Development brings changes to the hydrologic cycle. With development comes paved surfaces, which may well be the most ubiquitous structures ever built. In the United States alone, paved surfaces cover more than 43,000 square miles—an area nearly the size of Ohio—according to research published in the June 2004 issue of Eos, the newsletter of the American Geophysical Union.
But not all pavement is created equal. Impervious pavements can be concrete or asphalt, roofs or parking lots, but they all have at least one thing in common—water runs off of them, not through them. They collect and accumulate pollutants that run directly into water bodies. Because impervious surfaces promote less infiltration, peak flows of stormwater runoff are larger and arrive earlier, increasing the magnitude of urban floods.
By contrast, pervious pavement is designed to allow percolation or infiltration of stormwater through the surface into the soil below where the water is naturally filtered and pollutants are removed. Segmental pavements have been used since the Romans built the Appian Way over 2,000 years ago. In recent years, flexible segmental paver systems, notably permeable interlocking concrete pavements (PICPs), have provided environmentally sound engineered solutions for municipal, commercial, and industrial applications.
Managing stormwater supports sustainability goals, and municipalities and developers have created strategies to prevent stormwater pollution and designed systems that treat stormwater and route it safely back into the natural environment. Traditional stormwater management techniques have taken a collect, convey, and centralize approach that views water as a waste product. The methodology focuses on collecting stormwater in pipes and transporting it off site as quickly as possible, either directly to a stream or river, to a large stormwater management facility, or combined sewer system linked to a wastewater treatment plant. Common components of this method are impervious surfaces and retention ponds, both of which have their drawbacks. Traditional retention ponds use valuable surface area and have proven to be expensive to maintain, usually requiring draining and dredging. Impervious pavements have a high cost of maintenance; they transfer pollutants and sediment to sewers and waterways, and increase winter maintenance expenses, providing a poor life-cycle cost.
Stormwater Ecological Strategies
A more modern and sustainable view of stormwater management maintains the natural hydrologic cycle, prevents increased risk of flooding and stream erosion, protects water quality and the health of water bodies, and provides human uses of water. Low-impact development (LID) promotes these methods. Working to minimize impacts of development on the hydrological cycle of a watershed, LID addresses stormwater concerns through a variety of techniques, including strategic site design, measures to control the sources of runoff, thoughtful landscape planning, preserving and recreating natural landscape, and minimizing imperviousness to create practical, appealing site drainage systems that treat stormwater as a resource rather than a waste product. Examples of these techniques include bioretention facilities, rain gardens, vegetated rooftops, rain barrels, and permeable pavements. By implementing LID principles and practices, stormwater can be managed to reduce the impact of built areas and promote the natural movement of water within an ecosystem or watershed. Applied on a broad scale, LID can maintain or restore a watershed’s hydrologic and ecological functions.
Stormwater Best Management Practices
Best Management Practices (BMP) have been developed in order to help municipalities and other entities effectively control stormwater runoff. Comprising stormwater management and conservation practices proven to effectively control the movement of pollutants and prevent degradation of soil and water resources, BMPs can be divided into two categories: structural and nonstructural. Performance-based BMP tools allow for monitoring and adjustment to achieve wastewater volume and quality goals that will:
- Work within the landscape
- Focus on prevention
- Micromanage stormwater
- Keep it simple
- Allow for multifunctional landscape designs
- Capture and treat stormwater runoff at its source
- Maintain and sustain LID tools such as permeable pavement systems
In short, LID involves the three D’s of stormwater control: disconnect, distribute, decentralize, that is, disconnect storm sewers, distribute the stormwater on-site, and decentralize this runoff by promoting groundwater recharge where possible. Central to this system is permeable interlocking concrete pavement (PICP), which is able to capture rainwater for full exfiltration into the soils below or for capture and reuse locally.
A special thanks to Oldcastle APG Masonry and Architectural Record for supplying us with this article.
