Design Optimization of the Subsurface Gravel Wetland for Linear Transportation Right of Way and Stormwater Pond Retrofits for Nutrient Controls

Focus Area

Water Quality/Wetlands


Natural Resources






2-3 years

Research Idea Scope

Subsurface gravel wetlands have proven successful as a nitrogen control strategies however costly to construct. Studies show that these systems show a unique ability to remove bioavailable nitrogen in excess of 90% during summer months, and greater than 55% annual phosphorous removal. Gravel wetlands are being implemented as a TMDL compliance measure for roadway expansion in areas with impaired waters. A potentially significant application of GW is their simplicity use as a detention pond retrofit. Two alternate  designs that are reduced in size and scope will be evaluated to assess nutrient removal performance and engineering design andconstruction costs. Design alternate 1 is a subsurface gravel wetland that is narrow and long and intended for installation in thetransportation right of way typically reserved for roadside swales. Design alternate 2 is a subsurface gravel wetland that is a single treatment cell with precast pretreatment device intended as a low-cost stormwater pond retrofit. Research products will include two new designs and design and construction cost estimates for gravel wetlands as a nutrient control strategy.

Urgency and Payoff

There will be an improved ease and cost of DOT compliance with nutrient controls for water quality certification permits. There will be a reduced cost and improved flexibility of design for application of gravel wetlands.

Suggested By

Robert Roseen, University of New Hampshire Stormwater Center

[email protected]