San Francisco Bay Coastal System

Project overview

San Francisco Bay is a heavily urbanized estuary that is impacted by numerous anthropogenic activities, including channel dredging, aggregate mining, delta discharge and sediment load regulation, urban run-off, urban sediment trapping, heavy ship traffic, oil spills, exotic species introduction, and salt pond restoration. The Golden Gate strait is the sole inlet connecting the Bay to the Pacific Ocean, and serves as the conduit for over 2 trillion gallons of water daily in addition to the transport of mud, sand, biogenic material, and pollutants. Despite this physical, biological and chemical connection, prior research has typically treated the Bay and adjacent Ocean as separate entities, compartmentalized by artificial geographic boundaries, such as the Golden Gate Bridge.

However, recent research completed as part of the USGS Project "Coastal Evolution: Process-based, Multi-scale Modeling" has demonstrated the dynamic nature of processes at the mouth of San Francisco Bay, but more critically the important connection between San Francisco Bay physical processes and the adjacent coastal environment. This new project, the San Francisco Bay Coastal System, will treat the region as a single physical entity that is impacted throughout by physical processes and anthropogenic activities from the delta to the shelf edge.

The primary goal is to identify the physical processes and anthropogenic influences that have resulted in significant morphological changes to the San Francisco Bay Coastal System. This, in turn, will aid in the assessment of the future impact of sea level rise, climate change, and sediment management practices on the region's beaches, tidal wetlands, and submarine resources. Prior work in San Francisco Bay has focused almost exclusively on fine sediment transport (i.e., mud) due to its association with pollutants. However, sand in the San Francisco Bay Coastal system is a critical component for area beaches both inside and outside the bay, protective shoals, tidal wetlands, and aggregate mining. Recent USGS research shows that the San Francisco Bar, a massive sediment body covering over 100 square kilometers, has lost over 90 million cubic meters of sediment, primarily sand, in the last 50 years, and Central San Francisco Bay has lost a comparable volume. With sand dominating the active bed in these regions, understanding the source and potential transport of sand in this system is essential to identifying the reasons for this pattern of massive sediment lost.

Strategy and approach

The strength of this project is in the integration of work inside and outside the bay, past and present. We are building from a firm scientific base, but modifying the work to directly address relevant societal needs. Due to our strongly developed research and agency collaboration in the region, spin-up time for the new project is minimal and we can hit the ground running in year 1. The project framework is designed to understand physical processes in numerous portions of the San Francisco Bay Coastal System at a variety of spatial and temporal scales, combining ongoing and new work.

• Task 1, 'Synthesis,' ties all the tasks together to present a single, coherent presentation of San Francisco Bay Coastal System sediment transport pathways, historical changes, and anthropogenic impacts.
• Task 2, 'San Francisco Bight Coastal Processes' supports ongoing work along the open-ocean coastline immediately adjacent to the mouth of San Francisco Bay seeking to understand the processes controlling short- and long-term beach evolution, with emphasis on Ocean Beach. Research to date strongly suggests a direct link between bay sediment supply, ebb-tidal delta evolution, and beach response.
• Task 3, 'Crissy Field Coastal Processes,' primarily OFA funded by the National Park Service, represents an important link between bay and open-ocean processes as it is the first sand beach encountered inside the bay. The beach is supplied by littoral drift that moves into the bay, but the shoreline is also strongly shaped by wave and tidal current interaction that result in closure of an inlet leading to Crissy Marsh.
• Task 4, 'Processes and Morphology Near the Mouth of San Francisco Bay,' investigates the evolution of morphology near the entrance to San Francisco Bay over time scales of years to decades. Emphasis is on major sand features and transport pathways. These include the shape and evolution of the Golden Gate sand waves, the massive ebb tidal delta, pocket beaches near the Golden Gate, the Golden Gate narrows, and wind-blown sediment over the San Francisco peninsula.
• Task 5, 'San Francisco Bay Sedimentation and Geomorphic Evolution,' largely OFA-funded, supports ongoing work to quantify historical bay bathymetric changes and synthesize a gravity core data set (over 300 bay-wide), all in an effort to identify and explain system-wide historical and present-day patterns of erosion and deposition.
• Task 6, 'Shoal-Channel Sediment Transport,' is an NSF-funded project to determine the mechanism by which sediment is transferred between shoals and channels in South San Francisco Bay.
• Task 7, 'Persistence of the Cosco Busan Oil Spill in San Francisco Bay,' supports ongoing work to assess the short and long-term impact of this major oil spill on water quality and sensitive habitats in the San Francisco Bay Coastal System.