This series explores some of the Best Management Practices (BMPs) of Green Infrastructure and LID for both urban and rural applications. The IRWP is currently working with our local cities, counties and organizations to implement these projects within the Illinois River Watershed. Watch for these demonstration projects in public spaces to see first-hand stormwater management in action!

Tree Wells are another simple tool for your ‘Green Toolbox’ to help manage stormwater and reduce pollutants in our waterways! We continue our Watershed Landscape post about the elements of Green Infrastructure with today’s topic on these types of applications that have small footprints but yield BIG results.

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Example of Standard Filterra System Tree Well

Photo Credit: Filterra

You may be familiar with tree grates, as they are what you usually see around the base of a tree on a sidewalk. They allow for water to reach the roots while providing a walkable surface for pedestrians. Tree Wells take it a step further by providing a capacity for urban stormwater storage, pollutant removal and filtration system, within the context of an urban setting, such as a street or parking lot. The components that make up a tree well are a storage basin, typically made of concrete, a filter media mixture that supports trees or shrub species and also provides the pollutant removal services, and an underdrain system where the filtered water is discharged. They are well-suited for the urban environment and have high pollutant removal efficiency for many toxic substances such as petroleum and heavy metals.

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Expected Pollutant Removal capacity of a Tree Well System

Photo Credit: Filterra

Tree boxes generally capture and treat stormwater runoff from small frequently-occurring storms but are not designed to capture runoff from large storms or extended periods of rainfall. Each tree box is designed to treat approximately a quarter to half an acre. For example, to treat .25 acre (10,890 square feet) of parking area, you would need a 48 square foot Tree Well, or 8’x6’ planter. Multiple tree wells can be used together, to maximize the benefits.

In a case study in northern New Jersey, the cost of individual tree boxes was approximately $12,500 with each tree box treating 1/3 of an acre of impervious surface. Maintenance is very simple for Tree Wells, including a replenishment of mulch every year, tree inspection as needed and trash/debris removal. Its important to select appropriate tree and shrub species that can handle both wet and dry conditions and do not have invasive roots. Another benefit of these types of technology is that you can capture and harvest the filtered rain that goes into these wells and re-use for irrigation purposes on site! Check out this video to learn more about Tree Wells:


Learn More about Tree Wells- 3 Minute Video

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Rain Garden Design Series- Part III

Rain Garden Design Series- Part II

Additional Resources:


Rutgers University

The Illinois River Watershed Partnership works to improve and restore the Illinois River Watershed through public education, water quality monitoring, and conservation/restoration projects. Check out our website for current events that continue to educate stakeholders of the Illinois River Watershed about Green Infrastructure and Low Impact Development, as well as events that offer volunteer opportunities to make a positive difference!