UNHSC-NEMO Innovative Stormwater Management Database

bioretention/rain garden | gravel/constructed wetland | green roof | permeable pavement | swale retrofit | retention/detention pond retrofit

Gravel/Constructed Wetland

The gravel wetland is a recent innovation in Low Impact Development (LID) design. It approximates the look and function of a natural wetland, effectively removes sediments and many other common stormwater pollutants, and enhances the visual appeal of the landscape. Like other infiltration/filtration systems submerged wetland systems have a tremendous capacity to reduce peak flow and stormwater volume in general. They also have limited use as a replacement for septic systems. With a vertical flow path these systems should not be confused with free water surface wetlands such as more frequently designed pond systems. Vertical flow constructed wetlands have superior root distribution and water-root contact and tend to experience fewer problems of bad odor and insect infestation. A gravel wetland system utilizes a variety of biological, physical, and chemical processes for pollutant removal. Biological treatment occurs through the uptake of pollutants by vegetation and microorganisms that exist among the plant rhizosphere. Physical and chemical treatment occurs on and within the gravel sub-base and root matrices and includes unit processes such as sedimentation, filtration, oxidation, reduction, and adsorption with organic matter and mineral complexes.

Gravel wetlands like the one evaluated at UNHSC can be used in most parts of the United States, with the exception of those regions too arid to support a wetland system. Since gravel wetlands can be space intensive, they may not be appropriate for densely developed areas. Recommended maintenance mostly involves mowing and replacement of vegetation, as needed.