8209

• UCREFRP Catalog Number: 8209
• Author: Rochester, H., T. Lloyd and M. Farr.
• Title: Physical Impacts of Small-Scale Hydroelectric Facilities and Their Effects on Fish and Wildlife.
• USFW Year: 1984.
• USFW - Doc Type: 14-16-0009-82-020,
• Copyright Material: NO

result. (Construction activities and their impacts are discussed further
in Chapter 4.)

No two SSH projects ever are exactly alike, but projects can be
grouped into five general types according to the basic approach used to
place turbines in a position to obtain energy from water:

. Conventional hydroelectric plants;
. Multiple-use dams;
. Diversion projects;
. Canal drop systems; and
. Pipe network systems.

a. Conventional hydroelectric plants. The best-known and most common
form of hydroelectric plant is the single purpose hydro project (Fig. 7).
Most conventional projects that qual ify as SSH (<30 MW) are located on
tributary streams and are operated with comparatively little water storage;
that is, they are run-of-river plants (Section 7.1). However, projects
that expand the generating capacity of plants located in the mainstem of
some large rivers, such as the Susquehanna in Pennsylvania, are also
cons i dered SSH. Many of these expans i on projects are operated in the
peaking mode (Section 7.2).

The conventional hydro plant depends on nearly complete control of the
stream by means of a dam, which spans the entire stream. Conventional,
single purpose SSH plants account for more than one-third of the more than
2,000 sites identified by the U.S. Army Corps of Engineers (1981) as having
potential for small-scale hydroelectric development.

The best site for a conventional SSH plant has a maximum fall (head)
in a minimum horizontal distance, combined with comparatively steady
streamflow year-round. The construction involved in preparing such a site
for hydroelectric use can be extensive, even if the project is considered a
"restoration" project. For example, dam repair can involve anything from
minor clean-up and resurfacing to the total rebuilding of an existing1 dam
found to be structurally unsafe or incapable of supporting the additional
stress caused by raising the water level of the reservoir. Similarly, mod-
ifications to the power house, transmission equipment, or waterways may be
major.

lThe term "existing dam," as established in the PURPA legislation, does not
mean that a dam is fit for use. Rehabilitation may involve blocking the
stream completely, where minimal if any stream obstruction may have existed
for decades due to structural deterioration, or total breaching of the
existing dam.

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