Elsevier

Coastal Engineering

Volume 170, December 2021, 103984
Coastal Engineering

Drivers of extreme water levels in a large, urban, high-energy coastal estuary – A case study of the San Francisco Bay

https://doi.org/10.1016/j.coastaleng.2021.103984Get rights and content
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Highlights

  • A validated 1D/2DH model was used to analyze different physical processes to the extreme water levels over a 70-year hindcast.

  • Extreme water levels in the San Francisco Bay are mainly driven by tide and sea level anomalies at the Pacific Ocean (25%).

  • Deeper in the estuary, towards to the San Francisco Delta, local fluvial inflow increases in importance for extremes.

Abstract

Reliable and long-term hindcast data of water levels are essential in quantifying return period and values of extreme water levels. In order to inform design decisions on a local flood control district level, process-based numerical modeling has proven an essential tool to provide the needed temporal and spatial coverage for different extreme value analysis methods. To determine the importance of different physical processes to the extreme water levels we developed a process-based numerical model (Delft3D Flexible Mesh) and applied it to simulate a large, urban, high-energy coastal estuary (the San Francisco Bay). The unstructured grid with 1D/2DH model elements, allows for efficient model simulations and therefore it was possible to simulate over 70 years between 1950 and 2019. Results show significant skill in reproducing observations for the entire modeled time period with an average root-mean-square error of 8.0 cm. A process-based modeling approach allows for the explicit in- and exclusion of different physical processes to quantify their importance to the extremes. For the 100-year still water level (SWL), tide (70%) and non-tidal residual (NTR) (25%) explain the majority of the simulated high water levels in the Bay relative to Mean Higher High Water (MHHW). However, closer to the Delta, local fluvial inflow increases in importance. For longer return periods, the importance of tide decreases and the importance of remote NTRs and fluvial inflow increases.

Keywords

Still water level
Extreme value analysis
San Francisco Bay
Delft3D Flexible Mesh

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