The primary motivation of this study is to estimate the current and future flood hazard throughout the Sacramento-San Joaquin Delta in the context of sea-level rise. I also analyzed the effects of storm surge and river flow on extreme events to better understand how these events originate and vary spatially and in time. To address this goal, I combined digital water level records (primarily 1983-present) with archival data collected by the California Department of Water Resources (1929-1983) to reevaluate flood hazard in the Delta and investigate the possible sensitivity of the region different sea-level rise projections. Available archival records from 8 stations were digitized and quality assured, producing a length of record that approximately doubles previously available data. The records were then analyzed using the Generalized Extreme Value (GEV) and Generalized Pareto distributions (GPD). Additionally, the contribution of storm surge and river flow to water level events at each station was assessed using a regression approach. Finally, the impact of future sea-level rise on the 1-, 10-, 100-, and 500-year return period water level was assessed through 2150, using recently published sea-level rise projections. Results show that the total water level (tides + storm surge + river flow) during the 100-year event increases by roughly 0.5m between San Francisco and interior Delta stations such as Rio Vista and Venice Island. For present-day sea-levels, the 100y event increased from 2.59 meters at San Francisco to 3.08 meters at Rio Vista (river-km 100from the Golden Gate), using the GPD approach (relative to NAVD-88). Further upstream, river influence becomes an increasingly important component of high-water events. At Walnut Grove (river-km 123), more than 80% of high-water events were forced by river flow, as estimated by the Net Delta Outflow Index (on average). The water level caused by river flow was significantly higher than coastal surge, and the 100y event was estimated to be 4.71 meters (NAVD-88). Confidence intervals and uncertainty in the flood hazard increases as stations become more influenced by river flow, likely because river flow is more variable from year-to-year than the combination of coastal tides and storm surge. The largest high-water events measured in the Delta typically receive a larger contribution from river flow than smaller high-water events. Interestingly, GEV and GPD results are consistent with an earlier assessment of flood hazard in the Delta from the 1970s. Results show that future flood hazard is likely to be significantly influenced by sea-level rise, particularly in the western Delta region which is more coastally influenced. Under the assumption that sea-level rise will linearly add to existing flood hazard, I find that the 100-year event could reach 4.09 meters at San Francisco and 6.21 meters at Walnut Grove by the end of the century, under the “Intermediate-High” sea-level rise scenario. Based on available flood datums, the first flood stage datum may get exceeded once every 10 years by 2150, under the Intermediate scenario. However, since much of the interior Delta is subsiding, individual locations may reach actionable hazard levels earlier. More analysis with sea-level rise, changing precipitation patterns, and vertical land motion should be done to increase the accuracy of projected flood hazards.

The primary motivation of this study is to analyze the 1D-2DH hydrodynamic model of the San Francisco Bay and Sacramento-San Joaquin Delta (SFBD) outlined in Nederhoff et al. (2021). I compared model water level data to 70 tidal records from the National Oceanic and Atmospheric Association (NOAA), the United States Geological Survey (USGS), the California Data Exchange Center (CDEC), and from local municipalities throughout the Bay Area to investigate how the model captures water levels and tidal constituent amplitudes. While the Nederhoff et al (2017) model analyzed an extended time period from 1950-2019, I analyzed M2 amplitude and tidal water levels for the water year of 2017 (WY2017) with a larger dataset that extended into the Sacramento-San Joaquin Delta. Because WY2017 was a high river flow year for the Sacramento Delta, the model was able to be evaluated throughout a large range of flow regimes. I used harmonic analysis through the MATLAB package UTide (Codiga et al. 2011) to assess the model’s ability to replicate M2 amplitudes. I assessed the error for these M2 values as well as for tidal water levels. The average RMSE for M2 amplitude is 0.111 m across the entire model domain during WY2017, performing fairly consistent throughout the model. The one exception being the shallow and complex Grizzly Bay, which performed significantly worse, with RMSE values around 0.5 m. The model better replicated water levels in the 2DH grid representation of the San Francisco Bay ( Attempts to improve the model were mostly unsuccessful. I tried to increase the grid resolution at the Carquinez Strait to improve tidal propagation upstream, but altering the grid caused the coupling between the 2DH grid and 1D network to detach. This prevented the propagation of water flow in either direction at the coupling near Collinsville. The software required to fix this coupling was non-standard and unavailable for my usage, so I was unable to resolve the issue. I also attempted to create a new wind forcing file using in-situ data rather than the ERA5 reanalysis. This new wind forcing made negligible difference in water level and M2 model skill. An experiment in removing river flow showed that riverine impacts on elevating extreme water levels only have effects (>0.05 m) east of the Carquinez Strait. Extreme water levels west of this point in the San Pablo, Central, and South Bays are dominated by tides, storm surge, and to a lesser extent local wind. A decrease in tidal amplitude by river flow potentially decreases flood risk in some parts of the Bay during times of high outflow from the Sacramento-San Joaquin Delta. I also investigated maximum equilibrium effects of constant wind in the two prevailing wind directions (southerly and westerly) of the San Francisco Bay. The wind setup effect become more prominent (>0.05 m) at and above a steady 10 m/s in both directions. This study also showed that wind likely exerts a small influence on tidal properties, especially for winds greater than 10 m/s.