Adapting to Sea Level Rise in Hayward, California
The Hayward shoreline, located along east San Francisco Bay, is susceptible to inundation from wave action and flooding. Increasing sea level, which is predicted to rise by 16 inches in 2050 and 55 inches in 2100 in the bay, further threatens the area. To assess the impacts of anticipated sea level rise along the Hayward shoreline, the Hayward Area Shoreline Planning Agency (HASPA) commissioned a study by an engineering consulting firm, Philip Williams and Associates (PWA), to evaluate vulnerable infrastructure and examine strategies to protect wetlands and shoreline development.
The Hayward shoreline extends from San Leandro Creek to the Alameda Creek Flood Control Channel in east San Francisco Bay. In 1970, HASPA, which consists of the City of Hayward, the Hayward Area Park and Recreation District, and the East Bay Regional Park District, was established to “coordinate agency planning activities and adopt and carry out improvement of the Hayward shoreline for future generations.” HASPA has helped purchase, preserve, and restore over 3,000 acres along the Hayward shoreline. Several successful wetland mitigation areas are located along the shoreline and form a tidal buffer that helps protect public and private infrastructure. However, sea level is estimated to rise 16 inches by 2050 and 55 inches by 2100 in San Francisco Bay, which would expose the currently buffered shoreline to escalating wave action and flooding.
In response to projected sea level rise scenarios, HASPA commissioned a preliminary study by PWA to evaluate the impact of anticipated sea level rise on shoreline resources and the actions that can be taken to protect wetlands and shoreline development.
The HASPA Sea Rise Study Area comprises a 4.3 mile-long stretch of land, north of Highway 92 to San Leandro Creek. In order to assess the impact of anticipated sea level rise on the Sea Rise Study Area, PWA compared various sea level rise predictions and their appropriate interpretations; explored shoreline, marsh, and channel responses to sea level rise; and identified vulnerable properties. PWA also looked at state guidance for adaptation planning and developed four potential adaptation measures for HASPA to implement. The results of the PWA assessment are summarized in their report Preliminary Study of the Effect of Sea Level Rise on the Resources of the Hayward Shoreline.
Outcomes and Conclusions
The Hayward shoreline is already vulnerable to inundation from coastal flooding, and with higher sea levels, more infrastructure is threatened including storm drainage systems, landfills, utility corridors, wastewater treatment facilities, and public access trails. While projections show that sea level will rise in the future, the rate at which it will rise varies, thus adaptation planning will need to be flexible. Adaptation strategies suggested by PWA included:
- Hold the Line – protect land and infrastructure from erosion, inundation, and flooding through the use of levees and seawalls;
- Realignment – move the levee to a new location further inland to allow marshes and mudflats to naturally transgress landward;
- Gradual Steepening – combines the virtues of “hold the line” and “realignment” to create a more sustainable shoreline that can accrete vertically and does not transgress landward too rapidly; and
- Diffuse Armoring – a modified “hold the line” option where wave erosion buffers that emulate natural backshore wave-buffering processes are utilized.
Cost estimates for the first three adaptation strategies are also described in the PWA report. Finally, PWA recommended conducting a more detailed assessment of coastal hazards to specific infrastructure and, using this information, develop a Shore Realignment Master Plan that includes the design and implementation of specific adaptation measures. A more detailed study including a possible pilot project with additional partners is currently underway.
Kershner, J. (2010). Adapting to Sea Level Rise in Hayward, California [Case study on a project of ESA PWA]. Product of EcoAdapt's State of Adaptation Program. Retrieved from CAKE: http://www.cakex.org/ase-studies/adapting-sea-level-rise-hayward-california (Last updated December 2010)