Recent floods in Queensland and Rio de Janeiro reveal a stark contrast in consequences
In mid January two large urban populations were struck by devastating floods. Featured side by side in the world’s media, residents of Queensland, Australia, were unified in disaster with people from the Brazilian city of Rio de Janeiro. With similar coastal topographies where increasingly dense conurbations occupy the gullies, streams and flood plains that would naturally carry water between mountain and the sea, heavy rain, flash floods and landslides were experienced on both sides of the Pacific.
An experience that they didn’t share, however, was the cost to human life as the death tolls were far from comparable. Queensland’s loss of life remains in the low teens, whereas Rio’s could rise to more than 1,000. Authorities disclosed a list of at least 207 missing people in addition to the 730 confirmed dead at the time of writing.
While the expansion of both cities has dramatically altered natural water courses, the haphazard nature of Rio’s informal settlements contributed greatly to this tragic disparity. Additionally, Rio has less detailed mapping available for flood events, unlike in Queensland where lessons learnt following the catastrophic 1974 flood resulted in key mitigation measures.
One of Queensland’s leadingarchitects, Shane Thompson of BVN, recalls the effect of those floods: ‘1974 completely changed people’s perceptions of thenature of the river, the viabilityof the density, and theimportance of natural gullies.’
Situated 30km from the coast at Morton Bay, Brisbane is situated at the first upstream site where settlers discovered potable water. The flood plains were perfect for food cultivation, so this is where the city grew from 1823. At that time the effect of the river’s major tributaries was unknown, and few could have imagined the reality of extreme floods. As Thompson observes ‘this was the nature of early settlement’.
In 1893, the emerging city experienced its first major flood and 80 years later, following the post-war population boom, the city was devastated by its second major flood and faced an estimated $300 million repair bill. With this, city authorities acknowledged that 1893 was no freak event and accepted the fact that the city would always be vulnerable to this sort of natural event. Extensive flood mapping was undertaken and the 1974 flood levels set the benchmark for the official 1 in 100 year flood condition. All habitable floors are now built between 300-500mm above that so called Q100 event level.
Mitigation measures also included the construction of the Wivenhoe Dam, originally built to provide contingent capacity to detain run off from extreme rainfall and to avoid a repeat of the 1974 flood levels. However, the droughts of the past decade had changed the use of the dam and at the time of the flood it was held at 190 per cent of its intended capacity. Engineers were forced to release the equivalent of 6,000 swimming pools of water a second, which delayed but did not stop the eventual downstream floods.
Architect Mike Rayner, from firm Cox Rayner, whose own riverside house was badly flooded, says, ‘While many were grateful for the water during the drought, and while it’s not a good time to start blaming anybody, having no capacity in the dam certainly exacerbated the extent of the flood downstream.’ Rayner also raised caution over the accuracy of adhering to strict flood levels, as his now ruined house met all necessary standards. ‘While authorities may say that this year’s flood levels were lower than those experienced in 1974, on my site the Q100 event levels were exceeded by more than 2m.’ The problem is exacerbated by the failure of storm water drains due to rising river levels.
In response, and in acknowledgement that it would be unrealistic to evacuate and stop building on riparian land, both Thompson and Rayner advocate radically rethinking how to build in future, drawing on the traditional Queenslander model that touches the ground lightly and minimises its effect on natural water movement. But they also recognise that simply recalling more historic modes of construction will not be enough, and that this must be combined with carefully considered planning constraints, as many Queenslanders in low lying areas were also destroyed.
As the high death tolls suggests, Rio shows an extreme case of how a lack of planning can result in greater tragedy, in places where widespread informal planning has resulted in a condition increasingly referred to as Precarious Urbanism.
Speaking at a recent symposium on this theme organised by London-based practice Austin-Smith:Lord, Elisabete Franca, director of social housing in São Paulo, described how the Brazilian government is currently working hard to help safeguard the homes of tens of thousands of informal settlement dwellers who occupy areas at risk from flood and landslides. Franca and her team of 300 social workers and 200 architects and engineers are doing all they can to convince the dwellers that relocation does not necessarily mean displacement, stating that unlike the situation in the informal settlement of Dharavi in Mumbai (AR September 2010), ‘where developers want to move slum dwellers out to make way for a new economy, we cannot and will not displace people. They have rights, and as such we work with them, only moving those at risk.’
In Paraisópolis they have identified more than 1,000 families that need to be relocated for their own safety, and in one year they held more than 1,000 consultation meetings. The government is also working with practices, such as MMBB Architects, on schemes like the Corrego do Antonico, a new public space which is part of an ambitious flood mitigation programme.
Such initiatives demonstrate the resolve of São Paulo to be better prepared for the next flood. But like so many previous natural disasters, these simultaneous floods have exposed the tragic link between a nation’s economic wealth and its ability to cope with natural crises.