Mapping South San Francisco Bay's seabed diversity for use in wetland restoration planning

In an effort to understand the role of sediment of South San Francisco Bay (South Bay) salt ponds, an acoustic seabed classification was performed with the condition of over two hundred sediment samples.  The success of the large-scale tidal wetland restoration  of up to 15,000 acres of South Bay partly depends on the ability of the converted ponds to acquire and retain enough sediment to support marsh growth.  Determining the distribution of South Bay's seabed sediment types and understanding their potential erosive properties helps answer critical planning questions about sediment budgets and sediment transportation.

Acoustic seabed classification is the organization of the seafloor into discrete units based on the characteristics of the acoustic response generated by an echosounder.  Acoustic diversity is considered a proxy for geoacoustical parameters including acoustic impedance contrast, scatter and volume reverberation which all vary with sediment type.  In addition, biological and anthropogenic features can influence the acoustic response.

Data for an acoustic seabed classification were collected as a part of a California Coastal Conservancy funded bathymetric survey of South Bay in early 2005.  A QTC VIEW seabed classification system recorded echoes from a sungle bean 50 kHz echosounder.  Approximately 450,000 seabed classification records were generated from an are of of about 30 sq. miles.  Ten district acoustic classes were identified through an unsupervised classification system using principle component and cluster analyses.  One hundred and sixty-one grab samples and forty-five benthic community composition data samples collected in the study area shortly before and after the seabed classification survey, further refined the ten classes into groups based on grain size.  A preliminary map of surficial grain size of South Bay was developed from the combination of the seabed classification and the grab and benthic samples.  The initial seabed classification map, the grain size map, and locations of sediment samples will be displayed along with the methods of acousitc seabed classification.