FLOOD IMPACTS ON PUBLIC LAND ASSOCIATED WITH FAILURE OF WATER CONVEYANCE STRUCTURES AT HYDROELECTRIC PROJECTS

Hydroelectric facilities on public lands in the western United States have varied origins. Some are ancillary to reservoirs built for irrigation water storage or flood control. Others represent turn-of-the-20th Century efforts by business interests and municipalities to provide cheap electric power. These hydroelectric facilities are authorized through licenses to operate issued by the Federal Energy Regulatory Agency (FERC). Federal agencies responsible for land management, where these facilities are located, have a statutory responsibility to identify conditions in the license to ensure public safety and mitigate resource impacts. Economic loss and potential flood damage associated with dam failure results in significant geologic and engineering attention to their siting and design. However, flood potential also exists from the water conveyance structures such as canals, flumes, and penstocks used to divert water to reservoirs or direct it into power generation structures. Two examples from the central Sierra Nevada, Browns Ditch rockslide and Lost Canyon pipe crossing failure, illustrate how geologic conditions caused flooding from such structures. They illustrate how slope movement and foundation conditions can result in resource damage to public lands ranging from a few thousand to hundreds of thousands of dollars and effects that persist for months to many years. Consequently, attention to water conveyance structures associated with hydroelectric facilities should receive geologic and engineering attention during siting and design similar to that given to dams.