The sediment in San Francisco Bay, once thought of as a renewable resource, is eroding and being removed much more quickly than nature replenishes it — which could affect two companies’ requests to increase their sand-mining operations.
Sand has been removed from the Bay for more than 100 years, first for harbors and channels and later for use in construction. For decades it was assumed the sediment was quickly replenished. But new research shows that only 15 percent of the coarse sand mined for construction purposes is replenished.
This decrease in sediment is one cause of coastal erosion, including the southern part of Ocean Beach, which is one of the fastest eroding stretches in the state, said Patrick Barnard, a coastal geologist with the U.S. Geological Society. Such erosion threatens valuable city infrastructure, including Great Highway and a water treatment plant worth hundreds of millions of dollars.
“There has been concern about the connection to the outer coast,” program manager Brenda Goeden of the Bay Conservation and Development Commission said of the relationship between sand mining and beach erosion.
The issue arose Thursday during a commission hearing that considered the latest studies about the movement of sediment through the Bay and how it affects coastal erosion.
Some of this research was highlighted in an environmental study done before two companies, Hanson Aggregates and Jerico Products, can renew sand mining permits on state-owned land in San Francisco and Suisun bays.
Although the California State Lands Commission recently approved the environmental review, the permits now will be reviewed by several local, state and federal agencies, including the commission.
The two companies are asking for a 17.4 percent increase in how much sand they are permitted to remove for a 10-year period.
But Ian Wren, a scientist at San Francisco Baykeeper, pointed out that the rate of sand mining has not decreased proportionately with the amount being replenished.
Sediment flows through the delta, into the Bay and then onto the ocean floor and at beaches south of the bridge, Barnard said. But the amount of sediment ending up on beaches has decreased over time. The main reason is a steady reduction in sediment from Gold Rush-era hydraulic mining techniques, which pulverized the Sierra Nevada mountains. And dams and flood-management projects have reduced the water and sediment flowing through the delta.
Peter Baye, an independent coastal ecology consultant, said companies that mine sand should do so only at a rate of replenishment. Doing so would mean drastically reducing the amount of sand these companies are allowed to remove, he noted.
Other alternatives to mining construction sand from the Bay include mining it from regional land-based sources or increasing the amount imported from places including British Columbia, where it is taken from sediment left behind by retreating glaciers. Both sources could add to greenhouse gas emissions, which leaves environmental groups working to weigh the harms of shipping material from outside of the region and depleting sand in the Bay.
“We don’t want to encourage increased greenhouse gas rates from shipping or importing,” Wren said. But he acknowledged that the sand mining is an unsustainable practice that is also harmful and that a balance of the two is needed.
Representatives from the two companies told the commission Thursday that mining from the Bay is cheaper and more ecological than the alternatives.
Bill Butler of Jerico Products said shipping one barge of sand removes 100 trucks from the roads.
“This resource is valuable,” he said. “Having a local Bay Area source for our local Bay Area needs — one that’s efficiently extracted and then transported by water directly or very close to where it is used — is economically and
Proposed changes to mining permit
Hanson Aggregates and Jerico Products are seeking permission to increase the amount of sand they mine from
San Francisco Bay west of Alcatraz Island.
Central Bay lease area: 1,390,000
Average removed 2002-07:1,540,000
Proposed new limit Increase over average: 35%
Suisun Bay/Delta lease area: 1,490,000
Current limit: 1,226,785
Average removed 2002-07: 1,840,000
Proposed new limit Increase over average: 50%
Source: California State Lands Commission