Assessing the Influence of Shoreline Adaptation on Tidal Hydrodynamics: The Role of Shoreline Typologies

• Published in: Journal of geophysical research. Oceans 2021-02, Vol.126 (2), p.n/a
• Main Authors: Hummel, Michelle A., Stacey, Mark T.
• Format: Article
• Language: English
• Subjects: estuarine hydrodynamics; numerical modeling; sea‐level rise; shoreline modifications; shoreline typologies; tidal dynamics
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2020JC016705

In coastal embayments, tidal dynamics are influenced by mean sea level and shoreline configuration. As sea levels rise and coastal communities modify their shorelines to mitigate future flooding, spatial patterns of inundation, tidal amplitude, and tidal phase will change in response. Here we apply a hydrodynamic model to systematically investigate the effect of local‐scale, spatially refined shoreline protection on regional tidal dynamics and peak water levels in San Francisco Bay, California. We find that individual shoreline protection scenarios produce relatively small changes in tidal amplitudes at 50 and 100 cm of sea‐level rise but can result in amplification of the M2 tide by up to 40% at 200 cm of sea‐level rise. Protection of shorelines with gradually sloping topography and space for floodwater accommodation generally has the largest influence on tidal response, both locally and regionally. In the northern part of San Francisco Bay, tides down‐estuary of protected shorelines move closer to a standing wave, while up‐estuary tides become more progressive. In the southern part of the bay, which is already close to a standing wave, effects are more localized and variable. Overall, the tidal response to shoreline protection is a function of both the geographic location within the embayment as well as the geomorphic characteristics of the local landscape that is protected. Understanding the relative influence of local shoreline modifications on tidal dynamics under a range of sea‐level rise scenarios is critical to developing effective shoreline adaptation alternatives that maximize flood mitigation. Plain Language Summary In coastal bays, interactions between tides and shoreline infrastructure impact water levels. Understanding how shoreline changes affect tidal dynamics is critical to protecting coastal communities from negative impacts, such as flooding and erosion. Here we apply a hydrodynamic model to simulate a range of sea‐level rise and local shoreline protection scenarios in San Francisco Bay, California, and examine how tides and water levels in the bay are affected. We find that protecting individual shoreline segments produces relatively small changes in tidal amplitudes for low increments of sea‐level rise but can result in amplification of certain tidal constituents by up to 40% under higher sea‐level rise scenarios. Protection of shorelines with gradually sloping topography and space for floodwater accommodation generally has the largest