Imagine if, over a decade, San Francisco Bay lost enough sediment to fill about 5,000 Olympic swimming pools with sand and gravel, and some mud.

That's appears to be what happened.

According to research just published by CSU Monterey Bay professor Rikk Kvitek (pictured at right) and U.S. Geological Survey researcher Patrick L. Barnard, an analysis of bathymetric (or sea-bottom) measurements taken in 1997 and again in 2008 indicates that the west-central San Francisco Bay – roughly from the Golden Gate to about a mile east of Angel Island and Alcatraz – lost about 14.1 million cubic meters of sediment. That's the equivalent of about a square mile piled about 17 feet high – or those 5,000 pools.

The report appears in the current issue of San Francisco Estuary and Watershed Science. Access it here.

The 2008 analysis, they wrote, benefited from advances in Global Positioning Systems (GPS) that virtually eliminated inaccuracies due to changing tides or rocking vessels; and from recent improvements in multi-beam sonar, seafloor sampling and underwater video that more clearly reveal the depth and nature of sediments above bedrock.

"The seafloor position can now be mapped with unprecedented detail and precision," the researchers wrote.

Their mapping covered about 15.6 square miles, about one-fourth of which was under lease for aggregate mining. The leased areas, they found, lost sediment at more than four times the rate of the non-leased areas. (Overall, based on soundings taken from 1947 to 1979, San Francisco Bay appears to be losing sediment three times faster than it did in the mid- to late-20th century.)

Kvitek and Barnard conclude that the recently lost, predominantly coarse, sediment was "material that would otherwise have been available for transport to eroding, open-coast beaches" along the San Francisco shoreline.