Project Title: Episodic, Seasonal, and Long-Term Variations in Beach Morphology and Sediment Transport Adjacent to a Major Tidal Inlet on a High-Energy Coast, Ocean Beach, San Francisco, California
Mendenhall Fellow: Patrick L. Barnard (831) 427-4756, pbarnard@usgs.gov
Duty Station: Santa Cruz, CA
Start Date: October 1, 2003
Education: Ph.D., Geological Sciences, University of California, Riverside
(2003)
Research Advisors: Dan Hanes, (831) 427-4718, dhanes@usgs.gov; David Rubin,
(831) 459-3156, drubin@usgs.gov
Project Description: The vast majority of the California coastline is actively eroding. Major storms in 1982-83, 1995, and 1997-98 caused significant shoreline retreat and major property damage statewide. Erosion has been accelerated by human alterations to the environment. The accelerated rise in sea level during the past century combined with rapid coastal development has put enormous stresses on the coastal zone. During the next 100 years, sea level rates are projected to rise up to 3 times faster than at present, and thus it will become increasingly important to understand the complex sediment transport and sedimentation patterns that control beach morphodynamics. A greater understanding of the processes that control beach performance will enable us to make better informed coastal management decisions to mitigate erosion and storm damage, and better preserve sensitive coastal environments.
The mouth of San Francisco Bay is a region with a complex wave and current field that varies rapidly with space and time. This complexity stems from the variability in wave energy and direction, the uneven topography of the ebb-tidal delta, and tidal phase changes. Ocean Beach is strongly affected by tidal currents from adjacent San Francisco Bay inlet, as well as wave refraction around the ebb-tidal delta. Ocean Beach is a high-energy, dissipative system, with classic bar-and-trough morphology and strong cellular structures, such as rip currents.The scientific goals of this Ocean Beach project are to 1) identify processes responsible for changes in beach morphology, erosion, transport, and deposition of sediment, 2) evaluate littoral sediment budgets, interaction of littoral sediment with coastal geomorphology, and the role of surface waves and tidal currents on sediment transport and deposition, and 3) document the evolution of modern beach morphology and sedimentation patterns. Answering the following questions is integral to reaching the project goals:
- What is the seasonal variation in beach morphodynamics and shoreline change? Do episodic events or seasonal variations in nearshore processes control sediment transport?
- What are the effects of El Niño on beach performance?
- How do tidal currents affect near shore sediment transport?
- Is there significant onshore-offshore transport?
- Is there sediment transport potential from the ebb-tidal delta?
- What is the annual sediment budget for Ocean Beach? What are the major sediment sources? What are the major sinks?
Looking north at Ocean Beach, with the San Francisco shipping channel in the background. The West Coast of the United States is among the least understood of the coastal environments, because until recently high-wave energy has restricted the use of the traditional monitoring methods used to determine the processes controlling sediment transport. But the evolution of remote sensing techniques, such as airborne scanning laser (LIDAR) surveys and x-band radar, has allowed for unprecedented precision in monitoring large stretches of coast. Furthermore, advances in the strength and durability of instrumentation (e.g. current meters) now make their deployment possible in high-energy settings. Utilizing evolving technologies will be a key component of our research efforts at Ocean Beach.
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