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Facing Down the Floods | New York and London

Thames Barrier

New York and London are preparing for a wetter future with schemes to protect these world cities into the next century.

A new wave of engineering is facing down the threat of flooding, even in the world’s most prized cities.

The weather can be a fierce opponent when it comes to protecting urban environments. Disasters such as Hurricane Katrina and its tragic aftermath in 2005 serve as a cruel reminder that nature must not be underestimated.

Engineers are being tasked with finding ways to do more to protect the vulnerable, particularly those living in high density areas, because it was all too awful watching so many have their lives ripped apart while seemingly being neglected by their political leaders.

Post Katrina, New Orleans needed better defences. And that meant, among the levees, much monumental concrete engineering, which helped restore faith that no life in a developed nation should be left vulnerable to the elements.

However, what also emerged in the calm after the storm was a change in narrative – political leaders and engineering heads talking less of flood protection and more of flood risk management.

It is an approach that attempts to give due respect to nature’s might and work more with it than against it. Softer, more hands-off engineering is on trend, allowing flood plains to take the strain, while hard-concrete-wall building resistance has fallen out of favour.

New Civil Engineer explores how two iconic cities are balancing the desire for robust defence with community needs.

New York

The Big Apple is a city that knows how to sell itself. Off the back of the success of the Instagram-friendly High Line urban walkway, it hopes to recreate a similar buzz for Lower Manhattan with what is being dubbed the “Dryline” – a direct response to the devastation caused by Hurricane Sandy.

The 29 October 2012 storm took 44 lives and caused great economic losses – the New York Stock Exchange suspended trading for two days amid the chaos, in which 130km² of the city was flooded at a cost of $19bn (£14.8bn).

Infrastructure damage was illustrated by the many images beamed around the world showing the city’s subway system deluged with flood waters.

Once the shock began to subside, questions were asked about what a post-Sandy city should look like.

Those questions have taken time to answer in detail but the BIG U is the scheme favoured to make the most vulnerable part of Manhattan more robust. It is a 16km loop around Lower Manhattan created by a team led by architect BIG and comprising a series of small projects, ranging from raised landscaping through to berms and improved urban parkland areas, which will act as flood resilient plains during storm events.

One of the key elements now making headway toward construction is the 4km long East Side Coastal Resiliency (ESCR) project. Consultant Arcadis, which is acting as lead civil and structural designer for the ESCR, describes it boldly as “the first element of a coastal storm and sea level rise defence system” for the East Side and Lower Manhattan.

There are traditional and familiar engineered flood defences being built along the stretch between East 25th and Montgomery streets.

Renovated parks (most notably the East Park) will be flanked landside by “bridging berms” ranging between 910mm to 2.4m in height. These, along with flood gate and flood wall interventions, will both protect the area from 100-year storms and rising sea levels.

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East Side Coastal Resiliency project

East Side Coastal Resiliency project | Space for floodwater when required

The difference is that these soft engineering elements will also “offer waterfront access for relaxation, socialising, and enjoying river vistas by providing pleasant, accessible routes over the highway into the park”, according to the proposal. The idea is less about keeping people away from the water, and more about making spaces that can, in non-flood times, be accessible and useful for inhabitants. If a storm comes, the land is given over to the rising waters and the hard defences kick in.

Knitting together a sufficiently engineered design that works with the potentially wide-ranging desires of a local community has been challenging. And, no doubt, getting the right balance between consultation on community infrastructure and funding decision making has been a challenge too.

Questions remain over how well the project is delivering on this, given the design is yet to be fully agreed with local residents and construction is yet to get out the ground – early expectations were that construction would begin in mid-2017 and complete by 2020. But the plan is now in final stages of design with funding in place to the tune of $760M (£600M), and the hope is that construction will get underway next spring with a completion date of 2024.

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East Side Coastal Resiliency project

East Side Coastal Resiliency project | Space for leisure when floods are not a threat

According to a document addressing residents concerns, the city says: “Coastal protection infrastructure is just one of many measures that can be used to increase resiliency.

“While the ESCR project will help to reduce flood risk, no single measure can fully protect a neighbourhood from climate events.

“This is why the city is working to build awareness and ensure that communities take necessary precautions on multiple fronts, including implementing resilient building standards, expanding green infrastructure, increasing disaster preparedness, and planning for evacuation.”

London

Over the pond in the Big Smoke, the picture appears to be under control as far as storm surge threats are concerned.

London already has its highly effective hard engineering defence in the form of the Thames Barrier. And while the structure opened in the early 1980s with plans for it to last until 2030, a rigorous maintenance regime and conservative 1970s flood risk modelling mean it looks set to play a key role in defending the city into the next century. By 2050 a decision will have had to be made as to whether to construct a new barrier downstream at Long Reach to be operational by 2070.

There is no time for the city to rest on its laurels though – the tidal surge threat not only still exists, but increased pressure from city growth and climate change has put the problem front and centre.

For some, when the barrier is finally retired it will simply mean building a new one. And that may still happen. But a large-scale barrier will not, and currently does not, stem the tide alone.

What the Environment Agency describes as its “world class system of defences” includes the iconic barrier, along with seven significant but smaller barriers, 300km of flood walls and barriers and more than 400 other structures such as flood gates outfalls, pumps and pumping stations.

The Agency’s Thames Estuary 2100 plan, conceived over a six-year period to 2012, hopes to retain its world-leading role. In a programme stretching to the next century, its theories are based on current guidance on climate change as well as Agency-funded research on changes to fluvial flows, sea storm surges, and sea level rise due to thermal expansion and polar ice melt.

As an example of the intensity of the planning process for TE2100, the Agency explains that “modelling on sea level rise and river flows took up a year’s capacity of the Met Office supercomputer”.

The government gave the go-ahead to the first 10 years’ capital spending and a co-located team involving Agency staff along with its delivery partner, consultant Jacobs (previously CH2M) has been working on the £308M programme since 2015. Also involved are staff from contractor Balfour Beatty, contractor and designer Qualter Hall, consultant KGAL and designer and manufacturer Hunton Engineering.

The main works in this period focus on asset refurbishment and replacement along 175km of the tidal Thames, from Teddington in west London to Sheerness in Kent and Southend-on-Sea in Essex.

To date, it is the UK’s largest single programme of flood risk management work. It is based on a relative sea level rise estimate of 900mm by 2100 but is adaptable to differing rates of sea level rise up to 2.7m by 2100. Some of the most significant projects costing £64M have been completed.

  • Thames Barrier

    Facing Down the Floods | New York and London

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