Adapting Cities to Sea Level Rise: Green and Gray Strategies

Adapting Cities to Sea Level Rise: Green and Gray Strategies


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In 2012, Hurricane Sandy floods devastated coastal areas in New York and New Jersey. In 2017, Harvey flooded Houston. Today in Miami, even on sunny days, king tides bring fish swimming through the streets in low-lying areas. These types of events are typically called natural disasters. But overwhelming scientific consensus says they are actually the result of human-induced climate change and irresponsible construction inside floodplains.

As cities build more flood-management infrastructure to adapt to the effects of a changing climate, they must go beyond short-term flood protection and consider the long-term effects on the community, its environment, economy, and relationship with the water.
Adapting Cities to Sea Level Rise, by infrastructure expert Stefan Al, introduces design responses to sea-level rise, drawing from examples around the globe. Going against standard engineering solutions, Al argues for approaches that are integrated with the public realm, nature-based, and sensitive to local conditions and the community. He features design responses to building resilience that creates new civic assets for cities. For the first time, the possible infrastructure solutions are brought together in a clear and easy-to-read format.

The first part of the book looks at the challenges for cities that have historically faced sea-level rise and flooding issues, and their response in resiliency through urban design. He presents diverse case studies from New Orleans to Ho Chi Minh to Rotterdam, and draws best practices and urban design typologies for the second part of the book. 

Part two is a graphic catalogue of best-practices or resilience strategies. These strategies are organized into four categories: hard protect, soft protect, store, and retreat. The benefits and challenges of each strategy are outlined and highlighted by a case study showing where that strategy has been applied.

Any professional or policymaker in coastal areas seeking to protect their communities from the effects of climate change should start with this book. With the right solutions, Al shows, sea-level rise can become an opportunity to improve our urban areas and landscapes, rather than a threat to our communities. 

Product Details

ISBN-13: 9781610919074
Publisher: Island Press
Publication date: 11/20/2018
Edition description: None
Pages: 160
Sales rank: 1,127,117
Product dimensions: 7.90(w) x 8.90(h) x 0.40(d)

About the Author

Stefan Al is an architect, urban designer, and infrastructure expert at global design firm Kohn Pedersen Fox in New York. He has published several books, including Factory Towns of South China: An Illustrated Guidebook and The Strip: Las Vegas and the Architecture of the American Dream. As a practicing architect and urban designer, he has worked on renowned projects such as the Canton Tower in Guangzhou.

Read an Excerpt



* Sea level rise is already affecting our cities and, depending on where you live, may soon be coming to your home. In 2012, flooding from Superstorm Sandy devastated the Jersey Shore. In 2017, Hurricane Harvey flooded Houston. Today, in the low-lying areas that surround Miami, even on sunny days, king tides bring fish swimming through the streets. These and other events are typically called natural disasters. But overwhelming scientific consensus says they are actually the result of human-induced climate change and irresponsible construction inside floodplains.

Aftermath on the Jersey Shore

Flood-damaged homes dot the shore after Superstorm Sandy. Some homes even completely disappeared.

(Source: U.S. Fish and Wildlife Service-Northeast Region, Wikimedia Commons) Climate change is a severe and growing challenge for twenty-first century cities, from droughts to forest fires and from storms to rising sea levels. The most tangible changes are related to water. Some areas will have too little water; others too much. Coastal cities will be strongly affected by the latter, as rising seas increase the occurrence of disruptive or nuisance flooding in urbanized areas during high tides, not just during storms. Water threats in coastal cities can even come from all directions: increased rainfall from above, rising groundwater from below, floods from rivers, and floods from the sea — all worsened by climate change and land subsidence.

Currently, sea levels are rising on average 3.2 millimeters (0.13 in) per year,1but this number is expected to rapidly increase as average temperatures rise, with roughly seven and a half feet of sea level rise expected per degree Celsius of warming. Even the conservative 2 degrees Celsius of temperature increase, the goal of the Paris Agreement, would likely cause sea levels to rise an average 4.6 meters (15 ft), putting coastal cities at risk and some countries, such as the Maldives, entirely under water. Climate Central estimates that two degrees Celsius of warming would lock in 6.1 meters (20 ft) of sea level rise in Miami, leaving almost the entire city underwater. But a mere 0.91-meter (3 ft) rise in Bangladesh would submerge 20 percent of that country, displacing as many as 30 million people. Rising sea levels alone will usher in an entirely new category of human tragedy: the "climate refugee." Rising water also leads to more powerful storm surges and greater flooding on already vulnerable coastlines, forcing more residents to retreat and relocate.

Sea level rise, even a small increase, can dramatically disrupt the day-to-day operation of cities, potentially threatening people's access to power and safe water. Climate change causes extreme weather events, such as floods, to be more recurring and intense, jeopardizing not only the aboveground transmission and distribution electricity networks, but even areas with buried power lines. Furthermore, power outages can cause wastewater treatment plants to malfunction, leading to potentially unsafe water. But flooding can also threaten the functioning of the water system in other ways. Water and sewage plants are typically located at geographic low points, such as along coastlines, to aid wastewater flowing to plants by gravity, which makes them susceptible to overflows at high tides. In addition, stormwater could flow back into the system's discharge pipes, causing backflow. The higher the water level is, the larger the amount of river water flowing back into the drainage system outfalls. When saltwater breaches a plant's treatment system, it could leave permanent damage. Finally, floods can cause saltwater intrusion in coastal freshwater aquifers, as happened during Hurricane Katrina.

Compounding the problem is the rapid urbanization of coastal areas. Human settlement will continue to favor coastal areas, for their benefits of ports, recreation, fishing, and potentially moderate temperatures. In China, for instance, the fastest growing and largest cities, such as Shanghai, Guangzhou, and Tianjin, all face rising rivers and oceans. These three cities alone have added about 40 million people combined in the last thirty years. With the world urban population expected to grow by another two and a half billion by 2050, the problems will only increase. The World Bank predicts that by 2050, $1 trillion or more of assets will be at risk every year in cities worldwide.

Sea level rise will also threaten natural habitats in coastal areas. As seawater reaches farther inland, it can cause land erosion, flooding of wetlands, saltwater intrusion in aquifers, and contamination of agricultural land, potentially causing the loss of habitat for plants and various species of birds and fish.

The best way to prevent these losses would be to avoid climate change altogether, or to mitigate the effects by reducing emission levels of heat-trapping greenhouse gases, or to stabilize them, such as through the efforts of the Paris Agreement. But since we are already realizing the effects of climate change, cities will also need to adapt to challenges such as sea level rise. One way to respond to future or present flooding problems is by building flood management infrastructure.

A typical approach to floods deals only with the symptoms of the problem. This approach includes increasing a community's "resilience" — in the shallow definition of the term — by improving the capacity to bounce back from a disaster. Examples include evacuating areas before a disaster, temporarily housing people in emergency shelters, or paying out insurance claims after the damage is done, in order to rebuild afterward. But this is very costly, with billions of dollars of losses from floods. Experts advocate for disaster prevention rather than treatment. The Federal Emergency Management Agency estimates that every dollar spent on the reduction of a community's vulnerability to disasters saves people approximately six dollars in economic losses.

Another approach to floods — building dikes and seawalls — provides only a short-term stopgap. Imagine a beach house with a beautiful view of the shore. Suddenly, the view is of a concrete wall. A seawall can be a real beach killer in many ways. When a wave strikes a seawall, wave energy is reflected back and carries sand offshore. If the sand is not replenished, the shore will erode and the wall will eventually be undermined, and the environmental harm is done.

Flood management solutions need to be considered beyond their short-term effect to their long-term impact on communities, environments, and economies. They need to respect a community's relationship with the water, as well as the ecological and environmental health of the surrounding area. They should also lead to economic benefits beyond just protecting from floods — for instance, by unlocking the real estate and economic development potential of the newly secured areas, which could help pay for the infrastructure. In short, flood management infrastructure should not only protect from floods, but should be integrated into the landscape and the public realm. New infrastructure built in or near our cities should be balanced with place-making.


Before the storm

To enjoy sea views, beachfront development has been built on many parts of vulnerable shorelines.

After the storm

During the storm, wave action moves sand from the upper beach to the lower beach, weakening structural integrity underneath beach houses.

Before replenishment

Before sand replenishment, there is no exposed sandy beach. There is only a narrow beach at low tide.

Immediately after replenishment

Sand berm was constructed to prevent storm surge and to enhance recreational use.

1-3 years after replenishment

Most of the sand berm has been washed away, except at the top of the berm. However, neither purpose of the new beach — storm protection or recreation — is achieved.


Before the wall

Sand dunes are often eroded away as a result of natural processes.

Wall constructed

Homeowners react to the erosion by building a small-scale wall.

2-40 years later

People build higher walls to deal with erosion. In the process the beach disappears.

10-60 years later

Higher-density developments replace cottages and beach houses. A bigger seawall is required for storms.

This book, Adapting Cities to Sea Level Rise, aims to introduce design responses to sea level rise, drawing from examples around the globe. Going against standard engineering solutions, it argues for approaches that are integrated with the public realm, nature-based, and sensitive to local conditions and the community. In short, it features design responses to building urban resilience that create new civic assets for cities. Resilience here is used in the more complex meaning of the term, defined by the Rockefeller Institution's 100 Resilient Cities program as the "capacity of individuals, communities, institutions, business, and systems within a city to survive, adapt, and grow no matter what kinds of chronic stresses and acute shocks they experience." In contrast to the technical definition, this broader definition of resilience has the potential to transform a city.

Fortunately, there are ways in which smart design of flood management infrastructure can make a real difference. For instance, a standard solution of building a revetment — a sloped surface typically built of concrete rocks that dissipate wave energy — has all the charm of a military bunker and can block human access to the shore. In contract to this typical engineering solution, a "designed" solution incorporates other parameters beyond flood protection, such as human use. For instance, the beach town of Cleveleys, United Kingdom, integrated public spaces into flood protection. Instead of a standard revetment, the city built a sinus-shaped structure with amphitheater-like viewing spaces and steps. The steps accentuate the beautiful curvilinear shapes while creating access to the beach and even adding to public space, which is important for a coastal town that relies on tourists.

Nature can play an important role in flood management infrastructure. Instead of reinforced concrete defenses that get the full force of waves and will finally succumb to the undercurrent of the sea, there are solutions that rely on nature's long-term capacity to adapt. Dunes, for instance, are more sustainable sea barriers to absorb the force and velocity of waves, and can also add to the landscape and provide natural habitats. They require only a simple stabilization and wind erosion prevention measure: dune grass, a grass tolerant to high salinity and extreme glare. Landscape architect Ian McHarg was a big fan of this humble plant. "The dune grass, hero of Holland," he wrote in his classic book, Design with Nature. Another example is afforestation, planting trees in a drainage basin to help intercept and store water, and thus help reduce a river's discharge and the potential risk of flooding. In addition, coral reefs, seagrass meadows, and mangroves can offer natural ways to prevent coastal erosion, as well as promote biodiversity and water filtration. Today, this philosophy is steaming ahead through the organization EcoShape, which uses "ecosystem services" such as the force of waves and ocean currents to move dredged sand along the southern coast of the Netherlands to replenish beaches and promote dune development — a project called the Sand Engine. It also pioneered the "sandy foreshore," a natural and cheaper alternative to traditional dike reinforcement, in Houtribdijk, the Netherlands. It consists of a large quantity of sand, placed in front of a dike, that reduces the force of waves and also enhances the natural environment and recreational activities.

On the shore, seawalls and revetments can protect the inland areas. But in contrast to these hard edges, living shorelines and dunes can protect the inland area while also creating landscape and promoting biodiversity. Inland, floodable squares help drain floodwater inland, as can flood parks and wetlands, in addition to hosting a range of species, including birds.

This book addresses traditional gray-infrastructure strategies to flood protection, but it also features natural or "green" strategies. All of the functions of gray infrastructure can also be solved by nature. The motto is "soft when possible, hard when necessary."

Sandy foreshore, Houtribdijk

An example of a hybrid gray and green solution, the sandy foreshore uses natural processes to strengthen the existing dike.

(Source: EcoShape)

Gray solution

Gray solutions, often developed by civil and environmental engineers, are flood protection structures that are (almost always) permanent. Hard solutions focus on controlling flooding and sea level rise. Examples of hard solutions are seawalls, floodwalls, and revetments. The downside of these projects is their disruption of ecological systems. They are generally expensive and require maintenance.

Traditionally, heavy infrastructural solutions were implemented to minimize coastal flooding. Layers of hard interventions have been implemented by coastal engineers. Concrete breakwaters protect coastline from waves by reducing the intensity of wave action and thereby reducing coastal erosion. Revetments on shorelines reduce the dynamic force of tidal action. Dikes and floodwalls seal off the inland from tsunamis and floods. Existing and new developments can be placed on higher grounds or elevated to prevent further damage to property. Floodable squares and stormwater infiltration beds can help drain floodwater inland.

Green solution

Green solutions utilize ecological and environmental principles and practices to provide flood protection, as well as reduce erosion and stabilize shorelines, while also enhancing habitats and improving aesthetics (as compared to hard solutions). Often, soft solutions are less expensive than hard solutions and lower in maintenance, but they are not permanent and are subject to erosion.

Ecological interventions to flood management depend on natural processes and ecological systems. Natural and artificial breakwaters reduce the tidal action while providing habitats for underwater sea creatures. In contrast to a hard edge such as a seawall, living shorelines and dunes can protect the inland area while maintaining views and access to the waterfront. Inland, flood parks and wetlands help store and release floodwater.

Besides waterfronts driven just by defense, waterfront typologies can also be driven by the economy, community, or ecology.

(Source: Arcadis)

But, the soft ecological solutions to flood management depend on natural processes and ecological systems, which can take up more space. In addition, they often are vulnerable to human use. Although dune grass is strong in holding together the dunes, it is vulnerable to trampling. Therefore, people should not be allowed to walk on dunes, which makes them a complicated solution in dense, urban areas. Nevertheless, if the dunes are carefully designed with separate walking trails or elevated platforms, they are still viable solutions that not only protect people but also give them recreation space.

In summary, through marrying urban and landscape design with infrastructure, flood management can become a strategic civic asset for cities, communities, and environments. This philosophy considers sea level rise not as a threat, but as an opportunity to improve our urban areas and landscapes.

FOUR FLOOD MANAGEMENT STRATEGIES: Hard Protect, Soft Protect, Store, and Retreat

The solutions in this book are organized by four types of flood management strategies that describe their response to dealing with water: 1) hard protect, 2) soft protect, 3) store, and 4) retreat. The first two strategies are gray and green "attack" or "defend" strategies that try to keep the water out, either through holding the line (defending), or by aggressively advancing the line through dredging and land reclamation (attacking). The last two are "accommodation" strategies that let water in, either by storing and controlling floodwater inland, or through "retreat," by either raising ground plains or moving to higher grounds.


Excerpted from "Adapting Cities to Sea Level Rise"
by .
Copyright © 2018 Stefan Al.
Excerpted by permission of ISLAND PRESS.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

Table of Contents

Forward by Edgar Westerhof

Chapter 1: Introduction 
Part One: City Strategies
Chapter 2: Rotterdam, South Holland, The Netherlands
Chapter 3: New York City, New York, USA
Chapter 4: New Orleans, Louisiana, USA
Chapter 5: Ho Chi Minh City, Vietnam

Part Two: Local Strategies
Chapter 6: Hard-Protect Strategies
Chapter 7: Soft-Protect Strategies
Chapter 8: Store Strategies
Chapter 9: Retreat Strategies
Chapter 10: Conclusion


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