Pond Urbanism: Floating urban districts on shallow coastal groundwater

Kristina Hill & Greg Henderson

Shallow coastal groundwater is rising as sea levels rise, but most coastal cities do not have an extensive network of pumps to handle this, and subsidence risks can increase with additional pumping. Rising groundwater can remobilize capped soil contaminants, bring pollutants into coastal waters, cause foundations to heave, block sewer pipes, and increase soil liquefaction risks. Conventional development is likely to fail, requiring floodable development strategies. Our research analyzed the risk of rising groundwater in the San Francisco Bay Area, and identified opportunities for floodable development within existing policy restrictions. 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 urban districts. Our proposed design uses shared decking, supported by pontoons, to provide flexibility for placing pre-fabricated housing units on a stable platform in an artificial, excavated pond. A series of artificial ponds could produce multiple benefits as housing, wildlife habitat, and space for flood management. The region’s largest city, San Jose, has agreed to permit a version of this design, which could be used to adapt many similar urban districts.

KEYWORDS: groundwater, sea level rise, flood adaptation, coastal ecosystems, urban planning

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