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EXECUTIVE SUMMARY This manual contains information on the activities and equipment that comprise small-scale hydroelectric technology and reviews the potential impacts of small-scale hydro on fish and wildlife and their habitats. The manual is designed to provide guidance to persons reviewing applications for the development of sites capable of generating up to 30 MW of elec- tricity in terms of the consideration of potential impacts on fish and wildlife resources. Benefits of small-scale hydro include increased energy self- sufficiency, the dependability of the technology, and, occasionally, educa- tional, historical, and fish and wildlife benefits. Serious conflicts can exist between the goals of increased small-scale hydro development and fish and wildlife. Of particular concern is the potential blockage of fish migration, loss or degradation of habitat, changes in the amount and pat- tern of instream flow, mortality and morbidity of fish passing through tur- bines and over dams, and the degradation of water quality. Sma ll-sca 1 e hydroe 1 ectr i c plants capture the energy of fa 11 i ng water in direct proportion to the amount of fall (head or elevation difference) and the discharge of the stream. Sites on perennial streams can offer a dependable source of electrical power; other types of sites include multiple use projects, such as lock and dam structures or water storage impoundments, canal drops, and pipe networks. Each type of small-scale hydro project has unique advantages and disadvantages and potential environmental impacts. The construction activities needed to establish an operating small- scale hydro plant vary considerably depending on whether the project is new, restoration, or retrofit. Preconstruction activities include inspec- tions of existing facilities, surveys, geological investigations, and, sometimes, minor road construction. Construction steps vary according to the type of small-scale hydro plant, but typically include dredging or flushing, landfilling, removal of vegetation, excavation, and concrete work. Dewatering, channelization, and flow diversion, both temporary and permanent, may occur during construction. Dams and impoundments, spillways, intakes, waterways and their controls, turbines, the powerhouse and its auxiliary equipment including sub-stations and transmission lines make up the small-scale hydro plant. These components exist in many forms, and, in some types of plants, some of the possible components are absent or much reduced in relative size iv