Located along the Mission Reach section of the San Antonio River, Confluence Park is an
educational park focusing on the critical role of water in the regional ecosystems. The park
consists of 3.5 acres of native planting, a 2000 square foot multi-purpose building, a 6000
square foot central pavilion, and 3 smaller “satellite” pavilions dispersed throughout the park.
The central pavilion is composed of 22 concrete “petals” that form a network of vaults that
provide shade and direct the flow of rainwater into an underground cistern.
The development of the central pavilion focused on creating an inspirational and aspirational
space that helped communicate the client’s mission in providing environmental education
related to water conservation. Looking towards nature for inspiration, the pavilion geometry
was inspired by certain plants’ use of doubly curved fronds to cantilever out and collect
rainwater and dew and redirect the water towards its root stem. A modular system of
concrete “petals” was developed that collected rainwater and funneled it to the petals’
columnar bases and then on to a central underground cistern used for the park’s irrigation
In developing these petals, one of the central concerns was to make sure that they were
modular yet seemingly non-repetitive. The design uses 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 in a way
that results in only three unique modules: two asymmetrical triangles that are mirrors of each
other and one equilateral triangle.
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” thick column and tapers to a 4” 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.
Three digitally fabricated composite formworks were made in order to both increase
accuracy and decrease material waste and costs associated with traditional wooden forms.
After milling foam positives, a 2” thick composite structure composed of inner and outer
layers of fiberglass composite with a central core of balsa wood was applied. The formwork
was then shipped to the site and positioned in a way that it could be cast as a modified tilt-up
wall construction. This avoided the need for a fully enclosed form which decreased the cost
and allowed the top and bottom surfaces to have radically different finishes: the bottom is
cast against the smooth fiberglass while the top is broom-finished with the broom strokes
aligning with the direction of the water flow.
The pavilion embodies our deep interest in the integration of form, fabrication, and