Predicting effects of reservoir expansion with three-dimensional modeling: Case study of Los Vaqueros Reservoir

The use of three-dimensional (3-D) models to simulate the hydrodynamics and water quality of reservoirs and lakes can be a powerful tool in the development of management strategies. Models can be used proactively to predict how reservoirs will react to changes, either physical or operational. 3-D modeling aided the Contra Costa Water District management decisions for the 123 x 10(6) m(3) Los Vaqueros Reservoir (LVR) during a recent expansion that raised the dam. A well-calibrated and validated hydrodynamic and water quality model was used to evaluate the adequacy of the existing oxygenation system for the expanded reservoir and the potential water quality effects of incorporating an additional water source from a new intake. Available data from LVR were analyzed and used to construct a computational fluid dynamics model of the reservoir. Two predictive scenarios were run: (1) Drawdown, where LVR storage was about half the original volume during construction, and (2) Expanded Reservoir, where LVR storage was 60% greater than the original volume and the new Middle River Intake was incorporated. Model predictions for Drawdown confirmed elevated temperatures for coldwater fish habitats and allowed time to plan possible protective measures. This case study validated that 3-D modeling was able to predict conditions in LVR during Drawdown. It also illustrated how the model was used to provide initial predictions for conditions in LVR once expanded. Predictions were used to support design decisions for the oxygenation system and aid future operational decisions.