Pond Urbanism: Floating urban districts on shallow coastal groundwater in artificial ponds

Kristina Hill, PhD, University of California Berkeley
Greg Henderson, AIA, NCARB, Arx Pax Labs, Inc.

Shallow coastal groundwater is rising as sea levels rise. Pumping groundwater away can increase subsidence risks on former wetland soils, and capped soil contaminants can be remobilized where groundwater rises. In seismically-active regions, rising groundwater can also increase soil liquefaction risks. Conventional development in many flooded locations will fail, and new floodable development strategies are needed on today’s dry land.

Our research analyzed the scope of the risk of rising groundwater in the San Francisco Bay Area, making the first shallow groundwater map of the region using an interpolated surface based on thousands of existing wells. We reviewed soil contamination and liquefaction risks, and identified opportunities within existing policy restrictions, including laws that protect and encourage tidal wetland reconstruction. We combined this spatial and policy analysis with a study of a prototypical design for floating urban blocks in artificial ponds. Our goal was to identify a strategy for conserving protected coastal habitat while creating sustainable housing.

The proposed design aggregates precast floating concrete foundations to provide flexible building areas and land uses while dramatically increasing stability. This provides flexibility for placing pre-fabricated housing units and public spaces on a single stable platform. A honeycomb pattern of artificial ponds could produce multiple benefits as housing, wildlife habitat, and space for flood management, allowing flat urban areas to adapt to sea level rise. The region’s largest city, San Jose, supports a version of this design, and investors are being sought to implement this innovation. Our results indicate that the functional and taxable value of thousands of hectares of existing urban land could be lost to rising groundwater in the San Francisco Bay Area.

Keywords – Groundwater, Sea level rise, Flood adaptation, Coastal ecosystems, Urban planning

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Kristina Hill is a professor at the University of California, Berkeley. Her research is on flood risks and adaptation. She participated in the Dutch-American planning process for New Orleans after Hurricane Katrina, and has studied flood risks associated with stormwater, groundwater and seawater. Her PhD is from Harvard University. Kristina publishes in the scientific and design literature, and lectures internationally on strategies for flood adaptation that address both biodiversity and social inequality. She is the author and editor of the book, Ecology and Design (Island Press 2002), and is currently completing a book on coastal adaptation.

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