SALT SAND SIEVE
Winning entry: The I-280 Freeway Competition SEED Fund and the Center for Architecture and Design 2013
CONCEPT
Salt Sand Sieve proposes a field of urban dunes to generate a porous and ecologically diverse shoreline and to establish a sensory landscape informed by the meter of the highway and the forces of the bay.
PREHISTORY
The pre-modern landscape of San Francisco was one of tidal marshes, mudflats, sand dunes. Industrialization and speculation in the 19th and early 20th c. led to the loss of these highly performative ecologies: dunes were flattened, wetlands - like those at Mission Bay - were filled. Highly porous, ecologically and morphologically diverse areas along the city’s shore became impervious and flat.
OPERATIONS
[dredge] In 2011, 3.27 million cubic yards of dredged sediment was excavated from the San Francisco Bay. The removal and disposal of this dredge is energy-intensive and costly - millions of tons of sediment travel over 60 miles to deep-ocean dumping sites or via truck to “upland sites” on the California mainland. Salt Sand Sieve utilizes this misallocated asset as the foundation of its design: dredge becomes dune.
[columns] The Mission Bay section of the 280 Freeway is supported by 161 reinforced concrete columns: 10-12’ diameter; 20-50’ height; 40’ apart. This “column grid” not only registers the site history, it generates the rhythm and meter of the site as the columns catch sand and ballast the dunes.
[cisterna] The urban dunes of Salt Sand Sieve borrow formally and functionally from the Venetian cisterna: sand-filled filtration cisterns used to collect and cleanse rainwater in pre-20th c. Venice. The dune morphology mirrors the form of Venetian cisterns and performs in much the same way: sand and native plants filter stormwater that is channeled to freshwater wading pools along the edge of Mission Creek before entering the bay.
[buffer ecology] The dune landscape provides a valuable buffer zone to remedy the loss of ecosystem services once provided by the Mission Bay wetlands and tidal flats: protection against storm surge and rising sea levels, habitats for birds, wildlife, and native vegetation, and stormwater filtration.
[key species] Ammophila arenaria (Marram grass), Elytrigia Juncea (san couch-grass), Cakile maritima (sea rocket): Grasses responsible for the formation and stabilization of dunes through the binding and trapping of sand.
SPACE
[dune] The dune field renders an immersive counterpoint to the noise of urban San Francisco.
The troughs between dunes offer refuge from noise and wind. Runoff percolates through the dunes, resurfacing as pools and wetlands.
[paths] The Salt Sand Sieve landscape is traversed by walkways and bikeways that wend laterally and longitudinally between the dunes.
[pool] Fresh water is filtered and channeled to gravity-fed pools along Mission Creek. These pools disrupt the unbroken geometry of Mission Creek to enable multiple access points and a variety of programmatic possibilities along the water’s edge, including launching platforms for boats, kayaks, and swimmers.
Volatile, fluctuating, and stable habitats are coincident in sand dune ecosystems, making them particularly biodiverse. This collision of complex systems is a mirror and a support for the urban environment around Mission Bay Channel.