Urban Stormwater Treatment Trains – Flow Through Planters as an Urban Mitigation Tool

The integration of stormwater treatment for quality and quantity is always challenging on an urban site where traditional treatments require acreage that is simply not available.  To meet current regulations, the design team needs to look at creative options for removal of pollutants and detention of rainfall within a restricted area.

The flow through planter has become a regular tool utilized in conjunction with green roofs, cisterns, bio-retention and traditional basins.  The close coordination between civil engineers, architects and landscape architects from inception of the project enables the team to:

  • Correctly size the planter according to capture area and quantities,
  • Incorporate design with architecture for optimum aesthetics,
  • Utilize required buffer and foundation plantings for uptake of nutrients, and
  • Specify plantings that are tolerant of wet feet for up to 24 hours.

In designing DASH, an infill maintenance facility in Alexandria, Virginia, Timmons Group was challenged by the minimal space available for stormwater treatment.  To design an effective solution within this limited area, a flow through planter was used to capture the first inch of rainfall for pre-treatment and detention prior to entering a traditional basin.  The basin was able to be greatly reduced in size due to the successful design and fit of the planter in a tight space between the sidewalk and building.

The typical detail was updated to obtain enhanced horizontal flow of water from the roof drains to ensure that all plantings were getting equal saturation.  Emergency overflow measures were specifically designed to accommodate any additional precipitation.

Let us know your experiences both positive and lessons learned.  Continue to follow this thread for more on flow through planters; future discussions will focus on specifying planter components, mid-Atlantic plantings for use with flow through planters and long term maintenance requirements.