Environmental Engineering Reference
In-Depth Information
DID YOU KNOW?
With the advent of modern computer and satellite technology, the U.S. Geological
Survey can monitor the stage of many streams almost instantly. Because some
streams, especially those in the normally arid western United States, can rise
dramatically in a matter of minutes during a major storm, it is important to be
able to remotely monitor how fast water is rising in real time in order to warn
people that might be affected by a dangerous flood (USGS, 2014b).
species of aquatic insects that swim in pools can be physically flushed downstream
from a sudden increase in flow (Trotzky and Gregory, 1974). The biological effects
of unnatural flow increases are usually irrelevant in regulating hydropower opera-
tions because public safety concerns justify more stringent regulations than biologi-
cal concerns. Flow increases can strand and occasionally drown fishermen and other
people located on bars, rocks, or in confined canyons. Boaters might also be at risk
under some circumstances.
s
trandIng
Stranding is the separation of fish from flowing surface water as a result of declining
river stage. Stranding can occur during any drop in stage. It is not exclusively associ-
ated with complete or substantial dewatering of a river. Stranding can be classified
into two categories:
Beaching
is when fish flounder out of the water on the substrate.
Trapping
is the isolation of fish in pockets of water with no access to the free-flowing
surface water. Stranding cannot always be neatly classified as beaching or trapping.
Thus, in this text we use the term stranding unless a more specific term is appropriate.
Salmonid stranding associated with hydropower operations has been widely docu-
mented in Washington and Oregon (e.g., Bauersfeld, 1977, 1978a; Becker et al., 1981;
Fiscus, 1977; Olson, 1990; Phinney, 1974a,b; Satterthwaite, 1987; Thompson, 1970;
Witty and Thompson, 1974). Stranding can occur many miles downstream of the
powerhouse (Phillips, 1969; Woodin, 1984). The estimated numbers of fish stranded
in flow fluctuation events range from negligible to 120,000 fry (Phinney, 1974a).
Stranding mortality is difficult or impossible to estimate. Estimates are usually very
conservation or highly variable. Stranding can also occur as a result of other events,
including natural declines in flow (author's observation of Colorado River over time),
ship wash (Bauersfeld, 1977), municipal water withdrawals, and irrigation withdraw-
als. Many factors affect the incidence of stranding. A recurrent theme in much of the
following discussion is the high vulnerability of small sa l mon id f r y.
DID YOU KNOW?
Salmonids are a family of ray-finned fish that includes salmon, trout, chars,
freshwater whitefishes, and graylings.
