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Surface Water Quality at SAFL
Located in the midst of Minnesota's 10,000 lakes, SAFL has made major contributions in researching and re-mediating lake, reservoir, and river water quality problems. Our research comprises physical, chemical and biological aspects on water quality responses to changes in inflow quantity and quality, lake level, climate effects, and engineering management alternatives. A major thrust of our current research centers around the prediction of water quality, response of climate variability and climate change.
Studies performed at SAFL have addressed issues of mixing treated wastewater effluents, lake stratification, aeration techniques, efficiency of thermal power plans (cooling) and aquatic habitat response to water quality change. An integrated approach involving field monitoring, laboratory experiments and analytical and numerical modeling has been followed throughout.
The quality of water discharged from a hydropower facility depends on several factors including reservoir water quality and stratification, intake configuration, and discharge rate. Most commonly dissolved oxygen (DO) needs to be controlled to protect aquatic life in the downstream reaches and meet FERC licensing requirements and local water quality criteria.
Water temperatures can also require control for salmonid species such as trout. If a powerhouse is unable to meet these criteria, forced shutdown could result in lost power revenues. SAFL researchers have studied aeration alternatives for several dams with DO criteria.
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Research Projects
Byllesby Dam and Hydroelectric Plant
SAFL identified Byllesby Dam on the near Cannon Falls, Minnesota, as a feasible site for hydropower development in a 1983 state hydropower survey. When hydro developers decided to reactivate the 2,500 kW plant (it was decommissioned in 1966), SAFL assisted with studies of downstream dissolved oxygen (DO) required for the new license. SAFL conducted synoptic surveys of DO and temperature in the reservoir, and turbine discharge and downstream channel; we also conducted automated monitoring of discharge DO and temperature. Through data analysis and modeling of reservoir selective withdrawal, SAFL staff were able to predict the frequency of DO standard violations. This information, and economic considerations, were used to select the best DO enhancement strategy, in this case periodic spilling to meet a flow-averaged DO requirement. |
- Lake diagnostic and improvement studies
- Oxygen and nutrient dynamics
- Temperature dynamics
- Stratification in lakes
- Fish habitat analysis
- Water quality modeling
- Ice cover dynamics
- Water quality monitoring
- Measurement of numerical model parameters
- Hydropower licensing
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Urban Development Effects on Trout Streams
Stream temperatures respond to a variety of heat transfer processes in a watershed. The imprints of radiation, evaporation, conduction and convection are compounded in observed stream temperatures. Hydrologic and thermal parameters of a watershed that affect water temperatures include topography, surface cover, soil type, weather and hydrogeology. When urban development encroaches on a watershed, the drainage system is often dramatically altered by landscaping, changes in surface cover (pavements and buildings), and addition of a new drainage (storm sewer) system. Researchers at SAFL provide an overview on how these changes can be quantified, and how the interactive effects can be modeled to obtain stream temperatures. This project was commissioned by MPCA.
Sherco cooling water problem
Sherco No. 3 is a coal-fired power plant on the Mississippi River, 40 miles northwest of Minneapolis. With its addition to the original two units, cooling water requirements were increased, placing greater demands on the Mississippi River make-up water intake. Northern States Power Company pursued a completely new intake design with cylindrical intake screens with closely spaced wedge shaped bars. SAFL assisted with comprehensive model testing and provided input under all aspects of the conceptual design, including: 1) a backwash system to move sediment out of the intake area; 2) a diffuser to bathe the screens in warm water and prevent clogging by frazil ice; 3) an air backflush system for removal of debris from the screens; and 4) pump intake submergence requirements for vortex suppression. Testing led to design improvements in the warm water discharge manifold, the sediment backwash design flow rate, and the pump intake configuration. NSP plant operators attended training sessions at SAFL where they learned about the operational requirements of the system.
Platte River Water Quality Model
The 80-mile Big Bend Reach of the central Platte River, Nebraska is a "braided" river with a wide, shallow channel interlaced with sandbars. It serves as habitat for eight threatened or endangered species, and over 300 species of migratory birds. The discharge in this reach is controlled largely by hydropower dams. SAFL cooperated with a Minnesota consultant to perform thermal modeling and determine regulated flow regimes which result in water temperatures protective to resident fishes.
El Vado Dam and Hydropower Plant
This plant is located near Los Alomos, New Mexico. During summer months, turbine discharges were often low in dissolved oxygen (DO), forcing the plant to shut down and waste water over the spillway. SAFL researchers were requested to recommend a means to maintain summer operation while meeting downstream DO requirements. We reviewed plant data and evaluated eight alternatives to determine the most economical in terms of "recovered" energy savings, and installation and operating costs of the system. The owner installed the recommended turbine draft tube aeration system which has met the downstream oxygen requirements.
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