Civil engineers build rugged things designed to last for decades, like roads, bridges, culverts and water treatment plants. But a University of New Hampshire professor wants his profession to become much more flexible.
In a changing climate, civil engineer Paul Kirshen argues, facilities will have to adapt to changing conditions over their useful lives – and, in some instances, be allowed to fail. A leading example of this approach: The Netherlands' Room for the River project: Decades of thinking that floods must be held back are being tossed aside as workers move dikes to give the Rhine River room to spill.
The approach recognises that the country's famed network of dikes and dams will come under increasing stress as sea levels rise. Rather than building protective walls ever higher, the Dutch believe they can keep safer by accepting a certain amount of controlled flooding.
Kirshen, an expert on climate change adaptation and water resources, thinks the United States should take a similar approach.
"Historically we've built infrastructure to provide a certain level of safety," he said. A dam may be designed today to withstand a 100-year or 500-year flood, for example. But that approach assumes that engineers know how stresses – such as floods and storm surges – will vary over the dam's lifetime. As climate change alters natural cycles, Kirshen argues, those assumptions may prove false.
In some cases engineers will have little choice but to armor structures against rare extreme events – say, the 9.4-foot storm surge that Hurricane Sandy pushed into lower Manhattan last fall. But using such a rare flood or storm as a design standard is expensive, Kirshen said, since it means building new structures or retrofitting existing ones with enough protective features to withstand stresses that may occur only once in those buildings' lifetimes, if at all.
Designing projects so they are safe to fail, on the other hand, is often cheaper and more efficient, Kirshen believes. A community might opt to build a dam designed to contain up to a 100-year flood, then develop a comprehensive evacuation plan for the surrounding area in the event of a more severe flood. This strategy anticipates that the dam may not control extreme flooding, but adds other protective measures for higher levels of safety.
"We've got to stop tying designers' hands," said Kirshen. "Conventional civil engineering design can be more creative."
Flexible adaptation strategies can be retrofitted into existing facilities in stages, as climate change impacts become clear in different locations. Examples include modular seawalls that can be raised as needed; prefabricated highway bridges that can be elevated as peak flows beneath them rise; and floating intake systems at water treatment plants, designed to rise and fall as reservoir levels change.
"An incremental approach has fewer social and environmental impacts than building huge structures in one phase – if you can keep up with [climate-induced] changes," Kirshen said.
A city flooded
Kirshen co-authored a study by the Boston Harbor Association, motivated by Hurricane Sandy and released last month, that analysed potential flooding in Boston from the current 100-year storm surge (five feet above average high tide) and the estimated 100-year storm in 2050 (7.5 feet above average high tide). In the latter scenario, the study concluded, more than 30 per cent of the city would be flooded.
In response Mayor Thomas Menino ordered surveys of all buildings and subway lines in flood zones and announced that developers would be required to address climate change risks when applying for building permits.
Flexible adaptation is "a valuable approach and will be appropriate in certain situations" as Boston moves forward, said Carl Spector, executive director of the city's Air Pollution Control Commission and a member of its climate change adaptation advisory committee. "When you start doing adaptation, you have to go site by site and customise your analysis and time lines for each project. Changing sewer lines is a big project, and what you put in the ground stays in the ground for a long time."
Kirshen hopes New York City leaders will consider flexible adaptation measures as the city recovers from Sandy. A few other regions have already taken steps. The San Francisco Bay Conservation and Development Commission requires sea-level rise risk assessments for new shoreline projects around San Francisco Bay. And in south Florida, where rising sea levels are already stressing storm water systems, four counties (Broward, Miami-Dade, Palm Beach and Monroe) have formed a regional partnership and requested federal adaptation funding.
But the most advanced examples of flexible adaptation are in Europe.
In addition to the Netherlands, England has a large-scale flood control system for the lower Thames, including a 10-gate barrier system to protect London from storm surges. But planners are looking ahead. Last November the United Kingdom's Environment Agency released its Thames Estuary 2100 Plan which anticipates at least a three-foot sea-level rise by 2100 and can be adapted for higher levels. It projects that many existing flood control structures will be raised or upgraded between 2035 and 2050, and that a new Thames Barrier may be constructed between 2050 and 2070.
US officials are paying attention to adaptation models in Europe, according to Spector. "There's a lot of sharing going on," he said.
Civil engineers have always built 'demand flexibility' into systems – for example, designing a bridge so that a span can be added as traffic flow increases, said Kirshen.
"Now we need to add climate flexibility."