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Corps to Keep Snake River Pools
Up for Tug Operations

by Mike O'Bryant
Columbia Basin Bulletin - April 18, 2003

Hydro operating agencies and to a lesser extent fisheries agencies agreed this week that operations at lower Snake River reservoirs will remain at higher than the minimum operating pools (MOP) in order to give tugboat operators the depth they need to navigate certain sections of the river.

Although it is contrary to the NOAA Fisheries 2000 biological opinion of the Federal Columbia River Power System, the U.S. Army Corps of Engineers will likely keep the reservoir elevations at least at MOP plus one foot through the summer until the Corps again can dredge the navigation channel.

It has been three years since the Corps has dredged the lower Snake River channel and tugboat operators said that, as the river silts in, it is making it difficult and dangerous to both navigate the channel and to enter and leave locks at the dams. The Columbia River Towboat Association made that assertion at the April 9 Technical Management Team, but at this week's TMT meeting they added that spill at some lower Snake River dams and at the John Day Dam on the Columbia River is exacerbating the problem.

Since TMT's April 9 meeting, the Corps and the U.S. Coast Guard have taken soundings at seven location in the river identified by the tugboat operators, finding several that are shallow and difficult to navigate. Of particular concern was the approach to the Lower Granite Dam locks through the Ice Harbor pool.

"The soundings confirm in our mind that the river system, in the absence of dredging, is silting in," said Larry Johnson of Foss Maritime. "The soundings identified three areas, but the fact is all the river is silting in and reducing for us both the width and the depth of the river."

He said the tugboat operators can operate safely this year if the Corps operates the reservoirs at the same levels it did last year, which was MOP plus one foot.

The genesis of the problem is that the Corps has not been able to dredge the lower Snake River channel since the winter of 1997-98 due to court challenges. A U.S. District Court judge in Seattle issued in December 2002 a preliminary injunction prohibiting navigation channel dredging on the lower Snake River, saying that NOAA Fisheries had failed to ensure that dredging would not destroy critical habitat for fall chinook salmon, as required by the law and the BiOp was rescinded.

Chris Ross of NOAA Fisheries said at this week's TMT meeting that the Corps and NOAA Fisheries are now re-consulting on the dredging operations. He expects that the fisheries agency will reissue a BiOp sometime this summer and that the Corps could begin dredging this winter. If that happens, tugboats and their tows next year should be able to navigate a lower river.

The operations requested by the Columbia River Towboat Association conflicts with NOAA Fisheries BiOp, which calls for minimum operating pools when spilling water to aid juvenile salmon and steelhead passage through the dams. Spill began April 3. The low water, according to NOAA Fisheries, increases the velocity of the water over the dam by 7 percent from the velocity of water when pools are full.

"There is good information about the flow to travel time relationship," Ross said of the benefits of spill and operating the reservoirs at MOP. "Fish move faster through the reservoir, so we also have a good biological relationship."

Johnson said the problem is particularly severe when a tug and a typical four barge, 640-foot-long tow head downstream after leaving a lock. Locks at a dam are placed near the shore. He said the tug and tow have to crab -- move in the 250 wide channel at a 30 degree angle to the current and channel-- to counter a strong following flow caused by spill at a dam just to stay in the channel. That following flow tries to "throw" the tug and tow towards the beach, he said. At a 30-degree angle to channel, the tug and tow cross channel lines.

"When this happens, the width of the channel should be 375 feet rather than the 250 feet," Johnson said. "This explains the frequency in which we hit the bottom."

He added that the soundings are generally at least 14 feet in the channel, but not outside the channel. Without spill, the tug operators don't have to operate this way.

Spill at Lower Granite Dam this year is less than in past years due to the existence of the "removable spillway weir," according to Ross, and a 46-day spill test that alternates flows between day and night could provide an opportunity for tugs to time their arrival with certain spill patterns. However, adjusting spill at the dam when a tug arrives would affect the test.

Johnson said a similar problem occurs at John Day Dam. In fact, at about 2:30 a.m. Wednesday a tug operator having difficulty coming upstream into the dam's lock, asked the dam operator to alter spill for the fifteen minutes it takes to navigate into the lock, but the operator had refused to alter spill. He said in past years, the dam operator would alter spill slightly to help.

"We know through modeling that certain spill patterns are less difficult than others," Johnson said, pointing to a flat spill pattern when each spill bay across the dam spills the same amount of water as a pattern that is less difficult for the tugboat operators. Johnson said spill changes would only be needed for 15 to 20 minutes at a time for the approximately 12 to 15 tows per day that go through the John Day Dam locks. Fewer tugs go through the Lower Granite Dam locks.

However, a flat spill at low flows might actually be detrimental to fish, said Rudd Turner of the Corps. At lower flows, he said, the spill pattern at the dam spills more water from the north spillways where the water is deeper.

The Corps' Cindy Henriksen said the Corps would need to review its operational alternatives before making a decision, including the alternatives of changing to flat spill or even ceasing spill while a barge navigates the locks.

Related Sites:
Implementation Team:
Technical Management Team:

Mike O'Bryant
Corps to Keep Snake River Pools Up for Tug Operations
Columbia Basin Bulletin, April 18, 2003

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