But there's a growing strain on this relationship. Sediment has been building up at such a rate behind Lower Granite Dam -- the closest one to these river towns -- that the specter of floodwaters pouring over protective levees during high-water events can't be ignored much longer. There's also the chance boat launches, marinas and commercial ports could become so clogged they may have to be moved.
& lt;span class= "dropcap " & "A & lt;/span & new approach to sediment management," one PowerPoint slide announced at a Feb. 15 public hearing that introduced the latest corps plan. The new plan calls for a broader approach than simply dredging the reservoir behind Lower Granite. The corps will study the entire watershed -- some 32,000 square miles -- and assess methods to keep sediments out of the water in the first place. It will also look at altering flows to flush the sediments away from Clarkston and Lewiston, buying flood insurance for affected parties and even moving things (roads, bridges, intakes, businesses) that are clogged by sediment or threatened by flood.
The corps estimates 59 million cubic yards of sediment (about six million dump trucks) were carried down the Clearwater and Snake Rivers between 1974 and 1997, with three million more every year since. Some of it settled where the rivers converge at Lewiston and Clarkston. The rest deposited itself between there and Lower Granite, 30 miles downstream.
"Typically we would dredge every three to five years," Carl Christianson told the audience at the public hearing. Christianson is a corps biologist and manager of the sediment project.
The dredging primarily kept the navigation channel for commercial grain and container barges at a depth of 14 feet, he said, and had controversies of its own. On-land disposal of the muck created environmental concerns, so lately the corps has simply dumped sediment along the sides of the reservoir where the backed-up Snake has flooded a steep canyon. Christianson noted this "in-water disposal creates shallow-water habitat that out-migrating juvenile salmon can use as resting areas."
But his rosy view was challenged by Clint Chandler, a former federal fish biologist who now works for the Nez Perce Tribe: "The research I've been involved with has come to a different conclusion; I'd be concerned about (high) water temperatures." [Slack water is likely to be warmer than moving water.]
"Temperature is not part of the scope of this," Christianson answered.
That steams some observers. "I can't believe I can still get astounded at the Corps of Engineers," said Sam Mace, Inland Northwest project director of the Save Our Wild Salmon Coalition in Spokane. "I don't think they can dredge themselves out of this one. If Lower Granite stays in, they will have to raise the levees at Lewiston."
That, said Lewiston resident and whitewater river guide Dustin Aherin, "would be highly unpopular."
"If you raise the levees you will raise the sedimentation -- one will catch up to the other," said retired Lewiston mill worker Jerry Klemm.
"An obvious question that should be on the table but isn't ... is returning the river to a natural state," said Lewiston resident Jim Bradford. Bradford was one of several speakers who mentioned breaching the dams as a cheaper alternative.
This drew a quick hand-raise from Dave Doeringsfeld, manager of the Port of Lewiston, who urged the corps to make clear that the main purpose of the sedimentation management plan is to maintain commercial navigation on the lower Snake -- the reason the dams were authorized by Congress.
"We are looking at a national benefit when we ship wheat out. It goes to China and Japan ... and we weigh benefits against costs," said the corps' Craig Newcomb. "We will look at costs, and you are right," he added with a nod to Bradford, "at some point the costs may outweigh the benefits."
"Jet boat tours are a big part of our economy," Port of Clarkston manager Wanda Keefer told Christianson, but sediment is building up at the boat launches. Tour boats from Portland and Astoria dock at Clarkston so passengers can take jet boat tours in Hell's Canyon.
This is one of the businesses at risk as sediment continues to build. "De-watering" the river to flush sediments away from the confluence, or breaching the dams, could spell an end to regular tour boat traffic, but sediment buildup has lessened the effectiveness of emptying the dam's small reservoir.
& lt;span class= "dropcap " & O & lt;/span & pinions are beginning to shift in these cities that were longtime bulwarks of dam support.
"The only viable option I can see is to take the dams out when it comes to flood protection and economic sense," said Aherin, the river guide.
"This is still a minority view for sure -- in Lewiston and the whole state of Idaho -- but when you start talking about flooding downtown Lewiston and losing your livelihood and that it costs billions of dollars to keep the dams in, I think people change a bit," Aherin said. "And there are other ways to ship products out."
Save Our Wild Salmon has long advocated breaching the lower Snake River dams as the only way to save endangered salmon and steelhead runs. The group has formed a coalition of commercial and sport fishers and is trying to reach out to farmers and shippers in this latest effort to discuss breaching.
Getting rid of the lower four Snake River dams and 140 miles of slackwater doesn't mean an end to wheat transport, Mace said.
"Taxpayers may want to spend their dollars on an upgraded modern railroad and still have salmon and still have steelhead," she said.
But all this is a long way off, Christianson points out. Just writing a draft environmental impact statement could take three years, he explained, and that depends on adequate funding from Congress, which has not been so reliable in recent years.
Christianson admitted it could take decades to coordinate land-use practices among all the federal, state, tribal agencies and private landowners to minimize sedimentation.
The corps owns only a half of one percent of the land in the affected river basins, he said, and has almost no authority to tell anyone else what to do. In addition, 27 percent of the land is federal wilderness and 50 percent is owned by the U.S. Forest Service.
Some of the shorter-term options may mean moving the ports and marinas to other parts of the river where sedimentation is less of an issue, Christianson said, and raising the levees, which have become a linear green belt of popular hiking and biking trails.
And that, it appears, could draw a flood of complaints.
This story is part of an occasional series by Kevin Taylor about the Snake River dams and energy issues facing the Northwest. You can have your say on the Lewiston plans. Send comments to Sandy Simmons, Walla Walla USACE, 201 N. 3rd Ave., Walla Walla, WA 99362-1876. Or direct questions to Carl.J.Christianson@usace.army.mil or Sandy.L.Simmons@usace.army.mil. Deadline is March 31.