The Influence of Environmental Regulation in the Operations of the Idaho Power Company Hydrosystem

The bulk of Idaho Power Company’s (IPC) generating ability comes from 17 hydroelectric power plants (mostly licensed through FERC), 10 of which are on the mainstem Snake River from American Falls Dam (Rkm 1151) to Hells Canyon Dam (Rkm 397.5). Most of the mainstem facilities operate as run-of-the-river (mean daily inflow equals mean daily outflow) with no available storage, whereas the largest of the facilities includes the Hells Canyon Complex, a three dam and reservoir facility including Brownlee Reservoir, a large storage reservoir with up to 1 MAF of active storage.   Most of the facilities operate at some level to follow system electrical load, and as a consequence, flows fluctuate at some level on a daily basis below each of the dams. The ability to manage reservoir levels and flows and generate electricity at these projects is often constrained by measures required to protect or enhance aquatic species protected under the Endangered Species Act, or meet water quality standards under the Clean Water Act, as well as other potential effects to aquatic habitats including sediment transport.  Other constraints include flood control and navigation requirements. Most constraints focus on limits to reservoir and tailwater fluctuations, ramping rates, and minimum and maximum flows. Development of these constraints to protect aquatic species and their habitats has relied on application of scientific studies to better understand relationships between habitats and flow and the needs of the species. A concerted effort has been made to collect site-specific empirical data and in many cases, develop and integrate applicable decision support tools to simulate and quantify different operational constraints and responses of the physical environments and habitats of aquatic species.  These support tools have included 1-D and 2-D instream flow models, reservoir operations and water quality models, and 3-D physical models.  The application of these tools and the effort to collect site specific information has helped Idaho Power Company to optimize operations of the facilities while still affording critical environmental protection.