Putting New Hydropower Technology to Work
MWH originally provided technical and economical feasibility studies, as well as project design and construction management services for the completion of design and construction of the 848 MW Rocky Mountain pumped storage hydroelectric project.  Located 70 miles northwest of Atlanta, MWH is currently providing services to upgrade the project to increase the plant's peak generating capability to a maximum of 1,050 MW, while increasing the plant cycle efficiency.

The project provides peaking power to 39 electric membership co-operatives, serving almost two-thirds of Georgia's land mass. The 221-acre upper reservoir includes a 12,800-foot-long, 65-foot-high earth and rock-fill dam; a communications and instrumentation building; an emergency overflow spillway; and three miles of access roads. The 600-acre lower reservoir features seven earth and rock-fill dams with a total length of 2,470 feet; a 100-foot-high concrete-gravity and rock-fill dam; an ogee-type, controlled overflow spillway with two radial gates, a reinforced-concrete gate pier, and two reinforced-concrete retaining walls in the stilling basin; two uncontrolled broad-crested spillways; two low-level outlet works; five miles of access roads; four bridges; a 175-foot-high powerhouse with three reversible pump/turbines; and motor/generator units.

The MWH team established all constraints and benefits of the upgrade, integrated them into a comprehensive implementation plan, and is serving as Owner's Engineer for the duration of the project. Initial work included a detailed review of regulatory and environmental issues, and a detailed analysis of hydraulic, civil/ structural, mechanical and electrical issues, including transmission line constraints in both pump-motor and turbine-generator mode.

Later phases included field testing of various plant components, preparation and subsequent FERC approval of a capacity-related amendment, preparation of bid documents for all new required equipment and systems, contract administration, outage planning, and construction management. The modifications will replace the existing pump-turbine runners and modify other pump-turbine, motor-generator, and auxiliary equipment components, including new exciters, spherical valve servomotors, transformer bushings and unit breaker upgrades. Modifications will take place during planned major maintenance overhauls into 2011.

The modernization will not require any changes to the project's existing reservoirs, water conduits or transmission lines, and all installation will occur within the project powerhouse. In addition to significant power and energy benefits for the non-profit client and its members, there will be no significant adverse impact to the environment.

Services Provided

• Feasibility studies
• Field testing of existing units
• FERC Regulatory Consultation
• Economic analysis and asset management
• Detailed engineering evaluations and design
• Implementation plan
• Risk strategies
• FERC capacity related amendment
• Plans and specification preparation
• Geotechnical instrumentation upgrade program
• Bid review
• Negotiation of contracts
• Contract strategies and management
• Equipment design review
• Witness of model testing
• Shop inspections
• Construction management
• Witness of field testing of upgraded units
• Uprate and benefit evaluation

Project Highlights

• The upgrade will increase the plant's cycle efficiency from 77.2 percent to 78.3 percent.
• The upgrade will increase the pumping capacity, reducing the daily pumping period from 8.2 hours to approximately 7.2 hours.
• The project will increase the flexibility of the plant to take advantage of overall power grid efficiencies and economic benefits.
• The plant provides spinning and supplemental (non-spinning) reserves. When providing spinning reserves, a Unit is loaded to a part load, usually 120 MW, and the differential between operating power and 100 percent capacity is treated as spinning reserve. The present units have a large, undesirable rough operating zone from 120 MW to 220 MW that is not available for running. The upgrade will improve the operating range by reducing the minimum-operating load and decreasing the part-load rough operating bandzone.