Blended

Protection of Ocean Beach, San Francisco, CA

Assignment:

The objective of this activity is to help you develop an appreciation for coastal erosion and associated risks when placing major infrastructure proximal to coastal hazards.

Ocean Beach is a sandy beach backed by erodible bluffs that forms the boundary between the western edge of the city of San Francisco, CA and the Pacific Ocean. Like many sandy coasts around the world, portions of Ocean Beach have been experiencing significant erosion in the past decades. The long-term erosional trend along the southern reach of the beach has been punctuated by periods of intense erosion during particularly severe winter El Niño storm seasons, when the beach and backing bluffs can be exposed to very high waves.

The situation is complicated by the presence of critical infrastructure within the coastal zone. The Great Highway, an important transportation link, is located on top of the bluffs backing Ocean Beach, and recent erosional events damaged parking areas and forced the closure of one direction of traffic for much of the storm season. More importantly, a large sewage tunnel runs under the Great Highway, transporting the city's wastewater south to a treatment plant. Continued erosion threatens this piece of expensive, critical wastewater infrastructure, and it must be protected in the near term to prevent both the environmental consequences of a tunnel failure and the huge cost of relocation. During the most intense erosion episode during the 2009-2010 El Niño winter, the city constructed an emergency revetment of armored stone along the eroding bluff to protect the wastewater infrastructure; however, the use of "hard" coastal protection structures met stiff opposition from environmentalists and local regulatory agencies due to the inevitable loss of beach in front of the structure.

Reading

Read the following article, detailing the coastal erosion and management issues at Ocean Beach:

• SPUR: The Future of Ocean Beach

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Figure 7.16: A parking lot and bench between the Great Highway and the bluff edge at Ocean Beach before (2009) and after (2011) severe erosion.
Credit: Google Earth and SPUR

Navigate to Ocean Beach, San Francisco by searching for the coordinates 37.747519 ° -122.514184 °. Turn on "borders and places", and "roads" by checking the appropriate boxes in the lower left menu in Google Earth. Ocean Beach stretches from the rocky headland at Sutro Heights to the north, south to the Fort Funston, Lake Merced area. Zoom in and explore the full length of the beach, noting how the width varies and any structures on the beach.

Follow the video to learn how to use Google Earth to visual or measure erosion rates at a single location on the coast, or measure the average erosion across a barrier island (attached written example to be converted by video)

Now navigate to 37.728779 ° -122.506900 °. Turn on historical imagery and adjust the slider to the 6/2014 image. Note the position of the shoreline, bluff toe, roadway, and armor stone revetment. To see how much the shoreline position has changed, adjust the slider to the following dates:

• 7/1938 (what the beach looked like before construction of the Great Highway)
• 3/2000
• 10/2002
• 2/2007
• 9/2008
• 10/2009
• 2/2010 (note erosion of Great Highway shoulder)

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Figure 7.17: Example of Changing Shoreline
Credit: Google Earth

Files

Download the Worksheet (Microsoft Word 2007 (.docx) 36kB Sep7 16)

Download the Rubric (Microsoft Word 2007 (.docx) 39kB Sep7 16)

Instructions

In your opinion:

1. What is an alternative erosion mitigation method that could be used for this section of Ocean Beach instead of "hard" structures?
2. What could the city have done to reduce coastal vulnerability so that the risk from coastal erosion would not require "hard" coastal protection?

Your report needs to be about two pages long and consider the variety of means of coastal protection.

Submitting your assignment

Please submit your report using the tools available in your CMS.