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First Year Test Results Promising for Spillway Prototype by Barry Espenson Columbia Basin Bulletin - March 7, 2003

A final tally of data from last spring's initial test of a "removable spillway weir" at the Snake River's Lower Granite Dam shows that the device attracts young salmon and steelhead better, is more efficient in its use of water and sends the juvenile on their way faster than other means of passage, including spill.

The RSW device is bolted into a spillway, forcing the water to go over it like a waterfall. Since juvenile fish, and particularly steelhead, tend to be surface oriented, the surface flow is thought to be a more effective method to pass fish than existing pressurized 50-foot deep flow under spill gates.

The first year's biological data shows promise for the Lower Granite prototype.

"It's a significant gain in surface bypass technology. It's an exciting time for us," researcher Noah Adams of the U.S. Geological Survey told members of the Regional Forum's Implementation Team. A USGS research team led two of the primary studies evaluating the RWS at Lower Granite. Adams said the final report on the 2002 research would be forward to the Corps of Engineers next week. The Corps operates the dam.

The IT, which includes state and federal representatives, was initiated through NOAA Fisheries mainstem Columbia/Snake river hydrosystem biological opinion with the goal shepherding hydrosystem passage measures that improve the survival of salmon listed under the Endangered Species Act.

Both NOAA Fisheries' 2000 biological opinion and the Corps' Lower Snake River Juvenile Salmon Migration Feasibility Study prescribe the development of surface bypass technology.

The researchers used a variety of tools to track the test fish through the hydro project. Three-dimensional ultrasonic telemetry was used to track some fishes' behavior as they approached and passed the dam. Implanted radio tags in others sent signals there were picked up by antenna.

A key portion of the study involved following the course of some 1,600 radio-tagged fish (about 800 chinook and 800 steelhead smolts) through the dam under three basic operational "treatments." The young hatchery chinook and wild and hatchery steelhead were collected at the dam, then transported upriver and released.

Under the one scenario, the dam was operated with spill levels prescribed in the biological opinion -- passing the maximum amount of water through seven dam spillways that is allowed within a 120 percent total dissolved gas limit. Generally the more water that is spilled, the more gas is created in the tailwater below the spillways. High gas levels can be harmful to fish and other aquatic organisms. About one-third of the time was spent testing that operational strategy with the RSW "off."

Other expected advantages of the RSW are improved passage conditions for fish that reduce injury and passage delays at the dams.

The BiOp spills, were generally 45,000 cubic feet per second during the test period, are carried out during 12 nighttime hours. The average river flows during the mid-April to early June testing period were about 85 kcfs so roughly half the river was spilled during the BiOp spill portion of the test.

The other two operations or treatments involved passing about 6,500 to 7,000 cfs through the RSW (located in the spillway nearest the power house and its turbines) with two levels of "training" spill. The training spill -- targeted at 8,000 and 16,000 cfs from nearby spillways in two separate treatments-- is intended to help move the young fish out of the tailrace area below the dam after they pass. The RSW operations were 24 hours per day.

The RSW was operated in conjunction with the existing behavioral guidance structure that is intended to steer fish away from turbine intakes, the Corps said. The guidance structure is being removed before tests this spring to see how the RSW performs without it. The balance of the fish passed by other means, in the training spill, into the existing juvenile bypass system or under the screens and through the turbines.

The study result showed that the RSW/training spill operations passed as many or more fish as when spill was provided at all the dam's gates. That means with the RSW a lesser amount of water is being diverted from power generating turbines.

The RSW also showed to be more efficient, passing 6.5 to 7.3 fish per unit of water compared to only 1 fish per unit of water for spill.

"The fact that it passes as many fish as spill with a lot less water is the most promising result," from the tests, said Jim Ruff, NOAA Fisheries' hydrosystem branch chief.

The fish, and particularly the steelhead, are finding the RSW more easily even than the spill.

"They are moving fairly quickly, in a straight line, to the RSW," Adams said. They are not hesitating either before taking the plunge. With the BiOp spill occurring only at night, there is an automatic delay.

"The RSW has a significant impact on travel time," Adams said.

The Bonneville Power Administration -- which markets power from the dams -- spends hundreds of millions annually on fish and wildlife mitigation and recovery efforts due to its obligations under the ESA and the Northwest Power Act and the Endangered Species Act. The BPA repays the federal treasury for the majority of the capital projects at hydro projects that are intended to improve passage. It also foregoes revenue making opportunities when water is spilled for fish instead channeled through turbines to generate saleable electricity.

Adams said the single year of data shows promise but the agencies are not yet ready to claims the concept is a "silver bullet, a home run or a touchdown" technology that could be applied throughout in the system. That will take more testing.

BPA, and other agencies involved, are looking to the technology to improve survival and cut costs.

The RSW prototype was built in Vancouver, Wash., and shipped upriver to the southeast Washington dam early in the summer of 2001. The RSW was installed at Lower Granite Lock and Dam last winter. The cost to build and install the structure is estimated at $11.8 million.

The structure is designed to be "removable" by controlled descent to the bottom of the dam forebay. This allows the capability to return the spillway to original flow capacity during major flood events, then raised to operating position after the flood event. The RSW weighs over 2 million pounds, and is 115 feet tall, 83 feet wide, and 61 feet deep in the upstream to downstream dimension.

The Corps in November 2001 used balloon tagged fish in initial biological testing to ensure the RSW passage did not cause some unanticipated harm to the fish. The mortality proved to be on par with that of traditional spill.