Brian C. Nevin Welcome Center, Cornell Plantations

Challenge

Due to the already established botanical gardens at the Plantations and the value of the existing plantings, a key project goal was to limit the footprint of disturbance. Because of this emphasis, permeable pavements would have been ideal for new pavement because they generate much less runoff and therefore do not require that additional land area be dedicated to stormwater management practices. However, the clay soils in the area, extreme winter temperatures, and large quantities of mulch, compost and decaying plant matter on the site would make design and maintenance of permeable paving challenging.

Solution

Conventional asphalt and concrete were used for most of the new paved areas on the site, but a variety of strategies were used to minimize their impacts. The design limits disturbance and cost by reusing existing vehicular lanes as pedestrian walkways. The bioswale manages sheet flow from many walkways and the new parking lot. Permeable pavements were used for certain small areas of low traffic such as the ADA parking spaces and a fire truck turn-around. Originally the ADA parking was intended to be stone-dust, but it is not an accessible surface, so porous concrete was used instead. A reinforced “grass pave” was chosen for the fire truck access.

• The 12,000-sf Bioswale Garden is a popular horticultural display area that can store up to 0.13 acre-ft (5,663 cu ft) of stormwater. It uses a system of hardy, drought and inundation-tolerant perennials and grasses, bioretention soils, and hardscape elements. The bioswale receives runoff from adjacent lawn areas and from the filter strip adjacent to the visitor parking lot.
• The planted filter strip includes a river rock strip to capture sediment from the parking lot. Open grate foot paths over the filter strip and through the sidewalk reveal the movement of water from the parking lot to the bioswale.
• An acre of lawn provides flexible gathering space and formal views to and from the Welcome Center. This lawn also handles sheet flows of stormwater runoff from other garden areas, terraces, and walkways.
• The Bioswale Garden contains more than 50 species of perennials and shrubs, chosen for their ability to grow in both the wet and dry conditions. 82% of the species and 92% of plants selected are native to the lower 48 states, providing habitat and reducing the need for irrigation.
• Switchgrass is a dominant selection, planted in seven cultivars with variations in foliage and flower color. Flowering perennials, including cultivars of sneezeweed, Joe Pye weed, and milkweed were planted to provide continuous seasonal interest. Shrubs and small trees such as winterberry and American hornbeam add height and structure.
• Educational signage installed on the site and inside the building explains the functioning of the bioswale, describing it as ‘a ditch that cleanses.’
• A 2,390-sf extensive in-situ green roof with 6 in of growing media is planted with sedums and covers 68% of the Welcome Center building. The roof can be viewed from the adjacent Comstock Knoll Garden.
• Roof runoff, including any stormwater not absorbed by the green roof, is conveyed by downspouts to gravel infiltration trenches near the building.
• To reduce vehicular traffic within the site, only service vehicles and those needing ADA access can drive up to the Welcome Center building. A peripheral lot with 40 parking spaces is provided for other visitors. It offers prefered parking for alternative fuel vehicles. 
• A 300 ft long and 8 ft wide designated pedestrian access route connects the parking lot to the Welcome Center. It also provides emergency and ADA access. Accessible parking spaces along this route are constructed of porous concrete.
• 2,300 sf of permeable “grass-pave” system is used in the place of pavement for a fire access turn-around.

• The educational and horticultural elements of the Bioswale Garden increased installation costs by $121,500 or 92% as compared to standard turf. This increased cost can be seen as the cost of providing an educational landscape, meant to encourage an appreciation of the possibilities for creating a sustainable stormwater solution in the context of a botanical garden. Visitors also learn that they can create a similar garden at a different scale in their home landscapes.

• Several Katsura (Cercidiphyllum japonicum) trees planted in structural soil have not been thriving, with explanations varying from pH intolerance to inadequate soil volume and poor species selection. Tests and calculations show that at 7.4-7.6, the pH is within tolerable levels for Katsura trees. While soil volume is minimally adequate for trees of this size to survive 90% of dry periods in Ithaca, the species selected has poor tolerance for occasional periods of dry conditions and scrutiny of the site grading shows little water being directed to the tree openings in the pavement. While the species has the landscape qualities desired, a better selection could have been made based on research on CU Structural Soil.
• Bioswales are generally predicted to remove a variety of contaminants including nutrients, metals and suspended solids. However, input-output water sampling and tests have found that despite the practice’s success removing metals from runoff, it appears to be a net source of dissolved nitrogen and phosphorous. There are no definitive answers at this point, however there are two hypotheses: Despite the lack of institutional memory of this, excess nutrients leaving the bioswale could be coming from stripped and stockpiled topsoil, which may have originated in gardens that were historically fertilized through either compost or chemical fertilizers. Also, the enriched mulch made of bark and compost used in the bioswale may be contributing excess nutrients.
• The bioswale is proving to support more vigorous growth than anticipated, making it appear as a visually appealing mature garden but also requiring more maintenance. In the bioswale, rapid plant growth is also causing increased shade while perennials are requiring more maintenance than expected, including plant division. Staff believes that a higher percentage of woody plants might have been better in terms of maintenance.
• The green roof is constructed with deeper growing media (6 inches) than typical used for sedums (2-4 inches). Staff believe that this is causing more weed growth than anticipated due to the soil’s moisture holding capacity. This has not been independently verified. At this time, there is no solution except hand weeding, but the problem may resolve itself as the sedums are now covering most of the soil media.
• A drywell was suggested by the project designers to handle roof runoff from an adjacent existing building. This was not implemented due to the $10,000 cost. After project completion, continued water problems at the adjacent building required mitigation, and a drain was installed at a much higher cost becasue it had to connect out to the street through a lawn area so that it would not impact the recently constructed landscape. The solution was less environmentally beneficial and cost approximately $20,000.

Hardscape: Most was made up of commodity materials for which source names are unavailable. 
New York State Bluestone: Finger Lakes Stone Company
Plant Materials: North Creek Nurseries- Landenberg, Pennsylvania; Bluebird Nursery; Garden Crossings; Klyn Nurseries; Sooner Plant Farm; Canning Perennials; Santa Rosa Gardens; Seneca Hill; Rarefind Nursery; and Gilbert Wild & Son.  

Project Team

Client/Owner: Cornell Plantations, Cornell University
Architect: Baird Sampson Neuert Architects Inc.
Landscape Architects: Halvorson Design Partnership Inc.; Irene Lekstutis
Horticultural Specialist: Mary Hirschfeld, Cornell Plantations staff
Civil Engineers: T.G. Miller Engineers and Surveyors, P.C.
Cost Consultant: Vermeulens Cost Consultants

Role of the Landscape Architect

The landscape architect served as a sub-consultant to the architects, with assistance and detailed planting design provided by Cornell Plantations staff. All hardscape design was completed by the architects and integrated with the grading plan, conceptual planting plan, and conceptual plant selection completed by the landscape architect.