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Watershed Wonder

Concrete plays pivotal part in San Antonio’s Confluence Park

PHOTO: Anthony Terrebonne

The Estella Avery Education Center features a green roof that provides thermal mass for passive heating and cooling. A photovoltaic array on the roof of the multipurpose building is intended to offset 100% of the energy use for the park on a yearly basis. PHOTOS: Casey Dunn

The BHP Pavilion’s concrete “petals” collect and funnel rainwater, diverting it to a site-wide water catchment system that feeds rainwater into an underground cistern. With a rain collection area of over 20,000-sq.-ft., an average of 286,000 gallons per year of rainwater is collected annually as part of the park’s water capture plan.
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The inlay patterns in Keystone Hardscapes custom CityScape Pentagon pavers mimic meandering rivers and streams to complement the park’s location at the confluence of the San Antonio River and San Pedro Creek. PHOTOS: Anthony Terrebonne

Nestled at the junction of the San Antonio River and Sand Pedro Creek, the 3.5-acre Confluence Park was designed with confluence ingrained in every aspect—from its central pavilion’s concrete “petals” that are structured to funnel rainwater to their “roots,” to the scale of the paver patterns reminiscent of the flow and convergence of waterways. Designed as a collaboration between local firm Lake|Flato Architects and Oakland, Calif.–based Matsys, the so-called “living laboratory” recently received the 2019 Hardscapes North America Award for Concrete Paver – Commercial > 15,000 sq. ft. and the American Institute of Architects’ 2019 Institute Honor Awards for Architecture.

To better serve San Antonio’s most economically challenged communities, the San Antonio River Foundation tasked the design team with transforming a former construction storage yard into a unique outdoor education center that would not only be a destination for recreation, but also for learning about the region’s ecotypes and water conservation. Located along the Mission Reach section of the San Antonio River, Confluence Park features native planting, a 2,000-sq.-ft., multi-purpose educational building, a 6,000-sq.-ft. central pavilion, and three smaller “satellite” pavilions.

The multi-purpose Estella Avery Education Center can be used as a functional classroom and meeting space, and opens completely to the adjacent central pavilion. “This building was designed to contrast with and be a supporting actor to the pavilion—the board formed concrete walls are highly textured compared to the smooth, fiberglass formed petals, and the more geometric forms contrast with the curves of the pavilion,” notes the design team.


The BHP Pavilion or central pavilion of the park is truly a one-of-a-kind landmark. Constructed of 22 concrete “petals” designed thoughtfully to sit lightly upon the land, the pavilion forms a network of vaults, which provide shade and direct the flow of rainwater into a site-wide water catchment system. The pavilion geometry was inspired by many regional plants’ use of doubly curved fronds or petals to cantilever out and collect rainwater and dew and redirect the water toward its root stem.

In developing these petals, one of the central concerns was to make sure that they were modular, yet seemingly non-repetitive. The design was developed from the Cairo tile, an irregular pentagon, as the underlying base grid in order to resolve this tension between cost-effective modularity and the desire for spatial richness. The pentagon is subdivided into five triangles, one for each side of the pentagon. This results in only three unique modules: two asymmetrical triangles (A, B) that are mirrors of each other and one equilateral triangle (C). “One of the interesting relationships within this pattern is that pairings composed of either A-B or C-C petals make up structural arches,” recalls pavilion designer Andrew Kudless of Matsys in his article “Design and Construction of Confluence Park” in Tilt-Up Today. “This relationship allowed for only three concrete molds to make all 28 concrete petals of the main and satellite pavilions.”

From this irregular triangular base grid, a parametric model was used to create the three-dimensional solids of each petal. Structurally, each petal is half of an arch which starts out as a 16-inch thick column and tapers to a 4-inch deep curved roof. The double-curvature of the surface geometry helps with the structural rigidity of the petal. Each petal is connected to its paired half-arch by two structural pin joints. The petals’ capacity to shed water in the proper direction was tested through water flow analysis using particle simulations.

The petals were cast on site using a modified tilt-up construction technique and digitally fabricated fiberglass composite molds by American Canyon, Calif.-based Kreysler & Associates. A concrete mix was developed that could provide both flow and compaction into the lower column area without producing excessive voids while simultaneously providing the necessary stiffness on the higher sloped areas to resist sliding down the form. Due to the petals’ complex geometry, the molds were not enclosed. However, this allowed for the interior and exterior of the structure to have two dramatically different finishes. The exposed areas of concrete, Kudless notes, were broom-finished with strokes aligning with the direction of water flow—a nice contrast to the smooth finish from the fiberglass form. After roughly a week of curing, the 29-ft. tall petals were lifted into their final positions.


The Cairo tile geometry was reused at a much smaller scale for the thousands of concrete pavers used throughout the park. Four different inlay patterns were developed for the pavers such that a larger network of branching curves was created. The irregular network references the bifurcations and deltas of the local watershed.

Working with landscape architect Rialto Studio, Keystone Hardscapes’ Research & Development team created a new pentagonal paver—CityScape Pentagon—for the project. The new paver was developed to address both design and functional needs. To achieve the architect’s vision of grooves on the paver’s surface, the curves were made in the top, or head, of a mold and stamped into the top face of the paver during the manufacturing process. Depth, width and angularity of the depressions on the paver’s surface ensured a minimalistic effect, while a micro-chamfer provided a clean edge.

San Antonio-based Cribley Enterprises installed lighter colored Keystone pavers on the walkways and common areas of Confluence Park to complement the pavilions’ concrete petals. For the entire project, Cribley used 23,000-sq.-ft. of CityScape Pentagon pavers in custom Caststone, and 11,000-sq.-ft. of the Holland paver in Charcoal. The pavers were supplied by Keystone Hardscapes’ San Marcos, Texas plant.

“Our pavers, through function and design, help celebrate the south Texas eco-system and inspire the local community to engage and gather,” affirm Keystone officials.

Since opening in March 2018, the collaborative ethos evident in the San Antonio River Foundation’s directives to the design team has already made a positive impact on the community. Within its first year of operation, Confluence Park played host to more than 14,000 students and program attendees and partner to more than 30 nonprofits and 50 schools. “It was the collaboration that made this project so successful—we worked closely with the design team and the client to create a park that achieved the client’s vision of the design itself inspiring environmental education and stewardship,” says Tenna Florian, AIA, LEED AP BD+C, Lake|Flato Architects.