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.
| Identifer | oai:union.ndltd.org:CALPOLY/oai:digitalcommons.calpoly.edu:theses-4152 |
| Date | 01 September 2022 |
| Creators | McGuire, Nicholas L |
| Publisher | DigitalCommons@CalPoly |
| Source Sets | California Polytechnic State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Master's Theses |
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