North Carolina Museum of Art West Building Expansion

The primary issue for the design team was stormwater management, due the site’s prominent location at the top of a regional watershed. In keeping with the NCMA’s environmental and community values, the project required an integrated stormwater management system that would mitigate localized stormwater challenges, including the elimination of flooding that had long plagued downstream neighbors. The design of the stormwater facilities also had to complement the new building’s style and function. The design also had to respond to the limited space available around the existing facilities, most specifically to preserve the integrity of the popular existing art and amphitheater space, “PICTURE THIS.” Lastly, the design had to improve an existing poorly-functioning stormwater pond and set a new standard for the visual beauty and functionality of stormwater facilities.

Solution

In order to meet stormwater and flood prevention standards, the design team incorporates a system of both required and voluntary stormwater best management practices including high-infiltration and structural soils, pervious gravel, and cisterns. To preserve the amphitheater, concentrated flow is guided around it, then primary low-flows are directed through an undersized existing pipe, and a new subsurface pipe directs high-flows around the amphitheater path to a flow splitter. To improve the existing pond and site aesthetics, a new stormwater pond system was developed to achieve the same level of sculptural refinement expressed in the landscape adjacent to the new buildings. To promote visual beauty as well as functionality, bioretention terraces were designed with a sweeping form reinforced by bold plant massing and punctuated with monolithic red runnel structures. The runnel structures, sculptures in themselves, deliver excess runoff across the system during during significant rain events. 

• 5 acres of sculpture gardens and courtyards include a collection of Rodin sculptures on display in the Iris and B. Gerald Cantor Court and Garden.
• A large cistern, bioswales, bioretention area, wetland, wet pond, and permeable gravel paving areas make up a stormwater infrastructure network that manages runoff from 37.7 acres. 
• The 90,000-gallon underground cistern collects and stores rainwater from the roofs to recharge 3 large reflecting pools.
• A treatment swale slows and directs surface-generated stormwater while pervious soils, stilling basins, and rock weirs provide initial filtration.
• 32,670 sf of terraced bioretention trays provide secondary treatment via engineered soils and structured overflow into a wetland/pond complex. The trays are planted with native grasses and forbs such as Andropogon, Coreopsis, Eupatorium, Panicum, and Solidago, which filter stormwater before it flows into the wetland.
• A 55,757-sf permanent wet pond supports aquatic life and is home to crayfish, a keystone species and level 4 water quality indicator.
• 21 bald cypress trees and approximately 9,000 facultative wetland plants and plugs were planted in the 44,867-sf wetland and along the pond margins, including various species of Acorus, Peltandra, Pontederia, Juncus, Scirpus, Carex, and Iris.
• The expansion site can be accessed by the more than 5 miles of recreational trails that run through the adjacent Museum Park and connect to Raleigh’s greenway system. 

The innovative, art-driven approach to the NCMA stormwater pond treatment system was made possible through a $1.5-million grant from the North Carolina Clean Water Management Trust Fund (CWMTF). The CWMTF was an essential project partner because their mission focuses on high-performance stormwater solutions and supports innovative, non-traditional stormwater practices. Based on state-regulated requirements for upstream stormwater treatment, the NCMA expansion could have been built with only the pond and wetland system. Because of the CWMTF’s flexibility, the design team could explore other solutions that expanded the scope and influence of the project and were appropriate to the museum’s mission, including style and aesthetics. Without the additional funding provided by the CWMTF, the artfully functional elements like the terraced bioretention trays and sculptural runnels would not have been possible. Ultimately, the project far surpassed the CWMTF’s original goal of improving stormwater quality and enabled the project to elevate standards for stormwater devices by exhibiting both sculptural design and a high level of performance. 

The estimated construction cost of a traditional stormwater retention basin and wetland complex comparable to the NCMC’s stormwater system is $940,972. The actual construction cost of the NCMA stormwater pond, wetland, and bioretention trays was $3 million. Although the NCMA’s construction costs were over $2 million more than those estimated for standard solutions, a $1.5 million grant was acquired through a North Carolina Clean Water Management Trust Fund Grant, which reduced the net difference to $559,027. This grant could not have been applied to a conventional stormwater pond and wetland. The artistic stormwater management features are integrated into the museum park experience, thus reinforcing the museum’s guiding mission while also supporting visitation and revenue generation. 

The reduction in flow caused by the BMPs allowed for the use of smaller pipe sizes around the amphitheater. A 15-in HDPE pipe with an installed price of $37 per linear ft was used instead of a 24-in HDPE pipe with an installed price of $50 per linear ft, thereby downsizing 620 linear ft of pipe at a savings of $13 per linear ft (installed), or $8,060. 

• The project’s value engineering and cost-cutting efforts often proved to be shortsighted. For example, the pervious gravel in Cantor Court was not built with the recommended underdrains, resulting in the drowning of bamboo, which was integral to the design. Underdrains leading either to the cistern or stormwater treatment systems was an expense that, if undertaken, would have dramatically increased the likelihood of success for the plants.
• Project cost-cutting measures did not always save money in the long term, as illustrated in the installation of the cistern. To adequately supply the site’s irrigation demand, the cistern was sized to hold 200,000 gallons of stormwater. During construction, the project budget was reduced, thereby reducing the cistern’s installed size to 90,000 gallons. This reduction caused seasonal failure of the irrigation system due to water shortages during dry months, ultimately resulting in the failure of some landscape areas.

Cistern: Hancor, Inc.
Grasses: Hoffman Nursery
Concrete: Scofield (coral red)
HDPE Stormwater Piping: Hancor, Inc.
Bioretention Soil Media: Triangle Landscape Supplies
Structural Soil: Carolina Stalite
Bamboo: New England Bamboo Company
Lights: Kim Lighting, Bega, and Hunza
Fountains: Roman Fountains
Gravel Pavements: Southern Aggregates
Trees: Select Trees
Stabilized Aggregate Epoxy Binder: Klingstone
Metal Edging: Border Concepts
Granite Pavers: Hanover

Project Team

Client: North Carolina Museum of Art
Landscape Architect: Surface 678
Civil and Environmental Engineer: Artifex Environmental Design, Inc.
General Contractor: Balfour Beatty Construction
Architect (West Gallery): Thomas Phifer and Partners
Fountain Design: Roman Fountains
Landscape Contractor (West Gallery): Valleycrest Development
Landscape Contractor (Stormwater Pond): Davis Landscape

Role of the Landscape Architect

The landscape architect led an integrated process to ensure the design’s appropriateness with respect to both context and execution.The landscape architect and civil engineer worked in close collaboration to refine the design while implementing the project’s demanding engineering requirements. While the engineer did all calculations, the landscape architect was influential in the design and construction of the engineering items.