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Flood risk and management of California's Sacramento-San Joaquin Delta levee system


The Sacramento-San Joaquin Delta is a highly developed floodplain and the hub of the state’s water supply system. It is an agricultural, recreational, historical, and cultural center where 1800km of levees protect the current land uses and prevent salinity intrusion into the freshwater supply. For decades the region has been ripe with political controversies stemming from conflicting interests over its natural resources. The threat of climate change has added a layer of urgency to understanding the mobilization of narratives at different scales. This dissertation is comprised of three distinct parts. I used the Q methodology to explore the discourses of the broad range of stakeholders about flood risk and flood management in the Delta. The results of the Q-study reveal five distinct views regarding the risk of submersion of one or more islands due to either overtopping during high waters or structural levee failures. Proximity, sense of vulnerability, values, trust, and views of climate change are the underlying factors in these perspectives. Then, using a collection of 345 newspaper articles from twelve different publications written between 1972 and 2017, I examined the trends and shifts in the narratives about floods in the Delta. Results show changes in framing over time and differences between local, regional, and national media. Lastly, I analyzed the characteristics of atmospheric rivers that have preceded floods in the Delta using MERRA-2 0.5 × 0.625 6-hourly global atmospheric river (AR) reanalysis V2.0 and details about 57 documented floods from 1980 to 2019. Results show that most of the ARs that have made landfall in the watersheds that feed the Delta are not severe. Most of the floods, however, have been preceded by strong ARs. The most recent years (1999 to 2019) have had a small number of floods, and even fewer levee failures. However, the most recent ARs that impacted the Delta made landfall in the San Joaquin watershed, not the Sacramento watershed, which was the predominant origin of the more destructive floods in the earlier decades of this study.

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