ResSim employs a rule-based approach to replicate the decision-making process of reservoir operators, balancing competing demands such as flood control, power generation, water supply, and water quality. These various needs impose constraints on the storage and release of water from the reservoir. In the ResSim water quality model, a simplified water quality operation rule has been implemented to support water quality management both within the reservoir and downstream. By selectively withdrawing and blending water from different elevations, the model helps meet downstream environmental objectives.
To conduct a water quality withdrawal impact analysis, the user must define a water quality control device. This includes specifying the shape of the outlet and defining the withdrawal range from the outlet. The user can assign either a single outlet or a group of outlets for water quality management. The water quality control device is designed to allow the operator to withdraw varying amounts of water from different levels of the reservoir pool, thereby controlling how water is released at different elevations to achieve the desired water quality objectives. This approach ensures that water quality is effectively managed during reservoir releases.
Water quality rules in ResSim do not change the magnitude of the release flow that passes through the given outlet or outlet group which they are assigned to. That release flow is determined by the non-water quality rules in the operational rule stack. The water quality rule controls where this release flow is withdrawn from vertically in the reservoir pool, and only impacts the simulated water quality values. As such, the water quality rules are evaluated after all of the non-water quality rules have been evaluated and all release flows have been determined. For that reason, we recommend placing water quality rules at the bottom of the rule stack.