Bubble Plume Model
In 2019, a bubble plume model was coupled with the Reservoir model to mechanistically simulate the effects of the destratification system on mixing in Cherry Creek Reservoir. This allowed for a more realistic representation of the destratification system, and allows the model to be used for evaluating proposed modifications to the existing system and operations.
The modeling resulted in the following findings:
Due to continued water quality concerns, a water quality model of the Reservoir was developed to:
- Additional air flow and/or additional diffuser heads result in lower chlorophyll a concentrations.
- As the total system air flow increases, the additional decrease in chlorophyll a concentration decreases, leading to diminishing returns.
- The magnitude of the reduction in chlorophyll a differs from year to year. Factors that affect this include water temperature, reservoir storage volume, nutrient ratios, and the timing and magnitude of external nutrient loading.
- The simulated decreases in chlorophyll a concentrations with an expanded destratification system are not large enough to meet the chlorophyll a standard in all years, even with 50x the air flow of the existing system.
- The use of a compressed air destratification system to successfully control algae growth is limited in Cherry Creek by the shallow reservoir depth, large surface area, and high external nutrient loading.
Why a Bubble Plume Model?
The current version of the Cherry Creek Reservoir Water-Quality Model was developed using CE-QUAL-W2, version 3.71. The model accounts for artificial mixing in a simplified manner, in that mixing by the destratification system is simulated as a multiplier on vertical mixing in the depth interval above the diffusers. While the original Reservoir model included representation of the destratification system, bubble plume dynamics are not directly simulated. Use of the coupled bubble-plume model provides a more mechanistic simulation of the existing system and the ability to evaluate the water-quality response to specific design modifications.