It would take billions of dollars to repair and fortify a three-mile seawall along San Francisco’s waterfront to prevent it from sustaining major damage during an earthquake, according to a newly released study by the Port of San Francisco.
The port’s “Earthquake Vulnerability Study of the Northern Waterfront” report, which was commissioned for $500,000 in 2014, was publicly released during the San Francisco Port Commission’s April 7 meeting.
The report recommends seismic retrofitting that could cost up to $3 billion, as well as raising the wall to protect the city from rising sea levels, which could cost up to $2 billion.
Among the findings in the study:
- Most of the seawall is built over a weak, saturated, and highly compressible marine clay that tends to amplify earthquake shaking and is susceptible to earthquake-induced lateral spreading and settlement.
- Fill that was used to create the land behind the Seawall is susceptible to liquefaction, a phenomenon where the soil loses strength and behaves similarly to a liquid.
- Large earthquakes would likely cause most of the seawall to settle and move outward toward the Bay. Up to a foot is predicted in moderate-to-large quakes and more than several feet is predicted in a major earthquake.
- Seawall movement is expected to significantly increase earthquake damage and disruption along the waterfront, with historic bulkhead wharf structures built of non-ductile concrete particularly at risk to increased levels of damage.
The study also includes an economic analysis indicating that $1.6 billion in port assets are at risk from earthquake damage within the seawall zone of influence, and that over $2 billion in annual rents, business income, and wages would be disrupted by a major seismic event.
It is feasible to stabilize the seawall by improving the soils below and the fill behind, however construction is costly and disruptive, according to the report.
The study also found that rising seas and climate change will necessitate intervention that may include major changes to the Northern Waterfront and the seawall over the next 100 years.
There is scientific consensus, the report states, that a damaging earthquake “is nearly certain” to occur within the next 30 years.
