Evaluation of Hydrodynamic Mixing in Keswick Reservoir, California
Keswick Reservoir, on the Sacramento River, receives both water and contaminants from the Spring Creek Debris Dam. The term contaminants refers here to different kinds of chemicals that are in some instances delivered to lakes and rivers. These chemicals can have a detrimental effect on drinking water supplies and the health of humans, fish, and other aquatic species.
The Iron Mountain Mine site, northwest of the town of Redding, California, has been designated a “Superfund” site by the U.S. Environmental Protection Agency. This designation was made because of metals that leave the site, carried by rainfall runoff that arrives in the Spring Creek Arm of Keswick Reservoir downstream (Figure 1). With support from the California State Water Resources Control Board, the U.S. Geological Survey is investigating the mixing and dilution of contaminants introduced to the reservoir. This is being done primarily by way of numerical modeling of the hydrodynamics and mixing, coupled with a short-term experiment to provide data for model validation.
Of particular interest is the amount of dilution that occurs when flow from the Spring Creek Arm reaches the main stem of Keswick Reservoir, and how water management operations influence this mixing. There are four dams and powerplants (Shasta Dam, Keswick Dam, Spring Creek Power Plant, and Spring Creek Debris Dam) that control flow into and out of Keswick Reservoir, and the U.S. Bureau of Reclamation is responsible for managing the water to meet both human and ecological needs.
Project Tasks
1) Develop three-dimensional simulations of the hydrodynamics of Keswick Reservoir under a range of reservoir operational and forcing conditions.
2) Simulate the introduction of a neutrally buoyant, conserved contaminant through the Spring Creek Debris Dam, and assess its dilution at different points within the Spring Creek Arm and Keswick Reservoir.
3) Perform a field experiment to obtain data suitable for validation of model results of contaminant concentration.
4) Report the results to the cooperator and the public in an understandable way that makes clear the most significant results of the study.
Project Benefits
This study will help the State Water Resources Control Board meet its responsibility of balancing the needs of the environment and ecosystems with those of humans. The site is near the upstream end of the Sacramento River watershed, which is critical to the water supply of both northern and southern California.
Approach
Mixing within a surface water body is a complicated process affected by the hydrodynamics of the water body, winds, the roughness of the bottom of the water body, vegetation, stratification of the water due to temperature or salinity differences, and the substance that is undergoing mixing, among other things. All of these factors must be considered when developing a model of mixing processes. Some studies do not require the application of a three-dimensional model, but such a model is being applied in this case.
The USGS will develop a three-dimensional model of hydrodynamic mixing in the Keswick Reservoir. The mixing of water from the Spring Creek Debris Dam, Spring Creek Power Plant, Lake Shasta, and other relevant inflows will be evaluated.
The Delft3D-FM hydrodynamic model will be used for the simulations of flows and mixing. This is a three-dimensional, flexible mesh, unsteady numerical model that describes flows of water with a free surface. The model also simulates the movement and mixing of dissolved salt. This feature will be used in this study to simulate mixing of a conserved tracer (dissolved salt). Model inputs include bathymetry, initial water depth, water levels and discharges at boundaries, wind speed (optional), and bottom roughness. The Delft3D-FM model has been used in different environments, including rivers, lakes, reservoirs, coastal regions, and estuaries.
The field experiment will involve a dye release into the Spring Creek Arm, over a period of multiple hours. Rhodamine WT, a red, nontoxic dye often used in mixing studies, will be used as a tracer. Dye concentrations downstream will be monitored by submerged, tethered fluorometers.
Drifters will also be used to collect data for model validation (Figure 2). Each drifter consists of a four-armed submerged sail floating near the water surface. The drifters follow the current of the water and have onboard dual-frequency GPS receivers to track drifter position vs. time. This data will be used to validate model results describing water velocity, and the dye concentrations will reveal the effects of mixing, which of course are in turn affected by the water flow.
Iron Mountain: An Extraordinary and Extreme Environment
Keswick Reservoir, on the Sacramento River, receives both water and contaminants from the Spring Creek Debris Dam. The term contaminants refers here to different kinds of chemicals that are in some instances delivered to lakes and rivers. These chemicals can have a detrimental effect on drinking water supplies and the health of humans, fish, and other aquatic species.
The Iron Mountain Mine site, northwest of the town of Redding, California, has been designated a “Superfund” site by the U.S. Environmental Protection Agency. This designation was made because of metals that leave the site, carried by rainfall runoff that arrives in the Spring Creek Arm of Keswick Reservoir downstream (Figure 1). With support from the California State Water Resources Control Board, the U.S. Geological Survey is investigating the mixing and dilution of contaminants introduced to the reservoir. This is being done primarily by way of numerical modeling of the hydrodynamics and mixing, coupled with a short-term experiment to provide data for model validation.
Of particular interest is the amount of dilution that occurs when flow from the Spring Creek Arm reaches the main stem of Keswick Reservoir, and how water management operations influence this mixing. There are four dams and powerplants (Shasta Dam, Keswick Dam, Spring Creek Power Plant, and Spring Creek Debris Dam) that control flow into and out of Keswick Reservoir, and the U.S. Bureau of Reclamation is responsible for managing the water to meet both human and ecological needs.
Project Tasks
1) Develop three-dimensional simulations of the hydrodynamics of Keswick Reservoir under a range of reservoir operational and forcing conditions.
2) Simulate the introduction of a neutrally buoyant, conserved contaminant through the Spring Creek Debris Dam, and assess its dilution at different points within the Spring Creek Arm and Keswick Reservoir.
3) Perform a field experiment to obtain data suitable for validation of model results of contaminant concentration.
4) Report the results to the cooperator and the public in an understandable way that makes clear the most significant results of the study.
Project Benefits
This study will help the State Water Resources Control Board meet its responsibility of balancing the needs of the environment and ecosystems with those of humans. The site is near the upstream end of the Sacramento River watershed, which is critical to the water supply of both northern and southern California.
Approach
Mixing within a surface water body is a complicated process affected by the hydrodynamics of the water body, winds, the roughness of the bottom of the water body, vegetation, stratification of the water due to temperature or salinity differences, and the substance that is undergoing mixing, among other things. All of these factors must be considered when developing a model of mixing processes. Some studies do not require the application of a three-dimensional model, but such a model is being applied in this case.
The USGS will develop a three-dimensional model of hydrodynamic mixing in the Keswick Reservoir. The mixing of water from the Spring Creek Debris Dam, Spring Creek Power Plant, Lake Shasta, and other relevant inflows will be evaluated.
The Delft3D-FM hydrodynamic model will be used for the simulations of flows and mixing. This is a three-dimensional, flexible mesh, unsteady numerical model that describes flows of water with a free surface. The model also simulates the movement and mixing of dissolved salt. This feature will be used in this study to simulate mixing of a conserved tracer (dissolved salt). Model inputs include bathymetry, initial water depth, water levels and discharges at boundaries, wind speed (optional), and bottom roughness. The Delft3D-FM model has been used in different environments, including rivers, lakes, reservoirs, coastal regions, and estuaries.
The field experiment will involve a dye release into the Spring Creek Arm, over a period of multiple hours. Rhodamine WT, a red, nontoxic dye often used in mixing studies, will be used as a tracer. Dye concentrations downstream will be monitored by submerged, tethered fluorometers.
Drifters will also be used to collect data for model validation (Figure 2). Each drifter consists of a four-armed submerged sail floating near the water surface. The drifters follow the current of the water and have onboard dual-frequency GPS receivers to track drifter position vs. time. This data will be used to validate model results describing water velocity, and the dye concentrations will reveal the effects of mixing, which of course are in turn affected by the water flow.