Permeable pavements, green roofs, and cisterns : stormwater treatment practices for low-impact development

■ Permeable Pavements, Green Roofs, and Cisterns Stormwater Treatment Practices for Low-Impact Development Stormwater runoff continues to be a concern in communities large and small across North Carolina and the United States. State regulations targeting pollut¬ ants such as nitrogen, phosphorus, and total suspended solids have been in place since the 1990s. In 2003 , federally mandated stormwater programs were estab¬ lished in more than 100 municipalities in North Carolina. These communities must reduce flooding and improve the water quality of runoff from new residential and commercial developments by using stormwater treatment practices. Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. North Carolina State Uni¬ versity and North Carolina A&T State University com¬ mit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, or disability. In addition, the two Universities welcome all persons without regard to sexual orientation. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating. In 1999, North Carolina State Univer¬ sity Cooperative Extension published its first Urban Waterways fact sheet, an Overview of Structural Stormwater Best Management Practices. It described several stormwater practices, includ¬ ing wet ponds, stormwater wetlands, bioretention areas, sand filters, level spreader-riparian buffer systems, and grassy swales. Since then, additional structural practices have become com¬ monplace throughout North Carolina, including the use of permeable pave¬ ments, green roofs, and water harvesting systems or cisterns. This new fact sheet in the Urban Waterways series describes these three stormwater practices and supplements the original overview. These practices are incorporated within low-impact development (LID). LID uses site planning and engineer¬ ing to reduce or prevent the adverse STATE UNIVERSITY A&T STATE UNIVERSITY COOPERATIVE EXTENSION Helping People Pul Knowledge to Work impacts of stormwater runoff from both residential and commercial develop¬ ments. LID relies on both structural and nonstructural practices to conserve the site’s natural or predeveloped hydrologic response to rainfall - the way rainfall is distributed among runoff, infiltration, and evapotranspiration. Examples of nonstructural practices include minimizing site disturbance, preserving important site features, reduc¬ ing and disconnecting impervious cover (sufaces that do not allow water to filter through them, such as asphalt and con¬ crete), flattening slopes, utilizing native vegetation, minimizing grass lawns, and maintaining natural drainage features. Structural best management practices (BMPs), such as bioretention (see AGW- 588-05 for more information), permeable pavements, green roofs, and cisterns, are used in LID to provide further runoff control and treatment close to the run¬ offs source.