Optimization of the Subsurface Gravel Wetland for Linear ROW and Pond Retrofits for Nutrient Controls

Focus Area

Water Quality/Wetlands


Natural Resources




Under $99,000


Under 1 year

Research Idea Scope

Subsurface gravel wetlands(SGW) have proven successful as a nitrogen control strategies however costly to construct. SGW have been shown to remove >95% of NO3-N and >55% removal  of TP and are currently being used to meet TMDL requirements in nutrient impaired watersheds. However, currently SGW designs are large, costly to construct, and not easily accommodated in a transportation setting. Two alternate  designs that are reduced in size and scope will be evaluated to assess nutrient removal performance and engineering design and construction costs. Design alternate 1 is a subsurface gravel wetland that has dimensions intended for installation in the transportation 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. Designs exist for both of these systems however have yet to be implemented and tested.
SGWs can be one element of an effective nutrient control strategy as they are able to efficiently mimic the processes that occur in natural wetlands. Subsurface horizontal flow wetlands such as these move stormwater through a permeable substrate such as gravel which functions as a filtration system, in a heavily anaerobic environment providing nitrate removal. The surface of the substrate is vegetated, allowing root growth and subsequent plant uptake.  These systems combine biochemical removal processes coupled with physical filtration operations, making them some of the most effective options for stormwater treatment.

Urgency and Payoff

Products: Designs, performance data, and construction cost estimates for linear gravel wetlands for nutrient control strategies.
Changes: Reduced cost and improved flexibility for application of gravel wetlands
Outcomes: Improved ease and cost of DOT compliance with nutrient controls for water quality certification permits

Suggested By

Robert Roseen, PhD, PE, D.WRE, University of New Hampshire Stormwater Center

[email protected]