Coastal geography of rip currents: Pacific Ocean beaches and public safety, San Francisco area, California.

摘要

California's physical geography includes a long coast with many popular recreational beaches, with diverse characteristics. On some of these beaches rip currents have been found to be a public safety hazard. This dissertation looks at two beaches (Baker Beach and Ocean Beach), along the Pacific Coast in the San Francisco area, and studies how, why, and where rip currents pose a threat to public safety. The hazard to public safety is mostly the threat of drowning. The rip currents are documented with the use of vertical aerial photographs, still photographs and video film footage. These observations study general patterns of distribution of rip currents on these individual beaches. Information on wave data is studied to help understand the correlation between wave conditions and rip currents. A further study of beach types and rip current types was made to identify potential public safety hazards. Two beach types related to rip currents were observed; mega-rip currents on a dissipative beach (Ocean Beach), and a rip current-beach cusp coupled system on a reflective beach (Baker Beach). Both types of beach/rip currents can result in extremely dangerous conditions for both beach users and surf rescue lifeguards.; As a result of recent drownings, warning signs have been placed on pathways to these beaches warning beach users of the dangers of rip currents. At Ocean Beach lifeguards are stationed and patrol in mobile rescue vehicles to prevent drownings. Baker Beach has no lifeguard service and relies on public awareness and knowledge to prevent drownings.; The media has helped public safety awareness about the danger of rip currents. The author has during the early summer months given safety demonstrations on why and where rip currents are at the beach, how to identify rip currents on the beach, and how to survive if caught in a rip current. Another important aspect of public safety is identifying the difference between: rip currents, undertow, and rip tides. Many people have often confused these three beach/surf processes.