New Coastal Infrastructure Should Be Nature-based

Fully embracing nature-based design approaches could yield a 91% carbon improvement and a 30% cost savings on average, in comparison with business-as-usual approaches. / Climate Positive Design, Harvard Graduate School of Design

By Jared Green

Seas are expected to rise by 10-12 inches by 2050. In the U.S. alone, that means more than 170 million residents of coastal urban and suburban areas will be impacted.

New coastal infrastructure is needed to reduce communities' exposure to rising seas, storm surges, and coastal flooding. This future infrastructure can be grey - made up of carbon-intensive concrete and steel - or nature-based and incorporate trees, plants, soils, and local materials.

According to new research by Pamela Conrad, ASLA, PLA, and Charles Waldheim, Hon. ASLA, for the Harvard University Salata Institute for Climate and Sustainability, there are clear benefits to nature-based approaches to coastal infrastructure. They can emit up to 91 percent less greenhouse gas emissions and be up to 30 percent cheaper than grey solutions.

"Nature-based solutions cost less, emit less, and sequester more carbon. They deliver adaptation and mitigation at the same time while also providing cooling, habitat, and community benefits. With the right project support, they can truly be a win-win," said Conrad.

The research found that a business-as-usual approach that would create more grey coastal infrastructure in the U.S. could result in greenhouse gas emissions totaling 2.1 gigatons of carbon dioxide by 2050, which is equivalent to 40 years of New York City's annual emissions. Swapping in more local and low-carbon materials could reduce that climate impact by 80 percent. And using nature-based solutions could offset those 2.1 gigatons and lead to an additional 17 million tons of carbon sequestration.

"The findings show that the material choices we make with coastal infrastructure projects can have a tremendous impact on embodied carbon emissions. By educating ourselves on the choices and collaborating with suppliers and manufacturers on material sourcing, we can turn a coastal project from being a climate change contributor to a solution that prevents it," said Aida Curtis, FASLA, president, Curtis + Rogers Design Studio, and Chair, ASLA National Climate & Biodiversity Action Committee.

The study looked at 12 landscape architecture-led works of coastal infrastructure in the U.S. For each project, Conrad and Waldheim provided an estimate of the greenhouse gas emissions from business-as-usual conditions. They also provided a first optimized alternative, which would be "imperceptible, relying on changes to material composition, sourcing, content, and below-grade applications." And then they offered a second alternative, which would include more "substantial structural changes that may require additional coordination, permitting changes, or design approval with the client/owner and team. These changes are necessary to incorporate a truer nature-based solution as the foundation of the adaptation design." Some project case studies don't have alternatives because the landscape architect used nature-based approaches for maximum emissions savings and sequestration gains.

Business-as-usual approach for Resilient Norfolk Coastal Storm Risk Management, U.S. Army Corps of Engineers. / Climate Positive Design, Harvard Graduate School of Design

Alternative approach, using nature-based solutions for Resilient Norfolk Coastal Storm Risk Management, U.S. Army Corps of Engineers. / Climate Positive Design, Harvard Graduate School of Design

"Many solutions are straightforward: source local materials, minimize or replace lightweight fill, use cement substitutions, incorporate recycled materials, and maximize planting. These strategies can dramatically cut emissions and are summarized in the report and expanded in the Climate Positive Design Toolkit," Conrad said.

Chris Hardy, ASLA, associate principal at Sasaki and a peer reviewer of the research, said the findings shows it's important to "reduce or eliminate concrete and steel structures - the hardening of the shoreline. Instead, use natural materials and planting approaches that can stabilize shorelines."

Curtis contributed data on her project at Morningside Park in Miami, Florida to the research team. The park involved a partnership with the Nature Conservancy and uses mangroves and local limestone to reduce erosion and protect against storms. She emphasized that local and reused materials are key to reducing the emissions impacts of coastal adaptation projects. "Thinking local will guide you to products and materials that don't have high shipping costs and are indigenous to the area - local soils, rock, and aggregates. And look at recycled materials: In the case of Morningside Park, recycled steel for the pilings would have made a significant difference in emissions. When in doubt, add more trees."

Morningside Park, Miami, Florida. Curtis + Rogers Design Studio / Climate Positive Design, Harvard Graduate School of Design

If policymakers and communities follow the guidance provided in the research, it can lead to significant changes in how coastal infrastructure is planned and designed. "Replacing hard edges with soft, green infrastructure approaches requires a different relationship with the shoreline," Hardy said. "One that needs more space, providing longer littoral zones, and wider buffer zones - and a different expectation for maintenance and management." He sees no alternative to this approach: "Armoring waterfronts will directly contribute massive amounts of emissions from the embodied carbon of construction. These emissions are compounded by the relatively short lifecycles of marine structures."

Nature-based solutions like Hunter's Point South park in Queens, New York, which were designed by SWA/Balsley and Weiss/Manfredi, have been tested by major storms and proven safe and resilient. These kinds of projects show that "coastal communities can safely invest in strategic nature-based solutions, knowing they provide flood mitigation, storm surge attenuation, and habitat creation benefits while addressing the pressing need of our times - the reduction of embodied carbon emissions," Curtis said.

ASLA 2019 Professional General Design Honor Award. Hunters Point Park South, Queens, New York. SWA/Balsley and Weiss/Manfredi. / David Lloyd

Nature-based approaches will also provide so many more co-benefits than a steel and concrete coastline. "Let's not forget the added benefits of ecological restoration, biodiversity enhancement, and community well being."