Securing cities from sea level rises

One of the most significant water impacts of global warming is the anticipated rise in sea levels. With many cities now facing inundation, authorities are developing resilience strategies for a future underwater world.

A need for concerted action

In many respects, Hurricane Sandy marked a turning point for US cities and their approach to resilience.

One of the most powerful storms in decades, the 2012 event affected some 24 states and the entire eastern seaboard of the US. With New York and New Jersey hit hard and facing billions of dollars of damage, the issue of potential sea level rises and their economic impact was at the top of the agenda.

Since then, it's become clear that global warming means that events such as hurricanes will not solely be responsible for catastrophic flooding. Instead, an inexorable sea level rise is expected to see cities from Galveston in Texas and Seattle, Washington and from Hoboken in New Jersey to New Orleans in Louisiana gradually disappearing underwater my mid-century unless concerted action is taken.

Coping with a two-foot rise

Among the latest urban centres to establish an action plan is Miami-Dade in Florida, which is forecasting a two-foot (60 cm) sea-level rise over the next 40 years. Indeed, their strategy document notes that sea levels have risen by some 9 inches (20 cm) since 1930.

With much of the county just a few feet above the current sea level, any increase must be taken seriously. In response to current sea-level projections, a comprehensive adaptation pathway has been adopted that addresses the issues in both the short- and long-term.

"It's also acknowledged that it is not economically feasible to reduce all risk from sea-level rise; no single infrastructure project will resolve this growing challenge."

The county is already investing in adaptation to reduce physical risks and the growing future economic risk. However, it’s also acknowledged that it is not economically feasible to reduce all risk from sea-level rise; no single infrastructure project will resolve this growing challenge.

Miami-Dade’s Adapting to Sea Level Rise strategy outlines priority actions that are seen to have the most significant impact through regulatory and policy changes as well as investment and planning efforts to reduce future risk. The strategy includes county projects, totalling approximately $1.7 billion of investment.

However, the strategy also notes that studies from the US Army Corps of Engineers and others suggest that measures to reduce future storm surge risk in the most vulnerable areas could cost at least $6.1 billion.

Key measures proposed include raising the land by building on artificial fill, as well as elevating structures on pilings and live with more water as seen in the Florida Keys. The plan also envisages promoting new development in the least flood-prone high ground areas along transit corridors. The project also outlines the expansion of waterfront parks and canals in the most flood-prone neighbourhoods, as well as creating a network of small spaces for water across gardens, streets, and parks across the county.

“Fortunately,” the document notes, “there are many steps we can take now that will also help us address urgent short-term challenges while also setting us up to be better prepared for rising sea levels.”

Keeping NY awake to the danger of climate change

The New York City Panel on Climate Change projects that by the 2080s, sea level increases of up to 55 inches (1.4 metres) are projected, with the risks from severe storms and flooding inevitably expected to increase, too. And, while the gradual rise in water levels is hard to perceive except under exceptional circumstances such as spring tides and superstorms, it is already evident that when such events do occur, the impacts are felt more severely, and they last longer.

In a previous interview with Aquatech Online, Anusha Shah, director of Resilient Cities at Arcadis, explained that: “Building resilience means everyone preparing better for a disruption and improving current systems.”

In 2019 New York’s Mayor de Blasio revealed the details of his city’s resiliency plan study. According to the Resilience Study, by the 2050s, some 37 per cent of properties in Lower Manhattan will be at risk from storm surge with over six feet (two metres) of projected sea-level rise by the end of the century.

By then, almost half of all properties in the district will be at risk from storm surge, and 20 per cent of Lower Manhattan streets will see daily tidal inundation. Meanwhile, a rise in the water table rise is projected to put around 7 per cent of buildings at risk of destabilization.

“Protecting Lower Manhattan is critical for the 62,000 New Yorkers who live here and, big picture, for the long-term health of our city’s economy," said Jessica Lappin, President of the Alliance for Downtown New York.

The study makes a number of recommendations designed to protect lower Manhattan from climate change. Featuring some $500 million in capital projects, the strategy will project some 70 per cent of lower Manhattan under the auspices of the Lower Manhattan Coastal Resiliency (LMCR) project.

Securing future economic growth

Today action is already underway. For example, with $134 million in bonds Battery Park City Authority (BPCA) is working on four interrelated resiliency projects, including the creation of a continuous flood barrier.

Kicking off the design work in 2018, construction began last year and is scheduled to conclude in 2024. Battery Park City is committed to constructing a perimeter storm and flood protection system on its southern boundary. This structure will decrease vulnerability from storm inundation and flooding.

“Hurricane Sandy showed us how vulnerable areas like Lower Manhattan are to climate change,” said de Blasio. “Our actions will protect Lower Manhattan into the next century.”

“Hurricane Sandy showed us how vulnerable areas like Lower Manhattan are to climate change.”

By building resilience, global cities that are most effective are not just planning to minimise the impact of climate change; they are also putting the measures in place that will secure future economic growth.