Building on Our Mistakes: Sinking Sidewalks in Mission Bay

by Julie Zigoris : potreroview – excerpt

Mission Bay sidewalks continue to sink, a challenge that could point to greater problems than twisted ankles and scraped knees.

“People fall a lot,” said Brian L. who has worked at Cafe Reveille for the past three years. The café, located at 610 Long Bridge Street, is moated by a separated sidewalk edged with a yellow hazard line warning. “It’s always been a problem, but it’s gotten a lot worse in the past year.”

Spanning 300 acres, Mission Bay is built on piles of compacted debris, dirt and silt, making it prone to subsidence, or settling. New buildings are anchored to bedrock deep below; sidewalks aren’t. Since they were first installed barely fifteen years ago, paths along Fourth Street have sunk visibly, with gaps from four inches to almost a foot forming between sidewalks and buildings. Separations have been repaired with caulk, ramps, steps, and not at all.

The issue isn’t unique to Mission Bay, nor new to San Francisco, with the Marina, South-of-Market, and other neighborhoods experiencing intermittent sinking. The American Society of Civil Engineers published Subsidence and the Foundation Problem in San Francisco in 1932…

“Realty has more value than reality,” is the reason for the lack of reason when it comes to building on landfill…“Bayfill is not a great place to build for multiple reasons: subsidence, climate change, and sea level rise,” said San Francisco natural history educator and cartographer Joel Pomerantz. “But people are trying to make as much money as possible.”

Pomerantz is concerned that poor development choices will continue to be made in San Francisco. “Things are not likely to change when land values are so high,” he said.

“The City is becoming more dangerous all the time,” Brechin said. “It’s amazing how we don’t learn from history.”…(more)

It is all about sucking as much money out of the bay mud before the big one hits and knocks it all down.

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