Ice Harbor Fish Mortalityby Barry Espenson
Startlingly low juvenile salmon survival through Ice Harbor Dam's spillways has forced operators this week to shift to an evaluation of a newly hatched spill strategy vs. operations that shut off spill and send the young fish through the facility's mechanical bypass system or the turbines.
According to a memo from NOAA Fisheries' Jim Ruff, empirical PIT-tag, route-specific data for migrating Snake River juvenile fall chinook from tests in 2000 and 2002 showed survival at the dam to be 88 and 89 percent respectively. There was no spill at the dam during 2001. Ruff is NOAA's Northwest region hydrosystem chief and chairman of the interagency Implementation Team.
Those totals are well below the survival rate NOAA Fisheries assumed in its 2000 biological opinion. The BiOp judged that planned hydro operations jeopardized the survival of eight -- including wild Snake River fall chinook -- of the 12 salmon and steelhead stocks that are listed under the Endangered Species Act. It also describes measures both within the hydrosystem (such as spill) and off-site that can be taken to avoid jeopardy.
And while there is no empirical information on the survival of those subyearling fall chinook through Ice Harbor's turbines and juvenile bypass system, it is believed to be higher than spill survival. The BiOp used an estimate of 94 percent for "powerhouse" survival for fall chinook (a combination of the 90 percent turbine survival estimate and projected 98 percent bypass survival).
"There's something happening with the fish after they go through the spillways," Ruff said. Spill has long been considered the most benign means of passage through the Columbia/Snake hydrosystem's projects, but problems have been identified in recent years at The Dalles Dam on the Columbia and now at Ice Harbor, the last of four dams on the lower Snake River that the juvenile fish encounter on their outmigration. Ice Harbor is just above the Snake's confluence with the Columbia.
One thing The Dalles and Ice Harbor have in common is that they have the shallowest "stilling" basins -- the area where the fish-laden spill crashes below the dam -- in the hydrosystem. That could cause injury problems at mid and late summer when there is less flowing water to cushion the fall, Ruff said. Huge concrete "baffle blocks" intended to dissipate the turbulence below the dam could also be a cause of the fish injuries, again particularly in low water.
Ruff said that the Corps of Engineers, which operates the dam, experimented last winter with "sensor" fish -- mechanical devices that can detect the hydraulic pressures, blows and other sensations a fish might experience as it goes through the spillbays.
"Apparently there were some strikes on the sensor fish, some fairly severe strikes," Ruff said.
And spillbay deflectors -- designed to reduce the amount of dissolved gas created by the cascading spill -- that were installed on 1998 could also, potentially, be a source of injury at the lower water levels. Study is needed to better pinpoint the cause of injury and higher than anticipated mortality, Ruff said.
The low spill survival at Ice Harbor could have implications for the investigation about whether to outfit the dam with new "removable spillway weir" technology, Ruff said. If there is an inherent problem with the spillway passage route, in may be deemed unfeasible to install the costly technology. The weir device tested upriver at Lower Granite Dam has shown promise for its ability to pass more fish per unit of water, and as a result reduce the cost of spill. Spill is water passing through spillbays instead of through the power, and revenue, generating turbines.
The higher-than-expected mortality at Ice Harbor has affected a relatively small percentage of the summer juvenile outmigration. With full transportation in summer, a vast majority of the migrants are collected upriver at Lower Granite, Little Goose and Lower Monumental dams and barged to a point below Bonneville Dam, the lowermost dam on the Columbia. As few as 5 percent of the outmigration remain in the river at Ice Harbor. There are no collection facilities at Ice Harbor so spill is provided as a passage option.
The biological opinion called for a specific spill pattern through all 10 of the dam's spillbays around the clock with reduced levels during the day. Nighttime BiOp spill during 2000 and 2002 tests was as much water as could be spilled without exceeding total dissolved gas limits.
"A different spill operation that was anticipated to improve survival rates was tested this spring at the project," Ruff said in his June 20 memo to the IT. "However, test results from the balloon tag study conducted this spring indicated the fish were injured in the new spill operation, as well as in the BiOp spill operations."
That test involved spilling half the river's flow. Ruff said the balloon-tagged fish incurred direct injuries at rates of from 10 to 22 percent. Actual survival estimates are not yet available.
In the ensuing weeks, the idea of testing "bulk" spill was developed. The test strategy launched this week alternates two days of no spill (powerhouse passage only) with two days of bulk spill, in which the spill volume is being concentrated in two or three spillbays instead of across all 10. Ruff said it is hoped the increased volume will provide a watery cushion against injury as the fish land in the river below. The testing is scheduled for 21 days.
"Everybody agreed that it is worth trying," Ruff said. The tests will involve tracking between 36,000 and 52,000 PIT-tagged juvenile fish as they descend the system. Detection equipment is installed at McNary, John Day and Bonneville as well as aboard trawls below Bonneville. The fish are being collected at Lower Monumental.
The federal agencies plan to continue evaluations in 2004 of more complete project passage survival and the factors that may be contributing to the lower than expected spillway survival, Ruff said. That will involve releasing radio-tagged fish above the dam and allowing them to chose their own path -- toward the powerhouse and bypass or the spillbays -- and developing survival estimates for all routes.
The memo also said that the federal agencies will soon initiate discussions through the Regional Forum on how to best operate Ice Harbor once the summer survival evaluation ends in mid-July and through the summer migration period.
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