Interferometric Sidescan Bathymetry, Sediment and Foraminiferal Analyses; a New Look at Tomales Bay, California

Introduction

Perspective view of Tomales Bay and nearby San Francisco Bay area (http://www.sfbayquakes.org/northview.html).

The United States Geological Survey (USGS) in collaboration with Point Reyes National Sea Shore (PRNS), and the Tomales Bay Watershed Council [http://www.tomalesbaywatershed.org/] has completed a detailed bathymetric survey, and sediment and foraminiferal analyses of the floor of Tomales Bay, California.  The study goals are to detail the submarine morphology, the sediment distribution, sedimentary features, and distribution of foraminifera to provide a framework for future studies. The USGS collected swath bathymetric data with a SEA SWATHplus interferometric sidescan sonar system (2004, 2005) and an echo sounder system (2006). The data were processed into continuous mosaic images that show bathymetric detail of the bay floor with 0.2-m vertical and 4.0–m horizontal resolution.  Acoustic backscatter data from the 2004 and 2005 surveys were processed into 2-m resolution grids. In addition, 27 sediment samples were collected from various parts of the bay for grain size analyses and a comprehensive study of the distribution of foraminifera in Tomales Bay.  The foraminiferal analysis determined that the invasive foraminifera Trochammina hadai from Japan was present in Tomales Bay.

The project was conducted in response to a request from the National Park Service, and the Tomales Bay Watershed Council who voiced a need to look at the environmental impacts of human input to the surrounding watersheds that ultimately flow into the bay.  The mapping, sediment, and foraminiferal data establish a baseline survey for future comparisons of possible geologic and anthropogenic changes that might occur due to changes in land use or development in the surrounding watershed.  These data may also aid in determining the possible pathways of pollutants entering the bay from the surrounding watersheds.

Top

Report

Download the report as a 46-page PDF document (of2008-1237.pdf; 2.2 MB)

Map Sheets

	Map Sheet 1: Color-shaded bathymetry map from sidescan and single beam data, Tomales Bay, California. Scale 1:24,000. (28 x 35 in, 13 MB).
	Map Sheet 2: Backscatter amplitude map of the floor of Tomales Bay, California, from interferometric sidescan data. Scale 1:24,000. (28 x 35 in, 15 MB).

Top

GIS Data

Description	Preview	Metadata	Download
4-m resolution bathymetry grid	(13 MB)	text, html, FAQ, xml	ESRI ASCII grid in UTM Zone 10, WGS84 (3.6 MB zip) xyz: xy in geographic coordinates (decimal degrees WGS84), elevation in meters (5.0 MB zip)
2-m resolution backscatter amplitude grid	(15 MB)	text, html, FAQ, xml	ESRI ASCII grid in UTM Zone 10, WGS84 (15 MB zip) xyz: xy in geographic coordinates (decimal degrees WGS84), backscatter amplitude as ratio of mean (15 MB zip)
sediment samples		text, html, FAQ, xml	http://walrus.wr.usgs.gov/infobank/ f/f105tb/samp/f-1-05-tb.onoff.grabs.grab

Figures from the report

	Figure 1-1. Perspective view of Tomales Bay and nearby San Francisco Bay area, California.
	Figure 1-2. Geologic setting of new high-resolution bathymetry and sediment samples collected in Tomales Bay area (after Clark and Brabb, 1997).
	Figure 1-3. Interferometric sidescan sonar data collection equipment.
	Figure 1-4. Perspective views of interferometric sidescan sonar bathymetric data, Tomales Bay, California.
	Figure 1-5. Mouth (A), central (B), and south (C) areas of Tomales Bay, California, including new bathymetry described in this report.
	Figure 1-6. Grain size and locations of sediment samples from Tomales Bay, California.
Top	Figure 1-7. Comparison of 1982 and 2005 foraminiferal assemblages in Tomales Bay, California.
	Figure 2-1. Locations of bathymetric surveys, Tomales Bay, California.
	Figure 3-1. Location of the 1982 (McCormick et al., 1994) and 2005 sample sites in Tomales Bay.
	Figure 3-2. Dendrogram of the Q-mode cluster analysis based on the 1982 quantitative (percent frequencies) foraminiferal abundances of Tomales Bay from McCormick et al., 1994.
	Figure 3-3. Distribution of the 1982 foraminiferal assemblages of Tomales Bay.
	Figure 3-4. Dendrogram of the Q-mode cluster analysis based on the 2005 qualitative (presence/absence) distribution of foraminifera of Tomales Bay.
	Figure 3-5. Distribution of the 2005 foraminiferal assemblages of Tomales Bay.

Top

Tables from the report

For more information, contact

Roberto J. Anima, Emeritus
John L. Chin
United States Geological Survey
Coastal and Marine Geology Program
345 Middlefield Road, MS 999
Menlo Park, CA 94025

Suggested citation and version history

Top

Introduction

Report as PDF

Map Sheets

GIS Data

Figures

Tables