As urban areas grow in population and footprint, many coastal cities are creating land where there once was ocean. This so-called “reclaiming” of land is not new — in fact, civilizations have been building land on top of bodies of water dating back to the Ancient Egyptians. However, urban planners and city dwellers are increasingly looking for ways to build more sustainably without damaging ecosystems and without increasing flood risk. A new trend, called blue-green infrastructure, marries ecosystem science and green engineering to develop city plans that maximize water and land ecosystems with the dual purpose of reducing disaster and creating more livable cities.

aerial view of pens and markers on an urban planning design sheet

What is blue-green infrastructure?

Blue-green infrastructure is physical urban planning that prioritizes water management (blue) and natural spaces like parks (green) to reduce flooding, improve quality of life and adapt to climate change. Typically, architects, engineers and urban planners will utilize landscape, street and building designs to complement natural water cycles that are historically disrupted by concrete. Examples include strategic green roofs, rain gardens and parks that are designed to address and absorb water flow issues.

skyscrapers and green parks near the ocean

Why do coastal cities need this?

Blue-green infrastructure can have many benefits for all cities. By designing infrastructure to accommodate the natural flow of water (and additional water based on flood predictions), cities can reduce the costs of water damage, improve the aesthetics of their districts and create an environment that is more livable for both city dwellers and nature. For example, parks can increase the health and social connectivity of neighborhoods, but also reduce heat island effect and absorb rain water that would otherwise flood streets and sewers and run off into the ocean. While all cities are at risk of polluting their watersheds, coastal cities have the additional responsibility of protecting the ocean.

Related: Reimagine a resilient future with this nature-based tool

people lying in grass near waterway with city buildings in the distance

Blue-green ocean cities

Coastal cities, and especially those built upon reclaimed land, damage nearshore areas with pollution and sediment that smother ecosystems and disrupt natural connectivity between habitats. This means not only disrupted movement for migratory species like birds and whales, but also disrupted interactions within life cycles.

For example, along tropical coasts there is an intricate relationship between coral reefs, sea grass beds and mangroves. Fish that sustain the reefs and supply commercial fisheries often use the mangroves as a nursery to lay eggs. Young fish hatch in the mangroves and move out to sea grasses to mature before migrating to live in the reef. Creating land on top of these interconnected habitats can cut off this natural pattern and negatively impact species, ecosystems and fishing industries.

According to The Independent, land reclamation in Singapore has damaged approximately 40 percent of all reef flats. Reclamation and urban planning done in Singapore without consideration for reefs since the 19th century has caused some species like the porites astreoides to die off completely and cause significant biodiversity loss to the reef overall. However, green engineering, with an understanding of and respect for these ecosystems, promises significant reduction in such detrimental impacts.

Related: Can the Cayman Islands save the Caribbean’s remaining coral reefs?

In St. Vincent and the Grenadines, a multi-year project is underway to restore this essential eco-connectivity by digging channels into the remains of a failed marina development project. This will improve the flow and quality of water and revitalize the reefs, sea grass beds and mangroves that had suffered significantly.

revitalized wetland park in Portland

Ecologists and green engineers: a partnership

By understanding these important ecological linkages, engineers and architects can prioritize low impact development and build in ways that reduce impact or even improve conditions. Chinese urban planners, for example, have undertaken an initiative to retrofit 80 percent of all cities into “sponge cities,” which will absorb and reuse an ambitious 70 percent of all rain water.

The coastal city of Lingang in Shanghai, for example, uses rooftop gardens, wetland parks and permeable pavements that slow down rain water and allow it to be absorbed into plants or evaporated into the atmosphere. This massive plan isn’t accessible for all cities though, and cost the struggling city of Lingang (rebranded as Nanhui New City) an investment of approximately $119 million (USD).

Aerial view of river and green spaces with city buildings in the distance

The future is blue-green

With ongoing debt and funding concerns, few cities can prioritize blue-green infrastructure, and investors are often more comfortable with what they know — highways, utilities, etc. Blue-green elements are typically considered extras, added to blueprints for visual appeal but the first to be slashed when budgets are cut.

Successful examples of green infrastructure and sustainable urban planning will help build confidence internationally. Other challenges, certification mechanisms and knowledge sharing networks, such as 100 Resilient Cities, encourage and incentivize conversations not only between scientists and engineers but between municipalities and regions. These initiatives, if backed with funding, will continue to push coastal cities to design with nature, test their results and share models for a new blue-green future.

Images via Shutterstock