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Views of South San Francisco Bay Before Salt-Pond Restoration
 Above: R/V Parke Snavely mapping in Alviso Slough, October 27, 2011. Photograph by Helen Gibbons, USGS. [larger version] The largest tidal-wetland-restoration project on the U.S. west coast is underway in south San Francisco Bay, California, where more than 15,000 acres of industrial salt ponds are being restored to intertidal habitats. The U.S. Geological Survey (USGS) is a major player in the South Bay Salt Pond Restoration Project, a joint effort by federal, state, and nonprofit organizations. Among its many contributions, the USGS is making maps of the bay floor before and after the breaching of levees to restore natural tidal flows. The first of those maps—the “before” set—were recently released in USGS Open-File Report 2011-1315, “2010 Bathymetry and Digital Elevation Model of Coyote Creek and Alviso Slough, South San Francisco Bay, California.” The “before” mapping took place in 2010, when USGS scientists conducted three cruises—in January, September, and early December—to map the bathymetry of channels and shallow intertidal mudflats in the southernmost part of south San Francisco Bay. Data from the three surveys were merged to generate comprehensive maps of Coyote Creek (from Calaveras Point east to the railroad bridge) and Alviso Slough (from San Francisco Bay to the town of Alviso) to establish baseline bathymetry before the breaching of levees adjacent to Alviso Slough as part of the restoration project. The bathymetric surveys were done by the research vessel (R/V) Parke Snavely outfitted with an interferometric sidescan sonar for swath mapping (bathymetric mapping of overlapping swaths of seafloor) in extremely shallow water. These surveys yielded high-resolution bathymetric data that are presented in the new Open-File Report. Additionally, the authors merged the bathymetric data with aerial lidar (light detection and ranging) data collected for the USGS during the same time period. The result, also presented in the new report, is a seamless, high-resolution digital elevation model (DEM) of the study area—a view of the ground surface as it would look if both water and vegetation were removed.
On December 10, 2010, the South Bay Salt Pond Restoration Project breached a levee beside Alviso Slough and used that breach and a series of water-control structures to begin circulating water throughout a network of ponds that had not had natural tidal flows for decades. (See photographs at http://www.werc.usgs.gov/outreach.aspx?RecordID=24.) USGS scientists are monitoring how both the physical environment and the ecology respond to the changes in the tidal regime. The USGS conducted a followup bathymetric survey in October 2011 to see how the bay floor had changed over the 11 months after the initial levee breaches of December 2010. Plans are in place to survey the same area three more times in 2012 to monitor change as restoration progresses.
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in this issue:
Collaborative Seafloor-Mapping Program Completes Final Surveys Seafloor-Sampling Survey off Massachusetts
Climate Change Scenarios in California's Bay-Delta
Public Forum On Seafloor Mapping at the Ocean Explorium
Workshop on Fledermaus Software
Using Mangrove Peat to Study Ancient Coastal Environments and Sea-Level Rise |
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U.S. Department of the Interior |
U.S. Geological Survey
URL: http://soundwaves.usgs.gov/2012/02/pubs.html
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