The levee effect: flood protection, vulnerability and risk reduction

One of the things I keep running into while researching this blog is the concept of the levee effect: that construction of flood protection infrastructure can actually increase vulnerability to floods. Also known as the safe-development paradox, it's the reason we end up with so many people living in floodplains. People cluster behind defences, becoming less aware of flood risk and less prepared, thus increasing their vulnerability; if the infrastructure eventually fails, the resulting flood can cause a much bigger disaster.

A levee breach in New Orleans during Hurricane Katrina in 2005. Photo: Vincent Laforet/NYT

For years engineers have known that the construction of levees can actually increase flood risk: they narrow channels, causing bottlenecks and higher water speeds, pushing flood waters elsewhere and risking disastrous breaches (which happened in New Orleans during Hurricane Katrina). They can also exacerbate economic inequalities between communities; this is explained very well with a nifty model in the video below (the accompanying article has widgets to play about with to test various scenarios, highly recommended).

People aren't going to move out of risk areas any time soon, so increasingly engineers are exploring ways to provide rivers space to flood. A great example on a massive scale is the Room for the River project in the Netherlands (good overview here, espcially if you like heavy machinery and sad cows standing in puddles).

But non-structural approaches are equally important (more so in areas which don't have the funds for infrastructural works!). This infographic summarises the ways in which these approaches combine to reduce flood risk.

This infographic looks at approaches for managing flood risk at multiple levels, addressing hazard, exposure and vulnerability. Flood protection infrastructure has a role to play, but non-structural approaches shouldn't be neglected! Source: Associated Programme on Flood Management

The reason the levee effect is dangerous is because the perceived safety means that people are less risk-aware. Public engagement is an essential part of flood risk management: do people know how to prepare, what warnings to expect, and how to evacuate? Too often the answer is no: and this is what results in disasters.