Gray Infrastructure & Nature-Based Solutions

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Gray infrastructure, also known as hardened or conventional infrastructure, typically uses hard materials such as concrete, steel, or rock, while nature-based solutions, often called green infrastructure, rely on natural elements and processes. Both gray and green infrastructure can effectively address issues such as coastal erosion, urban stormwater runoff, and riverine flooding. However, nature-based solutions offer additional benefits to people and the environment, including recreational opportunities, wildlife habitat, and enhanced water quality, while also increasing resilience to environmental hazards. Gray infrastructure also tends to relocate the problem, rather than addressing the underlying cause. For example, breakwaters may stop coastal erosion from occurring directly behind them, but increase erosion in adjacent areas. 

There is no one-size-fits-all approach when designing infrastructure projects. In certain contexts, nature-based solutions can independently achieve project goals. For others, a hybrid approach–combining both gray and green elements–is needed. In hybrid projects, or when green infrastructure elements are added to existing hardened infrastructure, nature-based solutions can complement and protect the gray infrastructure elements, increasing their durability and sustainability. Sometimes, conventional gray infrastructure remains the best option. Nature-based projects are often designed to be multi-purpose, multi-benefit projects, while gray infrastructure is more often built for a single purpose. Both approaches require thoughtful consideration of the issue(s) being addressed, intended outcomes, anticipated climate change and future conditions, and ability to maintain the selected option into the future.