Environmental Effects of Hydropower Generation

The principal environmental effects regarding hydropower are generally focused on water quality impacts, hydrology impacts, erosion and sedimentation, land-use impacts, and fish and wildlife impacts. The environmental effects associated with any one hydropower project are site specific and therefore can be very different when comparing projects; for example, a project that involves adding generators to an existing non-powered dam or other existing water control structure will typically cause less of an incremental environmental impact than a project that requires new dam construction. There are few serious air emissions or solid waste issues associated with hydropower development or operation.

Of particular concern to the Council is the potential impact of hydropower on fish and wildlife. A hydropower dam presents a migration barrier to the passage of upstream (adult) and downstream (juvenile) anadromous and resident fish. Habitat is completely blocked by some projects in the system. At dams that allow passage, juvenile downstream migrants face the risk of mortality at each dam as a result of passage through turbines, exposure to water supersaturated with nitrogen, delay in start of migration, increased travel times, and increased predation. Filling an impoundment behind a hydropower dam inundates land and transforms a free-flowing river into a lake-like environment. This transition of habitat changes the composition of terrestrial and aquatic biota at the project site which may be beneficial or detrimental to wildlife. System storage operations to optimize power generation also alter flows important for the emergence, rearing, and migration of juvenile salmon and other fish, and for adult spawning.

Under the Northwest Power Act, the Council develops a program to protect, mitigate, and enhance fish and wildlife adversely affected by the development and operation of hydropower facilities on the Columbia and its tributaries. To address the effects from the existing system, the Council’s Columbia River Basin Fish and Wildlife Program includes measures and objectives to protect and benefit fish and wildlife. Measures to limit the direct impact of hydropower development include fish screens and bypass systems, bypass spills, and fish ladders to help fish navigate through the hydropower dam; minimum flows, flow augmentation requirements and stable storage reservoir operations; and the installation and implementation of systems to maintain powerhouse discharge and minimize or eliminate fluctuations in water and flow levels. Offsite protection and mitigation actions include both habitat protection and improvement measures and artificial propagation facilities and strategies. Mitigation for the effects of the development of the system on wildlife has focused primarily on the offsite acquisition, improvement, and protection of habitat for the affected wildlife species.