Available at: https://digitalcommons.calpoly.edu/theses/3233
Date of Award
3-2026
Degree Name
MS in Civil and Environmental Engineering
Department/Program
Civil and Environmental Engineering
College
College of Engineering
Advisor
Stefan A. Talke
Advisor Department
Civil and Environmental Engineering
Advisor College
College of Engineering
Abstract
The Sacramento-San Joaquin Delta (Delta) levee system faces threats from rising sea levels, land subsidence, and deteriorating levees, all of which pose risks to California’s primary surface water supply. The purpose of this thesis is to assess relative sea level rise (RSLR) and estimate the spatially varying factors that influence water levels in the Delta. This thesis extends the work of Baranes et al. (2023) to the period 1975-2022 by appending recently acquired water-level records (1975-1982) to modern datasets (1982-2022) from 10 water-level stations. These water level datasets were digitized, quality-assured, and referenced to a common geodetic datum, as described by Lee et al. (2025). This thesis evaluated the resulting full-length water levels time series by applying Baranes et al. (2023)’s physics-based nonlinear regression model. This statistical approach models water levels at each station as a function of independent variables, including river discharge, tides, non-tidal coastal sea level variability, wind, water exports, and long-term sea-level rise.
The model demonstrated effectiveness in predicting daily mean water levels (DMWL), with root-mean-square errors (RMSE) of 49-87 mm and adjusted R-squared (R2) values of 0.69-0.77 from 1975-2022. The model achieved the lowest errors and highest performance at stations near the coast (e.g., San Francisco) compared to those upstream (e.g., Rio Vista). These findings indicated that the model fit was more accurate for post-2004 observations than older records. The study also found that wind forcing significantly influences water levels, and any changes in this parameter can improve or reduce model performance. When predicting daily higher-high water levels (DHHWL), the model reported RMSEs of 111-154 mm and R2 values of 0.42-0.63. DHHWL model performance was highest at the Delta and decreased toward the coast.
The statistical model produced highly variable RSLR estimates ranging from -1.1 to +6.6 mm/yr, with 95% confidence intervals of -1.2 to +6.6 mm/yr. These results suggest an increasing trend in RSLR rates between the historical period (1975-2004) and the modern period (2004-2022). At some stations, the 1975-2022 RSLR rates exceed the 1993-2018 global sea level rate of 3.25 mm/yr. This implies that RSLR rates at the Delta deviate significantly from the global average rate, likely due to local vertical land motion. In the DHHWL study, the model indicated trends of +1.0 to +5.0 mm/yr, with 95% confidence intervals of +0.87 to +5.2 mm/yr across the study period. This variability in DHHWL trends suggests unmodeled factors that may have contributed to the variance. Overall, the results in this study are consistent with the hypothesis that sea-level rise rates are increasing, as projected by Kopp et al. (2014) and Griggs et al. (2017).
Results indicate that river discharge, coastal forcing, wind stress, and water exports have a strong contribution to water levels at the Delta, with their influence shifting seasonally. Median river flows (50th percentile) cause DMWL variations of 43-217 mm and DHHWL variations of 146-329 mm. High pumping rates can lower DMWL by 0-91 mm, and DHHWL by 0-95 mm across the evaluated stations. Results show that the tidal-fluvial interactions, coastal water level fluctuations, and wind under 95th percentile conditions elevate DMWL by 22-141 mm, 112-131 mm, and 19-173 mm, respectively. However, under very-high conditions (99th percentile), their impact on DHHWL causes variations of 345-607 mm, 196-240 mm, and 44-229 mm, respectively.