Date of Graduation
Master of Science in Environmental Management (MSEM)
College of Arts and Sciences
Stephanie B. Ohshita, Ph.D.
The research here focuses on two projected century sea-level rise scenarios (100 and 180 cm/century) and the potential to offset elevation loss to sea-level rise by supplying deteriorating tidal marsh habitat with a thin layer of dredge sediment via high-pressure spray disposal within San Francisco Bay. This adaptation strategy is then analyzed for potential integration into the Bay’s long term management plan for dredge material disposal. The Marsh Equilibrium Model (Morris, 2012) is used to evaluate elevation deficits for existing tidal marsh habitat around San Pablo Bay against future century sea-level rise scenarios and model marsh resiliency following elevation enhancement.
This research shows that applying a 15 to 20 cm thin layer of dredge sediment onto deteriorating tidal marsh habitat is optimal for improving marsh habitat function. The model indicates that enhancing existing tidal marsh habitat elevations could be necessary around the year 2045 under the high century SLR scenario. Maintaining tidal marsh elevations at this time shows enhanced resiliency for 15 to 25 years. Modeling 100 cm/century SLR, existing marsh habitat elevations will need enhancement around the year 2060 in which resiliency is maintained for more than 40 years. Based on this research, the potential for thin layer spray disposal to enhance marsh elevation in San Francisco Bay is promising. However, to achieve these prescribed layer placement depths, spray disposal is limited to distances of 70 meter thus requiring multiple spray locations to cover larger areas of deteriorating tidal marsh habitat.
The potential for thin layer spray disposal to enhance future LTMS goals is promising based on recent amendments to the Bay Plan and willingness of the LTMS agencies to consider new methods to reduce climate change related impacts. However, policy impediments in Section 404 permitting regulations for wetland fill need adjusting to account for climate change adaptation strategies in order to preserve existing tidal marsh habitat through the century. Planning and budgeting for future adaptation strategies is urgent now to ensure resiliency in tidal marsh habitat and overall shoreline resiliency for San Francisco Bay through this century.
Hine, Scott K., "Adapting to Rising Sea Levels in San Francisco Bay: The Potential for Thin Layer Sediment Application to Enhance Tidal Marsh Resiliency through This Century" (2015). Master's Projects. 275.