UC Davis

Rivers and their floodplains are a complex system that presents numerous challenges when coupled with human adaptation. The many adaptations humans have made to the landscape have come at the cost of aquatic ecology. Efforts have gone underway to mitigate those costs and begin to repair our relationship with the aquatic landscape via restoration and re-engineering systems to benefit habitat. Of the myriad of tools at our disposal to investigate different restoration strategies, this thesis explores the application of hydrodynamic models to ecosystems and how the linkages between numerical models can evaluate ecological outcomes.

The application of this thesis has centered around the Sacramento-San Joaquin Delta, a focal point of California’s Central Valley and a critical ecosystem in the state. The Sacramento-San Joaquin Delta has many “islands” which are essentially parcels of land that have levees surrounding them to protect against flooding from the Detla’s channels. One island in the Delta is the McCormack-Williamson Tract, which lies just below the confluence of the Cosumnes and Mokelumne Rivers. The McCormack-Williamson Tract is the study area for Chapters 2 and 3, where a hydrodynamic model was develope and calibrated to investigate natural phenomena. The models were calibrated against observed flood events and then used to compare against field data collected in the study systems within the model calibration period. By pairing observed field data with replicated modeling data, linkages between source water distribution, age, and general hydrodynamic features were drawn. These linkages provide useful tools in the field of floodplain restoration engineering.

Chapter 2 demonstrates a hydrodynamic model’s ability to resolve the spatio-temporal distribution of the water from the convergence of the Mokelumne and Cosumnes Rivers as they advance through the McCormack-Williamson Tract and its surrounding channels and sloughs. This modeling effort was coupled with an isotopic mixing model using water sampling in the study area, and shows that the two methods agree on source water distribution.

The subsequent chapter (Chapter 3) that focuses on the McCormack-Williamson Tract evaluates a modeled water age against field-collected zooplankton abundance. Although this study did not find a robust relationship between the two variables, the chapter lays out the methodology used to investigate the relationship.

The second study area centered around a key feature in the Delta’s hydrography - the Yolo Bypass. The Yolo Bypass is a major floodplain to convey flood waters from the Feather, American, and Sacramento Rivers around major cities and dwellings and into the Delta. Chapter 4 outlines the development and calibration of a model of the Yolo Bypass and discusses the applications the model can have to answer ongoing questions about the study system.