Under clear skies, San Francisco emerged from the weekend’s epic bomb cyclone and atmospheric river that brought lacerating winds and record-setting rainfall.
But The City returned to some semblance of normalcy by mid-morning Monday. Runners dodged large puddles on the Marina Green. Drivers circumvented fallen trees near the Embarcadero. Chainsaws whirred in Golden Gate Park as crews cleared truckloads of large branches and debris from roadways.
“Even after the rains and winds subside, cleanup will take days,” said Rachel Gordon, spokesperson for Public Works. “Our crews have been working non-stop in the downpour and high winds on storm response, with more than 700 calls for downed trees and large limbs throughout The City.”
All told, the widespread damage underscored San Francisco’s susceptibility to heavy rainstorms, which are projected to become more extreme in a changing climate. Sunday’s storm was the strongest in 26 years, according to Meteorologist Jan Null of Golden Gate Weather Services and revealed the vulnerability of San Francisco’s aging infrastructure to more extreme weather events.
“San Francisco has experienced an amount of rain this week, and we have had reports of localized flooding in some areas,” said Will Reisman, for the San Francisco Public Utilities Commission.
The wet weather prompted evacuation orders and delayed public transportation, including Muni, BART and the SF Bay Ferry.
But the most striking images that emerged this weekend were of submerged cars stranded on freeway off-ramps and backed-up storm drains inundating neighborhoods with murky water.
“No sewer system can handle the heaviest storms,” said Reisman. “We have been proactive in our preparation and response — clearing storm drains, delivering sandbags, and deploying barriers in flood-prone areas.”
San Francisco is the only coastal city in California with a combined sewer system that collects and treats both wastewater and stormwater in the same network of pipes. Under normal conditions, this system transports wastewater to a sewage treatment plant before discharging it into a body of water, like the Bay.
When heavy rainfall events occur, however, the volume of wastewater can exceed the capacity of the system and will cause untreated discharges directly to nearby streams, rivers, and other water bodies, according to the EPA, which called these shared systems a “priority water pollution concern.”
ConnectSF, a multi-agency working group, includes The City’s sewage system on its list of aging infrastructure, citing that over 300 miles of the system is at least 100 years old and not designed to withstand seismic activity.
In response to its aging sewage system, The City has rolled out a 20-year, multibillion-dollar project to better prepare for storms of the future. The Sewer System Improvement Project will make upgrades to treatment facilities and pump stations, according to SFPUC, and it will deploy natural processes to reduce stormwater flows into the system.
Construction is slated to be completed by 2030, leaving an aging system to manage what climate models predict will be more intensifying precipitation events, like Sundays, for years to come.