Tree Box Filters: Big Stormwater Impact in Small Urban Spaces

In dense urban environments where space is limited but stormwater challenges are significant, tree box filters have emerged as one of the most efficient low-footprint solutions. These compact, modular systems combine engineered soil media, vegetation, and underground infrastructure to capture and treat polluted runoff – all while enhancing streetscape aesthetics.

One of the most widely known manufactured systems is the Filterra® Tree Box Filter, a proprietary solution that follows the same general principles as other tree box filter designs but is engineered for consistent performance and ease of maintenance.

What Is a Tree Box Filter?

A tree box filter is a small-scale stormwater best management practice (BMP) designed to intercept runoff from streets, sidewalks, and parking lots. The system typically consists of:

• A concrete or precast box installed at grade level.

• A vegetation layer (often a tree or ornamental plants) for water uptake and shade.

• Specialized filter media to remove pollutants such as sediment, nutrients, metals, and hydrocarbons.

• An underdrain to convey treated water into the storm drain system or infiltration area.

How it works:

1. Runoff enters the box through a curb opening or storm inlet.

2. Water passes through the vegetation and engineered media, where pollutants are trapped or broken down.

3. Treated water flows out through the underdrain, reducing pollutant loads entering downstream waterways.

The Benefits of Tree Box Filters

Tree box filters are gaining popularity with municipalities, developers, and property owners because they:

• Fit in tight urban spaces where traditional BMPs like bioswales or detention ponds are not feasible.

• Provide measurable pollutant removal, especially for total suspended solids (TSS), phosphorus, and heavy metals.

• Enhance streetscapes with greenery and shade, contributing to urban heat island mitigation.

• Offer predictable maintenance schedules with simple sediment and vegetation management.

• Comply with stormwater regulations in many states and jurisdictions.

Filterra® Tree Box Filters

The Filterra® system, developed by Contech Engineered Solutions, is a proprietary version of a tree box filter designed for high treatment performance with minimal maintenance disruption.

Key features of Filterra® systems include:

• Pre-engineered, tested media with consistent pollutant removal rates.

• Modular sizing options to handle varying drainage areas.

• Rapid installation that integrates with existing curb and gutter layouts.

• Maintenance access via removable grates for easy sediment and trash removal.

Filterra® units have been third-party verified for pollutant removal under programs like the Washington State Department of Ecology’s TAPE certification, which makes them attractive for projects that need proven compliance.

Where Tree Box Filters Work Best

Tree box filters – whether a Filterra® unit or a custom-designed system – are ideal for:

• Urban streetscapes with direct curb runoff.

• Parking lot perimeters to treat sheet flow.

• Redevelopment projects where retrofit space is limited.

• MS4 compliance areas requiring pollutant reduction.

Maintenance Considerations

Like any BMP, tree box filters require periodic upkeep to remain effective:

• Sediment removal from the top layer of media.

• Trash and debris clearing to prevent inlet blockage.

• Vegetation care – pruning, replanting, or replacing as needed.

• Media replacement every 5–10 years, depending on loading.

Manufactured systems like Filterra® often come with detailed O&M guidance and service programs to simplify compliance.

Final Thoughts

In cities where stormwater runoff is a major contributor to water quality issues, tree box filters pack a lot of treatment power into a small footprint. Whether installed as a custom-designed BMP or as a manufactured system like Filterra®, these solutions help meet regulatory requirements, improve urban aesthetics, and protect waterways – all without requiring large tracts of land.

For commercial property managers, developers, and municipal planners, tree box filters are a smart way to make the most of limited space while achieving significant stormwater quality improvements.

📞 Call iSTORMWATER today at (410) 231-3455 for Filterra® Tree Box Filter inspection, maintenance, and install or 💬 Contact us online for more information.