By Kevin Beuttell, Stormwater E-Magazine, October 2008
Despite the proven environmental benefits of rain gardens, many people are reluctant to use them because they can be unattractive. But a close examination of the relationships between hydrology and vegetation in rain gardens suggests a solution for improving their looks and their function. Rather than think of rain gardens primarily as wet environments, we should design them as dry environments that experience only brief wet periods. This shift in thinking increases opportunities for ornamental planting without sacrificing environmental performance.
Rain gardens are one of the most frequently cited and promising strategies for managing stormwater responsibly, and because of the ubiquitous presence of impervious surfaces, these systems can be used on virtually any type of site. Rain gardens come in many forms (and go by many names, such as bioswale, bioretention, and bioinfiltration), but for the purposes of this article, the term “rain garden” is essentially meant to describe a shallow depressional area designed to use the natural capacities of soil and vegetation to retain, cleanse, and infiltrate stormwater.
The Pros of the Rain Garden
Infiltration-based stormwater management strategies, such as rain gardens, are crucial to downstream ecological health. Every parcel of land interacts with water. If water infiltrates, it can be used as a resource to nourish plants and replenish aquifers. When water runs off driveways, roads, and compacted soils, however, it becomes a liability, carrying sediments and pollutants downstream. The USEPA states that nonpoint sources, such as stormwater runoff from an urbanized landscape, are the leading causes of urban stream water-quality problems. To help, many designers are looking toward landscape solutions to water-quality and flooding problems, altering land surface functions to manipulate the way in which the land captures and absorbs stormwater.
Many other stormwater management techniques address only a portion of the problems caused by stormwater runoff. Rain gardens, however, have the potential to solve all the problems of stormwater runoff before they occur. Like other infiltration-based strategies, rain gardens mitigate the hazardous stormwater runoff aspects of development by decreasing peak flows responsible for storm surges and flooding. They reduce pollutant discharges, minimize streambank erosion, replenish groundwater, and restore base flows and aquatic habitats. Rain gardens can also offer real development cost savings by eliminating expensive belowground stormwater infrastructure in favor of combining stormwater management with ornamental landscapes.
Rain gardens can also help with temperature pollution problems. In a completely natural setting, water enters a stream or other water body almost entirely through groundwater that provides steady flows at low temperatures. But when development introduces impervious surfaces, higher temperatures often result as the runoff washes over those warmer surfaces. Higher temperatures, in turn, cause the loss of a diverse system of aquatic biota in receiving streams, ponds, and rivers that are sensitive to the warmer water.
Because of effects like these, traditional urban stormwater management has always viewed water as a burden on the landscape. Water is typically taken away through channels and pipes as quickly as possible to avoid flooding on site. But water and ecological quality can be improved when water is allowed to infiltrate, using it as a resource where it falls.
The (Perceived) Cons of the Rain Garden
Attractive and functional rain gardens are the exception, not the rule. Most rain garden installations do not include those elements that are culturally accepted as beautiful, like lush green lawns, flowering vegetation throughout the growing season, clean lines, and a maintained appearance. As a result, people see these landscapes as cluttered, unkempt, and unmanaged. Perceptions are just as important as environmental performance. If rain gardens are not perceived as attractive, cared-for environments, they will not be adopted during the design phase or managed after installation. Although preferences vary from person to person, a common theme for all is an appearance that communicates care to the viewer.
People design and manage landscapes as a reflection of who they are and how they want to be perceived. Too often, rain gardens planted with water-loving species appear unkempt and abandoned. Individual plants are often stressed and weak, particularly in areas that experience hot and dry summers. The negative perception of their ornamental character is an obstacle to their use in both new and retrofit development projects. Because many rain gardens do not come close to the ornamental quality of more traditional garden landscapes (especially from the perspective of the general public, who may be largely unaware of the environmental benefits), they are not a viable option in visually prominent areas of a site such as in parking lots or at site and building entrances. In high-visibility areas, environmental performance alone is not enough. Because one cannot see the ecological functioning of the root systems, water infiltrating through soil, and wildlife’s benefits from the landscape, it is difficult to include an ecological assessment in our judgment of landscape’s appearance. So rain gardens are not used, or are relegated to areas of the site where their messy appearance will not offend.
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