Designing Bioretention with an Internal Water Storage (IWS) Layer

Developed by North Carolina State University Cooperative Extension, this guidance document (Urban Waterways Journal, 2009) provides design recommendations for incorporating an internal water storage layer within bioretention systems to improve nitrogen removal and overall stormwater treatment performance. It helps designers understand when and how to include an IWS layer to enhance pollutant reduction, increase subsurface storage, and improve the long-term effectiveness of bioretention practices.