As colleges and universities become leaders in sustainability, they are exploring their campuses’ potential to provide “green infrastructure” that will protect watersheds, recharge aquifers, and support native birds and pollinators.A new bioswale at Cornell Plantations, the botanical garden of Cornell University, demonstrates how stormwater management can be integrated in campus landscapes.Conventional landscapes and hardscapes are designed to shed runoff quickly into drains and pipes. Most rainfall is gone from the site before it can soak into soils, support vegetation, or percolate into the groundwater. Instead, it empties quickly into rivers and streams where it can cause erosion, flooding, and pollution.
Vegetated swales offer an effective and attractive way to help restore natural water cycles. A vegetated swale collects runoff from rooftops, parking areas, roads, and lawns, and uses plants and soils to cool the water, slow its movement, and reduce its pollutant load. Vegetated swales are designed to fill with water during storms but drain completely within twenty-four hours, and they are planted with grasses, perennials, shrubs, and trees that can flourish through both inundation and drought.
At Cornell Plantations’ bioswale, plants, soils, and hardscape elements work together as a single system. As water runs off the adjacent parking lot, a “filter strip” slows its movement and precipitates out suspended particulates. Next, the water’s movement is further slowed by densely-planted grasses and flowering plants, which absorb pollutant-laden water, metabolizing hydrocarbons and releasing water vapor and oxygen into the atmosphere. Their roots aerate the soil, maintaining its capacity to absorb water quickly and to release it gradually to plants and into the underlying aquifer.
The bioswale’s plants are mostly native meadow species, which create a striking display in the summer and fall. This combination of beauty and function has made the Bioswale “one of Plantations’ most popular gardens,” according to Executive Director Don Rakow, who says the Bioswale has become “a model for university-based public gardens around the nation.”
Rakow and his staff laid the foundations for the Bioswale’s success through careful planning and design. The bioswale was conceived in Plantations’ 2002 Master Plan, which paired it with a proposed visitor parking area. This linkage helped assure that the bioswale would be funded and built.
Equally important was the decision to manage stormwater locally, as an element of a larger distributed system. Stormwater management works best when the system catches and “processes” each drop of water as close as possible to where it falls. The bioswale is sited and scaled to receive runoff from nearby buildings, pavement, and gardens, without exceeding the site’s ability to percolate runoff into the ground below.
Plantations’ boldest move was to locate the bioswale at its main visitor entrance. The prominent location committed Plantations to a high level of design and care; more important, it signaled Cornell’s belief that green infrastructure can be beautiful and that stormwater management is worthy of inquiry and display.
To create a bioswale worthy of its prominent location, the client team and the consultant team worked collaboratively, exchanging sketches and plant lists to create a plan that reflected both the outside designers’ vision and the staff’s detailed understanding of the site’s soils and microclimate as well as the day-to-day work of tending the gardens and sharing them with visitors.
Vegetated swales have no set “look” or style – they can be exuberant or restrained, organic or geometric. The style of Cornell’s bioswale was determined by its site and its purpose. To evoke the ancient creek whose route it traces, the bioswale’s plantings are massed to suggest the visual “movement” of an actual streambed. To provide a visual transition from the groomed landscape of the botanical garden to the wild hillsides around it, its plantings are “half-wild,” neither true meadow nor traditional garden. To advance Cornell Plantations’ horticultural mission, it creates a diverse new plant collection. And to greet visitors to the botanical garden, it invites them to follow narrow plants flanked by tall stands of grasses and perennials, giving them a memorable encounter with plants just moments after they’ve left their cars.
The bioswale demonstrates the inseparability of design and maintenance. Cornell’s expert gardeners keep it lush and exuberant without ever letting it slip into chaos. Not every owner can provide that level of care – but fortunately, not every owner needs to. Options to reduce maintenance requirements include simplifying the plant palette, relying on “indestructible” species, and creating larger single-species masses.
Conventional landscapes are designed for mechanized maintenance and copious application of fertilizers, water, and mulch. Vegetated swales need irrigation only during their first few years of establishment, and should never need fertilizer or mulch. Compared to conventional landscapes, they require less brute force and greater skill.
