Gray vs Green Infrastructure

Engineered and Natural Systems Work Together

As land is developed, more surfaces are covered with concrete and asphalt. These hard surfaces don’t absorb rainwater, so the water runs off instead of soaking into the ground. To manage this runoff, communities use two types of systems: gray infrastructure and green infrastructure. From underground pipes to green spaces, these systems work together to reduce flooding and support healthy waterways.

What Is Gray Infrastructure?

Gray infrastructure is the traditional storm drainage system. It includes inlets, ditches, pipes and other structures built to collect rainwater and move it away quickly. This helps reduce flooding in streets and neighborhoods.

Here’s how it works:

  • Storm drains and other inlets collect rainwater and runoff from streets, parking lots and other hard surfaces.
  • This water, called stormwater, moves through underground pipes and goes straight into creeks, lakes and ponds.
  • Stormwater does not go through a wastewater treatment plant, so it isn’t cleaned before reaching waterways.

Common examples of gray infrastructure include:

  • Storm drain inlets along curbs
  • Underground drainage pipes
  • Culverts that let water flow under streets

What Is Green Infrastructure?

Green infrastructure uses natural processes to manage stormwater. When rain falls on hard surfaces it can’t soak in. Green infrastructure acts like a living sponge, slowly absorbing and filtering out pollutants. It also creates habitats for wildlife, supports healthy ecosystems and adds beauty to communities.

Here’s what green infrastructure can do:

  • Control stormwater runoff to better mimic a natural response to rainfall.
  • Reduce the volume of stormwater runoff entering waterways through infiltration and rainwater harvesting.
  • Filter pollutants with the help of plants and microorganisms.
  • Provide habitat for birds, insects and other wildlife.
  • Support biodiversity and overall ecosystem health.
  • Enhance community spaces, create opportunities for environmental education and provide additional social and economic benefits.

Examples of green infrastructure include:

  • Rain gardens (bioretention)
  • Constructed wetlands
  • Permeable pavement
  • Rainwater harvesting
  • Bioswales (vegetated drainage channels)

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