Model Assessment of Dissolved Oxygen and Flow Dynamics in the San Joaquin River Near Stockton, California

DSM2 water quality model characterizes the spatial and temporal distributions of important water quality variables in an estuarine system. The model is capable of simulating the dynamics of dissolved oxygen including primary production and temperature. Using a dynamic flow field obtained from the companion hydrodynamics model, the model performs advective and dispersive steps of mass transport including net transfer of energy at the air-water interface. Changes in mass of constituents due to decay, growth and biochemical transformations are simulated utilizing relationships derived from the literature. Calibration and validation of the model were performed using field observations of water quality parameters. The model results matched well with dissolved oxygen and temperature observed in the San Joaquin River (SJR) near Stockton, California where dissolved oxygen levels frequently fall below 5 mg/l during warm, dry months. Low dissolved oxygen levels are of concern because they may adversely affect resident fish and other aquatic life. The current work is one of several projects established through the Total Maximum Daily Load (TMDL) stakeholder process aimed at exploring the ways of improving water quality of SJR. The TMDL stakeholder process was created for this portion of the SJR to meet the water quality standards established by the Federal Clean Water Act. Through evaluations of different scenarios, the DSM2 model can aid in developing potential management strategies to address low DO issues in the estuary. One such scenario is presented here. Historically, rock barriers are installed each year in the South Delta to protect San Joaquin salmon migrating through the Delta and provide adequate agricultural water supply in terms of quantity, quality, and increased channel water levels to meet the local needs. In this study, low head pumps are utilized to transfer water across the barriers and increase the flow in the SJR near Stockton.