Santa Barbara Littoral Cell Field Work
Map shows October 2005 lidar coverage area. [Larger version]
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.
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.
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, March 2006, October 2006, and March 2007. 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. (See a map of the survey lines.)
The USGS used a Real Time Kinematic Differential Global Positioning System (RTK-DGPS) mounted on a personal watercraft (PWC; see photo at right) to collect bathymetric horizontal and vertical position data in the study area. Two full surveys have been completed in the focus areas of Goleta, Carpinteria, and Ventura; one in the fall of 2005 and a second in the spring of 2006. In 2006, additional DGPS data were collected in Rincon, which is not in RTK because of monument access limitations, but can be post-corrected to a final product of similar data quality. This dataset consists of over 300 cross-shore and alongshore profiles in water depths ranging from 15 m to 1 m at inshore locations. (See a data example.)
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.
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 were 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 serve as numerical model calibration and validation points.
Ground-based Lidar was conducted by Brian Collins of the USGS in the
Goleta, Isla Vista/Ellwood region. This lidar is used to assess 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?