Some Performance Characteristics of Subsurface Gravel Wetlands for Stormwater Management

Subsurface gravel wetlands were originally purposed for wastewater treatment and more recently have been used for stormwater treatment as a green infrastructure technology. Systems are sized to hold the water quality volume above, and drain within 24–48 hours. Design guidance follows static sizing principles with very little hydraulic calculations, which has left a gap in hydraulic performance data. Data from 12 years of field monitoring of various systems constructed in the northeast United States is presented. These systems include fully-sized as well as undersized (hold less that the water quality volume). Hydraulics are controlled by a restrictive outlet. At the same time, this outlet also creates the wetland characteristics of the system. Pollutant removal efficiencies for common stormwater pollutants are some of the highest for green infrastructure systems, with a significant component being microbially-mediated in the low dissolved oxygen gravel layers.