Gravel wetlands remove nitrates from streams and drainage outflows. The University of New Hampshire Stormwater Center team designed this unique filtration system that works like this:
- Piped water enters a forebay, a 30 feet by 40 feet, five foot deep, grassed containment structure. This allows debris and sediment removal before entering the main containment area.
- Next, the water is piped into a 120 feet x 40 feet gravel wetland. This grassed structure is built with 24″ of 3/4″ stone, topped with 3″ of 3/8 stone (used as a bridge). An intricate piping system directs the water into the bottom of the 3/4″ stone layers where hungry bacteria consume nitrates.
- The stone is surfaced with 8″ of an organic plantable soil that we will plant with wetland shrubs.
- The water exits through a 12″ pipe that leads into a concrete manhole that terminates at stream discharge invert.
The completed installation has sodded slopes.