What is "impervious cover?"
Impervious cover is any built surface that prevents water from seeping or being absorbed into the ground. Impervious cover includes driveways, sidewalks, roofs, patios, pools, parking lots, and other areas of pavement. You might also see or hear this called impermeable.
The opposite of an impervious surface is a pervious or permeable surface, which allows for water to be slowed down and absorbed into the soil. Examples of permeable surfaces include parks, lawns, gardens, and green roofs.
Why is it important to reduce impervious cover?
Sidewalks and roads are important parts of our cities, but it's important that our city doesn't become too impervious. Here are just some of the ways these kinds of impervious surfaces can affect our communities and environment:
- Urban Heat Islands: Impervious surfaces reflect and retain more heat than green spaces. This increases temperatures in urban areas, resulting in an "urban heat island effect." Hotter temperatures lead to negative health impacts such as higher rates of heat stroke, and economic impacts such as more expensive electricity bills to keep our buildings cool.
- Water Quality: When rain or other stormwater flows over impervious surfaces, it collects oil, chemicals, and other pollutants. These pollutants are then carried into Denver's waterways, reducing the quality of water in the South Platte River and other lakes and streams. This process is interrupted when water can first pass through soil and vegetation to filter out contaminants.
- Flooding: Stormwater that flows over impervious surfaces often does so in high volumes and at fast speeds. This increases the likelihood and consequences of flood events, which can damage buildings, pose safety risks, and interrupt travel.
- Strain on Drainage Systems: When it rains, runoff is typically directed to stormwater infrastructure like drains and sewer pipes. Excessive rain can overwhelm these drainage systems, especially where upgrades are needed. By preserving and expanding green spaces and other permeable areas, we can extend the capacity of our drainage system capacity, enabling the system to function better and for longer.
- Ecosystem Health: Developing land by adding impervious cover, such as by constructing buildings or paving a road, can displace plants and animals in the natural landscape. This affects overall ecosystem health and decreases biodiversity. The heat that reflects off of impervious surfaces also makes it more challenging to grow trees, grasses, and other landscape elements, especially in Denver's dry climate.
How long is this project?
This project will last from March to November 2025. The strategies identified through this project will be further explored and implemented in 2026 and beyond.
Who will benefit from the dePave project?
The dePave project will identify strategies that contribute to better water quality, healthier ecosystems, reduced flood risk, and reduced heat. All Denverites—as well as employees and visitors who do not live in Denver—stand to benefit from these changes. Benefits to watershed and ecosystem health may also be enjoyed at a regional level.
What kinds of strategies will be identified?
Strategies will represent a variety of possible funding programs, educational initiatives, policy changes, and technical interventions. Using the PRT framework, these ideas will be organized into three categories:
- Preserving pervious areas and remaining green spaces
- Reducing or removing existing impervious cover where possible, or
- Treating stormwater runoff where impervious surfaces cannot be reduced.
How will strategies be prioritized?
The project team will use an evaluation framework to prioritize strategies based on criteria that aligns with the priorities of Denver communities. An advisory steering committee made up of key agency and community partners will identify the criteria used in this evaluation framework. Criteria may include equity, actionability, benefit, cost, or ease of implementation.
Where will on-the-ground projects take place?
No specific on-the-ground projects are planned yet, but greater attention will likely be given to communities and neighborhoods with higher percentages of impervious cover.
How can I get involved?
More information about upcoming engagement channels and events will be shared soon. We're excited to hear from people all across the city!