Subsurface gravel wetlands (SGWs) are an emerging stormwater control measure (SCM) that treat both the quantity and quality of runoff. Unlike more traditional free-water surface wetlands, SGWs maintain a saturated gravel layer completely beneath the soil surface. Following a storm event, ponded water will drain through this gravel layer within a few days. This design minimizes exposure to pathogens, prohibits habitat establishment for mosquitoes, and operates efficiently in colder weather.

Anna Dias is monitoring seven SGWs constructed alongside the Raleigh-Durham International Airport’s Economy Parking Lot 3 for water level, surface infiltration rates, rainfall, and vegetative growth. Two of these wetlands are also being monitored for water quality, focusing on the removal of total suspended solids, nitrogen, and phosphorus.

This project aims to show how SGWs perform in the field and provide the North Carolina Department of Environmental Quality (NCDEQ) with the data it needs to evaluate SGWs for primary SCM status. Achieving primary SCM status would allow SGWs to be used on sites where other SCMs are less appropriate, expanding our toolkit for combating urban flooding and environmental degradation.