A common theory on why Locke Island on the Hanford Reach is eroding doesn't appear to hold water.
The 150-acre island on the Columbia River beneath the White Bluffs lost as much as 120 feet of its east bank during the 10 years that ended in 2006.
It's believed to have continued to erode since then, but detailed measurements have not been kept, according to researchers.
The island, which is closed to the public, is prized for its salmon spawning habitat and for its American Indian heritage. It was used for thousands of years by Indians as a fishing spot, grazing area and village.
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Locke Island's difficulties began when the east bank of the river adjacent to it began to collapse. Throughout 20 years, landslides caused the channel between the bluffs and the island to narrow. On the other side of the river is the Hanford nuclear reservation.
Vanderbilt University in Nashville, Tenn., has been investigating the affect of the changed channel for the Consortium for Risk Evaluation with Stakeholder Participation, a consortium of universities that uses Department of Energy money to study methods of environmental cleanup at Hanford and other nuclear weapons sites.
"The generally accepted explanation for the increased erosion has been that the narrowing of the channel forced the water flowing through it to speed up significantly and the stronger current wore away the side of the island more rapidly," Grace Loy, a Vanderbilt earth and environmental sciences student, said in a statement.
"We were skeptical of this explanation and our analysis suggests that it isn't what happened," she said.
Professor David Furbish and students used a laboratory stream table to build a small model of the island and the landslide and then recorded what happened when water was sent down the stream table and past the island with and without the landslide.
A video camera was used to record the ride of green beads dropped into the water at the top of the stream table. The images were analyzed by computer to map the velocity of the currents at different locations.
Instead of more water rushing through the narrow channel at high speeds after the landslide narrowed it, the model showed that more water went around the island in the larger channel to its west -- the Hanford side of the river.
"The current in both channels increases slightly compared to what it was before the landslide," Loy said.
However, results are preliminary. Some aspects of the stream-table study cannot be scaled up to the size of the Columbia River and Locke Island.
Furbish will add to information with the completion of computer simulations in the next six months to estimate how the flow behaves in the Columbia River.
But he also has another hypothesis: The changed shoreline along the White Bluffs side of the river has caused the river channel to bend into the island in an L-shape.
Water flow in a bend is far more complicated that in a river channel, he said.
The problem of the landslides near Locke Island already has been addressed. The landslide area at the river shore does not appear to have grown since 1998 when ponds on the bluff above the river were drained. But researchers' further study of water flow could suggest solutions to stop the erosion.
Annette Cary: 582-1533; firstname.lastname@example.org