the film
Economic and dam related articles

Smolts Test Spillway Success

by Eric Barker
Lewiston Tribune, June 13, 2002

Removable weir at Lower Granite Dam is showing some promise

LOWER GRANITE DAM -- Though much of the data has yet to be processed, initial hunches indicate the Removable Spillway Weir at Lower Granite Dam may be an advance in juvenile fish passage.

But at this early stage, researchers are willing to say little other than the concept is promising.

The $11 million, 1,001-ton device is designed to attract and pass juvenile salmon and steelhead smolts over the dam more efficiently than other methods.

It was installed last year and tested for the first time this spring. Researchers are wrapping up their field season and have reams of data to process this fall and winter.

"It's got some hope," said John Plumb, a researcher with the U.S. Geological Survey testing the weir.

The delay young fish experience passing dams on their way to the ocean has long been one of the toughest problems to be solved if Snake River salmon are to recover.

So tough that many in the debate have thrown up their arms and said the four lower Snake River dams should be removed so the fish don't have to contend with the delay, warm water and increased predators caused by the dams.

That idea has been relegated to the back burner as state, federal and tribal entities try to implement an everything-but-breaching strategy to save the fish. Part of the everything-but-breach plan, adopted in 2000, includes improving fish passage at the dams.

Tim Wik, a U.S. Army Corps of Engineers biologist for the Walla Walla District, said they will know more about the spillway weir's performance in July when the first research reports begin to trickle in.

He doesn't expect survival of young fish passing the dam to improve greatly with the device.

"Fish passage and fish survival is quite high already so you aren't going to make any huge gains," he said.

But it is hoped the device will reduce the time fish spend trying to find a route through the dam.

Young fish depend on current to help them find their way to the ocean. With the damming of the Snake and Columbia rivers and the slack water the dams created, the young salmon have a much more difficult time reaching the ocean.

Juvenile salmon and steelhead face two main problems when passing dams. One is delay and disorientation caused by slack water reservoirs. The other is delay caused as the fish try to locate a way through the dam itself.

Surface bypass can address the dam passage delay but does nothing to speed the time it takes young fish to move through the eight reservoirs on Snake and Columbia Rivers.

"You can put any kind of mask you want on the face of that dam but it's probably not going to change the effect of the reservoir," Plumb said.

But he said surface bypass can mitigate for delay in dam passage which can be large in low flow years.

The time it takes young fish to pass dams is not constant. It varies by flow and by time of day. For example, fish that approach the dam during the night when there is a high rate of discharge, experience the least amount of delay. Conversely fish that approach the dam during the day, when discharge is low, experience the longest delay.

Many salmon managers continue to push for spill during salmon migration to aid fish passage. But the amount of spill each year is variable and depends largely on winter snowfall and spring rain.

"We are kind of at the mercy of the amount of water coming down the river," Wik said.

During low-water years it is hoped surface bypass, perhaps in the form of the removable spillway weir can efficiently pass fish using less water than open spillways.

Juvenile salmon and steelhead can pass the dam in one of three ways. They can dive some 90 feet to the turbines where they will either shoot through or be deflected by a series of screens and pipes through the dam. This method exposes them to injury and death in the turbines and to large changes in pressures as they dive and then resurface.

The smolts can pass through opened spillway gates at the dam that are about 50 feet beneath the water's surface or they can pass through the removable spillway weir, the corps latest in a line of techno-fixes that sits in front of one of the spillways.

The device creates a false waterfall in front of one of the spillways that attracts and passes fish traveling near the top of the water column.

The time it takes young fish to pass dams is not constant. It varies by flow and by time of day. For example, fish that approach the dam during the night when there is a high rate of discharge experience the least amount of delay. Conversely, fish that approach the dam during the day when discharge is low experience the longest delay.

Some think the removable spillway weir can be used to decrease the delay.

Few results are available from this year's research and Plumb of the U.S. Geological Survey and others are unwilling to speak in detail about the removable spillway weir until they have a chance to put this years testing in perspective.

He did say it has great potential and is a clear improvement on the surface bypass collector, a now-rusting hunk of steel floating in front of the dam and destined for the trash heap.

"It's by far the most efficient route of passage they have found, but not necessarily the most effective."

The defunct surface bypass collector, the precursor to the removable spillway weir, was efficient, according to Plumb. That means it passed a lot of fish per volume of water but did not pass a large proportion of the fish.

At times the devices used just 4 percent of the water discharged from the dam to pass 75 percent of the fish. That is what gives researchers like Plumb and Wik hope surface bypass can be one piece in the puzzle of improving passage time.

For example in 2,000 the old the surface bypass system passed four hatchery fish per 1,000 cfs of water. The power house passed 1 hatchery fish per each 1,000 cfs of water.

In 2000 the old device passed 6.8 wild steelhead per each unit of water compared to .6 wild steelhead passed for each unit of water that went through the power house.

For spring chinook the old system passed eight fish per unit of water compared to .5 fish per unit of flow through the power house.

But the power house and open spillways pass much more water and thus more fish.

It is hoped the removable spillway weir will pass much more water than the now defunct system and attract more fish through its one large opening in front of a spillway bay.

"It's the most common sense approach to mitigate for the delay in dam passage and an alternative route to the turbines," Plumb said. "Whether its worth all the money or not," he shrugged. "You can't put a price on salmon coming back to the Salmon River," he said.

Eric Barker
Smolts Test Spillway Success
Lewiston Tribune, June 13, 2002

See what you can learn

learn more on topics covered in the film
see the video
read the script
learn the songs
discussion forum
salmon animation