Santa Barbara/Ventura Coastal Processes Study

Field Work

• Lidar (Light Detection and Ranging)
• Topographic beach surveys
• Nearshore bathymetric surveys
• Multibeam/sidescan sonar mapping
• Grain size surveys, nearshore and onshore
• Instrument deployments
• Box coring (Summer 2007)
• Sub-bottom profiling (Summer 2007)
• Ground-based Lidar
• Mugu submarine canyon study

Lidar

In October 2005, the Bureau of Economic Geology (BEG) of the University of Texas at Austin, flew a coastal lidar (light detection and ranging) survey along the 150 km stretch of coastline from Point Conception (Latitude N34° 27', Longitude W120° 27') to Point Mugu (Latitude N34° 5', Longitude W119° 3'). Along this region, the beach topography was mapped from the surf zone to the point landward of any foredunes, bluffs or cliffs that bound the upper extent of the beach. This survey was a collaborative effort between BEG, BEACON, California Department of Boating and Waterways, UCSC and USGS. Using these data, the USGS will grid the topographic points and extract subaerial profiles from the 25 established BEACON transects plus the additional 12 requested lines for comparison with the historical transects. We will also compare the 2005 lidar with the 1997 lidar survey of this stretch of coast to assess short-term coastal change rates.

Map, above, shows October 2005 lidar coverage area.

	At right is an example of topographic data extracted from the lidar survey. This image focuses on the city beach at Carpinteria, with Linden Ave. running top to bottom (north to south) on the right hand side of the image.
	Lidar: was flown by University of Texas covers entire littoral cell from Pt. Mugu to Conception, ~150 km (see map below) features 1 m cell coverage with 8 cm accuracy is being used to assess shoreline, beach width, and volume change since last Lidar surveys in 1997-8 generated sub-aerial BEACON profiles

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Topographic beach surveys

Using all-terrain vehicles (ATVs; see photo at right), topographic surveys of the beach surface were collected at the three focus study areas in October 2005 and March 2006. These surveys, conducted with differential GPS (DGPS- accuracy ~2 cm horizontal and vertical), are being used to monitor seasonal beach changes and assess lidar accuracy. Additional survey sets are planned for October 2006 and March 2007. (See a map of the survey lines.)

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Nearshore bathymetric surveys

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Multibeam/sidescan sonar mapping

• Focus on three high resolution sites
• Quantify long term nearshore change
• Seabed classification
• Updated bathymetry for model input

The first map (above, left) shows bathymetry offshore of Santa Barbara; click image for a larger version, 223 kb. The next map (above, right) shows multibeam coverage areas; click image for a larger version. Areas in yellow were completed by the USGS in summer 2006. As part of a Coastal Conservancy grant, areas A-E were completed in summer 2006, and F-H and points west are scheduled for summer 2007.

Expanded multibeam

• Map inside 3 mi limit from Mugu to Goleta, Summer 2006 and 2007
• WCMG offshore work in 2004 and 2005

Hueneme Canyon bathymetry examples are pictured above. Click an image for a larger version (98 kb and 40 kb).

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Grain size surveys, nearshore and onshore

Swash, mid-beach and backbeach digital Beachball© samples and grab samples have been collected throughout the littoral cell. During July 2006 beach samples were collected at 94 locations from Gaviota to Pt. Dume. Except for large gaps due to limited access, sample locations were approximately one kilometer apart. To address seasonal grain size concerns, the beaches of the high resolution study areas (Ventura, Carpinteria and Goleta/Isla Vista) have been sampled during both summer and winter conditions. Images are now being processed for mean grain size.

In August, the Flying Eyeball© was used to collect sediment samples from the nearshore at 5, 10 and 20 meter water depths. Video samples were collected every kilometer between Isla Vista and Oxnard. In addition, samples were collected every 5 kilometers and 2 kilometers in the northwestern and southern portions of the cell. Grab samples were also collected at various depths and locations throughout the cell. Images have been extracted from the video and are now being processed for mean grain size.

To analyze the digital images, from both the Beachball© and the Flying Eyeball©, sand from many locations has been combined into one bulk sample for each sampling system. This sediment was sieved and imaged. These images are now being processed to determine a calibration curve which will be used to determine the grain size of samples collected in situ. Settling tube results from the grab samples are being used to check sample results. Once grain size has been determined, beach and nearshore sediment size will be mapped for the region.

Above, left and center, are photos of Flying Eyeball© operations aboard UCSB vessel, the R/V Connell. With the Flying Eyeball©, 1500 images were collected from 300 nearshore sampling stations. The map (above, right) showing mean grain size of nearshore (5, 10, 20 m) Flying Eyeball© samples in the Santa Barbara Littoral Cell. Click map for a larger version, 91 kb.

With the Beachball© (camera pictured above, left), 576 images were collected at 192 beach sample locations. The map (above, middle) shows Beachball© and Flying Eyeball© sampling locations; click map for a larger version, 177 kb. The plot (above, right) shows mean grain size of beach and nearshore samples. Horizontal axis is distance east of Pt. Conception. Click image for a larger version.

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Instrument deployments

Instrument packages containing current profilers were deployed offshore in 10 m water depth at each of the three focus areas in August 2006. After two months in the water, the instrument packages will be removed, and later redeployed over several months in the winter of 2006-7. The water levels, current profiles, and wave statistics extracted from these instruments will serve as numerical model calibration and validation points.

Above are photos of the instrument package being prepared for deployment offshore of Carpinteria. Map shows the instrument deployment locations; click map for a larger version.

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Box coring

• Summer/Fall 2007
• Approximately 50 cores throughout littoral cell
• Ground truth surface samples
• Identify potential sand bodies

Sub-bottom profiling

• Regional profile lines with some focused studies
• Determine Holocene sediment thickness in select areas

Ground-based Lidar

Ground-based Lidar was conducted by Brian Collins of the USGS in the Goleta, Isla Vista/Ellwood region. It is being used to asses cliff retreat rates. Data collected: 500,000 points/min, 10-50 cm resolution. An example is shown at left.

Mugu submarine canyon study

This study is being conducted by Jingping Xu of the USGS Pacific Coastal & Marine Science Center. Mugu Canyon is currently receiving ~1 million cubic yards of sediments (sand, mud) every year from longshore drift and other sources. Our research question: What are the processes within the canyon where such sediments are accumulated, eroded, and transported downcanyon?

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