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Felixstowe coastal defence, UK
Felixstowe’s coastal defence project halted severe erosion to provide improved protection, and gave back a valued amenity to local people.
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Working at the frontiers of coastal engineering

Diverse skills and experience are needed to manage the increasing risks brought by climate change.

More and more, communities are seeking to improve their resilience to the physical impacts of climate change, to create a sustainable future. Increasingly severe and frequent rainfall and storms, plus rising sea-level and more extreme storm surges, pose a particular threat in coastal areas.

Shorelines need to be protected against storm damage and erosion, and inland areas against rising water tables, waterlogging, saline intrusion and other impacts. In addition, the consequences of any solution have to be examined to ensure protecting from the sea does not increase inland flood waters as it is unable to drain away. These complexities have to be considered alongside various future predictions of different weather elements, increasing the challenge further.

Building resilience offers opportunities for environmental and community improvements that bring economic and social benefits beyond risk mitigation. All these factors need to be considered when developing a strategy and choosing how to invest public money to meet the greatest need and generate the greatest benefit.

The coast is a dynamic environment. Understanding it when tranquil, besieged by raging typhoons and everything in between is key to developing long-lasting solutions. Every coastline is unique and the various processes need to be understood.

“Our coastal team has worked on every continent except Antarctica and in every conceivable coastal environment,” says Josh Carter, deputy practice leader for coastal engineering at Mott MacDonald. The science of understanding the geography and the geometry of the coastline, as well as coastal processes – the effects of wind, waves and currents – is known as morphology. It explores the effects of the sea on the land.

Morphology is a relatively young discipline. Accurately representing how the coastal system behaves and changes was near impossible before the introduction of computer modelling, which started to become prevalent in the mid-90s. A quarter century on, and today’s computing power enables the effects of storms and tidal cycles to be understood and modelled, giving an accurate picture of the coastal processes now, and provides a tool to help understand how they may be in years to come.

Our 2D and 3D models of wind and wave formation, the interactions between waves and structures, and currents in the water have been validated and used to guide coastal solutions worldwide.

Supporting thriving communities

More than 600M people – around 10% of the world’s population – live in coastal areas that are less than 10m above sea level. Trade, tourism and leisure attract people to live near the sea. As a consequence, coastal erosion poses a threat to homes and social infrastructure, ports, roads, railways, airports, industrial complexes, business parks – assets of all varieties.

“The waterfront is often very heavily utilised by business and the community. In many locations commercial and recreational uses sit almost side by side. How you treat the coast and change it can have big social and economic impacts,” Josh says.

“It's an essential part of our job in developing coastal protection or restoration projects to engage with the public, government agencies, civil society organisations and businesses – all who have a stake in the coastal environment. Communicating with and co-ordinating between them is important for addressing their different needs aspirations, and how these would impact on the coast.”

Surfside Beach – simply Surfside to locals – is a village founded in 1975 in Brazoria County, Texas, US. It is located on a storm-battered part of the Gulf of Mexico coast. Surfside was ravaged by Hurricane Alicia in 1983 and by Hurricane Ike in 2008. In addition to hurricanes, erosion has eaten the shoreline back by more than 6m per year, with the loss of homes and roads, and threatening utilities.

In 2007, the Texas General Land Office employed us to study local erosion processes and develop a 25-year plan for shoreline protection and stabilisation. We used numerical modelling to simulate waves, currents, sediment transportation, erosion and accretion.

Our coastal engineers first designed and oversaw the construction of a 1.1km long straight stone revetment, initially designed only as a temporary measure that would protect the community in the event of a five-year storm. This was completed only seven days before Hurricane Ike struck. Although the structure was severely damaged by the storm, with 40% of the stones displaced, it protected Surfside’s main road, water supply and wastewater system, and blunted the force of the storm surge.

With the benefit of observing Ike’s impact, we redesigned the revetment so make it more resistant to hurricane damage, and improved two long jetties protecting Surfside’s harbour. We selected granite, the strongest rock we could find in Texas, which was cut into close-fitting blocks to minimise voids and achieve a structure with the best possible resilience to pounding waves. We also completed a beach nourishment in front of the revetment.

Mott MacDonald’s efforts have improved Surfside’s resilience while maintaining the community’s status as a stellar surfing destination.

Transferable technology

We have been continuously pushing barriers in terms of technological innovation. With use of gaming computer technology in model simulations, utilisation of multiple machines across the Mott MacDonald Network, and 24-hour working across global teams, we can achieve so much more than 10 years ago. We know the future will have greater technological advances and we are becoming more agile to embrace technologies as they are available, such as artificial intelligence (AI).

In 2015, Dwr Cymru Welsh Water (DCWW) launched the biggest coastal modelling investigation ever undertaken by a UK water company to enhance its understanding of the factors affecting water quality at 49 of its sites. Its goal was understanding how it can better invest resources so that Wales’ award-winning beaches can achieve crystal-clear bathing water quality.

We carried out coastal modelling, water quality modelling and surveys of its 1700km-long coast – a gargantuan task that included more than 10 major estuaries, over 900 assets and 70 sewer network models in both urban and rural areas, some of which were tourism hotspots. The challenge was made more difficult by a prolonged period of stormy weather right at the start of the project, with strong gales preventing survey boats from going to sea for months.

What brought the project back on track was our use of cloud computing, which reduced the time needed to run the large number of modelling simulations from months to weeks. Cloud computing enabled data to be collected and collated quickly – it was input by the survey team in the field. Our approach enabled more than 2500 simulations to be run simultaneously using processing power equivalent to 120 high-end computers.

Our team completed the equivalent of six months of water quality simulations in only two weeks.

We are now exploring how artificial intelligence can help improve and speed up calculations from three months to a few minutes’ time. “It's very much a new frontier in coastal engineering,” says Josh.

Kick-starting regeneration at Colwyn Bay

Just as waterfront regeneration can boost a coastal economy, lack of intervention can result in economic degradation. Scoured away by tides, currents and storms, the beach at Colwyn Bay in north Wales, UK, had all but disappeared. Without expansive sand, the town had lost its appeal to holidaymakers. It was in decline. And with no beach to ‘soak up’ the energy of crashing winter waves – and the promise of worse to come with climate change – the town’s aged sea wall was suffering damage and, in places, in danger of collapse, putting the town at risk.

Long term, patching up the sea wall solved neither the town’s economic woes nor its vulnerability to the sea’s relentless assault, and it was expensive. The conventional solution, to defend with a rock-armour wall, would forever cut off the sea from the town, kyboshing seafront regeneration. Physical and numerical modelling of coastal hydraulics showed that reinstating the beach, using tons of dredged sand, would improve the level of defence.

We designed a rock groyne to slow long-shore drift, and carried out further analysis to fine tune the design of groyne, beach profile and sea wall to achieve the former. And by engaging with the community and local businesses, we gained confidence that the project would kick-start regeneration.

Its new sea wall provides Colwyn Bay with a hard line of defence, but has also given the town a new promenade and the site for a brand new water sports centre and restaurant. Meanwhile, the beach buffers against winter storms while acting as a magnet for summertime sandcastle builders, sunbathers and surfers.

A decision based on cold, hard cash alone would have given the town an ugly rock barrier. Instead, the community and visitors got an attractive beachfront that has injected new economic life and hope. We were able to include the benefits of economic growth into the business case for investment rather than purely considering the avoidance of flood damage alone.

A stronger and safer future for Felixstowe

Not all solutions need to be rock and concrete. Our computer models help us understand and predict the erosion, and we can influence the processes to work with us in maintaining long-term protection.

Erosion has been a longstanding problem at the seaside town of Felixstowe, England. Starting at the beginning of the 20th century, 50 timber and concrete groynes were built to slow the drift of beach material. Despite repairs and replacements over the years, by the turn of the millennium the groynes were worn out and erosion accelerated. Over the course of a decade, the 1.5km-long beach had receded almost to the sea wall and lost 2m depth in places. Waves, tides and currents were shifting 10,000-20,000m3 of shingle and sand each year. Loss of the beach and damage to the sea wall placed approximately 1500 properties at risk of flooding by the sea.

We modelled the erosion process, drew up a range of defence options and simulated their effectiveness. The old groynes sliced the beach into 25m lengths and reflected wave energy back onto the beach. But the new rock structures we proposed are much more effective at absorbing wave energy, which meant fewer were needed. From a range of possible configurations we selected a solution involving construction of 18 large rock groynes to replace the old timber and concrete structures, plus beach recharge.

A priority for the project was to improve the value of the beach and seafront for the local community and stimulate the local economy through tourism. Enhancing the seafront was fundamental for accessing Environment Agency funding. We provided urban planning and landscape design as well as marine and coastal engineering expertise, to propose a new seafront promenade and revive the town’s existing park and gardens.

After steering the proposal through planning and helping Felixstowe Town Council to secure funding we carried out design and supervised construction, working with the contractor to recycle materials, include and communicate effectively with community groups, and accelerate delivery.

Felixstowe’s coastal defence project halted severe erosion to provide improved protection, gave back a valued amenity to local people, and provided a catalyst for seafront regeneration and economic growth.

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