Managing sediment to minimize environmental impacts
- Federal Energy Regulatory Commission, Washington, DC (United States)
When considering licensing of a hydroelectric project, FERC must give equal consideration to power and nonpower values such as environmental resources. A case study is the existing Rock-Creek Cresta Project, located on the North Fork of the Feather River in northern California, which is in the process of relicensing by the Commission. This project includes two reservoirs - Rock Creek and Cresta Reservoirs, each formed by a dam that diverts water from the river into a tunnel and to a powerhouse. The watershed includes large natural and man-made sediment sources. Rock Creek Reservoir has accumulated 3.9 million cubic yards of sediments since the dam was built in 1950; Cresta Reservoir has accumulated 2.9 million cy of sediments since 1949. Operational problems began in the 1980s. As part of the relicensing process, Pacific Gas & Electric Company (PG&E) initially proposed a combination of dredging 500,000 cy of sediment from each reservoir, land disposal of dredged sediments, followed by sediment pass-through to achieve a long term net balance of sediment inflow and outflow. This proposal had substantial economic costs and environmental impact. Potential environmental effects included impacts to water quality and aquatic organisms and to terrestrial habitat from disposal of a million cy of dredged sediments. PG&E used physical and mathematical models to develop an innovative approach that minimized the amount of sediment needed to be dredged by limiting dredging to the area immediately adjacent to the intake structures. This would also tend to minimize impacts to water quality and aquatic habitat by reducing the area of disturbance within the reservoirs. PG&E proposes to keep the intake areas open and provide for long-term sediment pass-through by providing additional low-level outlet capacity. This would permit reservoir drawdown, which would increase velocities and sediment movement out of the reservoirs.
- OSTI ID:
- 219926
- Report Number(s):
- CONF-9507190--
- Country of Publication:
- United States
- Language:
- English
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