San Francisco — Riffling through old maps while researching a history project for San Francisco public schools, landscape architect Bonnie Sherk made a discovery: a century ago a creek coursed where two school campuses stand today.
“There was Islais Creek, running where Balboa High School is now,” Sherk said. “All of a sudden it made sense: the school’s cafeteria had been flooding and the basements of homes in this neighborhood flood during heavy rains because they’re in this large watershed.”
Two wells have been drilled on the school campuses since Sherk’s discovery a decade ago, tapping the hidden creek’s water to irrigate community gardens, parks and street vegetation, while potentially reducing the threat of floods.
Now, as part of an estimated $4 billion sewer upgrade, Islais Creek and other streams that last saw daylight more than a century ago could flow openly once again through neighborhoods of one of the country’s most densely built cities.
Such “daylighting” of urban creeks is being embraced in cities throughout the world. Resurrecting old creeks can help remove hundreds of millions of gallons of storm water from sewer systems each year — meaning fewer sewage spills and cleaner water.
Covered up during and after the Gold Rush when the city’s booming population created demand for housing, San Francisco’s many creeks were diverted and sent underground into the sewer system — parts of it still using 1850s-era brick pipes. The water is mixed with the waste and sent to a treatment plant before being expelled into San Francisco Bay or the Pacific Ocean.
Each year, these rain-swollen creeks often overload the system — and about a dozen times a year raw or partially treated sewage spews into the bay and sea.
Islais Creek, once the city’s largest, can only be seen in a park in the southern part of the city, where it flows into concrete sewer pipes.
“We want to partially restore the natural hydrology of San Francisco,” said Tyrone Jue, spokesman for San Francisco’s Public Utilities Commission, the agency in charge of the project. “It helps the sewer system by reducing flow, beautifies neighborhoods and can bring back natural wildlife that may once have lived in an area.”
San Francisco is studying the best sites for unearthing these historic creeks, and officials say the first phase of projects would likely start in five to 10 years.
Islais Creek, which starts in the city’s Glen Park neighborhood, and Mission Creek, which runs beneath the trendy Mission and South of Market districts, are likely the first candidates.
Both creeks flow toward the bay through densely packed neighborhoods, which could expose the water to pollutants such as auto runoff and garbage.
Berkeley in the 1980s opened a stretch of Strawberry Creek in a public park. But after heavy rains the creek filled with a lot of debris.
Still, regulators say with proper monitoring and natural filters, opening the creeks can actually improve overall water quality by reducing raw sewage overflows.
“Growing plants and vegetation along the creek banks can be very efficient in filtering pollutants and making sure the water going into the bay is better quality,” said David Smith, manager of Clean Water Act permits for the U.S. Environmental Protection Agency office in San Francisco. “There’s a lot of environmental benefit in turning streams back into living systems.”