Flood protection infrastructure: the fine line between disaster generation and disaster prevention
By Karen MacClune, Kanmani Venkateswaran, and Rachel Norton
The illusion of protection
Flood protection infrastructure alone does not, and cannot, mitigate flood risk. Every post event flood review (PERC) conducted by the Zurich Flood Resilience Alliance contains examples of flood protection infrastructure that has incentivized bad behavior and/or failed catastrophically during floods. The response to these failures is often to allocate large sums of recovery funding to construct more protective infrastructure without asking why there was failure in the first place. Even within the disaster risk management and disaster risk reduction communities, there seems to be unquestioned faith in the ability of protection infrastructure to protect people.
Our newest post-event review, of Hurricane Harvey in Houston, Texas (planned for release June 21 2018), looks closely at some of the issues with flood protection infrastructure and provides clear ways forward to develop smarter infrastructure that will support greater flood resilience.
Hurricane Harvey in Houston
Houston is highly flood prone. The Houston metro area has experienced three greater-than-100-year floods in the last five years alone, with the third being Hurricane Harvey. Harvey made landfall near Rockport, Texas on August 25, 2017. Over the next four days Harvey dropped more than 40 inches of rain over eastern Texas. The resulting floods inundated hundreds of thousands of homes, forced more than 30,000 people into shelters and prompted more than 17,000 rescues. Total damage is estimated at USD 125 billion, making it the second-costliest tropical cyclone on record after Hurricane Katrina.
Harvey broke nearly all of the continental US rainfall records. So it is understandable that it overwhelmed drainage systems, caused overbank flooding, and prompted emergency releases from all water storage and flood control reservoirs in the greater Houston area. What is concerning, however, is that over 9000 homes and businesses were badly flooded because they were located within river floodways, flood control reservoirs, and emergency release areas. Furthermore, home and business owners lost assets and property in spite of the fact that the filling of the reservoirs and emergency releases were relatively predictable and entirely forecastable.
Missed opportunities for mitigation
This highlights how disasters are anything but natural — there is an enormous man-made component. There were numerous points at which these impacts could have been mitigated:
- When land was initially purchased for Houston’s two flood control reservoirs, but the dams were sized to impound water beyond the boundaries of the purchased land;
- When construction of homes and businesses within the reservoirs and their delineated floodways was approved in the 1990s/2000s, despite knowing they would be flooded if the reservoirs were to fill;
- When those homes were sold without adequate disclosure to either real estate agents or buyers regarding the risk;
- When areas upstream of the reservoirs were permitted for development, contributing to increased upstream runoff;
- When flood maps were developed and disseminated by county and national authorities that failed to show the full potential extent of flood risk;
- When authorities failed to evaluate, well in advance of an event, the possible impacts of floodwater within the reservoir and of emergency releases downstream, so they would be prepared to warn residents at risk;
- When, as the reservoirs began to fill rapidly during Harvey, the potential for in-reservoir and downstream flooding was not immediately communicated to the public with warnings to protect their assets. Many homes and businesses inside the reservoirs were in fact unaware that they were located in a flood zone.
“When I started to rent this house, nobody told me, Even the insurance company told me that it was not a flooding area.” — Jeremy Boutor, Addicks Reservoir resident
This list is not exhaustive, yet it points to just how broad responsibility often is and how many opportunities there are for protection infrastructure to fail. Interestingly, none of these modes address physical failure caused by design thresholds being overwhelmed and/or a lack of maintenance, though that has also been a recurring theme in Alliance PERC studies. Instead, this example highlights the ways in which simply building and maintaining flood protection infrastructure is not enough. Ensuring the integrity, functionality, and operability of flood protection infrastructure also requires substantial efforts to develop appropriate regulatory systems and build public awareness of the risk landscape.
Learning from the past: mix the hard with the soft
In the post-Harvey recovery phase, a leading solution being proposed to address flooding in Houston is the construction of a third reservoir. This is expected to cost over USD 500 million. However, there has been little discussion of the regulatory landscape that gave rise to the flooding at the existing two reservoirs. Unless the issues revealed by Harvey are addressed, a third reservoir is also likely to eventually fail.
Large-scale infrastructure projects — such as levees, canals and reservoirs — are expensive yet arguably important solutions to flood threats to development. However, it must be highlighted that these threats are substantially caused by the development itself, both in how and where it is built. In addition, all flood protection infrastructures come with residual risk and storm thresholds beyond which they will fail. Protecting these investments and dependent lives and assets requires parallel investments in soft solutions based on an understanding of how people interact with protection infrastructure.
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