Lack of Dredging Behind Lower Granite Forces
Balancing Act for Fish, Navigation, Flood Control
Columbia Basin Bulletin, April 8, 2011
The U.S. Army Corps of Engineers last week developed an interim operations plan it feels will provide a safe navigation route through Lower Granite Dam's reservoir while still attending to the needs of juvenile salmon and steelhead migrating toward the Pacific Ocean.
The new plan calls for a stair-step raising of the reservoir through time as the volume of water gushing down from the upper Snake River and its tributaries declines. The operations plan comes in response to a "system operations request" that the reservoir elevation be operated two feet above minimum operating pool.
The request was made by the Columbia River Towboat Association, the Ports of Clarkston, Wash., and Lewiston, Idaho, and related businesses, who say the shipping channel leading up the reservoir to the mouth of the Clearwater River has become silted in places and, as a result of those high spots, has become unsafe. The problems with running aground also make the navigation up the lower Snake and Clearwater less efficient and more costly.
"We find ourselves once again, in the absence of dredging since 2006, facing a problematic set of challenges triggered by mandated MOP operations in the Lower Granite pool and shoaling in the federal navigation channel," the SOR says. "This has created an unacceptably high safety risk for river system navigators."
"With today's siltation in the Granite pool grounding is an ever present threat once the pool drops to MOP. These groundings while in transit create an unacceptable safety risk for deck crews exposed to unexpected rigging failures and falls overboard. The possibility of holing a boat or barge hull is also an ever present danger along with the possibility of a pollution event.
"The economic loss resulting from all these events is significant as boat crews spend more time doing less work as maneuvering in mud and dealing with groundings consumes more of their time," the SOR says.
The problem has developed because of a lack of regular maintenance dredging of the navigation channel by the U.S. Army Corps of Engineers. Federal regulations require that the channel be maintained at a depth of 14 feet to accommodate tugs and barges bringing goods to and from the inland ports on the Washington-Idaho border.
The SOR asks that the reservoir level be kept two feet higher than MOP to help make up for the channel depth lost because of sedimentation. The reservoir level has in recent years been held at MOP, 733 foot elevation with an operational range up to 734 feet, from the beginning of April through August.
That operation is dictated by NOAA Fisheries Service's Federal Columbia River Power System Biological Opinion. The BiOp prescribes measures at dams and reservoirs that are intended to improve the survival of salmon and steelhead stocks listed under the Endangered Species Act.
The purpose for holding the reservoir at its lowest possible elevation is to minimize the surface area, which results in reduced water particle travel time. The intent is to quicken water travel time for juvenile fish headed downstream, which is believed to improve their survival.
The Corps is legally obligated to try achieve BiOp objectives. But the NOAA Fisheries document does say that "slight deviations from these levels, based on navigation needs, load following, and operational sensitivity, may be required on occasion."
The Corps has been unable to dredge the channel because of other reasons. It is partly due to a legal settlement reached in 2005. The lawsuit was filed in 2002 by conservation and fishing groups who feared potential impacts of dredging on fish and asked that a full environmental analysis be conducted.
A settlement of the lawsuit achieved in September 2005 allowed a 2005-2006 dredging plan to proceed on the Corps promise to develop a "Programmatic Sediment Management Plan" for reducing sedimentation and the need for dredging. The agency said at the time it planned to complete the plan in 2009. But the work has lagged because a lack of appropriated funds during the past few years, the Corps Steve Barton told the Technical Management Team Wednesday. It is now expected to be completed in 2013.
In the agreement the Corps says that, following completion of its planned maintenance dredging activities during the winter of 2005-2006, it would limit further routine dredging activities to those deemed necessary because of emergency conditions (hazard to human life or significant loss of property and/or severe economic hardship), when sediment impairs access to ports and navigation locks at four lower Snake River dams, or when Lewiston's levee system might be threatened.
Barton said that the Corps is evaluating whether it could legally exercise the emergency conditions language in the settlement agreement. But, even if it is deemed an option, such dredging could not take place until the allowed midwinter work window when few fish are migrating up or down the river.
Meanwhile, Lower Granite is operating to keep the reservoir at MOP, something it is required to do because of current high water conditions. The low elevation provides as much flood control capacity as possible. The discharge from the dam jumped from no higher than 80,000 cubic feet per second through much of March to as high as 138.6 kcfs this week after a brief warmup triggered snowmelt while rain continued to drench most of the region.
Under the operations plan developed by the Corps, the reservoir will be kept at MOP as long as long as inflows are at 120 kcfs or greater. Navigating the channel is not an issue when the tugs and barges are riding such high volumes.
Once the flows drop below 120 kcfs the reservoir elevation would be lifted to MOP plus one foot until flows drop below 80 kcfs. Below 80 kcfs the elevation would be lifted to MOP plus 1.5 feet and below 50 kcfs the elevation would be maintained at MOP plus two feet.
"Oregon has lot of heartburn over the operation," Rick Kruger of the Oregon Department of Fish and Wildlife said during this week's TMT meeting. He suggested that perhaps changes could be made at other hydro projects downstream to make up for the migration time lost as a result of the higher-than-MOP operation.
Russ Kiefer, representing the state of Idaho at the meeting, said that he had requested the Fish Passage Center and NOAA Fisheries to do an analysis to estimate what the effect of an above MOP operation would have.
"As the (volume of) flows go down there's an increasing effect," Kiefer said. In the worst case scenario, with 40 kcfs flows at MOP plus two feet, the modeling indicated that travel time down through the reservoir would be increased by about five hours for chinook and seven hours for steelhead. At 70 kcfs the chinook would be slowed by about two hours.
The Nez Perce Tribe's Dave Statler said a higher summertime pool filled with tepid water could reduce benefits cold water flow augmentation drawn from Dworshak Dam's reservoir on the North Fork of the Clearwater.
"That is a potential concern as well," Statler said.
Lack of Dredging Behind Lower Granite Forces Balancing Act for Fish, Navigation, Flood Control