February 19, 2003

PORTLAND — A committee of independent scientists issued a report today that challenges widely held beliefs about the relationship between river flows and survival of juvenile salmon and steelhead migrating past the eight hydroelectric dams of the lower Snake and Columbia rivers.

Based largely on data collected in studies of Snake River fish, the scientists said rapid fluctuations in flow, which are related to increases and decreases in electricity generation at the dams, may have the greatest impact on fish survival, particularly during periods of low flows. Closer management and stabilization of flows could lead to improved fish survival, the scientists suggest.

"The (flow/survival) issue requires re-evaluation," according to the 11-member Independent Scientific Advisory Board (ISAB). The ISAB advises both the Council and the federal NOAA Fisheries, which enforces the Endangered Species Act for salmon and steelhead in the Snake and Columbia rivers.

"This is important information for the region to consider," Council Chair Judi Danielson said. "The ISAB report should point research toward investigating the value of stable flows as a challenge to the conventional wisdom that all the fish need is higher volumes of water and faster flow, as has been the practice with flow augmentation."

In response to questions posed by the Council and the Columbia River Inter-Tribal Fish Commission, which helps appoint members to the panel, the ISAB said the prevailing rationale for flow augmentation is inadequate and "neither complete nor comprehensive." According to the report, "there is room for alternative explanations of available data that have both scientific justification and practical value for managing the hydrosystem for multiple uses including salmon recovery."

Snake River flow management historically has focused on releasing large volumes of water from upriver storage reservoirs in the spring and summer when the juvenile fish are migrating to the ocean. Observations of fish survival have been linked to these volumes of water and the timing of their release — higher flows during good water years yield higher survival than lower flows.

But after analyzing recent scientific studies, the ISAB hypothesizes that hourly flow fluctuations in the Snake impact juvenile fish survival, particularly for the tiniest fish, fall chinook salmon. Coincidentally, the same flow/survival relationship has not been demonstrated in the Columbia River above the confluence of the Snake. This may be because stable flows have been required through the five mid-Columbia dams since 1980, the scientists report.

ISAB member Dr. Chuck Coutant, an ecologist at the Oak Ridge National Laboratory in Tennessee, told the Council that during low Snake River flows the fish appear to become disoriented and expend more energy in response to the hydropower-related pulses that "induce an oscillation in the reservoirs, similar to water sloshing in a bath tub," at up to two-hour intervals, according to the report. During periods of low flow — below 100,000 cubic feet per second in the lower Snake River and particularly at flows below 40,000 cubic feet per second — the fish can become so disoriented by these oscillations that they simply stop migrating, increasing their exposure to predators. At higher flows in good water years, the power-related pulses are of less concern because they are overcome by the larger volume of water.

"What this tells us is that we know darn little about reservoir hydraulics, and we need to know more," Coutant said.

The ISAB suggests that stabilization of flows could be more effective in improving survival of juvenile salmonids than simply adding volumes of water, as in flow augmentation. The ISAB suggests that an experiment with stable flows be conducted to observe the impact on fish survival.

The flow/survival issue is timely because the Council is considering amendments to its Columbia River Basin Fish and Wildlife Program regarding dam operations and flows in the mainstem Columbia and Snake rivers. For that reason, the Council is inviting public comments on the ISAB report through Tuesday, February 25.

The Council is an agency of the states of Idaho, Montana, Oregon and Washington and is directed by the Northwest Power Act of 1980 to prepare a program to protect, mitigate and enhance fish and wildlife of the Columbia River Basin affected by hydropower dams while also assuring the region an adequate, efficient, economical and reliable power supply.

read ISAB report >