Projected Sea Level Rise for Ocean Beach - Why Managed Retreat as a Long Term Strategy

The Future of Ocean Beach? The beach at Sharp Park (Pacifica) is disappearing under a pile of armor. Click photo to see close-up.


Dear Surfriders and Friends,

Many may be surprised to hear that there is a looming threat of beach loss at central Ocean Beach. Below are a few links to scientific reports that have informed this projection. They deal with sea level rise. According to the Pacific Institute report, sea levels off the CA coast have risen 8 inches over the last 100 years. By 2100, sea level rise is predicted to rise another 1.0-1.4 meters (4’-5’). Although sea level rise projections are estimates, the trend lines behind this projection are serious. We should prepare for significant impacts. Middle Ocean Beach has been eroding for some time. We should expect beach loss to continue. However, as compared to Sloat, there is a greater opportunity to slow it down with sand nourishment and strategic sand management practices. This should allow us to buy time for proper planning.

Surfrider believes the sooner we embrace a strategy of Managed Retreat, the better off we will all be – taxpayers, beach users, and ecology. An encroaching high tide line is part of a natural process. If our city chooses to hold fast to existing boundaries, we can expect to see results like we have in the photo above. This is a group of revetments recently placed on the beach at Sharp Park, in the neighboring town of Pacifica. It's not a pretty picture. They are wiping out their beach.

This ia a graphic derived from the statewide study showing the potential erosion by 2100 based on 4.6’ of sea level rise. http://www.pwa-ltd.com/about/about_news.html#OPC_Report

The report by PWA:
http://www.pwa-ltd.com/about/news-CoastalErosion/PWA_OPC_Methods_final.pdf

Here is a link to the Pacific Institute report that this work fed into:
http://www.pacinst.org/reports/sea_level_rise/

Here is the State Adaptation Strategy that was affected by this work:
http://www.climatechange.ca.gov/adaptation/

Our Plan for Erosion Response at Ocean Beach

Greetings Surfriders and Friends,

The SPUR Ocean Beach Master Plan process is currently digesting comments from the Alternatives phase, and beginning to sketch out the Draft Master Plan. Surfrider San Francisco would like to take this time to release our preferred long term solution for Sloat, as well as our general erosion response strategy for Ocean Beach.

While we continue to call for a Managed Retreat solution, we feel it is important to recognize that any long term plan will take years to plan, permit and fund. DPW has asserted that during that time, the sewage transport box under the Great Highway could be exposed, which may cause it to rupture. A break in the box would trigger a sewage spill on Ocean Beach. None of us wants to see this happen. Therefore, our chapter has proposed a practical compromise for our long term plan: We are willing to condone a minimal impact, temporary structure to protect the transport box under specific conditions: It should come as a last resort only to avert a failure of the box, have a limited time span, and only in the context of a Managed Retreat strategy. See below.

We regret that this infrastructure was placed in such a precarious position. It is time to move forward and embrace a practical, commonsense long term plan. Managed Retreat is the best way to preserve our beach and solve the erosion conflict.

A Comprehensive Program of Managed Retreat for Ocean Beach
Surfrider Foundation, San Francisco Chapter’s Official Platform for Sloat Blvd / Ocean Beach Erosion

Summary Statement:

The Surfrider Foundation San Francisco Chapter favors infrastructure relocation and beach restoration as the primary methods to address Ocean Beach’s erosion problems. Sand nourishment is seen as a preferred interim strategy over armoring. Shoreline armoring will cause narrowing and ultimately the loss of the beach. The acceleration of sea level rise is expected to limit the effectiveness of sand nourishment in the latter part of the century, by year 2100. Therefore, retreat and realignment of development is expected to become increasingly important to provide space for the beach to survive. If critical infrastructure (e.g. the transport tunnel) is imminently threatened by erosion, armoring should be employed only as a last resort and a temporary measure in order to give The City time to plan and execute the reconfiguration or relocation of the infrastructure to a more sustainable condition.

We believe separate plans should be pursued for each of the two zones that have erosion issues: One plan for the Sloat Blvd. area / One for Central Ocean Beach. Due to the inherent uncertainty in sea level rise predictions and beach morphology, a fifty year plan, not a one hundred year plan, should first be executed for the two zones. At year thirty of the fifty year plan, an assessment and planning period should commence for both zones that will result in a new fifty year plan.

The Sloat Area: A 50 Year Plan of Managed Retreat
The City should commit to pursuing a Managed Retreat plan for Sloat. During the immediate planning/permitting/financing period of Managed Retreat, a small, temporary revetment (5ft high) could serve to protect the transport tunnel by stabilizing the toe of the bluff. Further temporary safeguarding of the tunnel may be achieved through interior reinforcement.

We are calling for a Managed Retreat plan that encompasses the following:

1. Re-route the Lake Merced Transport Tunnel and the connections from the Westside Transport Box and Pump Station so that they enter through the back side of the treatment plant. The southern section of the Westside Transport Box may also require modification to reduce the potential for exposure and loss of beach.

2. Re-route the Great Highway around the backside of the zoo.

3. Relocate Sloat’s North Parking Lot and bathroom facilities eastward from the current location to the area immediately in front of the Westside Pump Station.

4. Eliminate the Muni Bus turnaround.

5. At the south end of the affected area, relocate the south parking lot to the endpoint of the Great Highway (just before the intersection at Skyline Boulevard).

6. When opportunistic sand is available for beach nourishment, begin removal of all quarry stone revetments and rubble now littering the beach and construct a large sand berm to serve as a protective barrier for the entire area. Strengthen the dune with native plants, install sand ladder access trails, and construct a bike/walking path on the eastern side of the restored dune.

7. A plan for monitoring the new berm, as well as a plan for periodic sand nourishment should be in in place upon completion of the project.

With this strategy, the wastewater plant should have sufficient protection at its current location until its 100 year life cycle is completed. (Approximately 80 years remain).

Worst Case Scenario: If the new sand berm is severely eroded and the high tide line advances to a predefined point of emergency status at anywhere along the 3 reaches that include the pump station, zoo or the wastewater plant, then temporary armoring would be condoned only under the explicit condition to give the City time to plan and execute a relocation/reconfiguration of these structures. When complete, the temporary armor should then be removed and the beach returned to its natural state. There should be a formal mechanism to ensure future removal of any armoring.

Central Ocean Beach: A 50 Year Plan
For the next 50 years: A plan for monitoring erosion as well as aggressive sand dune nourishment/placement should be implemented along Central Ocean Beach. Nourishment areas would be identified as locations in which the high tide line has reached a certain distance from the seawall or road. As in the case of the Sloat area, a reassessment and planning period should occur at year 30. If at that time, if the beach is significantly narrower than when the first 50 year plan started, then planning should commence for the relocation of the Great Highway and the rest of the westside transport box.

Conclusion:
At Sloat, with infrastructure relocation and a renovated sand berm free of debris, the public and The City have a win-win solution. Infrastructure is protected and the public’s sandy shoreline/beach is preserved. At Central Ocean Beach, continual monitoring and timely sand nourishment should preclude the need for new armoring as well as give us the time we need to better evaluate sea level rise rates and beach morphology data. This plan does allow for flexibility if the high tide line moves inland to the point of threatening the remaining infrastructure. In such cases, temporary armoring is condoned as an emergency action under the express purpose to give The City time to relocate that infrastructure away from the ocean.