Nature-based solutions for rainwater management can be an effective way to improve urban sustainability and climate resilience. Many cities have already began implementing a ‘grey to green’ water management transition and are enjoying the multifaceted and cost-effective advantages of green water systems
The City of Vancouver has become a leading municipality in the integration of green water infrastructure. Bioswales, raingardens, green roofs, and other examples of green infrastructure are becoming prominent throughout the city. Photo by author.
In wild environments, rainwater is readily absorbed into the soil and taken-up by plants. Most rainwater, in fact, trickles into the ground where it recharges groundwater reserves or is evaporated back into the atmosphere. What is left, water which flows overland into nearby lakes or oceans – such as streams or rivers – represents a small portion of the precipitation which falls in a healthy watershed, usually around only 10%1.
In cities, however, impermeable surfaces can significantly interrupt natural infiltration, adsorption, and plant transpiration patterns. Dominated by buildings, streets, and parking lots, the average city block can generate more than five times as much runoff as a forested area of equal size.
To manage rainwater and runoff, many cities have historically relied on grey water management infrastructure. These systems often consist of a centralized network of subterranean pipes which collect water from storm drains and downspouts, and direct runoff into nearby water bodies. But these systems can be inefficient, prone to flooding after severe storm events, and pollute downstream ecosystems with any sediment, fertilizers, road salt, oil, heavy metals, or other debris picked up by runoff as it flows through the streets.
As urban populations grow, the negative environmental impacts of grey water systems grow as well. Green water infrastructure presents an alternative approach to urban water management, and its proliferation can help make the management of rainwater in built environments more efficient and sustainable.
What Is Green Water Infrastructure?
Green water systems incorporate aspects of wild ecosystems into grey water systems by protecting, restoring, or mimicking natural soil infiltration and plant transpiration processes. By enhancing the capacity of plants and the soil to absorb water at or close to the source of rainfall, green water infrastructure can reduce downstream pollution and erosion.
Green water infrastructure can take on a variety of styles based on the context of the environment including proximity to or integration with grey infrastructure. Examples of green infrastructure include green spaces and parks, rain gardens and bioswales, permeable pavers, green roofs, and more. These features increase a neighbourhood’s capacity to manage and filter its rainwater, and facilitate absorption back into the environment and atmosphere.
Why Green Infrastructure
By improving an urban environment’s capacity to hold and manage rainwater at its source, green infrastructure can act as a safety valve for grey infrastructure systems during severe rainwater events and increase resilience to flooding. As well as reduce the amount of rainwater that is piped into nearby waterways, green infrastructure can improve the water quality of runoff by exposing it to plants and soil organisms which absorb and filter pollutants and particulate.
As well as benefits to stormwater management, green infrastructure can also provide secondary benefits to urban environments if integrated into existing grey water systems. Green infrastructure such as parks, bioswales, raingardens, and green roofs can combat ‘heat island’ effects (a phenomenon where dark pavement captures and re-emits heat), by providing shade and lessening the amount of exposed pavement. Urban greening can also assist with air quality and smog reduction because plants absorb carbon dioxide.
As apart of a sustainable approach to urban water management, green water infrastructure can be effectively applied at all scales of integration from the individual building or garden plot to community or city-wide initiatives.
A Grey to Green transition is already underway in many communities as more planners, politicians, and community members realize the benefits of a nature-based approach to urban water management. In 2017, the Government of Canada laid out a plan to invest $2 billion towards infrastructure projects through the Clean Water and Wastewater Fund, which includes green water management infrastructure. And at the municipal level, the City of Vancouver in 2019 unveiled its Rain City Strategy – a green rainwater infrastructure and urban rainwater management initiative. Keep an eye out for raingardens, bioswales, permeable pavers, green roofs and more in your community.
1 DC Water, “Green Infrastructure Fact Sheet”. green-infrastructure-faq.pdf (dcwater.com)
2 United States Environmental Protection Agency, “Protecting Water Quality from Urban Runoff”. Protecting Water Quality from Urban Runoff (epa.gov)
Ryan Hayes is an urbanist and an advocate for environmental sustainability. He completed a Bachelors of Science in Physical Geography at Simon Fraser University and also holds a certificate in Cartography from ESRI.