Today, I read a very interesting and descriptive court case that discussed the pros and cons of various methods used by the U.S. Army Corps of Engineers to help juvenile salmon migrate from the rivers to the sea, since “it is generally accepted that the Basin’s [Columbia and Snake River Basin] hydropower system is a major factor in the decline of some salmon and steelhead runs to a point of near extinction.” From the United States Court of Appeals, Ninth Circuit:

[D]ams kill some fish as a result of “[b]lockage and inundation of habitat, turbine-related mortality of juvenile fish, increased delay of juvenile migration through the Snake and Columbia Rivers, increased predation on juvenile salmon in reservoirs, and increased delay of adults on their way to spawning grounds.” 57 Fed.Reg. 14,660 (1992).

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Three major methods are employed to help juvenile salmon in their migrations-river flow improvement, spill control, and surface transportation. Each of these methods has its advantages and disadvantages, both for the salmon and the hydropower interests that benefit from the inexpensive electricity generated by the dams. First, the Corps can increase the amount of water released from storage reservoirs and thus increase the flow in the rivers. According to some scientific studies, increased flow decreases the time juvenile salmon spend migrating through the system and reduces their exposure to predators and other adverse effects of the system. The peak natural flow period is in the spring and early summer due to the winter runoff. Increased flow may be of greatest benefit to the juvenile salmon during their downstream migration, which varies from species to species but generally occurs in the spring and summer. However, increased flow in the winter is of greater benefit to the electric utilities because that is when the peak demand for electricity occurs. By adjusting the amount of water that is drawn down from the system of storage reservoirs, the Corps can control the timing and amount of flow to some extent.

Second, the Corps can increase the amount of water that spills over the spillways to allow more juvenile salmon to pass the dams without going through the turbines. Turbines kill or injure a significant number of juvenile salmon in their downstream migrations; thus, increased spill should increase salmon survival. According to some scientific studies, however, increased spill also causes the water to become supersaturated with nitrogen, which in turn may cause gas bubble disease in the fish. But there are economic consequences: water spilled over the spillways does not pass through the turbines and thus does not produce electricity.

Third, the Corps can physically transport juvenile salmon around the dams. The existing transportation program involves collecting juvenile salmon at four dams along the rivers, piping them into barges or trucks, and transporting them down the river past the dams to be released. According to some scientific studies, transportation decreases migration time and avoids exposure to predation and other adverse effects of the system. Critics, however, point to studies suggesting that the transportation program kills some juvenile salmon due to stress from crowding and increased disease transmission.

The Corps currently uses a “spread-the-risk” approach. All juvenile salmon that are collected at Lower Granite Dam (the dam farthest upstream) are transported downstream. At subsequent dams, when the flow in the river exceeds a certain rate which excess is predicted to prevail for at least five consecutive days, the Corps leaves the fish in the river instead of collecting them for transport. Otherwise, the Corps transports the juveniles collected at these dams to a point below Bonneville Dam (the dam farthest downstream) where they are reintroduced into the Columbia River. The transportation program began in the 1970s, and the Corps has operated it since 1981. The Corps transports approximately 20 million juvenile salmon per year, more than half the total number of migrating juveniles.

For more see Nw. Res. Info. Ctr., Inc. v. Nat’l Marine Fisheries Serv., 56 F.3d 1060 (9th Cir. 1995).

Image of juvenile coho salmon is by Brian Lance/NOAA Fisheries.

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