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The USGS is providing support for an innovative project between the U.S. Army Corps of Engineers, California Coastal Conservancy, and Port of Redwood City to increase marsh resilience to sea-level rise.

In a groundbreaking pilot initiative to address sea level rise, coastal erosion, and habitat preservation in San Francisco Bay, researchers from USGS are monitoring a U.S. Army Corps of Engineers and Port of Redwood City project to test the efficacy of strategically placing dredged material in areas where natural wave energy and currents can redistribute mud to wetlands, bolstering resilience against rising seas.  

The San Francisco Bay Area has invested hundreds of millions of dollars over the past 25 years to restore former tidal wetlands that provide critical habitat for fish and wildlife, improve water quality, and provide coastal protection benefits for Bay communities. However, the long-term success of these efforts is at risk due to a deficit of sediment needed for wetlands to keep pace with rising seas.

Just as the region faces a critical need for sediment, mud that accumulates in San Francisco Bay ports, marinas, and navigation channels is periodically removed via dredging and disposed of primarily outside of the Bay. 

Dredged material management strategies have undergone significant evolution over time, guided by input from stakeholders concerned with coastal erosion, navigation safety, special status species, and benthic habitats. 

Local regulators, industry stakeholders, and state and federal agencies are working collaboratively to minimize the loss of sediment from the Bay, while simultaneously ensuring navigable channels and maintaining the health of nearshore habitats, particularly salt marsh, in the San Francisco Bay area. 

Animated GIF of a clamshell dredge in operation
A clamshell dredge in operation as part of the Shallow Water Strategic Placement Pilot Project.

Strategic placement of dredged materials 

The San Francisco District of the U.S. Army Corps of Engineers is conducting a pilot project to test the efficacy of strategic placement of dredged material to promote mudflat and tidal marsh sedimentation, the first of its kind in the San Francisco Bay region. Project partners include the California State Coastal Conservancy, the San Francisco Bay Water Board, the San Francisco Bay Conservation and Development Commission, and NOAA Fisheries.

By placing dredged sediment in shallow water near shore, natural transport processes such as wind and waves can move those sediments onshore. These processes provide a more cost-effective means of promoting marsh resilience to sea-level rise than direct sediment placement on tidal marshes—and, if successful, may offer a nature-based solution to the region’s sediment needs.

In this pilot project, more than 90,000 cubic yards of sediment dredged from the Port of Redwood City were placed in the eastern shallows of South San Francisco Bay, offshore of the marsh complex in Eden Landing Ecological Reserve, in December 2023.

USGS is monitoring several aspects of the pilot project during and following placement to learn about the fate of the placed sediment and document any unanticipated ecological impacts: 

  • Measuring currents, wave conditions, and turbidity in the region of the placement  
  • Characterizing benthic infauna to screen for effects of the placement on foraging resources for special status fish 
  • Measuring sediment deposition on the nearby marsh and restored ponds 
  • Tracking dispersal of the placed sediment through both repeat bathymetric mapping and conducting a tracer study in collaboration with ParTrac. 

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