Greening your site
By Heather Kinkade-Levario, Senior Planner,
Urban Design & Planning unit, Carter & Burgess - Phoenix

Adopt low-impact development techniques to maximize water conservation

Most Americans think of water as an endless resource. In fact, while water is the most widespread substance in the natural environment, only 2.5 percent of the earth's water is fresh, not salt. Of that 2.5 percent, about 68 percent is trapped in glaciers and ice packs. That leaves nearly 30 percent in the form of groundwater and a mere 0.3 percent in freshwater lakes and rivers.

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Groundwater can take up to 1,400 years to be replenished by rainwater that soaks through the soil. Currently, groundwater is being drained faster than it can renew itself. Furthermore, groundwater infiltration is disrupted as water rushes off paved surfaces into streams and rivers.

The problem? If something doesn't change, aquifers will run dry while rivers grow increasingly polluted. The solution? Low-impact development techniques that conserve water, keep it clean and channel it into the ground. These strategies can not only lessen the environmental impact of a site but also meet regulatory requirements, help achieve green building goals and cut costs.

The challenge of every rainstorm

Water that falls onto buildings, parking lots and roads has no way to get into the ground. Instead, it is forced into the storm drainage system, picking up pollutants along the way. These pollutants must be filtered when the water enters the rivers and lakes used for drinking water.

Federal regulations mandate stormwater pollution prevention through the National Pollutant Discharge Elimination System (NPDES) under the Clean Water Act. Projects greater than 1 acre in size must carefully control runoff during construction; however, federal law is less specific concerning post-construction runoff, and many completed projects can largely ignore stormwater issues. Nevertheless, several cities such as Austin, Phoenix and Seattle have made stormwater pollution prevention a priority and require developers to manage stormwater runoff.

Another driving force in the move to reduce water use is the green building movement, which advocates a whole-site approach to creating sustainable building projects.

Landscape architects and engineers working on green projects as well as those trying to meet regulatory requirements realized that significant savings in water usage could be achieved by approaching stormwater in a new way.

Low impact development strategies and benefits

Low impact development is an ecologically friendly approach to site development and stormwater management that aims to mitigate impacts to land, water and air. Armed with a thorough understanding of natural water cycles and a bevy of techniques, landscape architects design sites that slow water, trap it, clean it, flush it, use it for appropriate purposes and then return it to the ground. The goal is to keep runoff the same as it would be if a site were undeveloped. Therefore, if ten percent of rain falling on a site would run off naturally, only ten percent should run off after the site is developed.

Techniques in the low-impact development arsenal can either be passive or active.
They often involve some form of either rainwater harvesting or stormwater reuse. In rainwater harvesting, rainwater is collected from relatively clean surfaces such as building roofs. In stormwater reuse, water is also gathered from dirtier areas such as parking lots.

Passive approaches use natural, gravity-driven processes to slow and filter water.
Each site is considered as its own watershed, then divided into micro-watersheds that can each be managed to restrain runoff. Individual techniques include micro-basins, French drains and swales. Sidewalks, drives and parking lots can be sloped towards terraced open space where water can infiltrate into the ground.

Active approaches go beyond natural, gravity-driven process to include mechanical systems like pumps. Most involve capturing, storing and reusing rainwater for purposes for which potable (safe for drinking) water isn't necessary. For example, nonpotable water is ideal for irrigation. When combined with xeriscaping landscaping techniques that rely on native or naturalized plants, water requirements for irrigation can be reduced or eliminated. Rainwater water is also appropriate for washing cars and can be used in the cooling towers that are part of the heating, ventilation and cooling system of a building. Some innovative systems have been developed to pump rainwater to toilets through separate piping.

Low-impact development approaches provide several benefits to developers and owners, one being that stormwater regulatory requirements can be met using these strategies. Projects seeking certification through the U.S. Green Building Council's Leadership in Energy and Environmental Design system or LEED system, which measures energy efficiency and overall sustainability of a building, can gain up to 12 LEED points.

Further, these strategies improve the long-term cost-effectiveness of a project. Water bills go down when landscaping requires less irrigation, which means a site costs less to maintain over its lifecycle. Active stormwater reuse further cuts water bills.
Finally, low-impact development benefits the entire community by reducing the consumption of potable water, decreasing pollution to rivers and lakes and increasing groundwater infiltration and aquifer replenishment.

The United States is blessed with plentiful supplies of water. To maintain the quality of our water supply, we must develop sites that better conserve water and prevent pollution.

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