Moving fish safely
past the big dams on the lower Snake and Columbia rivers is one of the most
difficult and controversial challenges the dam operators face. It is a problem
that vexed dam planners and operators ever since the first dams were built in
the 1930s — in fact, even before they were built. In the late 1930s as
Bonneville Dam was being constructed, the U.S. Army Corps of Engineers fretted
over how to safely pass migrating fish both upstream and downstream at the dam.
The
challenge for dam operators, then and today, is to get as many fish past the
dams safely as possible. Fish ladders are effective for passing adult fish, but
juvenile fish passage is more problematic. There are four ways juvenile fish
can pass a hydroelectric dam. First, and least desirable, fish can be swept
through turbines. This is the most lethal passage alternative. Second, fish
bypass systems can channel some fish away from the turbines into a series of
pipes and channels that carry the fish through the dam and deposit them on the
downstream side. Third, the spill gates can be opened, creating a waterfall for
the fish. Or fourth, the fish can be collected and transported downstream in
barges or tank trucks operated by the Corps of Engineers.
Each
of these has problems. Not all fish can be deflected away the turbines into
bypass systems. Nonetheless, diversion
screens have been installed in front of the turbines at all but The Dalles Dam,
where experimentation showed that because of the configuration of the dam,
screens would be less effective than spilling fish or diverting them through
the dam’s ice and trash sluiceway (at The Dalles, juvenile fish passage
involves a combination of spill and sluiceway passage, and the result is that
about 72 percent pass via spill, 13 percent via the sluiceway, and 14-15
percent go through the turbines). Spillway passage is effective but can expose
fish to bubbles of nitrogen in the frothy water immediately below the dams when
there are high volumes of spill. Also, fish can be injured as they tumble down
the concrete spillways. In either instance, the fish are susceptible to
predators below the dams, such as sea gulls, Caspian terns and northern
pikeminnow. Barging or trucking (far more fish are barged than trucked) is effective
but creates an unnatural environment and an unnatural migration experience for
the fish, and some transported fish either lose their homing instinct or fail
to return for reasons that are not clearly understood. Research shows that more
transported fish survive to the release points below Bonneville Dam than fish
that migrate in the river, but that fish that migrate downstream in the river
return in greater numbers as adults than transported fish. The “delayed
mortality” of transported fish is a subject of ongoing research.
The
first fish-barging experiment took place in 1955 when, on April 19, the
Washington Department of Fisheries put 200,000 Chinook salmon in a barge at the
mouth of the Klickitat River and sent them downstream through Bonneville Dam to
a release site near Skamokawa, Washington. “The fish at that point had enjoyed
165 miles of predator-free migration over normal water route, and anticipatable
Bonneville mortalities had been wholly eliminated,” wrote researcher C.H. Ellis
in the March 1956 edition of the Department’s publication, Fisheries Research Papers.
Barging
the fish in 1955 was part of a fish-marking and planting study to assess the
impact of Bonneville Dam turbines and squawfish (now known as northern
pikeminnow) predation on migrating juvenile salmon. In all, 1 million fish from
the Klickitat Hatchery, located near Glendale, Washington, 40 miles upriver
from the mouth of the Klickitat River, were divided into five equal lots and
released at different locations. Each lot was marked in a way that would
identify its migration route. One lot was released at the hatchery; another was
trucked to the mouth of the river and put into the barge, which consisted of
floating net pens pulled by a boat; another was released at the mouth of the
river; the fourth was trucked to the barge release site near Skamokawa; and the
fifth was released a short distance upstream from Skamokawa. “Thus, by the
evening of April 21, 1955, as diverse a set of travel and river survival tests
as could be practically designed had been put into effect,” Ellis wrote. “A
means of comparison had been established on the merits of barge vs. truck
transport. In addition, the comparative diluting of homing instinct of Columbia
River fall Chinook eventually could be measured between the barge lot liberated
below the mouth of the Elochoman River [near Cathlamet] and the group allowed
to swim the 205 miles from the Klickitat Hatchery.”
Why
experiment with transporting juvenile salmon? Because fish were dying at
hydroelectric dams, and the state wanted to know what was the safest migration
route — in the river, in trucks, or in barges.
“Losses
of young migrant salmon through the direct effects of hydroelectric dams and
natural predation have become especially critical in the Columbia River
Watershed with the ascendancy of power and other water-use developments,” Ellis
wrote. “These dams also have created,
particularly in recent years, conditions ideal for fish that prey on migratory
salmon.”
Predation
by northern pikeminnow remains a problem today, and river conditions have
changed dramatically since 1955. There were only five dams on the mainstem
Columbia River in 1955; today there are eleven, and the last of these was
completed in 1975. There were no dams on the lower Snake River mainstem in
1955, but construction began at Brownlee Dam that year. Today, there are seven — four federal dams between the mouth of the river and the Lewiston/Clarkston
area, and three, including Brownlee, in the Idaho Power Company’s Hells Canyon
complex.
With
a hopeful sendoff in 1955, the Washington researchers waited three years — the
first year most salmon return to spawn — for the first fish to return to the
Klickitat Hatchery.
“The
returns were lousy,” said retired biologist Wes Ebel in a 1999 interview. Ebel,
whose research on Columbia River salmon for the National Marine Fisheries
Service spanned more than 25 years, said he discussed the early barging efforts
with the Washington researchers. “There were no baffles in the net pens, and so
a lot of the fish were impinged on the nets — a lot of them died before they
were released. That's why the returns were lousy.”
While
the Corps of Engineers financed many fish passage experiments and research
projects at the Snake River dams in the 1950s and 1960s, transportation did not
get another try until 1968, when the Corps funded an experiment by the National
Marine Fisheries Service to collect juvenile salmon and steelhead at Ice Harbor
Dam and transport them downriver in tank trucks to below Bonneville, where they
were released. In that year, 83,315 Chinook salmon (and no steelhead) were
collected and transported. The experiment continued in 1969 (28,311 Chinook and
20,430 steelhead) and in 1970 (20,332 Chinook and 52,217 steelhead). The experiment
continued at Little Goose Dam when it was completed in 1971 and at Lower
Granite Dam when it was completed in 1975. Reports indicated survival of the
trucked fish to the release point below Bonneville was 20 times higher than for
those that migrated downstream in the river. In 1977, in response to one of the
lowest Columbia River runoffs on record, the Corps met with fish and wildlife
agencies and electric utilities concerned about the impacts of the drought on
fish and hydropower, and decided to greatly expand the fish-transportation
program. In that year, the Corps began transporting fish downriver in barges.
The same year, the Corps even tried flying fish down the river, dropping them
from a low-flying airplane below Bonneville Dam. The “flying fish” experiment
did not work well, and it was not repeated in later years.
The
barges used in 1977 were different from those used by the state of Washington
in its 1955 experiment. That barge was 55 feet long and 21 feet wide with a
draft of five feet. It wasn’t really a barge as much as it was a series of
floating net pens. The Corps barges are 180 feet long, 42 feet wide and have a
draft of eight feet. They have solid steel hulls.
The
number of fish barged by the Corps grew steadily over the years, eventually to
20 million fish per year or more. Research indicates a mixed degree of success.
Some stocks did well, and others did not. Barging appears to work best for
steelhead and spring Chinook, which spend a year in their birth habitat before
migrating to the ocean, and less well for fall Chinook, which begin their
migration within a few months of their birth. The effectiveness of barging,
then, may have something to do with length of time in the birth habitat and
size of the fish.
