Date of Award

6-2020

Degree Name

MS in Civil and Environmental Engineering

Department

Civil and Environmental Engineering

College

College of Engineering

Advisor

Stefan Talke

Advisor Department

Civil and Environmental Engineering

Advisor College

College of Engineering

Abstract

The Sacramento San Joaquin Delta has been highly altered by human activity since the mid-1800s from mining, agriculture, dredging, and urbanization. Did the resulting modifications to channel width, depth, and length alter tidal range in the Sacramento San Joaquin Delta?

In this study, archival tidal records were evaluated at many stations throughout the San Francisco Bay and Delta, with a focus on San Francisco, Rio Vista, Sacramento, and Stockton daily, monthly, and annual tidal ranges. Monthly and seasonally averaged tidal ranges were analyzed to determine seasonal changes. In addition, tidal range was compared to daily Delta discharge to consider the effects of river flow.

Results show that the spatial pattern of tidal amplitude through the San Francisco Bay and Delta system have changed since the mid-nineteenth century and the changes are consistent with human and climate change impacts on the Delta landscape. There is a general 7% increase in mean annual tidal range in San Francisco from 1860 to 2018. In Stockton, mean annual tidal range increased from 0.6 meters to 0.9 meters between 1908 and the 1930s but decreased approximately 9% from the 1930s to 2011. Mean annual tidal range in Sacramento increased from zero to 0.5 meters between 1890 and the late 1930s and then decreased by 50% through the early 2000s to approximately 0.25 meters. Lower tidal ranges in the early 1900s are consistent with the effects of hydraulic mining. Increased tidal ranges in the mid-20th century are consistent with dredging throughout the system. Recent decreases in tidal ranges are consistent with wetland restoration, increased water storage, and further modifications to the geometry and management of the Delta. A peak river flow shift from late spring/early summer to early spring has contributed to increased tidal range between February and June by 0.1 and 0.6 meters in San Francisco and Stockton, respectively. In Sacramento, the least decrease in tidal range between 1939 and the present occurred during spring months, due to the decrease in river discharge during this period.

Tides have recorded the history of environmental change within the highly altered San Francisco Bay and Sacramento San Joaquin system. While not as notable as similarly altered systems, the changes described here were most significant in Sacramento where mean annual tidal range has ranged between zero and 0.5 meters since 1890 and, for any discharge below 1,000 cubic meters per second, mean daily tidal range is higher from 1938 to 1939 than from 1997 to 2018. Change in tidal range implies potential change in tidal velocities, salinity intrusion dynamics, and flood risk within the system, especially in Sacramento.

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