Dynamic Solutions

Delta EFDC Modeling

Sacramento District Delta EFDC Modeling: DSLLC was selected to identify key Sacramento-San Joaquin Delta resource, economic, and policy issues for application of USACE water resource policies. The US Army Corps of Engineers, Sacramento District selected DSLLC to identify the key Sacramento-San Joaquin Delta resource, economic, and policy issues that could be addressed through application of USACE water resource policies and authorizations. The issues of concern in the Delta include water supply, water quality, flooding, navigation, recreation, sedimentation, ecosystem health, economics, and aesthetics. The second phase was to recommend models to be used in addressing these issues and providing a model implementation and testing plan that successfully addresses priority water resources issues affecting the Delta. A watershed approach was recommended to confront the myriad of issues facing the Delta.

Numerical models have been designed to represent the major hydrologic and hydrodynamic processes, transport pathways and fate of nutrients, sediments, carbon and contaminants in surface waters. They can then be used to understand the system-wide effects of natural changes and improvement projects including changes in water levels, salinity, and water quality. The EFDC model was chosen as the basis for modeling efforts in the Delta.

A data collection effort included collection and review of available historical data for the Delta including meteorological data; flow, stage, and tidal data; bathymetric data; salinity and temperature data; data concerning suspended sediment; and water quality data.

A 3-dimensional hydrodynamic model of the Delta was built first. The model domain extends from Carquinez Strait through Suisun Bay and the Delta east to the Port of Stockton, north to Verona on the Sacramento River, and south to Vernalis on the San Joaquin River. Model stage, salinity, temperature, and flow were validated to observed data for 2003 and 2004.

A sediment transport model was built utilizing the sediment transport sub-model located within the EFDC which simulates both cohesive and non-cohesive sediment transport, deposition, and erosion. The model was calibrated to observed TSS and sediment deposition data, including navigation channel shoaling. Sensitivity testing was conducted to determine model response to changes in sediment loading from upstream and changes in flow regime. Also included in the sensitivity tests were changes to sediment loads representing variations induced by land use and land cover changes in order to place error bounds on predictions and identify future areas of erosion and deposition.

A Delta EFDC water quality model constructed and validated to the 2003 and 2004 water quality datasets at eleven water quality stations that are spatially-distributed throughout the Delta. The water quality data available for model calibration and validation includes dissolved oxygen, chlorophyll-a, ammonium, nitrate, dissolved organic nitrogen, total phosphate, and total phosphorus. The Delta EFDC water quality model couples water column oxygen, nutrients, and eutrophication processes with the predictive sediment diagenesis model that allows for internally simulated cause-effect interactions between particulate organic matter loading, deposition, and decay in the sediment bed and the resulting sediment oxygen demand and benthic exchange of nutrients across the sediment-water interface.
Comprehensive sensitivity testing analyses were performed for each of the hydrodynamic, sediment transport, and water quality pieces of the EFDC model. Critical parameters within the model were adjusted to examine the effects on model results. This allowed for statistical quantification of the uncertainty associated with model output.

At the conclusion of model development, DSLLC sent three staff members to USACE offices in Sacramento to give three days of hands-on training to USACE and partnering agency employees. Attendees were given information on the inner-workings of EFDC, how the models were developed, what issues were encountered and solved, and how to use the EFDC_Explorer (developed by DSLLC staff) pre- and post-processing software. At the end of this training session students were able to effectively use the modeling software and calibrated EFDC model to run alternative scenarios.

The calibrated Delta EFDC hydrodynamic, sediment transport, and water quality model provides an excellent base for further efforts in the delta. Dynamic Solutions has used output from this model to develop a detailed food web model for the major phytoplankton and zooplankton species groups using the Comprehensive Aquatic Systems Model (CASM) to simulate daily food web dynamics and demonstrate how much lower trophic level (LTL) biomass is supported throughout the system based on the changing physical and chemical conditions of the Delta. The CASM food web can be used to inform the prey dynamics of other higher trophic level models, such as the San Francisco Estuary EwE model and the Delta Smelt individual-based model. The EFDC model could also be used to explicitly model mercury in the Delta by modifying the model to include the “parent-daughter” kinetics.

The EFDC model framework has achieved a unique pinnacle in surface water models developed for the Delta because the coupled hydrodynamic, sediment transport, water quality, and sediment flux models are linked, for the first time ever, with ecological models to describe the interaction of flows, salinity and water quality on fisheries and other critical ecological resources of the Delta.

 

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