Phoenix Civic Space Park

Challenge

The design team was tasked with integrating the park into its context while responding to the input of multiple stakeholders. One of the most important partners was Arizona State University, which was concurrently developing its downtown campus with new residential facilities, a student recreation center, and a student union in the historic U.S. Post Office building. Civic Space is located in the midst of these developments, as well as the Downtown Family YMCA, Central and 1st Avenue light rail stops, and the Westward Ho housing complex. In addition, many community organizations and advocacy groups, such as the Roosevelt Action Association, had an interest in the impact of the park on their neighborhoods and whether the design would meet their expectations.

Solution

Engaging the different groups during the design process was essential to create a well-received park. Alongside the design team, a core group of individuals from the City of Phoenix, Arizona State University, and the Construction Manager At Risk (CMAR) contractor collaborated on design solutions. Public input on the design was solicited during three public meetings led by AECOM and Phoenix project managers, two Parks and Recreation Board meetings, and two Phoenix City Council Meetings. The selected design solution, the ‘Urban Weave,’ had the aim of responding to activity at the edges of the site and providing opportunities for the park to evolve as its context does. A major east/west pedestrian walkway through the park links the Taylor Street Pedestrian Mall on the ASU campus to the YMCA and new Sun Devil Fitness Complex. The large lawn south of the Post Office opens up the new student union to the activities within the park. The remaining plazas and lawns are located to maximize access to and from the light rail stops, encouraging commuters to take a detour through Civic Space Park.

• The park includes 111 new trees selected for drought tolerance and their ability to provide shade. The species utilized include: Arizona Ash, Heritage Live Oak, Chinese Pistache and Yellow Bird of Paradise.
• The 31 trees installed in hardscape areas were planted in structural soil to expand the effective root zone. The structural soil extends approximately 4 ft from the root ball in each direction.
• Permeable concrete sidewalk extends the Taylor Street Pedestrian Mall across the park, better connecting the main cluster of ASU campus buildings to the Sun Devil Fitness Complex and nearby light rail stop.
• Impervious surfaces are reduced by using 39,247 sf of permeable concrete paving, concrete unit pavers, and stabilized granite surfaces that are distributed throughout the plazas and walkways.
• All stormwater runoff is collected on-site and infiltrated in 128 subsurface infiltration chambers with a total capacity of 9,587 cu ft.
• The design incorporates passive cooling techniques such as the water wall that increases evaporative cooling in the lower level courtyard. The water wall is constructed with a stainless steel mesh that distributes water across the vertical surface, cooling the space as air blows across it.
• Currently, the project includes a 75-kW solar power array installed upon shade structures. Additional panels will be added as funding becomes available.

• Growth of trees in hardscape areas is often challenged by the highly compacted soil under the adjacent pavement. At Civic Space, each tree planted in a hardscape area was installed with structural soil surrounding the root ball to increase the effective root zone. When installed per minimum recommendations, the total additional cost for using structural soil for these 31 trees instead of compacted on-site soil is approximately $172,725. Although this is an increase in cost, the additional rooting volume provides better conditions for tree growth, which ultimately saves on tree maintenance and replacement.

• Although developments within the downtown are not required to detain stormwater on-site, the team explored a number of options to utilize the stormwater runoff. These alternatives included subsurface storage tanks for irrigation reuse, but the expected quantity of rainfall was far lower than the demand. Ultimately, the rainwater storage would have required significant maintenance and cost for a system that would rarely be activated. Geotechnical surveys revealed that a highly permeable alluvium layer was located just 30 ft below grade, making this site an ideal candidate for a subsurface infiltration system. The final design utilized a system of 128 subsurface infiltration chambers to collect stormwater and allow it to percolate through the pervious alluvium. This strategy avoids direct discharge of runoff into the storm sewer and provides groundwater recharge.
• The park includes a large installation of pervious concrete paving intended to infiltrate stormwater and allow direct percolation into the subsurface. This was relatively new material in the Phoenix area and after watching the installation, it was readily apparent to the design team that the installation on a highly compacted fill base was limiting water percolation into the subsurface. In the future, a more functional design would place the material on a visqueen (plastic) vapor barrier so that the water is collected in the pervious paving section, and then provide flow paths to direct this water to planting beds. This detail would allow the paving to become a collection and storage system that slowly meters water into planting beds.
• The design team had to work closely with the concrete contractor to develop a process for installing the permeable concrete to a satisfactory level. Initially, three mock up panels were created to test different finish options for the concrete, including a natural grey, stained, and ground finishes. The ground finish option was preferred by the design team, but ended up being significantly more expensive (approximately $12 per square foot) because it would have required a vacuum system to follow the grinder during installation to prevent the concrete pores from becoming clogged with dust. Even with a lower cost finish, there was still a cost premium over traditional concrete. The design team discovered that most of the increased cost was due to the expense of replacing sections with errors. Installing the material required very specific conditions, pours often had to occur at 2 am, and getting pours right each time was quite difficult.

Hardscape: Progressive Concrete Works
Structural Soil: AZ Best Materials, CU Structural Soil
Stormwater Tree Grates: Ironsmith
Infiltration Chambers: StormTech

Project Team

Owner: City of Phoenix
Landscape Architect: AECOM
Architect: Architekton & Swan Architects
Electrical Engineer: Wright Engineering
Civil Engineer: Wood Patel & Associates
Contractor: ForeSite Design & Construction, Inc.

Role of the Landscape Architect

The landscape architect served as the prime consultant and project manager, performing master planning, public workshops, final design, and construction administration. As the project evolved, the landscape architect assembled and managed a growing team of architects, historic architects and engineering sub-consultants. In addition, the landscape architect coordinated the installation of an art commission by Janet Echelman.