bills and major disruption every time there’s a flood.

The Greens want to ban new development on sites that are at high risk of severe flooding, and preserve this land for use as public parkland, nature reserves, sports fields or agricultural land.

For decades, the major parties have failed to prevent floodplain development, and are still encouraging more, because they don’t want to hurt the profits of big property investors and developers.

In some areas that are only moderately flood-affected, it’s possible to design ‘flood-resilient’ developments where habitable rooms and key infrastructure are raised above predicted flood levels. But in areas where floodwaters rise high and flow fast, or where future sea level rise means properties and roads will be inundated by high tides on a regular basis, new development should not be allowed.

Restricting new development on river and creek floodplains

Brisbane City Plan 2014 currently maps and identifies land where development is required to consider flood risks via its ‘Flood Overlay,’ with different Flood Planning Areas for river and creek flooding (these overlays can be viewed via the map at this link by selecting ‘Overlays’ > ‘Flood’ from the Map Tools).

Flood Planning Areas are defined in part based on how high flood levels could reach, and also on how fast floodwaters would be predicted to flow through a site - an important consideration for the design and engineering of buildings and public infrastructure.

In Flood Planning Areas 1 and 2 (the areas at highest risk), the Greens want to amend the City Plan to rezone sites as parkland, conservation reserve or farmland to prevent all new residential, commercial and industrial development.

In Flood Planning Areas 3, 4 and 5 (which are slightly less at risk) the Greens want to impose tighter restrictions on future development to ensure that in addition to existing restrictions, the following elements are located at least 2 metres above 1% Annual Exceedance Probability flood levels:

all habitable rooms of residential homes, retirement villages and short-term accommodation (current restrictions allow new homes just 50cm above 1% AEP levels)
essential electrical infrastructure (as defined in City Plan 2014) including fire alarm systems, elevator controls and water pump controls
medical facilities, educational facilities, offices and retail shops (including hardware and trade supplies)
storage areas for any material or substance which would cause significant environmental harm if released into a waterway

and the following elements are at least 50cm above 1% Annual Exceedance Probability flood levels:

Residential and hotel carparks with more than 10 parking bays
Emergency evacuation routes

What about existing buildings?

Banning new floodplain development wouldn’t prevent owner-occupiers raising their existing homes above flood levels, but ‘improving flood resilience’ should not be used as an excuse to increase the footprint of buildings on the floodplain or to increase the number of residences and businesses occupying land that’s highly vulnerable to flooding.

Where funding permits, owner-occupiers should be supported to voluntarily relocate to higher ground via buyback schemes.

For investment properties (both residential and non-residential zonings) in Flood Planning Areas 1 and 2 that have a high likelihood of being redeveloped for profit, properties should be compulsorily acquired and converted to green space if investor-owners don’t wish to sell, with appropriate support and flexible timelines for tenants to find new homes or business premises.

Other measures to mitigate flooding

In addition to banning floodplain development, we have also announced a sustainable development initiative to require all developers across the city to set aside at least 20% of their development site area for trees. The less land we cover in concrete, the more soil there is to soak up rainwater. Larger development projects would also be required to install on-site rainwater capture and storage systems – large water tanks – to reduce and slow down the amount of water entering our waterways.

We also want mandatory flood impact assessments for any development that adds more than 300m2 of impervious surface to a site to ensure that new buildings or concrete pads do not push more water onto neighbouring blocks.

What will this initiative mean in practice?

The most floodprone sites across the city will be protected from further development, and gradually converted into public green space and sports fields. Existing houses and apartments could remain on the floodplain for several decades if owners can’t or won’t relocate, but standalone investment properties will be progressively acquired.

Even in some areas that are only moderately flood-affected, the tighter restrictions and higher minimum floor levels might make certain kinds of new development unviable. Making it harder to develop on floodprone sites will help encourage new development where it is most needed - on higher ground close to public transport hubs. Meanwhile, new parks and sports fields will be created across the inner-city and the suburbs.

How much will this initiative cost?

The main cost to the council is gradually buying back sites over time that are too floodprone to develop. The bulk of buyback funding would ideally come from state and federal government climate adaptation grants, however we envisage that the council would also allocate some of its existing park acquisitions budget towards converting floodprone sites into parkland. Initially, we are proposing to allocate $20 million per year towards council-funded flood buybacks

In the long-term, this initiative will save Brisbane City Council money. After the February 2022 floods, the total cost to BCC of supporting flood-affected residents and repairing damaged infrastructure still exceeded $656 million (roughly half of this was eventually covered by insurance or State Government support). Reducing the city’s exposure to flooding saves the council money, while also creating new parkland and sports fields for residents to enjoy.